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Oceanography And Late-Quaternary Planktonic Foraminifera, Southwestern Indian Ocean

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Oceanography And Late-Quaternary Planktonic Foraminifera, Southwestern Indian Ocean

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Content OCEANOGRAPHY AND LATE QUATERNARY PLANKTONIC FORAMINIFERA, SOUTHWESTERN INDIAN OCEAN by E d ith S. V incent A D is s e r t a t io n P re se n te d to th e FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In P a r t i a l F u lf illm e n t o f th e R equirem ents f o r th e Degree DOCTOR OF PHILOSOPHY (G eo lo g ic a l S cie n c e s) August 1972 INFORMATION TO USERS This dissertation was produced from a microfilm copy of the original docum ent. While the most advanced technological means to photograph and reproduce this docum ent have been used, the quality is heavily dependent upon the quality of the original submitted. The following explanation of techniques is provided to help you understand markings or patterns which may appear on this reproduction. 1. The sign or "target" for pages apparently lacking from the docum ent photographed is "Missing Page(s)". If it was possible to obtain the missing page(s) or section, they are spliced into the film along with adjacent pages. This may have necessitated cutting thru an image and duplicating adjacent pages to insure you com plete continuity. 2. When an image on the film is obliterated with a large round black mark, it is an indication that the photographer suspected th at the copy may have moved during exposure and thus cause a blurred image. You will find a good image of the page in the adjacent frame. 3. When a map, drawing or chart, etc., was part of the material being p h o to g rap h e d the photographer followed a definite m ethod in "sectioning" the material. It is custom ary to begin photoing at the upper left hand corner of a large sheet and to continue photoing from left to right in equal sections with a small overlap. If necessary, sectioning is continued again - beginning below the first row and continuing on until complete. 4. The majority of users indicate that the textual content is of greatest value, however, a somewhat higher quality reproduction could be made from "photographs" if essential to the understanding of the dissertation. Silver prints of "photographs" may be ordered at additional charge by writing the Order Departm ent, giving the catalog number, title, author and specific pages you wish reproduced. University Microfilms 300 North Zeeb Road Ann Arbor, Michigan 48106 A Xerox Education Company 7 3 -7 2 7 1 VINCENT, E d ith S . , 1932- O CEA N O G R A PH Y A N D LATE QUATERN ARY PLANKTONIC FORAMINIFERA, SOUTHW ESTERN INDIAN OCEAN. U n iv e rs ity o f S o u th ern C a lif o r n ia , Ph.D., 1972 Geology University Microfilms. A X E R O X Company. Ann Arbor, Michigan THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED. UNIVERSITY O F SO UTHERN CALIFORNIA THE GRADUATE SCHOOL UNIVERSITY PARK LOS ANGELES. CALIFORNIA 9 0 0 0 7 This dissertation, written by Edith S. Vincent under the direction of h.fl.... Dissertation Com mittee, and approved by all its members, has been presented to and accepted by The Graduate School, in partial fulfillment of requirements of the degree of D O C T O R OF P H IL O S O P H Y Dtan Date August 1972 DISSERTATION COM PLEASE NOTE: Some pages may have indistinct print. Filmed as received. University Microfilms, A Xerox Education Company CONTENTS Page ABSTRACT ............................................................................................ x INTRODUCTION .................................................................................. 1 I G en eral ..................................................................................... 1 Study l o c a tio n and sample m a te r ia l .................... 7 Acknowledgments ............................................................... 9 H is to ry o f o cean o g rap h ic e x p lo r a tio n in th e ! Mozambique Channel 10 j Submarine topography .................................. . . . . 15 ( i N atu re o f th e s e a - f l o o r and o r ig i n o f th e Mozambique Channel ................................................. 21 Geology and geomorphology o f b o rd e rin g la n d s 29 OCEANOGRAPHY .................................................................................. 41 I n tr o d u c tio n ......................................................................... 41 Mozamblque-Agulhas C u rre n t system . . . 41 S easo n al v a r i a t i o n s In s u rfa c e c u r r e n t s 45 Deep l a y e r s o f th e Agulhas C u rre n t . . . 47 C o lle c tio n and p r e s e n ta tio n o f d a ta . . . . 50 T em perature d i s t r i b u t i o n ............................................ 87 S u rfa c e te m p e ra tu re ............................................ 87 V e r t i c a l d i s t r i b u t i o n ....................................... 92 S a l i n i t y d i s t r i b u t i o n ................................................. 94 S u rfa c e s a l i n i t y ...................................................... 94 11 Page V e r tic a l d i s t r i b u t i o n ............................................ 94 D isso lv ed oxygen and in o rg a n ic p h osphate d i s t r i b u t i o n ............................................................... 98 D isso lv ed oxygen c o n c e n tr a tio n .................... 98 In o rg a n ic pho sp h ate c o n c e n tr a tio n . . . . 103 W ater m a s s e s ........................................................... 104 S u rface w a te rs ................................................................... 105 T ro p ic a l W ater ......................................................... 106 S u b tro p ic a l W ater ..................................................... 106 S u rfa c e c u r r e n ts .................................................... 110 S u b su rface c u r r e n ts ....................................... 121 C e n tra l W ater ................................................................................. 125 Movement o f C e n tra l W ater ........................................... 126 A n ta r c tic In te rm e d ia te W ater ........................................... 127 Movement o f A n ta r c tic In te rm e d ia te W ater 129 N orth A t l a n t i c Deep W a t e r ................................. 140 Movement o f N orth A t la n tic Deep W ater . . 141 N orth In d ia n Deep W a t e r ................................... 150 Movement o f N orth In d ia n Deep W ater . . . 154 Bottom W ater ......................................................................... 157 SURFACE SEDIMENTS ................................................................................. 159 P re v io u s w o r k ........................................................... 159 Methods o f stu d y . . . . . ................................................ 162 i l l General composition, general sedimentary ! | p ro v in c e s ......................................................................... i ! Shallow w a te r d e p o s its ....................................... I | C o n tin e n ta l sh e lv e s ....................................... ; C o r a llin e d e p o s its ....................................... i ! Deep w a te r d e p o s its ................................................. j Halmeic sedim ents ............................................ I T e rrig en o u s sedim ents .................................. B iogenic sedim ents ....................................... Scoured rocky bottom and t h in i s u r f i c i a l c o a rse d e p o s its .................... I DISTRIBUTION OF FORAMINIFERS IN SURFACE SEDIMENTS ! P re v io u s work ......................................................................... Method o f stu d y .................................................................... G en eral fa u n a l c h a r a c t e r i s t i c s ............................. D i s tr i b u t i o n o f In d iv id u a l p la n k to n ic s p e c ie s I | STRATIGRAPHY .................................................................................. G en eral ....................................................................................... i Area o f f Durban, e a s t o f th e Mozambique ] P la te a u ............................................................................. i i ! Area o f f T u le a r .................................................................... A rea o f f Inhambane .......................................................... S o u th w ard -facin g c o n tin e n ta l S helf* e a s t o f th e Limpopo R iv e r ..................................................... Page C o n tin e n ta l slo p e s o u th e a s t o f Lourenco ! M a r q u e s ............................................................................... 288 C o n tin e n ta l Slope and C o n tin e n ta l R ise e a s t o f Lourenco Marques.................................................... 290 | Mozambique P la te a u ........................................................... 298 ! E a s te rn slo p e o f Mozambique P la te a u ..................... 298 M adagascar P la te a u .......................................................... 299 C e n tr a l a r e a o f th e Mozambique Channel . . . 300 N a ta l B a s i n ............................................................................. 302 ; DISCUSSION OP THE FAUNAL CHANGE AT THE PLEISTOCENE- HOLOCENE BOUNDARY ............................................................... 305 j DISCUSSION OF PALEOOCEANOGRAPHIC AND PALEO- I CLIMATIC LATE QUATERNARY CHANGE IN THE AREA AND COMPARISON WITH LAND RECORD.............................. 313 SUM M ARY AND CONCLUSIONS .......................................................... 320 REFERENCES....................................................................................... 334 ILLUSTRATIONS F ig u re 1. C ru ise t r a c k and h y d ro g rap h ic s t a t i o n s . . 2. B athym etry and bottom sam ples lo c a t i o n . . 3. P h y sio g ra p h ic p ro v in c e s ....................................... 4. Geology o f b o rd e rin g la n d s .................................. i 1 5. S u rfa c e c u r r e n ts in th e so u th w est In d ia n I Ocean .................................................................................. 6. Dynamic topography a t s u rfa c e o v e r 1000 db, S p rin g 1957 .......................................................... 7. T em perature v e rsu s depth ....................................... 8 . S a l i n i t y v e rsu s d ep th ............................................ 9. D isso lv e d oxygen and in o rg a n ic pho sp h ate v e rs u s dep th .................................................................... 10. T/S c u rv e s ........................................................................ 11. T em perature v e r t i c a l d i s t r i b u t i o n , Durban- T u le a r .................................................................................. 12. S a l i n i t y v e r t i c a l d i s t r i b u t i o n , Durban- T u le a r .................................................................................. 13. S lgm a-t v e r t i c a l d i s t r i b u t i o n , Durban to T u le a r .................................................................................. 14. T em perature v e r t i c a l d i s t r i b u t i o n , T u le a r to Inhambane .................................................................... 15• S a l i n i t y v e r t i c a l d i s t r i b u t i o n , T u le a r to Inhambane ........................................................................ 16. S lg m a-t v e r t i c a l d i s t r i b u t i o n , T u le a r to Inhambane ........................................................................ Figure Page 17• Tem perature v e r t i c a l d i s t r i b u t i o n , Lourenco Marques to W alter S h o als ......................................... 72 18. S a l i n i t y v e r t i c a l d i s t r i b u t i o n , Lourenco ; Marques to W alter S h o als ......................................... 74 | 19. Sigm a-t v e r t i c a l d i s t r i b u t i o n , Lourenco Marques to W alter S h o als ......................................... 76 20. Tem perature v e r t i c a l d i s t r i b u t i o n , N a ta l B asin to D u r b a n ............................................................... 78 21. S a l i n i t y v e r t i c a l d i s t r i b u t i o n , N a ta l Basin to D u r b a n ............................................................................. 80 22. Slgm a-t v e r t i c a l d i s t r i b u t i o n , N a ta l B asin to D u r b a n ............................................................................. 82 23* S a l i n i t y v e r t i c a l d i s t r i b u t i o n , n o r th - so u th s e c t i o n .................................................................... 84 24. S u rface w a te r te m p e ra tu re ........................................ 88 | 2 5 . S urface w a te r s a l i n i t y ................................................. 95 ! 26. S u rface w a te r sig m a -t ................................................. 99 I j 27> S urface w a te r oxygen c o n te n t ................................... 101 ! | 28. S urface T/S r e l a t i o n s h i p s ........................................ 108 29. Dynamic topography a t s u rfa c e o v e r 1000 db . I l l 30. Dynamic topography a t 1000 db r e l a t i v e to 2000 d b .................................................................................. 132 3 1 ' Dynamic topography a t 1500 db r e l a t i v e to 2000 d b .................................................................................. 134 | 32. Oxygen minimum d i s t r i b u t i o n ................................... 138 33. Dynamic topography a t 3000 db r e l a t i v e to 2000 d b .................................................................................. 145 34. D is tr ib u tio n o f deep w a te r s a l i n i t y maximum 151 vii Figure Page 35. Calcium ca rb o n a te c o n te n t In s u rfa c e s e d i m e n t s ......................................................................... 163 36. Sand f r a c t i o n c o n te n t In s u rfa c e sed im en ts 165 37. S u rface sedim ent t y p e ............................................. 168 38. G rain s iz e d i s t r i b u t i o n In s u rfa c e s e d i m ents o f th e N a ta l B asin and Zambezi Canyon a r e a .................................................................... 190 39. Calcium ca rb o n a te c o n te n t v a r i a t i o n s In c o re s o f th e N a ta l B a s i n ....................................... 197 40. F o ra m ln ife ra l number ( >62pi) In s u rfa c e s e d i m e n t s ......................................................................... 217 41. P la n k to n ic f o r a m ln if e r a l number ( ? 2 5 0 p ) In s u rfa c e sed im en ts ................................................. 219 42. P e rc e n ta g e o f p la n k to n ic f o r a m in lf e r s In th e f o r a m ln if e r a l fa u n a c o a r s e r th an 62;i . 222 43. R a d lo la ria n number ( > 6 2 p ) . 225 44. P teropod n u m b e r ........................................................... 227 45. R e la tiv e freq u en cy o f G lo b o r o ta lla l n f l a t a .............................................................................. 236 46. R e la tiv e freq u en cy o f G lo b o r o ta lla tr u n c a - t u l l n o l d e s ......................................................................... 240 47. C o llin g r a t i o o f G lo b o r o ta lla t r u n c a - t u l l n o l d e s ......................................................................... 243 48. R e la tiv e freq u en cy o f O rb u lln a u n lv e rs a . 250 49. R e la tiv e frequency o f G lo b lg e rln o Id e s r u b e r .................................................................................. 254 50. R e la tiv e frequency o f G lo b o r o ta lla m e n a r d l l ............................................................................. 257 51. R e la tiv e freq u en cy o f G lo b lg e rln o ld e s c o n g lo b a tu s . . . . . 259 v l i i Figure 52. R e la tiv e freq u en cy o f G lo b lg e rln a ru b e sc e n s ......................................................................... 53. R e la tiv e freq u en cy o f G lo b lg e rin o id e s | s a c c u l i f e r ......................................................................... I 54. R e la tiv e freq u en cy o f S n h a e r o id ln e lla d e h lsc e n s ......................................................................... 55. R e la tiv e freq u en cy o f P u l l e n i a t i n a o b l i a u i l o c u l a t a .......................................................... 56. R e la tiv e freq u en cy o f N eogloboauadrlna d u t e r t r e i ......................................................................... 57. R e la tiv e freq u en cy o f O andeina n i t l d a . . 58. C o r r e la tio n s between c o re s in th e a r e a n e a r T u le a r .................................................................... j 59* F aunal co m p o sitio n in c o re 361F .................... | 6 0 . F aunal co m p o sitio n in co re 361J .................... 61. C o r r e la tio n s betw een th r e e c o re s n e a r th e m argin o f T ro p ic a l and S u b tro p ic a l W aters Table i | I . D i s tr i b u t i o n o f oxygen a t th e maximum s a l i n i t y l e v e l in th e N orth A t l a n t i c Deep W ater ......................................................................... I I I . R e la tiv e fre q u e n cy o f p la n k to n ic fo ra m in l- f e r a l s p e c ie s in core 366B, 0 -2 cm . . . . | I I I . R e la tiv e freq u en cy o f p la n k to n ic fo ra m in i- f e r a l s p e c ie s in c o re 379B, 0 -2 cm . . . . IV. M arine t r a n s g r e s s io n s and p l u v i a l p e rio d s in th e A epyornlan s ta g e o f th e so u th e rn t i p o f M adagascar ..................................................... Page 262 264 267 269 272 275 283 291 293 296 149 230 232 315 ix ABSTRACT H ydrographic d a ta , s u rfa c e -se d lm e n t sam ples, and s h o rt g r a v ity c o res c o l l e c t e d In th e so u th e rn Mozambique Channel and a d ja c e n t Southw est In d ia n Ocean d u rin g th e so u th e rn w in te r o f 1964 a re used to d e fin e r e l a t i o n s h i p s : among o cean o g rap h ic f a c t o r s , sedim ent d i s t r i b u t i o n , and p la n k to n ic f o r a m l n i f e r a l tr e n d s . T ro p ic a l W ater l i e s a t th e s u rfa c e n o r th o f 2 4 ° S ., | flow s southw ard n e a r th e A fric a n and M alagasy c o a s ts , ; and c o n tr ib u te s to th e up p er la y e r s o f th e Agulhas C ur r e n t , th e w e ste rn boundary c u r re n t o f th e S outh In d ia n i Ocean. S u b tro p ic a l W ater form s two la r g e c y c lo n ic g y res a t th e s u r f a c e , n o r th and so u th o f 3 0 ° 3 0 'S ., r e s p e c t i v e l y , and s in k s b e n ea th T r o p ic a l W ater. The s o u th e rn g yre p e r s i s t s th ro u g h o u t th e y e a r , w hereas th e n o rth e rn one Is s e a s o n a l. C e n tra l W ater u n d e r lie s th e s u rfa c e w a te rs and u p w ells In th e c e n te r o f th e so u th ern eddy. At d ep th s o f 1000 and 1500 m, N orth In d ia n Beep W ater form s an a n tic y c lo n lc gyre n o r th o f 2 5 °S .; to th e s o u th , A n ta r c tic In te rm e d ia te W ater form s two a n tic y c lo n lc s w ir ls c e n te re d o v er th e N a ta l B asin and th e Mozambique P la te a u , r e s p e c tiv e ly , w ith th e l a t t e r c au sin g slow s e d im e n ta tio n . Mixed N orth In d ia n Beep W ater and A n ta r c tic In te rm e d ia te x W ater c o n tr ib u te to In te rm e d ia te la y e r s o f th e Agulhas C u rre n t. N o rth A t l a n t i c Deep W ater e n te r s th e N a ta l B asin from th e so u th on I t s w e ste rn sid e and I s fo rc e d down In th e n o rth e rn p a r t o f th e b a s in by th e o v e rly in g N orth In d ia n Deep W ater t h a t p e n e tr a te s th e b a s in from b o th I t s n o rth w e ste rn and n o r th e a s te r n c o r n e rs . The two : mixed w ate r m asses flow southw ard on the e a s t s id e o f th e i | N a ta l B asin . During th e L a te P le is to c e n e , S u b tro p ic a l W ater e x - I I tended f a r t h e r n o r th th an to d ay In to th e Mozambique Channel n o rth o f 2 3 °S .; I t s so u th e rn boundary, th e Sub t r o p i c a l Convergence, rem ained so u th o f 34°S. The A gul h as C u rren t flow ed n e a r th e A fric a n c o a s t in a p o s it i o n com parable to t h a t o f to d ay b u t was p ro b ab ly n arro w er and s tr o n g e r , and p o s s ib ly warmer. A reas o f n o n - d e p o s itio n o ccu r on th e A fric a n s h e l f and b e n e a th th e M ozamblque-Agulhas C u rre n t. R e l i c t fau n as and exposed b each ro ck show ev id en ces o f a form er low ered s e a - l e v e l on th e A fric a n s h e l f . D i s tr i b u t i o n o f f o r a m ln if e r a l ooze, d iv id e d In to m arl and c h a lk ooze, i s r e l a t e d to d is ta n c e from la n d and a c tio n o f tr a n s p o r t in g a g e n ts . N a ta l B asin sed im en ts In c lu d e t u r b i d l t e s , d e riv e d from n e r l t l c and b a th y a l d e p th s, which a re d is p e rs e d from n o rth w est to s o u th e a s t. S u r f l c l a l t u r b l d i t e l a y e r s d id x l n o t re a c h th e s o u th e rn p o r tio n o f th e b a sin f l o o r , which I s covered w ith p e la g ic c la y and manganese n o d u le s. : Average se d im e n ta tio n r a t e s o f sed im en ts younger th a n ; ab o u t 4000-6000 y e a r s range from 1 to 9 cm/1000 y e a r s , ! 1 depending on to p o g ra p h ic p o s it i o n and d is ta n c e from la n d . The averag e r a t e o f accu m u latio n f o r d e e p -se a ooze d u r ing th e e n t i r e L ate Q u atern ary i s 1 .5 to 2 .5 cm/1000 ! y e a r s . D is tr ib u tio n o f p la n k to n ic f o r a m ln if e r a l s p e c ie s in u n d istu rb e d s u rfa c e sed im en ts r e f l e c t s th e a r e a l p a t- : te r n o f T ro p ic a l and S u b tro p ic a l W aters and i s com parable ; to th e known d i s t r i b u t i o n o f liv i n g s p e c ie s in s u rfa c e ' w a te rs . A marked change in th e r e l a t i v e abundance o f j p la n k to n ic f o r a m ln if e r a l s p e c ie s o c c u rs in c o re s o f un- ! | d is tu r b e d ooze n e a r th e m argin o f T ro p ic a l and Sub- j i t r o p i c a l W aters. The te m p e ra te -w a te r s p e c ie s G lo b o ro ta lla j ' i n f l a t a , which com prises 25-30 p e r c e n t o f th e t o t a l p la n k to n ic p o p u la tio n > 250ji in th e lo w er p o r tio n o f th e c o re s , d e c re a se s to ap p ro x im a te ly 3 p e rc e n t a t th e to p . i T his d e c re a se i s accom panied by a sim u lta n e o u s in c re a s e ; in th e r e l a t i v e abundance o f w arm -w ater s p e c ie s o th e r | th a n G lo b o r o ta lla m e n a rd ll. N eogloboouadrlna d u t e r t r e l j ! in c r e a s e s upwards in th e c o re s from ab o u t 5 p e r c e n t to i | ap p ro x im a te ly 15 p e r c e n t, P u l l e n l a t l n a o b l l o u l l o o u l a ta x i l from ab o u t 1 p e rc e n t to 7-9 p e r c e n t, G lo b lg e rln o ld e s s a c c u l l f e r from 12-18 p e rc e n t to 20-30 p e r c e n t, and G lo b lg e rln o ld e s co n g lo b atu s from 1 p e r c e n t o r l e s s to 3 -6 p e r c e n t. This change, d a ted by ra d io c a rb o n a t a p p ro x im a te ly 10,000 y e a rs B .P ., r e f l e c t s a warming o f s u rfa c e w a te rs o f a few d eg rees C e ls iu s , and corresponds to th e P le lsto c e n e -H o lo c e n e boundary. T h is e v e n t was contem poraneous w ith a s i m i l a r warming re c o rd e d in th e s o u th e a s t In d ia n Ocean a t ab o u t th e same l a t i t u d e ; I t was i n o t contem poraneous w ith a younger m arine tr a n s g r e s s io n I : re c o rd e d In so u th ern M adagascar a t t r i b u t e d to th e | F la n d ria n . R a d io la rla n abundance in c r e a s e s m arkedly in | H olocene se d im en ts. i ! A s h i f t in th e c o i l i n g d i r e c t io n o f G lo b o ro ta lla tr u n c a t u ll n o l d e s ( ca . 6000 y e a rs B .P .) c o r r e l a t e s w ith th e end o f th e L avanonian, a p l u v i a l i n t e r v a l d efin ed In so u th e rn M adagascar. V a r ia tio n s in s a l i n i t y , r a t h e r | th a n te m p e ra tu re , ap p e ar to be th e p rim ary causes o f th e I | c o l l i n g change. xiii INTRODUCTION G eneral This stu d y concerns th e o cean o g rap h ic s e t t i n g , sedim ent d i s t r i b u t i o n and p la n k to n ic f o r a m ln if e r a l tre n d s In th e so u th ern Mozambique Channel and t h a t a re a o f th e so u th w estern In d ia n Ocean lo c a te d Im m ediately so u th o f th e C hannel. To d e fin e th e r e l a t i o n s h i p s between th e se f a c t o r s and e v a lu a te o c e a n o g ra p h ic , c l i m a t i c , and s e d i m entary changes In th e a r e a d u rin g th e l a t e Q uaternary I s th e o b je c tiv e o f th e s tu d y . For t h i s p u rp o se, h y d ro g rap h ic d a ta , s u rfa c e bottom sam ples, and s h o rt g r a v ity co res c o l l e c t e d In A ugust-Septem ber 1964 on c r u is e 7 o f th e R.V. ANTON BRUUN were examined (F ig s . 1 and 2 ) . U n til th e ad v en t o f th e I n t e r n a t i o n a l In d ia n Ocean E x p e d itio n , In 1961 to 1965, d a ta on th e In d ia n Ocean was s u r p r i s i n g l y s p a rs e . In p a r t i c u l a r alm ost n o th in g was known on th e so u th w estern p a r t o f th e o cean . P rev io u s ocean o g rap h ic work was u n d e rta k e n to th e so u th o f th e a re a o f I n v e s tig a tio n as w e ll a s In th e Mozambique Channel to th e n o r th . This re g io n I s , how ever, o f unique oceano g ra p h ic I n t e r e s t because o f th e v a r i e t y o f w a ter masses p r e s e n t and i t I s th e so u rce a r e a o f th e Agulhas C u rre n t, 1 Figure 1 C ru ise t r a c k and h y d ro g ra p h ic s t a t i o n s , R.V. ANTON BRUUN, C ru ise 7 , J u ly 29 to Septem ber 7, 1964. Thick l i n e s r e p r e s e n t th e c r u is e tr a c k and th e th in l i n e s , numbered I to IV, th e lo c a tio n o f h y d ro g ra p h ic p r o f i l e s . 2 3 45* - 20° - 0° 1 0 0 2 00 3 0 0 KILOMETERS INDIAN -20° OCEAN 20* 100° 120° I40E ULEAR 369. 38* 25* LOURENCOZ-^ MARQUESC*j{37 3 II f? I^Ns. W i 37i r * 358 DURI 30* 78 87 1 7 9 388 381 >82 35' 83 CRUISE TRACK .386 HYDROGRAPHIC STATION - I V - VERTICAL SECTION 4 5 * Figure 2 Bathym etry and bottom sam ples l o c a t i o n , R.V. ANTON BRUUN, C ru ise 7 (b ath y m etry ad ap ted from Heezen and Tharp, 1 9 6 6 ). 4 5 • PHLEGER CORE ° GRAB OR DREDGE BATHYMETRY IN METERS CONTOUR INTERVAL•500m 15° S >00 gOQ 300 KILOM ETERS 20' D A I N D I A IP A 1 ITULEAR rnasc*«/r« LOURENCO// m arquesrM D U R I 6 th e w estern boundary c u r re n t o f th e South In d ia n Ocean. The Agulhas C u rre n t I s dependent upon se a so n a l v a r i a t io n s o f th e South E q u a to r ia l C urrent* b u t I t s mode o f form a t i o n I s s t i l l n o t c l e a r l y u n d e rsto o d . G re a te r u n d e rsta n d in g o f t h i s c u r r e n t was g ain ed by a n a ly z in g th e so u th e rn w in te r s u rfa c e c i r c u l a t i o n p a t t e r n , a p a tte r n q u ite d i f f e r e n t from th e c i r c u l a t i o n scheme In th e s o u th e rn s p rin g (Menache, 1961, 1 9 6 3 ). In te rm e d ia te and d e e p -w a te r c i r c u la tio n p a t t e r n s a ls o were s tu d ie d u sin g a l l a v a ila b le h y d ro g rap h ic d a ta . No p re v io u s stu d y on th e deep sea sed im en ts o f th e so u th w este rn In d ia n Ocean has been u n d e rta k e n . The a r e a In c lu d e s rugged subm arine topography ra n g in g from sh allo w to a b y s sa l d e p th s , and c o n ta in s a la r g e v a r i e t y o f d e p o s l- t l o n a l e n v iro n m en ts. O ceanographic and p h y sio g ra p h ic f a c t o r s a re Im p o rtan t In c o n t r o ll i n g th e d i s t r i b u t i o n o f sed im e n ts. S tro n g ev id en ce e x i s t s h e re fo r th e s c o u rin g e f f e c t o f th e Mozamblque-Agulhas C u rre n t and f o r downslope t r a n s p o r t o f se d im e n ts. The d i s t r i b u t i o n o f p la n k to n ic f o ra m ln lf e rs In th e s u rf a c e sed im en ts o f th e r e s e a r c h a r e a , which I s flo o re d m ain ly w ith f o r a m l n i f e r a l ooze, I s an aly zed In d e t a i l and e v a lu a te d In r e l a t i o n to o c ean o g rap h ic and s e d lm e n to lo g lc a l f a c t o r s . The In d ia n Ocean was I n v e s tig a te d on a broad s c a le f o r p la n k to n ic f o r a m ln if e r a l d i s t r i b u t i o n (B e lia e v a , 1964) b u t i t s so u th w e ste rn p a r t h a s been n e g le c te d . Among d e ta i l e d f o r a m ln if e r a l I n v e s tig a tio n s o n ly a stu d y o f l i v ing p la n k to n ic f o ra m in lf e rs by Be' and T o ld e rlu n d (1971) covers t h i s r e g io n . D i s t r i b u t i o n a l tr e n d s o f p la n k to n ic f o r a m ln if e r a l s p e c ie s in b o th th e s u rfa c e w a te rs and th e s u rfa c e sed im en ts o f th e a re a r e f l e c t th e In flu e n c e o f th e Agulhas C u rre n t. The s t r a t l g r a p h l c and fa u n a l s u c c e ss io n w ith in th e c o res was e s ta b lis h e d f o r p urposes o f c o r r e l a t i o n and in d e fin in g sed im en tary and oceanographic changes in the r e c e n t p a s t. V a r ia tio n s in th e p la n k to n ic f o r a m ln if e r a l fauna a re used to show evidence o f warming a t th e P le isto c e n e -H o lo c e n e boundary r e p o rte d i n many d ee p -sea c o res from b o th h em isp h eres, but re c o g n iz e d f o r th e f i r s t tim e in th e southw est In d ia n Ocean. Study L o catio n and Sample M a te ria l T h is study i s concerned w ith o b s e rv a tio n s o o lle c te d by Dr. 0 . L . Bandy from J u ly 29 to Septem ber 9» 1964 on th e 7 th c r u is e o f th e R.V. ANTON BRUUN. D uring t h i s I n te r v a l , 37 h y d ro g rap h ic s t a t i o n s were occupied and 277 bottom sam ples w ere o b ta in e d from a p p ro x im a te ly 100 s t a t i o n s . Both h y d ro g ra p h ic d a ta and in fo rm a tio n from bottom samples a re in c o rp o ra te d in to th e p re se n t r e p o r t . The a r e a in v e s tig a te d , between ab o u t l a t i t u d e s 23°S. and 3 6 ° S ., co v ers th e s o u th e rn Mozambique Channel and p a r t o f th e southw est In d ia n Ocean d i r e c t l y so u th o f 8 th e Channel ( F ig . 1 ) . The c r u is e was com prised o f fo u r t r a n s e c t s from Durban to T u le a r, from T u le a r to Lourenco M arques, from Lourenco Marques to W alter S h o a ls , and from N a ta l Deep to Durban. S ta tio n s alo n g th e s e l i n e s were c lo s e ly sp aced a c r o s s th e c o n tin e n ta l B h elf and more w id ely spaced In g r e a t e r d e p th s. L o catio n o f h y d ro lo g ic a l s t a t i o n s and bottom sam ples a re shown r e s p e c t i v e l y on F ig u re s 1 and 2. Bottom sam ples were c o lle c te d w ith a v a r i e t y o f equipm ent In c lu d in g : F h le g e r ( g r a v ity ) c o r e r s used In tandem , bottom s n a p p e r, Campbell g rab (0 .6 m ^), Van Veen g ra b , M enzles tr a w l, A gassiz Trawl (w ith f in e mesh a t cod end) and Rock d re d g e . No s e t sam pling r o u tin e was f o l lowed s in c e th e equipm ent used was dependent on depth and bottom ty p e . U n fo rtu n a te ly no p is to n c o rin g equipm ent was a v a i l a b l e . Sach sample was d e s ig n a te d by u s in g th e number o f th e p re v io u s h y d ro g rap h ic s t a t i o n w ith a l e t t e r I n d ic a t in g th e s e r i a l o rd e r o f th e sam ple. L o c a tio n s o f bottom sam pling s t a t i o n s w ere, In some c a s e s , I d e n t i c a l to th o se o f th e h y d ro g ra p h ic s t a t i o n , b u t more o f te n were In te rm e d i a te In p o s it i o n betw een th e p re v io u s and su c c e e d in g hydro- g ra p h ic s t a t i o n s . S e v e ra l sam ples a re o f te n lo c a te d a t th e same s t a t i o n . A com plete s t a t i o n l i s t i s a v a ila b le In th e f i n a l c r u is e r e p o r t (Anon., 1965*)• On board th e s h ip th e to p o f th e c o re s were s ta in e d w ith ro s e b en g a l In o rd e r to re c o g n iz e l i v i n g f o r a m in lf e r s . 9 In th e l a b o r a t o r y , sam pling and p ro c e s s in g o f th e co res were a s fo llo w s : (1) m easurem ents o f com paction; (2) e x tr u s io n ; (3) s p l i t t i n g In two h a lv e s ( o n e - h a lf f o r s e d i ment a n a l y s is and o n e - h a lf f o r fa u n a l a n a l y s i s ) ; (4) pho to g rap h in g o f th e s p l i t s u rf a c e ; (5) ra d io g ra p h in g ; (6) d e s c r i p t i o n o f th e l l t h o l o g y ; (7) n o ta tio n o f o o lo rs (u s in g th e R o ck -co lo r c h a r t , G e o lo g ic a l S o c ie ty o f Am erica, 1961); (6) sam pling th e I n t e r v a l s 0-2 cm, 2-10 cm, and th e n 10 cm In crem en ts (e x c e p t when l l t h o l o g l c changes r e q u ire d a d i f f e r e n t sam pling I n t e r v a l ) . Acknowledgments The a u th o r w ishes t o e x p re ss h e r s in c e r e g r a titu d e to Dr. O r v ille L. Bandy, who was c h i e f s c i e n t i s t on c ru is e 7 o f th e R.V. ANTON BRUUN and who c o lle c te d th e m a te r ia l f o r t h i s i n v e s t i g a t i o n . He su g g ested t h i s s tu d y , and p ro v id ed p a t i e n t gu id an ce d u rin g i t s c o m p le tio n . S p e c ia l th an k s a r e extended to Dr. G erald J . Bakus, Dr. Donn S. G o r s lin e , and Dr. R ich ard 0 . Stone f o r t h e i r su g g e stio n s and c r i t i c a l rev iew o f th e m a n u sc rip t. The h e lp o f Mrs. B arb ara E. Haner and Mr. Louie N. M arln co v ich w ith E n g lish was much a p p r e c ia te d by a f o r e i g n e r . The a u th o r b e n e f ite d from d is c u s s io n s w ith Mr. R obert L. F l e i s h e r and Mr. F r i t z T heyer. S p e c ia l m ention sh o u ld be made o f th e k in d a s s i s ta n c e o f Dr. David A. H aner, o f C a l i f o r n i a S ta te P o ly te c h n ic U n iv e r s ity , who w rote th e com puter program used f o r t h i s r e s e a r c h , and o f Dr. Henry F. N elso n , o f Mobil R esearch and Development C o rp o ra tio n , f o r ra d io c a rb o n d a te s . Sedim ent te x t u r e s o f some sam ples were an aly zed by Mr. H. A. K a rl and Mr. B ria n R obinson, and Dr. John W . W ells o f C o rn e ll U n iv e rs ity I d e n t i f i e d th e c o r a l s . Sup p lem en tary h y d ro g ra p h ic d a ta were p ro v id e d by th e Oceano g ra p h ic D ata C en ter In W ashington, D. C. O ffic e and la b o r a to r y f a c i l i t i e s were p ro v id e d by th e A lla n Hancock F o u n d atio n o f th e U n iv e r s ity o f S o u th ern C a l i f o r n i a . This stu d y was su p p o rted by th e O ceanographic S e c tio n , N a tio n a l S cience F o u n d atio n , NSF G ra n ts GA-34145 and GB-8 6 2 8. H is to ry o f O ceanographic E x p lo ra tio n in th e Mozambique Channel A lthough a number o f o cean o g rap h ic s t u d i e s o f so u th w est In d ia n Ocean and th e Mozambique Channel a r e a were p u b lis h e d b e fo re th e Second World War (M ic h a e lis , 1923; F aech, 1926; S c h o tt, 1926, 1935; M o lle r, 1929, 1933; W llllm z lk , 1929; Thomsen, 1933, 1935; D i e t r ic h , 1935; Clowes and Deacon, 1935; Deacon, 1937), few o cean o g rap h ic s t a t i o n s had been o o c u p lsd . Among e a r ly e x p lo r e rs t h a t tr a v e r s e d th e Mozambique Channel were th e German sh ip M O W E (1912-1913) and th e D anish sh ip D A N A (1 929-1930). The Dutch v e s s e l GAUSS (1901-1903) and th e German sh ip PLANET (1906-1907) o c c u p lre d s e v e r a l s t a t i o n s in th e a r e a j u s t so u th o f th e 11 Mozambique Channel when s a i l i n g from Durban. I n v e s tig a to r s aboard th e R .K .S. DISCOVERY made a s e r i e s o f o b s e rv a tio n s In th e Mozambique Channel In 1935 and o ccupied a number o f s t a t i o n s e a s t o f Durban In 1930 and 1936. Ocean survey e x p e d itio n s In th e In d ia n Ocean were suspended d u rin g th e war and I t was n o t u n t i l 1950 t h a t o b s e rv a tio n s were c o n tin u e d . In 1950 th e B r i t i s h sh ip WILLIAM SCORESBY made th e f i r s t e a s t-w e s t t r a n s e c t In th e Mozambique C hannel, from B e lra to T u le a r. Ih e Danish sh ip GALATHEA c ro sse d th e Mozambique Channel In 1951 and th e R .R .S. DISCOVERY occupied a few s t a t i o n s s o u th e a s t o f Durban on h e r way to and from A n ta r c tic a . In 1957 th e f i r s t d e t a i l e d h y d ro lo g ic a l e x p lo r a tio n o f th e Mozambique Channel was u n d ertak en d u rin g th e f i r s t c r u is e o f th e French v e s s e l COM M A N D A N T ROBERT GIRAUD, w hich e x p lo re d th e e n t i r e chan n e l w ith a s e r i e s o f tr a v e r s e s from A fric a to M adagascar and a n o r th - s o u th l i n e o f s t a t i o n s . O ther s m a lle r French s h ip s In c lu d in g th e ORSOM I , th e LAPEROUSE, and th e NOSY-BE made l e s s e x te n s iv e e x p lo r a tio n and c o l l e c t e d o b s e rv a tio n s In l o c a l a r e a s o f th e Mozambique C hannel. In 1957-1958 th e American sh ip V EM A occupied a l i n e o f s t a t i o n s In th e a re a so u th o f th e Mozambique Channel d u rin g h e r 1 4 th c r u is e , and in 1958 th e South A fric a n sh ip S .A .S . NATAL occupied s t a t i o n s o f f th e c o a s t o f South A f r ic a , so u th o f Durban. D uring t h i s p e rio d r e l a t i v e l y few s tu d i e s concerned w ith th e sou th w est In d ia n Ocean and th e Mozambique Channel 12 were u n d e rta k e n . In th e southw est In d ia n Ocean, th e p a t t e r n o f w a te r masses and t h e i r movement was s tu d ie d by j Clowes (1950) from DISCOVSBY I n v e s t i g a t i o n s . Menache (1961, 1963) s tu d ie d s u rfa c e c u r r e n t p a t t e r n s and th e | d i s t r i b u t i o n o f w a ter mass c h a r a c t e r i s t i c s In th e Mozambi que Channel from th e o b s e rv a tio n s c o lle c te d by th e COM M ANDANT ROBERT GIRAUD. S e v e ra l s tu d ie s o f g e n e ra l c l r c u l a - i t l o n p a t t e r n In th e In d ia n Ocean, based on a v a ila b le d a ta 1 | a t t h a t tim e , were perform ed by T c h e m la £ t a l . (1951* i 1 9 5 8 ), Muromtsev ( i 960) , Ivanenkov and Gubin (I9 6 0 ), and | Le Plchon (I9 6 0 ). As a r e s u l t o f th e I n t e r n a t i o n a l G eophysical Year i | ( IGY) , th e p o s s i b i l i t i e s f o r I n t e r n a t i o n a l c o o p e ra tio n and l a r g e - s c a l e stu d y o f th e e n t i r e In d ia n Ocean was c o n s id e r ed In 1958. The S p e c ia l Committee on Oceanic R esearch (SCOR), w hich Is a f f i l i a t e d w ith th e I n t e r n a t i o n a l C ouncil f o r S c i e n t i f i c Unions (ICSU), developed a c o o rd in a te d p la n o f s tu d y . L ate In I9 6 0 , w ith in th e framework o f UNESCO, | f i n a l p la n s f o r th e e x p e d itio n were o u t l i n e d , and th e i I n t e r n a t i o n a l In d ian Ocean E x p e d itio n (IIOE) began In 1961. 1 D uring th e IIOE v a r io u s c o u n tr ie s c o n tr ib u te d to th e e x p lo r a tio n o f th e Mozambique Channel a r e a . U nited S ta te s e x p e d itio n s t h a t surveyed th e s o u th e rn p a r t o f th e Channel and th e a re a so u th o f I t were made aboard th e ATLANTIS I I ( c r u i s e 8 In 1963 and c r u is e 15 In 1965 ) » th e ARGO (e x p e d i t i o n s LUISIAD In 1962-1963) and th e R.V. ANTON BRUUN 13 ( c r u i s e s 7 and 8 In 1 9 6 4 ). The French e x p e d itio n s , aboard th e COM M ANDANT ROBERT GIRAUD ( c r u is e 2 In I960 and c r u is e 4 In 1962), and th e P o rtu g u e se e x p e d itio n s , aboard th e ALMIRANTE LACERDA ( c r u i s e s 1 and 2 In 1 964), occupied c lo s e ly spaced s t a t i o n s alo n g z ig -z a g tr a c k s I n s id e th e Mozambique Channel a t v a r io u s s e a so n s. P e rso n n e l o f th e R u ssian sh ip VOROBXEV made th r e e e a s t-w e s t p r o f i l e s In th e Mozambique Channel In 1965* South A fric a n o c e an o g ra p h ers, whose c o n tr ib u tio n to th e IIOE was th e e x p lo r a tio n o f th e A gulhas C u rre n t a r e a , e x p lo red th e so u th w e ste rn In d ia n Ocean so u th o f th e Mozambique Channel w ith th e s h ip s AFRICANA I I ( th r e e c r u i s e s d u rin g 1961-1963) and th e S.A .S . NATAL (fo u r c r u i s e s d u rin g 1962-1963)* They a ls o made l e s s e x te n s iv e e x p lo r a tio n In l o c a l a re a s w ith th e LADY THERESA. A f te r th e IIOE ended In 1965 th e M alagasy R epublic sh ip VAUBAN surveyed th e n o r th e r n p a r t o f th e Mozambique Channel d u rin g 1966-1968 and I s p la n n in g f u r t h e r e x p lo r a tio n In th e so u th e rn a r e a o f th e C hannel. A ll th e above e x p e d itio n s o c c u rred d u rin g th e so u th e rn s p r in g , f a l l and w in te r , w ith none In th e summer. O b se rv a tio n s o b ta in e d by South A fric a n r e s e a r c h e r s were f i r s t d is c u s s e d a t a symposium h e ld a t Cape Town, South A f ric a , In 1964, and r e s u l t e d In a number o f p ap ers r e l a t e d to oceanography (A nderson, 1964; D a rb y sh lre , 1964; H a r r i s , 1964; M ltc h e l In n e s , 1964; M o s te rt, 1966; N el, 1968; O rren, 1963» 1964, 1966; T a y lo r, 1964; V is s e r and 14 N iekerk, 1965; and o t h e r s ) . These s tu d ie s show th e s tr u c t u r e and s e a s o n a l v a r i a t io n s o f th e A gulhas C u rre n t so u th o f 30°S. N orth o f 30°S. few h y d ro lo g ic a l s tu d i e s have been p u b lish e d from th e d a ta accum ulated In th e Mozambique Channel d u rin g th e IIO E. French e x p e d itio n s were b r i e f l y m entioned In an a b s t r a c t by Menache (1966), and a map o f th e s u rfa c e Iso th e rm s o b ta in e d d u rin g th e two French ex p e d itio n s was drawn (A non., I960, 1963). D uring th e 1962 e x p e d itio n a towed e le c tr o d e G.E.K. c u r re n t m eter was used and th e r e s u l t s o f t h e m easurem ents s tu d ie d by Crepon (1965)* Some o f th e r e s u l t s o f th e P o rtu g u ese e x p e d itio n s were p u b lish e d (A non., 1965t>» 1967), and K h in lts a (1968) examined th e o b s e rv a tio n s from th e R ussian e x p e d itio n . However, he d id n o t draw c o n c lu sio n s about c u r r e n t p a t t e r n s as th e s t a t i o n s o ccu p ied by th e VOROBIEV d id n o t re a c h deep w a te r s . Donguy and P lto n (1969), from th e o b s e rv a tio n s o f th e Malagasy e x p e d itio n s , re c o g n iz e d th e g e n e r a l c i r c u l a t io n p a tte r n In th e n o r th o f th e Mozambique Channel between 16°S. and 7°S . a t v a r io u s s e a so n s. None o f th e r e c e n t s tu d ie s m entioned a r e d e t a i l e d I n v e s tig a tio n s o f t h e c i r c u l a t i o n p a tte r n in th e so u rce a r e a o f th e Agulhas C u r r e n t, which co rre sp o n d s to th e a r e a o f th e p r e s e n t s tu d y . B ro a d -sc a le o cean o g rap h ic r e p o r ts on th e In d ia n Ocean u n d ertak en a f t e r I960 In c lu d e works by Iv an o v - 15 F ra n ts k e v ic h (1 9 6 1 ), T a ft (1 9 6 3 ), Rochford (1964, 1 9 67), G a lla g h e r (1966), and S c h e rb in ln (1969)* Subm arine Topography P r i o r to th e I n t e r n a t i o n a l In d ian Ocean E x p e d itio n , l i t t l e was known a b o u t th e sea f l o o r topography o f th e In d ia n Ocean. B o tto m - r e lie f d a ta c o l le c te d d u rin g th e e a r ly y e a rs o f th e IIOE were used by Heezen and Tharp (1964, 1966, 1967) to c o n s tr u c t t h e i r p h y sio g rap h ic diagram s o f th e In d ia n Ocean t h a t d e fin e s th e m ajor p h y sio g rap h ic re g io n s o f th e In d ia n Ocean. S e v e ra l maps showing th e p r in c ip a l s t r u c t u r a l f e a t u r e s o f th e In d ia n Ocean a ls o were c o n s tru c te d by R u ssian s c i e n t i s t s ( L l s l t s l n and Zhivago, I960; B elousov e t a l . , 1964; Kanaev and Marova, 1964; U d ln tse v , 1 9 6 5) . A review o f th e s tr u c t u r e o f th e In d ia n Ocean was p re s e n te d by Laughton e t a ^ . (1 9 7 1 ). Dominated by a m ld -o ce an lc rid g e system , th e bottom c o n fig u ra tio n o f th e In d ia n Ocean has th e form o f an In v e rte d "7" and I s tr a n s e c t e d by numerous f r a c t u r e zones tre n d in g g e n e ra lly n o r th - n o r t h e a s t . A s t r i k i n g f e a tu r e o f th e In d ia n Ocean I s th e p re se n ce o f s c a t te r e d a se lsm lc r id g e s and p la te a u s a t r e l a t i v e l y sh allo w d e p th s , which were c a l l e d " m ic ro c o n tin e n ts " by Heezen and Tharp (1964, 1965, 1966) and " o c e a n ic r id g e s " by U d ln tsev (1 9 6 5 ). S e v e ra l o f th e s e , such a s th e S ey ch elles-M ascaren e bank, have c r u s t a l th ic k n e s s e s and se ism ic v e l o c i t i e s s im i l a r to 16 th o se on c o n tin e n ts (S hor and P o lla r d , 1963; D avis and F r a n c is , 1964; and o t h e r s ) . A selsm lc r id g e s and p la te a u s a re e lo n g a te and tr e n d l a r g e l y n o r th - n o r t h e a s t , p a r a l l e l to th e f r a c t u r e zones t h a t o f f s e t th e m ld -o ce an lc r id g e . The sea f lo o r o f th e so u th w estern p a r t o f th e In d ia n Ocean h as been I n v e s tig a te d p r im a r ily by South A fric a n r e s e a rc h e r s (M allo ry , 1964; M allo ry e t a l . . 1964; Simpson, 1964; W a lte rs, 1 9 6 4 ). In th e southw est In d ia n Ocean a s e r i e s o f f r a c t u r e zo n es, namely th e Mozambique F ra c tu re | Zone, P rin c e Edward F r a c tu r e Zone and M alagasy F ra c tu re I I | Zone, which u s u a lly tr e n d n o r th - n o r t h e a s t , c u t th e so u th w e s t e r n b ran ch o f th e m ld -o ce an lc r id g e . Two l i n e a r i " m ic ro c o n tin e n ts ," M adagascar (p ro lo n g a te d by I t s so u th e rn e x te n s io n th e M adagascar P la te a u ) and th e Mozambique P la te a u (which e x te n d s so u th from Mozambique) a ls o tre n d n o r th - n o r t h e a s t . These have ste e p l i n e a r s c a rp s on t h e i r e a s te r n s id e s , s u g g e s tin g a s t r u c t u r a l r e l a t i o n s h i p w ith th e f r a c t u r e zo n es. Thus th e so u th w e ste rn In d ia n Ocean f l o o r e x p re sse s th e g e n e r a l l i n e a r In d ia n Ocean f a b r i c . On F ig u re 2 th e bath y m etry o f th e stu d y a r e a i s d e p ic te d and F ig u re 3 shows th e p h y sio g ra p h ic p ro v in c e s . The f l o o r o f th e Mozambique Channel i s t i l t e d g e n tly southw ard, and s o u th o f l a t i t u d e 25°S. th e s u rfa c e I s broken in to s e v e r a l d i s t i n c t com ponents. The M adagascar and Mozambique a se lsm lc p la te a u s m a in ta in an av e ra g e d ep th F i g u r e 3 P h y sio g ra p h ic p ro v in c e s o f th e Mozambique Channel and Southw est In d ian Ocean (a d ap te d from Heezen and Tharp, 1966). 17 18 45* E W 15* S r~ 2 0 * h 25* H 30* h Z 5 * < £ • 7 5 ) Abyssal Plain \ S i d i n i n t S o u r e s o f ap p ro x im a te ly 2500 m betw een th e 25th and 3 5th p a r a l l e l s On th e M adagascar P la te a u , which i s a southw ard e x te n s io n o f th e c o n t i n e n t a l is la n d o f M adagascar, a t l a t i t u d e 3 3 °3 0 'S . a re th e W alter S h o a ls, which a re a s l i t t l e as 10 m below sea l e v e l . The Mozambique P la te a u i s t i l t e d tow ards th e so u th w e st, where i t p a s se s in to th e sm a ll l i n e a r T ra n sk e i B a s in , th e n o rth e rn e x tre m ity o f w hich i s e v id e n t on F ig u re s 2 and 3 a t deptEs o f 3000 to 4000 m. Between th e M adagascar P la te a u and th e Mozambique P la te a u i s a l i n e a r a b y s s a l p l a i n , th e N a ta l B a s in , th e w e s tw a r d - tilte d f l o o r o f w hich deepens p r o g r e s s iv e ly southw ard, p a ssin g i n t o th e N a ta l Beep o f o v er 6000 m d e p th . N om enclature o f In d ia n Ocean p h y sio g ra p h ic f e a tu r e s i s s t i l l u n s e t t l e d . In com paring works o f v a rio u s a u th o r s , one f in d s t h a t d i f f e r e n t names were used to d e s ig n a te th e same f e a t u r e , and t h a t one name has been u sed to d e s ig n a te two d i f f e r e n t f e a t u r e s . Some exam ples o f th e s e d i s c re p a n c ie s a r e : th e Mozambique P la te a u (Heezen and Tharp, 1967) has been r e f e r r e d to as th e "Mozambique Ridge" (Heezen and Tharp, 1964, 1965, 1966; Ludwig g t a l . , 1968; Ewing e t a l . , 1969), th e "Mozambique T e rrace"(S im p so n , 1964 W a lte rs , 1 9 6 4 ), th e "N a ta l Ridge" (K ing, 1962) and th e "S o u th Mozambique R ise" (Ewing and Ewing, 1971)• The M adagascar P la te a u (Heezen and T harp, 1967) has been c a lle d "M adagascar Ridge" by many a u th o r s . The N a ta l B asin i s d e s ig n a te d th e "Mozambique B asin" by R u ssian a u th o rs 20 (Belousov e t a l . , 1964; Kanaev and Marova, 1964) and a ls o h a s been term ed "M adagascar B asin" (Ewing e£ a l . , 1969; Ewing and Ewing, 1 971). The l a t t e r name i s used by Heezen and Tharp (1967) a s w e ll as R u ssian a u th o rs to d e s ig n a te th e b a s in e a s t o f th e M adagascar P la te a u and so u th o f M a u ritiu s and La R eunion, which has a ls o been c a lle d th e "Reunion B asin" (Le P ich o n , I9 6 0 ; W a lte rs, 1964) and th e "M au ritiu s B asin" (K ing, 1 9 62). N orth o f l a t i t u d e 25°S. th e Mozambique Channel e x h ib its a more g e n tle subm arine topography ra n g in g in d ep th from 1000 m to 3000 m. A sm all a b y s s a l p la in l i e s between th e 2 1 st and 23rd p a r a l l e l s a t d ep th s exceeding 3000 m. E ast o f t h i s a b y s s a l p la i n s e v e ra l seam ounts a re p r e s e n t in th e c e n te r o f th e C hannel, and two p ro tru d e above s e a - l e v e l . These two sm a ll v o lc a n ic i s l e t s a re Europa Is la n d (25 m above s e a - l e v e l ) and B a s s a s -d a -In d ia (3 m above s e a - l e v e l ) . A l a r g e , d e e p ly -c u t subm arine canyon, th e Zambezi Canyon, le a d s from th e c o n tin e n ta l m argin o u t to th e N a ta l B a sin . T his canyon, p ro b a b ly c u t by t u r b i d i t y - c u r r e n t a c t i o n , i s c h a r a c te r iz e d by la r g e n a t u r a l le v e e s covered by d u n e -lik e f e a tu r e s (L an g seth and Heezen, 1964, 1 9 65). C o n tin e n ta l s lo p e s in th e stu d y a r e a a re s te e p , w ith g r a d ie n ts o f a p p ro x im a te ly 1:30 to 1 :4 0 . C o n tin e n ta l sh e lv e s a re v ery n arro w , m ainly 3 to 10 km w ide, w ith g r a d ie n ts o f a b o u t 1 :1 0 0 0 . A b ro a d e r c o n tin e n ta l s h e l f 21 l i e s o f f th e p ro tr u d in g c o a s t o f so u th e rn Mozambique and o f f th e so u th e rn t i p o f M adagascar. N ature o f th e S e a -F lo o r and O rig in o f th e Mozambique Channel The n a tu re o f th e Mozambique Channel as w e ll as th e r e l a t i o n s h i p between M adagascar and A fric a rem ains a problem . I t I s a c c e p te d t h a t M adagascar i s a sm all con t i n e n t a l fragm ent o r " m ic ro c o n tin e n t" b u t th e n a tu re o f th e c r u s t b en eath th e Channel i s d is p u te d and v a rio u s i n fe re n c e s have been drawn. For th o se who re g a rd M adagascar a s rem ain in g in i t s p r e s e n t p o s itio n th ro u g h o u t g e o lo g ic tim e , th e c r u s t under th e Mozambique Channel i s i n t e r p r e t e d as c o n tin e n ta l (D ixey, 1956; Baker and M il l e r , 1963; P epper and E v e rh a r t, 1963; Holmes, 1965; Flow er and S tro n g , 1969; T a rlin g , 1971). Flow er and S tro n g gave as an "u nequivocal e v id en ce" o f n o n -o cean ic c r u s t b e n e a th th e Mozambique Channel th e p resen ce o f sand in c lu s io n s in th e la v a s o f th e Comorian i s la n d s , b u t W right and McCurry (1970) s tr o n g ly c r i t i c i z e d t h e i r c o n c lu s io n s . Talw anl (1 9 6 2 ), on th e b a s is of g r a v ity d a ta , showed t h a t th e Mozambique Channel i s i s o s t a t i c a l l y com p e n s a te d . He n o ted t h a t " t h i s means t h a t th e mass below i t must be d i f f e r e n t from t h a t u n d er th e c o n tin e n t," and added t h a t " th e c r u s t u n d er th e Mozambique Channel cannot 22 be a t y p i c a l o c e a n ic c r u s t . " F a irb r ld g e (1965) su g g ested t h a t th e w estern p a r t o f th e In d ia n Ocean I s i n te r s p e r s e d by an in te rm e d ia te - ty p e o r s e m ic o n tin e n ta l c r u s t ( " q u a s i- c ra to n " ) and re g a rd e d th e Mozambique Channel o f such a ty p e , w ith s tr e tc h e d o r th in n e d c r u s t . A s im i l a r ty p e was proposed by Holmes (1965) who re g a rd e d th e c r u s t u n d er th e Mozambique Channel a s b e in g " th in n e d o u t." The n a tu re o f th e Mozambique P la te a u i s s t i l l ob s c u re . T his f e a t u r e has been I n te r p r e t e d by a u th o rs a s a c o n tin e n ta l p r o je c t io n and a s s o c ia te d to th e l i n e a r n o r th - so u th m lc ro c o n tln e n ts o f th e In d ia n Ocean w hich a re f r a g m ents o f c o n tin e n ta l c r u s t (Heezen and T harp, 1965). Simp son (1964) c o n s id e re d th e Mozambique P la te a u (Mozambique T e rra c e ) to g e th e r w ith th e Agulhas P la te a u a s a down- f a u lte d and t i l t e d p o r tio n o f a fo rm e rly broad c o n tin e n ta l s h e l f . The age o f f a u l t i n g would be p o s t-C re ta c e o u s and p o s s ib ly even p o s t - T e r t l a r y . Simpson su g g e ste d t h a t th e p la te a u i s p ro b ab ly u n d e r la in by a th i c k accu m u latio n o f C retaceo u s and T e r t i a r y sed im en ts and t h a t th e Mozambique P la te a u may r e p r e s e n t th e p r e s e n t s i t e o f a p o r tio n o f th e K arroo b a s in and o f th e Cape fo ld e d b e l t m issin g on th e A fric a n c o n tin e n t. Ludwig e£ al.. (1968) re c o rd e d a s e r i e s o f s e l s m l c - r e f r a c t i o n - p r o f i l e s on th e c o n t i n e n t a l s h e l f o f s o u th e a s te rn A f ric a betw een l a t i t u d e s 29°S. and 35°S. and on b o th s id e s o f t h e Mozambique P la te a u . They e s ta b lis h e d an e a s t-w e s t s e c tio n from th e c o n tin e n ta l s h e l f o f f Durban 23 to th e N a ta l B a s in , and su g g e ste d t h a t th e Mozambique P la te a u may p o s s ib ly be a d e p o s ltlo n a l f e a t u r e b u i l t up o f f a i r l y lo w - v e lo c ity m a t e r ia l on an ooeanlc c r u s t . " A s e i s m i c - r e f r a c ti o n p r o f i l e In th e T ran sk ei B asin (Green and H a le s, 1966) r e v e a le d th ic k low v e l o c i t y se d im e n ts on o cean ic c r u s t a l m a t e r i a l . U n c e r ta in tie s w i l l rem ain u n t i l a d d i t i o n a l m easurem ents a re made on th e Mozambique P la te a u to d eterm in e w h eth er I t s u n d e rly in g s t r u c t u r e I s con t i n e n t a l o r o c e a n ic . In any e v e n t, I t can be concluded w ith Ludwig £ t f il. (1968) t h a t th e Mozambique P la te a u ap p e a rs to be bounded on b o th s id e s by o ce a n ic c r u s t . Laughton e t a l . (1971) proposed t h a t th e la c k o f any m ajor d i s c o n t i n u i t y betw een th e N a ta l B asin and th e Mozambique Channel to th e n o r th s u g g e sts a c o n t i n u i t y o f th e o o ean lc s t r u c t u r e found In th e N a ta l B a sin . The M adagascar P la te a u Is c o n sid e re d by many I n v e s t i g a to r s as th e southw ard e x te n s io n o f M adagascar and I s t h e r e f o r e p ro b a b ly u n d e r la in by c o n tin e n ta l c r u s t . I t I s bounded on th e e a s t by th e same l i n e a r f a u l t w hich I s a northw ard e x te n s io n o f th e M alagasy F ra c tu re Zone c r o s s in g th e so u th w est In d ia n R idge. C oncerning th e n a tu r e o f th e Mozambique C hannel, I t can then be co n clu d ed , a s Laughton ejj, a i . (1971) su g g e ste d In t h e i r s h o r t rev iew o f th e s tr u c t u r e o f th e In d ia n Ocean, t h a t "M adagascar and I t s southw ard e x te n s io n form an i s o l a t e d c o n t i n e n t a l b lo c k s e p a ra te d from A f r ic a by a c r u s t 24 t h a t may be o c e a n ic ." How th e Mozambique Channel o r ig in a te d h a s been an en ig m atic problem deb ated by many g e o l o g i s t s . P r i o r to th e c o n cep ts o f s e a - f l o o r sp re a d in g and p la te t e c t o n i c s , th e fo rm atio n o f th e Mozambique Channel was I n te r p r e t e d In v a rio u s ways. P ale o g e o g ra p h e rs q u e s tio n in g th e c o n tin e n ta l d r i f t th e o ry made d i f f e r e n t a tte m p ts to e x p la in s i m i l a r i t i e s between th e so u th e rn c o n tin e n ts . Land b rid g e s b e tween A fric a and M adagascar were su g g ested . The p a le o - g eo g rap h lc maps o f T erm ler and Term ler (1952) show th e "Canal de Mozambique" In e x is te n c e sin c e L a te Perm ian tim e, f i r s t as a g u l f (c lo s e d In th e so u th ern p a r t ) , o nly b re a k ing th ro u g h In L la s s lc tim es when a th ro u g h m arine con n e c tio n was p o s tu la te d between th e Himalayan re g io n and C h ile , v ia South A f r ic a . In th e p a s t many g e o lo g is ts c o n sid e re d th e Mozambi que Channel to be a g e o s y n c lin a l d e p re ssio n In which s e d i m ents accum ulated o v er tim e I n t e r v a l s , a t l e a s t s in c e th e Pernl& n, o r even p o s s ib ly th e l a t e r P recam brlan (D lxey, 1956. 1959* I960; Baker and M il l e r , 1963; P epper and E ver h a r t , 1963; Holmes, 1965; Flow er and S tro n g , 1969; T a r- l l n g , 1971)* Dlxey re g a rd e d th e Mozambique Channel a s a su b sid in g g e o s y n c lln e , "one o f th e w o rld 's d e e p e s t," which had undergone downward movements r e c u r r e n t a lo n g f a u l t s and In which 14 km o f sed im en ts accum ulated s in c e th e P erm ian. Pepper and E v e rh a rt (1963) fo llo w ed t h i s co n c e p t c o n s tr u c t - 25 ed two h y p o th e tic a l s e c tio n s a c ro s s th e Channel based on o u tc ro p s and w e ll d a ta on e i t h e r s id e o f th e C hannel. They showed t h a t th e Mozambique Channel su b sid e d alo n g s e v e ra l normal f a u l t s w ith su b seq u en t s e d im e n ta tio n . T h e ir e s tim a te o f d e p th to P recam brlan basem ent I s alm o st 7500 m. G e o lo g is ts w orking w ith th e c o n tin e n ta l d r i f t h y p o th e s is proposed t h a t M adagascar moved away from th e A fric a n c o a s t, b u t th ey do n o t a g ree on e i t h e r th e p a le o - p o s ltlo n o f M adagascar w ith r e s p e c t to th e A fric a n c o a s t o r on th e age o f I t s s e p a r a tio n . Suggested ages o f s e p a ra tio n range from Perm ian to C enozolc. On th e b a s is o f v a rio u s g e o lo g ic a l c r i t e r i a , two I n d e n ta tio n s o f th e A fric a n c o a s t have been proposed as a p r e d r i f t p o s itio n f o r M adagascar. F i r s t , M adagascar was f i t t e d by some I n v e s t i g a t o r s In to th e Mozambique p o s it i o n o f th e A fric a n m argin (C arey, 1958; Ahmad, 1968; S lg a l e t a l . , 1970; W right and MeCurry, 1970; H e i r t z l e r , 1971). In t h i s h y p o th e s is M adagascar would have moved to th e e a s t from A f ric a . Second, M adagascar h a s been f i t t e d In th e Tanzanla-K enya p o s it i o n o f th e A fric an m argin Im plying a southw ard movement o f M adagascar r e l a t i v e to A fric a (D uTolt, 1937; K ing, 1962; F a ir b r id g e , 1965; D ie tz and H olden, 1970; Sm ith and H allam , 1970; H e i r t z l e r and B urroughs, 1971). H e i r t z l e r and B urroughs (1 9 7 1 ), a f t e r a re c e n t g e o lo g ic a l and g e o p h y s ic a l survey In th e n o r th e rn a r e a o f th e Mozambique C hannel, observed a r i d g e - l i k e f e a tu r e tre n d in g a p p ro x im a te ly n o r th - s o u th alo n g th e 4 l° 3 0 'E . m e rid ia n . They n o ted t h a t n e i t h e r th e morphology n o r th e m agnetic an o m alies a re t y p i c a l o f a sp re a d in g a x i s . These a u th o rs examined th e h y p o th e s is in f e r r e d by v a rio u s a u th o rs and fa v o r th e th e o ry t h a t M adagascar moved so u th . M otion i s c o n sid e re d to have began in th e e a r l y to m iddle Cenozoic and c o n tin u e s to d a y . A n o r th e rn p o s it i o n o f M adagascar r e l a t i v e to A fric a a ls o i s fa v o red by D ie tz and Holden (1970) in t h e i r l a t e s t model f o r th e A t la n tic and In d ia n Oceans fo rm a tio n s based on s e a - f l o o r sp re a d in g and p l a t e t e c t o n i c s c o n c e p ts . F u rth erm o re , th ey made a r e c o n s tr u c tio n o f th e frag m en ta tio n and d is p e r s io n o f c o n tin e n ts which o c cu rre d in each m ajor g e o lo g ic p e r io d . In t h i s model a l l th e c o n tin e n ts were c o n fig u re d in to th e u n iv e r s a l landm ass o f Pangaea u n t i l th e end o f th e Perm ian. In th e T r i a s s l c , th e b re a k up o f Pangaea commenced, th e so u th w est In d ia n Ocean r i f t was c r e a te d opening th e In d ia n Ocean. D uring J u r a s s i c and C re ta c e o u s tim e th e m otions c o n tin u e d , f u r t h e r opening th e In d ia n Ocean. A f r ic a , w ith M adagascar a tta c h e d to i t s m arg in , was moving northw ard w ith a s i n i s t r a l r o t a t i o n , w h ile I n d ia was l i f t e d o f f A n ta r c t i c a . The s p l i t t i n g away and d ro p p in g o f f o f M adagascar from th e m ainland o f A fric a o c c u rre d in C re tac e o u s tim e . I t i s i n t e r p r e t e d as an e a r ly o f f s h o o t o f th e C a rls b e rg r i f t by D ie tz and Holden 27 who s t a t e d "w ith th e In v a sio n o f an o f f s h o o t o f the C a r ls - b erg r i f t In to th e A fric a n c r a to n , th e M adagascar sub c o n tin e n t was a r r e s t e d In I t s n o rth e rn movement and r o ta te d somewhat as a s e p a ra te c r a to n lc b lo ck " w h ile A fric a con tin u e d I t s n o rth e rn f l i g h t . During Cenozolc tim e, a c c o rd in g to D ie tz and Holden, th e branch o f th e C a rlsb e rg r i f t to o k up a new p o s itio n w ith in A fric a c r e a t i n g th e r i f t zone o f e a s te r n h ig h A f r ic a , and th e A fro -In d ia n r i f t be came l a r g e l y I n a c tiv e because the n o rthw ard m otion o f A fric a was blocked by Europe. A northw ard and a n tic lo c k w is e movement o f A fric a to g e th e r w ith A n ta r c tic a w ith r e s p e c t to th e rem ainder o f Gondwanaland a ls o has been p o s tu la te d by McElhlnny (1 9 6 8 ). In t h e i r v a rio u s p r e d r i f t r e c o n s t r u c t i o n s , th e I n v e s t i g a t o r s make no comments on th e p o s it i o n o f th e Mozambique P la te a u . I f , however, t h i s f e a tu r e I s u n d e r l a i n by a c o n tin e n ta l c r u s t and I s a s M adagascar and th e M adagascar P la te a u a r e a l m ic ro c o n tin e n t, i t m ust occupy a gap In th e f i t o f th e c o n tin e n ts . I f th e Mozambique and th e M adagascar P la te a u s a r e u n d e r la in by c o n tin e n ta l c r u s t , t h e i r s in k in g rem ains to be e x p la in e d . The p a t t e r n o f sp re a d in g a lo n g th e southw est m id- In d ia n Ocean r id g e i s d i f f i c u l t to e s t a b l i s h because i t s c h a r a c t e r i s t i c s d i f f e r from t y p i c a l m id-ocean r id g e s . No m agnetic p a t t e r n o v er th e r id g e I s r e c o g n iz a b le . Vine (1966) su g g este d t h a t t h i s b ran ch i s w ith o u t a c tiv e s p re a d - 28 in g now. Le Pichon and H e i r t z l e r (1968) r e p o r te d t h a t th e so u th w est branch h as not been th e s i t e o f any s i g n i f i c a n t s p re a d in g sin c e th e M esozoic e r a . These a u th o r s , more o v e r, as w e ll as Le Pichon (1968) would a llo w a slow s p re a d in g r a t e w hich, combined w ith th e p re se n c e o f numerous f r a c t u r e zones i n t e r s e c t i n g th e r id g e c r e s t , may e x p la in i t s anomalous c h a r a c t e r i s t i c s . A s im i l a r con c lu s io n o f slow s p re a d in g , o r r e l a t i v e l y r e c e n t i n i t i a t i o n o f a c tiv e s p re a d in g , i s re a c h e d by Ewing e t a l . (1969) from th e narrow ness o f th e zone b a rre n o f sedim ent n e a r th e c r e s t . S c h llc h and P a t r i a t (1968) and Sykes (1970) sug g e s te d t h a t th e tr u e o r i e n t a t i o n o f th e r id g e a x is is w est n o r th w e s t- e a s t s o u th e a s t and th e y a s c r ib e th e f a i l u r e to d e te c t m easurable s e a - f l o o r sp re a d in g alo n g t h i s branch to th e u n fo rtu n a te o r i e n t a t i o n o f s tu d ie d p r o f i l e s which would p a r a l l e l th e rid g e c r e s t . Sykes r e p o rte d t h a t se is m ic a c t i v i t y alo n g th e sou th w est m id -In d ia n Ocean r id g e i s a s g r e a t as t h a t alo n g o th e r p a r t s o f th e w orld r i f t sy stem , I n d ic a tin g t h a t s e a - f l o o r sp re a d in g i s o c c u rrin g t h e r e now. In c o n c lu s io n , th e s e a - f l o o r o f th e sou th w est In d ia n Ocean o f f th e c o a s t o f so u th w est A f ric a was i n i t i a t e d by s e a - f l o o r sp re a d in g a s s o c ia te d w ith th e fo rm a tio n o f th e sou th w est m id -In d ia n Ocean r id g e , p ro b ab ly a t th e end o f T r i a s s i c tim e . Hew s e a - f l o o r was formed d u rin g th e Meso z o ic e ra a lo n g t h i s b ran ch o f th e r id g e w hich a ls o may have been th e s i t e o f a d d i t i o n a l sp re a d in g d u rin g Cenozolc and R ecent tim e s . M adagascar, w ith i t s southw ard e x te n s io n th e M adagascar P la te a u , was carv ed away from th e A fric a n m argin p ro b a b ly from th e Tanzanla-K enya p o s itio n p o s s ib ly in C retaceo u s tim e . The p o s it i o n o f th e m ic ro c o n tin e n t r e l a t e d to th e A fric a n m argin s h i f t e d owing to th e northw ard movement o f A f r ic a , th e p r e s e n t p o s itio n b e in g reach ed in Cenozolc tim e . A ccording to t h i s scheme th e Mozambique Channel th u s would have e x is te d w ith i t s p r e s e n t con f i g u r a t i o n s in c e th e C enozolc. The Channel i s l i k e l y u n d e r la in by an o c e a n ic c r u s t o v e r w hich t h i c k l a y e r s o f u n c o n s o lid a te d sed im en ts have accum ulated (Ewing et. a l . . 1969)* The Mozambique P la te a u i s o f a y e t unknown n a tu r e . Many q u e s tio n s a re s t i l l posed on th e n a tu re and age o f th e Mozambique Channel basem ent, as w e ll as on th e p ro c e s s o f fo rm a tio n o f th e C hannel, and d e b a te w i l l no doubt c o n tin u e . Problem s m ight be so lv ed w ith d r i l l i n g to basem ent d u rin g th e fo rth co m in g Deep-Sea D r i l l i n g P r o je c t in 1972. Geology and Geomorphology o f B o rd erin g Lands The In d ia n Ocean i s b o rd ered by c o n tin e n ta l m asses which a re c o n s id e re d to be th e frag m en ts o f Gondwanaland. These a re oomposed p re d o m in a n tly o f igneous and m eta- m orphic ro c k s d a tin g back to th e P recam b rlan , b o rd ered by 30 a f r in g e o f younger se d im e n ts. The A fric a n s h ie ld l i e s to th e w est o f th e Mozambique C hannel, w h ile a detach ed p o r tio n o f t h i s s h i e l d , th e I s la n d o f M adagascar and i t s southw ard e x te n s io n th e M adagascar P la te a u , bounds i t to th e e a s t . The A fric a n s h ie ld i s b o rd ered by f a u l t s o r m o n o clln al downwarping (N atal m o n o c lin e ). U p l i f t s and downwarps o f re g io n s have o c c u rre d th ro u g h o u t g e o lo g ic tim e. Geomorphic s tu d i e s in E a st and S outh A fric a (D lxey, I960; K ing, 19^0, 1962) in d ic a te d t h a t th e h in te r la n d o f th e Gondwana c o a s ts show sig n s o f rem ark ab le and lo n g - l a s t i n g m a rg in a l u p l i f t . As a r e s u l t , th e p i c t u r e o f th e c o n tin e n t i s an u p t l l t e d blo ck n e a r th e c o a s t s lo p in g back g e n tly tow ard th e i n t e r i o r . M adagascar e x h i b i t s f e a t u r e s s im i l a r to th e m ain la n d . The i s l a n d form s a la r g e p la te a u i n c l i n e d westward which i s te rm in a te d a b r u p tly on i t s e a s te r n s id e by a l i n e a r f a u l t zo n e. T his marks th e edge o f th e Precam brlan block and has been a c t i v e s in c e C retaceo u s tim e (D ixey, I9 6 0 ). The l i n e a r f a u l t , whioh a ls o bounds th e e a s te r n sid e o f th e M adagascar P la te a u , i s th e no rth w ard e x te n s io n o f th e M alagasy F r a c tu re Zone. The whole o f th e e a s te rn p a r t o f M adagascar i s composed o f h ig h ly metamorphosed Archean ro c k s w ith tr e n d s s im i l a r to A fric a n P recam brlan tr e n d s . The w e s te rn c o a s ta l re g io n i s co v ered by a b e l t o f sed im en tary r o c k s , an averag e 150 km w ide, w hich d e c re a se s in age p r o g r e s s iv e ly tow ards th e c o a s t (F u ro n , I9 6 0 , 1966). 31 A resum e o f th e geology o f th e lan d s su rro u n d in g th e In d ia n Ocean was p u b lish e d by P ep p er and E v e rh a rt (1963) to g e th e r w ith a map showing th e g e n e ra l d i s t r i b u tio n o f th e s u rfa c e ro ck s and th e r e l a t i o n s h i p o f known f a u l t s . P a r t o f t h i s map Is rep ro d u ced on F ig u re 4 . F ra c tu re d o r m o n o clin al c o a s ts n o rm a lly have narrow s h e lv e s . T h is I s t y p i c a l o f S u e s s 1 " A tla n tic Type" o o a s ts and I s c h a r a c t e r i s t i c o f th e c o a s t o f S o u th e a st A fric a . As review ed by King (1 9 6 2 ), th e s h e l f o f f S o u th e a st A fric a I s "one o f th e n a rro w e st In th e w o rld ." The N a ta l c o a s tla n d s a re s te e p and ru g g ed . South o f Durban th e c o n ti n e n t a l s h e lf I s v e ry n arro w , b ein g o nly 3 to 16 km wide alo n g a s t r a i g h t c o a s t l i n e w hich extends southw ard to P o rt E liz a b e th . T his s t r a i g h t c o a s t li n e c u ts o b liq u e ly th e c o a s t a l edge o f th e K arroo b a s in . N orth o f 3 1 °3 1 'S . l a t i t u d e , th e Karroo b a s in I s fo ld e d down by an e a s t d ip p in g m o n o c lin a l fle x u re o f E a rly J u r a s s i c ag e, known a s th e N a ta l m onocline. A s e c t io n a o ro s s th e con t i n e n t a l s h e l f o f f th e N a ta l c o a s t I s p r e s e n te d by Ludwig e t a l . (1 9 6 8 ). These a u th o rs made a s e r i e s o f se lsm lc - r e f r a c t l o n p r o f i l e s on th e c o n tin e n ta l s h e l f betw een Cape S a in t F r a n c is and Durban and p r e s e n t a t e n t a t i v e c o r r e l a t i o n betw een th e o f fs h o re seism ic s e c t io n and th e s t r a t l - g ra p h ic s e c tio n o f th e a d ja c e n t o n sh o re a r e a . Of s p e c ia l i n t e r e s t I s t h e i r d isc o v e ry o f o f f s h o r e s e d im e n t- f ille d d e p re s s io n s In which C retaceous and younger sed im en ts r e s t Figure 4 Geology o f la n d s b o rd e rin g th e Mozambique Channel and Southw est In d ia n Ocean (a d a p te d from P epper and E v e rh a rt, 1963)* 1 . Q u atern ary and T e r t i a r y , c o n tin e n ta l 2. T e r t i a r y , m arin e . 3. C retaceo u s and J u r a s s i c , con t i n e n t a l . 4 . C re ta c e o u s, J u r a s s i c , and T r i a s s i c , m arin e . 5. K arroo s e r i e s . C a rb o n ife ro u s to T r i a s s i c , c o n t i n e n t a l . 6. Lower and M iddle P a le o z o ic . 7* V olcanic r o c k s , younger th an P recam b rlan . 8 . P recam brlan basem ent complex. 9* F a u lt. 32 4 0 ° 20° •20°S GREAT EUROPA TULEAR Barra UOURENCO I MARQUES MARIE ' CAP ST. LUCIA ZO O 300Kin 25° S 34 on a Cape-K arroo ( c o n t in e n ta l d e p o s its , C a rb o n ife ro u s to T r i a s s i c ) s u b stra tu m . These d e p re ss io n s a re o f a y e t un known c h a r a c t e r , t h e i r oceanward l i m i t s a r e n o t d eterm in ed . One o f them o c c u rs in th e Durban v i c i n i t y . About midway betw een Durban and Cape S a in t L u cia th e c o n tin e n ta l s h e l f w idens to 45 km, th e n narrow s a g a in to 6 km. As r e p o r te d by P epper and E v e rh a rt (1 9 6 3 ), th e w id er p a r t o f th e s h e l f l i e s seaward o f two e a s t-w e s t tre n d in g c o a s t a l f a u l t s . T his im p lie s t h a t th e s h e lf h e re may be p a r t o f a f a u l t b lo c k assum ing th e s e f a u l t s c o n tin u e o f f s h o r e . In t h i s a r e a o f th e s h e l f , n e a r th e Tugela R iv e r mouth, more c o n c e n tra te d s h e l f sam pling was accom p lis h e d d u rin g c r u is e 7 o f R.V. ANTON BRUUN. From Cape S a in t L ucia to Lourenco M arques Bay th e c o a s t i s s t r a i g h t , bounded by c l i f f s , w ith a b o rd e rin g s h e lf o f o n ly 5 to 6 km w id e. The c o a s t ro u g h ly p a r a l l e l s th e Lebombo M ountains. T h is m ountain ra n g e , r i s i n g ab o u t 80 km in la n d , i s a n o rthw ard c o n tin u a tio n o f t h e N atal m o n o clin al s t r u c t u r e . The s h e lf h e re may mark a f a u l t sc a rp p a r a l l e l i n g th e f a u l t alo n g th e e a s te r n edge o f th e Lebombo M ountains. In th e p r e s e n t stu d y no sam pling was done on th e v e ry narrow s h e l f , b u t o ffs h o re i n v e s t i g a t i o n o f th e up p er s lo p e r e v e a le d a scoured h a rd b ottom . The bay o f Lourenco M arques, commonly known in E n g lis h as D elagoa Bay, i s 32 km in w idth and 40 km in le n g th and i s f o r th e m ost p a r t sh a llo w . The b ay , w hich i s 35 th e drowned e s tu a ry o f s e v e r a l c o n flu e n t sm all r iv e r s * in d i c a t e s t h a t changes in s e a - l e v e l have o c c u rre d . O ther s ig n s o f s e a - l e v e l changes in t h i s a r e a a re shown by wave- out p la tfo rm s a lo n g th e ro ck s o f th e e a s te r n sh o re im ply in g an e le v a tio n o f th e s h o r e l i n e . Much o f th e bay i s l e s s th a n 10 m deep* th e r i v e r ch an n el b e in g d e e p e r. From th e o u t l i n e o f th e s h o a ls w ith in th e bay* Pepper and E v e rh a rt (1963) su g g e ste d t h a t th e banks may be a lig n e d alo n g s t r u c t u r e s t h a t a r e s im i l a r to and o f th e same g e n e r a l tre n d s a s th o se on la n d . Lourenco Marques bay i s bounded on th e e a s t by th e In h aca p e n in s u la p ro lo n g a te d to th e n o r th by In h aca i s la n d and a l i n e o f s h o a ls . The l i n e o f t h i s b a r r i e r form s a s p i t com parable w ith s e v e r a l o th e r n o r th - tr e n d in g s p i t s on th e e a s t c o a s t o f A fric a which formed as a r e s u l t o f th e a c tio n o f an in sh o re n o r th - flo w in g c u r r e n t (Macnae and K alk, 1958). C o ral grow th o c c u rs on th e m argin o f some o f th e ch an n els a t th e en tr a n c e o f th e bay* so u th o f In h aca i s l a n d . As r e p o r te d by Macnae and Kalk (1958) who p u b lish e d a d e t a i l e d stu d y o f th e fau n a and f l o r a around In h aca isla n d * th e s e c o r a l r e e f 8 a t 26°S. a r e th e m ost s o u th e r ly in th e w o rld . From Lourenco Marques to P o n ta da B arra* th e c o a s t, w hich tu r n s n o rth e a stw a rd fo llo w in g a long curve* i s low- ly in g and swampy o r sandy. B anging from 15 to 75 km in w idth* th e s h e l f h e re i s I r r e g u l a r . The re a so n f o r w iden in g o f th e s h e l f i s q u e stio n e d by Pepper and E v e rh a rt 36 (1963) who su g g e sted t h a t th e g r e a t e r w id th s a re due e i t h e r to s t r u c t u r e o r to accu m u latio n o f c u r r e n t d e p o s ite d sed im e n ts. Data from th e p r e s e n t stu d y make I t p o s s ib le to r e j e c t th e second h y p o th e s is . Among th e many sam ples r e covered on th e s h e l f and up p er slo p e o f f th e l a r g e - s c a l e prom ontory produced by th e curve o f th e c o a s t, no f r e s h te r r ig e n o u s sed im en ts were found. The f lo o r th e r e Is rocky and o nly ro c k -d re d g e s co u ld be used to sample th e h ard bottom . Hock frag m en ts and w eathered b io g e n ic d e b r i s , I n te r p r e t e d as r e l i c t , a re I n d ic a t iv e o f a low ered s e a - l e v e l . Wide changes o f th e s h o re lin e re c o rd e d by r a i s e d and submerged beach l i n e s were re p o rte d In t h i s a r e a (King, 1 9 6 2 ). The s tro n g Mozambique C u rre n t t h a t flow s so u th th ro u g h th e Mozambique Channel s t r i k e s th e p ro tru d in g c o a s t o f so u th e rn Mozambique n e a r P o n ta da B a rra and a p p a r e n tly p re v e n ts d e p o s itio n o f modern s e d i m ent. In t h i s I n v e s t i g a t i o n Miocene sed im en ts were found cro p p in g o u t on th e upper slo p e o f f P o n ta da B a rra . T his o ccu rren c e may be r e l a t e d to th e s tr u c t u r e s e x i s t i n g on la n d . Pepper and E v e rh a rt (1963) re p o rte d th e p rese n c e o f a s t r u c t u r a l b e l t a t ab o u t 50 to 100 km In la n d from P o n ta da B a rra , a b e l t t h a t In c lu d e s a n t i c l i n e s and s y n c lln e s w hich curve w ith th e c o a s t. These s t r u c t u r e s a r e a t some p la c e s t r a n s e c te d by c ro s s f a u l t s tre n d in g n o rth w estw ard , w h ile a t o th e r p la c e s f a u l t p a r a l l e l th e s t r u c t u r e s . Pepper and E v e rh a rt su g g ested t h a t s im ila r s t r u c t u r e s may 37 e x i s t o f f s h o r e . For th e most p a r t th e low land o f so u th e rn Mozambique i s covered w ith c o n tin e n ta l T e r tia r y and Q u atern ary de p o s its c a lle d th ro u g h o u t A fric a " C o n tin e n ta l te r m in a l." The s t r u c t u r e o f so u th e rn Mozambique i s m o n o c lin a l, c o a s t ward from th e Lebombo M ountains. Pepper and E v e rh a rt (1963), on th e b a s is o f w e ll d a ta o u tlin e d th e shape and d epth o f th e m onocline to th e top o f th e J u r a s s i c (?) b a s a l t s . The m onocline i s b ro ad ly a r c u a te n o r th and so u th . Cenozoic c o n tin e n ta l d e p o s its to g e th e r w ith u n d e rly in g C retaceo u s sed im en ts have a th ic k n e s s o f 600 m n e a r the Lebombo M ountains th ic k e n in g eastw ard to 4000 m n e a r the c o a s t. P epper and E v e rh a rt e s tim a te t h a t th e th ic k n e s s o f Karroo below th e J u r a s s ic (?) b a s a l t s may be a t l e a s t 2000 m alo n g th e c o a s t . S h allo w -w ater m arine sed im en ts o f Lower Miocene and P lio c e n e age have been re p o rte d n ear th e c o a s t in th e d i s t r i c t o f Inhambane (Hodson, 1928; Borges e t a l . , 1939; Nunes, 1966). The c o a s t o f so u th w estern M adagascar i s monotonous from T u le a r to Cape S a in t M arie, a d is ta n c e o f 300 km. Ex c e p t f o r th e S a in t A ugustin Bay, 25 km s o u th o f T u le a r, where th e O nilahy R iv er em pties i n to th e Mozambique C hannel, th e smooth c o a s t has no i n d e n t a t i o n . The tra d e winds blow a lo n g th e c o a s t a l l y e a r . T h is s tro n g wind, t o g e th e r w ith an a r i d c lim a te , f a v o rs th e fo rm a tio n alo n g th e c o a s t o f w e ll-d e v e lo p e d sand dunes whose age i s 38 P le is to c e n e (A epyornlan) o r H olocene. The o ld e s t a re c o n s o lid a te d and produce a r id g e o f c a lc a re o u s san d sto n e beh in d th e more re c e n t dunes. These f e a t u r e s were d e s c rib e d In d e t a i l by B a t t l s t l n l (1964) in h i s thorough m orphologic stu d y o f so u th ern m o st M adagascar. O ff th e c o a s t, c o r a l r e e f s form a f r i n g e w hich I s c o n tin u o u s In th e n o rth e rn p a r t and d is c o n tin u o u s In th e so u th ( 3 a t t i s - t 3 r l , 1964). Minor changes In s e a - l e v e l a r e re c o rd e d , as w e ll as In n o rth w e ste rn M adagascar, by r a i s e d b e a c h lln e s . The c o n t i n e n t a l s h e lf I s narrow betw een T u le a r and th e | L ln ta R iv e r, b e in g l e s s th a n 10 km In w id th , b u t widens ! so u th o f th e L ln ta R iv er and a t t a i n s a maximum w idth o f 63 km o f f Cape S a in t M arie. B a t t l s t l n l (1964) su g g ested t h a t th e change In w id th o f th e c o n tin e n ta l s h e lf I s r e l a t e d t o s t r u c t u r e . I t would co rresp o n d to th e so u th e rn l i m i t o f th e K arroo b a s in In w hich s e v e r a l thousand m ete rs o f sed im en ts have accum ulated w hereas to th e so u th th in l a y e r s o f sedim ents l i e d i r e c t l y on th e Precam brlan s u b stra tu m . A subm arine canyon c u ts th e s h e l f o f f th e mouth o f th e O nllahy R iv e r. The canyon h as been mapped from I t s h ead , In sid e th e S a in t A ugustin Bay I t s e l f , to a dep th o f 1700 m (map a t a s c a le o f 1 /4 5 ,0 0 0 ; Rade de T u le a r, B ale de S a in t A u g u stin ; S e rv ic e H y d ro jrap h iq u e de l a M arin e, P a r i s , 1893)* A b e l t o f sed im en tary ro c k s c ro p s o u t In th e so u th and w est o f M adagascar betw een th e P recam brlan ro ck s and th e o cean . The sed im en tary seq u en ce, w e ll-d e v e lo p e d In th e n o rth e rn p a r t o f th e I s la n d , p in c h e s o u t tow ard th e so u th where o n ly th e more re c e n t s ta g e s (Upper Senonlan and younger) a re r e p r e s e n te d . The sed im en tary ro ck s which b e come younger tow ard the c o a s t d eterm in e th e geomorphlc p ro v in c e s . Behind th e 15 km-wlde c o a s t a l dune-covered p la in l i e s th e M ahafaly C alcareo u s P la te a u . T his p la te a u I s bounded to th e e a s t by th e "Eocene C uesta" and to th e w est by a la r g e l i n e a r sc a rp o f t e c t o n i c o r i g i n . This I d e c l i v i t y I s a f a u l t so arp marking th e " f a i l l e de T ulear" ) | and I t s so u th e rn p r o lo n g a tio n . I t Is a ls o an a n c ie n t se a - c l i f f ( B a t t l s t l n l , 1964). Between A f ric a and M adagascar th e sm all v o lc a n ic Is la n d s o f B assas da In d ia and Europa slo p e s te e p ly from 3 and 25 m above s e a - l e v e l to d eep er th a n 2000 m. Pepper and E v e rh a rt (1 9 6 3 ), who re g a rd e d th e Mozambique Channel as a sunken b lo c k presumed to have sunk d u rin g Late M iocene, s t a t e d t h a t th e Is la n d s " r i s e from an e lo n g a te p la tfo rm o f p ro b a b le v o lc a n ic o r ig in t h a t a p p a r e n tly la y n e a r s e a - l e v e l d u rin g th e M iocene." In t h e i r view th e i v o lc a n ic is la n d s were formed in P lio c e n e o r P le is to c e n e tim e. However, th e age o f fo rm atio n o f th e s e is la n d s in f e r r e d by P epper and E v e rh a rt I s p u re ly h y p o t h e t i c a l . No p a le o n to lo g ic a l In fo rm a tio n e x i s t s on th e age o f th e c o r a l r e e f s su rro u n d in g them . In th e p r e s e n t su rv ey shallow w a ter c o r a l r e e f s were dredged a t th e base o f th e slo p e o f Europa Is la n d a t 2750 m. These a p p e a r to be r e c e n t o r s u b re c e n t and a re slumped from sh a llo w e r d e p th s alo n g th e s te e p s lo p e s . As Pepper and E v e rh a rt th em selv es e v in c e d * t h e i r r e p r e s e n ta tio n o f th e sed im en tary sequence and p o s i t i o n o f f a u l t i n g in t h e i r diagram m atic c r o s s - s e c tio n a c ro s s th e ch an n el i s c o n j e c t u r a l . F urtherm ore! t h e i r p ro p o sa ls r e g a rd in g th e r e l a t i o n s h i p between th e sed im en tary sequence o f M adagascar and th e ro c k s u n d e rly in g the Mozambique Channel i s based on th e c o n cep t t h a t th e i s la n d and th e channel had a common g e o lo g ic h i s t o r y s in c e P recam b rlan tim e and th a t th e ch an n el i s u n d e rla in by a c o n t i n e n t a l c r u s t . As d isc u s s e d e a r l i e r * i t i s l i k e l y t h a t o cean ic c r u s t u n d e r lie s th e Mozambique Channel and t h a t M adagascar reach ed i t s p r e s e n t p o s it i o n o n ly d u rin g th e T e r t i a r y . The p a t t e r n o f f a u l t i n g and o f r e c u r r e n t movements alo n g f a u l t s assumed by P epper and E v e rh a rt (1963) th e r e f o r e may be somewhat d i f f e r e n t th an what i s in d ic a te d on t h e i r c r o s s - s e c tio n * e s p e c i a l l y f o r th e f a u l t s on c o n tin e n ta l s h e lv e s and a t th e f o o t o f th e con t i n e n t a l s lo p e s . Normal f a u l t i n g and v e r t i c a l movement th ro u g h o u t g e o lo g ic time* moreover* have been w e ll docu m ented on la n d in A fric a and in M adagascar. OCEANOGRAPHY I n tr o d u c tio n In th e S outh In d ia n Ocean th e s u rfa c e c i r c u l a t i o n p a tte r n c o n s i s t s , as in th e o th e r so u th e rn o c ean s, o f an a n tic y c lo n ic gyre (c o u n te r-c lo c k w ise in th e so u th e rn hem isphere) bounded on th e so u th by th e West Wind D r i f t . The In d ia n Ocean, however, d i f f e r s from th e South A t la n tic and th e South P a c i f i c in i t s South E q u a to r ia l system . The l a t t e r flo w s w estward to th e so u th o f th e E q u a to r and undergoes marked s e a so n a l v a r i a t i o n s r e s u l t i n g from se a so n a l changes in wind c o n d itio n s due to th e land mass in th e n o rth e rn o n e - h a lf o f th e ocean. F u rth erm o re, th e s u rfa c e c i r c u l a t i o n i s d is r u p te d by th e p resen ce o f M adagascar which a c t s as a b a r r i e r . M ozamblcue-Agulhas C u rren t System The South E q u a to r ia l C u rre n t, caused by th e s o u th e a s t tra d e w inds, flow s w estw ard a c ro s s th e In d ia n Ocean somewhere betw een 5°S. and 1 5 ° S ., and i s d e f le c te d to th e l e f t by th e e a r t h 's r o t a t i o n . The so u th e rn p a r t o f i t im p in g es on M adagascar and r e s u l t s in a southw ard c u r r e n t to th e e a s t o f t h i s i s l a n d , known a s th e M adagascar C u rre n t, w hereas th e n o rth e rn p a r t s t r i k e s th e A fric a n c o a s t and 41 42 tu r n s so u th to form th e Mozambique C u rren t flow ing th ro u g h th e Mozambique C hannel. P a r t o f th e n o rth e rn p o rtio n o f th e South E q u a to ria l C u rre n t a ls o I s d iv e r te d to th e n o r th and s u p p lie s th e E q u a to r ia l C ounter C u rren t and In w in te r th e Somali C u rre n t. The c l a s s i c a l c u r r e n t scheme d e s c rib e d by many a u th o rs ( D ie tr ic h , 1935; S c h o tt, 1935; Deacon, 1937; Sverdrup e£ &1., 1942; Clowes, 1950; D efan t, 1961; M allo ry , 1961; O rren, 1963; D a rb y sh ire , 1964; G a lla g h e r, 1966; R ochford, 1967; and o th e r s ) shows t h a t th e a re a o f th e p r e s e n t stu d y Is th e so u rce a re a o f th e Agulhas C u rren t (P ig . 5 ) . T his c u r re n t I s a r e s u l t o f th e merging o f th e M adagascar and Mozambique C u rre n ts a t ab o u t 26° S ., a l though a sm all p o rtio n o f th e stream flow s n o rth along th e w est c o a s t o f M adagascar. The Agulhas C u rren t flow s southw ard down th e e a s t c o a s t o f South A fric a fo llo w in g th e tre n d o f th e c o a s t. To th e s o u th o f South A fric a a l i t t l e o f th e Agulhas C u rre n t a p p ea rs to co n tin u e In to th e A t la n tic Ocean by p a s s in g around th e Cape o f Good Hope, b u t th e m ajor p o rtio n o f th e stream Is d e f le c te d so u th - eastw ard s and doubles back to form a r e t u r n flow . The so u th e rn p a r t o f t h i s r e t u r n flow m erges In to th e eastw ard West Wind D r i f t , w h ile th e n o r th e rn p a r t I s d e f le c te d In a n o r th e r ly d i r e c t io n , tu r n in g back to form an a n tic y c lo n ic gyre known a s th e “R etu rn A gulhas C u rre n t." A c o n f l i c t i n g p a t t e r n o f w a te r c i r c u l a t i o n was p r o - Pigure 5 S u rface c u r r e n t s in th e Southw est In d ia n Ocean ( c u r r e n t scheme w ith th e Mozambique C u rren t flo w in g th ro u g h th e Mozambique Channel; com piled from v a rio u s s o u rc e s ). 43 10 °s 20 ° 30° 40° 10° S SOUTH EQUATORIAL CURRENT < % i WEST WIND DRIFT 90°E -> *5 posed by Menache (1961, 1963* 1966). From th e o b se rv a t i o n s o f t h i s a u th o r (F ig . 6 ) , th e Mozambique C u rren t a t a p p ro x im a tely 24°S. t u r n s to th e e a s t and r e t u r n s to th e n o r th alo n g th e w est c o a s t o f M adagascar. None o f th e w a te r o f th e Mozambique Channel would flow to th e so u th o f th e C hannel. A ccording to t h i s scheme, th e Mozambique C u rren t does n o t c o n tr ib u te to th e A gulhas C u rren t which i s formed e x c lu s iv e ly w ith th e p o r tio n o f th e South E q u a to r ia l C u rren t coming from th e e a s t around M adagascar and c a lle d by Menache (1966) "C ourant E st des A i g u i l l e s ." T his w a te r, a c c o rd in g to Menache, tu r n s around th e so u th ern t i p o f M adagascar and alm o st b e g in s to e n te r th e Channel from th e s o u th e a s t, b u t i s stopped by th e b a r r i e r produced by th e b ran ch o f th e Mozambique C u rre n t flo w in g to th e e a s t an d , h ence, t u r n s tow ard th e southw est to form th e A gulhas C u rre n t. A p i c t u r e o f th e c u r r e n ts as d e sc rib e d by Menache was i l l u s t r a t e d by M. D arb y sh ire (1966) and S c h e rb ln ln (1969)* The p r e s e n t stu d y c o n tr ib u te s a d d it i o n a l inform a t i o n on th e c u r r e n t p a t t e r n in t h i s c o n tr o v e r s ia l a re a d u rin g th e so u th e rn w i n te r , a season in w hich i t h as n o t y e t been d e s c rib e d . S easo n al V a r ia tio n s in S u rfa c e C u rre n ts D uring th e s o u th e rn w in te r th e South E q u a to ria l C u rren t i s d e f le c te d to th e n o r th owing to th e J o in t 46 a c tio n o f th e s o u th e a s t t r a d e s and th e southw est monsoon. As a consequence, th e p o r tio n o f th e South E q u a to r ia l Cur r e n t flo w in g so u th i s v ery s m a ll. During th e so u th e rn summer, th e South E q u a to r ia l C u rre n t flow s much f u r t h e r so u th and i s r e in f o r c e d by th e n o r th e a s t monsoon. The p o r tio n o f th e South E q u a to r ia l C u rren t flo w in g so u th i s t h e r e f o r e in c r e a s e d . These v a r i a t i o n s in th e so u th e rn bran ch o f th e South E q u a to r ia l C u rre n t le a d to v a r i a t io n s in th e s tr e n g th o f th e Mozambique and Agulhas C u rre n ts . S easo n al v a r i a t io n s o f th e Agulhas C u rren t s o u th o f about 30°S. have been s tu d ie d by D arb y sh ire (1 9 6 4 ). There i s l i t t l e s e a so n a l v a r i a t io n in th e d i r e c t io n o f th e o u r- r e n t b u t s e a so n a l v a r i a t i o n s in tem p e ratu re s t r u c t u r e and c u r re n t v e lo c ity o c c u r. L ocal winds can i n i t i a t e a c o u n te r c u r re n t alo n g th e A fric a n c o a s t and cause l o c a l u p w ellln g (M allo ry , 1961; A nderson, 1964; H a r r is , 1964), b u t a c c o rd in g to D arb y sh ire th e y do n o t a f f e c t th e c u r r e n t system which depends l a r g e l y on th e v a r i a t io n o f th e South E q u a to r ia l C u rren t and th e West Wind D r i f t . D arb y sh ire (1964) r e p o rte d t h a t th e A gulhas C u rren t alo n g th e c o a s t o f South A fric a i s v ery s tr o n g in A p ril (50 cm /se c ), s l i g h t l y w eaker in J u ly , v e ry weak in O ctober ( le s s th an 20 cm /sec a t Durban and w eaker a s i t goes s o u th ) , and s tr e n g th e n s ag ain in Jan u ary (20-30 c m /se c ). The c u r re n t th u s i s s tr o n g e r in summer and f a l l and w eaker in w in te r and s p rin g . 47 In th e n o rth o f th e Mozambique Channel, Donguy and P lto n (1969) no ted t h a t an a n tic y c lo n ic gyre develops around th e Comorlan I s la n d s d u rin g th e warm season ( n o r th e a s t m onsoon), w hereas d u rin g th e co ld season (n o rth w e st monsoon) a flow o f s u rfa c e w a ter moves from th e so u th ern p a r t o f th e Mozambique C hannel. In th e so u th o f th e Mozambique Channel, In th e a re a o f fo rm atio n o f th e A gulhas C u rre n t, se a so n a l v a r i a t i o n s In th e w a te r c i r c u l a t i o n a r e unknown. The c u r r e n t p a t t e r n d e sc rib e d by Me'naohe (1961, 1963) (Pig* 6 ) , ob serv ed d u rin g th e s p rin g , shows t h a t a t about 25°S .» in th e a r e a where th e Mozambique and M adagascar C u rre n ts o f o p p o s ite d i r e c t io n m eet, an u p w e llln g o ccu rs a s In d ic a te d on s a l i n i t y s e c tio n s (Menache, 1961, 1963)* T his was ob- t > serv ed by Menache In th e same season a t a y e a r I n te r v a l In October-November 1957 aboard th e CO M M A N D A N T ROBERT GIRAUD and In O ctober 1956 aboard th e ORSOM I . I t I s n o t known, how ever, w hether t h i s h y d ro lo g ic a l b a r r i e r was an I s o la te d o r s e a so n a l d is tu r b a n c e . Deep L avers o f th e Agulhas C u rren t Southward components o f flo w have been d e te c te d by v a rio u s a u th o rs a t a l l d e p th s a lo n g th e e a s te rn c o a s t o f S outh A f r ic a . I t a p p e a rs , t h e r e f o r e , t h a t th e Agulhas C u rre n t ex ten d s from th e s u rf a c e to a t l e a s t 3000 m. W ater o r i g i n a t i n g In th e N o rth In d ia n Ocean flow s th ro u g h Figure 6 Dynamic topography a t su rfa c e over 1000 db, F i r s t C ru ise COM M ANDANT ROBERT GIRAUD, O ctober 11 to November 28, 1957 ( a f t e r Menache, 1963; from V is s e r and N iek erk , 1965). 48 49 FIRST CRUISE OF THE COMMANDANT ROBERT GIRAUD 11th October- 28th November, 1957 < % > Dynamic topography °ltooo db. Elevations expressed- in dynamic centimetres. The • show the positions of the stations. line of the 1000 m. level. 50 th e Mozambique Channel to fe ed th e deep la y e r s o f th e Agulhas C u rre n t. The southw ard sp re a d in g o f w ater o f N o rth In d ian o r ig in a t In te rm e d ia te and deep d ep th s and th e northw ard m ig ra tio n o f A n ta r c tic In te rm e d ia te W ater and Deep Water from th e A t l a n t i c Ocean have been an o b je c t o f d is c u s s io n f o r many y e a r s . The Mozambique Channel I s an Im p o rtan t a r e a to stu d y t h i s problem s in c e th e N orth In d ia n Water I s o l a t e d by M adagascar p re s e rv e s I t s c h a r a c t e r i s t i c s f u r t h e r so u th th an In th e rem ain d er o f th e In d ia n Ocean. However, d e e p -w a te r s tu d ie s In th e Mozambique Channel r e main v ery r a r e . The a re a p r e s e n tly surveyed I s o f s p e c ia l I n t e r e s t b ecau se th e s e In te rm e d ia te and d e e p -w a te r m asses o f n o rth e rn and so u th e rn o r ig i n meet In t h i s re g io n and a re In d i r e c t c o n ta c t. The I n te r a c t i o n phenomena a re t h e r e fo re d e ta ile d In t h i s stu d y . C o lle c tio n and P r e s e n ta tio n o f Data A t o t a l o f 37 h y d ro g rap h ic s t a t i o n s were occupied between Ju ly 29 and Septem ber 9 , 1964. The l o c a t i o n o f th e s t a t i o n s , which a re numbered from 356 to 392, I s shown on F ig u re 1. At each h y d ro g rap h ic s t a t i o n a double Nansen b o t t l e c a s t was ta k e n from th e s u rfa c e to th e bottom to p ro v id e f o r s h ip b o a rd d e te rm in a tio n o f te m p e ra tu re , s a l i n i t y , d is s o lv e d oxygen, p h o sp h ate, n i t r i t e , n i t r a t e and s i l i c a t e . 51 For each h y d ro g rap h ic s t a t i o n diagram s o f tem pera t u r e , s a l i n i t y , d is s o lv e d oxygen and phosphate c o n te n ts , r e s p e c t i v e l y , were p l o t t e d a g a in s t d e p th , A te m p e r a tu re / s a l i n i t y curve was p l o t t e d f o r each s t a t i o n . R e p re se n ta t i v e diagram s a r e d e p ic te d In F ig u re s 7 -1 0 . V e r t i c a l s e c tio n s o f te m p e ra tu re , s a l i n i t y and slg m a -t were drawn alo n g fo u r l i n e s which co rresp o n d to th e fo u r t r a n s e c t s o f th e c r u is e tr a c k ( F ig s . 1 1 -2 2 ). The l i n e s , In d ic a te d on F ig u re 1, run as fo llo w s : l i n e I from Durban to T u le a r, l i n e I I from T u le a r to Inhambane, lin e I I I from Lourenco Marques to W alter S h o a ls, and l i n e IV from N a ta l Deep to Durban. S ta tio n s which did n o t f a l l on th e s t r a i g h t l i n e s were p r o je c te d . A n o r th - s o u th l i n e was chosen a t about 38°E. alo n g th e w estern s id e o f th e N atal B a sin . A lthough o n ly fo u r s t a t i o n s , r a t h e r w id ely spaced, f a l l on th e l i n e , th e s a l i n i t y d i s t r i b u t i o n was p l o tte d alo n g t h i s s e c tio n (F ig . 23) to I l l u s t r a t e a n o r th - s o u th tr e n d . The bottom topography a s shown In th e v e r t i c a l s e c tio n s I s sch em atic and was e s ta b lis h e d from th e b a th y m e tric map o f F ig u re 2 and th e soundings a t each s t a t i o n . In o r d e r to I l l u s t r a t e th e c h a r a c t e r i s t i c s o f th e s u rfa c e l a y e r s In d e t a i l , a d i f f e r e n t s c a le was used In th e v e r t i c a l s e c tio n s f o r th e u pper 500 m o f th e w a te r column and f o r th e d eep er l a y e r s . H o riz o n ta l d i s t r i b u t i o n c h a r ts were drawn f o r s u r- F ig u re 7 D i s tr i b u t i o n o f te m p e ra tu re w ith d e p th , R.V. ANTON BSUUN, C ru ise 7 ( s t a t i o n 362: August 3, 1964; s t a t i o n 376: August 28, 1964; s t a t i o n 383: Septem ber 1, 1964). 52 DEPTH METERS 53 TEM PER A TU R E °C 10 15 20 25 1000 2000 3000 4 0 0 0 5000 • Sta 383 ® Sta 362 x Sta 376 Figure 8 D is tr ib u tio n o f s a l i n i t y w ith d e p th , R.V. ANTON BRUUN, C ru ise 7 ( s t a t i o n 362: August 3 , 1964; s t a t i o n 367: August 13, 1964; s t a t i o n 382: August 31* 1964). 54 DEPTH M E T E R S SALINITY % 34.00 34.50 35.00 35.50 0 1 0 0 0 - 2000 - 3000 - 4000 5000 “ I • / i i i i • STA 382 oSTA 362 x STA 367 55 36.00 i 1 r Figure 9 D i s tr i b u t i o n o f d iss o lv e d oxygen and I n o rg a n ic p h o sp h ate w ith d e p th , R.V. ARTON BRUUN, C ru ise 7 ( s t a t i o n 363: August 4, 1964; s t a t i o n 383: Septem ber 1, 1964). 56 O XYG EN m l/l IOOO - 2000 - 3000 - 4000 - 5000 - — STA 383 — STA 363 T 1 ------1 ----- 1 ------1 ----- 1 PHO SPH A TE/cgA/l Figure 10 T e m p e r a tu r e /s a lin ity c u rv e s, R.V. ANTON BRUUN, C ru ise 7 ( s t a t i o n 363: A ugust 4, 1964; s t a t i o n 368: August 16, 1964; s t a tio n 378: August 28, 1964; s t a t i o n 384: Septem ber 2 , 1964; s t a t i o n 389: Septem ber 9 , 1964). 58 TEMPERATURE SALINITY , %• 35.00 35.50 35.00 3530 34.50 35 00 35.50 34.50 3500 3550 34.50 3500 35.50 125 m I T 4 4 4 m STATION 363 STATION 368 STATION 389 2 0 0 m STATION 37i 200 1 9 8 m !9Sm STATION 384 6 0 S m 8 0 3 m 8 8 9 m 1 0 4 4 m 1045 m 1001 m 1001 1342 m 1 3 4 6 2 3 2 8 m 3041 3081 m 3020 J 4926 5292 V J1 VO Figure 11 V e r t i c a l d i s t r i b u t i o n o f te m p e ra tu re from Durban to T u le a r. R.V. ANTON BRUUN d a ta , C ru ise 7, J u ly 29 to Septem ber 9 , 1964. (F or convenience, Iso th e rm s between 10°C and 5°C a re o m itted on t h i s f ig u r e and F ig u re s 14, 17 and 2 0 .) 60 362 363 364 361 356 359 360 1 0 0 8 * 200 - 300 - IS * 1 4 * 400 - 500 500 1000 5 * AFRICA 3 * 2000 MOZAMBIQUE PLATEAU 2 .0 * 3000 4000 ZAMBEZI CANYON NATAL BASIN 5000 TEMPERATURE ,*C LINE I DURBAN - TU L E A R VERTICAL EXAGGERATION 0 - 5 0 0 M - 670 X , 500 - 3000M - 6TX . Figure 12 V e r t i c a l d i s t r i b u t i o n o f s a l i n i t y from Durban to T u le a r. R.V. ANTON BRUUN d a ta , C ru ise 7 , Ju ly 29 to Septem ber 9 , 1964. 62 358 359 360 361 362 363 364 100 3 *S - 35. SO r 35.55 J0 200 - 3 5 .4 0 300 — 35.45 - 3 5.40 - 35.35 — 35 30 400 35 20 35.,0 - 35.30 33.25 _ 500 500 34 60 1000 3 4 .70 34.75 AFRICA 2000 MOZAMBIQUE PLATEAU 3000 NATAL BASIN ZAMBEZI CANYON 4000 5000 L J s 0. U J a LINE I DURBAN - T U L E A R VERTICAL EXAGGERATION 0 - 5 0 0 M - 670 X , 500 - 5000 M - 67X . SALINITY, % ON F ig u re 13 V e r tic a l d i s t r i b u t i o n o f d e n s ity from Durban to T u le a r. R.V. ANTON BRUUN data* C ru ise 7» J u ly 29 to Septem ber 9» 1964. 64 358 359 360 361 362 363 364 100 - •<«0 25.00 200 - ’ 26.00 26 2 0 - 26. 40 — 25 SO 26 00 300 - 26.20 26. 40 26 60 400 - 26 SO 500 - I 500 — 2 7.30 27 30 27 40 27 SO 1 0 0 0 27 40 2 7 SO AFR,CA^ X 2000 - MOZAMBIQUE PLATEAU 27.80____ 3000 - 4000 - ZAMBEZ CANYON NATAL BASIN 5000 - LINE I DURBAN - T U L E A R VERTICAL EXAGGERATION 0 -5 0 0 M - 6T0 X , 500 - 5000M - 67X . < T T CJ\ ui ! F ig u re 14 V e r tic a l d i s t r i b u t i o n o f te m p e ra tu re from T u le a r to Inhambane. R.V. ANTON BRUUN d a ta , C ru ise 7, J u ly 29 to Septem ber 9, 1964. 66 372-371-370 369 368 367 366-365 0 - 23 1 0 0 - 2 0 0 - -----16 3 0 0 - 4 0 0 - 5 0 0 - 5 0 0 - 1 0 0 0 - ■=■ 1 0 AFRICA 2000- 3000 - MOZAMBIQUE CHANNEL ZAMBEZI CANYON 4 0 0 0 - TEMPERATURE,°C VERTICAL EXAGGERATION* 0-500M-670X, 500-4000M-67X. LINE II T U L E A R -IN H A M B A N E Figure 15 V e r t i c a l d i s t r i b u t i o n o f s a l i n i t y from T u lea r to Inhambane. E.V. ANTON BRUUN d a ta . C ru ise 7» J u ly 29 to Septem ber 9 , 1964. 68 372-371-370 0 I U 1 V) <r U J 4 0 0 - i - U J 3 5 5 0 0 - 5 0 0 - z 1000- X 1 - 2 0 0 0 - 0 . U J O 3 0 0 0 - 3 6 6 -3 6 5 35 40 1 0 0 - 35 4 0 3 5 .3 5 35 30 35 25 3 5 35 0 5 3 5.00 34.8 0 ^----- 3 4 .8 0 34.80 4 0 0 0 - AFRICA MOZAMBIQUE CHANNEL ZAMBEZI CANYON LINE II TULEAR - INHAMBANE SALINITY,%« VERTICAL EXAGGERATION’ 0 - 5 0 0 M-670X,500-4000M-67X. MAX. M I N . O n VO Figure 16 V e r tic a l d i s t r i b u t i o n o f d e n s ity from T u le a r to Inhambane. R.V. ANTON BSUUN d a ta . C ru ise 7» J u ly 29 to Septem ber 9 . 1964. 372-371-370 3 6 9 3 6 8 3 6 7 3 6 6 -3 6 5 0 - 24.60 1 0 0 - 26.00 200 26.40 3 0 0 - co o c UJ H UJ 2 E 26.60 4 0 0 - 5 0 0 - 5 0 0 - 1 0 0 0 - 27.00 z 27.40 X I- AFRIC A 2000- o. UJ o 27.80 3000 - MOZAMBIQUE CHANNEL ZAMBEZI CANYON 4 0 0 0 - L1NE II T U L E A R -IN H A M B A N E <T T VERTICAL EXAGGERATION: 0-500M-670X, 500-4000M-67X. Figure 17 V e r tic a l d i s t r i b u t i o n o f te m p e ra tu re from Lourenco Marques to W alter S h o a ls. R.V. ANTON BRUUN d a ta , C ru ise 7, Ju ly 29 to Septem ber 9 , 1964. 72 379 380-381 378 377 376 374 375 373 100 200 300 400 500 500 1000 AFRICA MOZAMBIQUE PLATEAU S 2000 3000 MADAGASCAR PLATEAU 4000 5000 ^ < 'N A T A L ' BASIN'& 6000 LINE 1 1 1 LOURENCO MARQUES-WALTER SHOALS VERTICAL EXAGGERATION- 0-500M - 670X , 500-6000M - 67X. TEMPERATURE,*C Figure 18 V e r tic a l d i s t r i b u t i o n o f s a l i n i t y from Lourenco Marques to W alter S h o a ls. R.V. ANTON BRUUN d a ta , C ru ise 7 , J u ly 29 to Septem ber 9* 1964. 74 379 380-381 377 378 376 375 373 374 js so 100 200 300 4 o 400 500 500 1 0 0 0 v ,, x . , , jw<: MOZAMBIQUE V - v p l a t e a u AFRICA 3 < ? o s 2000 sc 3000 ;w.\\ 1 MADAGASCAR PLATEAU i 4000 5000 ‘-N A TA L B ASIN' 6000 LOURENCO MARQUES-WALTER SHOALS LINE VERTICAL EXAGGERATION- 0 -5 0 0 M - 670X , 5 0 0 - 6 0 0 0 M - 67 X . SALINITY, % . V J I Figure 19 V e r t i c a l d i s t r i b u t i o n o f d e n s ity from Lourenco Marques to W alter S h o a ls. R.V. ANTON BRUUN d a ta , C ruise 7 , Ju ly 29 to Septem ber 9» 1964. 76 3 7 3 3 7 4 3 7 5 3 7 6 3 7 7 3 7 8 3 7 9 380-361 0 - 24 60 100 — 2 S . 20 200 25 33 3 0 0 - 4 0 0 5 0 0 - 5 0 0 - 1000- 3C - ' 23 2 -.4 C AFRICA ' ^/WALTER _ ' • ; SHOALS 3 2 0 0 0 - MOZ AMBIQUE PLATEAU 3 0 0 0 2 ? 4 0 0 0 - MADAGASCAR PLATEAU 5 0 0 0 NATAL ' 8 A S I N ' 6 0 0 0 - LINE III LOURENCO MARQUES-WALTER SHOALS 0" T VERTICAL EXAGGERATION' 0-500M - 670X . 500 - 6 0 0 0 M -6 7 X . ______________________ Figure 20 V e r tic a l d i s t r i b u t i o n o f te m p e ra tu re from th e N a ta l B asin to Durban. R.V. ANTON BRUUN d a ta , C ru ise 7, J u ly 29 to September 9, 1964. 78 392 381390 399 398 397 398 389 3 8 4 100 - 200 300 V) < £ . UJ 400 I- U1 2 900 - 900 - 1000 • z 2000 X t 3000 - Q MOZAMBIQUE PLATEAU ' AFRICA 4000 9 0 0 0 - NATAL BASIN 6000 LINE IV NATAL BASIN - DURBAN TEMPERATURE VERTICAL EXAGGERATION' 0-500M 670X .500-S000M 67x . * C VO Figure 21 V e r t i c a l d i s t r i b u t i o n o f s a l i n i t y from th e N a ta l B asin to Durban. R.V. ANTON BRUUN d a ta , C ru ise 7 , Ju ly 29 to Septem ber 9, 1964. 8 0 3*2 3 (1 3 9 0 3(9 "li i ■ 388 387 388 389 3 8 4 99.60 1 0 0 20 0 - 900 to 400 UJ 500 - 500 - ■3500 1000 - 34 50 34.60 -------- 3 4 .7 0 ------- 34.75 -------- 34.80 ------- 34.70 34.75 .34,80 2000 > 3 4 .8 0 3000 UJ MOZAMBIQUE PLATEAU AFRICA 4000 - — 34.75 5000 NATAL BASIN 6000 DURBAN SALINITY % ^ M A X . V / S i M I N . LINE IV NATAL BASIN VERTICAL EXAGGERATION' 0 - 5 0 0 M 670X .5 00-G 000M 67X . Figure 22 V e r tic a l d i s t r i b u t i o n o f d e n s ity from th e N atal B asin to Durban. R.V. ANTON BRUUN d a ta , C ru ise 7* J u ly 29 to Septem ber 9, 1964. 8 2 DEPTH IN METERS 392 991390 389 38 8 387 388 385 3 8 4 100 - 26.00 2 0 0 - 900 400 26.60 500 - 500 - 26.80 .27.00 •2720 ■27.40 • 27.60 2700 •27.20 27.40 27.60 1 0 00 - 2000 27.80 300 0 ■ MOZAMBIQUE PLATEAU AFRICA 4 0 0 0 • 5000 - NATAL BASIN 6 0 0 0« 000 J - - - - - - - - —------ ----------------------------------------------------------------------------------------------------------------------- LINE IV NATAL BASIN - DURBAN 7 T VERTICAL EXAGGERATION' 0 - 5 0 0 M 670X .5 0 0 - 6 0 0 0 M 67X . 00 -------------------------------------------------------------------------------------------------------------------------------------------------------------- V > , Figure 23 V e r tic a l d i s t r i b u t i o n o f s a l i n i t y n o rth -s o u th p r o f i l e between 35°E. R. V. ANTON BRUUN d a t a , C ru ise 7 , to Septem ber 9 , 1964. alo n g a and 40° E. Ju ly 29 84 d e p t h in -m e t e r s 29*S 30* S 33*5 3 8 4 376 382 368 1 7 100 200 - J5 ao 300 3 3 4 9 3 9 . 4 0 400 3 3 . 3 9 33 30 500 500 1000 2000 \ v 3000 \ \ -^.V\ 3 4 * 0 4000 3 4 . 7 5 MOZAMBIQUE CHANNEL 5000 NATAL BASIN 8000 LINE N - S VERTICAL EXAGGERATION- 0-500M 670X . 3 00 - 60 00 M 67X. SALINITY % y - v - s i n it in . CD VJ1 86 fa c e te m p e ra tu re , s u rfa c e s a l i n i t y , s u rfa c e s lg m a -t, s u rfa c e d is s o lv e d oxygen, th e l a y e r o f minimum oxygen and th e l a y e r o f maximum s a l i n i t y o f th e deep w a te r. Dynamic h e ig h t v a r i a t i o n s were computed a t th e N a tio n a l O ceanographic Data C en ter in W ashington and were used to c o n s tr u c t dynamic topography maps. The 1000 db s u rfa c e was chosen as r e f e r e n c e l e v e l to c o n s tr u c t a s u rf a c e dynamic to p o g rap h y . T his map can be compared to th e s u rfa c e dynamic topography maps c o n s tr u c te d by Menache (1961, 1963) In th e so u th e rn s p rin g f o r th e Mozambique Channel a re a (rep ro d u ced In F ig . 6 ) , and by D a rb y sh ire (1964) In v a rio u s seaso n s f o r th e a r e a so u th o f th e p r e s e n t s tu d y . Both a u th o rs used 1000 db a s r e fe re n c e l e v e l . In a d d itio n to d a ta from th e p r e s e n t I n v e s tig a tio n , o th e r h y d ro g ra p h ic d a ta from d i f f e r e n t e x p e d itio n s were used t o c o n s tr u c t th re e dynamic to p o g rap h y maps a t th e 1000 db, 1500 db and 3000 db l e v e l s , a l l r e l a t i v e to a 2000 db s u r f a c e . A ll h y d ro lo g ic o b s e rv a tio n s a v a ila b le a t t h i s tim e betw een l a t i t u d e s 15°S. and 37°S. and lo n g itu d e s 30°E. and 48°E. were fu rn is h e d by th e N a tio n a l O ceanogra p h ic D ata C en ter in W ashington, and a l l s t a t i o n s re a c h in g 2000 m o r d eep er were c o n s id e re d . S t a t i o n s occupied b e tween June and November were s e le c te d to c o n s tr u c t th e 1000 db and 1500 db dynamic topo g rap h y maps, w h ile a l l s t a t i o n s re a c h in g 3000 m th ro u g h o u t th e y e a r were used to 87 c o n s tr u c t th e dynamic topography map a t 3000 db. These maps can be compared w ith dynamic topography maps con s tr u c t e d by V is s e r and N iekerk (1965) a t th e same le v e l s f o r th e a r e a so u th o f th e p r e s e n t stu d y . T em perature D is tr ib u tio n S u rfa c e Tem perature S u rface te m p e ra tu re s re c o rd e d d u rin g August 1964 a re p l o t t e d in F ig u re 24. They range from 23.25°C to 16.37°0 w ith a g e n e ra l southw ard d e c re a se th ro u g h o u t the a r e a . A tongue o f warm w a te r e x i s t s alo n g b o th th e A fric a n and M alagasy c o a s ts . Along th e A fric a n c o a s t the te m p era tu re in th e tongue i s above 22°C in th e n o r th o f th e a re a and d e c re a se s to v a lu e s betw een 22°C and 21°C so u th o f l a t i t u d e 2 7 °S ., w hereas th e tongue o f warm w a te r a lo n g th e M alagasy c o a s t h as a te m p e ra tu re g r e a t e r th a n 23°C. The tongue o f warm w a te r along th e A fric a n c o a s t c o rresp o n d s to th e co re o f th e Agulhas C u rre n t. In th e a re a o f f Durban th e te m p e ra tu re in th e core o f th e tongue was o bserved a t v a rio u s se a so n s d u rin g th e y e a r s 1962-1963 (D a rb y sh ire , 1964). The s u rfa c e te m p e ra tu re th e r e was 26°C in A p ril ( th e so u th e rn f a l l ) , 24°c in Jan u ary (th e so u th e rn summer), and 23°C in O ctober and J u ly (so u th e rn s p rin g and w i n t e r ) . O b se rv a tio n s c o lle c te d by th e S.A .S . NATAL in August 1958 in t h i s a r e a show a s u rfa c e te m p e ra tu re Figure 24 S u rfa c e w a te r te m p e ra tu re In th e Southw est In d ia n Ocean f o r Ju ly 29 to Septem ber 9, 1964. R.V. ANTON BEUUN d a t a , C ru ise 7 . (T em peratures g r e a t e r th a n 23°C and low er th a n 17°C a re n o t c o n to u re d .) 88 89 4 5 - SURFACE TEMPERATURE. °C 1 5 1 100 200 300 K IL O M E T E R S r 0 * I NOW ■ 22*: fTULEAR JNHAMBANE 1 2 5 * DURI 301 BO* 35* 90 betw een 21°C and 22°C. Both o f th e se v a lu e s and th e v alu es o f th e p r e s e n t I n v e s tig a tio n were o b ta in e d In August (th e so u th e rn w i n t e r ) . They agree w e ll and August I s th e month w ith th e c o o le s t s u rfa c e w ater te m p e ra tu re In the a re a o f f Durban. No s e a so n a l stu d y has been done f u r t h e r n o r th sin c e i th e e a r ly work o f Paech (1 9 2 6 ). However, from co m p ila tio n I j o f d a ta from d i f f e r e n t e x p e d itio n s , I n d ic a tio n o f s u rfa c e i | te m p e ra tu re v a r i a t i o n s th ro u g h o u t th e y e a r co u ld be ob- j ta ln e d . In th e co re o f th e warm tongue o f f th e A fric a n | c o a s t betw een Inhambane and Lourenco M arques, s u rfa c e ! te m p e ra tu re s were above 26°C In May ( d a ta from th e v e s s e l VOROBIEV, 1965), above 24°C In June (AFRICANA I I , 1961; ATLANTIS, 1965; VOROBIEV, 1 9 65), and J u ly (COM M ANDANT ROBERT GIRAUD, I9 6 0 ; VOROBIEV, 1965), and above 23°C In Septem ber (AIMIRANTE LACERDA, 1964) and O ctober (COM M ANDANT ROBERT GIRAUD, 1957, 1962). Not much In fo rm atio n Is a v a ila b le f o r th e so u th e rn summer (Jan u ary -M arch ) , b u t j Paech (1926) I n d ic a te s te m p e ra tu re s h ig h e r th a n 26.5°C In t h i s a re a In Ja n u a ry . In th e warm tongue o f f T u le a r, a v a lu e o f 23.25°C I s In c lo s e agreem ent w ith th o se o b ta in e d by th e WILLIAM SC0RESB7 In A ugust 1950 In the same a r e a . Few o b se rv a ti o n s from o th e r se a so n s a re a v a i l a b l e f o r com parison In t h i s l o c a l a r e a c lo s e to th e c o a s t. From COM M A N D A N T ROBERT GIRAUD d a ta , s u rfa c e Iso th erm s have been tra c e d 91 (Anon. I9 6 0 , 1963; Menache, 1963) and a c c o rd in g to th e maps p re p a re d th e s u rfa c e te m p e ra tu re o f f T u le a r was about 26°C In O ctober 1957, between 24°C and 25°C in O ctober 1962, and between 23°C and 24°C In J u ly I960. In Ja n u ary 1930 th e BAN! re c o rd e d In t h i s a r e a a s u rfa c e tem pera tu r e o f 26.60°C and Paech (1926) I n d ic a te a te m p e ra tu re o f j | about 23.5°C In Septem ber. In th e so u th e rn p a r t o f th e r e s e a r c h a r e a , a t 35°s «» 35 °E ., D arb y sh ire (1964) I n d ic a te s a s u rfa c e te m p era tu re ; between 19°0 and 20°C In J u ly 1962, between 21°C and 22°C | In Jan u ary 1963, and 22°C In A p ril 1962, w hile t h i s study i I n d ic a te s v a lu e s t h e r e betw een 17°C and 18°C In August | 1964. | In August 1964 th e d i r e c t i o n o f th e 22°C Isotherm In th e n o rth o f th e a r e a can n o t be drawn w ith c e r t a i n t y but can be I n f e r r e d . West o f s t a t i o n 367 th e 22°C i s o therm could tu rn n o r th o r s o u th . I t i s l i k e l y th a t i t tu rn s so u th based on th e s u rf a c e te m p e ra tu re v a lu e s in t h i s a re a o b ta in e d by th e WILLIAM SCORESBY In August 1950, which a re In good agreem ent w ith p r e s e n t v a lu e s . ! In summation, th e r e I s th ro u g h o u t th e r e s e a r c h a re a a d i s t i n c t c o o lin g in s u rfa c e w a te r te m p e ra tu re In A ugust, th e m id -w in te r month, when th e c o o le s t s u rfa c e tem pera tu r e s o f th e y e a r e x i s t . The absence o f o b s e rv a tio n s in F eb ru ary and March (m iddle and l a t e summer) does n o t p e r m it an assessm en t o f th e tim e o f th e y e a r w ith th e warm- 92 e s t s u rfa c e te m p e ra tu re . However, th e observed tem pera t u r e s were warmer In e a r l y f a l l (A p ril) th a n In e a r l y w in te r (Jan u ary ) and th e te m p eratu re v a r i a t io n between Jan u ary and May I s n o t v ery pronounced. The y e a r l y s u r fa c e te m p e ra tu re v a r i a t i o n I s ap p ro x im ately 4°C, b ein g more pronounced In th e a r e a o f f Durban w ith a v a r i a t i o n o f 5°C and l e s s marked In th e a r e a o f f T u le a r w ith a v a r i a t i o n o f 3°C. V e r t i c a l D is tr ib u tio n Curves o f te m p e ra tu re d i s t r i b u t i o n w ith d e p th , o f w hich s e le c te d ones a re r e p re s e n te d In F ig u re 7 , show t h a t a th e rm o c lln e i s p r e s e n t In s u rfa c e w a te rs o f th e n o rth e rn and w estern p a r t s o f th e a re a a t s ta t i o n s where th e s u r fa ce te m p e ra tu re i s above 20°C. The up p er d e p th o f th e th e rm o c lln e l a y e r Is s h a llo w e r a t th e s t a t i o n s n o r th o f 25°S. where I t l i e s a t about 50 m ( s t a t i o n 362 in F ig . 7) and deeper to th e s o u th where i t Is a t ab o u t 100 m ( s t a t i o n 376 in F ig . 1 0 ). No marked th e rm o c lln e I s p r e s e n t in th e s u rfa c e w a te r o f th e so u th e rn s t a t i o n s where th e te m p e ra tu re is a p p ro x im a te ly c o n s ta n t from th e s u rfa c e to 200 m ( s t a t i o n 383 In F ig . 7 ) . Between 200 m and alm ost 1000 m th e te m p e ra tu re d e c re a s e s from ab o u t 17°C to 5°0. Below 1000 m I t d e c re a s e s more slow ly to ab o u t 1°C a t 4500 m. D i s tr i b u t i o n o f te m p e ra tu re w ith d ep th a ls o i s 93 shown on v e r t i c a l te m p e ra tu re s e c t io n s ( F ig s . 11, 14, 17, 2 0). For co n v en ien ce, Iso th erm s betw een 10°C and 5°C were n o t drawn on th e v e r t i c a l s e c t i o n s . These show th e shape and d ep th o f th e tro u g h s o f warm w a te r ly in g alo n g th e c o a s ts . The tongue o f warm w a te r alo n g th e A frica n c o a s t I s c u t more o r l e s s p e r p e n d ic u la rly to th e a x is o f I t s flow a lo n g l i n e s I I I and IV, w hereas I t I s cu t ob l i q u e l y alo n g l i n e I . On th e l a t t e r l i n e , c o n s tr i c t i o n o f th e tongue I s e v id e n t betw een s t a t i o n s 360 and 361 (F ig . 1 1 ). The d ep th o f th e tongue o f w a te r warmer than 21°C Is 125 m, w h ile th e core o f w a te r warmer th a n 22°C l i e s above 50 m. S ta tio n s n e a r th e c o a s t o f M adagascar a re to o few and r e l a t i v e l y too f a r from s t a t i o n s In th e Channel to s p e c ify In d e t a i l th e t r e n d fo llo w ed by th e tongue o f warm w a te r th e r e . I t I s p ro b a b le t h a t th e l a t t e r Is cu t ob l i q u e l y alo n g l i n e I I , w h ile I t I s c u t more n e a rly p e r p e n d ic u la r ly to th e a x is o f I t s flow alo n g l i n e I . T his w a te r I s d eep er th a n th e tongue o f warm w a te r p re se n t alo n g th e A fric a n c o a s t, th e Iso th e rm 22°C ly in g between 100 and 125 m* There Is a g ra d u a l d e c re a se In s u rfa c e tem p eratu re from 21°C to 17°C In a n o r th w e s t- n o r th e a s t d i r e c t i o n , th e Iso th erm s b e in g w id ely spaced a lo n g l i n e I I I (F ig . 17) w h ile th e te m p e ra tu re g r a d ie n t I s much more marked alo n g l i n e IV (F ig . 2 0 ). The l a t t e r shows t h a t a body o f s u r face w ater w ith a homogeneous te m p e ra tu re o f 17°C l i e s b e tween s t a t i o n s 387 and 384. An eddy l a lo c a te d In t h i s a re a which I s d isc u sse d l a t e r . Iso th erm s betw een 21°C and 11°C extend to a d ep th o f about 500 m, showing a d e p re ss io n u n d e rn e a th th e to n g u e. Deeper th an 500 m, Iso th erm s tend to become h o r iz o n ta l. S a l i n i t y D is tr ib u tio n S u rfa c e S a l i n i t y S u rface s a l i n i t y o f th e a r e a ra n g e s from 35*25o/oo to 3 5«60 o / o o w ith an in c r e a s in g southw ard tr e n d ( F ig . 2 5). Low v a lu e s o f le s s th a n 35>40o/oo o ccu r alo n g th e A fric a n and Malagasy c o a s t s , w ith th e lo w est v a lu e in th e l a t t e r a re a ( 3 5 . 2 50/00 a t s t a t i o n 3 6 3 ). D i s tr ib u tio n o f s u rfa c e s a l i n i t y c o r r e l a t e s w ith th e tr e n d s in s u rfa c e te m p e ra tu re d i s t r i b u t i o n . Lower s a l i n i t y v a lu e s o c c u r in a re a s w ith h ig h e r te m p e ra tu re . V e r t i c a l Di s t r i b u t i o n S a l i n i t y d e c re a se s from th e s u rfa c e to a minimum o f about 34.50o/oo a t th e c o re o f th e A n ta r c tic In te rm e d ia te W ater. T his s a l i n i t y minimum i s a t a dep th o f about 1200- 1300 m a t th e s o u th e rn s t a t i o n s and r i s e s to n e a r ly 900 m to th e n o rth (com pare s t a t i o n s 362 and 382 In F ig . 8 ) . Below t h i s minimum, s a l i n i t y r i s e s s l i g h t l y to a l e s s Figure 25 S u rfa c e w a te r s a l i n i t y in th e S outhw est In d ia n Ocean f o r J u ly 29 to Septem ber 9* 1964. R.V. ANTON BRUUN d a t a , C ru ise 7. ( S a l i n i t y low er th an 35»30o/oo a r e not c o n to u r e d .) 95 96 42 SURFACE SALINITY. %. 100 200 300 KILOMETERS BEIRA ( 20° 20T 0 * INDIA E UROPA TULEAR JNHAMBANE CM 25* CA DURI 301 35' 97 marked maximum o f ab o u t 34 .8 0 o /o o a t 2500-3000 m I n d ic a t in g th e co re o f th e Deep W ater. N orth o f l a t i t u d e 25°S. th e tr e n d o f d i s t r i b u t i o n o f s a l i n i t y w ith d ep th i s d i f f e r e n t . The s a l i n i t y m in i mum , w hich i s n o t a s low, i s about 3 4 .7 5 o /o o a t a depth o f ab o u t 900 m and from t h a t dep th down s a l i n i t i e s s ta y homo geneous between v a lu e s o f 34.7 5 o /o o and 3 4 .8 0 o /o o . This i n d i c a t e s th e p re se n ce o f Deep W ater o f n o r th In d ian o r ig in w hich i s h ig h ly s a li n e ( s t a t i o n 367 in F ig . 8 ). In th e n o r th e rn p o r tio n of th e a r e a and a t s t a t i o n s a lo n g th e A fric a n c o a s t, a seco n d ary s a l i n i t y maximum o f 35*50o/oo to 3 5 * 6 0 o/ oo a p p e a rs a t ab o u t 2 0 0 m ( s t a t i o n 362 and 367 in F ig . 8) t h a t I n d ic a te s th e p resen ce o f a sub s u rfa c e c u r re n t (Clow es, 1950; O rren, 1 9 6 3). On th e v e r t i c a l s e c t io n s , a tongue o f low s a l i n i t y w a te r i s d is tin g u is h e d a t th e s u rfa c e a lo n g th e A frica n and M alagasy c o a s ts which co rre sp o n d s to th e tongues o f warm w a te r. The is o h a lln e s show c l e a r l y th e s a l i n i t y maxima a t about 200 m and 3000 m and th e s a l i n i t y minimum a t ap p ro x im a te ly 1200 m (w hich f o r convenience have been in d ic a te d w ith h a tc h in g on th e p r o f i l e s ) . Along th e n o rth e rn m o st l i n e ( l i n e I I , F ig . 15) i t i s a p p a re n t t h a t o f f th e c o a s t o f Inhambane a body o f low s a lin e w a te r i s sandwiched between th e s u p e r f i c i a l tongue which l i e s above 100 m and th e s a l i n i t y maximum which s in k s th e r e to 300 m. 98 D isso lv ed Oxygen and In o rg a n ic P hosphate D i s tr ib u tio n D isso lv ed Oxygen C o n ce n tratio n S u rface w a te rs a r e r e l a t i v e l y poor in d is s o lv e d oxygen. The d is s o lv e d oxygen c o n te n t a t th e s u rfa c e ra n g es from 5.63 m l / l ( s t a t i o n 383) to A .14 m l / l ( s t a t i o n 391)• The s u rfa c e d i s t r i b u t i o n p r e s e n ts good c o r r e l a t i o n w ith s u rfa c e te m p e ra tu re , s u rfa c e s a l i n i t y and s u rfa c e d e n s ity d i s t r i b u t i o n s (compare F ig s . 24-27)• H igher oxygen c o n te n t i s a s s o c ia te d w ith low er te m p e ra tu re , h ig h e r s a l i n i t y and h ig h e r s ig m a -t. G e n e ra lly , s t a t i o n s in a re a s where th e s u rfa c e te m p e ra tu re i s above 21°C have an oxygen c o n c e n tr a tio n o f 5 .1 0 m l / l o r l e s s (w ith th e e x c e p tio n o f th e h ig h e r v a lu e o f 5.33 m l / l a t s t a t i o n 387 e a s t o f S u ro p a ), w h ile in a r e a s where th e s u rfa c e te m p e ra tu re i s low er th a n 21°C th e oxygen c o n c e n tra tio n i s from 5*10 to 5*60 m l / l . Lower v a lu e s o f d iss o lv e d oxygen c o n te n t were observed a t s t a t i o n 381 a t th e W a lter S hoals (4 .7 3 m l/l)a n d s t a t i o n 391 o f f Durban (4 .1 4 m l / l ) . V e r tic a l d i s t r i b u t i o n o f d is s o lv e d oxygen i s shown on F ig u re 9. A s u b su rfa c e minimum i s p re s e n t which i s w e ll marked and s h a llo w e r in th e n o rth e rn a re a and in th e Agulhas a r e a (betw een ab o u t 3*60 and 4 .5 m l/l a t ab o u t 130 m, see s t a t i o n 363 on F ig . 9) and l e s s pronounced and Figure 26 S u rfa c e w a te r d e n s ity in th e Southw est In d ia n Ocean f o r J u ly 29 to Septem ber 29, 1964. R.V. ANTON BRUUN d a ta , C ru ise 7 . ( S ig m a-t low er th a n 24.20 and g r e a t e r th a n 26.00 a re n o t c o n to u re d .) 99 SURFACE CTT K I L O M E T E R S BEIRA ■USAS MINIMA e TULEAR LOURENCOFa? MARQUES^*/'' 25.40 s P Figure 27 D isso lv ed oxygen c o n te n t in s u rfa c e w a te r o f th e Southw est In d ia n Ocean f o r J u ly 29 to Septem ber 9 , 1964. R.V. ANTON BRUUN d a ta , C ru ise 7* (D isso lv ed oxygen c o n te n t low er th a n 5*0 m l / l and g r e a t e r th a n 5*6 m l / l a r e n o t c o n to u re d .) 101 102 45- SURFACE OXYGEN, m l/l 100 200 300 K IL O M E T E R S BEIRA teo* M INOU JNHAMBANE 25* DURI 301 B O * B5* 103 d e e p e r In th e so u th e rn a r e a (5*00 m l/l a t ab o u t 225 m, see s t a t i o n 383 in F ig . 9 ) . A maximum, s l i g h t l y above 5.00 m l / l , i s found a t ab o u t 500 m a t a l l s t a t i o n s in th e C e n tra l W ater. The minimum oxygen c o n c e n tr a tio n i s a t a d ep th o f 1000 m in th e n o rth w e ste rn a r e a ( s t a t i o n 363 in F ig . 9 ) , s in k in g to d ep th s o f 1500 to 2000 m in th e so u th e a s te r n a re a ( s t a t i o n 383 in F ig . 9 ), w h ile th e v a lu e of th e oxygen minimum in c r e a s e s in th e same d i r e c t i o n . Below th e d is s o lv e d oxygen minimum th e r e i s an In c re a s e to v a lu e s between ab o u t 5*00 and 5*10 m l / l a t ab o u t 3000 m in th e Deep W ater. Below t h i s depth oxygen v a lu e s a re c o n s ta n t o r e x h ib it a s l i g h t In c re a s e downward to th e bottom where a s l i g h t d ecrease a g ain a p p e a rs . In o rg a n ic P hosphate C o n c e n tra tio n The s u rfa c e in o rg a n ic phosphate c o n te n t i s low over th e whole a r e a ra n g in g betw een 0 .0 9 and 0.31 jig A /l. No c l e a r tr e n d co u ld be o b serv ed in s u rfa c e d i s t r i b u t i o n . P hosphate d i s t r i b u t i o n w ith d ep th i s shown on F ig u re 9 and some g e n e ra l tre n d s were fo u n d . The concen t r a t i o n i s r e l a t i v e l y homogeneous in th e s u rfa c e la y e r w hich i s th in n e r in n o rth e rn s t a t i o n s (ab o u t 75 ®) and t h i c k e r in th e s o u th (a b o u t 200 m). Below t h i s s u rfa c e l a y e r , th e r e i s a r a p id In c re a s e u n d e rla in by a l a y e r o f maximum c o n c e n tr a tio n (a b o u t 2 .5 f i g k / l ) which l i e s a t ab o u t 1200 to 1500 m. Below t h i s th e r e i s l i t t l e v a r l a - 104 t i o n w ith d e p th , a lth o u g h a d e c re a se in c o n c e n tra tio n u s u a lly o ccu rs a t ab o u t 3000 to 3500 m. From th e s u rfa c e to a dep th o f ab o u t 3000 m oxygen and phosphate c o n c e n tra tio n s a re I n v e r s e ly r e l a t e d (F ig . 9 ) . D i s tr i b u t i o n o f d is s o lv e d oxygen and In o rg an ic | p h osphate found In t h i s I n v e s tig a tio n a g re e c lo s e ly w ith th e f in d in g s o f M o ste rt (1966) from AFRICANA I I o b se rv a t i o n s . | ! W ater Masses j V arious c l a s s i f i c a t i o n s f o r th e w a te r m asses o f th e j In d ia n Ocean have been proposed ( S c h o tt, 1926, 1935; Thomsen, 1935; Sverdrup e t a l . , 1942; Muromtsev, I960; i Ivanenkov and Gubin, I960; and a few o t h e r s ) . Water m asses o f th e so u th w estern In d ia n Ocean were d e fin e d by O rren (1964) whose c l a s s i f i c a t i o n I s fo llo w ed in the p r e s e n t s tu d y . W ater m asses en co u n tered In th e r e s e a r c h a re a a r e d i f f e r e n t i a t e d by I n f l e c t i o n p o in ts on th e T em perature- S a l l n i t y cu rv es o b ta in e d from each h y d ro g ra p h ic s t a t i o n , some r e p r e s e n t a t i v e s o f which a re shown In F ig u re 10. The T-S cu rv es o f a l l s t a t i o n s a g re e w e ll and show f e a tu r e s s im i l a r to th o se cu rv es drawn from s t a t i o n s o f th e D A N A and DISCOVERY (S v erd ru p e t a l . , 1 9 4 2 ), th e AFRICANA I I (O rren , 1963, 1966) and th e NATAL (D a rb y sh ire , 1964) in 105 a r e a s o v e rla p p in g th e p r e s e n t a re a o r a d ja c e n t to I t . D is tr ib u tio n o f th e d i s t i n c t w a te r m asses th ro u g h o u t th e a r e a i s shown on v e r t i c a l s e c tio n s (F ig s . 11 to 23)* I n d ic a tio n o f t h e i r m otion can be o b tain ed from th e s lo p e s o f th e lso p y c n a ls ( i s o l i n e s o f slg m a-t) on th e v e r t i c a l s e c tio n s o f slg m a -t and from maps o f dynamic topography c o n s tru c te d a t v a rio u s l e v e l s . S u rfa c e Waters S u rface w a te rs in the so u th w est In d ia n Ocean d iv id e n a t u r a l l y in to th r e e r e g io n s : T ro p ic a l W ater, S u b tro p ic a l W ater and S u b a n ta r c tic W ater. The th re e s u rfa c e w a te r m asses a re s e p a ra te d by co n v erg en ces, th e T ro p ic a l Con vergence a t about 24°S. d iv id in g T ro p ic a l and S u b tro p ic a l W ater, and th e S u b tr o p ic a l Convergence a t ab o u t 42°S . d iv id in g S u b tro p ic a l and S u b a n ta rc tic W aters (O rren , 1964). The p o s itio n o f th e S u b tr o p ic a l Convergence i s s u b je c t to s e a so n a l v a r i a t i o n s , moving n o r th in th e so u th e rn w in te r . The a re a o f th e p r e s e n t i n v e s t i g a t i o n , between l a t i t u d e s 2 2 °3 4 'S . and 3 5 ° 4 4 'S ., i s f o r th e most p a r t in th e s u b tr o p ic a l re g io n and th e n orthernm ost s t a t i o n s are in th e a re a o f th e T ro p ic a l Convergence. There i s , how ever, in t r u s i o n o f T ro p ic a l W ater i n t o the s u b tr o p ic a l re g io n alo n g th e c o a s ts o f A f r ic a and M adagascar. The edge of th e Agulhas C u rre n t may be c o n sid e re d as a southw ard ex te n s io n o f th e T ro p ic a l Convergence (O rren, 1966). Two 106 s u rfa c e w a te rs a re th e r e f o r e p r e s e n t in th e r e s e a r c h a re a : T ro p ic a l W ater and S u b tro p ic a l W ater (P ig . 2 8 ). T r o p ic a l W ater T ro p ic a l W ater i s p r e s e n t a t s t a t i o n s n o rth o f l a t i t u d e 23°S. in th e c e n t r a l a re a o f th e Mozambique C hannel, and s o u th o f th lB l a t i t u d e a t s t a t i o n s lo c a te d alo n g th e M alagasy and A fric a n c o a s t s . I t s te m p e ra tu re i s h ig h e r than 21°C, and may be as much a s 23.25°C , and i t s s a l i n i t y i s alw ays lo w er th an about 35«45o/oo and may be as low as 35*25o/oo. Low s a l i n i t y s u rfa c e w a te r e x i s t s because p r e c i p i t a t i o n exceeds e v a p o ra tio n o v er th e re g io n o f i t s fo rm a tio n . D en sity o f th e T r o p ic a l W ater, ex p re ss e d w ith s lg m a -t, i s low er th an 2 4 .8 0 , d is s o lv e d oxygen c o n te n t ran g es from 4 .1 0 to 5*10 m l/l and th e p h osphate c o n te n t o f th e w a te r from 0 .1 2 to 0 .5 5 ^igA /l. This w a te r mass l i e s from th e s u rfa c e to a d e p th o f 50 to 75 m in th e c e n t r a l a re a o f th e Channel but i s d eep er n e a r th e M alagasy and A fric a n c o a s ts down to ab o u t 125 m. S u b tro p ic a l W ater S u b tro p ic a l W ater co v ers most o f the a r e a so u th o f 23°S. w ith th e ex c e p tio n o f th e s t a t i o n s alo n g the Ma la g a s / and A fric a n c o a s t s . I t i s p r e s e n t rrom th e s u rfa c e to a d epth o f ab o u t 200 m and s in k s a t su b su rfa c e d ep th s in the r e s t o f th e a r e a below th e T ro p ic a l W ater. I t may s in k as deep a s 300 m under th e T ro p ic a l W ater o f th e Agulhas Cur 107 r e n t (s e e th e w estern end o f v e r t i c a l s e c tio n s alo n g l i n e IV ). Tem perature ra n g e s betw een 21°C and 16.40°C w ith a southw ard d e c re ase a t th e s u rfa c e w hile th e s a l i n i t y , ra n g in g from 35 .4 5 o /o o to 3 5 . 60o /o o , shows a southw ard I n c re a s in g s u rfa c e t r e n d . There Is a s a l i n i t y maximum a t a b o u t 18°C s u rfa c e te m p e ra tu re (F ig . 2 8 ). The d eg ree o f e v a p o ra tio n In th e s u b tr o p i c a l reg io n m arkedly exceeds th e p r e c i p i t a t i o n , which le a d s to a c o n s id e ra b le I n c re a s e In s a l i n i t y , and t h i s w a te r mass Is c a lle d by French a u th o rs "Eau du maximum s u b tr o p ic a l de s a l i n i t e " (T c h e rn la et, a l . . 1951* 1958; Donguy and P lto n , 1969)* D en sity ran g es from s lg m a -t 24.80 to 25.90 w ith a southward s u rfa c e In c re a s e and th e oxygen c o n te n t ran g e s from 3*62 to 5*63 m l / l and th e phosphate c o n te n t from 0 .0 9 to 0 .7 5 /ig A /l. F ig u re 28, where th e s u rfa c e t e m p e r a t u r e - s a l l n l t y r e l a t i o n s h i p o f a l l s t a t i o n s h as been p l o t t e d , show th e d i s t i n c t i o n between T r o p ic a l and S u b tro p ic a l W aters. I t a p p e a rs t h a t th e m ost t y p i c a l c h a r a c t e r i s t i c s o f T ro p ic a l W ater a re found a t s t a t i o n s lo c a te d n e a r th e M adagascar c o a s t and In th e core o f th e Agulhas C u rre n t, w hile . s t a t i o n s lo c a te d on th e edge o f th e Agulhas C u rren t and a t 25°S. In th e c e n t r a l a r e a o f th e Channel have c h a r a c t e r i s t i c s In te rm e d ia te between th e two w ater m asses. The southernm ost s t a t i o n s w ith a tem p eratu re low er th a n 17°C have c h a r a c t e r i s t i c s ap p ro ach in g th e l i m i t s o f Sub t r o p i c a l W ater. They a r e s i m i l a r to s u rfa c e w a te rs d e s lg - Figure 28 S u rfa c e t e m p e r a t u r e / s a l i n it y r e l a t i o n s h i p s in th e Southw est In d ia n Ocean f o r J u ly 29 to Septem ber 9 , 1 9 6 b . R.V. ANION BRUUN d a ta . C ru ise 7* 108 TEMPERATURE S A LIN IT Y % 35.30 35.20 35.40 35.50 3 5 6 0 35.70 23 TW 22 20 SW * STATIONS NEAR MADAGASCAR (3 6 3 ~ 3 6 6 ) STATIONS NEAR AFRICA! A CORE OF MOZAMBIQUE - AGULHAS CURRENT (358,359,370,371.372, 374,309) ■ OUTER EDGE M O Z-AG CURRENT (360,361,369,375,388) □ INSHORE EDGE OF AGULHAS CURRENT (3 5 6 ,3 5 7 ,3 7 3 ,39 0 ,3 9 1 ,3 9 2 ) STATIONS IN CENTRAL PART OF MOZ. CHANNEL . • N. OF 25*S (367,368) O APPROX. 2 5 ° S (3 6 2 ) X STATIONS S. OF 29«S 8 E. OF 34* E (3 7 6 -3 8 7 ) TW ! TROPICAL WATER SW! SUBTROPICAL WATER 110 n a te d by O rren (1966) a s th e " t r a n s i t i o n re g io n " between S u b tro p ic a l and S u b a n ta r c tic W aters. S u rfa c e s a l i n i t i e s r e p o rte d in t h i s i n v e s t i g a t i o n a re com parable to s u rfa c e s a l i n i t i e s o b serv ed by O rren in J u n e -J u ly 1961-62, b u t s u rfa c e te m p e ra tu re s a re lo w er. In J u n e -J u ly 1961-62, 23°C marked th e l i m i t between T ro p ic a l and S u b tro p ic a l W aters compared w ith 21°C in August 1964, and th e maximum s u rfa c e B a l in lty was found a t 20°C s u rfa c e te m p e ra tu re in s te a d o f 18°C. D arbyshire (1964) used th e term s "Warm Agulhas W ater" and "Cool Agulhas W ater" to d e s ig n a te s u rfa c e w a te rs o f th e Agulhas C u rre n t and d e s ig n a te d th e s a l i n i t y maximum a s m arking th e l i m i t between them. S u rface C u rre n ts I n d ic a tio n s on th e m otion o f s u rfa c e w a te rs a re o b ta in e d from th e s lo p e s o f lso p y c n a ls on th e v e r t i c a l s e c tio n s o f slg m a -t and from th e c h a r t o f dynamic to p o graphy which was c o n s tr u c te d assum ing a l e v e l o f no m otion a t 1000 db ( P ig . 2 9 ). 1 . Movement of T ro p ic a l Water In th e a r e a T ro p ic a l W ater flow s southw ard as a sh allo w tongue o f l i g h t , waxm, low s a l i n e , p o o rly oxy g en ated w a te r on top o f d e n s e r, c o o le r , h ig h ly s a li n e and more oxygenated S u b tro p ic a l W ater alo n g th e A fric a n and M alagasy c o a s t s . C lose to th e A fric a n c o a s t t h i s flow of Figure 29 Dynamic topography a t s u rfa c e o v er 1000 d b , R.V. ANION BRUUN d a ta , C ru ise 7, Ju ly 29 to Septem ber 7, 1964. I l l 112 3Q L S S L 40- DYNAMIC TOPOGRAPHY, dyam SURFACE RELATIVE TO IOOO db 45* 20+ H IM K IN O M 25+ 30+ 351 BEIRA LOURENCO MARQUE TULEAR -05* T ro p ic a l W ater forms th e upper la y e r o f th e Agulhas Cur r e n t and fo llo w s th e tre n d o f th e c o a s t in a southw ard d i r e c t i o n . Both th e w id th o f th e c u r r e n t and i t s d is ta n c e from th e c o a s t v a ry . O ff Inhambane i t i s v ery narrow (a lo n g l i n e I I ) , th e upper l a y e r o f th e c u r r e n t from th e s u rf a c e to 75 m e x te n d in g from th e c o a s t o u t to about 30 km ( s t a t i o n 371) ly in g o nly over th e c o n t i n e n t a l s h e lf , w hereas th e s u b su rfa c e la y e r o f th e c u r r e n t i s w id er, ex te n d in g a p p ro x im a te ly 50 km seaw ard ( e a s t o f s t a t i o n 3 70). O ff Lourenco Marques in a s o u th e a s t d i r e c t i o n (alo n g l i n e I I I ) th e c u r r e n t in th e upper 75 m ex ten d s from Lourenco Marques Bay seaward to about 200 km ( e a s t o f s t a t i o n 374-) w h ile th e w a te r below 75 m shows a c u r r e n t whose tre n d i s in th e o p p o s ite d i r e c t i o n . In t h i s a r e a o f th e in d e n ta t i o n o f th e c o a s t, M allory (1961) d e sc rib e d a "w h irlp o o l e f f e c t " o f th e Agulhas C u rren t which form s a clockw ise s w i r l . The p re se n c e o f an eddy in t h i s a re a i s shown on s u rfa c e c u r r e n t maps o f Faech (1926) and a ls o i s d e sc rib e d by H a r ris (1961, 1964) and O rren (1 9 6 3 ). T his eddy e f f e c t a t th e tim e o f t h i s i n v e s t i g a t i o n o cc u rre d m ain ly a t sub s u rfa c e d ep th s and was accom panied by some v e r t i c a l move ment a s shown by th e u n s ta b le c h a r a c t e r i s t i c s v a lu e s o f th e s u rfa c e l a y e r a t s t a t i o n 373* Between Lourenco Marques and Cape S a in t L u cia th e c u r r e n t n arro w s, e x te n d in g from th e c o a s t to about 65 km seaw ard (betw een s t a t i o n s 359 and 3 6 0 ). S e c tio n s alo n g l i n e I , w hich t r a n s e c t th e Agulhas 114 C u rre n t o b liq u e ly , show th e narro w in g o f the c u r r e n t a t s t a t i o n 360. At Cape S a in t L ucia th e broadening o f th e s h e l f cau ses th e c u r r e n t to s h i f t o f fs h o re . The flo w r e cedes s l i g h t l y from th e c o a st and w idens a g a in . O ff the T ugela R iv e r, n o r th o f Durban (a lo n g l i n e IV ), I t eu :s from a few k ilo m e te rs from th e c o a s t to about 150 km out ( e a s t o f s t a t i o n 389)* N orth o f Durban, th e s t a t i o n s c lo se to th e sh o re ( s t a t i o n 356 and 357) were not p l o t t e d on th e v e r t i c a l s e c t i o n s . C h a r a c t e r i s t i c s o f t h e i r upper 20 m e x h ib it u n s t a b l l l t y su g g e stin g th e p resen ce o f up- w e llln g . On th e c h a r t o f s u rfa c e dynamic topography o v e r a r e fe r e n c e le v e l o f 1000 db (F ig . 29) th e p a tte r n o f the southw estw ard A gulhas flow cannot be shown In d e t a i l be cause many o f th e s t a t i o n s In t h i s a r e a are a t d e p th s l e s s th an 1000 m. The n arro w in g o f th e flow o f th e u p p er 75 m la y e r a t s t a t i o n 360 does not ap p e ar on F ig u re 29, b u t I s a p p a re n t on a s u rfa c e dynamic to p o g rap h y c o n s tru c te d over a s u rfa c e l e v e l o f 400 db, and I s c l e a r l y d e p ic te d on maps o f te m p e ra tu re , s a l i n i t y and slg m a -t s u rfa c e d i s t r i b u t i o n ( F ig s . 2 4 -2 6 ). O ff th e M adagascar c o a s t, s t a t i o n s 363* 365 end 366 a r e lo c a te d In th e co re o f th e flow o f T r o p ic a l W ater w hich, a c c o rd in g to th e s lo p e s o f th e iso p y c n a ls on sigm a- t s e c tio n s alo n g l i n e s I and I I ( F ig s . 13 and 16) flo w s southw ard, w h ile a no rth w ard c o u n te r c u r re n t flow s o v e r th e 115 c o n tin e n ta l s h e l f between th e co ast and s t a t i o n 365* S ta tio n 364 i s in th e a re a o f t h i s c o u n te r c u r r e n t and th e u n s t a b i l i t y o f w a te r c h a r a c t e r i s t i c s h e re i n d i c a t e s th a t some v e r t i c a l movement o c c u rs. A lthough th e southw ard c u r re n t i s c l e a r l y seen on th e s u rfa c e dynamic topography o v e r 1000 db, th e northw ard in sh o re flow does n o t appear because s t a t i o n s 364 and 365 are a t d ep th s too Bhallow to be p l o t t e d . I t i s n o t p o s s ib le to s p e c if y th e e x te n sio n o f t h i s c u r r e n t n o r th and so u th o f th e a r e a o f f T u le a r b e cause o f a la c k o f s t a t i o n s . 2 . Movement o f S u b tro p ic a l W ater The g e n e ra l c i r c u l a t i o n p a t t e r n o f th e S u b tro p ic a l W ater as seen on the s u rfa c e dynamic topography map (F ig . 29) c o n s is ts o f two la r g e cy c lo n ic (c lo c k w ise ) g y res n o rth and so u th o f 3 0 ° 3 0 'S . r e s p e c tiv e ly . A n o rth e a stw a rd move ment on th e o u te r edge o f th e Agulhas C u rre n t was d e sc rib e d by D arbyshire (1964) a t v a rio u s seaso n s d i r e c t l y so u th o f th e study a r e a . The f e a t u r e s o f th e s u rfa c e c u r r e n ts in th e reg io n s o u th e a s t o f Durban in August 1958 drawn by D arb y sh ire (1964, h i s F ig . 36) a re c o n s i s t e n t w ith th e p re s e n t f e a t u r e s from August 1964. In b o th c a se s th e boundary betw een th e southw estw ard A gulhas C u rre n t and th e n o rth e a stw a rd o u te r c u r r e n t l i e s on th e m e rid ia n 31°30'E . a t l a t i t u d e ±31°S. I t i s n o t p o s s ib le to s p e c ify w hether th e n o rth e a stw a rd flow c o n tin u e s n o r th o f l a t i t u d e 25°S. o r tu rn s back on i t s e l f , to jo in th e southw estw ard flow , 116 form ing th e r e f o r e an a n tlc y c lo n ic eddy In th e Agulhas C u rre n t. Data from more n o r th e r l y s ta t i o n s would be n e c e s s a ry a s w e ll as more c lo s e ly spaced s t a t i o n s between s t a t i o n s 369 and 370. From th e v e r t i c a l slg m a -t s e c tio n alo n g l i n e I I (F ig . 16) I t I s p ro b ab le t h a t th e r e I s a n orthw ard flow between s t a t i o n s 371 and 370. The la r g e c y c lo n ic eddy In th e so u th e rn p a rt o f th e a r e a , c e n te re d a t ab o u t 3 2 ° S ., 3 8 ° £ ., h as been reco g n ized In v a rio u s seasons by D arb y sh ire (1964) who showed th e so u th e rn p a r t o f th e g y re . T his eddy i s re s p o n s ib le f o r th e d ec re a se d s u rfa c e te m p e ra tu re s , In c re a se d s u rfa c e s a l i n i t i e s and In c re a se d s u rfa c e d e n s it i e s p r e s e n t In th e a r e a o f s t a t i o n 386 (se e F ig s . 2 4 -2 6 ). The w a te r flo w in g w estw ard a t 2 8 °-2 9 °S . (n o rth o f s t a t i o n 376) jo in s th e n o rth e a stw a rd flo w of th e o u te r edge o f th e Agulhas C u rre n t and r e s u l t s In a s tro n g n o r th e a stw a rd strea m . Bending o f t h i s flow around s t a t i o n 375 produces th e m eanders o f th e 21°C Iso th erm , 35*40o/oo ls o - h a lln e and 24.80 lso p y c n a l e v id e n t a t t h i s s t a t i o n on s u r fa c e c o n to u rs maps ( F ig s . 2 4 -2 6 ), and i s d o u b tle ss re s p o n s i b l e f o r th e narrow ing o f th e tongue o f T ro p ic a l W ater ob serv e d h e r e . Owing to a la c k o f more n o r th e r l y s t a t i o n s , I t Is n o t f e a s i b l e to d eterm in e i f th e northw ard flo w o f s u rfa c e w a te rs between 35°-38°E . and n o r th o f 25°S. c o n tin u e s f u r t h e r n o r th In th e Mozambique Channel o r bends eastw ard 117 tow ard M adagascar form ing a c y c lo n ic s w i r l . 3. Comparison o f S urface C u rre n ts In W inter and S p rin g Comparison o f s u rfa c e dynamic to p ography c h a r ts con s tr u c te d f o r October-November 1957 by Menache (1961, 1963) and In August 1964 In t h i s study show t h a t s u rfa c e c u r r e n t s p a t t e r n s a r e d i f f e r e n t f o r th e s o u th e rn sp rin g and w in te r (compare F ig s . 6 and 29). A ccording to th e I n t e r p r e t a t io n o f Menache th e r e i s no flow from th e Mozambique C u rren t I n to th e Agulhas C u rre n t, and th e Mozambique Cur r e n t forms an a n t l c y c lo n ic system n o r th o f 25°S. A greeing / • w ith Menache s f in d i n g s , an a n tlc y c lo n ic s w ir l c e n te re d a p p ro x im a te ly a t 2 4 ° S ., 40°E. was o bserved In O ctober 1962 by Crepon (1965) who s tu d ie d s u rfa c e c i r c u l a t i o n u t i l i z i n g th e towed e le c t r o d e s G.E.K. c u r r e n t m eter aboard th e CO M M A N D A N T ROBERT GIRAUD. He a ls o in d ic a te d t h a t In s id e th e Mozambique Channel th e c u r r e n ts a re complex and p ro b a b ly h ig h ly In flu e n c e d by lo c a l w inds. In th e p r e s e n t I n v e s tig a tio n a g y re I s found j u s t n o r th o f 25°S. b u t In a c y c lo n ic d i r e c t i o n , th e w ater com ing th e r e f o r e from th e so u th and n o t from th e n o r th . The p a t t e r n o f t h i s g yre i s c o n s is te n t w ith r e p r e s e n t a t i o n s o f s u rfa c e c u r r e n t s made by Paech (1926) who p re p a re d a s e r i e s o f s tr e a m lin e s maps f o r d i f f e r e n t months o f th e y e a r t h a t show complex p a t t e r n s . I t a p p e a rs , how ever, t h a t a c y c lo n ic s w i r l , whose d eg ree o f developm ent i s dependent 118 on th e se aso n , o ccu rred a t 25°S. o f f th e so u th w estern c o r n e r o f M adagascar. Owing t o a la c k o f n o r th e r ly s t a t i o n s , i t was not p o s s ib le to t r a c e th e p a t t e r n o f th e Mozambique C u rre n t in s id e th e Mozambique C hannel, but i t i s p ro b a b le t h a t T ro p ic a l W ater from th e Mozambique Chan n e l flow s so u th o f th e Mozambique Channel a t b o th w estern and e a s te r n e x tr e m itie s of th e C hannel. I t seems re a so n a b le to assume t h a t th e southw estw ard flow a lo n g th e A fric a n c o a s t a t 25°S. i s fed by w a te r from th e Mozambique C hannel r a t h e r th a n by w a te r from th e e a s t , as in Menache s scheme, because th e w a te r o f t h i s flow i s warmer and l e s s s a l i n e th an th e w ater to th e e a s t . C o n sid erin g th e narrow w id th and th e p ro x im ity to th e c o a s t o f th e southw estw ard flo w o f f Inhambane observed in t h i s stu d y , a southw ard ex te n s io n o f th e Mozambique C u rre n t o f th e same am plitude / / may have been overlo o k ed by Menache owing to a la c k o f s t a t i o n s c lo se to th e c o a s t. However, M enache18 (1963) s u rf a c e te m p e ra tu re and s a l i n i t y d i s t r i b u t i o n maps (M enache, 1963) i n d ic a te t h a t iso th e rm s and ls o h a lln e s w ere o r ie n te d w e s t- e a s t from Lourenco Marques Bay seaw ard, w h ile in t h i s stu d y th e y a re o r ie n te d s o u th w e s t-n o rth e a s t ( P ig s . 24 and 2 5 ). I t a p p e a rs , t h e r e f o r e , t h a t in th e s p r in g perhaps no T ro p ic a l W ater from th e Mozambique Chan n e l flo w s s o u th o f th e Channel alo n g th e A fric a n C oast, b u t in th e w in te r i t does flo w . Southward flow o f T r o p ic a l W ater alo n g th e Madagas- 119 c a r c o a s t o bserved In t h i s study o f f T u le a r has n o t been d e s c rib e d by o th e r w o rk e rs. Menache showed a northw ard c u r r e n t In t h i s a re a f o r th e s p rin g of 1957* The so u th ward c u r r e n t shown In t h i s stu d y , s im i l a r to th e c u r r e n t a lo n g th e A fric a n c o a s t, I s narrow and e a s i l y may have been overlooked because o f a p a u c ity o f s t a t i o n s c lo s e enough to th e c o a s t. The southw ard e x te n s io n o f t h i s c u r re n t could n o t be d eterm in e d so u th o f th e I s la n d . I t I s p o s s i b l e t h a t I t flow s so u th and tu r n s w est jo in in g th e w e st ward flow n e a r 29°S. I f t h i s were th e c a s e , th e w ater would have l o s t I t s t r o p i c a l c h a r a c t e r i s t i c s by th e tim e I t reached th e a r e a o f s t a t i o n 375* Also p o s s ib le I s th a t I t tu rn s back alo n g th e c o a s t form ing an a n tlc y c lo n ic eddy sin c e a northw ard c u r r e n t o f T ro p ic a l W ater e x i s t s alo n g th e c o a s t. 4 . The M adagascar C u rren t There I s g e n e ra l agreem ent t h a t s o u th o f th e Mozambique Channel th e r e I s an e a s t-w e s t flow o f w ater from th e M adagascar C u rre n t toward th e A fric a n c o a s t fe e d - / / . ln g In to th e A gulhas C u rre n t. A ccording to Menache s ob s e r v a tio n s , t h i s flow w hich he c a l l s "C ourant E st des A ig u ille s " (Menache, 1966) I s th e o nly so u rc e o f w ater f o r th e A gulhas C u rre n t, and Is w e ll-d e v e lo p e d so u th o f 25°S. on h is s u rfa c e to p o g ra p h ic map ( F ig . 6 ). In th e p re s e n t i n v e s t i g a t i o n an e a s t-w e s t c u r r e n t I s e v id e n t a t a l a t i t u d e o f ab o u t 29°S. There a r e n o t s u f f i c i e n t o b s e r 120 v a tio n s to t r a c e th e o r ig in o f t h i s flow , which bends n o rthw ard around s t a t i o n 375 and may bend southw ard a g a in . This would be a p ath f o r th e M adagascar C u rren t w a te r to Jo in th e Agulhas C u rre n t a t th e tim e th e s e o b s e rv a tio n s were made. Water a t s t a t i o n 3 7 5* however, has c h a r a c t e r i s t i c s c lo s e r to S u b tro p ic a l W ater th an to T ro p ic a l W ater and, I f th e w a te r a t t h i s s t a t i o n Is o f M adagascar C u rre n t o r i g i n , t h i s c u r r e n t would c a r r y w a te r c o o le r , l e s s s a l i n e , d e n s e r, and more oxygenated th a n th e Agulhas C u rre n t. P o s s ib ly w a te r from th e M adagascar C u rre n t form s th e la r g e c y c lo n ic s w irl o f th e n o rth e rn p a r t o f th e a r e a . I f t h i s were th e c a s e , how ever, th e southw ard flow alo n g th e M adagascar c o a s t I s n o t p a r t o f I t s in c e th e w a te r th e r e ( s t a t i o n s 366, 365, 364 and 363) i s much warmer, l e s s s a l i n e , l i g h t e r and l e s s oxygenated th an w ater o f th e s w irl and th u s has a d i f f e r e n t o r i g i n . The southw ard flo w a lo n g th e M adagascar c o a s t c a r r i e s t y p i c a l T ro p ic a l W ater which must be d e riv e d from th e Mozambique Channel and, a s n o ted e a r l i e r , i s i n t e r p r e t e d as an e x te n s io n o f th e Mozambique C u rre n t. In th e m id -w in te r, when th e p r e s e n t o b s e rv a tio n s were made, th e southw est monsoon i s a t i t s maximum. T hat p o r tio n o f th e South E q u a to r ia l C u rre n t flow ing so u th i s sm a ll, le a d in g to weak Mozambique and M adagascar C u r r e n ts , and t h a t p o r tio n o f th e M adagascar C u rren t flo w in g e a s t in th e a re a so u th o f th e Mozambique Channel (" E a s t A gulhas 121 / / C u rren t o f Menache, 1966) I s poorly developed o r a b s e n t. I t Is p o s s ib le t h a t l i t t l e , I f any, o f th e M adagascar Cur r e n t jo in s th e Agulhas C u rre n t. The l a t t e r may be fed m ain ly , o r o n ly , by th e Mozambique C u rre n t which flow s southw ard o u t o f th e Mozambique Channel a lo n g the A fric a n c o a s t In a narrow stream c lo s e to th e p ro tru d in g c o a s t o f so u th e rn Mozambique. In th e e a r ly s p r in g , which was th e tim e of M enache's (1961, 1963) o b s e rv a tio n s , th e monsoon changes d i r e c t io n and t h a t p o r tio n o f th e South E q u a to r ia l C urrent flo w in g s o u th i s in c r e a s e d , le a d in g to a s tr o n g e r Mozam biq u e and M adagascar C u rre n t. At t h i s tim e o f y e a r the "E ast A gulhas C u rren t" I s w e ll developed and Is th e only c o n tr ib u to r to th e A gulhas C u rre n t, w hereas th e Mozambique C u rre n t does n o t flow so u th o f th e Mozambique C hannel. S u b su rface C u rre n ts S u b su rfa ce c u r r e n ts g e n e ra lly a r e d e te c te d a s s a l i n i t y maxima, ly in g j u s t below th e s u rf a c e l a y e r , but u s u a lly n o t d e e p e r th an about 200 m. In th e A t la n tic Ocean th e s u b su rfa c e c u r r e n t , w e ll-d e v e lo p e d in summer b u t n o t so marked In w in te r , h a s been tr a c e d a lo n g 30°W. as f a r as th e S u b tro p ic a l Convergence (D eacon, 1937; Clowes, 1930). In th e so u th w estern In d ia n O cean, O rren (1963, 1966) d e te c te d in th e s u b tr o p ic a l r e g io n th e p re se n c e of s u b su rfa c e c u r r e n ts w hich, however, d id n o t ex ten d as f a r s o u th a s th e S u b tro p ic a l C onvergence. These were e v id e n t 122 o n ly n o r th o f ab o u t 33°S. In th e co u rse o f t h i s I n v e s t i g a tio n s u b su rfa c e c u r r e n ts shown by s a l i n i t y maxima a ls o were found, b u t n o t as f a r so u th a s a t th e tim e o f O rre n 's o b s e rv a tio n s (J u n e -J u ly 19 6 1 -6 2 ). They o ccu rred o nly n o rth o f l a t i t u d e 30°S. On th e v e r t i c a l s a l i n i t y s e c tio n s ( F ig s . 12, 15, 18, 21, 23) a s a l i n i t y maximum i s seen n o rth o f l a t i t u d e 30°S. w ith s a l i n i t i e s in ex cess o f 35*55o/oo. The la y e r o f maximum s a l i n i t y i s ab o u t 75 m th ic k and i t s co re i s a t a p p ro x im a te ly 200 m a t about 29°S, r i s i n g n orthw ard to ab o u t 100 m a t 25°S . N orth o f t h i s l a t i t u d e th e l a y e r o f maximum s a l i n i t y narrow s to a th ic k n e s s o f a p p ro x im a te ly 20 m where T ro p ic a l W ater i s a t th e s u r f a c e . T his s o u th - n o r th tre n d i s shown on th e n o r th - s o u th s a l i n i t y s e c tio n (F ig . 2 3 ). There i s a downward movement o f th e s a l i n i t y maximum, a s w e ll as a d e c re a se in v a lu e s between 35*55o/oo and 35»50o/oo, a lo n g th e A fric a n and M alagasy c o a s ts where th e S u b tro p ic a l W ater i s fo rced downward by th e tongue o f l i g h t , low s a li n e T ro p ic a l W ater. T his d e p re ss io n i s shown a t both w estern and e a s te r n e x tr e m itie s o f a l l v e r t i c a l s e c t io n s . Near th e M alagasy c o a s t th e s a l i n i t y maximum s in k s to 200 m. Along th e A fric a n c o a s t, s in k in g o f S u b tro p ic a l W ater i s more pronounced when th e s u rfa c e c u r r e n t o f T ro p ic a l W ater i s n arro w er and t h e r e f o r e s tr o n g e r . The s a l i n i t y maximum re a c h e s a d e p th o f 300 m a t s t a t i o n s 370 o f f Inhambane and 123 389 o f f Durban ( F ig s . 13 and 2 1 ), w h ile o f f s o u th e a s t o f Lourenco Marques Bay i t I s a t 200 m a t s t a t i o n s 374 and 361 ( F ig s . 18 and 1 2 ). Along l i n e I from Durban to T u le a r ( F ig . 12) th e r i s e o f S u b tro p ic a l W ater a t s t a t i o n 360 i s a p p a re n t in th e a r e a o f n arrow ing o f th e Agulhas C u rren t which i s c u t o b liq u e ly by t h i s t r a n s e c t . South o f 30°S. no s u b su rfa c e c u r r e n t i s d e fin e d in th e s a l i n i t y p a t t e r n ; th e w a te r i s is o h a lin e to a d e p th o f 200 m. From th e s lo p e s o f th e lso p y c n a ls on v e r t i c a l s e c tio n s o f sig m a -t i t i s e v id e n t t h a t th e r e i s a so u th ward component o f flow a t su b su rfa c e d e p th s as w e ll as a t th e s u rfa c e in th e Agulhas C u rre n t a r e a . The southw ard flo w , how ever, does n o t narrow a t s u b su rfa c e d ep th s as i t does a t th e s u r f a c e . T his i s seen on slg m a -t s e c tio n s alo n g l i n e I I ( F ig . 16) where th e southw ard su b su rfa c e c u r re n t ex ten d s from th e c o a s t a t Inhambane seaward to s ta t i o n 370 ( in s te a d o f s t a t i o n 371 f o r th e s u rfa c e c u r r e n t ) , and alo n g l i n e I (F ig . 13) where a su b su rfa c e southw ard c u r r e n t i s p r e s e n t a t s t a t i o n 360. T his ex p la in s why th e n arro w in g s o f th e p a th o f s u rf a c e T ro p ic a l W ater in th e Agulhas C u rre n t a re n o t d e te c te d from th e dynamic to p o g rap h y o v er a 1000 db r e f e r e n c e l e v e l and why th e y do a p p e a r on a dynamic topography o v e r a 400 db re fe r e n c e l e v e l . O ff Lourenco M arques, alo n g l i n e I I I (F ig . 1 9 ). th e flow o f s u b s u rfa c e w a te r does n o t p a r a l l e l th e southw ard 124 flo w o f s u rfa c e w ater between s t a t i o n s 373 and 374. As d is c u s s e d e a r l i e r , th e r e I s d o u b tle s s an eddy a t sub s u rf a c e d ep th s In th e a re a o f th e In d e n ta tio n o f th e c o a s t . O rren (1963) showed t h a t e a s t o f M adagascar, n o rth o f l a t i t u d e 3 0 °S ., th e s u b su rfa c e c u r r e n t moved northw ard as shown by a northw ard d e c re a se In s a l i n i t y and oxygen v a lu e s In th e core o f maximum s a l i n i t y . The co re o f th e s u b s u rfa c e c u r r e n t la y a t ab o u t 75 m a t l a t i t u d e 2 9 °4 3 'S . ( s t a t i o n AFRICANA I I , 20) and was d e p re sse d to a d ep th o f 250 m a t 2 2 °2 5 'S . ( s t a t i o n AFRICANA I I , 1 8 ). Orren sug g e s te d t h a t s in k in g was b ro u g h t ab o u t by th e la r g e volume o f T r o p ic a l Water n e a r th e T ro p ic a l C onvergence. T his phenomenon was n o t o bserved In th e c e n t r a l a r e a o f th e Mozambique Channel I n v e s tig a te d where th e core o f th e s u b s u rfa c e c u r re n t does n o t s in k u n d er s t a t i o n 368 (see n o r th - s o u th s e c tio n , F ig . 23)* T hinning o f th e la y e r o f maximum s a l i n i t y a t s t a t i o n 368 may be caused by m ixing a lo n g I t s p a th w ith T ro p ic a l and C e n tra l W aters. More n o r th e r l y s t a t i o n s would be n e c e s s a ry to determ ine th e n o rth w ard e x te n s io n o f th e s u b s u rfa c e s a l i n i t y maximum In th e Mozambique C hannel. A p o s s i b i l i t y I s t h a t I t I s m a in ta in e d northw ard as shown from th e s a l i n i t y s e c tio n In th e Mozambique Channel o f Clowes and Deacon (1935)* 0 * The n o r th - s o u th s a l i n i t y s e c tio n o f Menache (1963), In c o n t r a s t , shows t h a t th e s u b su rfa c e w a te r In th e s o u th o f 125 th e Channel does n o t p e n e tr a te In the Channel n o r th o f 25°S. Donguy and P ito n ( 1969) n o ted a su b su rfa c e s a l i n i t y maximum In th e n o rth e rn p a r t o f th e Mozambique Channel a t 1 3 °1 3 'S . and d is c u s s e d th e p o s s ib le a l t e r n a t i v e s f o r I t s so u th e rn o r n o rth e rn o r i g i n . They could n o t, how e v e r, be c o n c lu s iv e . C e n tra l W ater The C e n tra l Water l i e s In th e e n t i r e s u b tr o p ic a l re g io n as a l a y e r o f l i n e a r T/S r e l a t i o n s h i p s s e p a r a tin g th e h ig h ly s a li n e s u b su rfa c e and s u rfa c e w aters and th e p o o rly s a li n e A n ta r c tic In te rm e d ia te W ater. The o r ig in o f t h i s w a te r mass has been d isc u s s e d by v a rio u s a u th o rs (S verdrup ejt a l . , 1942; Clowes, 1950; Deacon, 1937) who p u t forw ard s e v e r a l p o s tu l a t e s . Orren (1963, 1966) I n d i c a te d t h a t I t I s l i k e l y t h a t th e C e n tra l W ater I s n o t formed as a consequence o f any s in g le p ro c e ss but r a t h e r by a com bination o f s e v e r a l . He proposed t h a t I t o r i g i n a t e s from s in k in g o f mixed S u b tro p ic a l Water and S u b a n ta r c tlc W ater n o r th o f th e S u b tro p ic a l Convergence and moves n o r th w ard, a t 200-800 m, m ixing alo n g I t s p a th w ith h ig h s a l i n i t y su b su rfa c e w a te r and low s a l i n i t y A n ta r c tic I n t e r m ed iate W ater. Throughout th e r e s e a r c h a r e a th e C e n tra l W ater c l e a r l y ap p ears as a s t r a i g h t l i n e on a l l T/S c u rv e s. In most o f th e a r e a , th e l i n e f a l l s between th e p o in ts T = 126 16°C, S = 35.50o/oo and T = 7°C, S = 3 4 .5 5 o /o o , between d e p th s o f a p p ro x im a te ly 200-300 m and 1000 m (se e T/S c u rv e s o f s t a t i o n s 378 and 384 on F ig . 1 0 ). In th e w e ste rn a re a th e s a l i n i t y a t th e low er end o f th e s t r a i g h t l i n e i s s l i g h t l y h ig h e r w ith a v alu e o f 35*60o/oo ( s t a t i o n 389 on F ig . 1 0 ). At s t a t i o n s n o rth o f l a t i t u d e 2 5 ° S ., th e s t r a i g h t l i n e ends a t a d ep th o f about 700 m a t th e approxim ate p o in t T = 9°C, S = 3 4.80o/oo ( s t a t i o n s 363 and 368 on F ig . 1 0 ). Here th e C e n tra l Water i s i n flu e n c e d by th e u n d e rly in g h ig h ly s a li n e w ater o f N orth In d ia n o r ig i n which in f lu e n c e s a ls o s l i g h t l y th e C e n tra l W ater o f th e w estern a r e a . D en sity o f C e n tra l Water ra n g e s between sig m a-t 25*90 and 2 7 .2 0 , oxygen c o n te n t betw een 4 .3 5 and 5*15 m l/l» and th e phosphate c o n te n t b e tween 0 .5 5 and 1.70 p g A /l. Movement o f C e n tra l W ater From th e slo p e s o f th e lso p y c n a ls on slg m a-t s e c tio n s in fo rm a tio n can be o b ta in e d on th e movement o f th e C e n tra l W ater. I t a p p e a rs t h a t th e C e n tra l Water r i s e s ab o u t 100 m in th e c e n t e r o f th e l a r g e eddy a p p a re n t on th e s u rfa c e dynamic topography w hich o ccu p ies th e s o u th e rn p a r t o f th e r e s e a r c h a r e a . T his upward movement i s e v id e n t a t s t a t i o n 386 a lo n g l i n e IV and between s t a t i o n s 378 and 379 a lo n g l i n e I I I . In th e w estern p a r t o f th e a r e a th e flow o f C e n tra l 127 W ater fo llo w s th e tre n d o f th e Agulhas C u rre n t. In a manner s im ila r to th e s u b s u rfa c e c u r r e n t, th e southw ard c u r re n t o f C e n tra l W ater does n o t narrow in th e a r e a s where th e s u rfa c e A gulhas C u rren t does. T h is i s shown by th e p a r a l l e l tre n d s o f th e lso p y c n a ls of C e n tra l W ater and su b su rfa c e w a te r on s lg m a -t s e c tio n s alo n g l i n e s I and I I . Southward flow o f C e n tr a l W ater i s w ider th a n a t sub s u rfa c e d ep th s alo n g l i n e s I I I and IV and e x te n d s a s f a r seaward as s t a t i o n s 376 and 388. t * Menache (1961) n o ted in th e sp rin g o f 1957 and 1958 a marked u p w e llln g o f C e n tr a l Water a t l a t i t u d e 25°S. in th e so u th o f th e Mozambique C hannel. W ater of s a l i n i t y h ig h e r th an 35.25o/oo r o s e to th e s u rfa c e from a d ep th o f 250 to 500 m. S ta t i o n s 362 and 368, lo c a te d in t h i s a r e a , do n o t show a s im i l a r d is tu r b a n c e , s u g g e s tin g t h a t th e u p w ellln g i s s e a s o n a l. A n ta r c tic In te rm e d ia te Water A n ta r c tic In te rm e d ia te W ater, between th e C e n tra l W ater and th e Deep W ater, i s c h a r a c te r iz e d by a marked s a l i n i t y minimum. T h is w a te r mass o r i g i n a t e s j u s t N orth o f th e A n ta r c tic Convergence by m ixing o f A n ta r c tic and S u b a n ta rc tic W aters w hich s in k s and sp re a d s northw ard a t a d ep th o f ab o u t 1000 m. In th e southw est In d ia n Ocean, O rren (1963, 1966) r e p o r te d t h i s l o w - s a l i n i t y w a te r mass to be a t d ep th s o f 300 to 400 m in th e s u b a n ta r c tic r e g io n 128 s in k in g r a p id ly northw ard to 900 to 1300 m n o rth o f th e Convergence, and th e n r i s i n g s l i g h t l y n o rth w ard . In t h i s a r e a th e A n ta rc tic In te rm e d ia te W ater found a t d ep th s o f 1000 to 2000 m i s c h a r a c te r iz e d by a s a l i n i t y minimum o f l e s s th a n 34.40o/oo in th e so u th ( s t a t i o n 382) which In c re a s e s n orthw estw ard to v a lu e s o f 3 4 .6 0 o /o o . S im u ltan e o u sly w ith th e s a l i n i t y In c re a se th e r e Is a s l i g h t r i s e o f th e w ater m ass, th e co re o f which I s a t a d ep th o f ab o u t 1300 m a t th e southernm ost s t a t i o n s ( s t a t i o n s 382-384) and a r i s e to ab o u t 900 m a t s t a t i o n 362. The northw ard s a l i n i t y In c re a s e and upward tre n d I s re c o g n iz a b le on th e s a l i n i t y s e c t io n alo n g th e n o rth - s o u th l i n e ( F ig . 23) and Is e v id e n t by comparing th e s a l i n i t y cu rv es o f s t a t i o n 382 and 362 on F ig u re 8 . A westw ard s a l i n i t y In c re a s e I s shown on w e ste rn e x tr e m itie s o f th e s a l i n i t y s e c tio n s alo n g l i n e s I , I I I and IV. As w i l l be d is c u s s e d , th e s a l i n i t y In c re a s e in d i c a t e s th e d i r e c t io n o f th e movement o f th e w a te r m ass. The te m p e ra tu re o f th e A n ta r c tic In te rm e d ia te W ater ran g es from 7°C to 2.5°C , w ith a c o re te m p e ra tu re o f 5°C. The d e n s ity ra n g e s from slg m a-t 2 7 .2 0 to 27*70, th e core fo llo w in g ro u g h ly th e slg m a -t 2 7 .3 0 . Oxygen c o n te n t ra n g es from 3 .8 0 to 4 .8 5 m l / l and th e p h o sp h ate c o n te n t from I .6 5 to 2 .3 5 /ig A /l. The A n ta r c tic In te rm e d ia te W ater i s not p r e s e n t a t s t a t i o n s n o rth o f 25°S. and e a s t o f 40°E. where i t i s r e 129 p la c e d by a n o th e r w ater mass o f N orth In d ia n o r i g i n , th e h ig h ly s a li n e N orth In d ia n Deep W ater. A n ta r c tic I n t e r m ed iate W ater, t h e r e f o r e , does n o t ap p ear a t th e e a s te rn end o f l i n e I I ( F ig . 1 5 ). A s l i g h t s a l i n i t y minimum of l e s s than 3 4.70o/oo o ccu rs a t t h i s l a t i t u d e w est o f 4o°E. ( s t a t i o n s 369 and 368) owing to th e m ixing o f N orth In d ia n Deep Water and A n ta r c tic In te rm e d ia te W ater. Movement o f A n ta r c tic In te rm e d ia te W ater The e x te n s io n o f A n ta r c tic In te rm e d ia te Water in th e w este rn In d ian Ocean has been d isc u sse d by a number o f a u th o r s . X chernla e t a l . (1931, 1958) r e p o rte d t h a t a s a l i n i t y minimum may be drawn c o n tin u o u sly from the South In d ia n Ocean to th e G ulf o f Oman and th e y concluded t h a t A n ta r c tic In te rm e d ia te W ater c ro s s e s th e E q u a to r in th e w e ste rn In d ia n Ocean and p e n e tr a te s to th e n o rth e rn boundary o f th e A rabian S ea. During t h i s northw ard move ment th e w a te r mass i s fo rc e d upward from i t s l e v e l o f 1000 m to s u b su rfa c e l a y e r s by th e N orth In d ia n W ater w hich flow s to th e so u th . T a ft (1963) q u e stio n e d t h i s c o n c lu sio n as he showed t h a t m aintenance o f a s a l i n i t y minimum in th e A rabian Sea does not r e q u ir e a flow o f A n ta r c tic In te rm e d ia te W ater a c ro s s th e E q u a to r. T eh ern ia e t a l . (1951) re p o rte d t h a t th e in flu e n c e o f A n ta r c tic I n te rm e d ia te W ater i s much l e s s im p o rtan t in th e Mozam b iq u e Channel th a n to th e e a s t o f M adagascar. 1 3 0 Clowes and Deacon (1935)* from t h e i r s a l i n i t y s e c tio n drawn from DISCOVERY s t a t i o n s , showed t h a t A n ta rc t i c In te rm e d ia te W ater flow s n o rth th ro u g h th e Mozambique Channel and t h a t i t s in flu e n c e i s e f f e c t i v e as f a r n o rth as J u s t so u th o f th e E q u a to r. They n o ted t h a t th e r i s e from 1000 m to ab o u t 500 m o f t h i s w a te r mass r e s u l t e d from i t s b ein g fo rc e d upward by th e southw ard flow o f N orth In d ia n Deep W ater. The f in d in g s o f Donguy and P lto n ( 1 9 6 9) a re in c lo se agreem ent w ith Clowes and D eacon's o b s e r v a tio n s . They d e te c te d in th e n o r th o f the Mozambique Channel th e p resen ce o f A n ta r c tic In te rm e d ia te W ater w ith a s a l i n i t y low er than 3 4 .7 5 o /o o ly in g a t 800 m a t 13°S. w ith a la y e r th ic k n e s s o f 200 m, r i s i n g to 500 m a t 8°S . w ith a la y e r th ic k n e s s o f 100 m. Menache (1 9 6 3 ), on th e o th e r hand* showed t h a t A n ta r c tic In te rm e d ia te Water r a p id ly l o s e s i t s i d e n t i t y on e n te r in g th e Mozambique Channel and e n c o u n te rin g th e North In d ia n Deep W ater a t about 24°S. In summary* a lth o u g h A n ta r c tic In te rm e d ia te Water p e n e tr a te s f a r n o r th in th e Mozambique C hannel, i t s flow i s much w eakened. A lso , th e w a ter mass lo s e s i t s i d e n t i t y , i t s s a l i n i t y in c r e a s in g northw ard w h ile m ixing w ith North In d ia n Deep W ater. From th e d i s t r i b u t i o n o f i d e n t i f y i n g p r o p e r tie s and dynam ical to p o g ra p h y , Clowes (1 9 5 0 ), O rren (1963* 1966), V ls s e r and Van N iekerk (1965) showed t h a t th e d ir e c tio n o f 131 th e A n ta r c tic In te rm e d ia te W ater in th e southw est In d ia n Ocean fo llo w s th e tre n d o f th e Agulhas C u rre n t and R eturn A gulhas C u rre n t. P a rt o f th e w a te r flow s southward alo n g th e South A fric a n c o a s t, tu r n s back in an e a s t e r l y d i r e c t i o n , then cu rv es a g a in in th e d i r e c t io n o f th e Mozambique Channel and Im m ediately so u th o f th e Channel changes d i r e c t io n and r e t u r n s so u th a g a in form ing in t h i s way a la r g e a n tlc y c lo n ic w ate r movement. V ls s e r and N iek erk (1965) I n fe r re d th e p re se n c e o f southw ard p ro - tu s io n s o f N orth In d ia n Deep W ater a t d ep th s o f 1000 m and 1500 m in th e a re a J u st so u th o f th e Mozambique C hannel. However, th e AFRICANA I I s t a t i o n s s tu d ie d by th e s e a u th o rs a r e a l l so u th o f l a t i t u d e 27°S. On th e o th e r hand, th e COM M ANDANT ROBERT GIRAUD s t a t i o n s s tu d ie d by Menache were m ain ly n o r th o f t h i s l a t i t u d e . S ince th e a r e a p r e s e n tly surveyed ex ten d s n o rth and s o u th o f t h i s l a t i t u d e , i t w i l l be p o s s ib le to s p e c ify th e p a t t e r n o f w a te r d i s t r i b u t i o n in th e a r e a where A n ta r c tic In te rm e d ia te W ater and N orth In d ia n Deep Water m eet. For t h i s purpose two dynamic to p o g ra p h ic maps were c o n s tr u c te d over a r e fe re n c e l e v e l o f 2000 db, one a t a 1000 db l e v e l and th e o th e r a t a 1500 db l e v e l (F ig s . 30 and 3 1 ). A ll o b s e rv a tio n s a v a i l a b l e a t t h i s tim e (p ro v id e d by th e N a tio n a l O ceanographic Data C e n te r in W ashington) were c o n s id e re d . Most s t a t i o n s were o ccu p ied d uring th e f a l l , w in te r and s p rin g s e a s o n s . Few were occupied d u rin g Figure 30 Itynamic topography a t 1000 db r e l a t i v e to 2000 db, d a ta from : V : AFRICANA I I X : ALMIRANTE LA CERDA • : ANTON BRUUN □ : ATLANTIS A : COM M ANDANT ROBERT GIRAUD * : DISCOVERY ■ : NATAL O : WILLIAM SCORESBY 1 3 2 133 20* ■ 25* ■ DYNAMIC TOPOGRAPHY AT 10 0 0 db RELATIVE TO 200 (d shaded area 0 100 200 300 KILOMETERS BEIRA ❖ I BASSOS D A INDIA TULEAR LOURENCO MARQUE 30* 35* ■ ■* t o* ------------------------ 43 * " Figure 31 dynamic to p o g rap h y a t 1500 db r e l a t i v e to 2000 db, d a ta from : ▼ : AFRICANA I I X : ALMIRANTE LACERDA • : ANION BRUUN □ : ATLANTIS ▲ : ARGO A : COM M A N D A N T ROBERT GIRAUD + : D A N A % : DISCOVERY ■ : NATAL O : WILLIAM SCORESBY 134 135 * 2 ---------------------- DYNAMIC TOPOGRAPHY AT I 5 0 0 db RELATIVE TO 2 0 0 (d^n. m .) shaded area shallower thw U U &ti K IL O M E T E R S BEIRA TULEAR LOURENCO/^ MARQUE%V th e summer. S t a t i o n s s e le c te d f o r drawing th e maps were occupied from June to November. T a ft (1963) p o in te d out t h a t th e d i s t o r t i o n In tro d u c e d by combining o b s e rv a tio n s from many e x p e d itio n s which o fte n have employed d i f f e r e n t m easuring te c h n iq u e s Is g r e a t e r than the e f f e c t s o f se a so n a l In flu e n c e . C o n s is te n t agreem ent was found between v a lu e s from d i f f e r e n t e x p e d itio n s d u rin g th e w in te r and s p rin g . Minor d is c r e p a n c ie s appeared between th e l a t t e r and v a lu es o b ta in e d In th e summer and In th e e a r ly f a l l as I n d ic a te d by d a ta from DANA, VEMA, NATAL and GALATHEA f o r Jan u ary and F e b ru a ry , and by ALMIRANTE LACERDA, V EM A and ARGO fo r A p ril and May. The g e n e ra l tre n d s shown by th e two dynamic to p o graphy maps a re com parable. The two w ater m asses, A n ta r c tic In te rm e d ia te W ater and N orth In d ia n Deep W ater, a r e d i s t i n c t . Both form an a n tlc y c lo n lc system n o r th and so u th o f l a t i t u d e 25°S. r e s p e c t i v e l y . The boundary b e tween th e two w a te r m asses I s o r ie n te d somewhat n o rth w e s t- s o u th e a s t. The N orth In d ia n Deep W ater te n d s to extend so u th o f th e Channel on I t s e a s te r n sid e n e a r M adagascar, w hereas th e A n ta r c tic In te rm e d ia te Water te n d s to p e n e tr a te In th e Channel on I t s w e ste rn s id e a t about 38°E. T his m otion o f th e two w a te r m asses I s r e f l e c t e d on s a l i n i t y s e c tio n s . Along l i n e I I (F ig . 13) a minimum s a l i n i t y o c c u rs a t s t a t i o n 369 a t ab o u t 1200 m which ta p e r s o u t a t s t a t i o n 368 and does n o t e x i s t f u r t h e r e a s t . Along l i n e I 137 (F ig . 12) th e s a l i n i t y minimum Is more pronounced a t s t a t i o n 361 th an a t s t a t i o n 362. The s a l i n i t y s e c tio n drawn by Menache (1963, h i s F ig . 15) alo n g a Lourenco M arques-T ulear l i n e I s In good agreem ent w ith th e se f in d - / > ln g s . Menache showed a w e ll marked s a l i n i t y minimum on th e w estern end o f th e s e c tio n which d e c re a se s to th e e a s t . Movement o f A n ta r c tic In te rm e d ia te W ater fo llo w s th e tr e n d s o f th e Agulhas C u rren t and R etu rn Agulhas Cur r e n t as d e s c rib e d by V ls se r and N lekerk (1 9 6 5 ). However, th e abundance o f d a ta used In th e p r e s e n t stu d y to c o n stru c t dynamic to p o g rap h y maps allo w s a more d e ta i l e d p ic tu r e than th e one th e y o b ta in e d . There a re two a n tlc y c lo n lc s w ir ls , one c e n te re d on th e Mozambique P la te a u which was n o t shown by V ls s e r and N le k e rk , and a n o th e r c e n te re d on th e N atal B asin a t ab o u t 3 7 °S ., 40°E. which th e y d e p ic te d . A com p a ris o n betw een F ig u re s 30 and 31 shows t h a t th e tendency f o r th e A n ta r c tic In te rm e d ia te W ater to p e n e tr a te n o r th ward In to th e Mozambique Channel Is more pronounced a t 1000 m th a n a t 1500 m. On e n c o u n te rin g th e N orth In d ia n Deep W ater, th e A n ta r c tic In te rm e d ia te W ater lo s e s p a r t o f I t s I d e n tity by m ixing. I t becomes more s a l i n e , a s shown on th e w estern ends o f p r o f i l e s I , I I I and IV a t s t a t i o n s lo c a te d In th e a r e a o f th e Agulhas C u rren t ( F ig s . 12, 18 and 21) and l e s s oxygenated as seen on a d i s t r i b u t i o n map o f th e oxygen minimum (F ig . 3 2 ). Figure 32 D is tr ib u tio n o f th e d is s o lv e d oxygen m in i mum in th e Southw est In d ia n Ocean f o r J u ly 29 to Septem ber 9, 1964. R.V. ANTON BRUUN d a ta , C ru ise 7. 138 139 301 -------------- OXYGEN M IN IM U M , ml/I -— DEPTH OF OXYGEN MINIMUM .m 1 0 0 2 0 0 3 0 0 KILOMETERS BEIRA 20* BASS AS D A -35 B O * 301 35* N orth A tla n tic Deep W ater 140 N orth A t la n tic Deep W ater I s re c o g n iz e d by a s l i g h t s a l i n i t y maximum ly in g below th e A n ta rc tic I n t e r m e d ia te W ater minimum. T his w a te r mass In th e A tla n tic Is betw een 1600 m and 3000 m w ith a southw ard movement. Clowes and Deacon (1935) r e p o r te d t h a t an e a s t e r l y d ir e c te d c u r r e n t of N orth A t l a n t i c Deep W ater e x is te d In the s o u th e rn In d ia n Ocean and th e Im p o rtan ce o f t h i s Inflow was l a t e r n o te d by s e v e ra l I n v e s t i g a t o r s . In th e r e s e a r c h a r e a th e N orth A t la n tic Deep W ater I s p r e s e n t w ith a s a l i n i t y maximum In ex cess o f 34.80o/oo betw een d ep th s o f 2300 m and 3500 m. Tem perature Is 2.5°C to 2°C, slg m a-t roughly 27*80, oxygen c o n te n t ranges be tween 4 .7 5 and 5*00 m l/l and th e phosphate c o n te n t between 1 .8 0 and 2 .0 0 jig A /l. At a l l s t a t i o n s lo c a te d e i t h e r In th e s o u th e rn p a r t o f th e N a ta l B asin covered h e re o r In I t s w e s te rn p a r t the l a y e r o f maximum s a l i n i t y h as a th ic k n e s s o f ab o u t 1000 m. I t Is th in n e r (ab o u t 230 m) a t s t a t i o n s 377 and 378 and lo c a te d In th e c e n te r and w estern p a r t o f th e N a ta l B asin ( F ig . 1 8 ). N orth o f l a t i t u d e 25°S. th e N orth A tla n tic Deep W ater a p p e a rs to be p re s e n t In a s much as s a l i n i t i e s in e x c e ss o f 34.80o/oo a re found. However, a t t h a t lo c a le th e s e a - f l o o r being sh a llo w e r th a n 3500 m, th e bottom l a y e r o f th e N orth A t l a n t i c Deep W ater core does not 141 stan d out c l e a r l y ( s t a t i o n s 363, 367» 368 alo n g l i n e I I , F ig . 15)* F u rth erm o re, m ixing w ith N orth In d ia n Deep W ater o ccu rs In t h i s a r e a and th e two w a te r m asses h av in g s im ila r v a lu e s o f s a l i n i t i e s ( c lo s e to 3 4 .8 0 o /o o ) a re n o t e a s i ly d is tin g u is h e d . I t I s l i k e l y , how ever, t h a t a t s t a t i o n 363 N orth A t l a n t i c Deep W ater w ith s a l i n i t i e s In ex cess o f 3 4.80o/oo Is fo rc e d down below 3000 m by an o v e r- ly in g homogeneous body o f N orth In d ia n Deep W ater w ith s a l i n i t i e s between 34.75 and 34.80o/oo (F ig . 1 2 ). A s im ila r e f f e c t was o b serv ed by Orren (1963, h is F ig . 30) on th e o th e r sid e o f th e N a ta l B asin a t AFRICANA I I s t a t i o n 7. Movement o f N orth A t l a n t i c Deep W ater The im portance o f th e I n f lu x o f N orth A t l a n t i c Deep W ater In to th e so u th e rn In d ia n Ocean h as been s tr e s s e d by a number o f a u th o rs (Deacon, 1937; C low es,1950; Stommel, 1958; Le P ich o n , I9 6 0 ; S c h e rb ln in , 1969; W arren, 1971). However, Z a l i n s k i i (1963) s ta t e d t h a t th e r o le o f N orth A tla n tic Deep Water in th e deep c i r c u l a t i o n o f th e In d ia n Ocean Is o v e re s tim a te d . A ll th e s e I n v e s t i g a t o r s s tu d ie d g e n e ra liz e d p a t t e r n s o f deep w a te r c i r c u l a t i o n , e i t h e r f o r th e e n t i r e In d ia n Ocean o r f o r th e S outhw estern In d ia n Ocean. U n fo rtu n a te ly th e a re a o f th e Mozambique Channel was n e g le c te d owing to th e p a u c ity o f d a ta in t h i s r e g io n . Le Pichon (I9 6 0 ) s tu d ie d th e deep w ater c i r c u l a t io n in th e Southw estern In d ia n Ocean and r e p o rte d t h a t 142 th e c i r c u l a t i o n o f deep w ate r below 2000 m In th e S outh w e ste rn In d ia n Ocean Is determ in ed c h i e f l y by th e I n flu x o f A tla n tic Deep W ater In to t h i s a r e a . By u s in g th e core method and g e o s tro p h lc co m putations Le Pichon tra c e d th e p ro p a g a tio n o f Worth A tla n tic Deep W ater I n to th e Agulhas B asin and I t s n o rth e rn p ro lo n g a tio n th e N a ta l B a sin , th e Reunion B asin and th e K erguelen B a sin . He used a l l a v a i l a b le o b s e rv a tio n s , a few o f which ta k e n in th e summer were n o t tak en in acco u n t f o r c o n s tr u c tin g h i s c o re maps. Ac c o rd in g to th e c i r c u l a t i o n p a t t e r n d e te c te d by Le P ichon, th e N orth A t l a n t i c Deep Water from th e A t la n tic Ocean flow s along th e c o n tin e n ta l slo p e o f A f r ic a . I t I s f i r s t d e f le c te d by the Agulhas P la te a u , th en d e f le c te d so u th e a s t by th e Mozambique P la te a u , f i n a l l y re c u rv in g s o u th e astw ard a c r o s s th e m id -o cean ic rid g e and i s d ir e c te d southw ard between th e K erguelen Ridge and 50°E. There i s a d e f i n i t e n o rth w ard movement in th e N a ta l B a sin . From a map o f d i s t r i b u t i o n o f s p e c i f i c volume anom alies a t 3000 m c o n s tru c te d by Le P ich o n , i t i s e v id e n t t h a t th e c u r re n t ru n n in g n o r th in th e N a ta l B asin tu r n s southw ard above 28°S . and t h a t th e c u r r e n t goes n o rth on th e e a s t s id e and s o u th on th e west s id e . However, Le Pichon s ta te d th a t t h i s i n t e r p r e t a t i o n i s d i f f i c u l t to b e lie v e and t h a t h is o b s e rv a tio n s on th e northw ard deep c u r r e n t a re n o t con c l u s i v e . The a v a ila b le o b s e rv a tio n s in th e N atal B asin a t t h a t tim e w ere s c a n ty . L a te r, Orren (1963, 1966) and V ls s e r and N lekerk (1965) s tu d ie d th e m otion o f N orth A tla n tic Deep W ater In th e Southw estern In d ia n Ocean from AFRICANA I I s t a t i o n s and some a d d itio n a l NATAL s t a t i o n s . O rren found t h a t N o rth A t la n tic Deep Water w ith a s a l i n i t y maximum was a t 2500 to 3000 m over th e g r e a t e r p a r t o f th e a re a so u th o f l a t i t u d e 30°S. N orth o f t h i s l a t i t u d e , alo n g th e Lourenco Marques lin e th e N orth A t l a n t i c Deep W ater a p p a re n tly l i e s a t about 2000 m In th e e a s t o f th e N a ta l B asin (between AFRICANA I I s t a t i o n s 9 and 1 0 ), w h ile to th e w est o f th e N a ta l B asin ( s t a t i o n s 8 and 7) th e N orth A tla n tic Deep W ater l i e s d e e p e r, a t 3000 m, and Is o v e r la in by N orth In d ia n Deep Water (O rren , 1963, h i s F ig . 2 0 ). Orren con clu d ed t h a t a northw ard-m oving c u r r e n t In th e N atal B asin appeared to be c o n c e n tra te d more to th e e a s te r n sid e and t h a t I t I s l i k e l y t h a t th e northw ard moving w ater m eets N o rth In d ia n Deep W ater In th e Mozambique C hannel, m ixes and r e tu r n s so u th In th e w e ste rn a r e a . V ls s e r and N lekerk ( 1 9 6 5) from a dynamic topography map a t 3000 db r e l a t i v e to a 2000 db s u rfa c e I n te r p r e te d th e c i r c u l a t i o n In th e N a ta l B asin n o r th o f l a t i t u d e 35°S. a s an a n tlc y c lo n lc movement ( c e n te re d on AFRICANA I I , s t a t i o n 9) r e s u l t i n g from th e ten d en cy f o r th e w ater from th e Mozambique Channel to p e n e tr a te th e N a ta l B asin from th e n o r th . South o f t h i s a n tlc y c lo n lc movement, th e s e a u th o rs showed a c y c lo n ic s w ir l a t ab o u t 37°S. (around AFRICANA I I , 144 s t a t i o n 5 0 ) a p p a r e n tly r e s u l t i n g from sh e a r betw een th e southw ard movement o f w a te r from th e N a ta l B asin and th e northw ard moving w a ter from f u r t h e r s o u th . V ls s e r and N lekerk a ls o showed an a n tlc y c lo n lc s w ir l In th e T ra n sk e l B asin between A fric a and th e Mozambique P la te a u (c e n te re d on s t a t i o n 3 2 ), p a r t o f which a p p a re n tly b ran ch es o f f and form s th e deeper p a r t o f th e Agulhas C u rre n t. U sing a l l o b s e rv a tio n s now a v a i l a b l e , a dynamic topography map a t a 3000 db l e v e l r e l a t i v e to a 2000 db s u rfa c e was c o n s tr u c te d (F ig . 3 3 ). Most o f th e s t a t i o n s were occupied between June and November and o n ly a few d u rin g th e summer (NATAL In J a n u a ry ). They were a l l used f o r p re p a rin g th e map because th e r e Is good agreem ent be tween v a lu e s . From t h i s map I t Is e v id e n t t h a t th e p a t t e r n o f c i r c u l a t i o n In th e a re a o f the N atal Basin c o n sid e re d I s a p p re c ia b ly d i f f e r e n t th a n th e one d e s c rib e d by V ls s e r and N lek erk . S t a t i o n s In t h i s a r e a used by th e s e a u th o rs were s c a n ty . T h e ir s t a t i o n s a re a ls o p lo tte d In F ig u re 33 and are a ls o In good agreem ent w ith th e p a tte r n developed In t h i s p a p e r. I t a p p e a rs t h a t th e r e I s a c y c lo n ic movement o f N orth A tla n tic Deep W ater In th e p o r tio n o f th e N a ta l B asin s tu d ie d ( n o t a n t l c y c lo n lc a s d e s c rib e d by V ls s e r and N le k e rk ). The N orth A t l a n t i c Deep W ater e n t e r s t h i s p o r tio n o f th e N a ta l B asin from th e s o u th , flow s n o r th ward on th e w estern s id e o f th e B asin and r e t u r n s so u th on Figure 33 Dynamic topo g rap h y a t 3000 db r e l a t i v e to 2000 db, d a ta from: ▼ : AFRICANA I I • : ANTON BRUUN □ : ATLANTIS A : COM M A N D A N T ROBERT GIRAUD ■ : NATAL 145 146 35* 30* DYNAMIC TOPOGRAPHY ■ AT 3 0 0 0 db RELATIVE TO 200 (d shaded area • / / / / ' / / . ? ■ ■ ^ ■ ' / / / , A ' ' / * 0 100 200 300 V / S / / / - / / / / / / / > ' - / / / / / ■ / / y ' ' KILOMETERS BEIRA TULEAR & LOURENCO// M ARQUESlx f-Vx / ' / / ' / ■ ' V - ' ' / 147 I t s e a s te rn s id e . S w irls occur on each sid e o f th e main flo w . The N orth In d ia n Seep W ater p e n e tr a te s In to th e N a ta l B asin from th e n o r th on each s id e o f th e Zambesi Canyon and p e n e tr a te s In th e n o rth w e ste rn c o m e r o f th e B asin above th e s i l l s e p a r a tin g th e N a ta l B asin and th e sm a ll a b y ssa l p la i n ly in g west o f Europa I s l a n d . I t I s In t h i s c o m e r o f th e N a ta l B asin th a t Orren (1963) found N orth A tla n tic Seep W ater fo rc e d down to 3000 m by o v e r- ly in g N orth In d ia n Deep W ater. The N orth I n d ia n Deep W ater p e n e tr a te s a l s o In th e n o r th e a s te r n c o m e r o f th e N a ta l B asin along th e M adagascar c o n tin e n ta l slo p e and the N orth A tla n tic Deep W ater a lso I s fo rce d down to 3000 m by o v e rly in g N orth In d ia n Deep W ater ( s t a t i o n 363, P ig . 12). N orth A t la n tic Deep W ater p e n e tr a te s In th e Mozambique Channel f u r t h e r n o r th th an th e N a ta l B asin In th e a re a o f th e Zambesi Canyon. I t cannot go too f a r , how e v e r , sin ce th e u p p e r boundary o f th e N orth A t l a n t i c Deep W ater la y e r Is a t ab o u t 2500 m which I s th e s i l l d e p th o f th e n o rth e rn Mozambique Channel (se e P ig . 2 ) . Donguy and P lto n (1969) found t h a t th e deep w ater In th e Channel a t 1 3 °1 3 'S . does not come from th e so u th . The s a l i n i t y s e c tio n o f Clowes and Deacon (1935) shows t h a t the N orth A tla n tic Deep W ater In flu e n c e does n o t extend beyond th e s i l l depth o f th e Mozambique Channel a t about 18°S. In th e n o rth e rn e x tre m ity o f th e N a ta l B asin , where b o th North A t l a n t i c Deep Water and N orth In d ia n Deep W ater 148 m eet, m ix tu re o f th e two w ater m asses o c c u rs aud th ey lo s e t h e i r I d e n t i t y In p a r t . The N orth In d ia n Seep W ater I s ly in g a t s t a t i o n s 368, 367 and 366 below 700 m (se e F ig . 1 3 ). The In c re a s e In s a l i n i t y (3 4 .8 lo /o o ) a t about 2750 m a t th e s e s t a t i o n s I s l i k e l y due to N orth A t l a n t i c Deep W ater In flu e n c e . The southw ard r e tu r n flow o f deep w a te r on th e e a s te r n s id e o f th e N a ta l B asin I s composed o f mixed N orth A t l a n t i c Deep W ater and N orth In d ia n Deep W ater. I t p a sse s o v er th e s i l l s o f th e M adagascar F la te a u and c o n tr ib u te s to th e fo rm atio n o f th e homogeneous mass o f w ater which o c c u p ie s th e depth o f th e Reunion B asin (Le P ich o n , i 9 6 0) . Along th e e a s te r n edge o f th e N a ta l B asin th e c y c lo n ic s w ir l betw een th e r e tu r n flow and th e M adagascar P la te a u may be r e l a t e d e i t h e r to a flow o f w a te r coming from th e s o u th e a s t o v er th e M adagascar P la te a u o r may be a r e tu r n flow o f th e w a te r which could n o t p a ss th e b a r r i e r o f th e M adagascar P la te a u . F u r th e r ev id en ce o f t h i s movement o f N orth A tla n tic Deep W ater in th e N a ta l B asin may be o b ta in e d from th e d i s t r i b u t i o n o f d is s o lv e d oxygen c o n te n t a t th e s a l i n i t y maximum (T able I ) . There i s a d e c re a se in oxygen c o n te n t as w e ll as a d e c re a se in s a l i n i t y v a lu e s in th e d i r e c t io n o f th e c u r r e n t . S ta tio n s in th e w e ste rn p a r t o f th e N a ta l B asin e x h i b i t a northw ard d e c re a se o f oxygen c o n te n t from 149 Table I . D i s tr i b u t i o n o f oxygen a t th e maximum s a l i n i t y l e v e l in th e N orth A t l a n t i c Deep W ater. S ta tio n s from th e w estern sid e o f th e N a ta l B asin a re l i s t e d from so u th to n o rth S ta tio n s Oxygen c o n te n t a t s a l i n i t y maximum m l/1 S a l i n i t y maximum o/oo 384 5.03 34.83 385 5 .0 0 34.83 376 4 .9 3 34.83 362 4 .8 4 34.82 1 5 0 5.03 m l / l a t s t a t i o n 384 to 4 .8 4 m l / l a t s t a t i o n 362 w ith a p a r a l l e l d e c re a se In s a l i n i t y v a lu e s . From th e s a l i n i t y s e c tio n a lo n g l i n e I I I (F ig . 18) I t I s e v id e n t t h a t th e volume o f th e maximum s a l i n i t y l a y e r d e c re a se s from w est to e a s t , a s w e ll as th e s a l i n i t y v a lu e o f th e maximum which Is 3 4 .8 3 o /o o a t s t a t i o n 376, 3 4 .8 lo /o o a t s t a t i o n 377 and 3 4 .8 0 o /o o a t s t a t i o n 378 ( F ig . 3 4 ). The o n ly s t a t i o n s In th e a r e a o f th e Agulhas Cur r e n t d e e p e r th an 2000 m a re s t a t i o n s 388 and 387 In th e n o rth e rn end o f th e T ran sk ei B a sin . But a t s t a t i o n 388 no m easurem ents were tak en d eep er th an 2000 m. The c i r c u l a tio n p a t t e r n In t h i s a r e a cannot be shown from s t a t i o n 387 o n ly , w hich Is n o t deep enough to show th e low er depth o f th e maximum s a l i n i t y l a y e r I f one I s p r e s e n t (s e e F ig . 2 1). N orth In d ia n Been W ater The e x is te n c e o f a southw ard deep c u r r e n t of h ig h ly s a lin e w a te r In th e n o rth e rn p a r t o f th e In d ia n Ocean was d e te c te d In th e second decade o f t h i s c e n tu ry (S c h o tt, 1926; M atthew s, 1927; M o lle r, 1 9 29). T h is c u r r e n t i s com posed o f h ig h ly s a l i n e , low oxygen c o n te n t s u rfa c e w a ter s in k in g from th e c o a s ta l re g io n s o f th e A rabian Sea and n e ig h b o rin g g u lf s in c lu d in g th e Red Sea and I t i s r e f e r r e d by S v erd ru p e t a l . (1942) as Red Sea W ater. Form ation o f N orth In d ia n Beep Water I s complex In t h a t i t I s a m ixture Figure 34 D is tr ib u tio n o f th e deep w a ter s a l i n i t y maximum in th e Southw est In d ia n Ocean f o r Ju ly 29 to Septem ber 9, 1964. R.V. ANTON BRUUN d a ta . C ru ise 7* 151 152 DEEP WATER SALINITY MAX.%*. -H 5 CO 200 300 KILOMETERS EO* 20* YULEAR 25T LOURENCO MARQUES^ DURI 30' BO* A 35* * 0 0 153 o f w a te rs from d i f f e r e n t a r e a s . Rochford (1964) I d e n t i f ie d th e r o le o f each c o n tr ib u tin g w a te r mass and t h e i r p a th s o f flo w . He showed t h a t th re e h l g h - s a l i n l t y w ater m asses e n t e r th e Mozambique Channel from th e Red Sea, th e P e r s ia n G u lf and th e A rabian S ea. In th e r e s e a r c h a re a th e N orth In d ia n Deep Water I s p r e s e n t In s id e th e Mozambique Channel a t s ta t i o n s lo c a te d n o r th o f l a t i t u d e 25°S. and e a s t o f 40°E. from a d e p th o f about 700 m to th e bottom ( s t a t i o n s 367, 366 and 363 a t w e ste rn end o f l i n e I and I I ) . I t h a s homogeneous s a l i n i t i e s o f 34.80 to 3 4 .7 5 o /o o (se e cu rv es a t s ta t i o n 363 on F ig s . 8 and 1 0 ), te m p e ra tu re s from 9°0 and a sigm a- t g r e a t e r th an 27*00. The oxygen c o n te n t ran g es from 2 .4 8 to 5*10 m l / l and th e phosphate c o n te n t from 1.70 to 2.60 jig A /l. West o f 40°E. and n o r th o f 25°S. th e N orth In d ia n W ater I s In flu e n c e d by m ix tu re w ith th e A n ta rc tic I n t e r m ed iate W ater as Is I n d ic a te d by th e s l i g h t s a l i n i t y minimum p r e s e n t a t s t a t i o n s 368 and 367 ( F ig . 1 5 ). S outh o f l a t i t u d e 25°S . t y p i c a l N orth In d ian Deep W ater I s n o t fo und. However, a t s t a t i o n s In th e a re a o f th e A gulhas C u rre n t alo n g th e A fric a n c o a s t th e re I s , b e low 700 m, a w a te r which Is more s a l i n e and l e s s oxygenated th a n t y p i c a l A n ta r c tic In te rm e d ia te W ater and Is th e r e s u l t o f a m ixing o f b o th w ater m asses. T his I s shown on th e w e ste rn end o f th e s a l i n i t y s e c tio n s as w e ll a s on a map o f d i s t r i b u t i o n o f th e oxygen minimum ( F ig . 32). 154 Movement o f N orth In d ia n W ater The e x te n s io n to th e so u th o f h ig h ly s a l i n e , low oxygenated N orth In d ia n W ater i s n o t w e ll- d e fin e d (M o lle r, 1929* 1933; Thomsen, 1933» 1935)• Clowes and Deacon (1935) s tu d ie d a s e r i e s o f DISCOVERY o b s e rv a tio n s a lo n g a n o r th - s o u th l i n e th ro u g h th e Mozambique C hannel. They c l e a r l y d is tin g u is h e d th e N orth In d ia n Deep Water on th e n o rth e rn end o f t h e i r s e c tio n sandw iched between A n ta r c tic I n t e r m ed iate Water and N orth A t l a n t i c Deep W ater. From th e oxygen d i s t r i b u t i o n , th e y su g g este d t h a t N orth In d ia n Deep W ater does not come to a sudden te r m in a tio n a t 2 0 ° S .t but flo w s much f u r t h e r s o u th w ith a s a l i n i t y low er th an 3 4 .8 0 o /o o . Deacon (1937) and Clowes (1950) th o u g h t t h a t i t i s d e te c ta b le as f a r so u th as 40°S. T e h ern la e t a l . (1951) showed t h a t th e e x te n s io n o f h ig h ly N orth In d ian W ater i s more Im p o rtan t in th e w est o f th e In d ia n Ocean th an in th e e a s t . They c o n sid e re d th e 3 4 .8 0 o /o o is o h a lin e a s th e l i m i t o f in flu e n c e o f th e deep h ig h ly s a li n e c u r r e n t and show th a t t h i s is o h a lin e l i e s a t a b o u t 20°S. in th e w e ste rn p a r t o f th e Mozambique C hannel, bends northw ard in th e e a s te r n p a r t o f th e Channel and does n o t go f u r t h e r so u th th an 7 °S . l a t i t u d e in th e n o r th and e a s t o f M adagascar. T e h e rn la £ t a l . (1 9 5 8 ), how ever, sug g e s te d t h a t a m ixing between N orth In d ia n Deep W ater and A n ta r c tic In te rm e d ia te W ater o c c u rs a t 1000 m n e a r 1 0 °S .; th e mixed w a ter s in k s to g r e a t e r d ep th s and c o n tr ib u te s to 155 th e fo rm a tio n o f th e deep w ater o f th e In d ia n Ocean. T a ft (1963) r e p o rte d a southw ard t r a n s p o r t o f h lg h - s a l l n l t y , low-oxygen w a te r alo n g th e w e ste rn boundary o f th e Mozambique C hannel, and on th e b a s i s o f a s tro n g s a l i n i t y g r a d ie n t, p la c e d th e boundary betw een N orth In d ia n Deep Water and A n ta r c tic In te rm e d ia te W ater between l a t i tu d es 20° and 25°S . Le Pichon ( i 9 6 0 ) c o n sid e re d the 34.75o/oo I s o h a lin e as th e l i m i t o f th e N orth In d ian Deep W ater. From th e d i s t r i b u t i o n o f th e l a y e r o f minimum oxygen, he tr a c e d th e s p re a d in g o f t h i s p o o rly oxygenated w ater mass and showed t h a t I t sp re a d s a l l o v er th e s o u th w est In d ia n Ocean n o r th o f 40°S. b ein g d i s t r i b u t e d by th e Agulhas C u rre n t and I t s r e tu r n c u r r e n t . Orren ( 1963) found p e n e tr a tio n o f f a i r l y s a lin e (34.75o/oo) and p o o rly oxygenated ( l e s s th a n 3 .4 m l/l) N orth In d ia n Deep Water in th e N atal B asin a t ab o u t 27°S . a t a depth o f ab o u t 1600 m o v e rly in g N orth A t la n tic Deep W ater. As p re v io u s ly m entioned, the N orth A t l a n t i c Deep Water la y th e r e (AFRICANA I I , s t a t i o n 7) a t 3000 m and ro se to th e e a s t a t d ep th s o f ab o u t 2000 m. O rren su g g ested t h a t i t was fo rc e d down by th e southw ard movement o f N orth In d ia n Deep W ater. O rren (1966) a lso noted t h a t t r a c e s o f N orth In d ia n Deep W ater were seen as f a r s o u th as 35°S. (AFRICANA I I , s t a t i o n 30, NIOE 1 5 , NIOE 11) w here low oxygen v a lu e s e x i s t . I t has been su g g ested t h a t th e s o u th e rn e x te n s io n o f 1 5 6 N o rth In d ia n Deep W ater may vary in d i f f e r e n t seasons o r in d i f f e r e n t y e a r s . However, Donguy and P ito n (1969), whose o b s e rv a tio n s in the n o rth e rn Mozambique Channel were made d u rin g v a rio u s se a so n s, found a good s t a b i l i t y o f th e in te rm e d ia te w ate r c h a r a c t e r i s t i c s . The c i r c u l a t i o n p a t t e r n o f N orth In d ia n Deep W ater i s shown in F ig u re s 30 and 31 a t in te rm e d ia te d ep th s and in F ig u re 33 a t deep d e p th s. At d e p th s o f 1000 m and 1500 m t h i s w ater mass forms an a n tlc y c lo n lc gyre in s id e th e Mozambique C hannel. The shape o f th e s w ir l fo llo w s ro u g h ly th e tre n d o f th e c o a s ts and i t s c e n te r i s in th e median a x is o f th e Mozambique C hannel. The N orth In d ian Deep Water e n te r s th e Mozambique Channel on i t s w estern s id e as a southw estw ard flow . Most o f th e w a te r tu rn s s o u th e a s t a t ab o u t 2 0 °S ., and th e n tu r n s n o rth a t about 2 6 ° S ., to flo w o u t o f the Channel on i t s e a s te rn s id e . P a r t o f th e w a ter c o n tin u e s i t s flow toward th e southw est a lo n g the A fric a n c o a s t in th e d e e p e r la y e r s o f th e Agulhas C u rre n t. T his i s shown by th e tre n d o f th e is o - h a lln e s 0 .5 5 dynamic m in F ig u re 30, and 0 .2 4 dynamic m in F ig u re 31. I t i s a ls o I n d ic a te d in F ig u re 32 which shows the d i s t r i b u t i o n o f th e oxygen minimum. D isso lv ed oxygen c o n te n t d i s t r i b u t i o n , which has been used by s e v e ra l a u th o rs to show th e sp re a d in g o f N o rth In d ia n Deep W ater, a p p e a rs to be a good i n d i c a t o r o f th e in flu e n c e o f t h i s w a te r m ass. Y et, as Le Pichon ( i 9 6 0 ) 157 n o te d , one should c o n s id e r th e l i m i t a t i o n s o f t h i s method s in c e oxygen c o n te n t Is n o t a t r u l y c o n s e rv a tiv e p ro p e rty and th e la y e r o f minimum oxygen Is g e n e r a lly a l e v e l o f v e ry slow m otion. Oxygen v a lu e l s o p l e t h s f o r th e BRUUN s t a t i o n s show a c u r re n t alo n g th e p a th o f th e Agulhas Cur r e n t w ith a so u th ea stw ard p r o tr u s io n a t ab o u t 29°S. T his p r o tr u s io n i s n o t easy to e x p la in p a r t i c u l a r l y s in c e i t i s n o t r e f l e c t e d on th e 1000 db and 1500 db dynamic to p o g ra p h ic maps. Bottom Water Below th e core o f N orth A t l a n t i c Deep W ater, the w a te r ly in g a t d ep th s g r e a t e r th a n 3500 m h as te m p e ra tu re s ra n g in g from 2°C to 0 .6 l° C , s a l i n i t i e s from 34.75o/oo to 34-.70o/oo and a sig m a-t o f 27.85* The d is s o lv e d oxygen c o n te n t ra n g e s from 4 .8 0 to 5*15 m l / l and th e phosphate c o n te n t from 1 .6 5 to 2 .3 0 p g A /l. Warren (1971) o bserved a northw ard flow o f A n ta r c tic Bottom W ater to th e e a s t o f M adagascar, ty p ic a l o f deep w e ste rn boundary ocean c u r r e n t s . A ccording to Le Pichon (I9 6 0 ) t h e r e i s a ls o a northw ard flow o f A n ta r c tic Bottom W ater in to th e N a ta l B asin w hich s tr e n g th e n s th e flow o f N orth A t la n tic Deep W ater and th e r e i s v e r t i c a l m ixing o f th e lo w er p a r t o f th e N orth A t l a n t i c Deep W ater w ith th e A n ta r c tic Bottom W ater. Such m ixing would ex p l a i n th e absence o f an oxygen maximum in th e N orth 158 A t la n tic Deep W ater o f th e N ata l B a sin . In agreem ent w ith Le P ic h o n 's o b s e rv a tio n s , no oxygen maximum was found In t h i s stu d y In th e N orth A t l a n t i c Deep W ater. The bottom te m p e ra tu re I s h ig h e r , how ever, th a n th e te m p e ra tu re c h a r a c t e r iz i n g A n ta r c tic Bottom W ater w hich, a c c o rd in g to Le P ich o n , c o rresp o n d s to th e 0°25C Iso th erm . Only a few BRUUN s t a t i o n s re a c h g r e a t d ep th s and hence I t Is n o t p o s s ib le to re a c h v ia b le c o n c lu s io n s on th e movement o f th e Bottom W ater. I t a p p e a rs, however, from th e sig m a-t s e c tio n alo n g l i n e I I I (F ig . 19) t h a t between s t a t i o n s 377 and 378 th e lso p y c n a l c h a r a c te r iz in g th e Bottom W ater does n o t p a r a l l e l th e ls o p y c n a ls from th e o v e rly in g N orth A tla n tic Deep W ater. T his may I n d ic a te t h a t In th e e a s te r n p a r t o f th e N a ta l B asin th e r e may be some northw ard component o f flow a s w e ll a s In th e w estern p a r t . SURFACE SEDIMENTS P rev io u s Work The I n i t i a l maps o f In d ia n Ooean f l o o r d e p o s its were p u b lis h e d a t th e end o f th e l a s t c e n tu ry (A non., 1889; Murray and R enard, 1891) • At th e tu r n o f t h i s o e n tu ry , P h i l i p p i (1901-1903) p l o t t e d th e bottom sed im e n ts co v erin g th e s o u th e rn In d ia n Ocean and d e s c rib e d th e s o - c a lle d "d e e p -se a san d s" In an a r e a so u th w est o f M adagascar f a r from th e A fric a n c o a s t. Murray (1910) mapped th e d i s t r i b u tio n o f seven ty p e s o f d e p o s its o v e r th e f l o o r o f th e In d ian Ocean, and re c o g n iz e d t h a t o n e - h a lf I s covered by d e p o s its c o n ta in in g o v e r 50 p e rc e n t calciu m c a rb o n a te . W. S ch o tt (In G. S c h o tt, 1935) p re p a re d a map o f th e bottom sedim ents In th e In d ia n Ocean which he r e v is e d a few y e a rs l a t e r (W. S c h o tt, 1939)* I b is work u p d ated M u rra y 's map o f calciu m c a rb o n a te d i s t r i b u t i o n and th e o u t l i n e o f th e N atal B asin I s I n f e r r e d on h i s map (W. S c h o tt, 1939, h i s P ig . 1 ) . A f te r th e s e p io n e e r w orks, bottom se d im e n ts o f th e In d ian Ocean w ere n e g le c te d and i t i s o n ly in th e l a s t two decades t h a t new I n v e s tig a tio n s were u n d e rta k e n . Some broad s c a le s tu d i e s were p u b lish e d c o n ce rn in g sedim ent 159 16P d i s t r i b u t i o n in th e so u th e rn In d ian Ocean (Hough, 1956; L i s l t z l n and Z hivago, 1958; L i s i t z i n , I960) and in th e n o rth e rn and c e n t r a l In d ia n Ocean (B ezrukov, 1961, 1964; Gorbunova, 1966; G oldberg and G r i f f i n , 1 970). S m aller s c a le a d d i t i o n a l i n v e s t i g a t i o n s d e a lin g w ith v a rio u s s e d i- m e n to lo g lc a l a s p e c ts ( c la y m in e ra ls , t r a c e m e ta ls , manganese n o d u le s) were perform ed by W illis and Ahrens (1 9 6 2 ), N e s te r o f f e t a i . (1 9 6 3 ), B ender a t a ^ . (1 9 6 6 ), and Eu and B ro eck er (1 9 6 9 ). None o f th e s e s tu d ie s co v er th e Mozambique Channel b u t t r e a t a d ja c e n t a r e a s to th e n o rth and so u th . Swing a t a l . (1969) u sin g se ism ic d a ta p re s e n te d th e g ro s s f e a t u r e s o f th e p a t t e r n o f u n c o n s o lid a te d sedim ent d i s t r i b u t i o n f o r th e In d ia n Ocean. These i n v e s t i g a t o r s showed t h a t th e r e i s a m ajo r sedim ent ac c u m u la tio n in th e b a s in s b o rd e rin g th e w e ste rn and e a s te r n s id e s o f th e In d ia n Ocean, th e l a r g e s t o f which a r e th e Som ali B asin and N a ta l B asin ( c a l l e d by Ewing e t &1. th e M adagascar B a s in ). The Iso p ach map o f u n c o n s o lid a te d sed im en ts th e y p re s e n t shows th e r e l a t i o n s h i p o f topography to sed im en tary a c c u m u la tio n s. The N a ta l B asin has a sedim ent th ic k n e s s ex ceed in g 1500 m w h ile th e c o n tin e n ta l s lo p e s b o rd e rin g th e B a sin , s lo p in g from M adagascar and th e M adagascar P la te a u and th e Mozambique P la te a u , r e s p e c t i v e l y , have a sedim ent th ic k n e s s in c r e a s i n g downward from 500 m to 1500 m. A sedim ent th ic k n e s s o f a p p ro x im a te ly 500 m e x i s t s on th e 161 i Mozambique P la te a u and from 300 m to 400 m on th e Madagas c a r P la te a u . S tu d ie s o f r e g io n a l I n t e r e s t were made on sed im en ts ' o f th e n o rth e rn and n o r th e a s te r n In d ia n Ocean (R odolfo, 1969; K e lle r and R ic h a rd , 1967; Subba Rao, 1964) b u t few s e d lm e n to lo g lc a l s tu d ie s In th e so u th w e ste rn In d ia n Ooean a re a v a i l a b l e . Some have been u n d e rta k en by P u l l e r (1961, 1962, 1964) m ainly from sh allo w w a te r d e p o s its . In fo rm a tio n on th e sedim ents o f th e Mozambique Channel a re r a r e . A few sh allo w w a te r s tu d ie s o f th e c o r a l l l a n environm ent were made In th e Comorlan I s la n d s (G u llc h e r fii a l * , 1965) and n e a r T u le a r (W eydert, 1970) and d e e p -se a f l o o r f e a t u r e s were d e s c rib e d from seism ic r e f l e c t i o n su rv ey s (L an g seth and Heezen, 1964, 1965; Ewing e t a l . . 1968; Ewing and Ewing, 1 9 7 1 ). L an g seth g t a l . ; (1964, 1965) found t u r b i d i t e s on th e f l o o r o f th e Zambezi ! I Canyon and d e s c rib e d th e o c cu rre n c e o f n a t u r a l le v e e s | covered by b ro ad d u n e -lik e f e a t u r e s i n d i c a t i v e o f tu rb u le n t! flo w . To th e so u th o f th e Mozambique C hannel, Ewing e t § 1 . j (1968) and Ewing and Ewing (1971) showed t h a t w e ll- s t r a t i f i e d , f l a t - l y i n g sed im en ts f i l l th e N a ta l Basin and i I " g ia n t r i p p l e s " co v er t h e i r s u r f a c e . These la r g e u n d u la t i o n s , Im plying a p ro c e ss o f c u r r e n t - c o n t r o l l e d d e p o s itio n , i tre n d w e s tn o rth w e s t-e a s ts o u th e a s t ro u g h ly t r a n s v e r s e t o th e a x is o f th e b a s in , and th e se d im e n ts, p re d o m in a n tly l u t i t e , th ic k e n on th e n o rthw ard s id e o f th e r i p p l e c r e s t . 162 P a r t o f th e m a te r ia l c o l l e c t e d f o r t h i s I n v e s tig a t i o n was an aly zed s e d lm e n to lo g ic a lly by Sherman (1966) in o r d e r to e v a lu a te th e p a ir e d c o rin g method used aboard th e R.V. ANION BBUUN w hich employed two P h le g e r c o r e rs spaced 1 m a p a r t . Sherman an aly zed 28 c o re to p s from th e t r a n s e c t D urban-T ulear f o r g r a in s iz e d i s t r i b u t i o n , c o a rse f r a c t i o n c o n s t i t u e n t s , carbon and n itr o g e n c o n te n t, o rg a n ic carbon and n itro g e n c o n te n t. A com parison o f sedim ent p a ra m e te rs between p a ir e d c o re s re v e a le d t h a t in m ost In s ta n c e s e x p e rim e n ta l e r r o r s en co u n tered d u rin g s e d im e n to lo g ic a l a n a l y s is were g r e a t e r th an d i f f e r e n c e s betw een th e co res and Sherman concluded t h a t s e d im e n to lo g ic a l changes d id n o t o c c u r w ith in a h o r iz o n ta l sp a c in g o f 1 m. Methods o f Study In o rd e r to d e lim it t r a n s p o r t p a th s , so u rc e s and d e p o s itio n a l environm ent, a l l s u rf a c e sam ples were con s id e r e d . Trawl and dredge sam ples were an a ly z e d q u a l i t a t i v e l y w hereas q u a n t i t a t i v e a n a ly s e s were made on c o re s , g rab and sn ap p er sam ples. A t o t a l o f 115 s u rfa c e sam ples were an aly zed f o r calcium c a rb o n a te c o n te n t (w ith a Leco carbon a n a ly z e r u s in g the te c h n iq u e p re s e n te d by Kolpack and B e ll, 1968), s a n d / s i l t - c l a y r a t i o , c o l o r , and co a rse f r a c t i o n com ponents. The f i r s t two p a ra m e te rs a re p l o t t e d on F ig u re s 35 and 36 and th e d i s t r i b u t i o n o f sedim ent ty p e | F ig u re 35 D i s tr i b u t i o n o f calcium c a rb o n a te c o n te n t in s u rfa c e se d im e n ts. j j t i i I 163 164 IN H A M B A N E V ' DURBAN, CaCO., % Figure 36 D is tr ib u tio n o f th e sand f r a c t i o n in s u rfa c e se d im e n ts. 165 166 INHAM B A N E S A SAND FRACTION.% 167 I s shown on F ig u re 37* R adiocarbon d a te s were o b ta in e d on th e t o t a l c a rb o n a te f r a c t i o n from th e s a n d -s iz e f r a c t i o n (>62/0 o f th e sam ples. G rain s iz e In a sample may produce c o n s id e ra b le v a r i a t i o n s In a g iv en ra d io c a rb o n d a tin g (O lsson and E rik ss o n , 1 9 65). I n v e s t i g a t i o n s from s e v e r a l a r e a s I n d ic a te t h a t u s u a ll y th e f in e f r a c t i o n I s o ld e r th a n th e c o a rse (H. F . N elson, p e r s . comm.). Thus, th e ages c i t e d In t h i s stu d y should be c o n s id e re d as minimum a g e s. G en eral C om position, G en eral S edim entary P ro v in ce s gfrallgy Wafer PflPffBUg C o n tin e n ta l S h elv es 1 . A fric a n C o n tin e n ta l S h e lf betw een Durban and Lourenco Maraues N orth o f Durban th e A fric a n c o n tin e n ta l s h e l f was sampled betw een l a t i t u d e s 2 9 °3 8 'S . and 2 9 °1 0 'S . In th e a re a o f f th e T ugela R iv e r. F if ty - s e v e n sam ples, m ainly c o re s and g ra b s, were c o l l e c t e d on th e m iddle s h e l f (30-100 m) and th e o u te r s h e l f (100-200m ). The c o n tin e n ta l s h e l f I s covered w ith w a te r - c o n tr ib u te d d e t r l t a l sed im en ts c o n s i s t in g o f s i l t s and sa n d s. Calcium c a rb o n a te c o n te n t I s low , commonly l e s s th a n 10 p e r c e n t, w ith th e e z o e p tlo n o f a few sam ples on th e o u te r s h e l f w hich c o n ta in between 10 and 20 p e rc e n t calciu m c a r b o n a te . The g r e a t e r c a rb o n a te p e r c e n t- F ig u re 37 S u rface sedim ent ty p e . 168 169 3 0'E 35* 40* 45*E I N H A M B A N E S ^ ^ .1 T ^ T F I Torrlgtnout Sad. (CoCOs <IO%) t = t=j Hemlpelogic Calc. Mud (10% - 30% CaC03 ) ^ 3 Foram Ooza Coarta Bloelastlcs "> m Rocky Floor Glauconito Pollott Mn Abundant ^ Mn Prosont ° ' 6 g g^g T T _ 'Rky /r r _ '« < 8 1 0 0 2 0 0 3 0 0 KM SEDIMENT TYPE i _________________I D U R B A N , 1 7 0 age th e r e I s due to a h ig h e r c o n te n t o f c o a rse s h e ll fra g m e n ts . G r a ln -s lz e I s h e te ro g e n e o u s, th e s a n d -s iz e f r a c t i o n ra n g e s from 2 to 90 p e r c e n t. However, th e m a jo r i t y o f sam ples a re sandy s i l t s w ith a sand f r a c t i o n be tween 10 and 50 p e r c e n t. S u b an g u lar to rounded q u a r tz g r a in s a r e th e main component o f th e c o a rse f r a c t i o n and com prise 65 to 85 p e r c e n t o f th e sed im en t. The r e s id u e c o n s is ts o f g la u c o n ite (3 -1 0 p e r c e n t ) , p h o s p h o rite (2 -5 p e r c e n t ) , c o arse b io g e n ic d e b r is (1 -3 p e r c e n t) and f o r a m ln lf e r a l t e s t s (2-5 p e r c e n t ) . M inor amounts o f m u sc o v ite , b l o t l t e , h o rn b le n d e, m a g n e tite , and p y r l t e a re p r e s e n t and sometimes form as much a s 1 p e rc e n t o f th e sed im e n t. Sponge s p ic u le s com m only c o n s t i t u t e 1 p e rc e n t o f th e sam ples. In w ater s h a llo w e r th a n 50 m p la n t d e b r is I s common and may be 1 p e r c e n t o f some sam ples. C a lc a re o u s s k e l e t a l d e b r is , found a t m ost s t a t i o n s , I s composed o f p e lecy p o d s, g a s t r o pods In c lu d in g p te ro p o d s , echlnoderm s and b ry o zo an s. T hroughout th e s h e lf a r e a s h e l l frag m en ts and f o r a m ln lf e r a l t e s t s have a f r e s h a p p e a ra n c e , e x c ep t f o r th o se on the n o rth e rn m o st p a r t o f th e o u te r s h e l f . In t h i s a r e a , a t a d e p th o f 168 m, s h e l l frag m en ts and worn t e s t s o f th e b e n th lc f o ra m ln lf e r Im n h ls te g ln a a re ab rad ed and a r e a s s o c ia te d w ith abundant g r a in s o f g la u c o n ite and p h o sp h a te . T e s ts o f o s tra c o d s a r e r a r e , but a re found a t some s t a t i o n s betw een 86 m and 115 m. F o ra m ln lfe ra l t e s t s , 171 which oom prise 2 to 5 p e rc e n t o f th e se d im e n t, a re m ainly b e n th lc s p e c ie s . These c o n s t i t u t e ab o u t 70 p e rc e n t o f th e t o t a l f o r a m ln lf e r a l p o p u la tio n on th e m iddle s h e l f and about 50 p e rc e n t on th e o u te r s h e lf ; th e rem ain in g I s made up o f p la n k to n ic s p e c ie s . Abundances o f f o r a m ln lf e r s r e f l e c t a low r a t e o f s e d im e n ta tio n , w hich Is h ig h e r on th e m iddle s h e lf th an on th e o u te r s h e l f . The number o f f o ra m ln lf e rs p e r gram o f sedim ent Is l e s s th a n 100 on th e m iddle s h e lf and I n c re a s e s to s e v e ra l th o u sa n d s on th e o u te r s h e l f , w ith low llv ln g /d e a d r a t i o s . In th e b e n th lc assem blages an averag e o f 3 p e rc e n t o f th e specim ens were l i v i n g a t th e tim e o f c o l l e c t i o n (as I n d ic a te d by s ta i n i n g te c h n iq u e s ) on th e m iddle s h e lf and l e s s th a n 1 p e rc e n t on th e o u te r s h e l f . No sam pling was made on th e e x tre m e ly narrow s h e lf , a few k ilo m e te rs w id e, between Cape S a in t L u c ia a t 28°35IS* and Lourenco M arques. 2. A fric a n c o n tin e n ta l s h e lf between Lourenco Marques and Inhambane Five grab and dredge sam ples were c o lle c te d o u ts id e th e sh allo w bay o f Lourenoo Marques betw een d ep th s o f 37 m and 175 m. Samples th e r e a re to o s c a rc e to be r e p r e s e n ta t i v e o f th e e n t i r e s h e l f o f t h i s a r e a , b u t have th e same g e n e ra l com p o sitio n as s h e l f sam ples o b ta in e d f u r t h e r n o r th o f f th e p r o tr u d in g c o a s t o f so u th e rn Mozambique, so u th o f Inhambane. Burrowed ro c k s o f e n c ru s te d lim esto n e 1 7 2 and w e ath ere d c o a rse b io g e n ic d e b ris were dredged o f f Lourenco Marques a t 135 m and 175 m. Sand composed o f a p p ro x im a te ly 60 p e r c e n t rounded q u a r tz and 40 p e rc e n t b io g e n ic d e b r is was re c o v e re d a t d ep th s o f 37 m and 42 m (th e abundant m o llu scan s fragm ents a r e m a in ly from th e V eneridae f a m ily ) . T his sand has a c a rb o n a te c o n te n t o f 21 p e r c e n t and c o n ta in s 377 fo ra m ln lfe rs /g m o f sed im en t. Of t h e f o r a m ln lf e r s , 97 p e rc e n t a r e b e n th lc s p e c ie s , 2 p e rc e n t o f w hich were l i v i n g . A ttem p ts to c o l l e c t c o re s from th e b ro a d , I r r e g u l a r s o u th e a s tw a rd -fa c in g s h e l f s o u th o f Inhambane f a i l e d , e x c e p t f o r two s t a t i o n s e a s t o f th e Limpopo R iv e r. E ight rock d red g es and two grab sam ples co nfirm ed th e p resen ce o f a h ard ro c k bottom w ith l i t t l e te r r ig e n o u s sed im en ts. At d e p th s betw een 20 and 42 m, dredged ro c k s o f u n d e te r mined age w ere e i t h e r a y ard y e llo w sa n d sto n e w ith a t ta c h e d m o llu sk s (Cfcaaa), o r e n c r u s te d , burrow ed lim e sto n e . F ine sand c o n s is t i n g o f w e ll-ro u n d e d q u a r tz g r a in s was c o lle c te d w ith th e s e ro c k s . At d e p th s betw een 55 and 190 m, p o ro u s f r i a b l e b lo g e n lo lim e s to n e , e n c ru s te d w ith o rg an ism s and e x h i b i t ing numerous b u rro w s, was c o l l e c t e d t o g e t h e r w ith c o a rse b io g e n ic d e b r i s . The b io g e n ic fra g m e n ts , w hich a re l a r g e l y a b ra d e d , c o n s i s t o f p e le c y p o d s, g a s tro p o d s In c lu d ing p te ro p o d s , and b ry o zo an s. G ra in s o f q u a r tz , g la u c o n i t e , and p h o s p h o rite commonly a r e a s s o c ia te d w ith th e 173 b io g e n ic se d im e n ts . Q u a n tita tiv e e s tim a te s o f th e com p o n en ts w ere n o t a tte m p te d owing to th e h etero g en eo u s n a tu re o f th e sam ples. For th e same reason* v a lu e s o f co arse f r a c t i o n p e rc e n ta g e and c a rb o n a te c o n te n t a re v a r i a b l e . The c o a rse f r a c t i o n co m p rises a h ig h p e rc e n ta g e o f th e se d im e n t, as much a s 99 p e r c e n t . C arbonate c o n te n t ra n g es from 20 to 80 p e r c e n t, d ep en d in g on th e amount o f s h e l l d e b r i s . From two g rab sam ples th e abundance o f f o r a m ln lf e r s co u ld be o b ta in e d . At 55 m th e f o r a m ln lf e r a l number ( f o r a m ln lf e r s >62|i) i s 1685, b e n th lc s p e c ie s making up 87 p e r c e n t o f th e p o p u la tio n w ith a l i v i n g p e rc e n ta g e o f 1 p e r c e n t. At 190 m th e f o r a m ln lf e r a l number (fo r a m ln lfe r s i s 9265, b e n th lc s p e c ie s com prise 74 p e rc e n t o f th e p o p u la tio n w ith a l i v i n g p e rc e n ta g e o f l e s s th an 1 p e r c e n t. F o r a m ln lf e r a l t e s t s a re r o l l e d and ab ra d e d , many a re g la u c o n itiz e d o r l r o n - s t a l n e d . B eachrock and o y s te r s h e l l s were o f te n dredged from d ep th s o f a b o u t 150 m. A s o f t bottom was en co u n tered a t th e southernm ost s t a t i o n s o c c u p ie d . These a re on the s o u th w a rd -fa c in g p o r tio n o f th e s h e l f , n e a r i t s change In w id th e a s t o f th e Limpopo R iv e r m outh, and w a te r - c o n tr ib u te d d e t r l t a l s e d i m ents in t h i s a r e a a re l i k e l y p a r t o f th e Limpopo lo a d . S i l t y sed im en ts were c o l le c te d betw een d e p th s o f 55 and 112 m. T h e ir c a rb o n a te c o n te n t ra n g e s between 20 and 30 p e r c e n t. The c o a rse f r a c t i o n , w hich c o n s t i t u t e s between 20 and 40 p e r c e n t o f th e se d im e n t, i s composed o f su b - a n g u la r q u a rtz g r a in s (5 to 20 p e r c e n t ) , g la u c o n ite g r a in s (1 to 2 p e r c e n t ) , f o r a m ln lf e r a l t e s t s (60 to 80 p e r c e n t ) , sponge s p ic u le s (1 to 2 p e rc e n t) and s h e ll d e b r is (2 to 10 p e r c e n t) made o f p e le cy p o d s, g a s tro p o d s In c lu d in g commonly p te ro p o d s , bryozoans and echinoderm s. S h e ll frag m en ts and f o r a m ln lf e r a l t e s t s p o s s e s s a f r e s h ap p earan ce and show l i t t l e sig n o f a b ra s io n . F o ra m ln lfe rs (>62p) whose number I s 7650/gm o f sedim ent a t a depth o f 106 m, a r e dom inated by b e n th lc s p e c ie s . These make up 60 p e rc e n t o f th e f o r a m ln lf e r a l p o p u la tio n a t 106 m w ith a l i v i n g p e rc e n ta g e o f l e s s than 1 p e r c e n t. 3 . M alagasy c o n tin e n ta l s h e lf S eventeen sam p les, m ainly co res and grab sam ples, were c o l le c te d betw een d e p th s o f 33 and 220 m on the s h e lf a d ja c e n t to th e bay o f T u le a r. In t h i s a r e a th e s h e l f is covered w ith s i l t y sands low in c a r b o n a te . The calcium c a rb o n a te c o n te n t ra n g e s between 6 and 15 p e r c e n t and g e n e r a lly i s l e s s th a n 10 p e r c e n t in m ost sam ples. The amount o f sand in a sample ra n g e s between 10 and 40 p e r c e n t and i s com prised o f dom in an tly a n g u la r q u a r tz (50 to 70 p e r c e n t ) , m u sco v ite (1 to 3 p e r c e n t) , b l o t i t e (1 to 2 p e r c e n t) and f e l d s p a r g r a in s (1 p e r c e n t ) . P h o sp h o rite and g la u c o n ite g r a in s a r e n o t p r e s e n t in th e sedim ent a t a l l s t a t i o n s ; th ey o ccu r only on th e o u te r s h e l f w here th e y c o n s t i t u t e 5 to 10 p e r c e n t o f th e sed im en t. P l a n t d e b r is 175 i s common, m aking up a s much a s 10 p e rc e n t o f th e sam ples. Sponge s p ic u le s com prise 1 p e rc e n t o f th e sed im en t a t s e v e ra l s t a t i o n s . B iogenic d e b r is o c c u rs o n ly in a few sam ples and co m p rises about 1 p e rc e n t o f th e t o t a l s e d i m ent. S h e ll fra g m e n ts , w ith an unw eathered a p p e a ra n c e , a re composed o f p e le c y p o d s, g a stro p o d s in c lu d in g p te ro p o d s and echinoderm s. F o ra m ln lfe ra l t e s t s , w hich have a f r e s h ap p e a ra n c e , c o n s t i t u t e 2 to 6 p e rc e n t o f th e sedim ent w ith a number o f 40 to 600/gm o f sedim ent ( f o r a m ln lf e r s } 6 2 j i ) . They a r e dom inated by b e n th lc s p e c ie s w hich c o n s t i t u t e 90 p e rc e n t o r more o f th e t o t a l f o r a m ln lf e r a l p o p u la tio n . At tim e o f c o l l e c t i o n 1 to 5 p e rc e n t o f th e b e n th lc fo ra m in l- f e r s were l i v i n g . 4. Summary and c o n c lu s io n s on c o n t i n e n t a l s h e lv e s s e d i ments In a r e a s c lo s e to r i v e r m ouths, th e T u g e la , th e Limpopo and th e O nilahy R iv e rs , th e narrow A fric a n and M alagasy c o n t i n e n t a l s h e lv e s a r e f lo o r e d w ith f in e t e r rig e n o u s sed im en ts c o n s is tin g c h i e f l y o f s i l t y c la y s , whose dom inant c o a rse f r a c t i o n c o n s ti t u e n t i s su b an g u lar q u a r tz . Sedim ents o f f th e T ugela R iv e r a re calcium c a rb o n a te -p o o r ( l e s s th a n 5 p e rc e n t) w hereas sed im en ts e a s t o f th e Limpopo and o f f th e O nihaly R iv e rs a re r i c h e r in calcium c a rb o n a te (5 to 30 p e r c e n t ) . The abundance o f a u th lg e n lc m in e r a ls , m ainly g la u c o n ite , and a sm a ll l i v i n g b e n th lc f o r a m l n l f e r a l p o p u la tio n r e l a t i v e to th e t o t a l 176 p o p u la tio n I n d ic a te a slow r a t e o f su p p ly o f sed im en ts. S e d im e n ta tio n Is more r a p id on th e m iddle s h e l f th an on th e o u te r s h e l f , a s shown by a lo w er number o f f o ra m ln lf e rs p e r gram o f sedim ent on th e m iddle s h e l f . On th e b a s is o f th e s e c r i t e r i a , se d im e n ta tio n I s more r a p id o f f th e O nllahy R iv e r on th e Malagasy s h e l f th a n on th e A frican s h e l f . These p o r tio n s o f th e A fric a n c o n t i n e n t a l s h e lf o f f th e T ugela R iv e r and th e Limpopo R iv e r where te rrig e n o u s sed im en ts were found a re a d ja c e n t to I n d e n ta tio n s o f th e c o a s t and a r e o u t o f th e p a th o f th e s tr o n g southw estw ard flow o f th e Mozamblque-Agulhas C u rre n t sy ste m . Accumula t i o n s o f te r r ig e n o u s sedim ents a r e p o s itio n e d between th e c o a s t and th e In n e r edge o f th e c u r r e n t . As m entioned e a r l i e r , a t Cape S a in t L u c ia , t h e r e I s a s l i g h t s h i f t o f th e A gulhas C u rre n t away from th e c o a s t p ro b a b ly owing to th e change In tre n d o f th e c o a st and th e b ro ad en in g o f th e s h e l f . A p art from th e s e a r e a s , no m odem te r r ig e n o u s s e d i m ents a r e d e p o s ite d on th e p o r tio n o f th e A fric a n con t i n e n t a l s h e l f su rv ey ed . A d jacen t to th e p r o tru d in g c o a st o f so u th e rn Mozambique, so u th o f Inhambane, th e s h e lf Is f lo o r e d w ith c o a rse c a r b o n a te - r ic h b io g e n ic sed im en ts com posed m ain ly o f w eath ered c a lc a re o u s s k e l e t a l d e b ris and b e n th lc f o r a m ln lf e r s a s s o c ia te d w ith rounded and p o lis h e d g r a in s o f q u a r tz and g la u c o n ite . The f o r a m l n l f e r a l t e s t s a re r o l l e d and a b rad ed , many a re g la u c o n ltlz e d o r ir o n - s ta i n e d . These a r e com prised c h i e f l y o f A m p h estlg ln a. A. l e s s o n l l d 'O rb ig n y , A. m a d a g a sc a rle n sls d 'O rb ig n y and A. q u o y ll d 'O rb ig n y , Ammonia b e c c a r i i (L in n e ), Elnhidium crlspum (L in n e ), O n e rc u lin a s p p ., M ilio lld a e and A lveo- l i n i d a e . Most o f th e s e s p e c ie s , w ith th e e x c e p tio n o f th e A lv e o lin id a e , were found in s i t u a t sh a llo w e r d ep th s on th e s h e l f a d ja c e n t to th e Tugela and O nilahy r i v e r s as in d ic a te d by th e f r e s h ap p earan ce o f t h e i r t e s t s and th e p re se n c e o f s ta in e d l i v i n g specim ens. In th e s e nearby a r e a s th ey were n o t found on th e o u te r s h e l f d eep er th an 100 m. I t i s concluded t h a t th e fau n a o c c u rrin g on th e o u te r s h e l f a d ja c e n t to th e p r o tru d in g c o a s t s o u th o f Inhambane was d e p o s ite d in an environm ent s h a llo w e r th a n th e d ep th a t which th ey a re now found. They co u ld be d i s p la c e d on th e o u te r s h e l f from s h a llo w e r d ep th s o f th e in n e r and m iddle s h e l f , which i s in agreem ent w ith th e n a tu r e o f th e r o l l e d , abraded t e s t s . T his i s n o t l i k e l y b ecau se th e fa u n a l assem blage i s d i f f e r e n t from th e modern assem blages found in s i t u on th e in n e r and m iddle s h e lf o f n earb y a r e a s . A lthough th e same s p e c ie s , w ith th e excep t i o n o f A lv e o lin id a e , a r e found in b o th c a s e s , t h e i r abundance i s d i f f e r e n t . A m phlsteglna i s r a r e in th e modern assem blage o f f Durban and T u le a r (a p p ro x im a te ly 1 p e rc e n t o f th e b e n th lc p o p u la tio n ) , w hereas th ey a re an Im p o rtan t c o n s ti t u e n t in th e assem blage o f f Inhambane (ab o u t 15 p e r 1 7 8 c e n t o f tn e b e n th lc p o p u la tio n ) . A lv e o lin id a e a re n o t p r e s e n t In th e modern p o p u la tio n s b u t a r e common In th e Inhambane assem b lag e. The fauna o c c u rrin g on th e s h e l f a d ja c e n t to th e Inhambane c o a s t I s a r e l i c t fa u n a , d e p o s it ed a t a tim e o f low ered sea l e v e l In an environm ent shallow * e r th a n th e d e p th s In which th e y a re now found. These r e l i c t sedim ents were n o t covered by subsequent s e d im e n ta tio n owing to th e combined winnowing e f f e c t o f th e Mozambique C u rre n t, which sweeps th e c o n tin e n ta l s h e l f h e re and b e cause of th e slow supply o f te r rig e n o u s sed im en t. A s im i l a r r e l i c t fau n a e x i s t s on th e o u te r s h e lf n o r th o f th e T ugela R iv e r mouth n e a r th e change in s h e l f w id th . T his p o r tio n o f th e s h e lf i s swept by th e Agulhas C u rren t p re v e n tin g modern te r r ig e n o u s s e d im e n ta tio n . Emery (1968) re p o rte d t h a t th e sed im en ts exposed on ab o u t 70 p e r c e n t o f a l l c o n t i n e n t a l s h e lv e s a re r e l i c t . A lthough con t i n e n t a l s h e lv e s su rro u n d in g th e In d ia n Ocean have been l i t t l e i n v e s t i g a t e d , r e l i c t sed im en ts, w ith fa u n a l com p o n en ts s im ila r to th e ones o f t h i s a r e a , were d e s c rib e d on th e s h e l f a d ja c e n t to th e e a s t c o a s t o f I n d ia (Subba Rao, 1964). Evidence o f a low ered sea l e v e l in th e stu d y a r e a a ls o i s shown by b eachrock exposed on th e m iddle s h e lf ad ja c e n t to Lourenco Marques and so u th o f Inhambane. R aised and submerged b e ach es were r e p o rte d in th e c o a s t a l a r e a o f Lourenco Marques (K ing, 1962). Such v a r i a t i o n s in sea 179 l e v e l a re d o u b tle s s r e l a t e d to P le is to c e n e c lim a tic changes, which a r e r e f l e c t e d e q u a lly in p e la g ic sed im en ts from deeper w a te r, s u b je c t which w i l l be d isc u s s e d l a t e r . C o ra llin e d e p o s its Europe, a sm a ll v o lc a n ic is l a n d , betw een M adagascar and A fric a a t l a t i t u d e 2 2 ° 3 0 'S ., s lo p e s s te e p ly from 25 m above sea l e v e l to a b y s s a l d e p th s. The n o rth e rn m o st sam pl ing s t a t i o n s o f th e c r u i s e are around th e i s l a n d . The bottom i s rocky and o n ly a rock dredge could be used f o r sam pling. Only a few p ie c e s o f c o r a l l in e ro c k s were r a i s e d from 2750 m t h a t c o n s is te d o f p o o rly p re se rv e d r e e f c o r a ls in c lu d in g A cronora sp . o f th e A. c a l i f e r a - c u n e a ta g roup, and P avla sp . c f . P. p a l l i d a (D r. John V. W e lls, p e r s . comm.). These a r e sh a llo w -w a te r r e e f c o r a l s , th e f i r s t one i s a form t y p i c a l o f v ery sh allo w , a g i t a t e d w a te r, as on a r e e f c r e s t . A lthough th e se c o r a ls c o n c e iv a b ly could be a s old a s M iocene, i t i s d o u b tfu l t h a t from t h e i r con d i t i o n th ey a re o l d e r th a n " s u b r e c e n t." P o ra m in ife ra l t e s t s in th e i n t e r s t i c e s o f th e c o r a l l in e ro c k s w ere p la n k to n ic s p e c ie s s im i l a r to th o se a t th e a d ja c e n t s t a t i o n s where f o r a m ln lf e r a l ooze o c c u rs . I t i s l i k e l y t h a t th e s h a llo w -w a te r r e e f c o r a ls dredged a t 2750 m r a t h e r th a n b e in g 4ft s i t u , had slumped from sh a llo w e r d ep th s alo n g th e s te e p slo p e o f th e v o lc a n ic i s l a n d . They have been d is p la c e d f o r some tim e , as shown by t h e i r p o o rly p re se rv e d ap p e a ra n c e and th e abundance o f p la n k - 1 8 0 to n ic f o r a m ln lf e r s In th e l n t e r s t l t l c e s o f th e m a t e r i a l . No p a le o n to lo g ic a l evidence could th e n be found to e s t a b l i s h th e age o f th e v o lc a n ic is la n d o f E uropa. Pepper and E v e r h a r t 's (1963) h y p o th e s is t h a t th e is la n d r i s e s from a v o lc a n ic p la tfo rm which la y n e a r se a l e v e l d u rin g th e Miocene co u ld n o t be t e s t e d . More c o r a l l i n e r o c k s , p ro b a b ly o f H olocene ag e, were c o lle c te d a t W alter S h o a ls, which l i e a t 33° 3 0 , S. on th e M adagascar P la te a u , and a re covered by 10 to 20 m o f w a te r. Rock dredge h a u ls between d ep th s o f 46 and 321 m c o lle c te d broken frag m en ts o f a l g a l mat covered w ith bryozoans and th e a tta c h e d f o r a m in if e r M ln la c ln a m ln lacea ( P a l l a s ) . Reen W ater D ep o sits The deep w a te r sed im en ts o f t h i s p o r tio n o f th e southw est In d ia n Ocean r e f l e c t th e in flu e n c e o f s te e p s lo p e s and th e two n earb y la n d m asses as im p o rta n t f a c t o r s in m odifying and s u s ta in in g slow d e p o s itio n from ex trem ely d i l u t e su sp e n sio n s o f p a r t i c u l a t e m a tte r c h a r a c t e r i s t i c o f p e la g ic se d im e n ts. A rrh en iu s (1963) su g g ested a d e f i n i t i o n o f p e la g ic sed im en ts based on th e maximal v a lu e f o r th e r a t e o f d e p o s itio n o f th e te r r ig e n o u s component. He e s tim a te d t h i s to be betw een 5 x 10"^ and 5 x 10"^ cm/ y e a r . In some p o r tio n s o f t h i s a r e a slo w er accu m u latin g p e la g ic sed im en ts o ccu r c lo s e to th e la n d owing to th e 1 8 1 narrow c o n tin e n ta l s h e l f and l a c k o f su p p ly o f d e t r i t a l sedim ent from r i v e r s and b e a c h e s. In o th e r l o c a l i t i e s th e d e e p -se a f l o o r i s co v ered w ith r a p i d ly accu m u latin g s e d i ments d e riv e d from slumped sed im en ts and p o s s ib le t u r b i d i t y c u r r e n t flo w s. In th e absence o f s u f f i c i e n t evidence on d e p o s itio n a l r a t e s th e s e two ty p e s a re t r e a t e d to g e th e r and a re d is tin g u is h e d a c c o rd in g to p ro v in c e d i f f e r e n t a t l o n . A lthough n o n -p e la g ic sed im en ts a r e in clu d e d in t h i s s e c tio n , th e c l a s s i f i c a t i o n o f A rrh e n iu s (1963) f o r p e la g ic sed im en ts i s fo llo w e d . On a g e n e tic b a s is he d is tin g u is h e d fo u r p r i n c i p a l ty p e s o f se d im e n ts: (1) halm eic se d im e n ts, in w hich th e m ajor component i s formed by p r e c i p i t a t i o n from s e a -w a te r; (2) te r rig e n o u s se d im e n ts, d o m inantly com posed o f m in e ra ls tr a n s p o r te d from th e c o n tin e n ts ; (3) p y r o c l a s t i c se d im e n ts, composed o f m in e ra ls c o n trib u te d by v o lc a n ic e r u p tio n ; and (4) b io g e n ic s e d im e n ts, in which th e components a re s e c r e te d by l i v i n g o rg an ism s. P yro- c l a s t i c s sed im en ts were n o t re c o v e re d d u rin g th e p r e s e n t I n v e s t i g a t i o n . The o th e r th re e ty p e s a r e d i s t r i b u t e d in r e l a t i o n to p h y sio g ra p h ic p ro v in c e s . Halmeic sedim ents Abundant ir o n and manganese ox id e m in e ra l on the s e a - f l o o r i s a w e ll known o c c u rre n c e . The n o d u les c o n s is t o f I n tim a te ly In terg ro w n c r y s t a l l i t e s o f d i f f e r e n t m in e r a ls . The r a t e o f fo rm a tio n o f t h e a s s o c ia te d s e d i- 1 8 2 m ents I s a m ajor f a c t o r a f f e c t i n g th e c o n c e n tra tio n o f th e n o d u le s . Large n o d u les and c r u s t s a p p e a r to a c c r e te In a r e a s w ith a low t o t a l r a t e o f d e p o s itio n where th e grow in g n u c le i a re n o t b u rle d by o th e r sed im en tary components. In t h i s a r e a , ferrom anganese a g g re g a te s occur as g r a i n s , n o d u les and c r u s t s . The nodule d ia m e te rs range In s iz e from a few c e n tim e te rs to s e v e r a l te n s o f c e n tim e te rs . | They a r e abundant w ith a c o n s id e ra b le amount o f la r g e - s iz e d n o d u les on th e Mozambique P la te a u where they a re a s s o c ia te d w ith f o r a m ln lf e r a l ooze, and a t th e so u th e rn m ost s t a t i o n s o f th e N a ta l B a sin where they a re a s s o c ia te d w ith re d c la y (F ig . 3 7 ). No manganese n o d u les were d i s co v ered on th e M adagascar P la te a u w hich o ccu p ies a to p o g ra p h ic s i t u a t i o n analogous to th e Mozambique P la te a u . T h is r e f l e c t s th e a c tio n of th e A n ta r c tic In te rm e d ia te W ater C u rre n t, which forms an eddy c e n te re d on th e Mozambique P la te a u ( F ig s . 30 and 31) and i s re s p o n s ib le f o r a slow r a t e o f d e p o s itio n h e r e . Ferrom anganese a g g re g a te s o f sm all s iz e are p re s e n t in lo w er c o n c e n tra tio n s in th e n o r th e rn p o r tio n o f t h i s a r e a where th e y a re a s s o c ia te d w ith f o s s i l f o r a m ln lf e r a l o ozes ( F ig . 3 7 ). T e rrig e n o u s sed lm en ta B e v e lle (1944) proposed t h a t 30 p e rc e n t s k e l e t a l rem ain s be re g a rd ed a s th e l i m i t betw een oozes and p e la g ic 183 c l a y s . T hat d e f i n i t i o n I s u sed In t h i s study as th e boundary between te r r ig e n o u s and b io g e n ic se d im e n ts. O lausson (I9 6 0 ) , fo llo w in g th e c l a s s i f i c a t i o n o f R e v e lle , p r e f e r r e d , In o rd e r to e lim in a te th e tim e-consum ing and u n c e r ta in e s tim a tio n o f th e p e rc e n ta g e o f t e s t s , to use 30 p e r c e n t calcium c a rb o n a te a s th e l i m i t between c la y + s i l i c e o u s ooze and c a lc a re o u s ooze. F u rth erm o re, In th e c l a s s i f i c a t i o n proposed by O lausson ev ery d e p o s it w ith a lim e c o n te n t o f 10 p e r c e n t to 30 p e r c e n t I s given th e a d j e c t i v a l term " c a lc a r e o u s ." F o llo w in g th ese c r i t e r i a th e te r r ig e n o u s sed im en ts In deep w a te rs o f th e so u th w est In d ia n Ocean a re d iv id e d a s fo llo w s : (1) sedim ents w ith a calciu m c a rb o n a te c o n te n t betw een 10 and 30 p e r c e n t. These c o n s t i t u t e " c a lc a re o u s muds" l y i n g on the u p p er con t i n e n t a l slo p e betw een d ep th s o f 200 m and 1500 m; (2) sed im en ts w ith a calcium c a rb o n a te c o n te n t l e s s th a n 10 p e r c e n t, w hich a re found a t a b y s s a l d ep th s on th e f l o o r o f th e N a ta l B a sin . Sedim ents w ith 10 to 30 p e r c e n t CaC03: The A fric a n c o n ti n e n t a l slo p e a d jo in in g th e Tugela R iv e r mouth h as a g e n tle g r a d ie n t o f 1:40 from th e s h e lf edge from ab o u t 200 m to 2000 m. Sedim ents p r e s e n t a re m ain ly sandy s i l t s in te rm e d ia te In n a tu r e between d e t r l t a l s h e l f sed im en ts and th e d e e p e r c a lc a re o u s oozes. Calcium c a rb o n a te c o n te n t ra n g e s betw een 10 and 27 p e r c e n t. The sand f r a c t i o n , between 10 and 50 p e r c e n t o f th e se d im e n t, 184 Is m ainly com prised o f su b an g u la r q u a rtz (a b o u t 55 p e rc e n t) and f o r a m in lf e r a l t e s t s (9 to 20 p e r c e n t ) . D if f e r e n t amounts o f m a g n e tite (a p p ro x im a te ly 2 p e r c e n t ) , p h o s p h o rite (2 to 7 p e r c e n t) , p l a n t d e b r is (1 to 3 p e r c e n t ) , and sponge s p ic u le s (1 to 3 p e rc e n t) a re found In a l l th e sam ples. G la u c o n ite does n o t ocour In a l l sam ples b u t c o n s t i t u t e s about 15 p e rc e n t o f sam ples a t d e p th s o f 420 m and 715 m* S k e le ta l frag m en ts o f m o llu scs and bryozoans a r e common o nly a t 420 m where th e y make up 16 p e rc e n t o f th e c o a rse f r a c t i o n and show s ig n s o f a b ra s io n . P te ro p o d s a re common a t 1355 m. In c o n t r a s t to th e f o r a m in lf e r a l s h e l f fau n a com posed c h i e f l y o f b e n th lc s p e c ie s , th e slo p e f o r a m in lf e r a l fauna Is dom inated by p la n k to n ic s p e c ie s . These com prise ab o u t 50 p e rc e n t o f th e t o t a l f o r a m in lf e r a l p o p u la tio n a t the s h e lf edge and in c r e a s e to 62 p e rc e n t a t 420 m, 80 p e rc e n t a t 715 m and 90 p e rc e n t a t 1255 m. Because o f th e o ffs h o re In c re a s e In th e p r o d u c tiv ity o f p la n k to n ic f o r a - m in ife r s and th e d e c re a se In d e t r l t a l su p p ly , th e r e i s an In c re a s e In th e f o r a m i n l f e r a l number w hich in c r e a s e s from ab o u t 10,000 a t th e s h e l f edge to a p p ro x im a te ly 65,000 a t 1820 m ( fo r a m in lf e r s > 6 2 p ) . F o ra m in lfe ra l t e s t s u s u a lly are f r e s h . S igns o f w e a th e rin g and rew o rk in g , however, a re e v id e n t in some sam p les, m ain ly a t a d ep th o f 1355 m. At t h i s d e p th some d e p o s its c l a s s i f i e d a s f o r a m in lf e r a l ooze because o f t h e i r s l i g h t l y h ig h e r calciu m c a rb o n a te 185 (33 p e r c e n t) a re r e s p o n s ib le f o r th e I n d e n ta tio n o f th e 30 p e rc e n t CaC03 c o n to u r on F ig u re 35* These c o n ta in abundant Miocene p la n k to n ic f o r a m in if e r s , s u g g e s tin g t h a t Miocene sed im en ts a re p ro b a b ly exposed on th e s e a - f l o o r . To summ arize, sed im en ts t h a t co v er th e upper con t i n e n t a l slo p e o f f th e A fric a n c o a s t between Durban and the Tugela R iv e r a r e u n d istu rb e d c a lc a re o u s muds on th e Inner edge o f th e Agulhas C u rre n t, w hereas In th e a r e a under the c o re o f t h a t s tr o n g c u r r e n t th ey r e f l e c t th e c u r r e n t a c tio n . In th e l a t t e r a r e a , w eathered s k e l e t a l fragm ents o f b ryozoans and m o llu scs a s s o c ia te d w ith g la u c o n ite g r a in s a r e ab u n d an t. These sed im en ts may be r e l a t e d to th e r e l i c t sedim ent found on p a r t o f th e o u te r s h e l f , ju s t n o rth o f th e T ugela R iv e r, and are l i k e l y rew orked and d i s placed southw ard under th e e f f e c t o f th e c u r r e n t . The winnowing a c tio n o f th e Agulhas C u rren t a ls o may be r e s p o n s ib le f o r a re a s o f n o n -d e p o s itio n a t a d e p th o f ap p ro x im a te ly 1355 m as su g g ested by th e o c c u rre n c e o f r e worked M iocene fa u n a . The M alagasy up p er c o n tin e n ta l slo p e o f f T u le a r is s te e p , w ith a g r a d ie n t o f 1:30 from th e s h e l f edge to 1000 m. Sedim ents a t s h a llo w e r d e p th s a r e s im i l a r to s e d i ments from th e A fric a n upper slo p e o f f th e T ugela R iv e r, b u t a re f i n e r . They a re s i l t y c la y s , w ith a calcium c a rb o n a te c o n te n t o f about 16 p e r c e n t, and a low sand f r a c t i o n o f 5 to 6 p e r c e n t. The main component i s a n g u la r 186 q u a r tz g r a i n s , w hich com prise ab o u t 70 p e r c e n t o f th e c o a rse f r a c t i o n . In clu d ed among th e c o n s ti t u e n t s a re m uscovite (a b o u t 3 p e r c e n t ) , m a g n e tite (1 p e r c e n t) , b i o t l t e (1 p e r c e n t ) , p h o s p h o rite and g la u c o n ite g ra in s (6 p e rc e n t a t two s t a t i o n s o n ly ) , and p la n t d e b r is (2 p e r c e n t In a few sa m p le s). B iogenic s k e l e t a l d e b r is I s n o t abundant and t o t a l s 1 p e rc e n t o n ly In some sam ples. P te ro p o d s a r e r a r e , th e y a re p r e s e n t a t 420 m w ith an abundance o f l e s s th an 1 p e r c e n t. F o ra m in lfe ra l t e s t s com prise ab o u t 15 p e rc e n t o f th e c o a rs e f r a c t i o n . They a r e composed c h i e f l y o f p la n k to n ic s p e c ie s which c o n s t i t u t e 25 p e rc e n t o f th e f o r a m in lf e r a l fa u n a a t ab o u t 420 m and In c re a s e to 96 p e rc e n t a t ab o u t 1350 m. F o ra m in lfe ra l t e s t s a re f r e s h w ith few s ig n s o f re w o rk in g , however some 0 d is p la c e d fau n a a r e o b serv ed , in n n n ia b e e c a r l 1 (L ln n e ), a sh a llo w w a te r b e n th lc f o r a m ln if e r , I s p r e s e n t as deep as 1000 m. S edim ents a re m odern, b u t from a tra w l sample betw een d e p th s o f 475 m and 695 m h e te ro g e n e o u s d e p o s its w ere re c o v e re d showing many s ig n s o f rew o rk in g . Among th e s e a re p ie c e s o f M iddle Eocene to M iddle Miocene lim e s to n e c o n ta in in g th e l a r g e r f o r a m ln if e r L e n ld o c y c lln a . and In d u ra te d mud w ith Upper Miocene p la n k to n ic f o r a m in if e r s . In th e ab sen ce o f f u r t h e r e v id e n c e , I t I s n o t p o s s ib le to s p e c if y th e I n i t i a l s i t e o f d e p o s itio n o f th e s e d e p o s its . They oould be p ro v id ed e i t h e r from n earb y o u tc ro p s on th e c o n t i n e n t a l slo p e o r from th e M alagasy lan d m ass. 187 Sedim ents w ith l e e s th a n 10 p e rc e n t 0a003: S u rface sed im en ts c o l l e c t e d on th e f l o o r o f th e N a ta l B asin between d ep th s o f 4800 m and 5450 m are c a rb o n a te -p o o r. They c o n ta in 5 p e r c e n t o r l e s s calcium c a rb o n a te and th e so u th ern m o st sam ples a d ja c e n t to th e N a ta l Beep a t 5450 m c o n ta in no calcium c a rb o n a te . i t g r e a t d e p th s s o lu tio n o f calcium c a rb o n a te , a c t ing s e l e c t i v e l y w ith r e s p e c t to s p e c ie s , e lim in a te s c a lc a re o u s t e s t s from th e sedim ent (B e rg e r, 1968; P a rk e r and B e rg e r, 1 971). The c r i t i c a l d ep th below w hich th e r a t e o f calcium c a rb o n a te s o lu tio n exceeds th e r a t e o f calcium c a rb o n a te d e p o s itio n c a lle d " c a l c l t e com pensation depth" o r a l s o , l e s s e x a c tly , "calciu m c a rb o n a te compensa tio n depth" (B e rg er, 1971)» d i f f e r s In e l e v a t i o n . In th e In d ia n Ocean I t I s around 3000-3200 m In th e s o u th o f th e ocean and around 4700-4800 m In o t h e r p a r t s o f th e ocean (B e lla e v a , 1964, 1971; Bezrukov, 1971; B u rm istro v a , 1971; K husid, 1971). 1 t u r b i d i t y - c u r r e n t o r ig i n was proposed by s e v e ra l a u th o rs from se ism ic r e f l e c t i o n su rv ey s f o r much o f th e N a ta l B asin se d im e n ts. Ewing e t a l . (1969) found a t h i c k n e ss o f sedim ent ex ceed in g 1500 m, and Ewing sJL a^ . (1968) and Ewing and Ewing (1971) showed t h a t w e l l - s t r a t i f i e d and f l a t - l y i n g sed im en ts f i l l th e b a s in . Zambezi Canyon l i k e l y i s th e main p a th f o r t r a n s p o r t . T his la r g e and deep canyon o f p ro b a b le complex t e c t o n i c and e r o s lo n a l 1 3 8 o r i g i n I s b e lie v e d to have been c u t by t u r b i d i t y - c u r r e n t a c tio n by L an g seth fit a i.. (1964, 1965)* O th er s m a lle r t r i b u t a r y canyons a re i n f e r r e d on b o th s id e s o f th e Zambezi Oanyon, a s shown by th e in d e n ta tio n s o f th e 3500 m to 4500 m b a th y m e tric c o n to u rs ( F ig . 2 ) . The n o rth e rn p a r t o f th e b a s in , betw een th e mouth o f th e canyon a t about 26°S. and 2 9 ° 2 0 'S ., was n o t sampled and hence i t was n o t p o s s ib le to t r a c e th e d i s p e r s a l p a t te r n o f se d im e n ts. From th e p h y s io g ra p h ic map o f Heezen and Tharp (F ig . 3) th e main a b y s s a l p l a i n ly in g in th e N a ta l B a sin , w here a l l th e p a th s f o r t r a n s p o r t o f s e d i m ents co n v erg e, i s in th e w este rn s id e o f th e b a s in be tween ab o u t 2 7 °-3 3 °S . and 36°-42°E . I t i s a ls o in t h i s a r e a o f th e b a s in , n o r th o f 31°S. and betw een ab o u t 37°E. and 42°E. t h a t th e t h i c k e s t ac c u m u latio n o f sedim ents is re c o rd e d (Ewing e t a l . , 1969). S u rfa ce sed im en ts sampled from th e N a ta l b a s in f l o o r s o u th o f 29°S. a re o f two d i s t i n c t ty p e s . The n o rth w e ste rn sam ples, in the a b y s s a l p la i n i t s e l f ( s t a t i o n 377)» and w est o f i t a t th e w e ste rn m argin o f th e b a s in ( s t a t i o n 3 7 6 ), a r e c o arse sed im en ts composed o f 43 p e rc e n t sand m a t e r i a l , w hereas sam ples e a s t ( s t a t i o n 378) and so u th ( s t a t i o n s 382, 383» 384) o f th e a b y s s a l p la in a re f in e sed im en ts w ith a sand f r a c t i o n l e s s than 7 p e r c e n t. A s iz e a n a ly s is was made by B. Robinson ( p e r s . comm.) on n in e c o re s . S ix were from th e N a ta l b a s in , two from th e Zambezi canyon w a ll and one from th e c o n tin e n ta l r i s e w est o f th e Zambezi canyon m outh. His f in d in g s a r e r e p o rte d In F ig u re 3 8. In th e n o rth w e ste rn a r e a o f th e N atal b a s in ( s t a t i o n s 376, 377) s u rfa c e se d im e n ts a re s i l t y san d . The main components o f th e c o a rse f r a c t i o n a re q u a r tz g r a in s (60 to 70 p e r c e n t) , a n g u la r In some sam ples, subrounded in o t h e r s , b i o t l t e (about 10 p e r c e n t ) , m uscovite (10 to 20 p e r c e n t ) , and f o r a m in lf e r a l t e s t s (a b o u t 10 p e rc e n t. G la u c o n ite i s p r e s e n t In two sam p les. Sponge s p ic u le s and r a d l o l a r l a n s were found in n o tic e a b le amounts in one tra w l sample o n ly . The c a lc a re o u s fau n a shows s ig n s o f d i s s o lu t i o n : (1) t e s t s a re w id e ly frag m en ted , (2) when whole t e s t s o cc u r, th e y a re u s u a lly f r a g i l e owing to th e r e s o r p tio n o f th e e a r l y cham bers, (3) only s p e c ie s r e s i s t a n t to s o lu tio n a re p r e s e n t. The f o r a m i n l f e r a l number has a low v alu e between 400 and 600 ( f o r a m i n i f e r s 7 6 2 ^ ). P la n k to n ic s p e c ie s make up about 94 p e rc e n t o f th e f o ra m in lf e ra l p o p u la tio n and b e n th lc s p e c ie s ab o u t 6 p e r c e n t. Such a h ig h p e rc e n ta g e o f p la n k to n ic s p e c ie s in an assem blage l y ing below th e ca rb o n ate com pensation d ep th i s anom alous. T his p la n k to n ic fau n a i s b e lie v e d to have been In c o rp o ra te d in to t u r b i d i t y c u r r e n ts and r e d e p o s lte d from t h a t medium o f t r a n s p o r t . The la r g e amount o f d e t r l t a l m a te r ia l in w hich th e p la n k to n ic f o r a m in if e r s a r e In clu d ed p re v e n ts t o t a l d i s s o l u t i o n . Some s o lu t i o n may o ccu r in th e p ro c e ss Figure 38 D i s tr i b u t i o n o f g ra in s iz e in s u rfa c e s e d i m ents sam ples o f c o re s in th e N a ta l Basin and th e Zambezi Canyon, u sin g th e c l a s s i f i c a t i o n o f S h ep ard , 1954 ( a f t e r B. R obinson, p e r s . comm.). 190 191 4 5° E S ’ 0 - 7 0 0 3 0 0 kilomV u«s fill* Sand /VCIoyoy Son vrv.'.v-/ . . v•_ * •* « ^ <•.♦•/ Sond y n uASSAR ... S o n d y C lo v ci«r V / y I I I I I I I - ■■ i \ BASSA? OA INDIA lllllll \ /a UNIT. SIM k sIII! Clo y*. _ ,in TULEAR ! CteLAHYR. lyJNHAMBANE ■ » LOURENCO MARQUES nJGELA - * **L« DURBA^*! '§££377 192 o f s e t t l i n g and by " s u b s o lu tio n " on th e s e a - f l o o r (H o ll- mann, 1962), as I n d ic a te d by th e s ig n s o f s o lu tio n ex h i b i t e d by th e t e s t s , b u t I t Is p o s s ib le t h a t no s o lu tio n ta k e s p la c e . I f th e fa u n a d e riv e s from a s i t e o f d e p o s i t i o n c lo se to th e c a rb o n a te com pensation d e p th , I t w i l l th e n e x h ib it s im i l a r s ig n s o f d i s s o l u t i o n . Among th e b e n th lc f o r a m in if e r s , are n a c e o u s s p e c ie s are dom inant, th e y c o n s ti t u t e ab o u t 97 p e r c e n t o f th e b e n th lc fo ra m in l f e r a l assem blage and a re com prised o f forms t y p i c a l o f a b y s s a l w a te r In th e w orld o cean s: Ammnhftnu i i t e s a g g lu - tln a n s (d 'O rb lg n y ), A schem onella sc a b ra Brady, C r lb r o s to - moldeB subglobosus ( S a r s ) , Cyclammlna c a n c e l l a t a B rady, Hormoslna g l o b u l l f e r a B rady, H. normanl Brady, Hvnfinupminft f r l a b l l l s Brady, M l l l o l l n e l l a su b ro tu n d a (M ontagu), R ecurvoldes tu r b l n a t u s ( B rady) , S a c co rh lz a ram osa (B rady) and Troohftmmina g l o b lg e r ln lf o r m ls (P a rk e r and J o n e s ) . The b e n th lc f o r a m in lf e r a l fau n a Is c h ie f ly In p la c e as most o f i t s c a lc a re o u s s p e c ie s have been d is s o lv e d . Some I n d i v i d u a ls o f Elnhldlum s p . , a sh allo w w a te r b e n th lc fo ra m ln i f e r , were found a t 4940 m. Among th e p la n k to n ic f o r a m in if e r s , rew orked s p e c ie s o f C retaceo u s, Eocene, and Upper Miocene ages were found In a number o f sam ples. To summarize th e te r r ig e n o u s sandy sedim ent ly in g In th e n o rth w e ste rn a r e a o f th e N ata l b a s in i s th e c o a rse f r a c t i o n o f t u r b i d i t e s composed c h i e f l y o f sed im en ts d e riv e d from sh allo w w a te r , as shown by abundant c o a rse 193 q u a rtz g r a in s , some g la u c o n ite , and a few sh allo w w a te r b e n th lc f o r a m in if e r s , b u t In which p e la g ic sedim ents from d eep er w a te r a ls o were In c o rp o ra te d . S u rfa c e sed im en ts from th e c e n t r a l a re a o f th e p o r tio n o f the b a s in I n v e s tig a te d ( s t a t i o n 378) a re c lay ey s i l t s , and In th e s o u th e rn a re a ( s t a t i o n s 382, 383# 3 8 4 ), s i l t y c la y s . The sm all re s id u e o f th e c o a rse f r a c t i o n In th e se f in e sed im en ts d id n o t allo w a p e rc e n ta g e e s tim a tio n o f th e com ponents. These a re sm a ll, a n g u la r q u a rtz g r a in s , m ica f la k e s , sponge s p ic u l e s , and sm all t e s t s o f r a d l o l a r l a n s and f o r a m in if e r s . Manganese ox id e Is f r e quent a t th e so u th ern m o st s t a t i o n s . The f o r a m in lf e r a l number h as r e l a t i v e l y h ig h v a lu e s , between 1200 to 1300 In th e clay ey s i l t a t s t a t i o n 378, and ex trem ely low v a lu e s , s m a lle r th an 10, in th e c la y o f th e so u th e rn s t a t i o n s . P la n k to n ic s p e c ie s a re dominant a t s t a t i o n 378 where they make up ab o u t 99 p e rc e n t o f th e f o r a m in lf e r a l fau n a, de c re a se to about 40 p e rc e n t a t s t a t i o n 383• a re about 14 p e rc e n t a t s t a t i o n 382, and are alm o st a b s e n t a t s t a t i o n 384. Among th e b e n th lc f o r a m in lf e r a l fa u n a , c a lc a re o u s s p e c ie s , composed m ain ly o f sm all B o llv ln a . a re dominant a t s t a t i o n 378, w hereas a t th e so u th e rn s t a t i o n s a b y s sa l aren aceo u s s p e c ie s a r e dom inant (same s p e c ie s as m entioned e a r l i e r ) . C alcareo u s f o ra m in if e rs In c lu d e few t e s t s o f la r g e p la n k to n ic s p e c ie s , which a r e p a r t l y d is s o lv e d , and a number o f w e ll- p r e s e r v e d , m inute t e s t s o f c a lc a re o u s 194 p la n k to n ic and b e n th lc s p e c ie s . The amount o f th e sm all c a lc a re o u s fau n a, e s p e c i a l l y h ig h In th e cla y e y s i l t a t s t a t i o n 378 and d e c re a s in g to th e so u th , r e p r e s e n t a m inor p e rc e n t o f th e sed im en t, which c o n ta in s only 2 p e rc e n t calcium c a rb o n a te . However, I t s o ccu rren ce below th e c a rb o n a te com pensation d ep th I s anomalous and I s e s p e c ia lly I n t e r e s t i n g because o f I t s sm all s i z e . Sm all c a lc a re o u s t e s t s should d is s o lv e a s much, o r more, th an l a r g e t e s t s . P la n k to n ic s p e c ie s c o n tr ib u tin g to t h i s sm all fau n a do n o t belong to s p e c ie s r e s i s t a n t to s o lu tio n , b u t to s p e c ie s abundant o n ly In th e f in e f r a c t i o n o f th e fauna a t sh allo w e r d e p th s. G lo b lg e rln a a u ln a u e lo b a N atland and T u rb o ro ta - l l t a h u m llls (Brady) a re th e main c o n t r ib u t o r s . Among th e sm all b e n th lc f o r a m in if e r s , I n d iv id u a ls o f B o llv ln a w ith a t r a n s l u c e n t t e s t a r e common and would be ex p ected to be non- r e s i s t a n t to s o lu tio n . They u s u a lly are n o t found a t a b y s sa l d e p th s In th e w orld oceans and In th e stu d y a re a o c c u r commonly a t b a th y a l d e p th s. I t Is p o s tu la te d t h a t th e sm all c a lc a re o u s f o r a m in lf e r a l fauna p r e s e n t In the c lay e y s i l t , which c o v e rs p a r t o f th e N a ta l b a s in f l o o r , Is d is p la c e d from s h a llo w e r d ep th s and re p re s e n ts p a r t o f th e f in e f r a c t i o n o f t u r b l d l t e s . Such fa u n a l t e s t s a re b e lie v e d to have been p re se rv e d from d is s o lu tio n f o r th e same reaso n as m entioned e a r l i e r ; t h a t I s , I n c lu s io n In a l a r g e amount o f d e t r l t a l m a t e r ia l. 195 Discussion of sedimentation In the Natal basin: I d e n t i f i c a t i o n o f d is p la c e d and X R s i t u sedim ents on th e f l o o r o f th e N a ta l b a sin i s n o t alw ays e a s y . In th e sandy sed im en ts In th e n o rth w e ste rn p o r tio n o f th e a re a o f I n v e s t i g a t i o n , betw een 4870 m and 5000 m, most o f the c o a rse com ponents a re re c o g n iz e d as d is p la c e d . These a re abundant c o a rse q u a rtz g r a in s , some g la u c o n ite and a few sh allo w w a te r b e n th lc f o r a m in if e r s . O th er components such as l a r g e p la n k to n ic f o ra m in if e rs (m o stly d i s s o lv e d ) , aren aceo u s deep w a ter b e n th lc f o r a m in if e r s , and m ica f la k e s , can be In s i t u in t h i s a b y s s a l en v iro n m e n t. The p la n k to n ic f o r a m in if e r s belong m ainly to modern s p e c ie s r e s i s t a n t to s o lu t i o n . A lthough th e s p e c ie s a re modern, I t does n o t n e c e s s a r i l y Imply a r e c e n t age as most modern p la n k to n ic f o r a m in if e r s range back th ro u g h a la r g e p a r t o f th e Neogene. Some d ia g n o s tic f o s s i l p la n k to n ic f o r a m in ife r s o f C re ta c e o u s, Eocene, and Upper Miocene ages a re s c a t te r e d in th e sed im en ts. The f o r a m in lf e r a l fauna ap p e a r s , th u s , to be a m ix tu re o f rew orked o r d isp la c e d e le m e n ts. In th e f i n e sedim ents o f th e s o u th e a s te r n a r e a , between 4800 m and 5450 m, d isp la c e m e n ts a r e n o t as e a s i ly re c o g n iz e d . Most o f th e components a re s im i l a r to com ponents o f p e la g ic "re d c la y ." Components a re c h ie f ly c la y and among th e rem ain in g te r r ig e n o u s c o n s ti t u e n t s a re m ica f la k e s and sm all a n g u la r q u a rtz g r a i n s . The o ccu r 196 re n c e o f th e l a t t e r le e x p e c te d In a p e la g ic c la y so c lo s e to c o n t i n e n t a l m asses. R a d lo la r la n s a re common (In e x c e ss o f 1000/gm o f sedim ent) and manganese oxide I s abundant a t th e so u th ern m o st l o c a l e . The low f o r a m in lf e r a l number can n o t be used to I n f e r a r a p id d e p o s itio n because e lim in a tio n o f c a lc a r e o u s f o r a m in if e r s by d i s s o l u t i o n a t such d ep th s would a ls o be r e s p o n s ib le f o r a low f o r a m in lf e r a l number. But sed im en ts which In c lu d e th e sm all c a lc a re o u s fauna m entioned e a r l i e r a re c o n s id e re d to have accum ulated r a p i d l y . S u b su rface sed im en ts o f th e N a ta l B asin argue In f a v o r o f a r a p id a c c u m u la tio n . The s u r f l c l a l l a y e r o f te r r ig e n o u s sedim ent I s 20 to 2 cm th ic k (d e c re a s in g s o u th e a s tw a rd ), and o v e r l ie s a f o r a m in lf e r a l ooze showing e v id en ce o f d is s o lu tio n b u t w hich I s co n sid e re d to have been b u rle d q u ic k ly b e fo re com plete d i s s o l u t i o n . A sub s u rf a c e c a lc a re o u s sedim ent I s p r e s e n t In a l l c o res ( F ig . 39) ex ce p t a t th e so u th e rn m o st, and a ls o d e e p e s t, s t a t i o n (3 8 4 ). The o bserved I n c re a s e In c a rb o n a te down th e c o re s can be e x p la in e d by s e v e r a l p r o c e s s e s , nam ely: (1) e l e v a t i o n o f th e calcium c a rb o n a te com pensation d ep th owing to e i t h e r a chem ical change In th e w a te rs o f th e b a s in o r su b sid e n c e , o r (2) r a p id b u r i a l p re v e n tin g com plete d i s s o lu t i o n . The second e x p la n a tio n I s fav o red by th e a u th o r . To r e c a p i t u l a t e , no u n d is tu rb e d sed im en ts were c o l l e c t e d from th e N a ta l b a s in f l o o r , e x c e p t p o s s ib ly a t V a ria tio n s c o re s from Figure 39 i n calcium c a rb o n a te c o n te n t in th e N atal B a s in . 197 PERCENTAGES 10 2 0 3 0 4 0 5 0 6 0 J 1 1 v l i V i \ \ • • 384 B OF CaC03 0 10 2 0 3 0 4 0 5 0 - I 1 I 1 ___ VO 00 199 th e so u th ern m o st and d e e p e st s t a t i o n s where sedim ents a re c la s s e d a s re d c la y o f norm al p e la g ic o r i g i n . The s u rfa c e sedim ents a re I n te r p r e t e d a s t u r b l d l t e h o riz o n s showing a l a t e r a l d e c re a s e In g ra in s iz e from th e n o rth w e st to th e s o u th e a s t. No graded bedding was o b serv ed In th e l a y e r s , n e i t h e r by th e p r e s e n t I n v e s t i g a t o r from X -ray a n a ly s is of c o res and l l t h o l o g l c ex am in atio n , n o r by B. Robinson (p e rs . comm.) from g r a in s iz e a n a l y s is . Bedding graded from c o arse a t th e bottom o f a t u r b l d l t e l a y e r to f in e a t th e to p , I s w id e ly re p u te d to be d ia g n o s tic o f t u r b l d l t e s . Yet, as r e p o r te d by Emery (1 9 6 4 ), ungraded beds a re common In t u r b l d l t e s o f modern m arine sed im en ts and a h o r iz o n ta l a r e a l g r a d a tio n as re c o g n iz e d In t h i s stu d y may be more Im p o rtan t th a n a v e r t i c a l one. One q u e s tio n re g a rd in g t u r b l d l t e s co n cern s t h e i r so u rce a r e a . The la r g e Zambezi canyon and o th e r s m a lle r subm arine canyons t h a t open on th e n o r th e rn s id e o f th e N ata l b a s in a p p e a r a t f i r s t g lan ce to be an obvious avenue o f t u r b l d l t e t r a n s p o r t . The d i s p e r s a l p a t t e r n o f s e d i ments on th e b a s in f l o o r n e a r th e mouths o f th e canyons could n o t be s tu d ie d owing to la c k o f sam pling. Samples were c o l l e c t e d betw een d e p th s o f 2200 m and 3950 m a t two s t a t i o n s on th e Zambezi canyon w a ll (367A, 367B, 367C, 362D, 362E) and a t a s in g le s t a t i o n on th e c o n tin e n ta l r i s e w est o f th e Zambezi canyon (363D, 363E ) • Sedim ents h e re a r e f o r a m in lf e r a l oo zes o f c la y e y to sandy 2 0 0 s iz e s whose co arse f r a c t i o n c o n ta in s 99 p e r c e n t p la n k to n ic f o r a m in if e r s . The p la n k to n ic f o ra m in if e rs show a m ix tu re o f (1) modern s p e c ie s w ith f re s h t e s t s , (2) modern s p e c ie s whose t e s t s show s ig n s o f rew orking, (3) f o s s i l s p e c ie s o f v a rio u s a g e s , b u t p r im a r ily M iocene. D e t r i t a l q u a rtz g r a in s a re r a r e in th e se se d im e n ts, Dut in c o re s lo c a te d in th e Zambezi canyon, some h o riz o n s a r e r i c h e r in q u a rtz g r a i n s . The low a n g le o f s lo p e from th e Mozambique channel to th e N a ta l B asin and th e absence o f c o a rse d e t r i t a l sand in s u r f l c i a l sed im en ts o f th e c o n tin e n ta l r i s e a t th e n o rth e rn end o f th e b a s in and on th e Zambezi Canyon w a ll does n o t r u l e out th e p o s s i b i l i t y t h a t th e t u r b l d l t e s follow ed th e canyon p a th . A n aly sis o f sm all C a lif o r n ia subm arine fa n s (H aner, 1971) in d ic a te s t h a t t u r b i d i t y c u r r e n ts a r e c o n fin ed to c h an n els in th e up p er s e c tio n of fa n s ; only in th e low er s e c tio n o f a subm arine fan do t u r b i d i t y c u r r e n ts sp read l a t e r a l l y . The ch an n els them s e lv e s p e r i o d i c a l l y s h i f t lo c a tio n c a u sin g a complex p a t t e r n o f o v e rla p p in g sedim ent ty p e s and a s h i f t in th e maximum d e p o s itio n a l a re a f o r t u r b l d l t e s . A t u r b i d i t y c u r re n t once in m otion i s s e l f - p e r p e t u a t i n g and does not need a s te e p slo p e to c o n tin u e forw ard m o tio n . A w e ste rn so u rce a r e a , such as th e Limpopo R iv e r r e g io n , i s p o s s ib le i f t h e s e sedim ents o r i g i n a t e as t u r b l d l t e s f o r a t r o u g h - l i k e f e a tu r e i s in d ic a te d on to p o - 2 0 1 g ra p h ic maps (F ig . 2) and d is p la c e d sedim ents o ccu r In c o re s c o lle c te d from th e s lo p e s . Sedim ents from th e Zambezi Canyon a ls o show s ig n s o f d is tu rb a n c e s a lth o u g h composed o f f o r a m in lf e r a l o o z e s. The p la n k to n ic fauna i s h e te ro g e n e o u s and c o n ta in s a m ix tu re o f f r e s h and rew orked t e s t s o f modern s p e c ie s and o f v a rio u s a g e s , c h ie f ly M iocene. These mixed o ozes, a s w e ll a s s im i l a r mixed oozes in th e sm all a b y s sa l p la in w est o f Europe and in th e s u b su rfa c e d e p o s its o f the N a ta l B a sin , are p ro b ab ly p a r t l y d is p la c e d . The age o f th e se oozes i s not obvious from fa u n a l assem b lag es, which a r e c h i e f l y composed o f modern s p e c ie s ra n g in g back in to th e Neogene w ith th e adm ixture o f a few C retaceous and P a le o gene s p e c ie s a s w ell as more common Miocene o n e s. These a s s o c ia tio n s could r e p r e s e n t modern assem blages c o n ta in in g some reworked and d is p la c e d e le m e n ts. R adiocarbon m easurem ents, however, in d ic a te d an age o f ap p ro x im a te ly 23,050 y e a rs B .P . a t 15 cm in a c o re from th e sm all a b y s s a l p la in w est o f E uropa. No a c t i v i t y was re c o rd e d f o r th e su b su rfa c e oozes o f th e N a ta l B asin , im plying an age o ld e r th an 30,000 to 40,000 y e a rs B.P. I f th e se f o r a m in lf e r a l oozes were in s i t u , i t would be s u r p r i s i n g t h a t l i t t l e o r no Holocene d e p o s itio n o ccu rred in th e a b y s s a l p la in w est o f E uropa, an a re a surrounded by s te e p s lo p e s and c lo s e to th e c o n tin e n t and is la n d s , and where slumps and t u r b i d i t y c u r r e n t s would be ex p ected to o c c u r. 2 0 2 Throughout th e N a tal B asin , I f th e s u b su rfa c e oozes a re c o n sid e re d to be in s i t u , sedim ents younger th an 40,000 y e a rs would be r e p re s e n te d o nly by a s u p e r f i c i a l l a y e r o f d e t r i t a l sed im en t ra n g in g in th ic k n e s s between 2 and 20 cm. I t has a lr e a d y been e s ta b lis h e d t h a t th e r e a re 1500 m o f u n c o n so lid a te d sed im en ts in th e N a ta l B asin (Swing e t a l . . 1969) w ith w hich t h i s slow r a t e o f se d im e n ta tio n i s i n co m p a tib le . T h e re fo re , i t i s re a so n a b le to a t t r i b u t e a d isp la c e d o r ig i n to th e su b re c e n t oozes in th e a b y s s a l p la in s and to c o n s id e r them as rew orked o r b i o c l a s t l c t u r b l d l t e s d e riv e d from b a th y a l d e p th s . A Miocene f o r a m in lf e r a l o o z e , d is c u s s e d l a t e r , c ro p s o u t on th e slo p e o f f Inham bane. O ther f o s s i l oozes o f u pper C re ta ce o u s, Eocene and Miocene ag es were r e p o r te d in the a re a by S a ito and Fray (1964) and Ubaldo (1 9 7 1 ). S o r tin g ta k e s p la c e d u rin g th e p ro c e ss o f r e s e d i - m en tatlo n as shown by v a r i a t io n s in th e s p e c ie s composi tio n o f fa u n a l a ssem b lag es. Some d is p la c e d oozes c o n s is t o f p la n k to n ic f o r a m i n l f e r a l s p e c ie s o f la r g e s iz e o n ly , w hereas o th e r s c o n s is t o f sm all s p e c ie s . S o u th e rn M adagascar i s a p o s s ib le so u rce a re a f o r th e N a ta l B asin se d im e n ts. Submarine canyons c ro s s th e M alagasy s lo p e (F ig . 2) and t u r b i d i t y c u r r e n ts p o s s ib ly a re o c c u rrin g in t h i s a r e a . Owing to a la c k o f sam pling, i t i s n o t p o s s ib le to d e fin e th e d i s p e r s a l p a t t e r n o f sedim ents on th e n o r th e a s te r n sid e o f th e N a ta l B a sin . 203 In review I t h as been shown t h a t sed im en ts o f th e N a ta l B asin a r e pro v id ed c h i e f l y from th e n o r th by t u r b i d i t y c u r r e n ts , which fo llo w th e p a th s o f subm arine canyons, w ith th e Zambezi Canyon a s th e main avenue o f t r a n s p o r t . C re ta c e o u s, Eocene and Miocene p la n k to n ic f o ra m in if e rs s c a t te r e d in th e sed im en ts may be d eriv e d from b o th A fric a and M adagascar, because sedim entary fo rm a tio n s o f th e se ages o ccu r alo n g th e Zambezi R iv er in Mozambique and in southw est M adagascar (F ig . A ). Miocene f o r a m in if e r s on the o th e r hand a r e d e riv e d from subm arine fo rm a tio n s because t h e i r oozy n a tu r e su g g e sts a b a th y a l d e p o s it and Miocene f o r a m in lf e r a l oozes a re cro p p in g o u t in th e a r e a . Sedim ents in th e N a ta l B asin a ls o may be d e riv e d in p a r t from th e s id e s o f th e b a s in by slum ping alo n g th e s lo p e s . A few specim ens o f T e x tu la r la s a g l t t u l a D efran ee, a b e n th lc f o r a m ln if e r , o f which l i v i n g i n d i v i d u a ls o cc u r commonly on th e M adagascar P la te a u n e a r th e W alter S h o als ( s t a t i o n 380C), were n o ted in th e e a s te rn sed im en ts o f th e N a ta l Basin f l o o r . S e d im en tatio n in th e N a ta l B asin i s c h i e f l y in flu e n c e d by th e topo g rap h y . Sedim ents en co u n tered a re te r r ig e n o u s and b l o c l a s t l c t u r b l d l t e s and do n o t r e f l e c t th e northw ard movement o f deep and bottom w a te r s . These c u r r e n ts may a f f e c t th e sed im en ts in a way n o t re v e a le d by t h i s s tu d y . Ewing e t a l . (1968) and Ewing and Ewing (1970) r e p o rte d " g ia n t r ip p le s " in th e b a s in tre n d in g 204 w est n o r th w e s t- e a s t s o u th e a s t, t h a t I s ro u g h ly tra n s v e r s e to th e d ir e c tio n o f th e bottom flo w . B iogenic sedim ents The main components o f b io g e n ic sed im en ts a re s e c re te d by l i v i n g o rg an ism s. Beep w a te r p e la g ic b io g e n ic sed im en ts a r e e i t h e r c a lc a re o u s o r s i l i c e o u s o o zes, a calciu m c a rb o n a te c o n te n t o f 30 p e r c e n t b ein g used a s the d iv id in g l i n e between c a lc a re o u s and s i l i c e o u s ooze. The c r i t e r i o n o f 30 p e rc e n t CaCOj f o r d e f in in g c a lc a re o u s oozes was f i r s t used by B ogglld (1916) and w id ely follow ed s in c e by o t h e r s . C alca reo u s oozes were d iv id e d by A rr h e n iu s (1952) and O lausson ( i 9 6 0) In to "ch alk " ooze, w ith a calciu m c a rb o n a te c o n te n t g r e a t e r th a n 60 p e r c e n t, and "m arl" ooze, w ith a calcium c a rb o n a te c o n te n t between 30 and 60 p e r c e n t. Chalk and m arl oozes a re f u r t h e r sub d iv id e d w ith re g a rd to th e dom inating f o s s i l group o f th e c a rb o n a te component In to f o r a m i n l f e r a l , c o c c o llth and p tero p o d ooze (R e v e lle , 1944; A rrh e n iu s , 1952). Olausson d e fin e d th e p ro p o rtio n o f t e s t s o f th e f o s s i l groups t h a t he used In h i s n o m en clatu re: 0-10 p e r c e n t t e s t s have no a d j e c t i v a l term s added to th e name o f th e d e p o s its , 10-30 p e r c e n t t e s t s are c o n sid e re d a s " ric h " In th e observed f o s s i l g ro u p , and ^ 3 0 p e rc e n t r e s u l t s In th e d e p o s it d e r iv in g I t s name from th e f o s s i l d o m in atin g th e sedim ent (O lau sso n , i 9 6 0). These d i v is io n s a r e u t i l i z e d in t h i s s tu d y ._____________________________________________________________ 205 C alcareous ooze I s th e dominant sedim ent e n c o u n te r ed . N an n o fo s8 ils, c a lc a re o u s p la n k to n ic forms s m a lle r th a n 5 0 ) i c o n s is tin g c h i e f l y o f c o c c o l l t h s , have not been I n v e s tig a te d In t h i s s tu d y . T h e ir abundance In th e s e d i m ents can be o b ta in e d by c o n s id e ra tio n o f th e combined v a lu e s o f calcium c a rb o n a te c o n te n t and sand f r a c t i o n ( F ig s . 35 and 36). Because c o a r s e r s iz e ro u g h ly c o r r e l a t e s w ith h ig h CaC03 c o n te n t, th e f in e f r a c t i o n ( < 6 2 p ) i s more l i k e l y to be d e t r i t a l s i l t and c la y r a t h e r th a n c o c c o l l t h s . I t can th en be concluded t h a t no c o c c o llth ooze Is p r e s e n t In th e a r e a . C o c c o llth s a r e common, how ever, a t s t a t i o n 361J, on th e c o n tin e n ta l r i s e n e a r the n o rth w e ste rn c o rn e r o f th e N a ta l B asin , where th e sand f r a c tio n I s c o n s id e r a b ly sm a lle r than a t a d ja c e n t l o c a le s (12 p e rc e n t In s te a d o f 48 p e r c e n t) . F o ra m in lfe ra l ooze co v ers th e main p a r t o f th e a re a I n v e s tig a te d . F o ra m in lfe ra l t e s t s a re th e most Im p o rtan t component In th e c o a rse f r a c t i o n o f th e ooze, making up 95 to 100 p e rc e n t o f th e f r a c t i o n . P la n k to n ic s p e c ie s u s u a lly com prise 99 p e r c e n t o r more o f th e f o r a m in lf e r a l fa u n a , w hereas b e n th lc s p e c ie s c o n s t i t u t e 1 p e rc e n t o r l e s s . Among th e rem ain in g components o f th e c o a rse f r a c t i o n s a re p tero p o d s (0 -7 p e r c e n t) , sponge s p ic u le s (0 -2 p e r c e n t) , m u sco v ite (up to 2 p e rc e n t) and sub- a n g u la r q u a rtz g r a in s (0 -1 5 p e r c e n t) . G la u c o n ite p e l l e t s c o n s t i t u t e about 5 p e r c e n t o f th e c o a rse f r a c t i o n In an 2 0 6 ooze lo c a te d on th e g e n tle slo p e s o u th e a s t o f Lourenco Marques under th e co re o f th e Agulhas C u rre n t. In t h i s a re a between d e p th s o f 1535 and 1910 n , f o r a m in lf e r a l t e s t s a re p a r t l y abraded and a re commonly g la u c o n ltlz e d . F o ra m in lfe ra l m arl ooze which c o n ta in s 30 to 60 p e rc e n t calcium c a rb o n a te covers a la rg e p a r t o f th e c o n tin e n ta l s lo p e s and c o n tin e n ta l r i s e . I t s d i s t r i b u t i o n ro u g h ly c o r r e l a t e s w ith th e d i s t r i b u t i o n o f th e 10-50 p e r c e n t s a n d - f r a c tlo n and a 1000 to 10,000 p la n k to n ic f o r a - m in if e r a l number l a r g e r th an 250/1. F o ra m in lfe ra l c h a lk ooze i s p r e s e n t on th e Mozambi que and M adagascar p l a te a u s , in th e sm all a b y s sa l p la in w est o f Europa I s la n d , and on the upper slo p e o f f In - hambane between 1140 m and 1185 m. The c h a lk ooze con t a i n s 61 to 94 p e rc e n t calcium carb o n ate and i s a c o a rse sedim ent w ith a s a n d -s iz e f r a c tio n g r e a t e r th an 50 p e r c e n t. The p e rc e n ta g e o f th e sand f r a c t i o n i s s l i g h t l y low er in th e c h alk ooze on th e e a s te r n sid e o f th e sm all a b y ssa l p la in w est o f Europa and on th e M adagascar P la te a u (42 to 45 p e r c e n t ) . The c o a rs e n e s s o f f o r a m in lf e r a l c h a lk ooze i s r e f le c t e d by th e c o r r e l a t i o n between i t s o c c u rre n c e and a p la n k to n ic f o r a m in lf e r a l number ( r e f e r r i n g to specim ens > 250/1) g r e a t e r th an 5000 and commonly more th an 10,000. D is tr ib u tio n o f ch alk and m a rl f o r a m in lf e r a l oozes i s c o n tr o lle d by s e v e r a l f a c t o r s . The main f a c t o r i s th e 207 d is ta n c e from th e la n d m asses. As one p r o g re s s e s f u r t h e r away from la n d , th e te r r ig e n o u s supply d e c re a s e s and t h e r e f o r e l e s s calciu m c a rb o n a te d i l u t i o n I s n o tic e d . T h is Is shown by th e In c re a s e In calcium c a rb o n a te w ith d is ta n c e o ffs h o re w ith th e e x c e p tio n o f th e a re a o f f I n - hambane. A nother f a c t o r I s th e a c tio n o f a g e n ts o f t r a n s p o r ta ti o n as c u r r e n t s , slumps or t u r b i d i t y c u r r e n ts which e lim in a te th e f in e p a r t i c l e s . This e x p la in s why a ch alk ooze o ccu rs c lo s e to th e A frican c o n tin e n t on th e upper slo p e o f f Inhambane In an a r e a swept by th e Mozambique C u rre n t and In th e sm all a b y s s a l p la in w est o f Europa, w here th e f o r a m in lf e r a l ooze I s c o n sid e re d d is p la c e d and c la s s e d as a b l o c l a s t l c t u r b l d l t e . The c o a rse c h alk ooze on the Mozambique P la te a u r e f l e c t s b o th th e d is ta n c e from land and th e e f f e c t o f the A n ta r c tic In te rm e d ia te W ater C u rren t which form s an eddy c e n te re d In t h i s a r e a and p robably p re v e n ts th e d e p o s itio n o f th e f in e components o f th e fau n a. The abundance o f manganese n o d u les a ls o I n d ic a te s a slow r a t e o f accum ula t i o n . Scoured rocky b o t t om and t h i n s u r f l c l a l c o a rse d e p o s its P a r t o f th e A fric a n upper c o n tin e n ta l s lo p e between Cape S t. L ucia and Lourenco Marques I s d o u b tle s s flo o re d by a h a rd bottom . A ttem pts a t c o rin g and g rab sam pling f a i l e d and o n ly a few tr a w l sam ples could be c o l l e c t e d . T h is la c k o f ev id en ce o f sed im e n ta tio n I s a t t r i b u t e d to the 2 0 8 sw eeping e f f e c t o f th e Agulhas C u rre n t. I t i s in t h i s a re a t h a t th e Agulhas C u rre n t i s c o n s tr i c t e d and fo rce d down by a w estward flow o f s u rfa c e w a te r , a change which p ro b a b ly r e i n f o r c e s i t s sweeping a c tio n and is re s p o n s ib le f o r th e rocky b ottom . O ffsh o re th e p r o tr u d in g c o a s t o f s o u th e rn Mozambique, s o u th o f Inham bane, th e p resen ce of a h a rd bottom was r e p o rte d in th e d e s c r i p t i o n o f shallow w a te r d e p o s its . T his h a rd bottom is t h i n l y covered w ith c o a rse d e p o s its composed m ainly o f b io g e n ic s k e l e t a l | d e b r is r e s p o n s ib le fo r th e h ig h c a rb o n a te c o n te n t p re s e n t and e x te n d s onto p a r t o f th e u p p e r s lo p e . A rocky bottom a ls o i s e v id e n t around Europa I s la n d . DISTRIBUTION OF FORAMINIFERS IN SURFACE SEDIMENTS P re v io u s Work A thorough rev iew o f f o r a m ln lf e r a l r e s e a r c h f o r th e In d ia n Ocean h a s been made by Bandy, L ln d en b erg , and V in o en t (1 9 7 2 ). They show t h a t u n t i l th e tim e o f th e IIOE, r e s e a r c h In v o lv in g In d ia n Ocean f o ra m in lf e rs was n e g le c te d In c o n t r a s t to t h a t o f o th e r o cean ic a r e a s , and t h a t more than o n e - h a lf o f a l l th e p a p e rs on modern a s sem blage o f th e In d ia n Ocean were p u b lish e d in the l a s t d e c a d e . D i s tr ib u tio n p a t t e r n s o f l i v i n g p la n k to n ic fau n as w ere d e fin e d on a broad s c a le in th e whole In d ia n Ocean by B e lia e v a (1 9 6 4 ), B oltovskoy (1969a) and Be and T o ld e r- lu n d (1 9 7 1 ). These a u th o rs reco g n ized t h a t in th e w a te rs and sedim ents o f th e In d ia n Ocean, a s w e ll a s in th e o th e r o c e a n s, p la n k to n ic f o r a m ln lf e r a l s p e c ie s a re d i s t r i b u t e d i n d i s t i n c t l a t i t u d i n a l b e l t s and can be d iv id e d in to groups a c c o rd in g to l a t i t u d i n a l p o s it i o n s o f g r e a t e s t abundance. S tu d ie s o f l i v i n g p la n k to n ic f o ra m in lf e rs on a more l i m ite d s c a le in c lu d e th e work o f U j i i e (1968) in tow s from th e e a s te r n e q u a to r ia l In d ia n Ocean. There are 209 2 1 0 only few s tu d ie s o f d i s t r i b u t i o n p a t t e r n s o f p la n k to n ic fo ra m in lf e rs in bottom sed im en ts o f th e In d ia n Ocean. A broad s c a le I n v e s tig a tio n in s u rfa c e sed im en ts o f th e e n t i r e In d ia n Ocean was perform ed by B e lia e v a (1964) who o bserved a c lo s e co in c id e n c e betw een th e b o u n d a rie s o f th e p r in c ip a l th a n a to c o e n o se s a t d ep th s l e s s th a n 4500- 4700 m and th e b o u n d aries o f th e p r in c ip a l b lo co en o ses. Among r e g io n a l s tu d ie s on f o ra m in lf e rs in sedim ents o f th e In d ia n Ocean a r e th e works by F r e r ic h s (1968, 1970, 1971) in th e n o r th e a s te r n p a r t o f th e o cean, C onolly (1967) in th e s o u th e a s t, and O lausson (I9 6 0 , 1969) and Oba (1967, 1969) in th e c e n t r a l e q u a to r ia l a r e a . These i n v e s t i g a t o r s re c o g n iz e d f a u n a l changes in d e e p -se a c o re s r e f l e c t i n g warmer w a te r a t th e end o f th e l a s t g l a c i a t i o n and which co u ld be c o r r e l a t e d w ith th e warming re c o g n iz e d a t t h a t tim e in deep sea c o res o f o th e r o c ean s. The Mozambique channel a r e a and th e southw est In d ia n Ocean have been n e g le c te d f o r f o r a m ln lf e r a l stu d y . Among th e i n v e s t i g a t o r s o f l i v i n g p la n k to n ic fo ra m in lfe rs o n ly Be and T o ld erlu n d (1971) c o v er t h i s a r e a . The p la n k to n ic assem blage from one bottom sample a t ab o u t 20°S. in th e ch an n el was d e s c rib e d by B oltovskoy (1 9 6 9 b ). Ubaldo (1971) s tu d ie d p la n k to n ic f o r a m in lf e r s in d e e p -sea co res from th e n o rth e rn Mozambique Channel c o l l e c t e d d u rin g th e P o rtu g u e se E x p e d itio n aboard th e A lm lran te la c e r d a b u t she d id n o t o b serv e d efin e d tr e n d s in th e d i s t r i b u t i o n p a t t e r n 2 1 1 o f p la n k to n ic f o r a m in lf e r s . A p re lim in a ry stu d y o f th e f o ra m in lf e rs from s e le c te d sam ples o f t h i s i n v e s t i g a t i o n was un d ertak en by Bandy and E chols (u n p u b lish ed l e c t u r e a t th e In d ia n Ocean Symposium, W ashington, D. C ., June 1965)* They e s ta b lis h e d some p a ra m e te rs such as p l a n k to n ic / b e n th ic f o r a m ln lf e r a l r a t i o , f o r a m ln lf e r a l number, and r a d i o la r l a n number from g ra b sam ples. These p a ra m e te rs were u t i l i z e d in t h i s stu d y and were f o r th e m ost p a r t con firm ed by a n a ly s is o f th e to p l a y e r o f th e c o r e s . S e v e ra l d is c re p a n c ie s were found p ro b a b ly owing to th e d i f f e r e n t sam pling te c h n iq u e s o f a n aly zed sam ples (c o re s and g rab sa m p le s ). Method o f Study Faunal p a ra m e te rs were e s ta b lis h e d in a l l s u rfa c e sam ples and in s u b su rfa c e se d im e n ts o f s e le c te d c o r e s . S p e c ia l care was g iv e n to t h e s e le c tio n o f s iz e f r a c t i o n s in th e analyzed sam p les. B ecause th e a d u l t t e s t s o f v a r io u s s p e c ie s have d i f f e r e n t s i z e s , th e r e l a t i v e p ro p o r tio n o f th e fa u n a l c o n s t i t u e n t s in an assem blage v a r i e s depending on th e s iz e f r a c t i o n a n a ly z e d . The im p o rta n t e f f e c t o f mesh s iz e on fa u n a l com position h as been n o te d by s e v e ra l a u th o rs in c lu d in g A rrh en iu s (1 9 5 2 ), B erg er and S o u ta r (1967), B e lia e v a (1 9 6 9 ), B erg er (1 9 7 1 ), P a rk e r (1 9 7 1 ), and Thiede (1971)* S e le c tio n o f a s p e c i f i c s ie v e mesh s iz e used in a stu d y i s im p o rta n t and i s o f s i g n i f i - cance In d a ta I n t e r p r e t a t i o n . S iz e f r a c t i o n s used In v a rio u s s tu d i e s a re n o t con s i s t e n t and t h i s , co u p led w ith th e f a c t t h a t some p ap ers la c k In fo rm a tio n on th e mesh s iz e u t i l i z e d , make I t d i f f i c u l t to compare th e r e s u l t s o f d i f f e r e n t w o rk e rs. Many f o r a m ln lf e r a l s tu d i e s from d ee p -sea sed im en ts have been made u sin g a mesh s iz e s ie v e o f about 150p. Ih e s e le c t io n o f a fau n a l a r g e r th a n 1 5 0 f i e lim in a te s most o f th e J u v e n ile s forms n o n l d e n t l f l a b l e b u t e lim in a te a ls o th o se s p e c ie s whose a d u l t t e s t s a re c h i e f l y s m a lle r than 150p. A lthough th e s e sm all s p e c ie s a r e n o t th e m ost numerous, th e y may be I n t e r e s t i n g ec o lo g lc and p a le o e c o lo g lc I n d i c a t o r s . Among th e s e a r e : (1) G lo b lg e rln a au ln a u e lo b a N atland and l u r b o r o t a l l t a h u m llls (B rad y ), w hich show d e f i n i t e tr e n d s In abundance In th e P le is to c e n e and H olo- cene sedim ents o f th e e a s te r n N orth A t l a n t i c (V in cen t, 1968; C a ra lp , 1971; X hlede, 1971); (2) T u r b o r o t a l lt a num lllo P a r k e r, whose d i s t r i b u t i o n has r e c e iv e d l i t t l e a t t e n t i o n b u t In th e p r e s e n t stu d y shows d e f i n i t e tre n d s r e l a t e d to te m p e ra tu re ; and (3) G lo b lg e rln a ru b e sce n s H ofker, w hich h a s been used by F r e rlc h s (1968, 1971) as an e x o e lle n t te m p e ra tu re I n d ic a to r In P le is to c e n e and Holocene sed im e n ts o f th e Andaman S ea. I h l s I n v e s t i g a t i o n , to o , re v e a le d t h a t d i s t r i b u t i o n p a t t e r n s o f &. ru b escen s a p p e a r to be r e l a t e d to te m p e ra tu re b u t In a re v e rs e manner th a n In th e Andaman S ea. Whereas t h i s s p e c ie s I s a o o ld - 213 w a te r I n d ic a t o r In th e Andaman S ea, I t i s a warm -water I n d ic a t o r in th e p re s e n t a r e a . This opposed tre n d w i l l be d is c u s s e d l a t e r . I f co u n ts a re made on th e whole fauna l a r g e r th a n 62p . t th e la r g e p ro p o rtio n o f ju v e n ile specim ens may mask d i s t r i b u t i o n a l tre n d s o f l a r g e s p e c ie s as th e s e a re p r e s e n t i n q u a n t i t i e s to o sm all in a co u n t o f 300 to 400 in d i v i d u a l s . Among i n v e s t i g a t o r s o f In d ia n Ocean f o r a m in lf e r s , B e lla e v a (1964) an aly zed a fau n a l a r g e r than 100/1 in s u r fa c e s e d im e n ts, B oltovskoy (1969a) and Be and T o ld erlu n d (1971) a fau n a l a r g e r th a n 200p . in p lan k to n tow s, U j i i e (1968) one l a r g e r th a n 330/1 in p la n k to n tow s, and F r e r ic h s (1968, 1971) a fauna l a r g e r th a n 62ji in s u rfa c e sed im en ts and l a r g e r th a n 125/i in su b su rfa c e sed im e n ts. In th e p r e s e n t stu d y co u n ts were made on d i f f e r e n t s iz e f r a c t i o n s in o r d e r to e v a lu a te b o th sm all and la r g e s p e c ie s . S e le c te d f o r a m ln lf e r a l sam ples were s p l i t in to th e s ta n d a rd p h i s iz e s and th e r e l a t i v e freq u en cy o f p la n k to n ic s p e c ie s d e riv e d from eaoh s iz e f r a c t i o n was c a l c u l a t e d and compared. T h is was accom plished by c o u n t in g ab o u t 300 p la n k to n ic in d iv id u a ls in each s iz e f r a c t i o n . In r e p o r tin g th e p ro b ab le e r r o r o f a g iv en f r e quency when c o u n tin g 100, 200 and 300 specim ens, and o th e r p o s s ib le e r r o r s in h a n d lin g and p ro c e s s in g th e sam ples, F h le g e r ( i 9 6 0) proposed t h a t " l i t t l e i f a n y th in g i s to be 214 g ain ed by c o u n tin g sam ples much l a r g e r th a n a p p ro x im a te ly 300 specim ens." Five f r a c t i o n s were c o n s id e re d : 62-88^, 88-125J1, 125-177JI, 177-250/u, and>250>i. Samples (10-cm I n t e r v a l o f c o re s o r r e p r e s e n t a t i v e p o r tio n o f grab sam ples) w ere d r ie d , w eighed, washed on a 250-mesh T y le r sc re e n (62/i o p e n in g s ), and then w eighed a g a in . The c o u n tin g te c h n iq u e developed i s : 1 . Sam ples a re s p l i t w ith a m l c r o s p l l t t e r to a sm a ll w orkable f r a c t i o n (som etim es th e r e s id u e l a r g e r th a n 62ji in a 10-cm c o re I n t e r v a l i s sm all and need n o t be s p l i t ) . 2. The s p l i t f r a c t i o n i s sie v e d on a s e r i e s o f s c re e n s w ith mesh openings o f 250ft, 177ft, 125jp, and 88ft. 3. Each s ie v e r e s id u e i s sp read a s evenly a s p o s s i b l e on a t r a y h a v in g a g r id system d iv id e d in to 405 sq u a re s (even s p re a d in g r e q u ir e s a c e r t a i n s k i l l w hich d evelops w ith p r a c t i c e . . . p o u rin g i s s t a r t e d in th e c e n t e r o f th e t r a y so th e rounded, b a l l - l i k e O rb u lln a can r o l l in a l l d i r e c t i o n s and be s c a t te r e d o v e r th e t r a y ) . 4 . A ll specim ens lo c a te d in s y s te m a tic a lly s e le c te d sq u a re s a re p ic k e d and p la c e d on a s li d e from w hich a count o f in d iv id u a l s p e c ie s i s made. The s e le c te d sq u are s a r e a lo n g o b liq u e l i n e s a c r o s s th e t r a y , so t h a t th e y r e p r e s e n t th e e n t i r e s u r f a c e . 5. A com puter program was d esig n e d by Dr. D. H aner ( p e r s . comm.) to o rg a n is e and s o r t th e d a ta in to e x p l i c i t form s. The program co n v e rte d th e d a ta o b ta in e d from th e t r a y a liq u a n t to th e t o t a l f r a c t i o n o f th e s p l i t and th e n to th e t o t a l sam ple. F or each s p e c ie s r e l a t i v e abundance (p e rc e n ta g e ), as w e ll a s a b s o lu te abundance (number/gm o f sedim ent) were d eterm in e d In each s iz e f r a c t i o n and cum ulated. The a r e a l d i s t r i b u t i o n o f each s p e c ie s In th e s u r fa c e sedim ents was an aly zed and maps o f p e rc e n t l s o l l n e s c o n s tru c te d f o r s e le c te d s p e c ie s . Because most o f th e | s p e c ie s I n d ic a tin g s i g n i f i c a n t tre n d s o c cu r In th e l a r g e r Isiz e f r a c t i o n , In o rd e r to e lim in a te th e tim e-consum ing |te c h n iq u e o f c o u n tin g sm a ll fa u n a s , m ostly specim ens i l a r g e r th an 250p were c o n s id e re d f o r s t r a t i g r a p h l c p u r p o s e s. Only f a u n a l assem b lag es w ith w e ll-p re s e rv e d t e s t s were c o n sid e re d f o r q u a n t i t a t i v e a n a ly se s In o rd e r to reduce th e b i a s In tro d u c e d by mixed fau n a. By making t h i s s e le c t io n i t Is a p p r e c ia te d t h a t p e rso n a l e r r o r cannot be e lim in a te d . However, even w ith th e e r r o r s in v o lv e d , th e |method is s u f f i c i e n t to o b ta in s i g n i f i c a n t p a t t e r n s o f th e a r e a l d i s t r i b u t i o n o f s p e c ie s . R a tio s o f th e r e l a t i v e abundance o f s e le c te d s p e c ie s , e s p e c ia lly r a t i o s o f warm to c o o l w ater s p e c ie s , have been used by some a u th o rs f o r b l o s t r a t l g r a p h i c and p a le o - te m p e ra tu re a n a l y s is (S tu b b in g s , 1939; Oba, 1967; Bandy et, a l . , 1971). T his te c h n iq u e was adapted f o r use In th e p r e s e n t s tu d y . R a tio s o f th e c o o le r s p e c ie s G lo b o r o ta lla 2 1 6 l n f l a t a to th e warmer s p e c ie s K eogloboauadrlna d u t e r t r e l were e s ta b lis h e d by co u n tin g ap p ro x im a te ly 100 specimens In th e f r a c t i o n c o a r s e r th a n 250p. C o llin g r a t i o s o f G lo b o r o ta lla tr u n c a t u ll n o l d e s were e s ta b li s h e d by co u n tin g a p p ro x im a te ly 100 In d iv id u a ls o f t h i s s p e c ie s In th e f r a c t i o n c o a r s e r than 250;i. G eneral Faunal C h a r a c t e r i s t i c s A b so lu te abundance o f f o r a m in lf e r s In th e su rfa c e sed im en ts I s I l l u s t r a t e d In F ig u re s 40 and 41. In th e same sample (c o re 379B, 0 -2 cm, a s an exam ple), a f o r a m ln lf e r a l number ( th e number o f f o r a m in lf e r s p e r gram o f dry sedim ent) o f ap p ro x im a te ly 170,000 when c o n s id e rin g specim ens l a r g e r th an 62ji c o rre sp o n d s to a f o r a m ln lf e r a l number o f a p p ro x im a te ly 30,000 f o r specim ens l a r g e r than 125ji, and to a v a lu e o f 6,000 f o r specim ens l a r g e r th an 250ji. These d if f e r e n c e s em phasize th e b ia s Involved In e x p re ss in g r e l a t i v e abundance o f f o ra m in lf e rs In a s e d i ment e i t h e r a s a w eig h t p e rc e n ta g e , o r a s a p a r t i c l e p e rc e n ta g e . The f o r a m ln lf e r a l number I n c re a s e s w ith d is ta n c e o ffs h o re and I n c re a s in g d ep th down to 3850 m. A fo ra m ln l f e r a l number ( c o n s id e rin g sp ecim e n s^ 6 2 j i ) o f l e s s th a n 10 e x i s t s on th e In n e r s h e l f n e a r th e Tugela and O nllahy R iv e r s , I n c re a s in g to s e v e r a l th o u san d s on th e upper s lo p e , and to v a lu e s In e x c e ss o f 50,000 (a s h ig h as F ig u re 40 Number o f f o ra m in lf e rs c o a r s e r th a n S 2 f i p er gram o f dry sed im en t. 217 218 30*E 35* 4 0 * 45'E I N H A M B A N E S ^ <10 10-100 100-1000 I0 0 0 -IQ 0 0 0 1 0 ,0 0 0 -5 0 ,0 0 0 > 5 0 ,0 0 0 D U R B A N /' F0RAM > 1 5 * S 20* 2 5 * 30* 3 5 * S Figure 41 Number o f p la n k to n ic f o r a m in if e r s c o a r s e r th an 250p p e r gram o f dry sed im en t. 219 220 ■ D A IN D IA * IN H A M B A N E S 1 0 0 -1 0 0 0 1 0 0 0 -5 0 0 0 5 0 0 0 -1 0 ,0 0 0 . > 10,000 PLANKTONIC FORAM > 250y7gm 2 2 1 s e v e r a l hu n d red s o f th o u san d s) below a p p ro x im a te ly 2000 m on th e low er slo p e and the c o n t i n e n t a l r i s e . A com parable tr e n d o f I n c re a s in g f o r a m ln lf e r a l number w ith In c re a s in g d e p th e x i s t s from W alter S h o a ls down th e s lo p e o f th e M adagascar P la te a u . On th e s h e l f and upper slo p e n e a r Inhambane, a h ig h e r f o r a m ln lf e r a l number r e f l e c t s th e winnowing a c tio n o f th e s tro n g Mozambique C u rre n t. On th e Mozambique P la te a u a h ig h number o f f o r a m in lf e r s ? 250jp, and a number o f f o r a m in lf e r s ^62ji low er th a n on th e a d ja c e n t slo p e s and In th e T ra n sk e i B a sin , r e f l e c t a low r a t e o f se d im e n ta tio n on th e p la te a u and th e p ro b a b le winnowing e f f e c t o f the A n ta r c tic In te rm e d ia te Water eddy c e n te re d th e r e . E s tim a tio n o f th e f o r a m ln lf e r a l number between d e p th s o f 3850 m and 4820 m was n o t p o s s ib le because o f a la c k o f sam p lin g . Below t h i s d e p th , which i s below the ly s o c l i n e (th e l e v e l o f g r e a t e s t change In fa u n a l com posi t i o n , B e rg e r, 1 9 7 0 ), th e f o r a m ln lf e r a l number f o r s p e c i mens } 6 2 p . in th e sedim ents o f th e N a ta l B asin d e c re a se s so u th e a stw a rd from s e v e ra l h u n d red s to l e s s th an 10. R e la tiv e abundance o f p la n k to n ic s p e c ie s In th e f o r a m ln lf e r a l p o p u la tio n s I n c re a s e s w ith d is ta n c e o f f s h o re . In th e fau n a l a r g e r th a n 62ji (F ig . 42) p la n k to n ic s p e c ie s com prise l e s s th an 15 p e r c e n t o f th e f o r a m ln lf e r a l assem blage on th e m iddle s h e l f , in c r e a s e s to a p p ro x i m a te ly 50 p e r c e n t a t th e s h e l f edge, and to 95 p e rc e n t o r Figure 42 P e rc e n ta g e o f p la n k to n ic f o ra m in lf e rs In th e f o r a m l n l f e r a l fauna c o a r s e r th an 62p. 2 2 2 223 IN H A M B A N E 1 % PLANKTONIC FORAM IN FAUNA > 6 2 ^ 224 more below a p p ro x im a te ly 1000 m down t o 3850 m. In th e N a ta l B asin , below 4620 m, p la n k to n ic s p e c ie s com prise a s l i t t l e as 15 p e r c e n t o f th e f o r a m ln lf e r a l fau n a a t th e so u th e rn s t a t i o n s . In th e n o rth e rn p o r tio n o f th e b a s in th e p e rc e n ta g e o f p la n k to n ic s p e c ie s h a s h ig h v a lu e s above 75 p e r c e n t, a p e rc e n ta g e anom alously h ig h a t d e p th s below th e calcium c a rb o n a te com pensation d e p th . Trends in f o r a m ln lf e r a l abundance, In th e N atal B a sin , c o n sid e re d p r e v io u s ly , a r e r e l a t e d to th e p re se n c e o f d is p la c e d s e d i m ents from b a th y a l d e p th s , which are r a p id ly b u r le d . R a d lo la rla n abundance I s d e p ic te d in F ig u re 43. The number o f r a d i o l a r l a n s l a r g e r th an 62ji o f dry sedim ent ra n g es from l e s s th a n 50 in m ost o f th e a re a to s e v e ra l th o u san d s In th e s o u th e rn p o r tio n of th e N a ta l B a sin . P tero p o d s o c c u r In abundance o n ly in s c a t t e r e d sam ples (F ig . 4 4 ). D i s t r i b u t i o n o f I n d iv id u a l P la n k to n ic S p e c ies The p la n k to n ic f o r a m ln lf e r a l fa u n a c o n ta in e d in th e s u rfa c e sedim ents o f th e a re a i s d i v e r s i f i e d and 35 s p e c ie s were i d e n t i f i e d . L iv in g s p e c ie s o f p la n k to n ic f o r a m in lf e r s in th e In d ia n Ocean have been grouped by v a rio u s a u th o rs in to zoogeographic p ro v in c e s which a r e in flu e n c e d p r im a r ily by ecology and c lim a te . In t h e i r broad stu d y o f th e A t l a n t i c Figure 43 Number o f r a d l o l a r l a n s c o a r s e r th a n 6 2 p p e r gram o f dry sed im en t. 226 IN H A M B A N E S ,' = 1 5 0 0 -1 0 0 0 > 1 0 0 0 D U RBA N , RADIOLARIANS > 6 2 /V g m Figure 44 Number o f p te ro p o d s p e r gram o f dry s e d i m ent. 227 228 IN H A M B A N E S ' D U RBAN, PTEROPODS/gm 229 and In d ia n o c e a n s, Be and T o ld e rlu n d (1971) d efin ed f iv e m ajo r p r o v in c e s : (1) a r c t i c and a n t a r c t i c , (2) s u b a r c tic and s u b a n t a r c t i c , (3) tem p erate o r t r a n s i t i o n zone, (4) s u b t r o p i c a l , and (5) t r o p i c a l . Each p ro v in c e c o n ta in s a d i s t i n c t s p e c ie s assem blage. B oltovskoy (1969a) re c o g n iz e d th e s e f i v e main w a te r zones in th e In d ia n Ocean and d is tin g u is h e d f iv e groups o f p la n k to n ic s p e c ie s : (1) c o ld - w a te r s p e c ie s , (2) c o ld -te m p e ra te s p e c ie s , (3) warm- te m p e ra te -w a te r s p e c ie s , (4 ) warm -water s p e c ie s , and (5) co sm o p o litan s p e c ie s . The te m p e ra tu re ra n g e o f each p la n k to n ic s p e c ie s h a s been o b serv ed by Be and T o ld erlu n d (1971) and was a ls o computed by com paring B o lto v sk o y 1s (1969a) d a ta on o ccu rren ce o f s p e c ie s to th e a c tu a l te m p e ra tu re d a ta g a th e re d a t each s t a t i o n (D iscovery Re p o r t s , Cam bridge, 1957, v o l. 2 8 ). U sing t h i s In fo rm a tio n , s p e c ie s were ranked a c c o rd in g to t h e i r maximum c o n c e n tra t i o n tow ard warmer te m p e ra tu re (T ab les I I and I I I ) . A few s p e c ie s a r e added which were n o t r e p o rte d by Be and T o ld e rlu n d and B oltovskoy in p la n k to n tow s, e i t h e r because th e y escaped th ro u g h p la n k to n n e ts (th e se i n v e s t i g a t o r s used p la n k to n n e ts w ith a 200ji mesh o p e n in g ), o r because th e y were lumped under a n o th e r ta x o n . These a re in d ic a te d w ith an a s t e r i s k in T ab les I I and I I I . G l o b o r o t a l l a pachyderm s (E h re n b e rg ). T his s p e c ie s o c c u rs m ain ly i n th e s iz e f r a c t i o n 125-177;: in th e so u th e rn a r e a u n d e rn e a th c o o le r s u rfa c e w a te r, and in th e s iz e 230 Table I I . P e rc e n ta g e s o f p la n k to n ic f o r a m ln lf e r a l s p e c ie s In f i v e s iz e f r a c t i o n s o f core 366B, 0-2 cm (2 3 ° 0 9 'S ., 43° o8 'E . ) . S p ecies a re ranked In the o r d e r o f th e te m p e ra tu re o f t h e i r maximum abundance In In d ia n Ocean w a te rs , u s in g d a ta from Be and T o ld e rlu n d , 1971, B oltovskoy, 1969a (combined w ith D iscovery R e p o rts, Cambridge, 1957, v o l. 2 8 ), and v a rio u s so u rces f o r s p e c ie s not r e p o rte d by th e s e I n v e s t i g a t o r s ( In d ic a te d w ith an a s t e r i s k ) . 250- 177- 125- 88- >250ix 177ii 125ii 88n 62m « I n v ’O V h w u o « « u > t o w « V u I 4J V •O < 0 D h m n o w U o. M g s 4J 4 i i a • » O 0 0 1 6 4J * H CO « H O O -4 V u o a a w i i m B V I C L O J S 4 J U m m v t v m m u m 9 Vi w • f f < 4 o « a. co M V * I g G lo b o r o ta lla p ach y derm a G lo b lg e r in ita u v u la G lo b lg e rln a q u in q u e- lo b a G lo b lg e rln a b u llo ld e s s.l. G lo b o r o ta lla i n f l a t a G lo b o r o ta lla tr u n c a - t u l l n o l d e s G lo b lg e r in ita g l u - t i n a t a G lo b lg e r in ita lo ta * G lo b lg e rln a d l g i t a t a * G lo b o g o ra lla h l r s u t a G lo b o r o ta lla c r a s s a - form ls G lo b o r o ta lla s c l t u l a T u r b o r o ta llta hum11Is* G lo b lg e rln a fa lc o n e n - s Is* G lo b lg e rln a sp . A* G lo b o r o ta lla c r a s s u la * O rbullna u n lv e r s a G lo b lg e rln a c a lld a * G lo b lg e r ln e lla slp h o n - l f e r a H a s tlg e rin a p e la g lc a G lo b lg e rln o ld e s ru b e r G lo b o r o ta lla m e n a rd ll s . l . G lo b lg e r ln e lla adam sl G lo b lg e rln o ld e s co n - g lo b a tu s 0 .4 0 .8 1 3 .4 3 2 .4 0 .7 1.1 3 .9 0 .6 5 .2 0 .3 0 .7 0 .3 0 .7 8.3 1 7 .9 0 .8 0 .4 1 3 .9 0 .8 0 .4 0 .9 0 .4 1 .2 0 .4 3 .3 0 .6 11 .4 0 .4 1.1 5.6 3 .0 1 .7 0 .4 3 .0 5.2 2 .4 0 .8 3 .0 0 .3 1 5 .0 10 .4 3 .2 0 .3 13.1 51 .7 36.1 4 .4 5.2 1.3 2 .8 3 .8 1 .1 3 .0 0 .8 Warm-water Species 231 Table I I . P e rc e n ta g e s o f p la n k to n ic f o r a m ln lf e r a l s p e c ie s In f i v e s iz e f r a c t i o n s o f core 366B, 0 -2 cm ( 2 3 ° 0 9 'S ., 4 3 ° 0 8 'E .) (C ontinued) 250- 177- 125- 88- >250p 177u 125P 8811 62u G lo b lg e rln a ru b e sc e n s 1 .7 7 .5 2 .7 0 .2 G lo b lg e rln o ld e s t e n e llu s * 0 .4 G lo b lg e rln o ld e s s a c - c u l l f e r 1 8 .0 6 .5 0 .4 S p h a e r o ld in e lla d e- h isc e n s* P u l l e n l a t l n a o b l i q u i - l o c u l a t a 1 0 .5 1 .3 N eogloboquadrina d u t e r t r e l 1 8 .7 7 .0 6 .7 1 .9 G lo b o ro ta lo ld e s h ex a- gonus Candelna n i t i d a 0 .4 T u r b o r o t a l lt a p u m illo 0 .8 6 .3 5*5 G lo b o r o ta lla tum ida G loboquadrina c o n g lo - m erata M is c e lla n e o u s , c h i e f l y J u v e n ile s 1 .9 1 .7 7 .3 1 5 .4 4 8 .0 Specimens/gm o f sedim ent 2670 2300 680419,76412,825 T able I I I . P e rc e n ta g e s o f p la n k to n ic f o r a m ln lf e r a l s p e c ie s In f iv e s iz e f r a c t i o n s o f co re 379B, 0-2 cm ( 3 2 ° 2 3 'S ., 4 2 ° 5 6 'E .) . S p e c ie s are ranked In th e o rd e r o f th e te m p e ra tu re o f t h e i r maximum abundance In In d ia n Ocean w a te rs , u s in g d a ta from Be and T o ld e rlu n d , 1971, B oltovskoy, 1969a (combined w ith D is covery R e p o rts, Cambridge, 1957* v o l . 2 8 ), and v a r io u s so u rces f o r s p e c ie s n o t re p o rte d by th e s e i n v e s t i g a t o r s ( In d ic a te d w ith an a s t e r i s k ) . j 2 5 0 - 172- 125- 88- _.250m 177)1 125M 88u 62ji 0 ) 1 M 01 •O 01 ^ u 0 G lo b o r o ta lla pachy- O * 01 U > CL derma 3 .8 7 .2 C O G lo b lg e r in ita u v u la G lo b lg e rln a q u in q u e- 0 . 6 0.3 <0 01 1 0) 0 lo b a 0 . 6 22.1 3 0 . 6 1 01 *0 < 0 CL G lo b lg e rln a b u llo ld e s , f-4 M C O 0 o> 8 . 1 . 2 . 6 8 .5 9 .7 a a u 6 0) G lo b o r o ta lla i n f l a t a 4 0 .1 1 9 .7 5 .9 2.8 Q ) 4J u (0 G lo b o r o ta lla tr u n c a - » t u l i n o i d e s 5 .7 1 .9 0 .9 1 C C O 1 0 0 1 0 ) G lo b lg e r in ita g lu - 18.1 6 4J *H W u t l n a t a 6 . 0 21.6 1 .4 O H O ) (j 0 a G lo b lg e r in ita io ta * 3.1 CL CO G lo b lg e rln a d i g i t a t a * G lo b o r o ta lla h l r s u t a 0 .5 1 1 C O E 3 0 ) 1 M 0 > 3 .6 0 . 6 0 .9 COfi 4 J4 J O XJ L j p t G lo b o r o ta lla c r a s s a - fo rm ls 1 .0 1 .2 C O G lo b o r o ta lla s c l t u l a 0 . 6 4 .1 2.1 0 .3 T u r b o r o t a l lt a h u m llls* 0 . 6 2 .5 5.1 G lo b lg e rln a f a lc o n - e n s ls * 1 .9 7 .2 0 .3 0 ) G lo b lg e rln a sp . A* 3 .1 4 .1 1 .8 O J •H G lo b o r o ta lla c r a s s u la * u V O rb u lln a u n iv e r s a 6 .3 0 .6 CL C O G lo b lg e rln a c a lid a * 3 .6 1 .3 L G lo b lg e r ln e lla slp h o n - 0) 4 -> l f e r a 9 .7 6 .6 3 .7 1 .2 5 H a s tig e r in a p e la g ic a 26.0 14.1 1 e G lo b lg e rln o ld e s ru b e r 1 0 .9 3 .1 E 4 G lo b o r o ta lla m e n ard li 3 s . l . G lo b lg e r ln e lla adamsl G lo b lg e rln o ld e s con- g lo b a tu s 1 .0 0 .3 0 .3 233 Table I I I . P e rc e n ta g e s o f p la n k to n ic f o r a m ln lf e r a l s p e c ie s In f iv e s iz e f r a c t i o n s o f co re 379B, 0 -2 cm ( 3 2 ° 2 3 'S ., 4 2 ° 5 6 'E .) (C ontinued) 250- 172- 125- 88- >250m 1 7 7 )X 125ft 88n_. 62^ to < D 0 a > P. m h a > + » as % 1 e a S :* G lo b lg e rln a r u b e s cens G lo b lg e rln o ld e s te n e llu s * G lo b lg e rln o ld e s s a c c u l l f e r S p h a e r o ld ln e lla d eh lscen s* P u l l e n l a t l n a o b l l q u i l o - c u la ta N eogloboquadrlna d u t e r t r e l G lo b o ro ta lo ld e s hexagonus Candelna n l t l d a T u r b o r o ta llta pu m lllo G lo b o ro ta lla tum lda G loboquadrina conglom erata M isc e lla n e o u s, c h i e f l y ju v e n ile s 1 0 .4 7 .2 Speclmens/gm o f sedim ent 0 .5 3 .1 0 .5 1.0 2.2 0 .3 3 .8 1 .9 0 .9 2.8 2.1 0 .9 9 .1 38.0 60.9 5537 7292 18,290 67,130 72,278 23 4 f r a c t i o n 88-125)1 In th e n o r th e rn and w este rn a re a s u n d er n e a th warmer s u rfa c e w a te r. T his s p e c ie s I s r a r e and was noted In o n ly about o n e - th ir d o f th e sam ples. I t o c c a s io n a l l y composes l e s s th an 1 p e rc e n t o f th e p la n k to n ic p o p u la t io n l a r g e r th an 125/1 In th e n o r th and w e st, In c re a s in g to about 5 p e rc e n t on th e M adagascar p la te a u . Specimens a re e n t i r e l y d e x t r a l ly c o lle d . G lo b lg e r ln lta u v u la (E h re n b e rg ). I n d iv id u a ls o f t h i s s p e c ie s a re m ainly s m a lle r th a n 88/i. O ccasio n al l a r g e r specim ens were n o te d , but alw ays s m a lle r th an 177/1. This s p e c ie s Is a b s e n t In th e n o r th and w est and con s t i t u t e l e s s than 1 p e rc e n t o f th e p la n k to n lc p o p u la tio n l a r g e r th an 62/i In a few s o u th e rn sam ples. G lo b lg e rln a a u ln a u e lo b a N a tla n d . T his s p e c ie s o ccu rs c h ie f ly In th e s iz e I n t e r v a l 62- 88/1 (a p p ro x im ately 60 p e rc e n t o f th e I n d iv id u a ls a re In t h i s s iz e f r a c tio n ) and a ls o in th e s iz e I n t e r v a l 88-125/1 (ab o u t 40 p e rc e n t o f th e i n d i v i d u a l s ) . Abundant th ro u g h o u t th e a r e a in the s m a ll-s iz e d fau n a, t h i s s p e c ie s c o n s t i t u t e s 15 to 20 p e r c e n t o f th e p la n k to n ic p o p u la tio n l a r g e r th a n 62/i. G lo b lg e rln a b u llo ld e s d 'O rb ig n y sensu l a t o . T y p ica l specim ens o f th e s p e c ie s , w ith a w ide-open a p e r tu r e , a re r a r e , w hereas forms w ith a more c o n s tr i c t e d a p e r tu r e , com parable m o rp h o lo g ic a lly to v a r i a t i o n s o f G. n ra e b u l- l o l d e s Blow, a re more common. The two form s were counted s e p a r a te ly b u t no d e f i n i t i v e tr e n d was n o ted in t h e i r r e - s p e c tlv e d i s t r i b u t i o n . The whole group o ccu rs p r in c ip a ll y in th e f r a c t i o n 125-177/1 (60 to 70 p e rc e n t o f th e i n d i v i d u a ls) and com prises ap p ro x im a te ly 3 p e rc e n t o f th e p o p u la t i o n l a r g e r th a n 125/1 in th e n o r th and w e st, in c r e a s in g to ab o u t 8 p e rc e n t in th e s o u th e a s t. G lo b o ro ta lla l n f l a t a (d 'O rb ig n y ) ( P ig . 4 5 ). M orp h o lo g ical v a r i a t i o n s o f t h i s s p e c ie s have been a n a ly z ed by Yen (1971) who in c lu d e d p o r tio n s o f th e m a te r ia l o f t h i s i n v e s t i g a t i o n in h e r s tu d y . G. l n f l a t a from t h i s I a r e a belong to th e " s u b tr ia n g u la r ty p e" o f Yen, c h a r a c te r - l jlz e d by a f l a t d o rs a l s id e and a r e l a t i v e l y a c u te p e r i p h e ry . This ty p e a ls o was n o ted by Yen in sedim ents o f th e s u b tr o p ic a l P a c i f ic Ocean. The w a ll t e x t u r e ran g es from smooth to h is p id w ith s h o r t b lu n t s p in e s . J u v e n ile forms have u s u a lly a more c o n s tr i c t e d a p e r t u r e , an a n g u la r p e r ip h e ry , a n g u la r - c o n ic a l chambers and a roughened w a ll. I n d iv id u a ls a r e l a r g e r th a n 125p and m ainly l a r g e r th a n 250/1. I t i s th e dom inant s p e c ie s in th e so u th u n d ern e a th th e S u b tro p ic a l W ater where i t com prises 40 to 55 p e rc e n t o f th e p la n k to n lc p o p u la tio n l a r g e r th an 250/ 1, and de c r e a s e s in r e l a t i v e abundance northw estw ard to v a lu e s as low as 1 p e r c e n t. The h ig h abundance observed in th e c e n t r a l p a r t o f th e ch an n el p ro b a b ly a re due to rew orking o f sed im en ts. In th e open S o u th In d ia n Ocean, B e lia e v a (1964) n o ted c o n c e n tra tio n s o f more th a n 1000 specim ens (> 1 0 0 /i)/ Figure 45 R e la tiv e freq u en cy o f G lo b o r o ta lla i n f l a t a in th e p la n k to n lc f o r a m in if e r a l fauna c o a r s e r th a n 250ji in s u rfa c e s e d im e n ts. 236 237 I N H A M B A N E s / 1 0 -4 0 % G. INFLATA (> 2 5 0 /0 238 gm o f sedim ent between l a t i t u d e s 40°S. and 5 0 °S ., d e c re a s ing to l e s s th an 100 between l a t i t u d e s 40°S. and 2 0 °S ., and a ls o p a tc h e s o f h ig h abundance o f f th e t i p o f South A fric a and n e a r th e P rin c e Edward and C ro zet I s la n d s . The a b s o lu te abundance o f G. l n f l a t a (>125;i) In th e s u rfa c e sed im en ts o f t h i s stu d y a re a I s 1000 to 6000 speclmens/gm In th e so u th , d e c re a s in g n orthw estw ard to ap p ro x im a te ly 30. These v a lu e s a re low er th a n v a lu e s a t th e same l a t i tu d e In th e open o cean, and may p o s s ib ly be r e l a t e d to th e p a tc h e s o f h ig h e r c o n c e n tr a tio n s o f f th e t i p o f South A fric a and n e a r th e P rin c e Edward and C ro zet I s la n d s . G. l n f l a t a p e rc e n ta g e i s o p l e t h s c o n s tru c te d by Be and T o ld e rlu n d (1971) from s u rfa c e p la n k to n d a ta In t h i s a re a a r e s i t u a t e d f u r t h e r so u th th an e q u iv a le n t I s o p le th s In th e sedim ents of t h i s s tu d y . N e ith e r s e le c t iv e s e le c t io n nor th e p re se n c e o f f o s s i l m a te r ia l a re re sp o n s i b l e f o r t h i s d isc re p a n c y b ecau se d ep th s o f o ccu rren c e a re above th e l y s o c l l n e , and a ra d io c a rb o n d ate f o r th e top 2 cm o f co re 385B in d i c a t e s a modern ag e. A w ider d i s t r i b u t i o n o f G. l n f l a t a In sed im en ts th an In o v e rly in g w a te rs was re p o rte d In th e N orth A t l a n t i c by Be and Hamlin (1967)* who a t t r i b u t e d t h i s d isc re p a n c y to re c e n t warming. T his h y p o th e s is I s n o t fa v o red by th e w r i t e r f o r th e study a r e a because d i s t r i b u t i o n o f o th e r s p e c ie s In both s e d i m ents and s u rf a c e w a te r a re In c lo s e agreem ent. The d i s crep an cy may be due to th e f a c t t h a t tows o f Be' and T o ld e r- 239 lu n d sampled o nly th e up p er 10 m o f w a te r. The d i s t r i b u tio n o f G. l n f l a t a In bottom sedim ents p ro b a b ly acco rd s w ith d i s t r i b u t i o n o f th e same s p e c ie s in in te rm e d ia te and d eep er w a te r m asses. G lo b o r o ta lla t r u n c a t u ll n o l d e s (d 'O rb ig n y ) ( P ig . 4 6 ). Throughout th e a re a th e s p e c ie s I s h ig h ly c o n ic a l, a s d es c rib e d by K enneth (1968) who used p a r t o f t h i s m a te r ia l to i l l u s t r a t e th e In te rd ep en d en c e between th e m orphology o f th e s p e c ie s and s u rfa c e w a te r te m p e ra tu re . Specimens are u s u a lly l a r g e r th a n 125;i and a re most abundant in th e f r a c t i o n l a r g e r than 250p. I t com prises 5 to 10 p e rc e n t o f th e p la n k to n lc p o p u la tio n l a r g e r th an 250J1 in th e so u th and d ecrease northw estw ard to 1-2 p e r c e n t. P ro v in c e s o f dom inantly d e x t r a l l y o r s l n i s t r a l l y c o ile d G. t r u n c a t u ll n o l d e s have been re p o rte d in w a te rs and sedim ents o f th e A t l a n t i c and In d ia n Oceans (E rlc so n and W ollin, 1954; Be and T o ld e rlu n d , 1971; P a r k e r, 1 9 71). The cause f o r th e change in c o i l i n g i s n o t f u l l y u n d e r sto o d alth o u g h th e r e i s an a p p a re n t r e l a t i o n s h i p w ith s u r fa c e te m p e ra tu re . D e x tra l p o p u la tio n s c o r r e l a t e w ith warmer s u rfa c e w a te r, and s i n l s t r a l p o p u la tio n s w ith c o o le r s u rfa c e w a te r, b u t th e te m p e ra tu re dependence i s n o t a s c l e a r l y d e fin e d a s f o r th e c o i l i n g r a t i o s o f G lo b o r o ta lla pachyderm a. In th e w a te rs o f th e South In d ia n Ocean, Be and T o ld erlu n d (1971) no ted a d i s t i n c t l a t i t u d i n a l b e l t o f s i n l s t r a l G. tr u n c a t u ll n o l d e s between Figure 46 R e la tiv e freq u en cy o f G lo b o r o ta lla tr u n c a - t u l i n o i d e s in th e p la n k to n lc f o r a m in if e r a l fau n a c o a r s e r th a n 250ji in s u rf a c e s e d i m en ts. 240 241 IN H A M B A N E D U R B A N , G . TRUNCATULINOIDES > 2 5 0 / 242 30°S. and 5 5 ° S ., which te n d s so u th o f M adagascar in a southw estw ard d i r e c t io n In acco rd w ith th e A gulhas C u rren t p a t t e r n . The boundary betw een s i n l s t r a l and d e x t r a l popu l a t i o n s o f G. tr u n c a t u ll n o l d e s they d e p ic te d c o in c id e s ro u g h ly w ith th e boundary n o ted In t h i s stu d y In the s e d i ments o f th e southw est In d ia n Ocean (F ig . 4 7 ). A d iffe re n c e e x i s t s between th e p a t t e r n o f t h i s study and th e one p r e sen te d by Be and T o ld erlu n d , nam ely, th e p ro v in c e of dom inantly s i n l s t r a l G. t r u n c a tu lln o ld e s in th e sedim ents e x te n d s tow ard th e e a s te r n s id e o f th e Mozambique Channel in th e a re a n e a r T u le a r (no p la n k to n d a ta were a v a ila b le fo r Be and T o ld e rlu n d In th e T u le a r a r e a ) . I t I s In th e a re a n e a r T u le a r t h a t warm est s u rfa c e te m p e ra tu re s were re c o rd e d , and sedim ents in t h i s p a r t o f th e channel I n clude t r o p i c a l fa u n a l assem b lag es. Thus, I t i s proposed th a t th e c o i l i n g d i r e c t io n o f G. tr u n c a t u ll n o l d e s i s n o t e n t i r e l y c o n tr o lle d by te m p e ra tu re and i t i s p ro b ab le t h a t more th a n one p a ram e ter Is In v o lv e d . Thlede (1971) su g g e ste d t h a t th e r e may be a r e l a t i o n s h i p between th e c o l l ing r a t i o d i s t r i b u t i o n o f G. tr u n c a t u ll n o l d e s in the N orth A t l a n t i c and th e averag e s a l i n i t y . No d e f i n i t e c o n clu sio n i s a tte m p te d from d a ta o f th e p r e s e n t stu d y because o f I t s r e s t r i c t e d g e o g ra p h ic a l e x t e n t . As w ill be d is c u s s e d , a s h i f t in th e c o i l i n g r a t i o o f G. t r u n c a t u l l n o l d e s . which o c cu rre d h e re a t ap p ro x im a te ly 6000 y e a rs B .F ., may p o s s ib ly be r e l a t e d w ith a s u rfa c e w a te r s a l i n i t y change. Figure 47 D i s tr i b u t i o n o f dom inantly s i n l s t r a l and dom inantly d e x tr a l p o p u la tio n s o f G lo b o r o ta lla t r u n c a tu lln o ld e s c o a r s e r th a n 250f i in s u rfa c e sed im en ts. 243 244 IN H A M B A N E S / SINISTRAL m DEXTRAL D U R B A N , COILING G . TRUNCATULINOIDES 249 G lo b lg e r ln lta g lu tln ftta (Egger). Sixty to 70 p e r cen t o f the in d iv id u a ls o f t h i s sp ecies occur in the f r a c t i o n 88-125 p $ 20 to 30 p e rc e n t in th e f r a c tio n 125- 177/i» 2 to 5 p e rc e n t in the f r a c tio n 177-250/1, and only o ccasio n a l specimens occur in th e f ra c tio n 250/1. G. g l u t l n a t a is an abundant component o f s m a ll-siz e d plank- to n ic p o p u la tio n s. I t comprises 10-20 p e rc e n t o f popula tio n s la r g e r than 88/x, 10-20 p e rc e n t o f p o p u latio n s la r g e r than 125/1, 3-4 p e rc e n t o f popu latio n s l a r g e r than 177/1, and l e s s than 1 p e rc e n t o f p o p u la tio n s la r g e r than 250/1. No a r e a l tren d in th e d i s t r i b u t i o n o f t h i s sp ecies was ob served. G lo b lg e r ln lta l o t a P ark er. This sp ecies is ra re and sc a rc e ly d i s t r i b u t e d and occurs la r g e ly in the size f r a c tio n 88-125/1 and 125- 177/1. I t s frequency in th e fauna la r g e r than 88/1 u s u a lly i s l e s s than 0 .5 p e rc e n t and r a r e l y reaches 1 p e rc e n t. This small sp e c ie s is not re p o rte d from th e plankton b u t in South P a c if ic sediments occurs w ith high fre q u e n c ie s in the t r o p i c s and low f r e quencies in A n ta rc tic reg io n s (P arker and Berger, 1971). In Tables I I and I I I t h i s sp ecies i s Included w ith the cosmopolitan s p e c ie s , to g e th e r w ith G. g l u t l n a t a . i t s p re sumed an c e sto r (P a rk e r, 1967)- G loblgerlna d l g l t a t a Brady. This sp e c ie s i s ra re and occurs only in a few samples. L i t t l e in form ation is a v a ila b le on th e a r e a l d i s t r i b u t i o n o f t h i s sp ecies in 246 both w aters and sedim ents. G lo b o ro ta lla h l r s u t a (d 'O rb lg n y ). This species Is mainly la r g e r than 125/1 and approxim ately 50 p ercent o f the In d iv id u a ls occur In the f r a c tio n 250/1. I t occurs In most samples and comprises 1 to 2 p e rc e n t o f th e planktonlc fauna la r g e r than 250/i In the n o rth and w est, in cre a sin g to 4 p e rc e n t to the so u th e a st. G lo b o ro ta lla crassafo rm ls (Galloway and W lssle r). This sp e c ie s, which i s mainly l a r g e r than 177)1, i s ra re and comprises 1 p ercen t o r l e s s o f the fauna la r g e r than 177)i as w ell as o f th e fauna l a r g e r than 250ji. Patches of h ig h e r freq u en cies (3-4 percent) in the Zambezi Canyon area probably a re due to the presence o f reworked f o s s i l s . G lo b o ro ta lla s c l t u l a (Brady). For th e most p a r t t h i s sp ecies occurs in the f r a c tio n 88-125/1 (approximately 60 p e rc e n t o f th e In d iv id u a ls ), and in the f ra c tio n 125- 177/1 (approxim ately 30 percen t) and was n o t found in the f r a c tio n l a r g e r than 250/1. Specimens from the northw estern samples are s l i g h t l y c o a rse r than in th e rem ainder o f the a re a . I t c o n s titu te s le s s than 1 p ercen t o f the fauna l a r g e r than 88/1 in the n o rth and w est, and in c re a se s to 2-3 p e rc e n t in th e s o u th e a st. T u r b o r o ta llta hum llls (Brady). Approximately 70 p e rc e n t o f the specimens occur in the f r a c t i o n 62- 88/1, 30 p e rc e n t in the f r a c t i o n 8 8- 125/1, 1-2 p e rc e n t in the fraction 125-177u, and none in f r a c tio n s c o a rs e r than 177/1. This 2471 sp e c ie s comprise 3 to 5 p ercen t o f the fauna la r g e r than 62p and shows no d e f i n it e d i s t r i b u t i o n a l tre n d . Because of I t s small siz e t h i s sp e c ie s I s not re p o rte d In plankton tows (although Boltovskoy, 1969a, r e f e r s to ra re Globl g e r l n l t a sp. c f. G. h u m llls ) . and I t s d i s t r i b u t i o n In sediments has been poorly in v e s tig a te d . In the South P a c i f ic , T. hum llls is r e l a t i v e l y most abundant in d i s solved t r o p i c a l and high l a t i t u d e samples (P arker and B erger, 1971). I d the Andaman Sea i t composes as much as 40 p ercen t o f the fauna l a r g e r than 62ji (F re ric h s , 1971), a value much h ig h er than in th e southern Mozambique Channel a re a . D is tr ib u tio n a l tre n d s of I . hum llls were observed In P le isto c e n e and Holocene sediments o f the N ortheast A tla n tic w ith h ig h e r abundances In the Holocene (V incent, 1968; Caralp, 1971; Thiede, 1971). From th ese d a ta , T. h u m llls Is Included w ith warm-water species (Tables I I and I I I ) . G lo b lg erln a fa lc o n e n sls Blow. This sp ecies is most common in th e f r a c tio n s 8 8- 125;* (40 to 50 percen t of th e in d iv id u a ls ) and 125-177;* (a ls o 40 to 50 p e r c e n t), Is l e s s common in th e fra c tio n 177-250J* (3 to 10 p e rc e n t), and only o c c a s io n a lly in the f r a c t i o n >250;*. I t c o n s titu te s 4 to 8 p e rc e n t o f th e fauna l a r g e r than 125^ w ith no d e f i n it e d i s t r i b u t i o n a l tre n d . This s p e c ie s has n o t been re p o rte d from the p lan k to n , except f o r one sample a t 17°S. in th e South P a c if ic (P arker, 1962). I t was included w ith G lo b lg erln a b u llo ld e s by Be and Tolderlund (1971) who c ite d a m orphological c lln e from G. b u llo ld e s s . s . of sub p o la r w aters to G. fa lc o n e n s ls o f s u b tro p ic a l w a te rs. Dis t r i b u t i o n of th e sp e c ie s In sediments Is poorly known because I t has probably been grouped w ith G. b u llo ld e s by most workers. In th e South P a c if ic I t Is more common In tem perate zones than In th e tr o p ic s (P a rk e r, 1962, 1967. ! j G loblgerlna sp . A. A form which p re se n ts morpho l o g i c a l a f f i n i t i e s w ith th e sp ecies G lo blgerlna bulbosa LeRoy has been counted s e p a ra te ly . Like G. b u llo ld e s and £.. fa lc o n e n s ls . t h i s form occurs p rim a rily in the f r a c tio n 125-177)1, i t s frequency is from l e s s than 1 p ercen t to 2 i p e rc e n t o f the fauna la r g e r than 125p , and no d i s t r i b u t l o n - jal tre n d is a p p a re n t. i G lo b o ro ta lla c r a s s u la Cushman and S tew art. Forms comparable to th e ones p resented by P arker (1962) as G lo b o ro ta lla h l r s u t a v a r ia n t group 3* which she r e f e r r e d l a t e r to G. c r a s s u la (P a rk e r, 1967), occur In t h i s area w ith a low frequency. P ark er and Berger (1971), in a re c e n t fo ra m ln ife ra l study in the South P a c if ic , discussed j !th e taxonomy o f t h i s form. They noted t h a t the holotype o f G. c ra ss u la as re fig u r e d by Blow (1969) is k eeled , but t h a t examined topotypes are n o t, and they r e f e r t h e i r P a c i f ic sp ecies to G lo b o ro ta lla sp. A (= G. h l r s u t a group 3, P ark er, 1962; and G. c r a s s u la P a rk e r, 1967), and G lo b o ro ta lla sp. B (= G. h l r s u t a p a r t o f group 1, P a rk e r, 249 1962, h e r p i. 5» figs* 12, 14; a form In te rm ed iate between &. sp. A and &• h l r s u t a ) . This sp ecies l i k e l y has been Included by workers w ith £. h l r s u t a . U nlike the l a t t e r , forms r e f e r r e d to as G. c r a s s u la In t h i s study have a f l a t d o rsa l sid e and a narrowly rounded p e rip h e ry (o cca sio n a lly w ith a poorly developed k e e l ) . They occur In f ra c tio n s l a r g e r than 125/1 and c o n s ti t u t e approxim ately 1 percent of the fauna l a r g e r than 250/x In most samples under Tropical Water, and l e s s than 1 p e rc e n t o r are ab sen t In samples under S u b tro p ic a l Water. A patch o f h ig h e r frequency, about 3 p e rc e n t, Is p re se n t In th e n o rth e rn are a . Right i c o llin g In d iv id u a ls a re dominant. O rhullna u n lv ersa d'O rblgny (P ig . 4 8 ). Various sp ecies and genera were found a tta c h e d in s id e orbullne chambers In th e p re se n t m a te r ia l in clu d in g Neoglobocuadrlna d u t e r t r e l . The m a jo rity o f o rb u lln e s broken by th e a u th o r, however, rev ealed an empty chamber, and many showed a t tached G lo b lg erln a b u l l o l d e s . One o f th e l a t t e r specimens was I l l u s t r a t e d by Bandy (1966), who r e p o rte d th a t ”0 r b u lln a u n lv e rs a ” is a f i n a l s p h e ric a l chamber a s so c ia te d w ith d i f f e r e n t sp ecies and genera. ”O rbullna u n lv e rs a ” occurs dominantly In the f r a c tio n >250^ (70 to 90 p ercen t o f th e I n d iv id u a ls ) , has h ig h e r fre q u e n c ie s on the Madagascar and Mozambique P la te a u s and n ear Europa (5-10 p ercen t) and lower f r e quencies (1-5 p ercen t) In the rem ainder o f th e are a . Figure 48 R elativ e frequency o f Orbullna u n lv ersa in the p lan k to n lc f o ra m ln lf e ra l fauna c o a rs e r than 250p In su rfa c e sedim ents. 2 5 0 251 30* E IN H A M BA N E 1- 5 % D U R B A N /' /o t 5 - 1 0 % 3 5 * S 0 W O 200 3 0 0 0. UNIVERSA 0 2 5 9 /') ^ ^ 5 ™ _______________ I----------------------------1 --------- --------- 377115^8 ; 252 G loblgerlna c a lld a P a rk e r. This sp e c ie s was r e p o r t ed In tows o f the Indian Ocean only by U jiie (1968) who noted I t s h ig h e r c o n c e n tra tio n In th e C entral Water. Be and Tolderlund (1971)* f o r whom G. c a lld a may be an I n t e r m ediate form between G. b u llo ld e s and G. s ip h o n I f e r a , grouped forms th a t resemble G. c a lld a w ith G. s ip h o n I f e r a . Most I n v e s tig a to r s who did not recognize G. c a lld a l i k e l y have included t h i s sp ecies w ith e i t h e r G. s lp h o n lfe ra or G. b u llo ld e s ( f o r example, B e lia e v a , 1964). Pull-grow n forms a re l a r g e r than 177ji and m ainly la r g e r than 250/1. Sm aller specimens resemble c lo s e ly G. b u llo ld e s and a re not easy to d i f f e r e n t i a t e . G. c a lld a i s ra re w ith freq u en cies o f le s s than 1 p ercen t to 4 p e rc e n t in th e fauna >250ji, w ith h ig h e r abundances u s u a lly noted under T ropical Water. G lo b lg e r ln e lla s lp h o n lfe ra (d'O rbigny). All gradual v a r i a t io n s in tig h tn e s s o f c o l l i n g , from t i g h t to lo o se , and in method o f c o ilin g , from tro c h o id a l to p l a n l s p i r a l , were observed. Young forms are u s u a lly tro c h o id a l and resemble G. b u l l o l d e s . M orphological types were d i s tin g u ish e d and counted s e p a ra te ly , but no d e f i n i t e tre n d in t h e i r d i s t r i b u t i o n was n oted, and a l l forms were, t h e r e f o r e , c l a s s i f i e d to g e th e r. G. slp h o n lfe ra occurs mainly in the f r a c t i o n s l a r g e r th an 12^i, and c o n s ti t u t e s 13 to 18 p e rc e n t of th e fauna l a r g e r than 250p w ith h ig h e r fre q u e n c ie s under T ropical Water. Be and Tolderlund (1971), who noted th a t the p r e fe r r e d h a b i t a t of t h i s s p e c ie s , to - 253 g e th e r w ith u n lv e r s a . i s in c u rre n t systems o r along c o n tin e n ta l m argins, re p o rte d i t s high abundance in th e i Agulhas-Somali C urrent. H a stlg e rln a n e la g lc a (d 'O rb ig n y ). This sp ecies occurs only in a few samples. I t s r a r i t y in sedim ents i s / probably r e la te d to the f r a g i l i t y of i t s w a ll. Be and jTolderlund (1971) re p o rte d a h igh c o n cen tratio n (>20 p e r cent) in t h i s a re a . G reater abundance of t h i s sp e c ie s in I surface w aters than in u n d erly in g bottom sedim ents has been rep o rted in the In d ia n Ocean (B ellaev a, 1964) and in th e j iSouth P a c if ic (P ark er and B erg er, 1971). | G lo b lg erln o ld es ru b er (d'Orbidny) (P ig . 4 9 ). This sp ecies occurs m ainly in th e f r a c t i o n 125-177)1 (30-50 p e r cent o f the in d iv id u a ls ) , and i s common in the f r a c t i o n s 88-125)* (10-20 p e rc e n t) and 177-250)* (20-30 p e r c e n t). Ap proxim ately 10 p e rc e n t o f the in d iv id u a ls occur in the f r a c tio n >250)*. I t s c o n trib u tio n to the fauna l a r g e r than 250)* i s g r e a te r in th e reg io n o f th e T ropical Water (15- 30 p e r c e n t). S a l i n i t y is an Im portant c o n tr o llin g f a c t o r in the d i s t r i b u t i o n o f G. ru b e r (Be and T olderlund, 1971) and may p o ssib ly in flu e n c e i t s d i s t r i b u t i o n in sedim ents of t h i s a re a . The low est frequency (5 p ercent) i s in th e area o f the eddy c e n te re d a t 3 5°S ., 35°®»* where su rfa c e s a l i n i t y i s th e h ig h e s t, whereas f u r th e r e a s t on th e Madagascar P la te a u G. ru b e r is more freq u en t (5-10 p ercen t) even though the tem p eratu re i s lower (compare F ig s. 24, 25 Figure 49 R e la tiv e frequency o f G lo b ig erln o ld es ru b er In the p la n k to n lc f o ra m ln lfe ra l fauna c o a rse r than 250ji in su rface sedim ents. 254 255 IN H A M B A N E S 'j DURBAN, G. RUBER > 2 5 0 / 256 and 49). G lo b o ro ta lla m enardll (d'O rbigny), senau l a t o (P ig. 50). Typical specimens of the species are r a r e . Rare specimens of G. m enardll flm b rla ta and G. o f. u n g u lata are Included In t h i s group because of t h e i r r a re o ccu rren c es. Specimens of th e group are g e n e ra lly la rg e r than 177)1 and dominantly l a r g e r than 2 50 ( 70 percent o f th e in d iv id u a ls are in the l a t t e r c a te g o ry ). At a few s ta t i o n s n ear T ulear, sm aller s iz e s a r e common. The r e l a t i v e frequency of members o f t h i s group is 2 to 5 p ercent in the a rea under T ropical Water n e a r the A frican and Malagasy c o a s ts , in c re a se s to 5~10 p e rc e n t on th e o u te r edge o f t h i s w ater mass and d ecreases southward to le s s than 2 p e rc e n t. Be and Tolderlund (1971) noted a fragm entation of the maximum abundance range o f l i v i n g G. m enardll in the Indian Ocean w ith two peaks o f abundance a t 16-17°C and 20-25°C. The tem perature i n t e r v a l 17°C-20°C between these two peaks correspond to th e w in te r tem perature of S u b tro p ic a l Water. Specimens o f G. m enardll are u su a lly en cru sted in samples deeper than 500 m, but in shallow er samples they are not. G lo b lg e rln e lla adamsl (Banner and Blow). Only a few in d iv id u a ls o f t h i s sp e c ie s occur in th e n o rthw estern a re a . G lo b lg erln o ld es conglobatus (Brady) (P ig. 51). This sp ecies i s l a r g e r than 125)» and occur mainly in th e f r a c - Figure 50 R e la tiv e frequency of th e G lo b o ro ta lla m enardll group in the p lan k to n lc foram in i- f e r a l fauna c o a r s e r than 250^ in su rfa c e sedim ents. 257 258 IN H A M B A N E 1 D U R B A N , 6. MENARDII GROUP (> 2 5 0 /) Figure 51 R e la tiv e frequency o f G lo b lg erin o id ee conglo- b a tu s in the p lan k to n ic f o ra m in if e ra l fauna c o a rs e r than 250ji in su rfa c e sedim ents. 259 2 6 0 IN H A M B A N E S / G . CONGLOBATUS (> 2 5 0 /) 2 6 1 t lo n ^ 250/ 1, w ith approxim ately 60 p ercen t o f th e I n d iv i duals In the l a t t e r f r a c t i o n . I t s frequency Is l e s s than 1 percent o f th e fauna la r g e r than 250/1 In the south, In c re a sin g northw estward to 5 p e rc e n t, w ith h ig h e r values between 5 and 10 p e rc e n t a t two s ta t i o n s on the c o n tin e n ta l r i s e In th e southern p a r t o f th e channel. G lo b lg e rln a rubescens Hofker (P ig . 52). Ninety percent o f the In d iv id u a ls o f t h i s sp e c ie s occur In the I n te rv a l 88-177/t. At s ta tio n s under T ro p ical Water G. rubescens occurs eq u ally in th e two f r a c t i o n s 88- 125/1 and 125-177/1, whereas in samples from beneath S u b tro p ic a l Water I t I s more common in th e f r a c t i o n 88-125/1. A tre n d In the a r e a l d i s t r i b u t i o n o f t h i s sp e c ie s e x i s t s when con s id e rin g th e fauna from the s iz e f r a c tio n 125-177/1. G. rubescens comprises 3-5 percen t o f th e fauna from t h i s s iz e I n te r v a l , in the south, and in c re a se s northwestward to 5-10 p e rc e n t. G lo b lg e rln o ld e s te n e l l u s P ark er. This sp ecies which occur mainly in th e f r a c t i o n 125-177/1 is r a r e and never reaches 1 p e rc e n t of th e fauna l a r g e r than 125/i. I t was found only in a few samples lo c a te d under T ro p ical Water. Secondary d o rsa l a p e rtu re s a re o fte n c o n s tr ic te d and the sp ecies may be taken f o r w hite G lo b lg erln a ru b e sc e n s. G lo b lg e rln o ld e s s a c c u l l f e r (Brady) (F ig . 53). Larger than 125/1, t h i s sp ecies occurs mainly In the f r a c t io n ^250/i. I t i s a dominant sp ecies a t th e northw estern Figure 52 R e la tiv e frequency o f G lo b lg erln a rubeecene In th e p lan k to n lc fo ra m ln lfe ra l fauna In the s iz e f r a c t i o n 125-177)1 In su rfa c e s e d i ments. 2 6 2 IN H A M B A N E S < D U R B A N , G . RUBESCENS (1 2 5 /-1 7 7 /) Figure 53 R e la tiv e frequency of S lo b ig e rin o id e s sac- c u l i f e r in the p la n k to n lc f o ra m in if e ra l fauna c o a rse r th an 250p . in su rfa c e sedim ents. 264 265 IN H A M B A N E 1 DURBAN J> G . SACCULIFER (>250/») 2 6 6 s t a t i o n s , where I t com prises 15-30 percen t o f th e fauna la r g e r than 250/1, and decreases southeastw ard to ap p ro x i mately 5 p e rc e n t. The low est frequency of G. s a c c u l l f e r Is as G. ru b e r In th e a rea o f the southern su rfa c e eddy. Forms w ith and w ithout a f i n a l s a c - lik e chamber are both p re s e n t. S p h a e ro ld ln e lla dehlscens (P arker and Jo n e s)(F ig . 54). This sp ecies Is not re p o rte d In plankton tows by Boltovskoy (1969a) and Be/ and Tolderlund (1971). The l a t t e r in v e s t i g a t o r s reg ard I t as an ab eran t te rm in a l stag e o f G. s a c c u l l f e r and in clu d e i t w ith t h i s s p e c ie s . Bel- iaev a (1964) noted r a r e occurrences of S. d ehlscens in w aters o f th e Indian Ocean in is o la te d patches n o rth of 10°S. I n te r n a l chambers o f broken specimens o f S. de h lsce n s in t h i s m a te r ia l are r e f e r r a b l e to G. conglobatus and to £ . s a c c u l l f e r . w ith a h ig h e r frequency o f th e l a t t e r . S. dehlscens occur e s s e n t i a l l y in the f r a c t i o n >250/1 but never reach 1 p e rc e n t o f the pop u latio n l a r g e r than 1 p e rc e n t and i s p re s e n t only in the western a r e a . P u l l e n l a t l n a o b ll a u l l o c u l a t a (Parker and Jones) (F ig. 55). This sp e c ie s occurs predom inantly in the f r a c tio n >250/i (approxim ately 80 p ercen t o f the in d iv id u a ls ) , and comprises 5-10 p e rc e n t o f the fauna la r g e r than 250/1 in the n o rth w est, d e c re a sin g southeastw ard to l e s s than 1 p e rc e n t. Figure 54 R e la tiv e frequency o f S p h a e ro id ln e lla de- hisce n s in the planfctonic fo ra m in ife ra l fauna c o a rse r than 250^1 in su rface sedim ents. IN H A M B A N E S ' DURBAN; < 1% S. DEHISCENS ( > 2 5 0 /) Figure 55 R e la tiv e frequency o f P u lle n ia tln a o b l i a u i - lo c u l a t a in the p lan k to n ic fo ra m in lf e ra l fauna c o a rse r than 250)i in su rfa c e s e d i m ents. 269 2 7 0 i n h a m b a n e v ''A DURBAN; P . OB IQUILOCULATA 0 2 5 0 /) 271 Neogloboauadrlna d u t e r t r e l (d'O rbigny) (P ig . 56). In t h i s p o rtio n o f the southw est Indian Ocean specimens of t h i s sp ecies are r e f e r r a b l e to the su b sp ecies N. d u t e r t r e l d u t e r t r e l w ith u m b ilic a l fla p s and were i l l u s t r a t e d by Bandy, P re ric h s , and Vincent (1967, t h e i r p i . 14, f ig s . 10-12). I t occurs mainly in th e f r a c tio n s la r g e r than 125}i and i s eq u ally re p re s e n te d in th e f r a c tio n s 125- 177^1, 177-250jj and ^250ji. N. d u t e r t r e l i s a main component o f the fauna la r g e r than 250p n e a r the A frican c o a s t, with freq u en cies o f 20-25 p e rc e n t, decreasing southeastw ard to l e s s than 5 p e rc e n t. In su rfa c e w aters o f th e Indian Ocean Be and T older- lund (1971) re p o rte d a tem perature range o f 14 to 30°0 f o r t h i s sp ecies w ith peaks o f abundances at 18°C, 22°C, and 24°C, whereas Boltovskoy (1969a) noted a warmer tem perature range o f 25°C to 29°C w ith a maximum a t 27°C to 29°c. The data o f th e l a t t e r au th o r were se le c te d in ranking th is s p ecies in Tables I I and I I I because Be and Tolderlund b e lie v e t h a t N. d u t e r t r e l grades in to G lo b o ro ta lla pachy derms, a concept not shared by the w r i te r . D iscrepancies in the d i s t r i b u t i o n a l tre n d s o f N. d u t e r t r e l in th e su r- / face w ater of t h i s a re a , as noted by Be and Tolderlund, and in the sedim ents is no t discussed fo r th e same reaso n . G lo b o ro ta lo ld es hexagonus (N atland). This sp ecies is r a r e and s p a rs e ly d i s t r i b u t e d . I t s frequency never reach es 1 p e rc e n t o f th e fauna l a r g e r than 250p. Figure 56 R e la tiv e frequency o f Neogloboauadrina d u t e r t r e i in th e p la n k to n ic f o ra m in if e ra l fauna c o a rs e r than 250p in su rface s e d i ments. 2 7 2 273 30*E IN H A M B A N E 5 -1 0 % 10- 20 % 2 0 - 2 5 % 0 1 0 0 2 0 0 3 0 0 K N N. DUTERTREI 0 2 5 0 / ) I ________________ I DURBAN, 2 7 4 Caodelna n l t l d a d 'O rb ig n y (P ig . 5 7 ). O ccu rrin g a t m ost w estern s t a t i o n s and n e a r th e M alagasy c o a s t, t h i s s p e c ie s has a freq u en cy in th e fau n a l a r g e r th an 250^ o f l e s s th an 1 p e r c e n t. T u r b o r o ta llta n u m lllo P a r k e r. T his s p e c ie s is p r e dom inantly between 88 and 125ji. S ix ty to 70 p e rc e n t o f th e specim ens o ccu r in t h i s s iz e i n t e r v a l , and th e rem ain d er in th e f r a c t i o n s 62-88ji and 125-177^* I t com prises a p p ro x i m ate ly 4 p e rc e n t o f th e fau n a l a r g e r th an 88;i a t most s t a t i o n s under th e T r o p ic a l W ater and ap p ro x im ate ly 1 p e r c e n t, o r l e s s , a t th e m a jo r ity o f s t a t i o n s b en eath th e Sub t r o p i c a l W ater. In th e p la n k to n t h i s sm all s p e c ie s was n o t re p o rte d by Be and T o ld e rlu n d (1971) b u t was n o ted by B oltovskoy (1969a) w ith a te m p e ra tu re ran g e o f 27°C-29°C. G lo b o r o ta lla tum lda (B rad y ). T y p ic a l specim ens o f th e s p e c ie s a re r a r e . They a re m ainly l a r g e r th an 250p and n ev er re a c h 1 p e rc e n t o f th e fau n a l a r g e r th an 250j i . G loboouadrlna co n g lo m erate (S chw ager). Only s c a t t e r e d o c c u rre n c e s o f t h i s s p e c ie s a re n o ted w ith a low freq u en cy ( le s s th an 1 p e rc e n t o f th e fauna >250/i) in th e w este rn sam ples. Figure 57 R e la tiv e freq u en cy o f Oandelna n i t l d a in th e p la n k to n ic f o r a m in if e r a l fau n a c o a r s e r than 250p in s u rf a c e se d im e n ts. 275 IN H A M B A N E S ; DURBAN, C. NITIDA (> 2 5 0 /) STRATIGRAPHY G eneral S u b su rface sed im en ts were a n aly zed In c o re s a t a 10-cm I n t e r v a l f o r l i t h o l o g y , c o lo r , calcium c a rb o n a te c o n te n t and sand s iz e f r a c t i o n c o n te n t. R adiocarbon m easurem ents were made on s e le c te d sam ples. F aunal con t e n t was q u a l i t a t i v e l y a n a ly z e d In a l l sam p les, and some c o re s were s e le c te d f o r q u a n t i t a t i v e s tu d y . G rain s iz e p a ra m e te rs were s tu d ie d on s e le c te d c o re s by Sherman (1 9 6 6 ), and by H. K arl and B. Robinson ( p e r s . comm.). B o u n d aries were p la c e d a t th e m id p o in t o f th e co re I n t e r v a l In which th e y a re re c o rd e d . A rea o f f Durban, E a st o f th e Mozambique P la te a u Most o f th e 14 c o r e s from th e s h e l f and slo p e s h a llo w e r th a n 1820 m show a marked downcore I n c re a s e In t h e i r sand f r a c t i o n c o n te n t (an a v e ra g e In c re a s e o f 40 p e r c e n t ) . Calcium c a rb o n a te c o n te n t shows a p a r a l l e l downward in c re a s e o f a p p ro x im a te ly 15 p e rc e n t In c o re s from th e slo p e b u t was n o t m easured In c o res from th e s h e l f . G rain s iz e p a ra m e te rs o f th e to p 10 cm and bottom 10 cm o f m ost co res from th e s h e l f and o f one c o re from 277 278 th e slo p e were s tu d ie d by Sherman (1966) an d H. K a rl ( p e r s . comm.). The sam ples a n a ly z e d range betw een s i l t s , sandy s i l t s and s i l t y sa n d s. Cores Bhow an averag e In c re a s e o f 1 1 .4 p e r c e n t In mean g r a in siz e from sam ples In th e to p 10 cm to sam ples In th e bottom 10 cm. S o r tin g w hich ranged from poor to v e ry p o o r g e n e r a lly d e c re a se d w ith I n c re a s in g g ra in s iz e . There i s no s i g n i f i c a n t downcore change e i t h e r in c o a rse f r a c t i o n components o r in fa u n a l c o m p o sitio n . 1 weak downward tr e n d o f in c r e a s in g f o r a m in if e r a l number may r e f l e c t a lo w er r a t e o f s e d im e n ta tio n a t th e bottom o f th e c o r e s . Sm all v a r i a t i o n s in p la n k to n lc /b e n th ic f o r a m in i- f e r s r a t i o s d id n o t p e rm it in f e r e n c e s re g a rd in g p o s s i b l e b a th y m e tric ch an g es. The c o n s is t e n t v e r t i c a l tr e n d of in c r e a s e in c o a rse sed im en ts co u ld r e f l e c t : (1) an in c re a s e in winnowing o f th e f in e p a r t i c l e s by th e A gulhas c u r r e n t i n p re v io u s tim e s , o r (2) a c o a r s e r - g r a in e d su p p ly from th e T u g ela R iv e r in th e p a s t . The r e l a t i v e c o n t r ib u t i o n o f th e s e two f a c t o r s cannot be s p e c if ie d b u t b o th f a c t o r s may be i n v o lv e d . The weak tr e n d o f b e t t e r s o r t i n g w ith in c r e a s in g g r a in s iz e a rg u e s f o r th e f i r s t f a c t o r , w hereas th e down- c o re in c re a s e in calciu m c a rb o n a te c o n te n t in th e c o re s from th e u p p er slo p e may a rg u e f o r th e second. F lu c tu a t i o n s in th e amount and s iz e o f d e t r i t a l m a t e r ia l s u p p lie d to th e a r e a by th e T u g ela R iv e r may p o s s ib ly be r e l a t e d to 279 f lu c tu a ti o n s In r a i n f a l l caused by c lim a tic changes. T his change In s e d im e n ta tio n on th e s h e l f and u p p e r slo p e o f f Durban o c c u rs a t ab o u t 15 cm in th e c o re s b u t i t s age cannot be d e fin e d c o n c lu s iv e ly . A lthough th e r e i s a la c k o f fa u n a l e v id e n c e , i t p o s s ib ly may be r e l a t e d to th e e f f e c t s o f c l im a tic change r e p r e s e n te d a t th e P le ls to c e n e - Holocene boundary, w hich i s r e f l e c t e d in th e f o r a m ln if e r a l ooze o f d eep er c o re s f u r t h e r n o r th . I f t h i s w ere th e c a s e , i t would mean an a v era g e d e p o s itio n r a t e o f ab o u t 1 .5 cm/ 1000 y e a rs in t h i s a r e a d u rin g th e H olocene. T h is seems slow f o r an a r e a a d ja c e n t to a te r r ig e n o u s supply (th e T ugela r i v e r ) , i f compared t o th e 10 cm/1000 y e a r s i n d i c a te d by c o re s o f f th e Limpopo and O nllahy R iv e r s . The sed im en tary change may p o s s ib ly be much younger and be r e l a t e d to a r e c e n t in c r e a s e in th e te r r ig e n o u s supply o b serv ed a t ab o u t 20 cm in c o res from th e M alagasy slo p e d a te d by ra d io c a rb o n a t 2200 y e a rs B.P. The p o s s i b i l i t y t h a t th e In c re a s e in c o a r s e r , b e t t e r - s o r t e d sedim ents down th e c o re s o f th e A fric a n C o n tin e n ta l s h e l f n e a r Durban i s due to th e a c tio n o f m ajo r storm waves should n o t be r u le d o u t (S w ift a t a j .. , 1 9 7 1 ). Two c o re s a t th e b ase o f t h e slo p e a t a b o u t 3000 m on th e c o n tin e n ta l r i s e form ing t h e n o rth e rn end o f th e T ra n sk e l B asin c o n s is t th ro u g h o u t t h e i r le n g th o f a f o r a m ln if e r a l ooze w ith no s i g n i f i c a n t fa u n a l change. A l a y e r r i c h i n co arse te r r ig e n o u s m a t e r i a l o c c u rs a t th e 280 bottom of one of those cores (387E). Area Off T u le a r C ores from th e c o n tin e n ta l s h e l f betw een 51 m and 220 m c o n s is t th ro u g h o u t t h e i r l e n g t h o f s i l t y c la y s w ith t h i n l a y e r s o f c o a r s e r se d im e n ts. No s i g n i f i c a n t changes a re ob serv ed e i t h e r in coarse f r a c t i o n components o r In fa u n a l c o m p o sitio n . Calcium c a rb o n a te c o n te n t was not a n a ly z e d in th e s u b s u rfa c e sed im en ts o f th e s e c o re s e x cep t In th e bottom sample o f one c o re (363B a t 220 m ). In th e l a t t e r , th e calcium carb o n ate c o n te n t (6 to 7 p e rc e n t) i s com parable in top and bottom o f th e c o re . Two c o re s from th e upper s lo p e (3650 a t 439 m and 363M a t 1006 m) a r e com prised o f s i l t y c la y . They e x h ib it a s l i g h t downward in c r e a s e in c a lc iu m c a rb o n a te c o n te n t from n e a r ly 17 p e r c e n t a t the to p to 25 to 30 p e r c e n t a t the bottom , which p a r a l l e l s a s l i g h t downward in c r e a s e in th e f o r a m ln if e r a l num ber. This v e r t i c a l tr e n d i s weak when th e whole sedim ent i s c o n s id e re d b u t I s c l e a r I f o n ly th e c o a rse f r a c t i o n (>62j i ) I s exam ined. Q uartz g r a i n s , w hich com prise a b o u t 70 p e rc e n t o f th e f r a c t i o n a t th e to p o f th e c o r e s , d e c re a se to about 15 p e rc e n t a t th e b ottom , w hereas f o r a m ln if e r a l t e s t s I n c r e a s e from ab o u t 15 p e r c e n t a t th e to p to n e a r ly 60 p e r c e n t a t th e bottom . P la n k - t o n i c s p e c ie s a re dom inant and a c c o u n t f o r 50 to 80 p e r c e n t o f th e f o r a m ln if e r a l fauna th ro u g h o u t th e c o r e s . A 281 ra d io c a rb o n d a te o b ta in e d from th e 20-30 cm I n t e r v a l In co re 3650, j u s t below th e se d im en ta ry change, g iv e s an age o f 2200 ± 158 y e a rs B .P. I n d ic a tin g an averag e r a t e o f a c cu m u latio n o f 10 cm/1000 y e a rs f o r modern se d im e n ts. Cores r a i s e d from th e low er p a r t o f th e s lo p e , b e tween 1300 m and 3000 m, c o n s is t o f f o r a m ln if e r a l ooze. Two o f th e s e c o re s (363H and 363F, a t 1310 m and i860 m) show an In c re a s e o f ab o u t 15 to 20 p e r c e n t In calciu m c a rb o n a te c o n te n t In th e I n t e r v a l 10-20 cm. No c l e a r c o r r e l a t i o n can be seen w ith re g a rd to g r a in s i z e . There I s no s i g n i f i c a n t change In th e p la n k to n lc f o r a m ln if e r a l assem blage th ro u g h o u t th e s e two c o re s and th ro u g h o u t co re 3630 a t 2980 m. The r e l a t i v e freq u en cy o f f o r a m ln if e r a l s p e c ie s does n o t v ary much. A s h i f t In th e c o l l i n g r a t i o o f Q r . t r u n c a t u ll n o l d e s from s l n l s t r a l a t th e to p o f th e c o re s to d e z t r a l th ro u g h o u t th e re m a in d e r o f th e c o res o c c u rs a t ab o u t 30 cm In a l l 3 c o r e s . These 3 c o re s a re lo c a te d s o u th o f T u le a r o f f th e O n llah y R iv e r. Core 366B from th e n o rth e rn m o st p o r tio n o f th e a r e a , lo c a te d a t 2300 m n o r th o f T u le a r and f u r t h e r away from th e O nllahy R iv e r , shows l i t t l e v a r i a t i o n In calcium c a rb o n a te c o n te n t. There I s a ls o a s h i f t In th e c o l l i n g d i r e c t i o n o f G. tr u n c a t u ll n o l d e s from s l n l s t r a l a t th e to p to d e z t r a l a t th e b o tto m . T h is s h i f t o c c u rs h ig h e r In th e co re a t ab o u t 15 cm and I s d a te d by ra d io c a rb o n a t 5426 - 192 y e a r s B .P. A s i g n i f i c a n t change In th e r e l a t i v e 2 8 2 abundance o f p la n k to n lc f o r a m l n i f e r a l s p e c ie s o ccu r a t ab o u t 25 cm. There Is a marked downcore In c re a s e In th e r e l a t i v e abundance o f th e c o ld -te m p e ra te -w a te r s p e c ie s , e s p e c i a l l y 6 . I n f l a t a , and a sim u lta n e o u s d e c re a se o f warm- w a te r s p e c ie s . T his fa u n a l change, w hich r e f l e c t s a warm in g In s u rfa c e w a te r te m p e ra tu re , I s d a te d by ra d io c a rb o n a t 10 ,2 3 5 * 292 y e a rs B .P . and c o rre sp o n d s to th e H olocene- P le ls to c e n e boundary. The r a d l o l a r l a n number, s l i g h t l y above 500 a t th e to p of th e c o r e , d e c re a s e s to l e s s th a n 50 below th e boundary. S im ila r f a u n a l tr e n d s were ob se rv ed In c o re s from o t h e r p a r t s o f th e r e s e a r c h a r e a . These changes and t h e i r s ig n i f i c a n c e I s d is c u s s e d l a t e r In more d e t a i l . C o r r e la tio n s betw een c o re s o f th e M alagasy slo p e In th e a r e a o f f T u le a r are summarized In F ig u re 58. There Is a marked r e l a t i o n s h i p betw een th e r a t e o f s e d im e n ta tio n and th e s i t e o f th e c o re s In r e l a t i o n to th e O nllahy B lver m outh. Core 366B which I s f u r t h e r away from th e r i v e r show a much slo w er r a t e o f a c c u m u la tio n th a n c o re s In th e a r e a In flu e n c e d by th e O n llah y lo a d . At s i t e 366B, a t 2300 m, th e av erag e r a t e o f s e d im e n ta tio n f o r th e p a s t 5400 y e a rs I s ab o u t 2.8 cm/1000 y e a r s , w hereas a t s i t e s 3630, 363F, and 363H, betw een 1310 and 2980 m, I t I s ab o u t 5*5 cm/1000 y e a r s . In t h e a r e a o f f th e O nllahy R iv e r th e a v era g e r a t e o f se d im e n ta tio n f o r th e l a s t 2200 y e a rs te n d s to d e c re a se w ith d is t a n c e o ffB h o re . I t I s about Figure 58 C o r r e la tio n s between c o re s in th e a re a n ear T u le a r . C o r r e la tio n s a re based on: 1 . Changes in r e l a t i v e freq u en cy o f p la n k to n lc f o r a m l n i f e r a l s p e c ie s and in th e r a d i o l a r l a n number. ______ 2 . C o ilin g r a t i o s o f G lo b o r o ta lla t r u n c a t u ll n o l d e s (d o m in an tly s l n l s t r a l above th e boundary and dom inantly d e z t r a l b elo w ). 3 . Changes in th e c o a rs e f r a c t i o n components ( d e t r l t a l m a t e r ia l more abundant above th e b o u n d ary ). 4 . E x tra p o la te d c o r r e l a t i o n based on an assumed c o n s ta n t s e d im e n ta tio n r a t e . B lack i n t e r v a l s i n d ic a te ra d io c a rb o n sam ples, and h a tch ed I n t e r v a l s an in c r e a s e in calcium c a rb o n a te c o n te n t. B oundaries a r e p la c e d a t th e m id p o in t o f the core i n t e r v a l in w hich th e y a re re c o rd e d . 283 366B 363F 2300M I860M 5426* 192 10235* 292 17,254*730 363H I3I0M 363M 365C 1006 M 439M \ \ r 0 -10 -20 1-2200* 158 -3 0 co (Z U 1U 2 UJ o -4 0 - 5 0 ro 00 2 8 5 9*1 cm/1000 y e a rs a t 439 m, a b o u t 6 .8 cm/lOOO y e a rs a t 1006 m, and ab o u t 4 .5 cm/1000 y e a r s betw een 1300 and 3000 m. Because o f th e slo w er ac c u m u latio n r a t e a t th e n o rth e rn m o st l o c a l i t y (366B) o ld e r sed im en ts were p en e t r a t e d and r a t e s o f s e d im e n ta tio n f o r th e e n t i r e Holocene and l a t e P le is to c e n e co u ld be m easured. I t Is 2 .1 cm/ 1000 y e a r s f o r th e I n t e r v a l 5»426-10,235 y e a r s B .P . and 2 .9 cm/1000 y e a r s f o r th e I n t e r v a l 10,235-17*254 y e a rs B .P. At t h i s l o c a l e r a t e s o f ac c u m u la tio n f o r H olocene and L ate P le i s t o c e n e sed im en ts a r e th u s s im i l a r . S e d im e n ta tio n on th e M alagasy s lo p e In th e a r e a n e a r T u le a r does not a p p e a r to be d is tu r b e d by th e s u rfa c e w a te r c u r r e n t s (F ig s . 13, 16, 29) In c o n t r a s t to th e s e d i m e n ta tio n on th e A fric a n s lo p e u n d er th e d e ep e r A gulhas C u rre n t. S l i g h t v a r i a t i o n s In calciu m c a rb o n a te c o n te n t o b serv ed In c o re s from t h i s a r e a p o s s ib ly r e f l e c t v a r i a t i o n s In su p p ly from th e O n llah y R iv e r, w h ich , In t u r n , may be r e l a t e d to f l u c t u a t i o n s In r a i n f a l l owing to c l i m a t i c c h a n g e s. They do n o t a p p e a r to r e f l e c t changes In p r o d u c t iv i t y r e l a t e d to v a r i a t i o n s In th e warm s u rfa c e c u r r e n t b ecau se o th e r c o r e s , a ls o l o c a te d u n d er th e c u r r e n t , show no change In calciu m c a rb o n a te c o n te n t. A rea O ff Inhambane A ttem p ts to c o re th e h ard -b o tto m e d s h e l f In the 2 8 6 a r e a o f th e Mozambique c u r re n t f a i l e d . Cores r a i s e d on th e c o n t i n e n t a l slo p e between 910 m and 2270 m c o n s is t th ro u g h o u t o f f o r a m in if e r a l o o ze. Among th o s e , only co re 3700 a t 910 m in c lu d e s a f r e s h fa u n a o f non-w eathered t e s t s o f f o r a m ln lf e r s and p te ro p o d s . The l o c a le o f t h i s co re p o s s ib ly may be s h e lte r e d from c u r r e n t a c tio n f o r m ic ro to p o g ra p h lc r e a s o n s . A ra d io c a rb o n d a te a t 35 cm y ie ld e d an age o f 28,440 ! 4125 y e a r s B .P . I f sed im en ta t io n h as been c o n tin u o u s a t t h i s s i t e u n t i l r e c e n t tim e s, t h i s im p lie s a s l i g h t l y slow er r a t e o f d e p o s itio n than f o r f o r a m in if e r a l oozes to the s o u th e a s t (361P and 361J) and on th e o th e r s id e o f th e Mozambique Channel (366B). But i f p a r t o f th e s e c tio n i s m is s in g , i t a l s o i s p o s s ib le t h a t ac c u m u la tio n was more r a p i d . T h is can n o t be s p e c i f i e d from th e fa u n a l c o n te n t. P o p u la tio n o f G. tru n c a - t u l l n o l d e s a re r ig h t c o llin g th ro u g h o u t th e c o r e . Changes in r e l a t i v e abundance o f p la n k to n lc s p e c ie s a re n o t p ro nounced. T here i s , how ever, a s l i g h t downward in c re a s e in th e r e l a t i v e freq u e n c y o f th e two te m p e ra te s p e c ie s G. l n f l a t a and G. t r u n c a t u l l n o l d e s . a t ab o u t 25 cm, j u s t above th e p o s i t i o n o f the ra d io c a rb o n m easurem ent. T h is m ight i n d i c a t e a change in w a te r te m p e ra tu re , b u t o f s m a lle r a m p litu d e and o ld e r th a n th e one re c o rd e d f u r t h e r e a s t a t th e P le isto c e n e -H o lo c e n e boundary. T h is c o re shows l i t t l e change in calciu m c a rb o n a te c o n te n t and no tre n d in v a r i a t i o n o f g r a in s i z e . A change in c o lo r a t 16 cm can n o t be 287 e x p la in e d from the p r e s e n t d a ta . No o t h e r c o re s In t h i s a re a a p p e a r to c o n ta in un d is tu r b e d modern se d im e n ts. Core 369H a t 1185 m h a s a 4 cm s u r f l c l a l la y e r o f f o r a m i n i f e r a l ooze c o n ta in in g worn and rew orked t e s t s . The rem ain in g 6 cm o f t h i s s h o r t c o re do n o t e x h ib it a s much rew o rk in g . The amount o f w eath ered and broken t e s t s I s s m a lle r and p tero p o d s h e lls a re a b u n d a n t, as In co re 370C. T his downward tr e n d In b e t t e r p r e s e r v a tio n c o r r e l a t e s w ith an In c re a s e In calcium c a rb o n a te and sand f r a c t i o n c o n te n ts . G. t r u n c a tu lln o ld e e a re d e x t r a l th ro u g h o u t th e c o r e . R e la tiv e abundances o f G. l n f l a t a and £. tr u n c a tu lln o I d e s a r e s i m i l a r to v alu es In th e low er p a r t o f co re 370C, but th e c o re Is to o s h o rt to p e rm it c o r r e l a t i o n s . A s h o r t core a t 1690 m (369E) c o n s i s t s o f a Miocene to P lio c e n e In d u ra te d f o r a m in if e r a l ooze w ith a sm a ll amount o f lo o s e ooze a t th e to p . The b l o s t r a t l g r a p h l c p o s i t i o n o f t h i s ooze I s In th e I n te r v a l betw een Zones N3 and N20 o f Banner and Blow (1965) and Blow (1 9 6 9 ). I t cannot be s p e c i f i e d more p r e c i s e l y owing to common rew ork in g , a s ev id en ced by th e c o n c u rre n t o c c u rre n c e o f Lower Miocene s p e c ie s to g e th e r w ith M iddle M iocene to Lower P lio c e n e s p e c ie s . The p la n k to n lc f o r a m i n i f e r a l fa u n a In c lu d e s commonly: G lo b o r o ta lla a c o s t a e n s l s . G. c r a s s a - f o rm ls . G. m lozea o o n o ld e a . G. n e r ln h e ro n d a . G. pseudo- k u g l e r l . G. s l a k e n s l s . G. sp . A, G lo b o au ad rln a a l t l s p l r a . G. V e n ez u ela n s. S p h a e r o ld ln e llo n s ls a e m ln u lln a . and S. sub- j dshlassM* i At 2270 m co re 369B shows no change In components th ro u g h o u t I t s le n g th and c o n ta in s a p p re c ia b le reworked Miocene form s. S o u th w ard -facin g C o n tin e n ta l S h e lf , E a st o f th e Limpopo R iv e r On t h i s p o r tio n o f th e A fric a n s h e l f , p r o te c te d from th e Agulhas c u r r e n t by th e I n d e n ta tio n o f th e c o a s t, two c o re s a t 55 m and 106 m show l i t t l e l l t h o l o g l c and fa u n a l c h an g es. A ra d io c a rb o n d ate I n d ic a t e s an age o f 4150 y e a rs B .P . a t ab o u t 35 cm In c o re 372N Im plying a r a t e o f s e d i m e n ta tio n o f ab o u t 10 cm/1000 y e a r s . i ! C o n tin e n ta l Slope S o u th e a st o f Lourenco Marques j I i Core 374A a t 896 m on th e lo w - g ra d ie n t slo p e con- | s l o t s o f a f r e s h f o r a m in if e r a l ooze w ith no change e i t h e r j In f a u n a l co m p o sitio n o r in calcium c a rb o n a te and sand f r a c t i o n c o n te n t. Core re c o v e ry was from u n d er and n e a r th e in n e r edge o f th e Agulhas c u r r e n t , and s e d im e n ta tio n th e r e does n o t ap p e a r to be in flu e n c e d by th e c u r re n t a c tio n a s I t i s f u r t h e r to th e s o u th e a s t un d er th e core o f th e c u r r e n t . At d e p th s o f 1335 m and 1919 m, two c o re s (374C and 375B) c o n s i s t o f a f o r a m in if e r a l ooze c o n ta in in g a fauna p a r t l y w eath ered and l a r g e l y g la u c o n itiz e d a s s o c ia te d w ith numerous g la u c o n ite p e l l e t s . No s e d lm e n to lo g ic a l o r fa u n a l change was o b s e rv e d . These sed im en ts a re b e lie v e d to be d is p la c e d from s h a llo w e r d ep th s o f th e a re a o f f th e Limpopo R iv e r. Evidence o f a sh allo w dep th o f d e p o s itio n I s shown by th e abundance In th e se sed im en ts o f non e n c ru s te d G lo b o r o ta lla m e n a r d ll. Throughout th e r e s e a r c h a r e a , n o n -e n c ru s te d forms o f t h i s s p e c ie s a r e found m ainly above 500 m, w hereas below t h i s d ep th e n c ru s te d forms o c c u r. F u rth erm o re, th e p re se n c e o f numerous p e l l e t s Imply an a r e a o f d e p o s itio n w ith abundant I n v e r t e b r a t e s , which s tr o n g ly s u g g e st s h a llo w e r w a te r. Because b u ry in g In mud I s r e q u ir e d f o r g l a u c o n l t l z a t l o n , th e a r e a o f f th e Limpopo R iv e r I s c o n s id e re d th e a r e a o f o r ig i n r a t h e r th an th e a re a o f f Inhambane t h a t I s f lo o r e d w ith a rocky b o tto m . A nother re a so n f o r assum ing t h i s o r ig i n Is th e p re se n c e o f th e c a n y o n -llk e b a th y m e tric c o n to u r o f 500 m o f f th e Limpopo ( F ig . 2) w hich could have been an avenue o f t r a n s p o r t . R adiocarbon d a te s In d ic a te a g es o f 16,600 - 1084 a t th e to p o f c o re 3740 and 31,500 t 4200 a t a b o u t 25 cm. R a te s o f ac cu m u la tio n based on th e se two d a te s cannot be I n f e r r e d owing to sedim ent d isp la c e m e n ts . They do I n d i c a te t h a t th e sed im en ts a re P l e is to c e n e , a p p ro x im a te ly e q u iv a le n t In age to th e m a te r ia l a t th e b a se o f co re 370C lo c a te d o f f Inham bane. Thus I t Is proposed t h a t P l e i s t o cene sed im e n ts from th e a r e a o f f th e Limpopo R iv e r sh a llo w 290 e r than 300 m w ere d is p la c e d downslope tow ard th e s o u th e a s t , p o s s ib ly th ro u g h th e canyon t h a t c r o s s e s th e s lo p e . The a re a o f r e d e p o s i t i o n i s u n d er th e A gulhas C u rren t w hich p re v e n ts d e p o s itio n o f H olocene sed im e n ts. C o n tin e n ta l Slope and C o n tin e n ta l B ise E a st o f Lourenco Marques Cores o f homogeneous f o r a m in if e r a l ooze r a i s e d from t h r e e s i t e s betw een 1829 m and 3800 m show good c o r r e l a t i o n s . S i g n i f i c a n t fa u n a l changes, s im i l a r to th e changes in core 366B o f f T u le a r, a re o b serv ed ( F ig s . 59, 6 0 ). There i s a s h i f t in th e c o i l i n g r a t i o o f G lo b o r o ta lla t r u n c a t u ll n o l d e s from s l n l s t r a l a t th e to p o f th e c o re s to d e z t r a l th ro u g h o u t th e rem ain d er o f th e c o r e s , which o c c u rs a t about 5 cm in c o re s 361C and 361F and a t about 15 cm in core 3 6 1 J. T h is s h i f t i s d a te d , by ra d io c a rb o n , a s 6,315 - 515 y e a r s B .P . in c o re 36IF and 6,748 t 653 y e a r s B .P . in c o re 36I J . There i s a marked downcore i n c re a s e o f c o ld - te m p e ra te - w a te r s p e c ie s , e s p e c i a l l y G lo b o r o ta lla i n f l a t a , and a sim u ltan e o u s d e c re a se o f warm- w a te r s p e c ie s . T his fa u n a l change, w hich r e f l e c t s warming o f s u rfa c e w a te r, o c cu rs a t ab o u t 15 cm in c o re s 361C and 361F and a t a p p ro x im a te ly 25 cm in c o re 361J and i s d ated by ra d io c a rb o n a t 10,357 t 1166 y e a rs B.P. in co re 361F and 9160 t 1007 y e a rs B .P . in core 36I J . T h is co rresp o n d s to th e P le ls to c e n e /H o lo c e n e boundary. The r a d i o l a r i a n Figure 59 Faunal co m p o sitio n in c o re 361F ( 2 5 ° 5 0 'S ., 3 7 ° 2 1 'E .) . a . P r o p o r tio n a l c o n t r ib u t i o n by f o u r d ia g n o s tic s p e c ie s o f p la n k to n ic f o r a m ln lf e r s to th e t o t a l p la n k - t o n ic f o r a m in if e r a l fa u n a c o a r s e r th an 250/1. T em p erate-w ater s p e c ie s : G lo b o r o ta lla i n f l a t a ( s o l i d l i n e j T W a r m - w a t e r s p e c ie s : G lo b lg e rln o ld e s s a c c u l l f e r ( s m a ll- dashed l i n e ) , N eogloboauadrlna d u t e r t r e l d u t e r t r e l (la rg e - d a s h e d l i n e ) and P u l l e n l a t l n a o b l l a u l - l o c u l a t a (dashed and d o tte d l i n e ) . b . P r o p o r tio n a l c o n t r ib u t i o n by two s p e c ie s o f p la n k to n ic f o r a m ln lf e r s to th e t o t a l p la n k to n ic f o r a m in if e r a l fa u n a c o a r s e r th a n 250/i. G lo b lg e r l- n o ld e s r u b e r (dashed l i n e ) , G loboro t a l l a m e n ard ll group ( s o l i d l i n e ). c . C o ilin g r a t i o s o f G lo b o r o ta lla t r u n c a t u ll n o l d e s (100 p e r c e n t s i n i s t r a l on th e l e f t and 100 p e r c e n t d e z t r a l on th e r i g h t ) . 291 CENTIMETERS P E R C EN TAG E S 0 10 20 0 10 S O 1 0 - 20 - £ U J C O 3 £ C D 4 0 - b a 292 Figure 60 F aunal c o m p o sitio n in co re 361J ( 2 5 ° 3 9 'S ., 3 7 ° 4 5 'E .) . a . P r o p o r tio n a l c o n tr ib u tio n by f o u r d ia g n o s tic s p e c ie s o f p la n k to n ic f o r a m ln lf e r s to th e t o t a l p la n k to n ic f o r a m i n i f e r a l fauna c o a r s e r th a n 250u. T em p erate-w ater s p e c ie s : G lo b o r o ta lla l n f l a t a ( s o l i d l i n e ) , tfarm -w ater s p e c ie s : G lo b lg e rln o ld e s s a c c u l l f e r (sm a ll-d a sh e d l i n e ) , N eogloboQ uadrlna d u t e r t r e l d u t e r t r e l (la rg e - d a s h e d l i n e ) and P u l l e n l a t l n a o b llQ U llo c u la ta (dashed and d o tte d l i n e ) . b. P r o p o r tio n a l c o n tr ib u tio n by two s p e c ie s o f p la n k to n ic f o r a m ln lf e r s to th e t o t a l p la n k to n ic f o r a m in if e r a l fau n a c o a r s e r than 250ja. G lo b lg e r ln o ld e s r u b e r (dashed l i n e ) . G loboro t a l l a m e n a rd ll group ( s o l i d l i n e ) . c . C o ilin g r a t i o s o f G lo b o r o ta lla tru n o a - t u l l n o l d e s (100 p e rc e n t s i n l s t r a l on th e l e f t and 100 p e rc e n t d e z t r a l on th e r i g h t ) . 293 CENTIMETERS P E R C E N T A 6 E S 20 o \ 4 I (0 I < *> / V / / / 30- / / O D I 40 © i y 36ij b a 294 295 number show a downcore d e c re a s e , from n e a rly 500 above th e boundary to about 50 below , In c o re s 361F and 3 6 1 J, and show no tr e n d in c o re 3610. C o r r e la tio n s betw een th e s e th re e c o re s a r e shown in F ig u re 61. The a v e ra g e r a t e o f accu m u latio n o f sed im en ts younger th a n ab o u t 6000 y e a rs B.P. ran g es from 0 .8 cm/1000 y e a rs on th e c o n t i n e n t a l slo p e to 1 .6 cm/1000 y e a r s on th e c o n tin e n ta l r i s e . The av era g e r a t e o f a ccu m u latio n o f Holocene sed im en ts d u rin g th e i n t e r v a l between a p p ro x i m ately 6000 and 10 ,0 0 0 y e a rs B .P. i s 1 .6 cm/1000 y e a rs on th e c o n tin e n ta l s lo p e and 4 .2 cm on the c o n t i n e n t a l r i s e . P le is to c e n e sed im en ts accum ulated a t a r a t e of 1 .2 to 3 .7 cm/1000 y e a rs on th e c o n t i n e n t a l slo p e and 3 .6 cm/1000 y e a rs on th e c o n t i n e n t a l r i s e . The av e ra g e r a t e o f accum ulation f o r the e n t i r e Holocene i s s l i g h t l y low er on th e c o n tin e n ta l s lo p e (a p p ro x im a te ly 1 .5 cm/1000 y e a rs ) th a n on th e c o n tin e n ta l r i s e (a p p ro x im a te ly 2 .5 cm/1000 y e a r s ) . There i s no d e f i n i t e change in th e se d im e n ta tio n r a t e s d u rin g th e Holocene and L ate P l e i s t o c e n e . In c o re 361F a d e c re a s in g tr e n d in calciu m carb o n a te c o n te n t, o f ab o u t 10 p e rc e n t from th e bottom to th e top o f th e c o re , p a r a l l e l s a d e c re a sin g tr e n d in g ra in s i z e . These tr e n d s co u ld r e f l e c t : (1) a h ig h e r c o n tr ib u ti o n o f f i n e t e r r ig e n o u s components from th e la n d in Holocene se d im e n ts, w hich would be in agreem ent w ith th e Figure 61 C o r r e la tio n s betw een c o re s 361F (2505 0 'S . , 3 7 ° 2 l 'E . ) , 361J ( 2 5 ° 3 9 'S ., 3 7 ° 4 5 'E .) , and 366B ( 2 3 ° 0 9 'S ., 4 3 ° 0 8 'E .) . S o lid l i n e in d ic a te s a change in b o th th e p la n k to n ic f o r a m in if e r a l fa u n a and th e r a d i o l a r l a n number. Bashed l i n e in d i c a t e s a s h i f t in th e c o i l i n g d i r e c t i o n o f G lo b o r o ta lla t r u n c a t u l l n o l d e s . Samples used f o r carbon 14 d a te s a re in d ic a te d by h a tc h e d a r e a s . 296 CENTIMETERS CORE 36IF CORE 36IJ O-i 1 0 - 0 - 3 0 - 4 0 - 50J YEARS a P . 6315*815 10357 * 1166 17594* 1950 20300 * 2720 26940 * 5500 YEARS B.P. 536 * 1724 n HOL&CENE 6748 * 653 cooltr 9160 * 1007 PLEISTOCENE 12034 * 889 CORE 366 B YEARS B.P. 5426 * 192 10235 * 292 17254 * 730 297 tr e n d s ob serv ed In h e m ip e la g lc sed im en ts on th e s lo p e o f f Durban, o r (2) a h ig h e r p ro d u c tio n o f calcium c a rb o n a te in P le is to c e n e se d im e n ts. No c o n c lu s io n can be made b ecau se th e tre n d s o f co re 361F a r e n o t e v id e n t in any o f th e o th e r c o re s showing th e H o lo c e n e -P le isto c e n e boundary. Mozambique P la te a u A ttem pts to c o re th e so u th e rn Mozambique P la te a u co v ered w ith manganese n o d u le s f a i l e d and o n ly sm all r e c o v e r ie s o f f o r a m i n i f e r a l ooze were made from c o re c u t t e r s and c a t c h e r s . The a p p ra is e d r a t e o f t h i s ooze i s low , evidenced by th e c o a rs e n e s s o f th e ooze (F ig . 3 6 ) and by th e abundance o f m anganese n o d u le s which fa v o r a r e a s w ith slow d e p o s itio n . The slow se d im e n ta tio n and th e c o a r s e n ess o f th e f o r a m i n i f e r a l ooze on th e Mozambique P la te a u r e f l e c t th e winnowing a c t i o n o f th e A n ta r c tic I n te rm e d ia te W ater C u rre n t w hich makes a c o u n te r-c lo c k w is e eddy c e n t e r ed h e re ( F ig s . 30 and 31)* E a s te rn S lope o f Mozambique P la te a u On th e s o u th e rn p o r ti o n o f t h i s s te e p slo p e a co re a t 3090 m ( 385B) t r a v e r s e d 50 cm o f homogeneous f o r a m in if e r a l ooze w ith no f a u n a l change. The to p 2 cm were d a te d by ra d io c a rb o n m ethods a t 3935 - 302 y e a rs B .P ., an age s im i l a r to th e age o f s u rf a c e sed im en ts a t th e n o rth e rn end o f t h i s s lo p e (4422 t 350 y e a rs f o r th e to p 299 sample o f 361F ). A lthough th e r e I s no e v id en ce f o r th e r a t e o f se d im e n ta tio n from co re 385B, I f th e average r a t e o f accu m u latio n o f th e f o r a m i n i f e r a l ooze d e p o s ite d f u r t h e r n o rth on t h i s slope i s e x tr a p o la te d (ab o u t 1 .5 cm/1000 y e a rs In Holocene tim e ) , t h e H o lo c e n e -P le isto c e n e boundary I s c ro sse d i n core 385B a t ab o u t 15 cm. No fa u n a l change i s o b serv ed in t h i s homogeneous f o r a m in if e r a l ooze im p ly in g t h a t t h i s l o c a l e , a t about 3 5 ° S ., 3 5 °E ., is b e n e a th t h e same s u rfa c e w a te r m ass, th e S u b tro p ic a l W ater, d u rin g P l e i s t o c e n e and H olocene tim e s . Core 375F a t 3840 m i s s h o r t e r (30 cm) and no fa u n a l change i s observed i n th e c o r e , b u t a l i t h o l o g i c change o ccu rs a t ab o u t 18 cm. A f o r a m i n i f e r a l ooze o v e r l ie s a fin e te r r ig e n o u s sedim ent and from o b s e rv a tio n s o f b a th y m e tric c o n to u rs ( F ig . 2) t h i s c o re a p p e a rs to be lo c a te d on an in d e n ta tio n o f th e s lo p e w hich may p o s s ib ly con s t i t u t e th e mouth o f a subm arine canyon h e ad in g from th e Limpopo R iv e r. The p re se n c e o f te r r ig e n o u s sedim ent u n d er ly in g a f o r a m in if e r a l ooze in t h i s c o re arg u es fo r a p o s s ib l e e a s te r n so u rce from p a r t o f th e t u r b i d l t e s o f th e N atal B a sin . M adagascar P la te a u Core 379B a t 2600 m on th e M adagascar P la te a u t r a v e r s e d a homogeneous f o r a m i n i f e r a l ooze. At t h i s so u th e rn s i t e , lo c a te d as c o re 385B u nder S u b tro p ic a l 300 W ater, th e H o lo c e n e -P le isto c e n e boundary i s p ro b a b ly en co u n te re d b u t I s n o t r e f l e c t e d by fa u n a l changes. C e n tra l Area o f th e Mozambique Channel Cores from th e ch an n el f l o o r , betw een d e p th s o f 3000 and 4000 m, a re In th e sm all a b y s s a l p l a i n w est o f Europa (368B, 367H), on th e Zambezi Canyon w a ll (367B, 362C), and on th e c o n tin e n ta l r i s e w est o f th e canyon mouth (362E ). These c o re s c o n s is t p r im a r ily o f fo ra m in i f e r a l oozes which c o n ta in a m ix tu re o f f r e s h and reworked t e s t s o f modern s p e c ie s and s p e c ie s o f v a r io u s ages (C re ta c e o u s, P aleogene and c h ie f ly Upper Miocene to Lower P lio c e n e ) . These mixed oozes a re s im i l a r to th e oozes a t s u b su rfa c e d e p th s In th e N a ta l B asin and have been con s id e r e d e a r l i e r t o g e th e r w ith th e se d im e n ta tio n In th e N a ta l B asin b ecau se o f t h e i r l o c a t i o n d i r e c t l y to th e n o rth o f th e b a s in . Two ra d io c a rb o n d a te s In c o re 367H gave an age o f 23,050 t 2025 a t 15 cm and 26,130 t 1925 a t 4 2 .5 cm. These I n d ic a te an av erag e s e d im e n ta tio n r a t e o f ab o u t 10 cm/1000 y e a r s , w hich I s h ig h e r th a n th e av e ra g e 1 .5 to 2 .5 cm/1000 y e a rs found f o r u n d is tu rb e d oozes In th e r e s e a r c h a r e a . But th e n a tu re o f t h i s mixed ooze makes I t d i f f i c u l t to I n t e r p r e t ra d io c a rb o n m easurem ents. F u rth erm o re, a s men tio n e d e a r l i e r , I f th e ooze d a te d 23,050 y e a rs a t 15 cm were In s i t u . I t would be s u r p r i s i n g t h a t l i t t l e o r no Holocene d e p o s itio n o c c u rre d In th e a b y s s a l p la in w est o f Europa. T his a re a I s surrounded by ste e p s lo p e s , c lo se to c o n tin e n ts and i s l a n d s , where slumps and t u r b i d i t y c u r r e n ts would be ex p ected to o c c u r. A s tro n g bottom c u r re n t i s n e c e ssa ry to p re v e n t any modern se d im e n ta tio n th e r e . The sp a rse number o f h y d ro g ra p h ic s t a t i o n s does not perm it tr a c in g o f c u r r e n t p a t t e r n a t 3000 m In th e a b y s sa l p la in (F ig . 3 3 ). At t h i s d e p th , how ever, th e N orth In d ian Deep Water flow s southw ard o u t o f th e Mozambique Channel on I t s w estern s id e , w hereas th e N orth A t l a n t i c Deep W ater flow s northw ard e n te r in g th e ch an n el in th e a re a o f th e Zambezi Canyon. Movement o f th e two w a te r m asses i s re s p o n s ib le fo r a c o u n te r-c lo c k w ise gyre in th e n o rth w este rn co rn e r o f the N a ta l B a sin . The f l o o r o f th e a b y s s a l p la in w est o f Europa Is p ro b a b ly u n d er p a r t o f t h i s g y re . Movement o f w ater i s n o t c o n sid e re d s u f f i c i e n t l y s tro n g to p rev en t s e d im e n ta tio n . A d is p la c e d o r ig in I s a t t r i b u t e d to the mixed ooze ly in g In th e a b y s s a l p l a i n and a re co n sid e re d to be in p a r t b i o c l a s t l c t u r b l d l t e s d eriv ed from b a th y a l d e p th s. Some h o riz o n s o f th e co res i n the c e n t r a l a re a o f the channel show a d e c re a se in calciu m c a rb o n a te c o n te n t, a low er f o r a m in if e r a l number, a d e c re a se In g ra in s iz e and an In c re a s e in q u a rtz g r a in s abundance. S ed im e n to lo g lc a l v a r i a t io n s in th e c o re s arg u e f o r sedim ent d isp la c e m e n t. Graded bedding was n o t o b serv ed from a g r a in s iz e a n a ly s is 3 0 2 In c o re s from th e Zambezi Canyon and th e c o n tin e n ta l r i s e w est o f th e Zanbezl Canyon, b u t i t a p p e a rs t h a t some s o r t in g o c c u rs d u rin g the p ro c e ss o f re s e d lm e n ta tlo n as shown by fa u n a l assem b lag es. Miocene p la n k to n ic s p e c ie s in oozes w est o f Europa a re m ainly c o a rse forms ( Globoauad- r l n a ) . w hereas in oozes o f th e Zambezi Canyon th ey a re sm all ( c h i e f l y G lo b lg e rln a n e p e n th e s Todd). These d i f fe re n c e s in s p e c ie s com p o sitio n co u ld be due e i t h e r to p r e f e r e n t i a l s o lu tio n o f sm all s p e c ie s in th e a b y s sa l p la i n o r p o s s ib ly to s o r t i n g d u rin g t r a n s p o r t . N a ta l B asin Cores from th e N a ta l B asin f l o o r between d ep th s o f 4820 and 5350 m were d isc u s s e d e a r l i e r . Except a t th e so u th ern m o st and d e e p e st l o c a l e , a l l c o re s c o n s is t o f a l a y e r o f te r r ig e n o u s sedim ent o v e r ly in g c a lc a re o u s s e d i m en ts. S u r f l c l a l te r r ig e n o u s sed im en ts d e riv e d from sh allo w w a te r , in which some p e la g ic sed im en ts from deeper w a te r were in c o r p o ra te d , a re i n t e r p r e t e d as a t u r b l d i t e h o riz o n . The th ic k n e s s o f th e l a y e r d e c re a s e s s o u th e a s t ward from 2 to 20 cm and a ls o a l a t e r a l so u th ea stw ard de c re a s e in g r a in s iz e e x i s t s . These sed im e n ts were t r a n s p o rte d m ain ly th ro u g h subm arine canyons from th e n o rth e rn and e a s te r n s id e s o f th e N a ta l B a sin . There i s a marked downcore in c r e a s e in calcium c a rb o n a te c o n te n t in a l l c o re s b u t th e southernm ost (384B) from l e s s th an 10 p e rc e n t a t th e to p to as much as 60 p e rc e n t (F ig . 3 9 ). The p re se n c e o f c a r b o n a te - r ic h sed im en ts in co res below th e calciu m c a rb o n a te com pensation d e p th i s ex p la in e d by r a p id b u r i a l . They c o n s is t o f p a r t l y d i s so lv ed mixed f o r a m in if e r a l oozes c o n ta in in g modern and f o s s i l s p e c ie s o f v a r io u s ages (C re ta c e o u s, P aleo g en e, and c h i e f l y Upper Miocene to Lower P lio c e n e ) . These are com parable to th e mixed oozes from th e c e n t r a l a re a o f th e Mozambique Channel and a re I n te r p r e t e d as b i o c l a t l c t u r b i d l t e d e riv e d from b a th y a l d e p th s . A ra d io c a rb o n m easurem ent a t 25 cm in c o re 377B y ie ld e d no a c t i v i t y , im p ly in g an age o ld e r th a n 30,000 to 40,000 y e a r s B .P . I f th e s e oozes were in s i t u , sed im en ts younger th an 40,000 y e a rs would be r e p re s e n te d only by sed im en ts 2 to 20 cm t h i c k . Such a slow r a t e o f s e d im e n ta tio n i s in c o m p a tib le w ith th e 1500 m o f u n c o n s o lid a te d sed im en ts d e s c rib e d by Ewing e t a l . (1 9 6 9 ). There i s no e v id en ce f o r a r a t e o f se d im e n ta tio n in c o re s o f th e N a ta l B asin b u t i t i s p o s tu la te d from th e t u r b i d i t y c u r r e n t o r ig i n o f most o f th e sed im en ts t h a t th e s e accum ulated r a p i d l y . The p re se n c e o f common manganese m icro n o d u les in th e bottom 10 cm o f c o re s from th e c e n t r a l and s o u th e a s te r n l o c a l e s (378B, 382B and 383B) su g g e sts t h a t sed im en ts in t h i s a r e a once accu m u lated more slo w ly . At th e southernm ost and d e e p e st lo o a l e (385B), c o re s c o n s is t o f c a r b o n a te - f r e e f in e c lay ey sed im en ts o f p ro b a b le p e la g ic o r i g i n . These sed im en ts and th e abundance o f manganese n o d u les co v e rin g t h i s a r e a Imply a slow r a te o f a c c u m u la tio n . The slow d e p o s itio n , I n d ic a te d by the p re se n c e of b u r r le d manganese m icro n o d u les In th e c e n t r a l and s o u th e a s te r n a re a and s u rf a c e manganese n o d u le s In th e so u th , c o n t r a s t s w ith ra p id d e p o s itio n o f t u r b l d l t e s , and hence d e p ic ts th e v a rie d sed im en tary h i s t o r y o f th e N atal B asin. DISCUSSION OF THE FAUNAL CHANGE AT THE PLEISTOCENE-HOLOCENE BOUNDARY C ores 361C, 36IF , 361J and 366B show p a r a l l e l tr e n d s In th e d i s t r i b u t i o n o f p la n k to n ic f o r a m in if e r a l s p e c i e s . The bottom p o r tio n o f th e c o re s I s c h a r a c te r iz e d by an abundance o f te m p e ra te -w a te r s p e c ie s . Among th e s e , G lo b o r o ta lla I n f l a t a , a c o ld -te m p e ra te -w a te r s p e c ie s , makes up 25 to 30 p e rc e n t o f th e t o t a l p la n k to n ic p o p u la t i o n l a r g e r th a n 250>i. A s m a lle r c o n t r ib u t i o n to th e fa u n a I s made by a n o th e r c o ld -te m p e ra te -w a te r s p e c ie s G lo b o r o ta lla tr u n c a t u ll n o l d e s (a b o u t 3 p e r c e n t) and th r e e w arm -te m p era te -w ate r s p e c ie s : G lo b o r o ta lla c ra s s a fo rm ls (1 p e r c e n t ) , G lo b o r o ta lla h l r s u t a (2 p e r c e n t) and G loboro t a l l a s c l t u l a (1 p e r c e n t ) . The re m a in d e r o f th e p o p u la t i o n c o n s is t s o f th e co sm o p o litan s p e c ie s G lo b o g e rln lta g l u t l n a t a (1 p e r c e n t) and numerous w arm -w ater s p e c ie s . Among th e l a t t e r , G lo b lg e rln o ld e s c o n g lo b a tu s com prises 1 p e r c e n t o r l e s s o f th e t o t a l p la n k to n ic fa u n a , G lo b lg e r l- n o ld e s s a c c u l l f e r ab o u t 12 to 18 p e r c e n t, N eogloboquadrlna o b l l q u l l o c u l a t a ab o u t 1 p e r c e n t. These s p e c ie s a re c h a r a c t e r i s t i c o f T r o p ic a l W ater. A marked d e c re a se In th e r e l a t i v e abundance o f G. l n f l a t a o c c u rs a t a p p ro x im a te ly 15 cm In c o r e s 36IC and 305 306 361F and 25 cm in c o re s 361J and 366B, t h i s s p e c ie s making up o n ly 3 p e rc e n t o f the p la n k to n ic p o p u la tio n a t th e to p o f th e c o r e s . T his I s accom panied by a c o rre sp o n d in g de c re a se In th e r e l a t i v e abundance o f o t h e r te m p e ra te -w a te r s p e c ie s . 0 . t r u n c a t u l l n o 1des d e c re a s e s to 1 p e rc e n t and G. h l r s u t a t o le s s th a n 1 p e r c e n t, w hereas G. c ra ss a fo rm ls and G. s c l t u l a a lm o st d is a p p e a r. With a d e c re a se In f r e quency o f te m p e ra te -w a te r s p e c ie s In t h e upper p a r t o f th e c o r e s , th e r e I s a sim u ltan eo u s In c re a s e In th e r e l a ti v e abundance o f w arm -w ater s p e c ie s . G. c o n g lo b atu s In c re a s e s to 3 to 6 p e r c e n t, G. s a c c u l l f e r to 20 to 30 p e r c e n t, N. d u t e r t r e l to ab o u t 15 p e r c e n t, and P. o b l l a u l l o - c u la ta to 7 -1 0 p e r c e n t . R e la tiv e fre q u e n c ie s o f d ia g n o s tic s p e c ie s In c o re s 361? and 361J a r e p l o t t e d In F ig u re s 59 and 60. Warmer f a u n a l assem blage a t th e to p o f th e c o re s r e f l e c t modem o cea n o g ra p h ic c o n d itio n s , w hereas th e c o o le r fa u n a l assem blage a t the bottom o f th e c o res r e p r e se n t p a s t o ce a n o g ra p h ic c o n d itio n s u n d er which th e re was d isp lace m e n t o f h ig h e r l a t i t u d e c o o le r fa u n a s toward th e e q u a to r. T h is a l t e r a t i o n o f w a te r m asses c o rresp o n d s to a s h i f t i n g o f th e t r o p i c a l and s u b tr o p i c a l s u rfa c e w a te r s . The m ag n itu d e o f th e change in s u rf a c e - w a te r te m p e ra tu re I n f e r r e d from th e te m p e ra tu re to le r a n c e s o f l i v i n g p la n k to n ic f o r a m in if e r a l p o p u la tio n s (Be and T o ld e rlu n d , 1971; B o lto v sk o y , 1969a) i s eq u ated w ith an 307 in c re a s e In te m p e ra tu re o f a p p ro x im a te ly 5° C e ls iu s . R adiocarbon d a te s d e riv e d from th r e e o f th e fo u r c o re s were d is c u s s e d e a r l i e r and a re in d ic a te d in F ig u re 61. These ag es should be c o n s id e re d a s minimum a g e s . The - v alu e f o r th e top sample o f core 361J i s la r g e f o r th e in d ic a te d age because th e sample was too sm all to o b ta in a r e p r e s e n t a t i v e c o u n t. The fa u n a l change i s d ated a t ab o u t 10,000 y e a r s B .P ., w hich co rre sp o n d s to th e reco g n ized w orldw ide o n s e t o f a warmer c lim a te a t th e end o f th e l a s t g l a c i a t i o n . Some d is c r e p a n c ie s in r a d io m e tr ic d a te s r e p o rte d by o th e r I n v e s t i g a t o r s , from d e e p -se a c o r e s , e x i s t f o r t h i s e v e n t. Examples o f d if f e r e n c e s a r e : 7000 to 8000 yea?*s B .P. in th e s o u th e a s te r n P a c i f ic (Blackman and Som ayajulu, 1 9 6 6 ), 8775 y e a rs B .P. in th e n o r th e a s te r n In d ia n Ocean ( F r e r l c h s , 1968), 10,000 y e a rs B .P. in th e s o u th e a s te r n and c e n t r a l e q u a t o r i a l In d ia n Ocean (C o n o lly , 1967; Oba, 1 9 6 9 ), 11,000 y e a rs B .P. in th e e q u a t o r i a l and n o rth e rn A t l a n t i c Ocean (E ric so n e£ s i . . , 1 9 5 6 ), 11,000 y e a rs and 12,000 y e a rs B .P. in th e n o r th e a s te r n P a c i f ic Ocean (Bandy, I9 6 0 , 1967; Bayudu, 1 9 6 4 ), 12,200 y e a rs B .P . in th e so u th w e ste rn A t l a n t i c Ocean (G root e t & 1., 1967)* 16,500 y e a r s B .P . in th e C aribbean Sea (E m illa n i, 1955)* Such d is c r e p a n c ie s a r e n o t u n re a so n a b le c o n s id e rin g a c curacy and p r e c is io n o f r a d io m e tr ic d a tin g m ethods. Also t h e r e i s commonly a 5-cm u n c e r ta in ty in th e p o s it i o n o f th e boundary due to m ethods o f sam p lin g . The d a te o f 308 1 0 .0 0 0 y e a r s B .P. In th e so u th e rn Mozambique Channel Is w ith in th e ran g e o f p u b lish e d d a te s and c o in c id e s w ith th e 1 0 .0 0 0 y e a r s B.P. d a te r e p o r te d by C onolly (1967) f o r th e e a s t e r n edge o f th e so u th e rn Indian Ocean a t ab o u t th e same l a t i t u d e . In th e f iv e d e e p -se a c o re s from th e con t i n e n t a l s lo p e o f f - s h o r e o f so u th w estern A u s t r a l i a , s tu d ie d by C o n o lly , th e r e i s an a b ru p t downward in c re a s e o f £ . l n f l a t a a t th e 10,000 y e a rs B .P . boundary, o f about | th e same m agnitude as th e one f o r th e Mozambique Channel ! c o r e s . i I T here i s a ls o a change in th e abundance o f r a d lo - l a r i a n s in t h r e e o f th e c o re s (361F, 361J , 366B) a t th e P le is to c e n e -H o lo c e n e boundary, the r a d i o l a r l a n number i n c r e a s in g by s e v e ra l o rd e rs o f m agnitude above th e 10,000 y e a r s l i m i t . The number o f r a d i o l a r l a n t e s t s in th e s e d i m ent f r a c t i o n c o a r s e r th an 62p. i s s m a lle r th a n 100/gm o f d ry sed im en t a t th e bottom o f th e c o re s and I n c re a s e s to ab o u t 500 o r more a t th e to p . S im ila r In c re a s e d abundances o f r a d i o l a r i a n s in Holocene sed im en ts a ls o have been r e p o rte d in th e n o r th e a s te r n P a c i f ic Ocean (Bandy, 1967; K h e ra d p lr, 1970; Nayudu, 1964) and th e n o r th e a s te r n In d ian Ocean ( F r e r l c h s , 1968). An in c r e a s e in th e abundance o f G lo b o r o ta lla m e n a rd ll o f te n h a s been used by v a rio u s a u th o r s to de l i n e a t e warm I n t e r v a l s o f th e P le is to c e n e (S o h o tt, 1935; E rlc s o n and V o llln , 1968; C o n o lly , 1967; Oba, 1967; and o t h e r s ) . T his c r i t e r i o n I s not a p p lic a b le to t h i s p o r tio n o f th e so u th w e ste rn In d ia n Ocean. In c o re o f t h i s a r e a I v a r i a t io n s in abundance o f th e G. m en ard ll group show an In v e rse r e l a t i o n to te m p e ra tu re (M orin, Theyer and V in c e n t, 1970). The G. m en a rd ll group in c r e a s e s from 1 -2 p e rc e n t a t th e to p o f c o re 361F to 7-9 p e rc e n t a t th e bottom (F ig . 59b). The g r e a t e r abundance in th e lo w er segment o f th e i c o re s o f G. m e n a r d ll. a s p e c ie s r e s i s t a n t to s o lu tio n | (B e rg e r, 1968; P a rk e r and B e rg er, 1971) i s n o t because o f I I s e l e c t i v e s o lu tio n o f f o r a m ln if e r a l t e s t s , as ev idenced i ! by freq u en cy v a r i a t i o n s o f G lo b lg e rln o ld e s r u b e r , a s p e c ie s i s u s c e p tib le to s o lu t i o n , which i s a lso more abundant in | th e lo w er p a r t o f th e c o re s ( F ig s . 59b and 6 0 b ). I D i s t r i b u t i o n a l tr e n d s o f G. m en ard ll in w a te rs and s u rfa c e sedim ents o f th e a r e a i n d ic a te t h a t a s h i f t i n g o f w a te r m asses tow ard th e e q u a to r, compared to th e p r e s e n t oceanographic s e t t i n g , would r e s u l t in an in c re a s e in abundance o f g . m e n ard ll a t s i t e s on th e m argin o f th e j | T r o p ic a l W ater. These fin d in g s show t h a t p a le o c llm a tlc j i n t e r p r e t a t i o n s based s o l e l y upon G. m e n a rd ll in c o re s o f j m a rg in a l t r o p i c a l a re a s a r e o f q u e s tio n a b le v a lu e , j Changes in th e freq u en cy o f the G. m en ard ll group j a re n o t a p p lic a b le in o th e r a re a s as w e l l . F r e r ic h s (1968) ' in a stu d y o f th e n o r th e a s te r n In d ian Ocean was u n ab le to | use t h i s fa u n a l c r i t e r i o n to d e fin e P le is to c e n e te m p e ra tu re I f l u c t u a t i o n s . Doubts were ex p ressed (M orin, Theyer and 310 V in c e n t, 1970) on th e s ig n if ic a n c e o f th e v a r i a t i o n s In abundance o f th e 0 . m en ard ll group r e p o rte d by B ricson and jW ollln (1970) In c o re s from th e s o u th e a s te r n P a c i f i c . V a r ia tio n s In abundance o f a n o th e r warm -water s p e c ie s , G. r u b e r , a ls o should be I n te r p r e t e d w ith c a u tio n . 1 jIn c re a s e In abundance o f t h i s s p e c ie s In th e c o re s s tu d ie d i |does n o t c o r r e l a t e w ith h ig h e r te m p e ra tu re . G. ru b e r I n c re a s e s from 7-13 p e rc e n t a t th e to p o f th e c o r e s , to 18 i ip e rc e n t a t th e bottom (P ig s . 59b and 6 0 b ). S iz e f a c to r s jmay In flu e n c e t h i s tr e n d as G. r u b e r Is more abundant In f r a c t i o n s s m a lle r th a n 250p. S a l i n i t y a l s o may In flu e n c e th e d i s t r i b u t i o n o f G. r u b e r . ; In sed im en ts o f th e Andaman Sea, betw een l a t i t u d e s I |5 °N .-1 5 °N ., F r e r ic h s (1968) p o s tu la te d t h a t G lo b lg e rln a ru b e sc e n s was an e x c e l l e n t te m p e ra tu re I n d i c a t o r , I t s freq u en cy I n c re a s in g d u rin g c o o le r p e r io d s . A re v e rs e tre n d o c c u rs In t h i s a r e a , an In c re a s e In G. ru b escen s c o r r e l a t e s w ith h ig h e r te m p e ra tu re s and I t s freq u en cy d e c r e a s e s In c o re s below th e H o lo c e n e -P le ls to c e n e boundary. |F r e r ic h s e x p la in e d th e In c re a s e In G. ru b e sc e n s In c o ld e r !I n t e r v a l s by an In c re a s e In p r o d u c t iv i t y o f t h i s s p e c ie s i i a t th e expense o f o th e r p la n k to n ic s p e c ie s . In c o n t r a s t , j I t I s proposed t h a t I t I s caused by an ex p an sio n o f w a te r im asses. The d i s t r i b u t i o n o f l i v i n g G. ru b e sc e n s in w a te rs i |o f th e In d ia n Ocean i s n o t w ell-know n b u t t h i s s p e c ie s !o c cu rs p re d o m in a n tly In low l a t i t u d e s (Be and T o ld e rlu n d , 311 1971; B o lto v sk o y , 1 9 6 9 a). In s u rfa c e sed im en ts o f th e so u th e rn Mozambique Channel I t s h ig h e r fre q u e n c y c o r - l I r e l a t e s w ith T r o p ic a l W ater. I f th e maximum c o n c e n tr a tio n ! o f G. ru b e sc e n s o c c u rs In th e t r o p i c a l zone o f th e In d ia n i Ocean, somewhere betw een l a t i t u d e s 5°N. and 25°S.» a s h i f t o f w a te r m asses to th e n o r th d u rin g c o o le r tim e s would i I j r e s u l t In an I n c re a s e In G. ru b escen s In th e Adaman Sea | a s w e ll a s a d e c re a se In th e so u th e rn Mozambique C hannel. | T his view I s In agreem ent w ith F a i r b r i d g e 's (1964, 1965) i 1 | I n f e r e n c e , b ased on o b s e rv a tio n s from A f ric a and th e M e d ite rra n e a n , th a t d u rin g g l a c i a l p e rio d s th e w estw lnd i b e l t s w ith a s s o c i a t e d r a i n f a l l were d is p la c e d 5 to 10° | northw ard and th e e q u a t o r i a l p lu v ia l zone was com pressed | r a t h e r th a n e x te n d e d . These f in d in g s em phasize the Im portance o f c o n s id e r ing th e d i s t r i b u t i o n o f th e e n t i r e fa u n a r a t h e r th an a s in g le s p e c ie s f o r d e f in in g p a le o c llm a tlc t r e n d s . A nother e x c e l l e n t example o f t h i s I s th e v a r i a t i o n in freq u en cy o f | G. I n f l a t a . In th e so u th w est In d ia n Ocean t h i s s p e c ie s i s | | an i n d i c a t o r o f c o o le r p e r io d s , w hereas in th e n o r th - ! e a s te r n A t l a n t i c and w e ste rn M ed iterran ean i t s h ig h e r i freq u en cy c o r r e l a t e s w ith warmer p e rio d s (B lanc V ern et and P a s to u r e t , 1969; C a ra lp , 1971; T h ied e, 1 9 7 1 ). In th e l a t t e r a r e a s th e v a r i a t i o n in abundance o f G. l n f l a t a p ro b a b ly Is c lo s e ly r e l a t e d to v a r i a t i o n s in th e C a n a rie s C u rren t ( B e and T o ld e rlu n d , 1971). In a d d i t i o n to 312 te m p e ra tu re , Yen (1971) su g g e ste d t h a t s a l i n i t y has an Im p o rta n t r o le In th e d i s t r i b u t i o n o f G. I n f l a t a . These d is c u s s io n s show t h a t d i f f e r e n t te c h n iq u e s must be used f o r p a le o c llm a tlc s tu d ie s depending on th e o cean o g rap h ic s e t t i n g o f th e a r e a . V a r ia tio n s In c o l l i n g r a t i o o f G. t r u n c a t u ll n o l d e s p ro v id e a good t o o l f o r c o r r e l a t i o n , a t l e a s t w ith in lim ite d a r e a s , and were used f o r c o r r e l a t i o n s between deep- s e a c o re s In v a r io u s re g io n s ( f o r exam ple, In th e M e d ite r r a n e a n , P a rk e r, 1965; Todd, 1958; Herman, 1968; R e is s , 1 9 7 1 ). In the s o u th e rn Mozambique Channel I t a l s o p ro v id e s a good c o r r e l a t i o n mechanism ( F ig . 6 1 ). No change In th e c o l l i n g d i r e c t i o n o f t h i s s p e c ie s o c c u rre d a t th e te m p e ra tu re change o f th e H o lo c e n e -P le lsto c e n e boundary when a s i g n i f i c a n t change In fa u n a l com p o sitio n I s e v id e n t. On th e o th e r h an d , a change o ccu rs l a t e r when th e f a u n a l co m p o sitio n does n o t v ary ( F ig s . 59 and 6 0 ). A s im i l a r s i t u a t i o n Is o b serv ed In c o re s from th e M e d ite rra n e a n where th e l a s t s h i f t from d o m in an tly d e x tr a l to dom inantly s l n l s t r a l Is c o n s id e re d to o c c u r n e a r and above th e P le ls to c e n e -H o lo c e n e boundary (P a rk e r, 1958; Todd, 1958; R e is s e t a l . , 1971)* DISCUSSION OF PALEOOCEANOGRAPHIC AND PALEOCLIMATIC LATE QUATERNARY CHANGE IN THE AREA AND COMPARISON WITH LAND RECORD ! Q uaternary c l i m a t i c changes have been w e ll- documented on la n d f o r t h e n o r th e rn h em isphere (Europe and N orth America) b u t l i t t l e I s known ab o u t A f r ic a . F l i n t | (1959) from com parison o f fo rm er and r e c e n t sn o w lin es on | th e t r o p i c a l e a s t A fric a n m o u n tain s, I n f e r r e d th a t ; te m p e ra tu re changes o f a b o u t 5 to 7°C could have o o cu rred In A f ric a d u rin g th e Q u a te rn a ry . Only r e c e n t l y have p o lle n I s tu d ie s b ro u g h t a la r g e c o n t r ib u t i o n to knowledge o f i i A fric a n p a le o c llm a te s . R e se arc h on p o lle n I n d ic a te t h a t I th e r e was a c o o le r I n t e r v a l betw een 14,000 and 26,000 y e a r s B .P ., c a lle d th e Mount Kenya G la c ia tio n o r Hypo- th e rm a l, w hich Is c o e v al w ith th e l a t t e r p a r t o f th e l a s t Ice age (= Wurm, = W isc o n sin ). T his co ld p e r io d was ' preceded by a warmer p e rio d whose te m p e ra tu re was n o t as | g r e a t as to d a y . i A f ric a Is now a s e m i- a r id r e g io n . S tu d ie s o f la k e l e v e l s in e a s t A f ric a re v e a le d t h a t changes in r a i n f a l l o c c u rre d w hich were c o r r e l a t i v e w ith g l a c i e r grow th and r e t r e a t . T h is le d to th e s o - c a l l e d P lu v ia l th e o ry in i w hich i t i s p o s tu la te d t h a t p l u v i a l c o n d itio n s p re v a ile d i i i I 313 in E ast A fric a d u rin g g l a c i a l maxima and n o n - p lu v ia l d u r in g i n t e r g l a c i a l s . T his w idely a c c e p te d th e o r y , w hich i s s t i l l used by c h r o n o s tr a tlg r a p h e r s , has been shown to be ill- f o u n d e d as p l u v i a l and n o n - p lu v ia l c o n d itio n s m ust have o c c u rre d s im u lta n e o u s ly in d i f f e r e n t p a r t s o f A fric a ( F l i n t , 1959, 1963; Z in d eren B akker, 1966, 1969; C oetzee and Z in d eren B akker, 1 9 7 0 ). Coetzee and Z inderen Bakker who d isc u s s e d tr e n d s in r a i n f a l l changes in A fric a con cluded t h a t th e p a t t e r n i s co m p licated and n o t y e t w e ll ! u n d e rsto o d . Some s e c tio n s o f A fric a must have re c e iv e d i | more r a i n f a l l w h ile sim u lta n e o u s ly o th e r s e x p e rie n c e d non- : p lu v ia l c o n d itio n s . A lthough c lim a tic changes were sy n chronous, o fte n th e y were d i f f e r e n t in n a tu r e , e s p e c i a l l y a s f a r as h u m id ity o r r a i n f a l l i s concerned. B a t t i s t i n i (1959a, 1959b, 1966, 1971) s tu d ie d P llo q u a te rn a r y la n d s e c tio n s and c o a s ta l f e a t u r e s a lo n g th e M alagasy c o a s t . S outhern M adagascar i s a s e m i- a r id c lim a te b u t d u rin g th e Q u atern ary i t e x p e rie n c e d a c lim a te ! w ith h ig h e r r a i n f a l l , s u f f i c i e n t l y g r e a t to f i l l la k e b a s in s . In th e s o u th e rn t i p o f M adagascar th e A epyornlan s ta g e c o n s is t o f m arine and c o n tin e n ta l c a lc a re o u s san d sto n e and t e r r e s t r i a l m o llu sk s. In t h i s u n it B a t t i s t i n i d e fin e d t h r e e m arin e tr a n s g r e s s i o n s , none o f w hich was o v e r 3 to 4 m above p r e s e n t s e a - l e v e l , s e p a ra te d by " p lu v ia l" p e rio d s w e tte r th an to d a y . H is i n t e r p r e t a t i o n i s summarized on Table IV. 315 Table IV. M arine t r a n s g r e s s i o n s and p lu v ia l p e rio d s In th e A epyornian s ta g e o f th e so u th ern t i p o f M adagascar (d e fin e d by B a t t i s t i n i , 1959a, 1959b, 1966, 1 9 7 1 ). (U n its In o rd e r o f In c r e a s in g a g e .) M arine t r a n s g r e s s io n s ____________ " P l u v i a l s 1 1 ___________________ j j F la n d rlan __________________________________________________________ I Lavanonlan: Two C d a te s : ( a t 80 cm from to p : 6760 - 100 and a t 240 i cm: no a c t l v - ; ___________________________________________________ U y )_____________ i K arlm bollan = R eef I I = O u ljia n Morocco = T y rrh e n ia n I I I = 1 s t Wiirm I n t e r - j ________________ s ta d e ______________________________________________ ! ____________________________________ Ambovomblan___________________ T atsim ian = R eef I____________________________________________ I t I s p ro b a b le t h a t v a r i a t i o n s In th e amount o f d e t r l t a l sed im en ts re c o rd e d In c o re s from th e c o n tin e n ta l s sh e lv e s and s lo p e s o f f th e T ugela and O nilahy r i v e r s a re I r e l a t e d to changes In th e r i v e r d isc h a rg e s because o f | v a r i a t io n s in r a i n f a l l . No a tte m p t to r e l a t e th e s e e v e n ts | to a g e n e ra l c l im a tic s c a le i s made because l i t t l e I s | known about p a le o c llm a tic v a r i a t i o n s h e re and v a r i a t i o n s ! in r a i n f a l l on b o th s id e s o f th e Mozambique Channel may | n o t have been contem poraneous. j The c l i m a t i c change a t 10,000 y e a rs B.P. re c o rd e d 1 In deep sea c a lc a re o u s oozes o f t h i s a re a r e f l e c t an_______ 316 o cean o g rap h ic change contem poraneous to a com parable ocean o g rap h ic m o d ific a tio n a t th e same l a t i t u d e In the s o u th e a s te rn In d ia n Ocean (C o n o lly , 1967). This change, w hich marks th e P le isto c e n e -H o lo c e n e boundary, does n o t c o in c id e w ith th e F la n d ria n tr a n s g r e s s i o n a s d e fin e d by B a t t i s t i n i in the so u th e rn t i p o f M adagascar. The F la n d ria n , d e fin e d by Dubois (1 9 2 4 ), r e f e r s to sed im en ts | d e p o s ite d by th e m arine t r a n s g r e s s i o n t h a t accompanied j th e d e g la c ia tio n fo llo w in g th e l a s t ic e age maximum. The I | base o f th e F la n d ria n in s o u th e rn M adagascar i s d e fin e d by B a t t i s t i n i as younger th an 6760 1 100 y e a rs B .P . (T able i IV ). The l a t t e r d a te c o in c id e s ro u g h ly w ith th e s h i f t in c o i l i n g o f G lo b o r o ta lla t r u n c a t u ll n o l d e s re c o rd e d in t h i s s tu d y , d ated a t ab o u t 6000 y e a r s B .P. I t a p p e a rs , th u s , t h a t th e change in c o i l i n g o f G. tr u n c a t u ll n o l d e s c o r r e l a t e s w ith th e end o f a p l u v i a l p e rio d in so u th ern M adagascar, th e L avanonlan. A d e cre ase in th e an n u al d isc h a rg e o f th e r i v e r s owing to th e o n se t o f a d r i e r j c lim a te l i k e l y was accom panied by a d i l u t i o n o f th e s a l t i | c o n c e n tr a tio n o f c o a s ta l w a te r s . I t i s p o s s ib le t h a t a i change in s a l i n i t y o f s u rf a c e se a w a te r, even o f sm all I I a m p litu d e , i s re s p o n s ib le f o r th e s h i f t in c o l l i n g o f G. t r u n c a t u l l n o l d e s . Compared to to d a y , in P le is to c e n e tim e s t h e r e was a i I s h i f t o f s u rfa c e w a te r m asses tow ard th e e q u a to r . In th e Mozambique C hannel, the S u b tr o p ic a l W ater s h i f t e d n o rth o f 317 23°S. a s re c o rd e d In c o re s from th e c e n t r a l and e a s te r n p a r t o f the c h a n n e l. I t p ro b ab ly d id n o t ex ten d to o f a r n o rth because In c o re s o f th e n o rth e rn Mozambique Channel no ev id en ce o f te m p e ra tu re change I s re c o rd e d (U baldo, 1971). Cores lo c a te d In th e w e ste rn p a r t o f th e s tu d y a re a un d er th e T r o p ic a l W ater o f th e M ozambique-Agulhas C u rre n t, and whose se d im e n ta tio n I s n o t d is tu r b e d by th e I c u r r e n t winnowing, do n o t show ev id en ce o f te m p e ra tu re I j ch an g es. T h is s u g g e s ts t h a t th e Agulhas C u rre n t e x is te d I In th e P le is to c e n e , b u t was p ro b ab ly n arro w er and s tr o n g e r . iHow f a r so u th d id I t extend? In o r d e r to o b ta in an I ! answ er, I t would be I n t e r e s t i n g to study c o re s f u r t h e r i | so u th , c lo se to S outh A f r ic a , an a r e a s u g g e ste d f o r f u tu r e I n v e s t i g a t i o n . A lthough th e L ate P le is to c e n e Is a p e rio d o f g e n e r a l c o o l e r c lim a te , th e te m p e ra tu re In th e Agulhas C u rre n t may have been warmer th an to d a y . T h is I s I n f e r r e d by th e p re s e n c e o f a r e l i c t fauna on the o u t e r ! s h e lf o f f Inhambane w hich c o n ta in s an assem blage w ith ' warmer c h a r a c t e r i s t i c s than modern assem b lag es now l i v i n g | j on t h i s s h e l f . Cores re c o v e re d from s i t e s so u th o f 32°S. u n d e rn e a th I th e S u b tr o p ic a l W ater show no evidence o f te m p e ra tu re ch an g es, Im plying t h a t t h i s re g io n was s t i l l covered w ith I th e same s u rf a c e w a te r m ass. T h e re fo re , i t a p p e a rs t h a t th e S u b tr o p ic a l C onvergence, which bounds S u b tr o p ic a l W ater to th e so u th , d id n o t s h i f t as f a r n o rth a s 32°S. These r e s u l t s show how c r i t i c a l Is th e lo c a tio n o f s i t e s in a m a rg in a l p o s it i o n o f w a te r m asses b o u n d a rie s, e s p e c i a l l y | in a r e a s where changes a re o f an am p litu d e as sm a ll a s in s u b tr o p ic a l r e g io n s . P a le o c llm a tic f l u c t u a t i o n s re c o rd e d in deep se a c o re s m o stly have been ob serv ed in te m p era te a re a s where th e m agnitude o f change i s la r g e ( f o r exam ple, j o f f w e ste rn U n ite d S t a t e s in th e P a c i f i c , o f f F ran ce and i | P o rtu g a l in th e A t l a n t i c ) o r in e q u a t o r i a l a re a s a s th e [ ] ! C arib b ean , b u t few o b s e rv a tio n s from s u b tr o p ic a l a r e a s a re ' a v a i l a b l e . In t h i s s u b tr o p i c a l re g io n o f th e sou th w est i In d ia n Ocean, o n ly th e few c o re s lo c a te d on th e o u te r edge : o f th e Mozambique-Agulhas C u rren t n e a r th e boundary o f th e two s u rfa c e w a te r m a sse s, and n o t in p a th s o f t u r b i d i t y j flo w s, re c o rd a te m p e ra tu re change a t th e P le is to c e n e - t | Holocene bou n d ary . k | Warmer c o n d itio n s o f th e l n t e r s t a d i a l w ith in th e | L ate P le is to c e n e re c o rd e d on d e e p -se a c o re s o f th e n o r th - j | e a s te r n In d ia n Ocean betw een 22,500 and 42,000 y e a r s B .P . ! ( F r e r ic h s , 1968) a r e n o t found in th e p r e s e n t stu d y a r e a , I w hich may have n o t been a f f e c t e d by t h i s c l im a tic change. i I The base o f co re 56IF d ated 28,940 1 5»500 y e a rs B .P . c o n - ! t a i n s a p la n k to n ic fa u n a t h a t does n o t r e f l e c t w a te r | | c o n d itio n s warmer th a n th e o v e rly in g younger P le is to c e n e | se d im e n ts. In c o re s lo c a te d un d er th e Agulhas C u rre n t, i j sedim ents t h a t a r e 23*000 to 31*000 y e a rs old c o n ta in a 319 p la n k to n lc fauna s i m i l a r to th e 16,000 y e a r s - o ld s e d i m ents as w e ll as to modern sed im en ts o f t h i s a r e a . SUM M ARY AM D CONCLUSIONS T his I n v e s t i g a t i o n co n c e rn s th e so u th e rn Mozambique Channel and a d ja c e n t so u th w est In d ia n Ocean w hich h av e been p o o rly I n v e s t i g a t e d . I t I s an a r e a w ith rugged sub m arin e to p o g rap h y In c lu d in g narrow s h e lv e s , s te e p s lo p e s , j th e Mozambique and M adagascar P la te a u s a t an averag e depth o f 2000 m, and th e n o r th e rn p o r tio n o f th e deep N a ta l I B a s in . A number o f subm arine canyons c r o s s th e slo p e o f | th e a r e a . The g e n e r a l n o r th n o r th e a s t- s o u th so u th w est ! s t r u c t u r a l tr e n d I s r e l a t e d to p a r a l l e l f r a c t u r e zones w hich c ro s s th e so u th w est In d ia n Ocean. The wide ra n g e | o f to p o g ra p h ic f e a t u r e p ro v id e s a v a r i e t y o f s o u rc e s f o r s e d im e n ts. As a r e s u l t o f th e s tu d y , th e fo llo w in g con c lu s io n s were re a c h e d : 1 . S u rfa c e w a te rs show a so u th e a stw a rd d e c re a se In te m p e ra tu re w ith a p a r a l l e l In c re a s e in s a l i n i t y and d is s o lv e d oxygen c o n te n t. Comparison w ith o b s e rv a tio n s ! ! from o th e r e x p e d itio n s r e v e a ls t h a t th e y e a r ly s u r f a c e - j Q te m p e ra tu re v a r i a t i o n I s ab o u t 4 C, b e in g more pronounced in th e re g io n n e a r Durban (w ith a ran g e o f 5 ° 0 ) and l e s s i marked In th e a r e a n e a r T u le a r (w ith a ran g e o f 3 0 ) . 2. Seven w a te r m asses were i d e n t i f i e d in t h i s p o r tio n o f th e so u th w e st In d ia n Ocean. S u rfa c e w a te rs a re 320 321 T ro p ic a l W ater and S u b tr o p ic a l W ater. T ro p ic a l W ater l i e s In th e Mozambique C hannel n o r th o f 24°S. and so u th o f t h i s l a t i t u d e a lo n g th e A fric a n c o a s t and flow s southw ard alo n g b oth A fric a n and M alagasy c o a s ts a s a shallow tongue o f l i g h t , warm, p o o rly oxygenated w a te r o f low s a l i n i t y on to p o f d e n s e r, c o o le r , h ig h ly s a lin e and more oxygenated S u b tro p ic a l W ater. These to n g u es o f T r o p ic a l W ater c o n tr ib u te to southw ard e x te n s io n s o f th e Mozambique C u rre n t on b o th s id e s o f th e Mozambique Channel and t o th e | j u p p er la y e r o f th e A gulhas C u rre n t. S u b tro p ic a l W ater form s two la rg e c y c lo n ic (c lo c k - I w ise) g y res a t th e s u r f a c e n o r th and so u th o f 3 0 ° 3 0 'S ., r e s p e c t i v e l y , and s in k s b e n e a th th e T ro p ic a l W ater. The s o u th e rn g y re , c e n te re d a t ab o u t 3 2 °S ., 3 8 ° E ., Is r e s p o n s ib le f o r th e d e cre ase d s u rf a c e te m p e ra tu re , I n c re a se d s u rfa c e s a l i n i t y and In c re a se d s u rf a c e d e n s ity o v e r th e s o u th e rn Mozambique P la te a u , and I s a f e a t u r e o f th e s u rfa c e c i r c u l a t i o n th ro u g h o u t th e y e a r . The n o rth e rn g y re , c e n te re d a t ab o u t 2 4 ° S ., 4 0 °E ., has a d i r e c t io n op p o s it e to th e s w ir l o f th e Mozambique C u rre n t o b serv ed d u rin g th e s p r in g seaso n by o th e r I n v e s t i g a t o r s . Sub s u rfa c e c u r r e n ts were d e te c te d a s s a l i n i t y maxima a t th e n o rth ern m o st s t a t i o n s In th e c e n t r a l a re a o f th e Channel and alo n g th e A fric a n and M alagasy c o a s ts . C e n tra l W ater u n d e r l ie s s u rfa c e w a te rs and b u lg e s upwards In th e c e n te r o f th e l a r g e eddy In th e s o u th e rn 3 2 2 p a r t o f th e a r e a . U pw elling o f C e n tra l W ater observed a t ab o u t 25°S. d u rin g th e s p rin g o f two s u c c e s s iv e y e a rs by | Menache (1961) was n o t n o te d In t h i s I n v e s tig a tio n and may be a s e a so n a l d is tu rb a n c e r e l a t e d to th e s u rfa c e c i r c u l a tio n p a t t e r n . At d e p th s o f 1000 m and 1500 m N orth In d ia n Deep W ater, from th e n o r th , and A n ta r c tic In te rm e d ia te W ater, from th e s o u th , form b o th an a n tlc y c lo n lc ( c o u n te r clo ck w ise) system n o r th and so u th o f 2 5 °S ., r e s p e c t i v e l y . The boundary between th e two w a te r m asses I s o rie n te d j { n o r th w e s t- s o u th e a s t. N orth In d ia n Deep W ater te n d s to | ex ten d so u th o f th e Mozambique Channel on I t s e a s te rn I s id e , w hereas th e A n ta r c tic In te rm e d ia te W ater ten d s to i p e n e tr a te I n to th e channel on I t s w estern s id e . Two a n t i - c y c lo v s w ir ls o f A n ta r c tic In te rm e d ia te W ater a re c e n te re d o v er th e N a ta l B asin and th e Mozambique P la te a u . At 3000 m N orth A t l a n t i c Deep W ater e n te r s the s tu d ie d p o r tio n o f th e N a ta l B asin from th e s o u th , on th e w e ste rn s id e o f th e b a s in . I t I s fo rc e d down In th e n o rth e rn p a r t o f th e b a s in by th e o v e rly in g N o rth In d ia n i j Deep W ater t h a t p e n e tr a te s In to th e N a ta l B asin from b o th I t s n o rth w e ste rn and n o r th e a s te r n c o r n e rs . A r e tu r n flow , composed o f a m ixing o f th e two w a te r m asses, flow s on th e e a s t sid e o f th e N a ta l B a sin . Bottom W ater was en co u n tered a t a few s t a t i o n s re a c h in g d e p th s g r e a t e r th a n 3500 m. Local u p w e llin g was o b serv ed c lo se to sh o re In th e a r e a s o f T u le a r, Lourenco Marques and n o r th o f Durban. 3. The re g io n I n v e s tig a te d I s th e so u rce a re a o f th e Agulhas C u rre n t, th e w e stern boundary c u r r e n t o f th e S outh In d ia n Ocean, whose mode o f fo rm a tio n v a r i e s depend in g upon s e a so n a l v a r i a t i o n s In th e p o s it i o n o f th e South E q u a to r ia l C u rre n t. F a r t o f th e S outh E q u a to r ia l C u rre n t flo w s In th e Mozambique Channel to form th e Mozambique i C u rre n t, and p a r t flow s to th e e a s t o f M adagascar to form I | th e M adagascar C u rre n t. I t I s p ro b a b le t h a t s e a s o n a lly th e | A gulhas C u rre n t d e r iv e s i t s supply from e i t h e r o f th e se I : stre a m s o r from b o th jo in in g to g e th e r s o u th o f M adagascar. During th e so u th e rn w in te r , th e s u rfa c e c i r c u l a t i o n i p a t t e r n i s d i f f e r e n t from th e p a t t e r n p re v io u s ly o bserved in th e s p rin g . None o r v ery l i t t l e o f th e M adagascar C u rre n t jo in s th e A gulhas C u rre n t. There i s a southw ard flo w o f th e Mozambique C u rre n t In th e e a s te rn s id e o f th e Mozambique Channel which e x ten d s from a few k ilo m e te rs o f f T u le a r to ab o u t 200 km seaw ard, and a northw ard c o u n te r- ! c u r r e n t alo n g th e c o a s t o f s o u th M adagascar o v er th e narrow | c o n tin e n ta l s h e l f . 4. The Agulhas C u rre n t flow s c lo se to th e A fric a n | c o a s t from th e s u rfa c e to g r e a t d e p th s . I t s s u rfa c e l a y e r , com prised o f T ro p ic a l W ater, I s n o t c o n s ta n t In w id th o r d is ta n c e from th e c o a s t . O ff Inhambane I t i s n arro w , ex - l | te n d in g from th e c o a s t to 30 km seaw ard and flow s only o v e r th e c o n t i n e n t a l s h e l f . O ff Lourenco Marques th e c u r r e n t w idens and e x te n d s from Lourenco M arques seaward to a d is ta n c e o f 200 km. At ab o u t 2 8 °3 0 'S . a westward flow o f S u b tro p ic a l W ater c o n s t r i c t s th e c u r r e n t where I t narrow s to a w id th o f 65 km. At Cape S a in t L u cia th e c u r re n t s h i f t s o f f s h o r e , p ro b ab ly owing to th e change in th e tre n d o f th e c o a s t and th e b ro a d e n in g o f th e c o n tin e n ta l s h e l f , j and n o r th of Durban i t e x te n d s from a few k ilo m e te rs away I from th e c o a s t to ab o u t 150 km. A d jacen t to th e Agulhas I | C u rren t th e r e i s a n o rth e a s tw a rd flo w in g c u r r e n t on i t s i | o u te r edge. I ! At s u b su rfa c e d e p th s a southw ard c u r r e n t i s ap- I p a re n t a l s o , b u t w hereas th e u p p er la y e r o f th e c u r re n t i s I c o n s tr i c t e d in some a r e a s , th e s u b su rfa c e l a y e r s a r e n o t. The in te rm e d ia te l a y e r s o f th e A gulhas C u rre n t c o n s is t o f mixed A n ta r c tic I n te rm e d ia te W ater and N orth In d ia n Deep W ater. 5* S h e lf s u r f l c l a l d e p o s its a re te r r ig e n o u s s e d i m ents o f v a r io u s g r a in s i z e , c h i e f l y s i l t y and poor in I calcium c a rb o n a te . Upper slo p e s u rf a c e sed im e n ts, b e tween 200 and 1500 m, a re h e m ip e la g ic c a lc a re o u s mud con t a i n i n g 10 to 30 p e r c e n t calciu m c a rb o n a te , in te rm e d ia te betw een d e t r i t a l s h e l f sedim ent and th e d e e p e r c a lc a re o u s ooze. A reas o f n o n -d e p o s itio n n o te d on th o se p o r tio n s o f th e A fric a n s h e l f and u pper slo p e u n d er th e oore o f th e I Mozambique-Agulhas C u rre n t r e f l e c t th e winnowing a c tio n o f th e s tro n g c u r r e n t . A ro ck y f l o o r co v ered w ith th in 325 s u r f l c l a l d e p o s its , com prised m ain ly o f ab rad ed c a lc a re o u s s k e l e t a l d e b r is , o c c u r o f f th e p r o tr u d in g c o a s t o f so u th e rn Mozambique and so u th o f Cape S a in t L u c ia . Miocene s e d i m ents a r e exposed o f f Inhambane and n o r th o f th e Tugela R iv e r, and a P le is to c e n e ooze c o v e rs th e slo p e s o u th e a s t o f Lourenco Marques between d e p th s o f 1335 and 1910 m. The p re sen c e o f r e l i c t f o r a m i n i f e r a l fa u n a s on the o u te r s h e l f n e a r Inhambane and th e T ugela R iv e r r e f l e c t s a form er low er s e a - l e v e l w hich i s su g g e ste d a ls o by b each - ro ck exposed on th e m iddle s h e l f a d ja c e n t to Lourenco Marques and so u th o f Inhambane. | Lower c o n tin e n ta l s lo p e s below 1500 m, c o n tin e n ta l I r i s e s and p la te a u s a r e covered w ith f o r a m i n i f e r a l oo zes. D i s tr i b u t i o n o f f o r a m in if e r a l m arl ooze, w ith a CaOO-j con t e n t o f 30 to 60 p e r c e n t, and o f f o r a m i n i f e r a l c h alk ooze, w ith a CaCOj c o n te n t h ig h e r th a n 60 p e r c e n t, c o r r e l a t e s in p a r t w ith g r a in s iz e d i s t r i b u t i o n . The sand f r a c t i o n o r m arl ooze i s from 10 to 50 p e r c e n t, w hereas i t i s g r e a t e r th a n 50 p e rc e n t in c h a lk o o ze. D i s t r i b u t i o n o f f o ra m in i f e r a l m a rl and ch alk ooze i s c o n tr o lle d by (1) d is ta n c e from th e la n d m ass, and (2) th e a c tio n o f tr a n s p o r t in g a g e n ts such a s c u r r e n t s , slum ps o r t u r b i d i t y c u r r e n t s . A c o a rse c h a lk ooze o c c u rs c lo s e to th e A fric a n c o n tin e n t in an a re a swept by th e Mozambique C u r r e n t, in th e a b y s s a l p la in w e st o f Europa where th e f o r a m i n i f e r a l ooze i s d i s p la c e d , and on th e Mozambique P la te a u sw ept by an eddy o f A n ta r c tic In te rm e d ia te W ater. 3 2 6 6 . A rocky se a f l o o r I s p r e s e n t around Europa be tween d e p th s o f 2200 m and 2750 m. Fragm ents o f c o r a l l i n e ro c k s dredged from 2750 m c o n ta in p o o rly p re s e rv e d r e e f c o r a ls o f sh allo w w a te r o r i g i n . These ro c k s , p ro b ab ly o f r e c e n t a g e , owe t h e i r p o s i t i o n to th e e f f e c t s o f slum ping. 7 . The p la n k to n lc f o r a m i n i f e r a l fau n a Is d i v e r s i f i e d and t y p i c a l o f warm w a te r . T h i r t y - f i v e s p e c ie s | w ere I d e n t i f i e d . D is re g a rd in g m inor d is c r e p a n c ie s , th e r e j | I s an agreem ent betw een d i s t r i b u t i o n a l p a t t e r n s o f p la n k - I ! t o n ic s p e c ie s In b o th s u rfa c e w a te rs (Be and T o ld e rlu n d , I 1971) and s u rfa c e sed im en ts o f th e a r e a . Both l i v i n g and j dead assem blages r e f l e c t th e a r e a l d i s t r i b u t i o n o f T ro p i c a l and S u b tr o p ic a l W aters and th e A gulhas C u rre n t p a t t e r n . 8 . Sedim entary changes are a p p a re n t In c o re s from th e s h e l f and upper slo p e s h a llo w e r th a n 1820 m In th e a r e a c lo s e to th e T ugela R iv e r . A marked g r a l n - s l z e de c re a s e from th e bottom o f th e c o res to th e to p and a p a r a l l e l d e c re a se In calciu m c a rb o n a te c o n te n t I n d ic a te | an I n c re a s e In f in e d e t r l t a l com ponents In more r e c e n t tim e s . The change may r e f l e c t v a r i a t i o n s e i t h e r In th e T ugela R iv e r lo a d o r In th e winnowing a c tio n o f th e A gulhas C u rre n t, and b o th f a c t o r s may be In v o lv e d . The se d im e n ta ry change, w hich o c c u rs a t 15 cm from th e to p of th e c o r e s , I s n o t d a te d . C ores o f th e M alagasy slo p e o f f th e O nllahy R iv e r, between 439 m and 1006 m, show a se d im e n ta ry change d ated 327 by ra d io c a rb o n a p p ro x im a te ly 2200 y e a rs B .P . There Is a m inor d e c re a se In calcium c a rb o n a te c o n te n t from th e bottom to th e top o f th e c o r e s , which p a r a l l e l s a s l i g h t d e c re a se In th e f o r a m i n i f e r a l number. T h is tre n d I s e s p e c i a l l y w ell-m arked In th e c o a rs e f r a c t i o n o f th e s e d i m ent. F lu c tu a tio n s In th e amount and s i z e o f d e t r l t a l m a t e r ia l s u p p lie d by th e T ugela and O nllahy R iv e rs may p o s s ib ly be r e l a t e d to f l u c t u a t i o n s In r a i n f a l l caused by c lim a tic changes. An a b ru p t se d im e n ta ry change Is e v id e n t In co res ! o f th e N a ta l B asin d eep er th a n 4800 m, e x c e p t a t th e so u th ern m o st and d e e p e st l o c a l e . There I s a marked down ward In c re a s e In calcium c a rb o n a te c o n te n t from l e s s th a n 10 p e rc e n t a t th e to p o f th e c o re s to v a lu e s as h ig h as 60 p e r c e n t. The c a r b o n a te - r ic h sedim ent c o n s is ts o f p a r t i a l l y d is s o lv e d , mixed f o r a m i n i f e r a l o o zes, which a re I n te r p r e t e d a s b l o c l a s t l c t u r b i d l t e s and whose p re se n c e below th e calciu m c a rb o n a te com pensation depth Is a t t r i b u t e d to r a p id b u r i a l . A few co res o f f o r a m i n i f e r a l ooze, a t th e base o f j s te e p s lo p e s o r on subm arine canyon w a l l s , c o n ta in la y e r s o f c o arse te r r ig e n o u s m a t e r ia l I n d ic a t iv e e i t h e r o f slump in g o r t u r b i d i t y c u r r e n t s . C ores com prised th ro u g h o u t t h e i r le n g th o f f o r a m in if e r a l ooze do n o t e x h ib it d e f i n i t e tr e n d s In calcium c a rb o n a te c o n te n t v a r i a t i o n s , a lth o u g h a few c o re s show an upward d e c re a s e In calciu m c a rb o n a te . 328 T h is d e c re a se may be r e l a t e d to calcium c a rb o n a te d i l u t i o n and to f l u c t u a t i o n s In r i v e r lo a d s , w hich may In tu r n r e f l e c t changes In r a i n f a l l . However, no I n t e r p r e t a t i o n o r c o r r e l a t i o n I s attem p ted on t h i s b a s is b ecau se v a r i a t i o n s In r a i n f a l l , a lth o u g h r e l a t e d to c l im a tic v a r i a t i o n s , may n o t have been contem poraneous on b o th s id e s o f th e Mozambique C hannel. 9 . S i g n i f i c a n t fa u n a l changes o c c u r In c o re s o f u n d is tu rb e d f o r a m in if e r a l ooze lo c a te d n e a r th e m argin o f | t r o p i c a l and s u b tr o p ic a l s u rfa c e w a te r m a sse s. There I s i ! a marked v a r i a t i o n In the r e l a t i v e abundance o f te m p e ra te - | w a te r and w arm -w ater s p e c ie s o f p la n k to n ic f o r a m ln if e r s . j In th e sample f r a c t i o n c o a r s e r th an 250}i th e tem p erate s p e c ie s G lo b o r o ta lla I n f l a t a com prises 25 to 30 p e rc e n t o f th e t o t a l p la n k to n ic p o p u la tio n a t th e bottom o f th e c o res and d e c re a s e s t o a p p ro x im a te ly 3 p e r c e n t a t th e to p . There I s a sim u ltan e o u s In c re a s e In th e r e l a t i v e abundance o f w arm -w ater s p e c ie s o th e r th a n G lo b o r o ta lla m e n a rd ll. From t h e bottom to th e top o f th e c o re , N eogloboauadrlna d u t e r t r e l In c re a s e s from ab o u t 5 p e rc e n t to ab o u t 15 p e r c e n t, P u l l e n l a t l n a o b l l q u l l o c u l a t a from a b o u t 1 p e rc e n t to 7 -9 p e r c e n t, G lo b lg e rln o ld e s s a c c u l l f e r from 12-18 p e rc e n t to 20-30 p e r c e n t and G lo b lg e rln o ld e s c o n g lo b a tu s from 1 p e r c e n t o r l e s s to 3-6 p e r c e n t. T h is f a u n a l change, j w hich r e f l e c t s a warming In th e s u rfa c e w a te r , I s dated by | j ra d io c a rb o n t o be a p p ro x im a te ly 10,000 y e a r s B .P. and c o in - c ld e s w ith th e P le lsto c e n e -H o lo c e n e boundary. T his boundary a ls o I s marked by an I n c re a s e o f r a d l o l a r l a n abundance In sed im en ts o f th e H olocene. The r a d l o la r l a n number I n c re a s e s from l e s s th a n 100 below th e boundary to 500 o r more above. Comparable In c re a s e d abundances o f r a d l o l a r l a n s In Holocene sed im en ts have been r e p o rte d In th e N o rth e a st P a c i f i c Ocean and th e N o rth e a s t In d ia n Ocean. I In t h i s p a r t o f th e w o rld th e c lim a tic change r e p r e s e n te d a t th e P le lsto c e n e -H o lo c e n e boundary h a s not ! been re p o rte d p r e v io u s ly . Warming I s contem poraneous w ith a s im i l a r warming In th e w a te rs o f th e s o u th e a s t In d ia n Ocean a t about th e same l a t i t u d e and co rresp o n d s t o th e p o s t - g l a c i a l o c e a n ic warming re c o g n iz a b le In v a r io u s p a r t s i o f th e w o rld . T h is , however, does n o t c o r r e l a t e w ith a younger m arine t r a n s g r e s s io n re c o rd e d In th e s o u th e rn t i p o f M adagascar, w hich was d a te d y o u n g er than 6760 - 100 y e a r s B .P . and I s a t t r i b u t e d to th e F la n d r ia n . i ; 10. In c o r e s n e a r th e boundary o f t r o p i c a l and i s u b tr o p i c a l s u rfa c e w a te r m a sse s, t h e r e i s a s h i f t in th e i I c o i l i n g d i r e c t i o n o f G lo b o r o ta lla t r u n c a t u ll n o l d e s from s i n i s t r a l a t th e to p o f th e c o re s to d e r t r a l th ro u g h o u t th e rem ain d er o f th e c o r e s . T h is change i s n o t acoompanled by v a r i a t i o n s i n th e r e l a t i v e abundance o f te m p e ra te and w arm -w ater p la n k to n ic f o r a m in if e r a l s p e c ie s , which sug g e s ts t h a t no s i g n i f i c a n t te m p e ra tu re v a r i a t i o n o c c u rre d . 330 The s h i f t , d ated by ra d io c a rb o n te c h n iq u e s to be a p p ro x i m a te ly 6000 y e a rs S .P ., c o r r e l a t e s w ith th e end o f th e L avanonlan, a p l u v i a l p e rio d d e fin e d In so u th e rn Madagas c a r . I n s t a l l a t i o n o f a d r i e r c lim a te In t h i s a r e a , which d e c re a se d th e an n u al d isc h a rg e o f r i v e r s and, hen ce, d i l u t e d th e s a l t c o n c e n tra tio n o f c o a s t a l w a te r s , may be r e l a t e d to th e change In c o llin g o f G. t r u n c a t u l l n o l d e s . T h is r e l a t i o n s h i p Im p lie s th a t s a l i n i t y Is a c o n t r o ll i n g f a c t o r o f th e d i r e c t io n o f c o l l i n g o f G. t r u n c a t u l l n o l d e s . 11. C o r r e la tio n s based on ra d io c a rb o n d a te s between deep sea c o re s o f t h i s stu d y and lan d s e c t i o n s o f so u th e rn M adagascar I n f e r t h a t th e p aleo o c e a n o g ra p h lc change r e co rd ed In th e Mozambique Channel a t th e P l e l s t o c e n e - j H olocene boundary o c c u rre d d u rin g the p l u v i a l Lavanonlan I n t e r v a l , and was n o t accom panied by a change In r a i n f a l l In s o u th e rn M adagascar. 12. The f a u n a l change a t th e P le ls to c ene-H olocene boundary r e f l e c t s a warming o f a p p ro x im a te ly 5°C o r l e s s In th e s u rf a c e w a te rs o f th e a r e a d u rin g th e H olocene. In L a te P le is to c e n e tim e th e S u b tro p ic a l W ater ex ten d ed In th e Mozambique Channel n o r th o f 23°S. B ecause c o re s of u n d is tu rb e d ooze from th e s o u th e rn p o r tio n o f t h i s study r e f l e c t no s u rf a c e te m p e ra tu re change, I t I s assumed t h a t a t a l a t i t u d e o f 34°S. P l e is to c e n e and H olocene sed im en ts w ere d e p o s ite d u n d er th e same s u rf a c e w a te r m ass, t h a t I s , S u b tr o p ic a l W ater. I t Im p lies t h a t th e S u b tr o p ic a l Con- 331 v erg en ce w hich bounds S u b tro p ic a l W ater to th e s o u th d id n o t s h i f t a s f a r n o r th as 34°S. d u rin g th e L ate P l e i s t o cene. No te m p e ra tu re change Is re c o rd e d In deep sea c o re s i un d er th e A gulhas C u rre n t which shows t h a t d u rin g th e L a te P le is to c e n e t h i s c u r r e n t was flo w in g In t h i s a r e a n e a r th e A fric a n c o a s t In th e same p o s it i o n a s to d a y . The c u r r e n t | was p ro b a b ly n a rro w e r and s tr o n g e r th an to d a y , and p o s- I | s lb l y warmer a s I n d ic a te d by th e p resen ce o f a r e l i c t fau n a on th e A fric a n o u te r s h e l f , which c o n ta in s an a s semblage w ith w arm er-w ater c h a r a c t e r i s t i c s th an modern assem blages now l i v i n g on th e s h e l f . No p a le o o c e a n o g ra p h lc change Is re c o rd e d d u rin g th e | l a t e P le i s t o c e n e betw een th e I n te r v a l 10,000 to 28,000 y e a rs B .P . 13. A verage s e d im e n ta tio n r a t e s o f u n d is tu rb e d r e c e n t se d im e n ts , younger th a n a p p ro x im a te ly 4000 to 6000 y e a r s , based on ra d io c a rb o n d a te s , range betw een 9 and 1 cm/1000 y e a r s . T his r a t e I s dependent on to p o g rap h y and ; d is ta n c e from th e a d jo in in g la n d m ass. S e d im e n ta tio n r a t e s a r e h ig h e r f o r h em ip elag lc c a lc a re o u s mud and f o r a m i n i f e r a l ooze In a r e a s n e a r to r i v e r s . O ff th e O nllahy R iv e r th e r a t e d e c re a se s from 9 .1 cm/1000 y e a rs a t 440 m to 4 .5 cm/1000 y e a rs a t 1860 m. E a st o f th e Limpopo, a t 55 m» I t I s 8 .4 cm/1000 y e a r s . The r a t e I s low er f o r th e f o r a m i n i f e r a l ooze w hich a c cu m u la te s f u r t h e r 332 away from r i v e r mouth. Accumulation r a t e s f o r ooze younger th an 6000 y ears B.P. range from 0.8 to 2.8 cm/ I 1000 years a t s t a t i o n s on the c o n tin e n ta l slope and th e I I c o n tin e n ta l r is e between depths o f 1829 and 3800 m. The average r a t e o f accum ulation of u n d istu rb ed j f o ra m in if e ra l ooze f o r th e e n t i r e Holocene ranges from i ! approxim ately 1.5 to 2.5 cm/1000 y e a rs . There is no s ig n i f i c a n t change in the sed im en tatio n r a t e s o f Holocene and I P le isto c e n e oozes. Appraised sed im en tatio n r a t e s in the , N atal Basin range from ra p id f o r sediments o f t u r b i d i t y c u rre n t o r ig i n to slow f o r p e la g ic c la y . 14. Study o f an e n t i r e fauna r a t h e r than of a j s in g le sp ecies i s im perative to make paleooceanographlc l i i n t e r p r e t a t i o n s . D i s t r i b u t i o n a l tre n d s of a sin g le ! sp ecies can lead to i n t e r p r e t a t i o n s in o p p o sitio n to the a c tu a l s i t u a t i o n . This i s exem plified by re v e rs e d i s t r i b u tio n a l tre n d s o f G lo b o ro ta lla m e n a rd ll. G. i n f l a t a . | G lo b lg erln o ld es r u b e r and G lo blgerlna ru bescens in v a rio u s ! g eo g rap h ical a re a s w ith d i f f e r e n t oceanographic s e t t i n g s . 15. Size fa u n a l a n a ly s is must be considered in a study o f fauna d i s t r i b u t i o n a l tr e n d s . Species composition i was determ ined in f iv e s iz e f r a c t i o n s o f s e le c te d samples. i In th e same assemblage, th e sp e c ie s com position is dependent on the grade s i z e . This shows t h a t the s e le c tio n o f a c e r t a i n grade s iz e in a fa u n a l a n a ly s is in tro d u ce s a b ias which can y i e l d m islead in g i n t e r p r e t a - tions. Once they a re d e p o site d , fo ra m in ife rs a re an I n t r i n s i c p a r t o f th e t o t a l sediment. They a c t then as c l a s t i c p a r t i c l e s and t h e i r g ra in s iz e is an im p o rtan t param eter f o r r e d e p o s itio n a l p ro c e sse s. L i t t l e is known about r e d e p o s ltlo n o f f o ra m in if e ra l sediments and the | amount o f reworking on the sea f lo o r . Because s o r tin g i occurs w ith d isplacem ent, i t is u se fu l to know in which ! | grade s iz e each s p e c ie s i s normally d i s t r i b u t e d in o rd e r | to o b ta in c l e a r e r u n d erstan d in g o f t h e i r displacem ent. I In t h i s study c o n c e n tra tio n s of c e r t a i n sp ecies in some ! fo ra m in ife ra l ooze r e f l e c t a process o f s o r tin g . 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Creator Vincent, Edith S. (author)

Core Title Oceanography And Late-Quaternary Planktonic Foraminifera, Southwestern Indian Ocean

Degree Doctor of Philosophy

Degree Program Geological Sciences

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

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Advisor Bandy, Orville L. (committee chair), Bakus, Gerald J. (committee member), Gorsline, Donn S. (committee member), Stone, Richard O. (committee member)

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