Processes influencing transportation and deposition of sediment on the continental shelf, Southern California

PDF

Download

Open document

Flip pages

Download a page range

Download transcript

Copy asset link

Request this asset

Request accessible transcript

Transcript (if available)

Content PROCESSES INFLUENCING TRANSPORTATION AND DEPOSITION OF SEDIMENT ON THE CONTINENTAL SHELF, SOUTHERN CALIFORNIA by Herman Adolf Karl A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSPHY (Geological Sciences) November 1976 UMI Number: DP28544 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMI Dissertation Publishing UMI DP28544 Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 UNIVERSITY OF SOUTHERN CALIFORNIA THE GRADUATE SCHOOL UNIVERSITY PARK------------------------------------------------------------------ LOS ANGELES. CALIFORNIA 9 0007 K . O G e » y y K \ § This dissertation, w ritten by ....................... H ejrn a n.. A d o 1 _f. _Ka, r 1............................. under the direction of /Lis... Dissertation Com mittee, and approved by a ll its members, has been presented to and accepted by The Graduate School, in p a rtia l fu lfillm e n t of requirements of the degree of D O C T O R O F P H I L O S O P H Y Date January *0* I977 TxATIQN COMMITTEE A/^v> Chairman ______________ -------------------- DEDICATION This dissertation is dedicated to the memory of my father, who was an uncommon and good man. "Two roads diverged in a wood, and I -- I took the one less traveled by, And that has made all the difference" Robert Frost i i CONTENTS PAGE INTRODUCTION ........................................ 1 General statement .............................. 1 Purpose ........................................ 1 Acknowledgments ................................ 2 Historical background and previous work .... 5 Principles of sediment transport ............... 9 General ...................................... 9 Nature of currents............................10 Fluid f l o w .................................... 10 Velocity profile and fluid stress .......... 11 Initiation of grain movement ............... 19 Mass sediment transport ..................... 26 Suspended l o a d ................................ 28 Comparison of Atlantic and Pacific coasts . . . 32 REGION OF S T U D Y ...................................... 37 General...........................................37 Area of field work ........................38 Bathymetry and geologic structure ............. ^ Physical oceanography ......................... ^6 General borderland circulation............... k-6 PAGE Vicinity of San Pedro B a y..................... ^7 General surface circulation ............ ^7 T i d e s .......................................50 W a v e s .......................................50 Bottom currents ......................... 51 PROCEDURES AND METHODS .............................. 52 Sampling g r i d .................................... 52 Sampling methods ................................ 52 Turbidity, temperature and salinity ........ 55 Substrate...................................... 55 Bottom current measurements ................. 59 Side scan sonar................................ 60 RESULTS...............................................62 Substrate.........................................62 Textural properties of surficial sediments . 63 Bedforms.......................................76 Internal sedimentary structures ............ 95 Water column..................................... 102 Suspended sediment ......................... 102 General................................... 102 Regional trends ......................... 102 Detailed surveys ......................... 112 Seasonal trends ....................... 112 Vertical variation ................... 125 PAGE Variability over time.................1 ^7 Continuous monitoring of the thermocline........................... 155 Temperature..................................l6l Near-bottom current measurements ............... 162 17-21 December, 1973 ....................... 162 16-19 March, 1976 ........................... 166 12-15 April, 1976 ........................... 169 DISCUSSION AND INTERPRETATION ..................... 170 General statement .............................. 170 Surface waves .................................. 170 General......................................170 Wave equations............................. 171 Calculated bottom velocities ............... 173 Bedforms .. .. .. .. . . ... ... .. 190 Directions of transport.....................20^+ Palimpsest sediments ..................... 206 Origin of compound ripples ................. 209 Origin of mesoscale bedforms ............... 212 Meteorological driving forces ................. 217 General......................................217 Shelf hydraulic regime ..................... 219 Storm-induced bottom features ............... 222 Mesoscale current lineations ............. 223 PAGE Small-scale bedforms ..................... 22k Suspended sediment ......................... 228 Internal waves .................................. 229 Near-bottom currents ........................... 24*0 Nature of currents.........................24*0 Sediment transport and substrate response . . 244 Determination of particle transport history................................. 244 Regional patterns of textural variables . 265 Shelf parallel hydrodynamic provinces . . 268 Inner shelf...........................275 Central shelf ......................... 275 Outer shelf...........................276 Anomalies in regional textural trends . . 276 Shelf transverse hydrodynamic provinces . 278 CONCLUSIONS........................................281 Conceptual model of shelf processes .......... 281 Major implications............................. 294- REFERENCES..........................................297 APPENDICES..........................................314* ILLUSTRATIONS FIGURE PAGE 1. Relative velocity profile in bottom boundary layer for hydrodynamically smooth and turbu lent flow.........................................14 2. Threshold curves for unidirectional flow, after Inman (1963) 22 3. Threshold curves for oscillatory flow, after Clifton (1976) 25 4. Regional location m a p ............................ 4l 5. Geographic boundaries of San Pedro shelf, land marks and bathymetric provinces ............... 43 6. Box core, shipek grab and current meter loca tions (a), and median grain diameter of surfi- cial sediment (b) , San Pedro s h e l f............. 65 7. Mean grain diameter (a) and standard deviation (b) of surficial sediment, San Pedro shelf . . 78 8. Skewness (a) and percent sand (b) of surficial sediment, San Pedro shelf ..................... 80 9. Percent silt (a) and sand/mud (silt and clay) ratio (b) of surficial sediment, San Pedro shelf.............................................82 10. Station locations of bottom photographs taken on San Pedro shelf (a), and track lines of side scan sonar survey of San Pedro shelf (b) . . . 84 11. Photographs showing typical bedforms and bottom features observed on San Pedro shelf ........ 86 12. Photographs of complex and unusual bedform ob served on San Pedro shelf........................91 13- A series of photographs illustrating the sea sonal occurrence and absence of ripple marks . 94 14. Side scan sonar records showing mesoscale cur rent lineations.................................. 97 FIGURE PAGE 15. Radiographs of cores: "chaotic" signature in deposits on the central shelf (a); a core from the upper slope (162 m) (t>) , and a core from 350 m off Pt. Hueneme (c)...................100 16. Stations occupied during cruise 1250, July- August, 1973 (a) and 1273 > January, 197^ ("b) . 104 17. Maps showing regional patterns of relative turbidity (percent light transmission) .... 107 18. Maps showing regional distribution and con centration (mg/l) of suspended sediment on the surface (a) and 1 m above the bottom (b) for January, 1974 (cruise 1273) from Pt. Mugu to Dana P o i n t ................................. 109 19. Maps showing regional patterns of relative turbidity (percent light transmission) 5 m. below the surface (a) and 1 m above the bottom (b) for July-August, 1973 (cruise 1250) from Pt. Mugu to Dana P o i n t .......................... Ill 20. Station locations of transmissometer casts, Cruise 1294, August, 197^ (a) a^d cruise 1316, December, 197^ (t>) . Locations of profiles depicted in Figs. 35> 37» 38 and 39 are shown on (b).............................................114 21. Areal patterns of relative turbidity (percent light transmission) at the surface (a) and 1 m above the bottom (b) for August, 1974 (cruise 1294) , San Pedro B a y ............................ 116 22. Areal patterns of relative turbidity (percent light transmission) at the surface (a) and 1 m above the bottom (b) for December, 197^ (cruise 1316) , San Pedro B a y ............................ 118 23. Station locations of transmissometer casts, cruise 1310, November, 197^ (a) and areal pat terns of relative turbidity (percent light transmission) 1 m above the bottom for November, 197^ (cruise 1310) , San Pedro B a y............... 120 FIGURE PAGE 24. Vertical profiles of relative turbidity (percent light transmission) along a transect occupied during August, 1974 and June, 1975> San Pedro B a y .....................................124 25. Vertical profiles of relative turbidity (percent light transmission) along a transect occupied during August and December, 1974, San Pedro Bay.....................................127 26. Vertical profiles of relative turbidity (percent light transmission) along a transect reoccupied over an interval of 2 days in November, 1974, San Pedro B a y ................... 129 27. A series of transverse (north-south) profiles showing relative turbidity (percent light transmission), from east to west, San Pedro Bay, December, 1974 ............................ 131 28. A series of transverse (north-south) profiles showing relative turbidity (percent light transmission) from east to west, San Pedro Bay, December, 1974 ............................ 133 29. A series of transverse (north-south) profiles showing relative turbidity (percent light transmission) from east to west, San Pedro Bay, December, 1974 ............................ 135 30. A series of longitudinal (east-west) profiles showing relative turbidity (percent light transmission) from north to south, San Pedro Bay, December, 197^.............................. 137 31. A series of longitudinal (east-west) profiles showing relative turbidity (percent light transmission) from north to south, San Pedro Bay, December, 1974 ........................... 139 32. A series of maps showing changes in areal patterns of relative turbidity (percent light transmission) at 5 and 10 m intervals (10- 25 m) down through the water column, San Pedro Bay, December, 1974 ....................... l4l i x FIGURE PAGE 33* Areal patterns of relative turbidity (percent light transmission) at 30 m below the surface (a); and at 40 m below the surface (b); and an illustration of the limits of a mid-water plume.............................................143 34. Transmission profiles along three north- south transects in the vicinity of San Gabriel Submarine Canyon ...................... 145 35* A series of transmissometer records from casts made every 0.5 hours over several hours in March, 1 9 7 6 .................................. 149 36. Graph showing the correlation between transmission (percent) and weight (mg/l) of suspended sediment ........................... 154 37. Fluctuations in percent light transmission and temperature with respect to time during continuous monitoring at a level within the seasonal thermocline ......................... 157 38. Graph showing the oscillation of the seasonal thermocline.......................................160 39* Vertical temperature profiles for each season showing the depth to the seasonal thermocline . 164 40. Polar diagrams showing current speeds and directions recorded during December, 1973» March and April, 1976............................168 41. Diagram illustrating the seasonal changes in depth of the threshold velocities for fine and very fine sand based on the "average" wave (Table I) for each month of 1973 .......... 181 42. A series of maps depicting the possible area of active rippling of fine sand during Decem ber (a), January (b) and February (c), 1973» San Pedro B a y .................................... I83 43. A series of maps depicting the possible area of active rippling of fine sand during March (a), April (b), and May (c), 1973j San Pedro B a y ............................................... 185 x FIGURE PAGE A series of maps depicting the possible area of active rippling of fine sand during June (a), July (b) and August (c), 1973» San Pedro B a y ............................................... I87 ^5. A series of maps depicting the possible area of active rippling of fine sand during Septem ber (a), October (b) and November (c), 1973 San Pedro Bay .. .. .. .... ... ... . I89 ^6. Graph showing the near-bottom horizontal velocities generated in depths of 20 m (inner shelf), 50 m (central shelf) and 100 m (outer shelf-shelf break) by surface waves.............................................193 ^7. The distribution and orientation of bedforms on San Pedro shelf as observed in photographs taken during September, October and December, 1973 (a) and January, April and December, 197^ (b) 195 ^8. The distribution and orientation of bedforms on San Pedro shelf as observed in photographs taken during August, 197^ (a) and October and December, 1975 (b) 197 ^9. The distribution and orientation of bedforms on San Pedro shelf as observed in photographs taken during June and August, 1975 (a) and March, 1976 (b).................................. 199 50. The distribution and orientation of bedforms on San Pedro shelf as observed in photographs taken during April, 1976 201 51. Photographs showing slabs from three box cores collected along a north (shallow) to south (deep) transect in San Pedro B a y ............... 208 52. Schematic diagram depicting the relationship of Langmuir circulations in the overlying water to mesoscale current lineations on the sea-floor.........................................216 x i PAGE 221 238 2^9 251 253 255 258 26l 267 270 xii Schematic diagram showing conceptualized flow fields on the inner and central shelf (after Swift, 1978) ....................... Transmission profiles during January, Dec ember and August, 197^ showing zones of turbid water, possibly generated by internal waves ...................................... Partial progressive vector diagrams showing the transport history of various diameter grains and resultant net displacement for December, 1973 at a depth of 51 m ........ Partial progressive vector diagrams showing the transport history of various diameter grains and resultant net displacement for December, 1973 at a depth of 27 m ........ Partial progressive vector diagrams showing the transport history of various diameter grains and resultant net displacement for March, 1978 at a depth of 45 m ............. Partial progressive vector diagrams showing the transport history of various diameter grains and resultant net displacement for April, 1978 at a depth of 28 m ............. Resultant vectors for each grain class compiled on one diagram for December, 1973 deep (a); December, 1973 shallow (b); March, 1978 (c) and April, 1978 (d) ............... Resultants vectorally summed for both deep stations, December, 1973 and March, 1978 (a) and both shallow stations, December, 1973 and April, 1978 (b) ................... Areal patterns of skewness (using values calculated by comparison to a standard reference distribution) surficial sediment, San Pedro s h e l f ........................... Fifth degree trend surface maps of skewness (a), sorting (b) and mean grain diameter (c) surficial sediment, San Pedro shelf (after Grant, 1973) ................................ FIGURE PAGE 63. Histograms of samples collected along a north-south transect across San Pedro s h e l f ...........................................272 64. Conceptualized diagrams depicting the hydrodynamic processes contributing to complex current systems of the continental shelf (a) and the seasonal and shorter term fluctuation in relative energy levels . . 274 65. Schematic diagram illustrating bedform zonation on the shelf under summer fair- weather (a) and storm (b) conditions...........284 66. Schematic diagram illustrating bedform zonation on the shelf under winter fair- weather (a) and storm (b) conditions...........286 67. Schematic profile depicting the disper sion of suspended particulate matter across the shelf in summer (a) and winter (b).......................................288 68. Conceptualized textural patterns on the shelf resulting from the interaction of the substrate with the complex hydro- dynamic processes characterizing over- lying waters.....................................290 69. Schematic diagrams showing the concep tualized movement of bedload across the shelf (a), and the conceptualized dis persion of near-bottom suspended parti culate matter (b) 292 TABLE I. "Average" wave for each month of 1973 .... 35 II. Comparison of textures in top 1 mm and upper 2 cm of selected cores................. 56 III. Textural variables for samples collected from same locations: November, 1974 and August, 1975 ........................... 67 71 73 150 152 165 174 191 233 234 246 256 263 Shipek grab samples ....................... Shipek grab sample color description . . . . Variation in percent light transmission at surface and 1 m above bottom with respect to time at same location ................... Variation in weight (mg/l) suspended sedi ment at surface with respect to time at same location, August, 1975 ............... Variation in depth to thermocline ........ Near-bottom velocities generated by "aver age” surface waves for each month of 1973 at 10 m intervals from 1-100 m water depth . Frequency (percent) near-bottom wave velo cities exceeded presumed threshold for a given depth ................................ Representative temperature, salinity and Sigma, data for depths of the summer and winter thermocline ......................... Values of y /c for internal waves of vari ous frequencies (l/T) over typical slopes on San Pedro shelf ......................... Critical shear stresses and corres ponding velocities (UqoOc) required to move grains of a given diameter .......... Approximate maximum net transport distance (m/day) for grains of a given diameter . . . Ratio between settling velocity (ws) and frictional drag velocity (U*) for selected grain diameters, with UqoOc required to transport grains in suspended mode ........ ABSTRACT Based upon a three-year study it is seen that four hydrodynamic provinces comprise San Pedro shelf, the main study area. Three of these are aligned approximately par allel with the shoreline: (1) an inner zone from shore to approximately the 20 m isobath, grading into (2) the cen tral shelf which continues to about 60-70 m before merging with (3) the outer shelf bounded seaward by the break in slope at about 75-100 m. A fourth transverse province, present where submarine canyons incise the shelf, is superimposed on shelf parallel provinces. In area, this zone approximates the width of the associated submarine canyon as projected onto the shelf and trends from the canyon head shoreward. Characteristic flow fields, re vealed by diagnostic features of the substrate, concentra tion and distribution of suspended particulate matter, and direct measurements of currents, dominate in each zone. Oscillatory currents, produced by shoaling surface waves, govern sediment transport on the inner shelf. Rip currents supply sediment to this region from the beach. Ubiquitous ripple marks are evidence of almost constant agitation of the substrate, which consists of fine and x v medium sands. Skewed to the coarse grain size distribu tion relative to the central shelf reflect the escape of fine particles with material equal to or greater than medium sand passing out to deeper waters less frequently. More intricate and subtle depositional processes influence physical sedimentation on the central shelf. Temporal, spatial, and morphological changes in bedforms not only suggest periodic fluctuations in intensity of hydraulic regimes, but also indicate the existence of two major flow fields within this zone. Meteorologically- induced currents prevail over other types on the central shelf, producing net transport of grains in preferred directions. These currents carry all grains offshore or along shore, sorting progressively coarser particles in divergent directions (usually with a stronger onshore component) and moving them shorter distances. At the shallow inshore end of this region, surface waves may generate near-bottom horizontal currents of sufficient strength to form symmetric ripples in depths as great as 25 m most of the year. However, a transition to another hydraulic province apparently occurs at about 35-^0 In winter, high energy surface waves ripple the substrate at these depths, but less strong summer waves cannot ini tiate extensive grain movement. During these periods of relative quiesence, activities of benthic organisms obliterate evidence of bedload transport. Seaward of this diffuse boundary, tides replace surface waves as primary subordinate currents in the meteorologically- dominated system. Near-bottom currents generally flow faster with more consistent net mass transport offshore in this deeper subprovince than in shallower water. Strongly unimodal, normal to fine skewed, very fine and fine sands distinguish substrate populations on the cen tral shelf. Sorting tends to decrease away from the mid dle of the platform. Internal waves propagating shore ward along density discontinuities shoal, steepen and break where the thermocline intersects the sea-floor. These waves resuspend particles dispersing them horizontally and eventually removing them from the shelf system. Vertical migration of the seasonal thermocline influences the depth at which internal waves impinge upon the shelf. The thermocline may define a major boundary between inner and outer flow fields on the central shelf, and semi-monthly tidal cycles may Influence the sense of water mass transport. Turbulence, probably produced by boundary currents, upwelling, internal waves and edge waves at the shelf break, rapidly diffuses plumes of concentrated suspended particulate matter passing over the outer shelf. Coarse skewed bottom samples (relative to the central shelf) x v i i imply that sufficient energy exists in this region not only to inhibit sedimentation of suspensates, but also to winnow fine-grained sediment out of the bedload popula tion. Upon reaching quieter slope and basin environments, suspended solids settle out of the water column. Anomalies in regional trends of textural variables, major perturbations in turbidity patterns near the bottom, and lobes of resuspended sediment within the water column are some lines of evidence suggesting that San Gabriel Submarine Canyon influences sediment dispersal systems on the adjacent shelf. Evidently, dynamic processes within the submarine canyon produce a narrow, diffuse zone ex tending transversely shoreward. This shelf transverse hydrodynamic province possibly impedes cross canyon flow, but does not affect, and may even enhance, onshore-off shore flow. Storms alter depositional processes and shift or erase boundaries of hydraulic provinces described above. Mesoscale current lineations suggest fields of helical flow cells on shallow portions of the central shelf. Com pound bedforms are evidence of unusually intense near bottom currents. The water mass responds almost instan taneously to these exceptional atmospheric events, and the effects may last many days after the storm has ended. Al though storms last only very short periods of time, they probably cause significantly greater mass transport of sediment than do fair-weather regimes which prevail over a much higher percentage of the year. Modern sediments appear to be texturally mature, and relict sediments are being reworked as the substrate returns to a totally graded state (palimpsest sediments). Hence, surficial deposits are in dynamic equilibrium with depositional processes operating on southern California shelves. x v x INTRODUCTION General Statement Processes governing transportation and deposition of sediments on continental shelves have heen the object of much study and speculation by marine sedimentologists for over 70 years; these efforts have intensified during the past decade. Several conceptual models of shelf dynamics have evolved from this research. While these models provide a framework for structuring future experi ments, many of them lack sufficient observational data to serve as definitive statements. Consequently, contro versy exists as to primary processes governing sediment dispersal (Creager and Sternberg, 1972; Swift, 1972). Purpose The purpose of this study is to discuss and define as specifically as possible the role various agents and mechanisms play in controlling sediment transportation and deposition on southern California shelves. In order to accomplish this goal, I have established a detailed network of stations on selected shelf segments. Data acquired from repeated observations leads to determination 1 of not only the processes of sediment dispersal, hut also to evaluation qualitatively of the state of shelf equili brium with respect to the prevailing hydraulic regime. Results of this study, with proper precaution, may be generalized into a model of shelf processes for narrow, leading-edge shelves. Moreover, criteria established from modern shelves can be used to interpret ancient sedimentary rocks, thereby increasing our understanding of geologic processes operating in the past. Ideas expressed herein represent a stage in devel opment of a dynamic model of depositional processes operating on southern California shelves. Those reading this dissertation should view my conclusions in the light of Chamberlain's (1897) concept of multiple working hypotheses, remembering that few scientific works are definitive, but most reflect progress. Acknowledgments During the course of this study, many people con tributed in various ways; some by time and effort spent in data collection and reduction, and others by discussion and criticism of ideas and interpretations set forth by the author. Dr. D. S. Gorsline, my major professor, offered counsel and encouragement, and my years as his student 2 have matured me as a scientist. For this I gratefully thank him. Dr. G. J. Bakus, Department of Biological Sciences, and Drs. R. H. Osborne and B. W. Pipkin, De partment of Geological Sciences, University of Southern California, read the rough draft of this manuscript. Their constructively critical comments improved the final copy. Of my colleagues in the Sedimentology Research Laboratory, although grateful to all, I must especially thank B. D. Edwards. Brian's participation as watch leader on many cruises eased considerably the burdens of Mbreaking-inM a new scientific crew each time, and his congenial companionship made the tedious hours at sea bearable. Dennis Thurston, Sedimentology Research Lab oratory technician, ably reduced most of the data col lected on many cruises; his compentence freeing me from more routine chores for the exciting task of interpreta tion. George Feneht and Lee Ann Musgrove provided as sistance in laboratory analyses and data reduction, and I thank them for their efforts. Connie Anderson drafted many of the figures for this dissertation for which I am most appreciative. Noel Plutchak of Interstate Electronics, Anaheim, California helped immensely in interpretation of current meter records; his expertise added substantially to several conclusions of this study. I want to thank Prof. F. P. Shepard and N. F. Marshall of Scripps Institution of Oceanography (SIO) for lending current meters used during part of the field program. P. A. McLoughlin and G. G. Sullivan of SIO emplaced the meters in the field. Roger Pappas, Marine Meteorologist, National Atmospheric and Oceanic Administration, gave me access to wave and wind records. The officers, crew and technicians of R/V YELERO IY and staff of the University of Southern California Marine Facility (USCMF) supported my field endeavors and aided in maintaining equipment. R/V YANTUNA, her of ficers and crew, provided ship support for my last three cruises. Many students, too numerous to mention each hy name, served in the scientific crew of more than 20 cruises; Julia Benham, H. M. Crawford, T. R. Nardin, and S. P. Yonder Haar served as watch leaders on some cruises. The efforts of all of those contrihuting to my field re search are gratefully acknowledged. The National Science Foundation funded this pro ject under grants GA ^00^9, DES75“01^38 and DES75-01^38, Amendment #A01. Finally, I am indehted to my family and friends, especially my parents and wife, Suzanne, for their enthusiastic encouragement. The ways in which my parents and wife buoyed my spirits throughout the long years of study and research cannot be measured, and their intan gible contribution to this dissertation is the largest of all. Historical Background and Previous Work Several papers at the turn of the century mark the beginning of modern sedimentological study of continental shelf sediments and processes. Foremost among these are the classic works of Barrell (1906, 1912) and Johnson (1919)• Barrell's work is particularly interesting in that it anticipates modern thinking about shelf processes. From ships' records of sand thrown up on deck and suspen sion of mud in the water column, he recognized that waves affect the bottom to depths on the order of 90-100 m. Barrell also noted the importance of long period swells generated by periodic storms. These waves rework shelf sediments at greater depths than those typical of the "normal" fair-weather regime. Storm deposits resulting from this episodic vertical and horizontal reworking are easily distinguished in the sediment record. Most geologists, during these early years, thought that wave-base controlled the morphology and evolution of continental shelves. Johnson's (1919) profile of equili- 5 brlum best embodies this concept. According to Johnson (1919)> shelves consisted of a wave-cut bench and a wave- built terrace which prograded seaward. A concave profile developed in response to prevailing wave energy. Extend ing this hypothesis, geologists concluded that once this profile reached equilibrium, sediment on the shelf would show a uniform decrease in grain-size seaward. Although reasonable In theory, the concept of a texturally graded shelf is not substantiated by empirical data. On the basis of sediment textures recorded on nau tical charts, Shepard (1932) concluded that no consistent gradation of grain size can be found across a typical shelf. Geologists then speculated that deposits of sedi ment relict from the Pleistocene caused deviation from the predicted pattern. A detailed description of shelf sedi ments ensued during the next two decades, culminating in Emery's (1952) comprehensive classification of shelf sedi ments. In that paper, Emery pointed out that detrital (contemporary) sediment does show a progressive decrease in grain size seaward, but patches of relict, residual, biogenic and authigenic sediment mask this trend. Later Emery (1968) described the seemingly great extent of re lict deposits on the world's shelves, and suggested that with the rapid rise in sea level since the melting of the Pleistocene glaciers, shelves have not yet had time to return to grade. Present thought tends to regard shelf sediments as consisting of a relict sand blanket, a shelf modern mud blanket and a nearshore modern sand prism (Curray, i960 ; 1965; Emery, 1968 ; Swift, 1970; Swift et al. , 1971)* Many of these studies have concluded that most shelves, with the possible exception of the inner portion, are not in equilibrium with the present hydraulic regime; although accumulating petrographic evidence indicates that shelves are gradually returning to a graded condition (Swift, 1970). Swift and his colleagues (Swift et, al., 1971) have introduced the term palimpsest sediment to describe re lict deposits which are being actively reworked as sedi ment distributed on the shelf equilibrates with the mod ern hydraulic climate (see also Booth and G-orsline , 197*0 • This work of the late 1960's and early 1970's marks the close of the descriptive period of shelf study and ushers in a host of papers which focus on shelf processes. Winds, tides and surface waves induce currents which disperse sediment across the continental shelf. Other physical oceanographic processes, such as upwelling, geostrophic flow, internal waves and density currents also influence sediment transport, but in more subtle ways. These numerous driving mechanisms combine to generate 7 complex flow fields, which greatly complicate the study of sediment transport. Often one or two energy inputs dominate shelf hy draulic regimes. For example, in the North Sea around the British Isles, tidal currents reach near-surface velocities in excess of 2 knots (Kenyon, 1970). Physical aspects of the surficial sediment on the sea bed reflect such dominant processes. In this case, strong tidal flow generates mesoscale bedforms. Marine geologists use these characteristic substrate responses to elucidate the nature of the flow fields prevailing on continental shelves. A review of sediment textures and bedforms typify ing particular shelf processes would be prohibitively long. Instead, the interpretation, in later sections, of mechanisms governing sediment dispersion across southern California shelves calls upon specific references from this vast literature. Two recent volumes, Shelf Sediment Transport: Process and Pattern (Swift, Duane and Pilkey, 1972), and Marine Sediment Transport and Environmental Management (Stanley and Swift, 1976) summarize present concepts of sediment transportation and deposition in the oceans. 8 Principles of Sediment Transport General Sediment moves across the shelf as bedload and sus pended load. In order to define pathways of dispersal and magnitude of transport, certain basic questions must first be answered. These include: At what point does sediment on the sea bed begin to move? How frequently does it move? What is the duration of transport? What conditions suspend sediment in the water column? How long does it remain suspended? Where does it go? The answers to these questions, and others, require a basic knowledge of the principles of sediment transport. Once we understand what conditions initiate grain movement we can evaluate the relative importance of the various mechanisms that disperse sediment. The purpose of this section is to summarize briefly the fundamentals of sediment transport, and to illustrate the necessary measurements for obtaining estimates of sed iment transport. Therefore, my intention is not to rigor ously develop equations of fluid flow and hydraulics of sediment motion, but to show the importance and applicabi lity of these relationships to sediment dispersal across the shelf. (For a rigorous mathematical treatment, the interested reader is referred to appropriate sources.) Nature of Currents On continental shelves “ both oscillatory and uni directional currents affect the transportation, erosion and deposition of sediment. Oscillatory flow produced hy shoaling surface waves probably exercises greater influ ence on the central and inner shelf. Of course, wave surge dominates in the surf zone. Asymmetrical compon ents of the oscillatory current become stronger as the waves steepen and break, moving sediment on to and along the beach. Further seaward of the littoral zone, oscil latory currents suspend sediment as waves pass, but probably produce no net displacement. Unidirectional currents, however, superimposed on the to-and-fro hori zontal motion near the bottom may transport sediment sus pended by this motion in a preferred direction. With increasing depth, the effects of wave surge lessen and unidirectional currents dominate depositional patterns of physical sedimentation. Fluid Flow Motion in a moving fluid is either laminar or tur bulent. In laminar flow, thin layers of fluid glide smoothly past each other, while turbulent flow consists of fluid "parcels" moving about in a random fashion. Tur bulence results from tangential shear at a fluid boundary. 10 Along a solid interface, eddies initiated by some irreg ularity in the boundary generate turbulence. Flow in the oceans is inherently turbulent because of very large Rey nolds numbers (see Shapiro, 1961; and Blatt et al., 1972 for a discussion of Reynolds numbers) and the tangential shear produced by wind stress at the surface. Turbulence causes fluctuations in the velocity of the flow. Velo city, U, at any instant is the vector sum of mean velo city, U, and a random fluctuation related to turbulence, U* (Inman, 1963)* As a fluid moves over a surface, a boundary layer develops (see Prandtl and Tietjens, 193^; Shapiro, 1961; and Graf, 1971)* In open channels this layer may com prise the whole flow field from bottom to surface. In the ocean, the boundary layer occupies only a small por tion of the flow field near the bottom; typical thick nesses range from about 1 m in deep basins to 10 m on the shelf (Wimbush and Munk, 1970). Flow above the bottom boundary layer (BBL) is nearly free of turbulence relative to the BBL. Thus, the nature of flow in the BBL influ ences bedload transport. Velocity Profile and Fluid Stress Marine geologists commonly use velocity as a measure of sediment transport. Velocity represents the distance 11 a parcel of water moves in a given time (L/T). As velo city increases, grains are lifted more easily from the substrate (Bernoulli effects), but in order to move in a horizontal direction some force must be exerted against their surface. Therefore, instead of velocity, we should measure some variable of the flow reflecting force exert ed by the fluid. Shear stress, tangential force per unit area, is that variable. However, velocity is easily determined in the mar ine environment and it is convenient to view sediment transport in terms of velocity. Thus, this subsection develops equations relating velocity to the more import ant variable -- shear stress. In previous paragraphs, I have shown that in the ocean, flow high in the water col umn does not necessarily reflect conditions at the water- sediment interface. Consequently, we must restrict our measurements to the BBL, if we want to estimate bedload transport. For hydrodynamically smooth surfaces, the velocity profile in the boundary layer consists of a relatively thin viscous sublayer at the bottom separated by a buffer zone from a turbulent zone orders of magnitude thicker (Fig. la). Since conditions in the viscous sublayer govern grain movement, it is worthwhile to examine the nature of flow in this layer. 12 Figure 1 Relative velocity profile in bottom boundary layer for hydrodynamically smooth (a) and turbulent (b) flow. 13 FREE FLOW LOGARITHMIC TURBULENT ZONE BUFFER ZONE VISCOUS SUBLAYER SMOOTH BED FREE FLOW LOGARITHMIC TURBULENT ZONE 10 m I mm{ ROUGH BED Shear stress within the viscous sublayer is con trolled by the dynamic molecular viscosity (a measure of a fluid*s resistance to change of form) according to the following relationship: _ _ du C / e = u U) dz where is shear stress and --- is the rate of change of dz velocity U with respect to the distance z above the bottom (Inman, 1963)* At this point I want to introduce a velo city term: u* = (2) where p is the fluid density and U* is the frictional drag velocity which exists within the viscous sublayer. It can be shown by mathematical manipulation of these two relationships that velocity increases linearly with in creasing distance from the bottom (Komar, 1976). Although many textbooks state that flow in the viscous sublayer is laminar, vertical exchange of fluid into and out of the viscous sublayer disrupts laminar flow. Periodic horizontal velocity fluctuations are as sociated with these turbulent bursts (Kline ejt al. , 1967; Rao et_ al., 1971; others). In marine environments, this bursting phenomena may contribute 80 percent of the total 15 stress, while occurring only 20 percent of the total flow time (Komar, 1976). A narrow buffer zone exists above the viscous sub layer. This grades into a turbulent zone, in which the velocity profile increases logarithmically upward in con trast to the linear velocity gradient within the viscous sublayer. Roughness elements on the bottom cause the viscous sublayer and buffer zone to deteriorate. In fully hydro- dynamically rough flow, the turbulent zone comprises the total boundary layer (Fig. lb), and the exponential velo city profile essentially extends to the bottom. The next few paragraphs illustrate techniques for determining shear stress at the bottom by measuring velocity within the BBL. The first of these methods involves use of the Karman-Prandtl velocity profile equations (see Sternberg, 1972 for complete development of these equations). For turbulent flow, the mean velocity a given dis tance z above the bottom is determined by: U =U„-1 --(z+z)/z (3) z * k o ' o where zq is the roughness length (relief of the microto pography of the sea bed) and k is von Karman's constant. Assuming that shear stress within the boundary layer is constant, the boundary shear stress, > mazy be calculated 16 from the slope of the velocity profile; U U z 1 C f o = f> 5-75(log - log ) 2 Z1 (Several steps have been skipped in going from equation (3) to equation (4)). In the field this method requires at least three current meters stacked vertically within 1.5 m of the sea- floor; hence, the high degree of instrumentation (which greatly increases cost) limits its practical application for many investigators (Sternberg, 1972). An alternate approach for estimating C f o involves use of the Quadratic Stress Law (Sternberg, 1972). It has been shown experimentally that; Introducing a proportionality coefficient C-^ (the drag coefficient) equation (5) may be written as; In the marine environment, the mean velocity is usually measured 100 cm above the sea-floor. This assures sam pling in the BBL. Using 100 cm as a subscript, equation (6) becomes; Cfo 0 0 f L 2 (5) Cfo = cD p L 2 (6) 17 0 C100 U1002 (7) or, in terms of friction velocity: U* 2100 uioo (8) The drag coefficient is a function of the fluid viscosity. Consequently, its value varies under natural conditions. However, for hydrodynamically turbulent flow, assumes a constant value related to roughness length, zq (Nikuradse, 1933)- On the continental shelf, roughness length corresponds to bed configuration. Nat urally sorted sands and gravels and rippled sands are sufficiently rough to cause turbulent flow when mean vel ocity 1 m above the bottom reaches 15 cm/sec (Sternberg, 1972). From the foregoing relationships, we can see that if is correctly evaluated by empirical experi ment only one measurement of mean velocity, U-^q q, is By compiling data from existing■boundary layer and sediment transport measurements in the marine environ ment, Sternberg (1968; 1972) suggested that the constant _ 3 value of equals 3x10 . Inserting this value in equation (7) gives: (9) 18 or, in terms of friction velocity: u* = 5.^7xl0-2 u100 (lp) These procedures provide a means for estimating shear stress within the BBL. Sediment will begin to move when the shear stress equals and exceeds a critical value. Initiation of Grain Movement Shear stress that initiates a grain movement is called the threshold stress of sediment transport, and it depends upon: (1) grain size D, (2) submerged specific weight of the grain g(pj -p). where g is the acceleration of gravity (980 cm/sec ) and^ is the density of the par ticle, (3) shear stress t3o acting on the bottom, and (4) viscosityand density p of the fluid. Several threshold curves have been developed for predicting initial grain movement under unidirectional flow, by knowing some com bination of grain diameter and density or water velocity and stress (Shields, 1936; Hjulstrom, 1939; Sundborg, 1956; Bagnold, 1963; Inman, 1963)• Shield's diagram relates the critical entrainment function (relative stress) to a Reynolds number. It is easier to visualize grain thresholds in terms of grain size, shear stress or velocity. Several subsequent re searchers have modified Shield's diagram in this way 19 (Bagnold, 19&3; Inman, 1963) (Fig* 2). These diagrams illustrate that movement begins over a range of conditions. For sand and gravel the critical shear stress is roughly proportional to grain size. All the curves demonstrate that fine sand is the most easily moved grain fraction. Coarser particles require more stress because of greater mass. Fine particles may resist erosion because of cohesive effects (Sundborg, 1956); or because well-sorted sediment smaller than fine sand forms an essentially smooth bottom, causing the drag to be evenly distributed over the bed instead of acting on in dividual particles. These conditions necessitate higher velocities to initiate grain movement (Inman, 1963; p. 128-129). Field observations (Sternberg, 1971) agree reason ably well with these curves for coarser grain sizes (0.3 mm - 1.1 mm). More work is needed to accurately predict incipient motion of finer grain sizes in the marine envir onment; where poorly sorted sediments generate turbulent eddies which possibly cause fine-grained material to move at lower critical velocities and shear stresses than indi cated by controlled laboratory experiments. While the conditions initiating grain movement un der unidirectional flow are fairly well known, less is known about the conditions under oscillatory flow. More- Figure 2 Threshold curves for unidirectional flow after Inman (1963) 21 'L- 30 GRAIN DIAMETER (D) (m.m) over, agreement among studies is not always very good. Komar and Miller (1973* 1975a-c) reviewed existing data and determined that for a grain diameter of less than ahout 0.5 mm, the threshold is hest predicted by the fol lowing relationship: C =0.21 (11) f S ' f )g D where U is maximum near-bottom orbital velocity, and d m o is the bottom orbital diameter. This relationship holds for sediment ranging from medium sand to fine silt, below which cohesive forces become important. For grain diamet ers greater than 0.5mm, the threshold is best approximated by an empirical curve derived from the following equation (Komar, 1976): ------ J»!------ = q.IkJTT f--0 ^ (12) (|Os - p )gD \ D / (Equations for calculating and dQ from wave heights and periods are presented in the section on sur- ace waves; see p. 172.) Thresholds under oscillatory flow correspond fairly well with those determined for uni directional currents (Komar and Miller, 1975a). Figure 3 illustrates the bottom orbital velocity necessary to ini tiate grain movement under oscillatory flow for wave of various periods (see Komar and Miller, 1975a for other 23 Figure 3 Threshold curves for oscillatory flow after Clifton (1976). 24 Um = r 0 * iq5) ? / j U s 7|.4T^?03 / 7 U m 2 3 3.3 (TO)'/* 050 ^o'l B'r t ' r \ Q62. 2&0 6**'H threshold curves) Mass Sediment Transport After determining what critical conditions are nec essary to move grains, we want to estimate the mass trans port of sediment resting on the sea-floor. Most investigators (see Smith and Hopkins, 1972, for an alternate approach) have hased their estimates of bed- load transport under unidirectional flow on the theoretic al relationship devised by Bagnold (1963)- Equation (13) relates the rate of mass sediment transport as bedload to the power exerted by the fluid moving over the boundary: Po — P K gj = K (j) (13) Ps where j is the mass discharge of sediment in g/cm sec, U is a measure of the power the fluid expends on the bed and K is a dimensionless proportionality coefficient that expresses the ability of a flow to transport sediment. Fluid power can be expressed as (Bagnold, 1963): U) =°Jou (li0 where U is the mean fluid velocity near the boundary, or (Inman el: al. 1966) : U = p u*3 (15 ) If equation (15) is used, equation (13) may be written as: 26 ft- p gj = K p U*3 (16) P Field measurements by Kachel and Sternberg (1971) show that the value of K is empirically related to the grain diameter D of the sediment and to the excess boundary threshold stress required for initial grain movement. Sternberg (1972) has developed a method, employing Equation (16), for estimating mass bedload transport; the step-by-step procedure for this approximation is not pre sented herein and the interested reader is referred to Sternberg (1972, p. 79-80). This technique is limited to grain sizes between 0.20 mm to 1-2 mm and to flow with low concentration of suspended sediment. Also, the presence of large scale bedforms may restrict use of this method (Ludwick, 1975)■ Bedload transport by waves and the combined effect of waves and superimposed unidirectional currents is very complex and poorly understood. No reliable equations ex ist for estimating sediment transport on the continental shelf under these conditions. One relationship devised by Bagnold (1963) for unidirectional currents superimposed on oscillatory surge has been used successfully by Komar (1975c) for approximating bedload transport in the long shear stress the critical 27 shore zone, but it breaks down when applied to regions farther offshore. For a good review of existing theoret ical and field studies on the transport of sediment by waves and the combined effect of waves and unidirectional currents, the reader is referred to Komar (1976b, c). Estimations of mass sediment transport, besides bedload, must include the suspended load in order to ap proximate magnitude of cross shelf dispersal for the total load. Suspended Load Particles become entrained in the water column by resuspension of fine-grained sediment from the bottom, in put of wind-blown dust, and discharge of suspended clays and silts from rivers. The residence time of suspended solids depends, in part, upon their settling velocity. Small particles in the water column settle according to Stoke's Law: 7\ where w is the settling velocity of the particle, n S the fluid viscosity and r is the particle radius. Increasing velocity causes significant amounts of grains from the bedload population to become entrained in the flow. The following equation defines the approximate conditions producing suspension of particles having a 28 o density of 2.65 gm/cirn (Bagnold, 1966) : 2 w ___________ 0 k_____^ lps ^. p) gD U*^ gD (18) where 9 is the relative stress. When this relationship is plotted along with the curve for the threshold of sediment movement, it is seen that grains less than 0.17 mm in dia meter become suspended immediately after the threshold is exceeded (Komar, 1976a). As long as upward components of sediment diffusion equal or exceed the settling velocity of any particle, that particle remains in suspension. The following equa tion shows this relationship: Where c is the concentration at level z and v is the s sediment diffusion rate. Increasing turbulence suspends heavier particles and retains smaller grains in suspen sion for longer periods of time. Even in very still water, some of the smaller particles may remain in sus pension for weeks, months or years (Drake, 1976). Once entrained in the water column, particulate matter may be moved across the shelf by advection, horizontal diffusion and vertical diffusion. Three-dimensional convective-diffusion conservation of mass equations exist to fully describe dispersion of a 29 CW + V s s (19) substance in a fluid. Unfortunately, owing to the com plexity of these equations and the inadequacy of our knowledge about suspended solids in the ocean and vari ables influencing transport of these suspensates, it is impractical to apply such equations to problems of sedi ment dispersal on the continental shelf (Drake, 1976). steady-state, two-dimensional model for predicting long term suspended sediment dispersal in shelf waters. Al though they lack empirical data, they conclude that much fine-grained sediment escaping estuaries by-passes the shelf to accumulate on the slope and deep ocean floor. Other research indicates that a great amount of fine grained material may be trapped in estuaries and deposit ed in deltas or as mud blankets on various portions of the continental shelf (McCave , 1972; Meade, 1972). Sites on the continental shelf may serve as temporary "resting places" for mud until it is resuspended and transported beyond the shelf edge. known. Recent work relates critical friction velocities to sediment yield strength (Migniot, 1968 in McCave, 1972) according to the following equations: Schubel and Okubo (1972) have developed a simple, Thresholds for cohesive sediments are not well 2 20 dynes/cm ( 2 0) 30 u* = y 4 fo:r 10 dynes/cm^ (21) where^^ is the yield strength. Even though much work needs to he done, we do know that the critical shear stress for the erosion of cohesive mud is higher than for sands; and even higher velocities are needed to erode co hesive sediment after it has been deposited and compacted on the bottom even for only a short period of time (Young and Southard, 1975)• The foregoing discussion emphasizes the complexi ties involved in estimating sediment transport on the con tinental shelf. While theoretical arguments and labora tory experiments provide a basis for approaching problems of sediment transport, field studies have more clearly defined the real situation in the marine environment. Definition of processes governing sediment dispersal across the shelf requires many more empirical observations. Subsequent chapters of this dissertation contribute to that end. Before examining the southern California shelf, it is worthwhile to discuss the general physical aspects of shelf depositional environment by comparing east and west coast shelves of the United States. 31 Comparison of Atlantic and Pacific Coasts Over the years many researchers have developed coastline classifications (Suess, 1906; Johnson, 1919; Shepard, 19^8, 19&3; Cotton, 1952; Valentin, 1952; Zenkovich, 1967; Bird, 1970). Recently Inman and Nord strom (1971) have presented a new tectonic and morpho logic classification of coasts based on the broad scale effects of plate tectonics. According to this classifi cation, fundamental differences exist between the Atlantic and Pacific coasts of North America. A complex system of spreading centers and faults (the San Andreas being a major element) defines the boun dary of the North America Plate and Pacific Plate (Bird and Isacks, 1972). Active tectonism reflects the con stant movement (collision) between these two plates. Thus, Inman and Nordstrom (1971) class the Pacific con tinental margin (the transition zone from shore to the deep ocean) as a collision or leading-edge coast. The Atlantic coast, on the other hand, is a tectonically stable region situated in the middle of the North America Plate. It represents a trailing-edge, or non-collision, margin. Morphological differences characterize these tec tonically dissimilar coasts. Atlantic-type continental 32 margins consist of a relatively wide (^100 km) continen tal shelf, a continental slope incised by submarine can yons, and a well-developed continental rise (Emery and Uchupi, 1963; Heezen, 197^0 • Being a mature margin, sedi ment accumulations are generally thicker than those of young, Pacific-type coasts. A narrow shelf (^30 km) typifies Pacific-type margins. Submarine canyons not only indent the continental slope, but also frequently cut into the shelf (Shepard and Dill, 1966). In contrast to Atlantic-type margins, no thick wedge of sediment, the continental rise, exists at the base of the slope (Fisher, 197^). Instead, trenches occupy this position in many Pacific-type margins (Mitchell and Reading, 1969)* Except for Alaska, however, no active trenches occur a- long the coasts of the western United States; this region has a particularly complex plate tectonic history (Ham ilton, 19^9; Atwater, 1970; Christiansen and Lipman, 1972). The gross tectonic and morphologic differences be tween these two general classes of coasts cause funda mental differences in depositional processes and products (Inman and Nordstrom, 1971). Most of the world's largest rivers discharge on to trailing-margin coasts, building up deltas and prograding shelves. Because the drainage area is smaller along leading-edge coasts, the shelf re- 33 ceives less sediment. However, the steep, mountainous regions associated with collision margins, introduce coarser sediment to the shelf. Besides discharge of sediment by rivers, prevail ing hydraulic regimes strongly influence erosion and deposition of sediment on continental margins. Wave cli mate is one component of the hydraulic regime. Thus, wave energy serves as a measure for comparing the Atlantic and Pacific coasts of the United States. Wave energy a- long a given coast typically correlates with latitude; usually stronger waves occur in higher latitudes. Topo graphy, however, may modify this relationship. Relatively low energy waves characterize the East Coast (Emery and Uchupi, 1963 > P* 2^8-249; Howard and Reineck, 1975* P- 7^-75)• in contrast, large, strong waves typify the West Coast. Relative energy levels, pro gressing from south to north, along the California coast range from moderate to high (Cook, 1969; Howard and Reineck, 1975; Table I), and exceptionally severe waves characterize the coasts of Oregon and Washington (Komar et al., 1972; Smith and Hopkins, 1972). From the foregoing, it can be seen that more energy (at a given latitude) is delivered to the inner shelf on narrow collision shelves than on wide, trailing-margin shelves. This produces differences in sedimentation pat- 34 TABLE I "Average" Wave for Each Month of 1973> San Pedro Bay, California! Period (T) H (m) max ' Hl/10 ^ H1/3 (m) J anuary 11. 76 1.51 1.15 0 00 February 12.35 1.18 o\ 0 0 0. 67 March 11.^7 0.96 0.75 0.52 April 12.02 O.58 0.^5 0 0 May 1^.93 0.52 0 .^0 0.26 June 12.^9 0.63 0. kk 0.3^ July 13.01 0.56 0.^3 0.29 August 12.93 0.50 0.^3 0.29 September 13.16 0.56 0 .kk 0.31 October 13.36 0.59 0.^7 0.33 November 11. 80 0.66 0.51 0.36 2 December 13. 08 0. 89 0.75 0.58 "'"Calculated hy averaging each observation obtained during the month. 2 December represents 5 days (17-21) of observation. 35 terns and bedform zonation on Pacific and Atlantic shelves (Howard and Reineck, 1975)• REGION OF STUDY General Although categorized as a leading-edge coast, the continental margin off southern California represents a province unique in the world. Instead of the normal shelf, slope, rise (trench) physiographic divisions com mon to other continental margins around the world, an ir regular topography of ridges and basins characterizes the offshore region of southern California. This area ex tends shoreward of the 1600 fathom (2880 m) isobath from Point Arguello, California to Isla Cedros, Baja Califor nia, Mexico. This geographic province has undergone a complex tectonic history (see Howell, 1976). Because of its unique physiography, Shepard and Emery (19^1) named this region the Continental Borderland. The true continental slope occurs at a distance of about 80-270 km from shore. The intervening borderland is essentially an ’ ’extended" continental shelf consisting of mainland shelves and island shelves separated by basins. Mainland shelves vary in width from about 1.7 km 37 to 25 km and average 6.7 km, and are arranged in a series of alternating wide and narrow segments (Emery, i960). Submarine canyons and promontories frequently mark the boundaries between segments. Wide shelf segments (max imum width more than 12.5 km) define "cells" of which San Pedro Bay is a good example. Palos Verdes Peninsula marks the western boundary of San Pedro shelf and Newport Canyon terminates the wide portion of the shelf on the southeast. The shelf narrows north of Palos Verdes and south of Newport Canyon. Island shelves range in width from less than 0.16 km to 36.7 km, and show no systematic variation in width similar to that of mainland shelves. A geographic trend, however, exists in that shelves around the easternmost islands are narrower than those around the westernmost. Several submerged terraces, erosional remnants of lower sea levels during the Pleistocene, occur on the shelves, one of which corresponds to the shelf break. The shelf break ranges in depth from about 75 m in the vicinity of Los Angeles to about 150 m to the south of San Diego. Area of Field Work During twenty cruises beginning July, 1973 and ending April, 1975, I collected samples from several shelf segments. These include San Pedro Bay, the Port Hueneme-Point Mugu area, and the Northern Channel Is lands; two semi-annual cruises of less detailed sampling cover the shelf from Point Mugu to Dana Point (Fig. 4). Of these, I selected the portion of continental shelf ly ing between Point Fermin and Newport Beach, designated henceforth as San Pedro shelf (Fig. 5&), as my major study area for the following reasons; (1) San Pedro shelf is a discrete shelf segment with well-defined boundaries -- Palos Verdes Peninsula and Newport Submarine Canyon. (2) Sediment enters the shelf system predomin antly via the Los Angeles, San Gabriel and Santa Ana Rivers, and by longshore transport around Palos Verdes Peninsula. Flood-control dams limit the amount of river discharge (Norris, 1964; Rodolfo, 1970) and Redondo Submarine Canyon in Santa Monica Bay to the north intercepts most sediment moved southward by longshore currents. Consequently, insig nificant amounts pass the narrow shelf seg ment off Palos Verdes to reach San Pedro shelf. (3) Reasons (l) and (2) above combine to make San Pedro shelf essentially a closed depositional Figure Regional location map 10 SANTA BARBARA NORTHERN CHANNEL ISLAND! S.M .I. S . C.l. PT. HUENEME PT. MUGU O 1 0 20 30 40 50 KM DETAILED SAMPLING \ SEMI ANNUAL SAMPLING ~ 9 2 — = METERS LOS ANGELES STUDY Q AREA Figure 5- Geographic boundaries of San Pedro shelf, landmarks and bathymetric prov inces referred to in text (a) and detailed bathymetry of San Pedro Bay (b). k2 LONG uEACH SAN PEI BREAKWATER EVA SA M G A BR IEL S ilB N A R /M E KM S A M PEDRO C H A N N E L LONG BEACH 5 SAN PEDRO \\ HUNTINGTON BEACH system. Hence, it is a good site for studying the effects of hydraulic processes on the dis tribution of shelf sediments. Bathymetry and Geologic Structure Figure 5~b shows the submarine topography of San Pedro shelf. As a basis for discussion, I have separated the shelf into bathymetric provinces. The inner shelf is that region from shore to about 20 m (10 fathoms) water depth, where it grades into the central shelf which con tinues to about 60-70 m (35 fathoms) before merging with the outer shelf, bounded by the break in slope at about 75-100 m. Significant topographic features include irregu larities on the wide central portion south of Long Beach and two canyons incised in the outer shelf and slope. The break in slope at the shelf edge represents a terrace as described by Emery (1958)• Other well-defined terraces occur at 30» 60 and 80 m on Palos Verdes shelf, but mant ling of sediment may subdue the topographic expression of terrace "nick-points" making these elements difficult to discern on other segments of the shelf (Moore, 1957)• Along this section of the coast, the shelf break ranges in depth from 75-150 m; Moore (1951> 195^0 used 75 m (40 fathoms) to mark the seaward limit of San Pedro shelf. LA Maps and charts in this report show 92 m (50 fathoms) as the shelf edge. Areas of positive and negative relief on the cen tral portion of the shelf are formed by outcrops of Mio cene rocks. These are part of a structural dome, which has been truncated by waves and currents, underlying San Pedro shelf (Moore, 195*0 • Pliocene rocks crop out in deeper areas, but show no significant relief. Relict Pleistocene sands are associated with the irregular features in this central region. San Pedro Sea Valley and San Gabriel Canyon, the reentrants cutting the slope and outer shelf, are of questionable origin. These features may be slump scars associated with fault trends (Gorsline and Grant, 1972) rather than canyons eroded by rivers crossing the shelf during lower sea-levels in the Pleistocene. In contrast, Newport Canyon, the eastern terminus of San Pedro shelf, is related to the Santa Ana River (Felix and Gorsline, 1971)• Seismic reflection profiles indicate that undif ferentiated Late Quaternary sediment cover on San Pedro shelf ranges from a thin veneer of less that 3 m to thick lobes of more than 20 m (pers. commun., T. R. Nardin, Dept, of Geological Sciences, Univ. So. Calif.). Net sedimentation rates are extremely variable. Using un- 45 published data, courtesy of T. R. Nardin, I calculated net rates ranging from 0.003 cm/yr to 0.06 cm/yr, with best estimates being between 0.01-0.06 cm/yr and higher in some areas. Physical Oceanography General Borderland Circulation Three water circulation seasons occur along the coast of California (Pirie et_ al., 1975)- The Oceanic Period, characterized by the California Current, begins in July and lasts until November. From the middle of November to mid-February, the Davidson Current dominates nearshore current patterns. The third season, Upwelling, starts around the middle of February and continues to the end of July, but is best developed in May and June off southern California. As the California Current flows southward into the Southern California Bight past Point Conception, it gen erates the Southern California Countercurrent, a perma nent cyclonic eddy which is situated over or to the west of Santa Cruz Basin (Emery, I960; Barnes, 1970; Pirie jet al., 1975)• This eddy dominates surface circulation over the Borderland as it rotates counterclockwise, most of the water inshore of it turns to flow southeasterly along the coast (Emery, i960). In essence, surface circulation over ^6 the Borderland consists of a southerly offshore current, a northerly flowing countercurrent in the central region south of the Channel Islands, and a southerly return flow inshore (Gorsline, 1958; Emery, i960). These surface currents usually flow at less than 25 cm/sec (Pirie et al. , 1975)• A northwesterly current flows below the surface during most of the year (Sverdrup and Fleming, 19^1). This current remains in the subsurface during spring and summer when the northwest winds generated by the North Pacific High Pressure Cell drive the California Current toward the coast. As this pressure cell deteriorates in fall and winter, the California Current moves farther off shore permitting the northwesterly flowing countercurrent to develop at the surface producing the Davidson Current, or California Countercurrent (Sverdrup and Fleming, 19^1; Pirie et al., 1975)• Surface currents within the Southern California Bight form a more or less independent system. Local winds, river discharge and topography cause numerous variations and complex circulation patterns over the continental shelf. Vicinity of San Pedro Bay General Surface Circulation Hydrographic observations by Bunnell (1969) during ^7 fall, 1967, and. spring, 1968 suggest strong convergence in central San Pedro Channel that possibly represents a shear boundary between northerly (?) offshore flow and southerly (?) inshore flow (Gorsline and Grant, 1972). The southerly flowing current dominated flow in the in shore region of the channel in fall and winter, 1967» perhaps affecting sediment transport over the outer shelf. Small eddies, possibly flowing northwards as close as 1-2 km of the shoreline, bounded this southerly flow. Speeds in the upper 400 m of this current ranged from 20-100 cm/sec with surface waters attaining velocities of 10-60 cm/sec. In spring, 1968 the northerly flowing current was better developed and pushed the southerly current closer to the edge of the shelf. Although speeds in the upper ^00 m in the southerly flowing current increased slightly, ranging from 60-120 cm/sec, surface water in the top 5 m decreased slightly in velocity to values of 5-30 cm/sec. Pirie et al. (1975) studied nearshore current patterns using remote sensor data acquired from 1969-197^* Davis, in preparation, also studied surface circulation using satellite imagery. Their observations pertain to water over the continental shelf, whereas Bunnell (1969) studied circulation farther offshore. During the Oceanic Season Pirie et al. (1975) found ^8 that south of Point Fermin nearshore transport is normally to the south, hut appears to he mixed or northeast south of Long Beach. Current patterns change again adjacent to Dana Point and Oceanside where material is often trans ported 3 km offshore and then carried southeast. When the Davidson Current dominates nearshore cir culation, patterns hecome more complex. Although an east-southeastward current seems to develop inside Los Angeles Harhor, sediment outside the breakwater (discharge from the Los Angeles, San Gabriel and Santa Ana Rivers) is moved offshore and westward by currents influenced by the Davidson Current system. Although major oceanographic seasons influence nearshore circulation, local winds, tides, waves, river discharge and topographic irregularities produce very complicated surface circulation patterns over the contin ental shelf. The observations of Bunnell (1969) seaward of the shelf and Pirie et al. (1975) closer to shore evidence these spatial and temporal complexities. In general, however, at distances greater than ^-8 km offshore (central and outer shelf) surface trans port in the region of San Pedro Bay appears to be either towards the west or south. Areas closer to shore seem to be dominated by a series of small, local gyrals causing mixed transport. A9 Tides The tidal wave in the southern California area propagates from southeast to northwest and produces cur rents on the open shelf which theoretically reach maximum speeds between high and low tides (Emery, i960). Shore line configuration and topographic irregularities produce mixed tides along the southern California coast. Tidal range for spring tides in the vicinity of San Pedro is about 2 m. Large, dome-like units of cool water which form and break up in response to the semi-monthly tidal cycle may form over the shelf. Gyral currents associated with this cycle may influence circulation patterns, particu larly near the heads of submarine canyons (liepper, 1955; Stevensen and Gorsline, 1956). Current meter measure ments show strong diurnal tidal components in bottom water circulation over San Pedro shelf. Waves Long period waves approach San Pedro shelf from the west and south. Local winds and storms generate much shorter period waves. Diffraction and refraction by islands and banks dampen much of the westerly long period swell reaching San Pedro Bay (Horrer, 1950; O'Brien, 1950; Caldwell, 1956). Southern swell tends to converge 50 over portions of San Gabriel Canyon and along parts of the breakwater (Horrer, 1950). Refraction would not be as strong for waves of shorter period. Roger Pappas, Marine Meteorologist for the Nation al Atmospheric and Oceanic Administration, has provided me with data from wave gauges located on Platform EYA (Fig. 5a) surf reports, hindcasts and forecasts. Table I summarizes monthly wave periods and heights for 1973* These data indicate that waves of intermediate energy characterize San Pedro shelf. Bottom Currents Limited near-bottom current meter measurements indicate a strong tidal component. Superimposed on the tidal current is a strong flow event which may be gener ated by meteorological forces (pers. commun., N. Plutchak). General directions of transport as shown by progressive vector diagrams (PVD) seem to be offshore and alongshore, with speeds sometimes exceeding 25 cm/ sec, but more typically less than 15 cm/sec. Studies by Hendricks (1976a, b) indicate that velocities of sub- thermocline currents average 9-8 cm/sec and that these currents generally flow alongshore. 51 PROCEDURES AND METHODS Sampling Grid Determining regional trends of sediment dispersal requires sampling large areas of the sea floor and over- lying water. However, stations should he closely spaced to define local effects. The basin sampling grid for this project consisted of stations spaced 1 nautical mile (1.9 km) apart, and covered portions of the shelf lying between the 20-200 m isobaths. I chose these depth limits because (1) the dynamics of sediment transport landward of the 20 m isobath are relatively well known (Ingle, 1966; Vernon, 1966; Cook, 1969)1 and (2) the shelf break occurs at about 75-150 m and sampling to 200 m assures adequate coverage of the outer shelf and upper slope. The total area sampled within these depth limits varied from cruise to cruise, depending on purpose of the cruise, weather, etc. Sampling Methods Routine sampling, for what I term general survey cruises, consisted of: (1) a transmissometer/STD cast, 52 (2) a Niskin bottle cast to collect water within 1 m of the sea-floor, (3) a surface cast made with a plastic bucket or taken 0.5 m below the surface with a 15-liter Niskin bottle, (^) a sediment sample collected with a NEL box core, and (5) a photograph of the bottom taken with either a small camera mounted on the box core frame or separately using an EG&G camera system. Turbidity, Temperature and Salinity A light-beam transmissometer (ot -meter) constructed at the Visibility Laboratory of Scripps Institution of Oceanography (Petzold and Austin, 1968) measures the transparency of water by the attenuation of a reflected light beam. With it we can obtain continuous records of relative turbidity versus depth (see Drake, 1972 for a detailed discussion of the instrument, its limitations and use on board ship). In order to measure temperature, salinity and light transmission (inverse of turbidity) simultaneously, an Interocean Model 513 CSTD (replacing the original thermister included with theo^-meter) was attached to a frame and fitted on the transmissometer. Transmissometer/ STD profiles are recorded graphically on a Hewlett-Packard X-Y-Y' recorder. Usually, I recorded transmission and temperature as a function of depth on the downcast, switching over to salinity and temperature as the instru- 53 ment package returned to the surface. Since this system was newly designed, we experienced many failures before it was operational. Water samples were collected at each transmisso meter station, or at the beginning and end of each transect, from the surface, and 1 m above the sea-floor to determine absolute concentrations of suspended solids. Immediately upon return to the deck, water from the bucket and Niskin bottle was funnelled into gallon plastic bot tles, and standard laboratory thermometers inserted to record temperature. While at sea, aliquots (usually 2-4 1) taken from the gallon bottles were passed through preweighed filters by vacuum pumps. Highly turbid water often clogged filters after only 0.5 1» while very clear water required more than ^ 1 to grab sufficient sediment ® . for gravimeter analysis. Instead of Millepore filters ( r) employed by Drake (1972), I used Nucleopore filters, 47 mm in diameter with a nominal pore size of 0.4 urn, be cause physical properties of these filters made them easier to use in the laboratory and onboard ship (Anony mous, 1976). Upon return to the laboratory, the filters were dried in an oven and weighed, and the concentration of suspended particulate matter calculated as mg of suspensate/l of seawater. None of the filters were "ashed" to determine the percent of organic debris 54 in the total sample. Substrate A new box core liner system permitted storage of many cores on ship for later analysis at our research laboratory at University of Southern California (Karl, 1976). Processing of each core included grain-size analy sis of the top 2 cm, and x-radiography of slabs cut at 90° to each other. Since I wanted grain size distributions to reflect modern hydraulic processes, it was necessary to sample only a very thin layer of the uppermost portion of the core; but over a sufficiently large area to assure enough material for analysis and archive collections. Sedimen tation rates on portions of the shelf in the vicinity of San Pedro range from 0.1-1.22 cm/yr (Murray, 1975)• Sure ly the upper 2 cm represents modern deposition (relict sands are easily distinguished), and I chose this interval as the best compromise to satisfy the conditions outlined above. For several cores, I analyzed the top 1 mm in addition to the upper 2 cm. Although stirring of the sample as the core is retrieved from the sea-floor mixes some of the surface sediment, probably invalidating this test, results indicate no appreciable differences between the two samples (Table II). 55 TABLE II Comparison of Textures in Top 1 mm and Upper 2 cm of Selected Cores AHF Station X mm s l v Diff- mm 21644 0-1 mm 0.018 5.75 1.27 0.001- 0-2 cm 0.017 5.86 1.20 21650 0-1 mm 0.025 5-33 1.44 0. 000 0-2 cm 0.025 5.33 1.4l 21651 0-1 mm 0.06l 4.03 1.42 0.003+ 0-2 cm 0. o64 3.97 1.56 21652 0-1 mm 0.0 4-7 4.41 1.42 0.016- 0-2 cm 0.031 4.99 1.59 21730 0-1 mm 0.018 5.79 1.57 0.001+ 0-2 cm 0.019 5.74 1.66 56 Occasionally, as the box core breaks the surface of the water and before it is secured on deck, the rubber base plate on the spade, forming the bottom of the sam pling container, does not seal properly, allowing water to flow through the core. When this happens, some of the sediment slumps and washes down the inside of the sampling container with consequent loss of fine-grained sediment from the surface. Badly washed samples were retaken; those evidencing slight washing were judged to be satis factory, but care was exercised to avoid sampling the washed portion of the core. Before taking sediment sam ples, the core was slabbed and radiographed. After radio graphing slabs from the core, the upper cm of each slab and remaining portion of the core was removed and put in sample containers. A portion of each sample was used for grain size analysis; the rest was archived and saved for other studies. Grain size analysis consisted of wet sieving to separate the fine fraction from the coarse frac tion. The fine fraction was pipetted according to stand ard procedures (see Folk, 1968; Royse, 1970), an(3 "the coarse fraction analyzed utilizing the settling tube after techniques described by Cook (1969) and Felix (1969). Various statistical variables may be computed from the resulting data. 57 Two slabs, approximately 2 cm thick, were cut from adjacent sides of the sediment core. Surfaces of the slabs were smoothed before radiographing on Kodak Type M or Type AA film with a Penetrex Industrial X-Ray unit. A thickness of about 2 cm represents a compromise in that it is thick enough to resolve the three-dimensional aspect of many biogenic structures, but sufficiently thin not to distort and obscure primary sedimentary structures (pers. commun., J. D. Howard, Skidaway Institute of Oceanography, 1973)• Photographs from the frame-mounted camera and EG&G camera show bedforms and other surface features; a com pass attached to the box core frame or suspended from the EG&G frame gives orientation of bedforms and internal structures. Repeated observations over several years provided excellent background from which to design more special ized experiments. Results of the earlier survey cruises influenced the location of current meters on the shelf. Specific objectives of later cruises included the deploy ment of recording thermographs and current meters to mon itor internal waves and measure near-bottom currents, and one cruise was dedicated to a detailed side scan sonar survey of San Pedro shelf. 58 Bottom Current Measurements On cruise 1271, 17-21 December, 1973» bottom cur rents were measured by in situ recording Savonious current meters. These meters descend to the sea-floor as a "free- vehicle" system (Isaacs and Schick, i960; Schick and Isaacs, 1961; Isaacs et al., 1966). After a predeter mined length of time, an explosive device separates the meters from their mooring weights and they return to the surface. A radio signal and strobe light aid in locating the meters for retrieval aboard ship. The free-vehicle apparatus, in this case, prohibited emplacing the meters closer that 3 ni to the bottom. Data from the meters were computer analyzed at Scripps Institution of Oceanography. The types of graphs resulting from this analysis are de scribed by Shepard and Marshall (1973) and Shepard e_t al. (197*0 • (Since I emplaced the meters on the shelf, up and down canyon symbols shown by Shepard and Marshall (1973) indicate north-south flow, respectively, on our records.) In situ recording Braystoke current meters were used on cruise 15-19 March, 197& and 12-16 April, 1976. Three of these meters, spaced at fixed intervals, were attached to a metal frame free to pivot about a rod in the center. This instrument package was lowered to the sea- 59 floor by a nylon line secured to the frame. The line extended from the frame to the surface where it was at tached to a marker buoy. When the frame rested on the sea bed, all three meters were within 1.5 m. of the bottom. Data can be recorded at preset intervals varying from 1-30 minutes on cassette tapes. A device reads the tapes and prints out the day, time, direction and flow rate expressed in revolutions per minute. These data are punched on to computer cards and interpreted by various techniques, including spectral analysis and progressive vector diagrams (PVD). Mr. N. Plutchak of Interstate Electronics has provided the expertise in these inter pretations . Side Scan Sonar Side scan sonar records defined large-scale bottom features. A Model 606 Side Scan System leased from Edo Western Corporation was used for a detailed survey of San Pedro shelf, 8-12 December, 1975* R/V VANTUNA maintained a speed of 3-4 knots, keeping the deep-tow vehicle ("fish") off the bottom by about 5-10 percent of the total depth. The maximum range of the recorder was usually set at 200 m, giving total coverage of 400 m side-to-side. Papers reviewing interpretation of sonographs include, Chesterman et al. (1958); Clay et al. (1964); Tucker 60 (1966); and Belderson et al. (1972); the reader is re ferred to these for details of the techniques involved and limitations of the method. 61 RESULTS Substrate When lacking direct current measurements, sedi- mentologists can still estimate direction and magnitude of bedload transport by analyzing physical properties and features of the substrate deemed sensitive to depositional processes. Many workers have demonstrated the value of various textural and mineralogical characteristics of sediments as indicators of dispersal (for example see van Andel and Postma, 195^; Smith and Hopkins, 1972; Booth, 1973)• Although the distribution and relative concen tration of heavy minerals are useful for delineating routes of sediment transport, I did not employ this tech nique in my study, but relied instead on specific textural variables of the sediment used by some investigators to deduce mechanisms of transport (see for example Smith and Hopkins, 1972 ; Booth, 1973)* Currents, exceeding the threshold of grain move ment, generate bedforms on the surface of the sea-floor. The orientation of these surface features accurately indicates the direction of flow, and hence, sediment 62 transport. A systematic change in the morphology of bed- forms occurs as the current progressively increases in velocity (Simons at al., 1965)• Moreover, investigations of many depositional environments demonstrate that spe cific types of bedforms are associated with certain depositional processes (Allen, 1963* 1966, 1968). Con sequently, bedforms are powerful diagnostic tools for interpreting specific currents and mechanisms responsible for dispersing sediment on the continental shelf (see McKinney at al., 197^; Karl, 1975; Swift and Ludwick, 1976). Textural Properties of Surficial Sediments Processing of over 100 box cores collected from San Pedro shelf included grain-size analysis of the top 2 cm of each (Fig. 6a). Hydrography of shelf waters changes with the sea sons. Textural characteristics of the substrate might change in response to the physical oceanography. Kulm et al. (1975) noted such changes on the Oregon shelf. Since the collection of cores on San Pedro shelf spanned oceanographic seasons, seasonal differences in textural variables might be masked if all grain-size distributions are compiled on one map. In order to test for seasonal effects, I collected cores from the same stations in 63 Figure 6. Box core, shipek grab and current meter locations (a), and median grain diameter of surficial sediment (b), San Pedro shelf. 6k STATION LOCATIONS CURRENT METERS SHIPEK SAMPLES 38 40 5655 59 • •• • 25i» 3 4 7 ,©5 4 • % © 36 42 68 88 95 96 y 66 SAN GABRIEL94 CANYON =METERS LONG BEACH M EDIAN DIAMETER IN MICRONS SAN PEI O KM November, 197^ and August, 1975* Table III shows that only slight differences exist between cores. As a check on errors induced by different operators, I had the analy sis of August cores repeated by two laboratory techni cians. Even without running a statistical test, visual inspection of the data indicates that the error induced by change of operator can easily account for the varia tion between cores collected in different months. Un fortunately, time considerations prohibited having the same operator run repetitive analyses on each sample. In the few cases, where the same technician analyzed dupli cate cores from one station location, differences between samples were as large as those between operators (Table II, AHF 22552, 22539)* To minimize error resulting from a change of operators, the same technician analyzed vir tually all samples described herein. At any rate, the consistent errors between operators shown in Table III are probably not large enough to be geologically signifi cant . When reoccupying stations, precision navigation becomes very important. R/V VELERO IV, the vessel used for most of the field work, fixes position largely by radar. Her officers (pers. commun., G. V. Colyer, Capt.) estimate the precision of their navigational techniques to be about 100-300 m when operating on the continental 66 TABLE III Textural Variables for Samples Collected from the Same Locations: November 197^ and August 1975 AHF # M mm X mm SD^ Sk % Sand % Silt Sand/Mud Diff. X mm Nov. - Aug. - 21379 22 555 22555* 0.084 0.081 0.080 0.060 0.060 0.054 1.44 1.28 1.29 0.91 I.38 1.29 72.45 78.05 76.00 24.50 18.58 22.04 1.49 3.56 3.17 0.000 -0.006 21384 22554 22554 0.067 0.072 0.073 0.038 0.043 0.029 1.43 1.47 I.67 0.52 1.38 1.29 54.98 62.51 63. 64 40.26 31.43 33.35 1.22 1.67 1.75 0.005 -0.014 21393 22553 22553 O.078 0.079 0.077 0.053 0.053 0.054 1.29 1.32 1.29 I.38 1.44 I.29 73.11 73.60 70.91 23.12 21.93 25. 84 2.71 2.79 2.44 0.000 -0.001 21398 22543 22543 0.063 0.075 0.082 0.035 0.046 0.049 1.50 1.66 1. 85 0.43 0.67 0.77 51.04 62.42 67.8I 41.87 28.41 25.94 1.04 1.73 2.11 0.011 +0.003 21399 22542 22542 0.079 0.112 0.135 O.056 0.085 0.098 1.48 1.98 2.09 0.62 0.63 0. 60 70.81 74.15 76.44 25.47 19.58 21.25 2.43 2.87 3.24 0.029 +0.013 21401 22540 22540 O.O85 0.085 0.091 0.069 0.070 0.075 1.02 1.05 1.30 1.37 2.19 1.74 86.22 87.68 86.87 11.89 9.4 7 11.24 6.26 7.12 6.62 0.001 0.005 TABLE III (Continued) Textural Variables for Samples Collected from the Same Locations: November 197^ and August 1975 AHF # M mm X mm SD/ Sk $ Sand $ Silt Sand/Mud Diff. X mm Nov. - Aug. - Aug. - 21402 22539 22539* 22552 22552* 0.078 0.085 0.085 0.079 0.082 0.052 0.069 0.064 0.054 0.058 1.29 1-13 1.34 1.30 1.35 1.37 2.19 1. 74 1.53 1.68 72.81 86.14 83. 06 74. 96 80. 64 23,47 10.55 19.40 20.61 16.65 2.68 6. 22 3.80 2.99 4.17 0.017 -0.005 0.015 0.004 Nov. - Aug. - 21403 22538 22538 0.082 0.084 0.083 0.061 0.065 0.061 1. 72 1.13 1.28 1.85 2.14 1.50 80.39 84.19 80. 95 16.61 12.65 18.02 4.10 5-33 4. 25 0.004 -0.004 21404 22537 22537 0.088 0.087 0.088 0.075 0.074 0.075 1.00 1.06 1.14 2.53 2.53 2.45 89.29 89. 66 89.52 8. 66 7.24 8.44 5. 68 8.67 8.55 -0.001 0.001 21405 22536 22536 0.084 O.O87 0.104 0.068 0.074 O.O83 1.04 0.97 1.23 2.31 2.79 I.87 85.71 89.75 88.62 12.15 7.92 10.14 6.00 8.76 7-79 0.006 0.009 21406 22535 22535 0.091 0.090 0.125 0.074 0.079 0.097 1.26 1.16 1.57 1.61 1. 76 1.27 83.02 88.07 85.53 14.31 9-35 12.64 4.89 7-37 6.13 0.005 0.018 ON 00 TABLE III (Continued) Textural Variables for Samples Collected from the Same Locations; November 197^ and August 1975 AHF # M mm X mm SDjzf Sk f h Sand f o Silt Sand/Mud Diff. X mm Aug. - 21411 22551 22551 0.083 0.086 0.099 0.065 0.074 0.086 1.10 1.00 1.24 2.36 2.40 2.02 84. 74 89.17 89.63 12.16 8.67 8.63 15.26 8.23 8.64 0.009 0.012 *The second set of the 22,000 series was analyzed by a different operator. VO shelf, with precision decreasing at greater distances from well-defined landmarks. The lack of precision navigation could he a significant factor contributing to "within station" variation, especially in areas where sediment textures change drastically over a short dis tance. As an example of this, samples collected at ap proximate 0.10 nautical mile (0.19 km) intervals over transects about 1 nautical mile (1.9 km) long show sur prisingly large variation in texture and color (Tables IV and Y). More consistent trends undoubtedly typify other portions of the shelf covered by strongly unimodal silty sands and sandy silts, but these tables illustrate the importance of precision navigation. Kelley and McManus (1970) performed a 3-level hierarchal analysis of variance on samples collected on the Washington and Oregon shelf. They estimated the var iance (1) within a sample, (2) within a station, and (3) between stations and determined the minimum resolvable difference between variables (for example, percent sand and percent silt have a minimum resolvable difference of about 10 percent, while that for median and mean grain diameter is about 0.70 phi-units) (see Kelley and McManus, 1970, Table 3» P* 1338). Moreover, Kelley and McManus (1970) concluded that median grain diameter, percent sand, percent silt and sand/mud ratio were the variables most TABLE IV Shipek Grab Samples lample # M mm X mm SD^ SK^ Diff. X mm Diff X/ IV 0.155 0.212 0.76 1.66 0.031 0.19 IV-1 0.230 0.243 O.83 0.54 0.184 0.82 IV-2 0.418 0.427 0.89 0.15 1.68 0.154 0.65 IV-3 0.289 0.273 0.70 0.635 1.7^ IV-4 0.914 0.908 1.24 0.70 0. 685 2.03 iv-5 0.213 0.223 0.71 0.75 0.043 0.26 IV-6 0.274 0.266 0.75 1 --1 1 --1 I --1 0.470 0.247 0.94 IV-7 0.513 I.07 0.3 7 0.183 0.64 IV-8 0.342 0.330 0.79 1.76 0.150 0.87 IV-9 0.182 0.180 0.84 2.86 0.006 0.05 IV-10 0.184 0.186 0.96 1.98 Lat. Long. 33°39.9' 118°10.4' (Intervening sta tions spaced equal' ly along this transect; lack of precise naviga tional equipment precluded exact positions.) H TABLE IV (Continued) Shipek Grab Samples Sample # M mm X :;m SD/ SK^ Diff. X mm Diff. Lat. Long. 0.036 0.25 IV-11 0.218 0.222 1.00 2.01 0.027 0.18 III 0.192 0.195 0.80 2.57 33°4l.4' 118°11.3’ I 0.070 0.058 1.23 1.98 33°42.2' 118°12.3' 0.018 0.54 1-1 0.053 0.040 1.58 1.29 0.005 0.20 1-2 o.o45 0.035 1.77 0.72 0.007 0.31 1-3 0.03^ 0.028 2.21 0.07 0.152 2.65 1-4 0.216 0.180 1.54 1.89 0.060 0.44 1-5 0.250 0.24-0 0.94 2.49 0.040 0.28 1-6 0.196 0.200 0.96 2.97 0.060 0.47 II 0.179 0.140 1.58 2.35 33°4l.3’ 118°12.3' ro TABLE V Shipek Grab Sample Color Description 0 n Munsell , Sample # Color Remarks IV 5Y ^e/^f white shell fragments IV-1 5Y 5/6 some white- and peach-colored shell fragments IV-2 5YR (somewhat redder than this ex act color) contains large shell fragments and comparitively less dark minerals IV-3 somewhere between 1>Y 5/6 and 5YR ^/4 IV-4 5YR 5/6 large and some unbroken shell fragments with large iron- stained quartz grains IV-5 slightly redder than 5Y 5/6 with very little white shell fragments IV-6 lying between 5YR ^/^ and 5Y 5/6 IV-7 5YR ^/^ white shell fragments IV-8 a combination of 5Y 5/6 and a slight touch of 10YR k/2 IV-9 5Y 5/2 close to 5Y h/h IV-10 (same as IV-9) IV-11 (same as IV-9) III (same as IV-9) II 5Y V7 * I 5Y ^/^ somewhat grayer than this exact color I-I (same as I) 73 TABLE V (Continued) Shipek Grab Sample Color Description Sample # ^Color"*" Remarks 1-2 (same as I) i H 10 Y V 2 1 H a mix between 5Y and 10Y V 2 VO 1 H 5Y 5/6 (somewhat redder than exact color) 1-6 (same as 1-5) 7^ diagnostic of depositional processes. Viewing data from San Pedro shelf In the light of their results indicates that generally textural variation between samples collected from the same station in dif ferent months lies within the limits of minimum resolv able difference. Skewness often is an exception to this statement In that the difference between samples Is fre quently greater than the minimum resolvable difference of 0.22 given by Kelley and McManus (1970)* Kelley and McManus estimated textural variables by graphical methods, whereas data presented herein were calculated as moment measures. This difference in computational techniques may account for the erratic variation In skewness, a particularly sensitive moment measure since It Is cubed, and the minimum resolvable difference for samples In this study may be greater than that determined by Kelley and McManus. The other textural variables are much less sensitive, which is reflected by less variation between samples. Thus, on balance, data from cores collected over a period of months can be compiled on one map. By contouring grain size parameters using Inter vals, In part, suggested to me by the results of Kelley and McManus, Interesting patterns emerge on San Pedro shelf. Anomalies In the regional trends of median dia meter, mean diameter, standard deviation, skewness, 75 percent sand, percent silt, and sand/mud ratio correspond roughly with the axis of San Gabriel Canyon as it projects on to the shelf (Figs. 6, 7> 9)• No similar anomalies occur on the shelf adjacent to San Pedro Sea Valley; how ever, very few samples were collected in this area. Clo sures in the contours and other somewhat linear trends in regional patterns will be elaborated upon in the Discus sion and Interpretation chapters; as will trend surfaces shown by Gorsline and Grant (1972) which complement and supplement these hand-drawn maps. Bedforms Photographs of San Pedro shelf taken in every month, except February and May, on 15 cruises over three years illustrate many details of the ocean bottom. Sono- graphs depict major surface elements, dimensions of which prevent definition by cameras with a field of view encom- passing areas usually less than 10 m . Surveys (Fig. 10) of San Pedro shelf, employing these two methods, reveal a great variety of features. These include ripples, pos sible sand waves, mesoscale lineations, biogenic traces, epi- and infaunal organisms, rocky surfaces and struc tural trends. Figure 11 illustrates a typical transect across the shelf. Bedforms equilibrate to prevailing hydraulic 76 Figure 7 Mean grain diameter (a) and standard deviation (b) of surficial sediment, San Pedro shelf. 77 LONG BEACH SAN PEI MEAN DIAMETER EVA ' * 2 i KM LONG BEACH STANDARD DEVIATIO N SAN PEI 40 KM Figure 8. Skewness (a) and percent sand (b) of surficial sediment, San Pedro shelf. 79 LONG BEACH SAN PEI BREAKWATER SKEWNESS HUNTINGTON KM LONG BEACH % SAND SAN PEI <70 HUNTINGTON KM Figure 9 Percent silt (a) and sand/mud (silt and clay) ratio (b) of surficial sediment, San Pedro shelf. 81 long b ea c h WILMINGTON % SILT SAN PEI // tti KM SAND / MUD RATIO SAN PEI < 5 HUNTINGTON BEACH KM A Figure 10. Station locations of bottom photo graphs taken on San Pedro shelf (see Appendix for AHF station numbers) (a), and track lines of side scan sonar sur vey of San Pedro shelf (shading shows location of mesoscale current linea- tions referred to in text) (b). 83 { CAMERA STATIONS \ DRIFT STATION • 60 • 6 1 •w .•85 • 36 • 62 , 38- 12 • • 63 •8 3 •82 c n O / L 2 s8# • _ _ ca ,•71 •9 0 •81 •e •91 80 •7 •75 • 5. • 96 • 6 93 97 25 10 5 SIDE SCAN SONAR TRACK LINES f MESOSCALE CURRENT \ LI NEATIONS \ ? PROBABLE 0 es 5 KM 10 '^ 1 8 '- ' = METERS Figure 11. Photographs showing typical bedforms and bottom features observed on San Pedro shelf. Photographs A-H show stations lj, 2, 2j, 3» 5» 6 and 7» respectively, along Transect A-A' on Figure 50 and described in the text on page 225- The water depth in meters is as follows: A-18 m, B-20 m, C-22m, D-25 m, E-29 m, F-36 m, G-^8 m, H-66m, I-5^ m, J-86 m. 85 regimes. Consequently, their orientation, morphology and distribution reflect depositional processes governing sediment transport on the shelf. Most bedforms are either oriented parallel with the current (longitudinal) or normal to the current (transverse). Ripples (wave- length ^60 cm) and sand waves (wavelength ^ 60 cm) are transverse forms, while parting lineation and mesoscale current lineations represent longitudinal forms. Trans verse ripples and mesoscale current lineations exist on San Pedro shelf, but no small-scale longitudinal bedforms (parting lineation) have been observed in bottom photo graphs . Compass directions mentioned in the text and plotted on maps refer to the trace of the long axis of longitudinal bedforms and to an imaginary line normal to the crest of transverse forms. Frequently, the compass suspended from the EG&G camera frame hung outside the field of view, or the compass on the box core did not function. Consequently, few photographs are oriented with respect to the bottom. Sometimes the compass was visible in a frame immediately prior to a good photograph of the bottom. In this case, since the EG&G camera system shoots one frame every 12 seconds, I used that direction for orientation. The few oriented photographs indicate that mesoscale current lineations and transverse 87 ripples trend NNE-SSW or NE-SW. This preferred orienta tion seems to be areally and temporally uniform. For reasons just discussed, many photographs lack a scale by which to determine the size of features on the sea bed. Therefore, dimensions of bedforms often must be inferred by comparison with familiar objects (e.g., large fish, small crustaceans, etc.). Study of photographs containing a scale in the field of view, indicates that ripples (wavelength £ 60 cm) comprise the vast majority of transverse bedforms on San Pedro shelf. Sand waves prob ably exist, but have not been positively identified for the above reasons. Ripples exhibit a variety of morphologies. Most, however, are relatively long crested, symmetrical forms, which occasionally bifurcate (Fig. 11). Wave lengths of these ripples range from 5-12 cm. Height could not be determined with confidence, but none probably exceed 5 cm. Ripple height can be approximated by assuming a ratio of 0.15 of height to wave length (Dingle, 197*0. Cook (1969) noted that on the inner shelf, spacing of ripple crests depended upon grain size. Other studies (Komar, 197*0 indicate that in fine and very fine sands, ripple wave length decreases shoreward. Paucity of absolute measure ments, however, precludes detection of any trends in wave length with respect to other variables on San Pedro shelf. 88 More complex bedforms also occur on the shelf. These include relatively short wavelength ripples super imposed upon and oriented normal to crests of ripples spaced farther apart; the ratio of wavelength varies, but in well-developed forms is about 3=1 (Fig. 12a). For ease of discussion, I call these Type A. Other bedforms of this general morphology consist of two perpendicular sets of ripples with nearly equal spacing between crests (Fig. 12b). In this case, one set appears dominant, while the crests of the other set form ridges spanning, or bridging, troughs of the better developed ripples. These are re ferred to as Type B. Figure 12c shows a probable mor phological variation of Type B ripples, designated Type B', where neither set dominates, but interact in a com plex pattern. None of these evidence any distinct asym metry, although Type B' bear a superficial resemblance to lunate or linguoid ripples. While I have no reference for defining the dimensions of these bedforms, I suspect the wavelength to be less than 60 cm. These forms occur in depths of 20-35 m and were observed in April, 1976. Type A ripples were photo graphed in 18 m of water in October, 1975 (Fig* 12). Orientation of the dominant ripple trains remains con sistent with that reported earlier, but, of course, the smaller ripples indicate directions normal to the main 89 Figure 12. Photographs of complex and unusual bedform observed on San Pedro shelf and described in the text. Photo graphs A, B and C show Type A, B and B' bedforms, respectively. Photo graphs D-F show Type A bedforms ob served 6 October, 1975 with E and F being oblique and vertical views of these features at the same station. The water depth in meters is: A-21 m, B-28 m, C-28 m, D-20 m, E-l6 m, F-l6 m. 90 trend. Type A ripples are associated with mesoscale cur rent lineations in the central portion of the shelf, about 3-5 km south of the Los Angeles breakwater. Types B and Bf occur farther seaward. In deeper water, these appear to grade into symmetrical ripples. The signifi cance of this distribution is elaborated upon in later chapters. Observations compiled from photographs taken over the past 3 years reveal a characteristic zonation of bed- forms on San Pedro shelf. Ripples are ubiquitous from the surf zone to depths of 20 m, since the normal wind generated waves in this area regularly affect sediment to that depth (Cook, 1969). In the greater depths of the central shelf, the activities of organisms may overwhelm evidence of physical bedload transport (Karl, 1975)• For example, photographs taken in January, 197^ at a depth of Ao m show well-developed ripples. Photographs at the same location the following April show no strong rippling. Reoccupation of this station during June and December, 1975 confirms this observation (Fig. 13)* Also, March, 1975 photographs show how the burrowing and crawling of bottom dwelling animals disrupts and eventually oblit erates ripples and other bedforms (Fig 13c, d). Thus, ripples in the central shelf (20-50 m), particularly Types A, B and B', are ephemeral features. Extensive 92 Figure 13. A series of photographs illustrating the seasonal occurrence and absence of ripple marks in the transition zone on the central shelf and one of the pro cesses by which benthic organisms destroy ripple marks. Photographs A and B were taken at the same location on San Pedro shelf at a depth of 38 m in December (AHF 21705) and June (AHF 22AA0), 1975, respectively. Photo graphs C and D were taken on San Pedro shelf at a depth of 20 and 26 m, re spectively, in March, 197&. 93 bioturbation characterizes the outer shelf and upper slope (Fig. 11), and I have rarely observed ripples in this outer zone. Sonographs reveal mesoscale current lineations at depths of about 25 m on the central shelf; these show up as alternating dark and light streaks on the side scan record (Fig. 1*0. Dark streaks are probably erosional furrows, while light streaks are sand ribbons. Sand rib bons consist of finer sand over a substrate of coarser material, whereas erosional furrows are areas in which coarser substrate has been exposed by winnowing of over- lying finer sediment (Swift, 1976). The wavelength (width) of the erosional furrows varies from about 15-50 m; the width of the intervening sand ribbons ranges from about *1*0-120 m, with narrower current lineations occurring on a substrate of finer sediment in shallower water (Fig. 1*0 . Surficial sediment in the vicinity of the current lineations shows a great deal of variability (Tables IV, V), although no uniform sequence of alternating coarser and finer sand was apparent. Internal Sedimentary Structures Ordinarily as ripples form and migrate, they pro duce sets of cross-laminations within the sediment. The distribution and types of sedimentary structures are reasonably well-known in depths landward of the 20 m 95 Figure 1^. Side scan sonar records showing meso- scale current lineations of alter nating sand ribbons (light areas) and erosional furrows (dark areas) from two locations on San Pedro shelf. 96 EROSiONAI — FURROW S A N D • RIBBON CORRECTED ORIENTATION isobath (Clifton et al., 1971)> "but less is known about those on the central and outer shelf. Primary structures have been observed only rarely in radiographs of box cores collected from the central shelf. Instead of being cross laminated, the samples usually are uniform and homogene ous, and marked with burrows and traces of organisms. This is surprising in that well-developed ripples have been observed frequently in bottom photographs, although if symmetric ripples do not migrate, no internal strati fication is formed (Clifton, 1976). Photographs taken during December, 1975 at a depth of 35 m show a strongly rippled surface (Fig. 13)• Yet, radiographs of a box core collected from the same location only a month earlier show no recognizable cross lamination (Fig. 15a). Note, however, that many short, broken "laminae" occur in the lower 2/3 of the radiograph (Fig. 15a). This "chaotic" signature characterizes many radiographs from cores collected in the zone of periodic active rippling/biogenic reworking (central shelf). After discussion with Dr. J. D. Howard (pers. commun. , 197*0 » I thought this signature might indicate disrupted ripple marks. From dives on the Hueneme shelf, Dr. Howard and Dr. H. E. Reineck, Senkenberg Institute, Germany, have noted what they describe as a thin algal (?) film covering inactive ripples. During periods of reduced 98 Figure 15. Radiographs of cores described in the text; "chaotic” signature in deposits on the central shelf of San Pedro Bay, this core (AHF 21^11) collected at a depth of 35 m (a) ; a core (AHF 216^) from the upper slope (162 m) of San Pedro Bay (h), and a core (AHF 21056) from 350 m off Pt. Hueneme showing depositional cycles revealed by bio genic reworking (c). White bar is 5 cm in length. 99 >*r . 1 current activity, organisms burrow through the sediment destroying any internal stratification. We speculate that this surface coating, however, preserves the ripple form. The inclined surfaces observed in radiographs may represent remnants of ripple surfaces. Alternately, and more likely, these inclined "laminae" may represent heavy mineral deposits concen trated in a ventral duct of the worm Ophelia (pers. commun., H. E. Clifton, U. S. Geological Survey, Menlo Park, California, 1976). University of Southern Calif ornia biologists (Susan Williams) state that Ophelia is widely distributed from the inter-tidal zone to shelf and slope depths. Yet, I have observed strong "chaotic" sig natures only in cores collected from the central shelf -- the zone of transitory ripples. Cores from progressively deeper areas show less evidence of primary sedimentary structures. Figure 15b is a radiograph of a box core collected from the upper slope at a depth of 162 m. No discernible primary struc tures are present and the core is extensively bioturbated. While biogenic reworking may destroy evidence of sediment transport, it can be very useful for depicting deposi- tional episodes. For example, distinct sedimentation un its can be detected in some radiographs (Fig. 15c) col lected in deep water (350 m) off Port Hueneme. 1 0 1 Water Column Suspended Sediment General Distribution and concentration of suspended parti culate matter in the water column reflects hydraulic con ditions prevailing on the shelf. Sediment enters the shelf system from land via rivers, erosion of sea cliffs, etc. In addition, waves and currents resuspend fine grained material previously deposited on the bottom. Particulate matter occurs in suspension throughout the water column, but accumulates particularly at density discontinuities (Drake, 1971)* Major concentrations of suspended particulate matter occur at the surface (water- air interface), density gradients within the thermocline, and near the bottom. Maps and cross-sections constructed from concentration and distribution data of suspended sediments define pathways of sediment dispersal. Regional Trends Data from numerous cruises demonstrate that con centration and distribution of suspended sediment change seasonally and monthly, and even over shorter time per iods during storms on the continental shelf. Two cruises in July-August, 1973 and January, 197^ establish regional trends along the coast (Fig. 16). For January, both 102 Figure 16. Stations occupied during cruise 1250, July-August, 1973 (a) and 1273 > Jan uary, 197^ (b). 103 PT. MUGU •3 995 SANTA M ONICA BAY 009 • ’ 003 . ’ 0 0 2 > •008 • 20,000 ’ o o i 007 • 009 013 014 • 014 • 019 SA N PEDRO BAY 0 1 9 • PALOS VERDES 020 0 2 1 19972 9 7 3 ' " .9 8 8 * * 85 030 v DANA V _ P T . 0 9 9 2 VNS Nautical M ila * PT. MUGU SANTA MONICA BAY i s a • 157 134 . 139 S A N PEDRO BAY PALOS VERDES DANA v ___PT. light transmission (5 m. below surface) and absolute values for surface suspensate concentrations, obtained from filtering seawater, show that the concentration of suspended sediment decreases seaward across the shelf (Figs. 17 and 18). This regional gradient parallels the shelf break. Superimposed upon this pattern are anom alous areas of high and low concentrations of suspended sediment. Many of the high values occur near harbors, mouths of rivers or openings of inlets, reflecting sedi ment input from these areas. Other anomalies probably indicate a natural patchy distribution of suspended mat ter; these may represent entrained masses of turbid water in surface eddies which have "broken loose" from coastal turbid plumes (see also Davis, in preparation). Distri bution of suspended particulates 1 m above the bottom parallels that of the surface (Figs. 17 and 18), but bot tom concentrations in shallow water are frequently higher from sediment resuspended by currents and density flow from nearshore. Consequently, isopleths are shifted far ther seaward. Light transmission data for July-August, 1973 show the same relative areal trends in distribution and concen tration of suspended solids as does January, 197^ data (Fig. 19). Vertical trends differ in that there is not as much contrast between surface and bottom values. Often 105 Figure 17* Maps showing regional patterns of rela tive turbidity (percent light transmis sion) 5 m "below the surface (a) and 1 m above the bottom (b) for January, 197^ (cruise 1273) from Pt. Mugu to Dana Point. 106 PT. MUGU □ ^o ^ ^ 5 0 - 70 W7M 30-50 <30 PALOS VERDE: DANA I V PT PT. MUGU P. V. DANA PT. Figure 18. Maps showing regional distribution and concentration (mg/l) of suspended sedi ment on the surface (a) and 1 m above the bottom (b) for January, 197^ (cruise 1273) from Pt. Mugu to Dana Point. 108 PT. MUGU PALOS VERDES DANA \ P T - p t . m ugu DANA U pT Figure 19* Maps showing regional patterns of rela tive turbidity (percent light trans mission) 5 m "below the surface (a) and 1 m above the bottom (b) for July- August, 1973 (cruise 1250) from Pt. Mugu to Dana Point. 110 PT MUGU >70 50-70 30-50 P A LO S VERDES DANA PT PT. MUGU P. V. DANA PT. surface transmission values are lower than near bottom values. Overall, concentrations are generally lower in July-August than in January. This reflects less discharge from rivers during summer months, and less resuspension of fine-grained sediment on the bottom. (Incorrect proce dures used in filtration of seawater on cruise 1250 pro duced erratic weights of suspended sediment. Consequent ly, I have not used these values in my results or inter pretations . ) Detailed Surveys Seasonal trends: Results of detailed surveys of San Pedro shelf in August, November and December, 197^ (Figs. 20 and 23) re main consistent with broad trends in distribution and concentration shown by July-August, 1973 and January, 197^ data. Owing to the high density of stations, much additional information can be gleaned from analysis of these data, particularly light transmission profiles. Water overlying the continental shelf is notably less turbid in summer than in winter. Stations occupied in August and December, 197^ provide examples for compar ison of seasonal differences (Fig. 20). Figure 21, com piled from data collected from 13-1^ August, 197^* shows the relative distribution of suspended particulate matter 112 Figure 20. Station locations of transmissometer casts (cruise 129*0 > August, 197*^ (a) and (cruise 1316) December, 197^ (b) . Locations of profiles depicted in Fig ures 35» 37» 38 and 39 are shown on (b) . 113 SAN PEDRO SHELF a T R A N S M I S S I O M E T E R S T A T I O N S • S U R F A C E & I m. A B O V E B O T T O M O S U R F A C E O N L Y 20831 A U G U S T , 1 9 7 4 33 60 20872 59 35 50 58 39 56 o/ .55 68 53 67 . 180 10 0 1 2 3 4 5 8 — = M E T E R S K M SAN PEDRO SHELF T R A N S M I S S O M E T E R S T A T IO N S • S U R F A C E 8 Im. A B O V E B O T T O M O S U R F A C E O N L Y 703 D E C E M B E R , 1 9 7 4 702 687 685 ■695 684 676 675 691 701 677 674 667 688 683 696 705 666 659 682 I 678 673 690 700 679 6 7 2 6 6 9 6 65 6 6 0 6 5 8 2 1 655 589— 681 697 21706 680 661 657 ^656 699 O ' O 663 662 — 698 10 12 3 4 5 — 18— = M E T E R S Figure 21. Areal patterns of relative turbidity (percent light transmission) at the surface (a) and 1 m above the bottom (b) for August, 197^ (cruise 129^-), San Pedro Bay. 115 SAN PEDRO SHELF % T R A N S M I S S I O N , S U R F A C E X hid <60 \ 6 0 - 8 0 \ E%81>80 A U G U S T , 1 9 7 4 180 K M = M E T E R S SAN PEDRO SHELF b % T R A N S M IS S IO N , Im A B O V E BOTTOM ^ < 2 0 6 0 - 8 0 VZX 2 0 - 4 0 ^ > 8 0 \ [ H D 4 0 - 6 0 \ A U G U S T , 1 9 7 4 18 = M E T E R S Figure 22. Areal patterns of relative turbidity (percent light transmission) at the surface (a) and 1 m above the bottom (b) for December, 197^ (cruise 1316), San Pedro Bay. 117 SAN PEDRO SHELF A % TRANSMISSION, SURFACE \ IZ3 20 £=1 60-80 DECEMBER, 1974 0 12 3 4 5 10 1 — 18— = METERS SAN PEDRO SHELF % TRANSMISSION, Im ABOVE BOTTOM V E22 20 |==] 60-80 ES3 20-40 ^ 80 ; \ ED) <*0-60 DECEMBER, 1974 0 12 3 4 5 K) 11 ' ' — 1 8 - " ' = METERS Figure 23. Station locations of transmissometer casts (cruise 1310) , November, 197^ (a-) and areal patterns of relative tur bidity (percent light transmission) 1 m above the bottom for November, 197^ (cruise 1310), San Pedro Bay. 119 SAN PEDRO SHELF TRANSMISSOMETER STATIONS NO VEM BER, 1974 440 425 424 407 406 389 2)388 439 493 4 8 7 468 4 75 4 61 4 8 2 456 467 481 460 486 443 494 427 476 462 483 457 .498 437 492 488 469 • • • 4 4 5 495 429 4 2 0 4 466 480 459 485 > 02\ 497 435 491 489 470 477 463 48. 4 ^ 458 490 — 471__ 478__464 1 8 0 SAN PEDRO SHELF T R A N S M IS S IO N , Im A B O V E B O T T O M m N O V E M B E R a 0 1 2 3 4 5 K M 10 18— = METERS at the water's surface. Note the rather high transpar ency values, indicating low turbidity. Low absolute con centrations of suspended solids more or less mirror transmission isopleths. Local anomalies reflect more closely-spaced contour intervals which define such things as clumps of material held by surface tension and patchy distribution of plankton superimposed on trends. Because of this, I will usually discuss only transmission data collected in different months. In general, concentration of suspended sediment decreases seaward with most iso pleths paralleling contours of the shelf break or shore line. The 70 percent isopleth, however, is markedly con volute, suggesting a somewhat patchy distribution within the overall uniform trend (Fig. 21a). Patterns of tur bidity 1 m above the bottom differ from surface concentra tion and distribution (Fig. 21b). Basically, bottom waters are more turbid nearshore (with increasing depth, surface and bottom concentrations show less difference and frequently surface turbidity will exceed bottom turbidity) and the trend of isopleths is oblique to that of surface waters. Data collected in winter provides good contrast to summer conditions. Surface waters in December, 197^ are significantly more turbid than those in August. Also, contour patterns are far more irregular (Fig. 22a). Near 121 bottom water is also more turbid; average concentration of suspended particulate matter 1 m above the bottom (1.73 mg/l) is almost twice that calculated for August (0.91 mg/l). Again, patterns of transmission isopleths within 1 m of the sea-floor differ from surface trends. As an example, note the tongue of very turbid water extending seawards towards San Gabriel Canyon (Fig. 22b). Within-season differences exist in the concentra tion and distribution of suspended particulate matter. Results of a detailed survey in November, 197^ (Fig. 23a), while consistent with seasonal fluctuations, show differences in detail from patterns the following Dec ember (Fig. 23b). In Figure 23b, note the incipient tongues of highly turbid water moving seaward. These, very possibly, are early stages of well-developed tongues observed in December. Dramatic changes occur between summer months as well. Rains in June, 1975 increased river discharge, causing very turbid conditions in, what should be, a low turbidity month. Figure 2^ illustrates this point quite well; the August, 197^ profile shows relatively high transmission values (low turbidity), but, in contrast, the June, 1975 profile along the same transect evidences a remarkable increase in concentration of suspended sedi ment throughout the water column. 122 Figure 2^. Vertical profiles of relative turbidity (percent light transmission) along a transect occupied during August, 197^ and June, 1975> San Pedro Bay. (Refer to Fig. 20 for location.) 123 S f— I nautical milt 20837 20836 i t 1 —I 20835 20834 20833 20832 20831 | I n a ulica I mI la | AUG. 1974 10m 50m 22455 JUNE 1975 % LIGHT TRANSMISSION ■ 0 -20% § g § 20-40% □ 40-60% ■ 60-80% > 80 % Figures 2k through 26 summarize this seasonal and month-to-month variability In concentration and distribu tion of suspended solids in waters overlying the contin ental shelf. Vertical variation: In addition to temporal fluctuation, striking hor izontal and vertical changes occur through the water col umn at any given time. As an example of this, using data collected in December, 197^ (Fig. 20b), I have constructed a series of longitudinal and transverse sections (Fig. 27- 31). These illustrate configurations of lobes and plumes of suspended matter. A series of maps drawn at 10 m in tervals in a horizontal plane depict the progressive growth and disappearance of these lobes down through the water column (Figs. 32 and 33)* In Figure 33c, I have tried to define the limits of mid-water plumes by measuring the thickness of a well- defined turbid layer and dividing by the average transpar ency of that layer (m/percent). In effect, these patterns indicate the relative concentration of suspended matter in a plume and represent a form of "isopach" map. Repre sentative transmission profiles suggest systematic differ ences between mid-water plumes on the eastern and western parts of San Pedro shelf (Fig. 3^)• 125 Figure 25* Vertical profiles of relative turbidity (percent light transmission) along a transect reoccupied during August and December, 197^» San Pedro Bay. (Refer to Fig. 20 for location). 126 21697 20857 20858 % LIGHT TRANSMISSION Figure 26. Vertical profiles of relative turbidity (percent light transmission) along a transect reoccupied over an interval of 2 days in November, 197^> San Pedro Bay. (Refer to Fig. 23 for location.) 128 Figure 27. A series of transverse (north-south) profiles showing relative turbidity (percent light transmission) from east to west, San Pedro Bay, December, 197^. (For station locations of Figs. 27-31 refer to Fig. 20b.) 130 \- I / V . M. j f\N fcO-80 I I > 80 2^59 Figure 28. A series of transverse (north-south) profiles showing relative turbidity (percent light transmission) from east to west, San Pedro Bay, December, 197^• 132 O n x 80 2 It, 7 0 go J Figure 29. A series of transverse (north-south) profiles showing relative turbidity (percent light transmission) from east to west, San Pedro Bay, December, 197^. | — 2 N.M. — | o 80 J 21106 2i6c n "21703 2(702 o ~ | 80 2/698 -,„n 21695 V/Athf' ? 21610 2/68b 2I68S f 0-20% F71 20-40 I j40-60 E3 60- so □ > 80 Figure 30. A series of longitudinal (east-west) profiles showing relative turbidity (percent light transmission) from north to south, San Pedro Bay, December, 197^* 136 ■ w y v Z c m a m Figure 31 • A series of longitudinal (east-west) profiles showing relative turbidity (percent light transmission) from north to south, San Pedro Bay, December, 197^. 138 sniz 7 7 7 V 7- Z Z Z 7 2 J - ^ J .rF Z W f& X T ? .2 ± J L S J U -jU L J M souz lour OQ < 08* 09 [SI ^ 0^-0* PH S81IZ 0*-07 07-0 'S NV Hi % 3 HUJS oC at 98912 ^ v a ) <10L\Z M •ww 3 Figure 32. A series of maps showing changes in areal patterns of relative turbidity (percent light transmission) at 5 and 10 m intervals (10-25 m) down through the water column, San Pedro Bay, Dec ember, 197^* Other intervals are de picted in Figure 33- 140 ■ 0-20 % S 3 2 0 - 4 0 % EHM 4 0 - 6 0 % 6 0 - 8 0 % £ □ > 8 0 % m m m m A Figure 33* Areal patterns of relative turbidity (percent light transmission) at 30 m below the surface (a); and at AO m below the surface (b) and an illustra tion of the limits of a mid-water plume (c) . 1^2 W 0 - 20 % fZffl 2 0 - 4 0 % ^ 1 4 0 - 6 0 % A E S 6 0 - 8 0 % 1=1 > 8 0 % B SAN PEDRO S H E L F THICKNESS (m) / TRANSMISSION 00 M ID -W A TER PLUME >6 DECEMBER, 1974 0 1 2 3 4 5 KM 1 0 — 18'— * METERS Figure 3^- Transmission profiles along three north-south transects in the vicinity of San Gabriel Submarine Canyon showing the change (transition) in character of the records going from east to west. 21659 21662 SAN PEDRO SHELF _ TRANSMISSOMETER RECORDS EAST -IOm 1900m 8S£% TRANSMISSION DECEMBER. 1974 TURBIDITY INCREASES TRANSPARENCY DECREASES - 1 00 21675 21671 0 % - 1 0 -100 2 1665 WEST - IO Transect A-A1 shows a consistent decrease in sur face turbidity seaward. The top 20-25 m of water shows uniform transparency in contrast to the variable values of deeper water. The shallowest station in the transect reveals a turbid layer near the bottom. The next station seaward shows that part of this turbid layer has broken off, probably along a density discontinuity, to form a mid-water plume. Continuing 2 km seaward, this plume be comes very well developed. However, within the next 2 km the plume diffuses rapidly and disappears. Transect B-B*, approximately A km to the west, shows features which ap pear to be transitory between the easternmost (Transect A-Af) and westernmost (C-Cf) transects. In B-Bf, turbid ity decreases consistently seaward. Note, however, that the surface layer shows signs of stratification. Also, there are no well-developed mid-water plumes. Transect C-C' represents a series of stations within the western plume, shown on Figure 33c. Again, turbidity decreases seaward. In this region, the upper 25 m are well strati fied, and although not as pronounced as In profile A-A', there is a well-defined mid-water plume. At this point, I think a word of caution, applying to these figures and descriptions, and others of this type, is in order. These maps assume synoptic observa tions, but it takes anywhere from 1 to 3 days to collect 1A6 data over the areas encompassed on these plots. Conse quently, the profiles and patterns described above may not represent eastern and western provinces separated by a zone of transition, but merely reflect changing condi tions within the time required to collect the data. LANDSAT imagery suggests that patterns on the shelf (under normal weather conditions) remain consistent for periods of several days to over a week (Davis, in prep aration) . Variability over time: To check variability in transmission profiles, I remained on station for several hours, during which time I made repeated casts of the the transmissometer. Figure 35 shows these profiles in a time sequence. I observed no marked change in the general configuration of the profile over this period. (However, certain aspects of this ex periment did aid in solving an enigma, which will be dis cussed later in this section.) Fluctuation in percent light transmission at the surface and 1 m above the bot tom indicates that patterns defined by 20 percent contour intervals should remain consistent over a few days (Table VI). A similar experiment in which I collected samples of surface water every hour for 38 hours demonstrates 1^7 Figure 35* A series of transmissometer records from casts made every 0.5 hours over several hours in March, 1976 illustra ting the rhythmic vertical migration of the seasonal thermocline, San Pedro Bay. (See Fig. 20b for locations.) 1A8 8 2 8 2100 1 9 0 0 2000 2 0 3 0 1 9 3 0 3/17/76 0 m 20. 3a 2 1 3 0 2 2 0 0 __________ 2 2 3 0 2 3 0 0 __________ 2 3 3 0 ___________2 4 0 0 10 n 3/18/76 1 4 0 0 1 4 3 0 1 5 0 0 1 5 3 0 1 6 0 0 1 6 3 0 I0_m 2a 3a 1 7 0 0 1 7 3 0 1 8 0 0 1 8 3 0 1 0 m 20. 30. TABLE VI Variation in Percent Light Transmission at Surface and 1 m Above Bottom with Respect to Time at Same Location Transmission {%) Time Sur. Bott. Time Sur. Bott. 3/17 1828 54 81 3/18 1400 43 78* 1900 48 81 1430 4 5 61 1930 51 83 1500 45 61 2000 48 79 1530 44 56 2030 48 81 1600 43 57 2100 ^7 81 1630 44 42 2130 AA 83 1700 43 41 2200 A9 82 1730 49 46 2230 58 82 1800 49 48 2300 57 81 1830 50 58 2330 57 81 3/18 0001 57 79 Range: 14 04 07 37* Mean: 56 81 46 55 Stan. dev.: 2.88 1.26 2.75 11.10 *Delete high value; range=20$, mean=52, S.D.=7«99 150 change in absolute concentration of suspended solids (Table VII). Unfortunately, light transmission was not monitored at the surface during this experiment. However, variation in absolute concentration of suspended matter (^ / mg/l) over this time period corresponds to about 10 to 20 percent change in light transmission based on data collected during other cruises (Drake, 1972) (Fig. 36). Thus, the change with respect to time in these variables is comparable. Figure 36 illustrates the poor correlation between weights of suspended sediment and values of light trans mission. This probably evidences, among other things, the effects of surface tension inhibiting many suspended solids from dispersing and settling, patchy distribution of plankton, the time at which the measurement was taken, and possible contamination from the ship. Davis (in prep aration) found more consistent trends by taking samples 0.5 m below the surface; this overcomes the problems of surface tension, contamination, etc. For these reasons I place more confidence in surface patterns defined by transmission records than absolute weights determined from surface water samples. Bottom water samples are generally more reliable, but sometimes the trip-weight on the Niskin bottle stirs up mud before the caps close, contaminating the samples. 151 TABLE VII Variation in Weight (mg/l) Suspended Sediment at Surface with Respect to Time at Same Location, August, 1975 Time Cone, (mg/l) Time Cone, (mag/l) 7/6 1815 2.80 1^15 0. 66 1915 1.20 1515 0.66 2015 0.50 1615 0.40 2115 0.65 1715 0.20 2315 0.25 1815 0 .60 7/7 0015 0.65 1845 0.70 0115 0. 65 1945 0.45 0215 0.40 2045 0. 65 0315 0.54 2145 0.50 0415 0. 60 2245 0.60 0515 1.00 2345 1.00 0615 0.80 7/8 0045 1.00 0715 0.80 0145 0. 94 0815 ---- 0245 0. 80 0915 0.50 0345 0.66 1015 0.40 0445 0. 60 1115 0.14* 0545 0.40 1215 0. 54 0645 o.4o 1315 0.50 0745 0.40 Range: 1.66*; Mean: 0.65; Stan. Dev. : 0.42 ^Delete high and low value: range=1.00, mean=0.60, stan. dev.=0.22 152 Figure 3 Graph showing the correlation be tween transmission (percent) and weight (mg/l) of suspended sedi ment . 153 (* o' Contaminated samples are retaken, but frequently the bottom is so soft that contamination cannot be prevented. In light of the above, by choosing proper contour intervals and exercising suitable care, I feel justified to interpret patterns of turbidity as synoptic observa tions . Continuous monitoring of the thermocline: Since suspended particulate matter concentrates at density discontinuities within the water column as well as along the surface, on several occasions I emplaced the transmissometer/CSTD at a depth coincident with a parti cularly steep gradient within the seasonal thermocline; and continuously monitored transmission and temperature for lengths of time varying from 12 to 36 hours (Fig. 37)• Because concentration of suspended sediment and tempera ture changes very quickly over a short distance in this zone, vertical displacement of the density interface is easily noticed on the chart recorder. Results of these measurements show periodic fluc tuations in percent light transmission and temperature (Fig. 37). I n August, 1975> fluctuations were most fre quent and intense immediately after lowering the instru ment to the thermocline, occurring about every 5 "to 15 minutes. They decreased in frequency and intensity within 155 Figure 37• Fluctuations in percent light transmis sion and temperature with respect to time during continuous monitoring at a level within the seasonal thermocline. (See Figs. 16 and 20 for locations.) (Note that temperature scale varies for each figure). 156 A OCT. 1973 ■V 8 B Xfc, prr^inf ■ -T1 t ! * 1 ~ i ——~ i --r MAR 1976 \^T'RIMi '"| i * i - l ' ’ fm,t> IHr" 11 1 E. ‘ r v f r v - T l a short time and did not reappear for hours. Repeated transmissometer/CSTD casts every half hour for several hours in March, 1976 demonstrate that the thermocline oscillates as much as 16 m within the water column (Fig. 38)• This up and down migration seems to show tidal periodicity with minor perturbations of shorter period superimposed on the major cycle (Fig. 38). Thus, it is necessary to lower or raise the transmissometer occasionally in order to stay within the thermocline, or to monitor a particular density discontinuity. This phenomenon probably accounts for the decrease in activity shortly after emplacing the instrument in the thermocline and renewal of activity several hours later. In April, 1976 I periodically checked the position of the seasonal thermocline and relocated the transmisso meter as necessary. This, plus the fact that the thermo cline did not migrate significantly, produced records with intervals of extended activity (Fig. 378.) . Specta cular changes in percent light transmission reflect the sharp boundary between highly turbid water in the surface mixed layer and much lower concentrations of suspended matter (relative to the surface) within the thermocline (Fig. 37d). Examination of time-function profiles shows that fluctuations in transmission (and temperature) often take 158 Figure 38* Graph showing the oscillation of the seasonal thermocline (as measured at the base of the surface mixed layer) with respect to time in March, 1976, correlated with the tidal cycle, San Pedro Bay. 159 .. 183 m MARCH 1976 tidal -- 1.53 3 0 - 25- -.0 92 2. ; 20- -.0.61 1 0 - - 0 . 3 0 - 0 5 - 2000 2030 2100 1828 1900 1930 2230 2130 2200 2300 2330 MARCH 1976 1.53 3 0 . 1.22 2 3.. 0.92 th a r m o c lln a 0.61 13. . tidal 0.30 3 . 1730 1800 1830 1530 1400 1430 1300 1600 1630 1700 the form of sinusoidal waves with flattened crests or troughs. In October, 1973 a^d August, 1975* these wave shaped fluctuations often occurred in sets of two with intervening periods of relative quiesence (Fig. 37a> b). Records in April, 1976 consist of a spectrum of waves with varied frequencies, periods and amplitudes (Fig. 37d). Meaningful analysis of these profiles requires high- powered statistical techniques, and this will be part of a continuing study during my tenure as National Research Council Research Associate with the U. S. Geological Sur vey at Menlo Park, California. In order to complete the investigation of variation in turbidity with respect to time, I monitored temperature and transmission near the sea-floor, the third area of major concentration of suspended particulate matter. Figure 37© shows the nature of the fluctuations occurring within 3 m of the bottom in March, 1976. Because no steep vertical gradients exist in either temperature or concen tration of suspended sediment, these perturbations are less pronounced than those in the thermocline. Temperature Besides turbidity, I measured two other variables in the water column -- salinity and temperature. Owing to repeated malfunctions in our CSTD system, I have only a l6l very few salinity profiles and will not report on these herein. Temperature data is also limited because of fre quent problems with either the electrical cable or therm istor on the transmissometer/CSTD. Temperatures recorded in August and December, 197^ document seasonal variation on San Pedro shelf. Surface and near-bottom temperatures averaged 17.5°C and 12.4°C for August and 15-1°C and 12.2°C for December, respective ly. In addition, transmissometer casts in July-August, 1973> October, 1973> January, 197^> March, 1976 and April, 1976 provide representative seasonal temperature profiles. These show that the thermocline is best developed in spring, summer and early fall, and less pronounced in winter (Fig. 39)• Below the zone of mixing, typically 5 to 15 m thick, temperature decreases rapidly in summer, but as winter approaches, surface water cools producing a more uniform vertical distribution temperature. Thus, a strong, near-surface temperature gradient characterizes summer months, while a weak thermocline, deeper in the water column, typifies winter months (Fig. 39* Table VIII). Near-bottom Current Measurements 17-21, December, 1973 Two meters, emplaced in depths of 27 and 51 m > measured currents 3 m above the bottom for 8^ hours 162 Figure 39* Vertical temperature profiles for each season showing the depths to the seasonal thermocline. 163 DEPTH W INTER SUMMER FA LL SPRING 2 0 0 3 4 2 0 0 3 3 2 0 0 3 0 19148 I95H 19519 1828 2130 C M 8 .I4 0 0 17.4' 18.2' 13.4* 13.4 13.7' OCT. JAN OCT. MAR. APR. JAN. JAN. AUG. 20 (scolt ?) 40 seal* lOVin. (other* at 1 0*/3.4*) 60. 10.6* 60 1 0 0 9.3' 200 8.6' 8.8 TABLE VIII Variation in Depth to Thermocline Month A B C D August, 1973 AHF 1911*8 159 m £ 0 1 —1 20 m 30 m October, 1973 AHF 195H 21*5 7 32 AHF 19519 22 8 20 16 January, 197^+ AHF 2003^ 70 1*6 51* 7 AHF 20033 228 37 62 7-11 AHF 20030 225 52 62 7-14- March, 1976 1828 40 10 20 2130 1*0 27 32 April, 1976 GM 8, 11*00 25 5 13 A : Water depth in meters; B : thickness of mixed layer in summer or depth at which steepest gradient begins in winter; C: depth at which steepest gradient ends as marked by pronounced break in slope; Ds depth at which any minor, but marked, "kinks" occur in major profile; frequently many "kinks" occur in summer thermocline. 165 (Fig. 6a). Higher speeds occurred in the deeper meter, with most values lying between 15 to 20 cm/sec and a few greater than 25 cm/sec (Fig. ^0). At 27 m, no speeds ex ceeded 15 cm/sec (Fig. ^0). (To determine speeds 1 m above the sea-floor, multiply 3 m. values by 0.9-) While higher speeds at the deeper station exhibited a preferred direction of WSW-ENE, lower speeds appeared randomly distributed as did all values at the shallow station (Fig. kO). At 51 m main current flow was roughly towards the west for approximately the first two days, but turned southerly during the last two days of record (Fig. 5 5^ * e). In contrast, the shallow meter during this time in terval shows southerly flow for the first half of the record, but easterly flow thereafter (Fig. 56c). Net flow at the deep station is directed towards the SW, whereas that at the shallow stations is ENE. Spectral analysis reveals a strong diurnal tidal component in currents measured at 51 This diurnal period is weak at the shallow station and may be masked or overwhelmed by meteorological events. 16-19 March, 1976 Of three current meters deployed in a vertically- stacked array at a depth of ^5 m » only one, situated 1.2 m 166 Figure ^0. Polar diagrams showing current speeds and directions recorded during Decem ber, 1973 and March and April, 1976. 167 DECEMBER. .1973 51m DECEMBER. 1973 2 7 a + M/SE 1 5 .00 it . o o -15. 6o 5.0C -5.00 976 45m MARCH 976 28m APRIL '•c (considered 1 m) above the sea-bed functioned properly (Fig. 6a). This meter operated for 72 hours. Speeds ranged from less than 5 cm/sec to slightly greater than 15 cm/sec, with most values under 10 to 12 cm/sec (Fig. ^0). Although not analyzed statistically, visual inspec tion of progressive vector diagrams (PVD) and comparison with tide charts suggests a strong tidal influence at this depth. Higher speeds show a preferred westerly and southwesterly direction. Net current flow is towards the SSE (Fig. 58d). 12-15 April, 1976 One current meter was emplaced 1 m above the bot tom in a depth of 27 m for about 72 hours (Fig. 6a). Speeds rarely exceeded 5 cm/sec; only occasionally reach ing values as high as 8 to 9 cm/sec (Fig. ^0). As of yet, no spectral analysis has been applied to this record, but correlation with tide tables indicates a weak tidal component. During this time interval net flow was towards the WSW (Fig. 58b). 169 DISCUSSION AND INTERPRETATION General Statement Although current meter records exhibit a strong tidal component, some other forces generate currents which over-ride tidal effects. These include surface waves, meteorological forces, and internal waves. Such processes exercise greater influence than tides over sediment trans port, and are of sufficient importance to merit separate sub-sections. Near-bottom currents reflect input of several sources, and the concluding section synthesizes sediment responses to this complex hydraulic regime. Surface Waves General As surface waves propagate landward, these waves shoal and generate currents near the bottom. Since the currents are oscillatory in nature, they consist of al ternating onshore and offshore surges as the wave passes a given point. Onshore surge is stronger, but the off shore component lasts longer (Cook, 1969). Effects of asymmetric surge become stronger with decreasing water 170 depth until the wave breaks and forms a wave of transla tion flowing shoreward. Several papers have documented the influence of wave-induced currents upon sediments within and slightly seaward of the surf zone (Vernon, 1966; Cook, 1969; Clifton et al., 1971; Cook and Gorsline, 1972). Surface waves are also capable of ini tiating sediment movement in much deeper water (greater than 100 m), particularly along high energy coasts such as Oregon and Washington (Smith and Hopkins, 1972; Komar et al., 1972; Komar and Miller, 1973)* Some of these papers suggest that seasonal absence and presence of rip ples at a particular depth on the shelf reflects differ ences between higher energy winter waves and less intense summer conditions. This phenomenon might be responsible for transitory ripple fields observed on San Pedro shelf; indeed, seasonal changes in surface waves account for the marked differences between summer and winter beaches (Shepard and La Fond, 19^0; Cook, 1969). In order to test this assumption and to estimate the general impor tance of surface wave-induced currents on shelf sediments, I calculated near-bottom velocities generated by surface waves moving across the shelf. Wave Equations Heights and periods obtained from wave gauges 171 operated by NOAA on Platform EVA are variables which can be used to compute deepwater wave length, Loo , wave length as the wave shoals, L, orbital diameter at the bottom, d , maximum horizontal velocity of the to-and-fro motion at the bottom, U , and velocity asymmetry A U f f l (see Komar and Miller, 1973; Komar, 197^; Clifton, 1976). Starting with a known period, T, the following equation: L = (g/27T)T2 (22) gives the deep water wave length where g is the accelera tion of gravity. The wave length as the wave shoals can be estimated using the following relationship from Eckart (1952)s L = L<*a| tanh(27r h/L)f ® (23) where h is the water depth. Linear Airy wave theory gives the bottom orbital diameter by inserting L and wave height. H, in this equation: H d = -------------- (24) sinh (2 yc h/L) Maximum horizontal velocity associated with to-and-fro water motion at the bottom is given by: „ , _?0_ , (25) m T T sinh (2 7T h/L) 172 Velocity asymmetry is estimated from Stokes second order wave equation: AU 14.8h2 ^ m = (26) L T sinh^ (2TT /Lh) but this approximation becomes invalid for h/L below about 0.1 (Adeymo, 1970; Clifton, 1976). Alternately, asymmetry may be attributed to water mass transport in the turbulent boundary layer as described by Longuet-Higgins (1953)• 5/Au 2T A U = 2 ----^ — (27) 1 1 1 L Clifton (1976, p. 6) states "... that mass transport con tributes relatively little to the total asymmetry as a wave approaches the breaker zone." Calculations using the "average" wave for each month of 1973 (Table I) indicate thatAU is usually much m less than 5 cm/sec in water depths exceeding 20 m. Since 5 cm/sec is the minimum velocity necessary to produce asymmetric bedforms, wave-generated ripples should be symmetric in the area of study (Table IX). Unidirectional currents superimposed on wave surge, however, may increase the asymmetric velocity enough to form asymmetric ripples. Calculated Bottom Velocities In order to determine the depth at which surface waves initiate grain movement, I calculated maximum velo- 173 •hfZt TABLE IX Near-bottom Velocities Generated by "Average" Surface Waves for each Month of 1973 at 10 m Intervals from 1-100 m Water Depth VELOCITY (cm/sec)* 10 20 30 40 Depth in 50 Meters 60 70 80 90 100 A 71.0 45.0 32.0 24.0 J anuary 18.1 13-7 10.3 7-7 5.8 4.3 B 22.3 2.8 0.6 0.2 0.06 0.02 0.01 0.0 0.0 0.0 C 12.9 3-8 1.7 0.9 0.5 0.3 0.1 0.07 0.05 0.02 D 38.6 24. 9 18.0 13.0 10.0 7.0 5.0 4.0 3.0 2.0 E 6.9 0.9 0.2 0.06 0.02 0.01 0.0 0.0 0.0 0.0 F 3.8 1.2 0.5 0.2 0.1 0.07 0.03 0.02 0.01 0.01 February A 55.0 36.0 26.0 20.0 15.0 11.0 9.0 7.0 5.0 4.0 B 15.9 2.1 0.5 0.2 0.05 0.02 0.01 0.0 0.0 0.0 C 7.8 2.A 1.1 0.6 0.3 0.2 0.1 0.06 0.03 0.02 D 31.0 20.0 15.0 11.0 8.0 6.0 5.0 4.0 3.0 2.0 E 5.1 0.7 0.2 0.05 0.02 0.01 0.0 0.0 0.0 0.0 F 2.5 0.8 0.4. 0.2 0.1 March 0.05 0.03 0.02 0.01 0.01 A 44.0 28.0 20.0 15.0 11.0 8.0 6.0 4.0 3.0 2.0 B 8.3 1.1 0.2 0.06 0.02 0.01 0.0 0.0 0.0 0.0 175 TABLE IX (Continued) Near-bottom Velocities Generated by "Average" Surface Waves for each Month of 1973 al 10 m Intervals from 1-100 m Water Depth VELOCITY (cm/sec)* 10 20 30 Depth in Meters 4o 50 60 70 80 90 100 C 5.0 1.5 0.7 0.3 0.2 0.1 0.0 5 0.02 0,01 0.01 D 24.0 15.0 10.0 8.0 4.0 4.0 3.0 2.0 1.0 1.0 E 2.4 0.3 0.07 0.02 0.01 0.0 0.0 0.0 0.0 0.0 F 1.5 0. A 0.2 0.1 0.04 April 0.02 0.01 0.01 0.0 0.0 A 26.0 17.0 12.0 9.0 7.0 5.0 4.0 3.0 2.0 1.0 B 3.5 0.4 0.1 0.03 0.01 0.0 0.0 0.0 0.0 0.0 C 1.8 0.5 0.2 0.1 0.07 0.03 0.02 0.01 0.01 0.0 D 13.0 8.0 6.0 4.0 3.0 2.0 2.0 1.0 1.0 0.9 E 0.9 0.1 0.03 0.01 0.0 0.0 0.0 0.0 0.0 0.0 F 0.4 0.1 0.06 0.02 0.01 0.01 0.01 0.01 0.0 0.0 May A 25.0 16.0 12.0 10.0 8.0 7. ,0 5* 0 4.0 4.0 3- ,0 B 4.6 0.7 0.2 0.08 0.03 0,,01 0.01 0.0 0.0 0,,0 c 1.6 0.5 0.2 0.1 0.08 0,, 06 0. 03 0.02 0.02 0,,01 D 12.0 8.0 6.0 5.0 4.0 3. ,0 2.0 2.0 2.0 1,,0 E 1.2 0.2 0.05 0.02 0.01 0,,0 0.0 0.0 0.0 0.,0 F 0.4 0.1 0.06 0.03 0.02 0,,01 0.0 0.0 0.0 0.,0 TABLE IX (Continued) Near-"bottom Velocities Generated "by "Average" Surface Waves for each Month of 1973 at 10 m Intervals from 1-100 m Water Depth VELOCITY (cm/sec)* Depth in Meters 10 20 30 40 50 60 70 80 90 100 June A 29.0 19.0 14.0 10.0 8.0 6.0 5.0 3.0 3.0 2.0 B A.5 0.6 0.2 0.05 0.02 0.01 0.0 0.0 0.0 0.0 C 2.1 0.7 0.3 0.2 0.1 0.05 0.03 0.01 0.01 0.01 D 15.0 10.0 7.0 5.0 4.0 3.0 2.0 2.0 1.0 1.0 E 1.3 0.2 o.o4 0.01 0.0 0.0 0.0 0.0 0.0 0.0 F 0.6 0.2 0.08 0.04 0.02 July 0.01 0.01 0.01 0.0 0.0 A 25.0 17.0 12.0 13.0 7.0 6.0 4.0 3.0 3.0 2.0 B 3.8 0.5 0.2 0.05 0.02 0.01 0.0 0.0 0.0 0.0 C 1.6 0.5 0.2 0.2 0.07 0.05 0.02 0.01 0.01 0.0 D 13.0 9.0 6.0 5.0 4.0 3.0 2.0 2.0 1.0 1.0 E 1.1 0.2 o.o4 0.01 0.0 0.0 0.0 0.0 0.0 0.0 F 0. A 0.2 0.0 6 0.04 0.02 August 0.01 0.01 0.01 0.0 0.0 A 23.0 15.0 11.0 8.0 7.0 5.0 4.0 3.0 2.0 2.0 B 3.0 0.4 0.1 o.o4 0.01 0.01 0.0 0.0 0.0 0.0 C 1.4 0.4 0.2 0.09 0.07 0.03 0.02 0.01 0.01 0.0 - V ! o\ TABLE IX (Continued) Near-bottom Velocities Generated by "Average" Surface Waves for each Month of 1973 at 10 m Intervals from 1-100 m Water Depth VELOCITIY (cm/sec)* 10 20 30 Depth in 40 50 Meters 60 70 80 90 100 D 13.0 9.0 6.0 5.0 4.0 3.0 2.0 2.0 1.0 1.0 E 1.1 0.2 o.o4 0.01 0.0 0.0 0.0 0.0 0.0 0.0 F 0.4 0.2 0.06 0.04 0.02 0.01 0.01 0.01 0.0 0.0 September A 26.0 17.0 13.0 10.0 8.0 6.0 5.0 4.0 3.0 2.0 B 4.1 0.6 0.2 0.05 0.02 0.01 0.0 0.0 0.0 0.0 C 1.7 0.5 0.3 0.1 0.09 0.05 0.03 0.02 0.01 0.0 D 15.0 9.0 7.0 5.0 4.0 3.0 2.0 2.0 1.0 1.0 E 1.3 0.2 0.05 0.02 0.01 0.0 0.0 0.0 0.0 0.0 F o. 6 0.2 0.08 o.o4 0.02 0.01 0.01 0.0 0.0 0.0 October A 27.0 18.0 13.0 10.0 8.0 6.0 5.0 4.0 3.0 2.0 B 4.4 0.7 0.2 0.06 0.02 0.01 0.0 0.0 0.0 0.0 C 1.9 0.6 0.3 0.1 0.09 0.05 0.03 0.02 0.01 0.0 D 15.0 10.0 7.0 6.0 4.0 3.0 3.0 2.0 2.0 1.0 E 1.4 0.2 0.05 0.02 0.01 0.0 0.0 0.0 0.0 0.0 F 0.6 0.2 0.08 0.05 0.02 0.01 0.01 0.0 0.0 0.0 H - nJ TABLE IX (Continued) Near-bottom Velocities Generated by "Average" Surface Waves for each Month of 1973 at 10 m Intervals from 1-100 m Water Depth VELOCITY (cm/sec)* 10 20 30 Depth in 40 50 Meters 60 70 80 90 100 November A 30.0 19.0 14.0 10.0 8.0 6.0 4.0 3.0 2.0 1.0 B 4.4 0.5 0.1 0.04 0.01 0.0 0.0 0.0 0.0 0.0 C 2.3 0.7 0.3 0.2 0.09 0.05 0.02 0.01 0.01 0.0 D 16.0 10.0 7.0 5.0 4.0 3.0 2.0 1.0 1.0 1.0 E 1.3 0.2 0.04 0.0 0.0 0.0 0.0 0.0 F 0.7 0.2 0.08 0.01 0.01 0.0 0.0 0.0 December A 4l.O 27.0 20.0 16.0 12.0 10.0 7.0 6.0 5.0 4.0 B 1.4 0.4 0.1 0.04 0.02 0.01 0.0 0.0 0.0 C 4.3 1.4 0.6 0.4 0.2 0.1 0.06 0.05 0.03 0.02 D 27.0 17.0 13.0 10.0 8.0 6.0 5.0 4.0 3.0 2.0 E 4.0 0.6 0.2 0.05 0.02 0.01 0.0 0.0 0.0 0.0 F 1.9 0.5 0.3 0.1 0.09 0.05 0.03 0.02 0.01 0.0 *A = Um(Hmax) calculated using equation (25); B = Um(St) calculated from equation (26); C = Um(L-H) calculated using equation (27); D = Um(Hl/3) using equation (25); E = Um (St) for Hi/3 calculated using equation (26); F = Um(L-H) for H1/3 calculated "Average" wave for each month given in Table I. H CO city generated by shoaling waves for fixed depth intervals on the shelf (Table IX). As expected, more severe winter waves effect the bottom to greater water depths than smal ler summer waves. Assuming that the threshold velocity for fine and very fine sand covering San Pedro shelf lies somewhere between 10-20 cm/sec, It is seen that seasonal fluctuations in surface wave energy can account for trans- istory ripples occuring In 35 "to 40 m of water on the cen tral shelf (Fig. 4l) . The minimum velocity necessary to initiate rippling of sediment of a particular size class occurs at a fixed depth for a given wave. If we assume this depth to be con stant for the whole shelf, we can superimpose this isobath on a chart of median grain diameter. If sediment of that size class occurs within boundaries of the "minimum velo city" isobath, we conclude that It is rippled. Thus, it is possible to approximate the extent of active rippling for a given set of conditions. Figures h-2 through ^5 rep resent this approximation for each month of 1973* These approximations are misleading in that they are based on the "typical" wave for each month. The "typical" wave Ignores the extreme waves which may be more important for moving sediment. Indeed, bedforms may re flect these "catastrophic" waves rather than more normal waves. In other words, a short duration of large waves 179 Figure *KL. Diagram illustrating the seasonal changes in depth of the threshold vel ocities for fine and very fine sand based on the "average" wave (Table I) for each month of 1973- Cross-hatched areas show the zone of possible rip pling. 180 Velocity [ c m / sec) Velocity (c m /,e c ) WINTER SPRING MO May Ap Jun MAR. 20 MARCH, TRANSITION \M O N T H MARCH, TRANSITION MONTH Apr May Juna 4 0 MAR 33m 35 SUMMER 20 SEPT TRANSITION MONTH OEC TRANSITION MONTH I’ Sept 40 Ocl,No* Aug Sapl Juna 40 Oac. 35 D e p th (m l Figure ^2. A series of maps depicting the possible area of active rippling of fine sand using 10, 15 and 20 cm/sec isopleths calculated from "average" wave statis tics (Table I) during December (a), January (b) and February (c), 1973> San Pedro Bay. The substrate within the small open area on the central shelf consists of sediment coarser than fine sand, thus velocities greater than 20 cm/sec are required to initiate rip pling. 182 10 - 13 cm/sac. (o ra o of posaibta rip p la a ) z > 15 cm/sac. (ored o f probobla ripplaa) Extanda from isoplath to ahora. DEC 197 3 (ora o of possible rip plaa) :> 15 cm /sac (oraO of probobla ripplaa) Extends from isoplath to shore. JAN 1973 (orao of posaibta ripplaa) > 15 cm /sec (orad of probobla ripplaa) Extanda from isoplath to ahora. Figure A3. A series of maps depicting the possible area of active rippling of fine sand using 10, 15 and 20 cm/sec isopleths calculated from "average" wave statis tics (Table I) during March (a), April (b) and May (c), 1973* San Pedro Bay. 18A Figure 4^. A series of maps depicting the possible area of active rippling of fine sand using 10, 15 and 20 cm/sec isopleths calculated from "average” wave statis tics (Table I) during June (a), July (b) and August (c), 1973» San Pedro Bay. 186 i 1 10 - 15 cm/see. (orao of possible ripples) > 15 cm /sac (orao of probobla ripplaa) Extanda from isoplath to shora. V 10 -15 c m /*a c (orao of possible ripplaa) H H > 1 5 cm /sac (orao of probobla ripplaa) Exiands from isoplath to shora JULY '73 I I 10 - 15 cm/sec. (orao of posaibla ripplaa) C l~ s i > 15 cm/sac. (orao of probobla ripplaa) Extends from isaple**" to ahora. AUGUST 1973 Figure 45. A series of maps depicting the possible area of active rippling of fine sand using 10, 15 and 20 cm/sec isopleths calculated from "average" wave statis tics (Table I) during September (a), October (b) and November (c), 1973 San Pedro Bay. 188 □ . 10 - 15 cm/sec. (area of posaibta ripples) > 15 cm/sec. (area of probable ripples) Extends from isopleth to snore. SEPT. 1973 □ 10 -15 em/sec. (areo of possible ripples) £=~| > 15 cm /sec (areO of probable ripples) Extends from isopleth to shore OCT. I9?3 □ JO - 15 cm /sec (area of possible ripples) fs=l > 15 cm/sec. (area of probable ripples) Extends from isopleth to shore. during the month may he responsible for generating bed- forms observed in bottom photos. Therefore, charts and tables constructed from "typical" wave values should be used for only a relative comparison of seasonal differ ences. In order to estimate the importance of maximum waves, it is necessary to determine Um for each observa tion during the month. In this way, the percentage of time during which the threshold velocity is exceeded can be determined for each month and for any given size class. Table X gives the percentage of time that waves in January, April, July and October, 1973 exceeded the minimum thresh old velocities for movement of fine sand as these waves propagated across the outer, central and inner shelf; this is represented graphically in Figure ^6. Bedforms Bottom photographs taken during different months provide data to test the above assumptions. Figures ^7 through 50 summarize these observations. In general, these maps support the conclusion that rippling occurs at greater distances (deeper water) from shore in winter than in summer. Orientation of ripple crests suggests that waves approaching from the south and southwest produce these bedforms. This is consistent with surf directions reported by lifeguards. 190 TABLE X Frequency (Percent) Near-bottom Wave Velocities Exceeded Presumed Threshold for a Given Depth Month Depth (m) 20 cm/sec 10 cm/sec 20 83.076 IOO.O7 6 January 50 33.3 70.2 100 1.2 9.5 20 22.076 89.076 April 50 00.0 12.2 100 00. 0 00.0 20 28.276 96.5f* July 50 00.0 20.0 100 00.0 00.0 20 30.276 18.876 October 50 00.0 25.6 100 00.0 00.0 191 Figure 46. Graph showing the near-bottom hori zontal velocities generated in depths of 20 m (inner shelf) , 50 m. (center shelf) and 100 (outer shelf-shelf break) by surface waves during Janu ary, April, August and October, 1973 > and at 40 m in August, 1974. 192 no ibo- -g^x 20. 50 n il 30 ioqs in Month ( Number of qbs 40. Af^RIL 1973 ilO. -v 20 No. qf pbqefyotiojna. 20m ■^V/ r 100m / 2 0 Nq. q f O b s e r v a t io n s 0GT.ll9f3L.4- 30 20 m 1 50 m tOOim 30 25 2 P No Of AUG 40 m No. of Pb tervd tiono Figure ^7* The distribution and orientation of bedforms on San Pedro shelf as observed in photographs taken during September, October and December, 1973 (a) and January, April and December, 197^ (t>) . (r=ripples, but no orientation; dr=doubtful ripples; crb=coarse, rocky bottom.) In Figures ^+7-50, the seaward limit of ripple mark formation presumably is the depth at which near-bottom currents exceed the threshold velocity of grains comprising the substrate. Isopleths depict near-bottom velocities (calculated from the "average" surface wave propagating across San Pedro Bay during the cruise on which the data were collected) at this deep limit. See the text for a complete discussion of this concept. The following also pertains to Figures ^7~50. Large numbers in parentheses are near-bottom velocities in cm/sec calculated for the depth marked on the isopleth. Double-headed arrows depict orienta tion of ripples (relative to magnetic north). Single-headed arrow connecting stations indi cates a drift station and shows direction of drift. Solid station symbols indicate ripples and open symbols indicate featureless or bio- turbated bottom. Small numbers near station symbols identify stations listed in the Appendix. 1 9 ^ LONG BEACH DEC '7 3 SAN PEI OCT. ‘ 73 crb muhtthgton BEACH N r KM LONG BEACH WILMINGTON '74 DEC. *74 SAN PEI 37 m ► 20 KM Figure ^8. The distribution and orientation of bedforms on San Pedro shelf as ob served in photographs taken during August, 197^ (a) and June and August, 1975 (t>) • (See the caption of Fig. 47 for more detail.) (t=turbid water which prohibited accurate identifica tion of features on the bottom.) 1 9 6 LONG BEACH 4 0 * • JOCN / I K SAN PEI AU4 a - 14 BREAKWATER r • 2 i KM LONG BEACH SAN PEI BREAKWATER — SOw- • E i NEWPORT CANYON KM \ Figure ^9« The distribution and orientation of bedforms on San Pedro shelf as ob served in photographs taken during October and December, 1975 (a-) a^d March, 197& (t>) . (See the caption of Figure ^7 for more detail.) (fr=faint ripples; ftr=faint traces of ripples; vftr=very faint traces of ripples; a= Type A ripples.) 198 LONG BEACH SAN M tM M T E R ■m e. *rs Ur °TZ .(14 ftr v f t r KM c a n t o n LONG BEACH SAN PEI BREAKWATER E O KM Figure 50* The distribution and orientation of bedforms on San Pedro shelf as observed in photographs taken during April, 1976. (See the caption of Figure ^7 for more detail.) Long, double-headed arrows show orientation of long wave length ripples, and short, double- headed arrows show orientation of short wave-length ripples (relative to mag netic north). Small numbers in paren theses along Transact A-A refer to sta tion numbers discussed in the text (a= Type A ripples; b=Type B ripples). 200 V.O*_ i * 2 2 = S 2 — • * o , (n Some data show that periodic storms ripple the substrate at greater depths than normally expected for certain months. Photographs taken 12-13 April, 197& il lustrate the effects of recent high winds. Highly turbid water nearshore (which may be, in part, due to run-off from light rains) made it difficult to discern features on the bottom even when the camera was within 1.5m of the sea-floor. Well-developed ripples are present in depths as great as ^0 m, which is possible if velocities of 10 cm/sec are capable of rippling very fine sand. These ripples vary in morphology; Type A, B and B' ripples characterize shallower portions of the shelf, but long- crested oscillatory ripples are typical forms in deeper water (Figs. 11, 12). A similar zonation was observed on 6 October, 1975 (Fig. 12). I have not detected these rip ples any other time. Strong winds (as determined from inspection of the log of the VELERO IV) were frequent in the weeks prior to the time these photographs were taken in April, and large waves occurred during the time the photographs were taken in October. This suggests that higher energy currents produce Type A, B and B' bedforms. In contrast to April, 197&, photographs taken only a month earlier (15-19 March, 197^) show clear water near the sea-floor and reveal very subdued ripples in depths shallower that 28 m (Fig. 13). Lower energy surface 202 waves and mild weather reflect conditions prevailing at this time. Winds increased towards the end of this week in March, thereby accounting for the change in bedform morphology and zonation observed later in April. Depth limits of active rippling often correspond to the 10 cm/sec isopleth, and always lie within the area bounded by the 10 and 20 cm/sec isopleths. Thus, it seems that currents flowing at speeds as low as 10 cm/sec not only initiate grain movement, but also ripple the sub strate. This conclusion merits discussion, because, as mentioned earlier, velocity isopleths shown on figures in this dissertation have been calculated from the "typical" wave for that time period. Data obtained on 5 and 6 August, 197^ serve as a good basis for discussion. For the "typical" wave (T=13-25 sec; Hmax=0.6 m) the 10 cm/sec isopleth occurs at A0 m. However, the bot tom at this depth is not rippled, although nearbottom currents flowing 10 cm/sec should be able to move very fine sand on this portion of the shelf (Komar et al., 1972). Wave-generated currents do not attain speeds of 20 cm/sec until depths of 18 m. Thus, speeds higher than 10 cm/sec seem to be necessary to ripple very fine sand in this area; and data presented by Clifton (1976) indi cates that rippling of very fine sand requires velocities closer to 20 cm/sec. 203 Surface waves produce bottom velocities at this depth (^0 m) exceeding 10 cm/sec only 29*2 percent of the time in the interval from 1-16 August (Fig. ^6). Conse quently, development and maintenance of ripples may be dependent upon the frequency with which bottom velocities exceed the minimum threshold velocity. So, although the infrequent, unusual wave may generate near-bottom currents strong enough to move sediment resting on the sea-bed, these waves must occur with sufficient frequency, other wise ripples will not form. Furthermore, ripple marks on deeper portions of the shelf may be remnants of storm activity occurring shortly before photographing these areas. Therefore, estimates of near-bottom velocities calculated from wave data during the period of observation may be misleading in that the 10 cm/sec isopleth may correspond only by coincidence with ripple marks formed days or weeks earlier by currents flowing greater than 15 cm/sec. Direction of Transport Several investigators have been concerned with dir ections of net sediment transport along the shore and sea ward of the surf zone on the inner shelf (Vernon, 1966; Cook, 1969; Cook and Gorsline, 1972; Felix and Gorsline, 1971). The following excerpt from Cook (1969; p. 138-1^0) 20^ concisely summarizes wave-induced, transport in this zone: ... Rip currents sort out fine and medium sand from the foreshore and carry it beyond the breakers. ... Once deposited, the parti cles migrate as a unit in the direction of predominant surge velocities. Regions of coarse sand are common on many shelves and represent relict Pleist ocene strand lines. In these areas sedi ment is transported by bottom drift. During winter seasons, local storms cause high, short period waves and strong onshore winds. Large rip currents carry sand from the beach to the inner shelf. After the grains are deposited on the bottom, they either tend to remain in place or mi grate offshore under the influence of sea ward surge asymmetry. The result is an accumulation of sediment outside the break ers at the expense of the beach. In summer the rigorous conditions ameliorate, winds blow with less force, and long period swells generated at great distance reach the coast. Bottom sand is moved towards land by dominant onshore surges and re-enters the littoral zone. Rip currents are weak, and the beach is replenished while the offshore reservoir of sand is depleted. Eventually all sand either is per manently deposited on the shelf or is funn elled through a submarine canyon to the ocean basins. Thus, while sediment is moved offshore and onshore seasonally, the net displacement of grains is offshore. The beach acts as a source of supply for the shelf. Part icles escaping the littoral zone either settle permanently or reside on the shelf for a variable period of time; 205 eventually some of these grains are carried to the shelf edge (or submarine canyon) and deposited on the slope and deep ocean floor (Swift, 1970; Swift et al., 1972b). Palimpsest Sediments Box cores collected along a transect approximately normal to the shoreline support the model of net offshore transport (Fig. 6a; AHF 21375, 21376, 21377). The shal lowest core (15 m) penetrated only iron-stained "medium" (X = 0.29) sand (Fig. 51a). In the next core, 1 nauti- mm ° cal mile (1.9 km) seaward, reddish-brown medium sand (0.29 mm) overlies gray-green fine sand (0.19 mm) (Fig. 51b). The deepest core (24 m) consists only of gray-green very fine (0.09 mm) sand (Fig. 51c). Unfortunately, at the time these cores were collected, bottom water was too turbid to discern any bedforms. Photographs taken at the same stations in April, 1976 show well-developed Type A ripples at the inshore station and Type B at the deeper station and are evidence for active transport. The quality of the photographs prohibits definitive determination of ripple asymmetry, and hence, direction of sediment transport. However, the lateral and stratigraphic sequence of sediment types and textures argues that relict sand from nearshore is being carried seaward over finer-grained modern sand. Inclusion of blotches of gray sand within overlying red sand (AHF 206 Figure 51* Photographs showing slabs from three box cores collected along a north (shallow) to south (deep) transect in San Pedro Bay. The shallowest core (AHF 21375. 15 m) shows only red sand (a), the next core seaward (AHF 21376; 20 m) shows red sand overlying gray sand (b), and the deepest core (AHF 21377; 24 m) shows only gray sand. 207 21376) supports this interpretation. Therefore, currents on San Pedro shelf rework relict deposits in the sense of the model of palimpsest sediments promulgated by Swift and his colleagues (1971)• Origin of Compound Ripples Type A, B and B* ripples are not produced by nor mal shoaling surface waves. It is tempting to attribute these sets of ripples, with crests at or near right angles to each other, to wave trains moving perpendicular to one another. In the introduction, I mentioned that swell from the west and south effects the San Pedro shelf. Most westerly swell, however, is dampened by offshore islands and Palos Yerdes Peninsula. During the days I observed these bedforms, I noticed no interfering wave trains. There have been cruises, however, during which we were unable to maintain position "down swell" because two op posing sets of waves buffeted the vessel. Because Type A, B and B* ripples have been observed on occasions associ ated with periods of moderate (6 October, 1975) and oc casionally strong bid-March-early April, 1976) northwest erly winds, I suspect that they are not interference rip ples, but reflect intense flow conditions generated by meteorological events. Several investigators have reported concurrent sets 209 of two ripple trains with crests oriented approximately normal or nearly so to each other (Bagnold, 19^6; Manohar, 1955* Clifton et al., 1971; Swift et al., 1972a; Komar, 1973; Clifton, 1976). In the laboratory, Bagnold (19^6) found that by oscillating a section of bed through still water, he could duplicate oscillatory ripple marks produced by waves gen erated in a wave tank. When he reduced the amplitude of harmonic motion to about l/3> ridges developed at right angles to the crests of the oscillatory ripples; he termed these "brick pattern" oscillatory ripples. Spacing be tween ridges was either one, two or three ripple lengths. Bagnold hypothesized that bridges form as water vortices break up into separate or nearly separate packages. Komar (1973) reported "brick pattern" ripples in very shallow water (0.28 m) of Mono Lake, California. He speculated that during a waning storm, waves of decreasing orbital diameter produce this ripple pattern. Although ripples on San Pedro shelf had been observed during or shortly after storms, the pattern of these ripples differs significantly from those reported by Bagnold (19^6) and Komar (1973)• Clifton (1976) describes a bedform which consists of two sets of ripples, both oriented oblique to the oscillatory current. Relatively short crested ripples 210 occupy the trough of longer crested ripples. He terms these "cross-ripples." Interfering sets of waves do not generate these ripples. Ripples aligned in an oblique en echelon pattern to oscillatory flow often grade into "cross-ripples." Helical flow occurs behind the crest of oblique ripples, and Clifton hypothesizes that "cross ripples" form in response to the rapid acceleration of oscillatory currents in the nearshore. Development of these ripples follows a normal sequence from symmetric ripples to asymmetric lunate ripples as the intensity of unidirectional flow increases; but lunate forms do not develop in fine sand (Allen, 1968; Clifton, 1976). Al though morphologically resembling "cross-ripples," Type A and B ripples occur in greater depths than those re ported by Clifton (e_t aJ_. , 1971; 1976). A paper by Swift et_ al. (1972b) includes a photo graph (Fig. 227c, p. 559) which shows a bedform similar in appearance to Clifton*s (1976) description of "cross ripples" and to Type A ripples observed in this study. Swift and his colleagues attribute the longer crested ripples to waves and the superimposed small-scale ripples to tidal currents. These ripples occur on a sand ridge, a mesoscale bedform. Type A ripples have been observed in fields of mesoscale current lineations revealed by side scan sonar. Association with these features may be a key 211 to unlocking the origin of Type A and B ripples. Origin of Mesoscale Bedforms A detailed side scan sonar survey (Fig. 10b) re veals alternating light and dark streaks on portions of the side scan record (Fig. 14). This signature can be interpreted as either sand waves (transverse bedforms) or current lineations (longitudinal bedforms). Presumably these are active features forming in response to modern depositional processes. Relict structures of this size in shallow depths would not survive intense flow regimes generated by strong storms. If sand waves, they indicate flow parallel to the coast. I have never observed small- scale bedforms (ripples) in the region of these features oriented in such a way as to suggest longshore transport. This, together with the very low relief (probably less than 1-2 m) and the absence of strong asymmetry argues against these structures being transverse bedforms. Current lineations (sand ribbons and erosional fur rows) seem to be the most common mesoscale bedform on the continental shelf (pers. commun., D. J. P. Swift, National Oceanic and Atmospheric Administration, Miami, Florida, 1975)• Sand ribbons and erosional furrows form in re sponse to large-scale helical flow (Allen, 1966, 1968, 1970; Duane e_t al. , 1972; McKinney e_t al. , 197^0 • Seif dunes and related features in deserts have been attributed 212 to helical vortices in the atmosphere (Bagnold, 19^1). Folk (1971)5 hy rolling and sliding bars over plates covered with grease, reproduced patterns in the grease strongly resembling longitudinal desert dune fields. He invokes helical flow as the probable mechanism generating these structures. Large-scale helical flow cells exist in the ocean. Processes generating helical cells include tides, winds and surface waves. Kenyon (1970) describes sand ribbons on the sea-floor of the North Sea, an area where tidal currents reach speeds in excess of 2 knots (100 cm/sec) near the surface. Tidal currents in the San Pedro Bay area rarely attain speeds beyond 0. ^ knots (20 cm/sec) (Emery, i960). Therefore, almost certainly, tides are not responsible for current lineations on San Pedro shelf. Storm winds and surface waves can generate helical flows called Langmuir circulations. Effects of storm winds will be discussed in the chapter on Meteorological Driving Forces. Surface waves generate helical cells by eddy pressure and this may be the dominant process producing Langmuir circulations in the ocean (Faller, 1969). Depth to the thermocline or sea-floor in shallow bod ies of water limits dimensions of Langmuir cells. When so limited, horizontal wave length of the helical cells is be tween two to three times the depth of the boundary layer 213 (Faller, 1969; Scott et al., 1969). On the other hand, in the open ocean where no boundaries limit dimensions of the cells, the ratio of row spacing to mixed layer depth aver ages 1.1 (Faller and Woodcock, 196^). Current lineations observed on San Pedro shelf oc cur in water about 25 m deep and shallower. Since the seasonal thermocline frequently coincides with or is deep er than this depth, the sea-floor is the boundary limiting the size of Langmuir circulations for a large percentage of the year. Maximum horizontal wave length of these cells should be on the order of 50 to 75 Following the hypothesis currently in vogue, stronger diverging currents of these cells where they contact the bottom, erode narrow furrows, and weaker converging currents construct wider sand ribbons (Swift, 1976), thereby developing a system of alternating low amplitude ridges and troughs. A schematic diagram, Figure 52, illustrates that the scale of current lineations agrees with estimated spacing and wave length of possible Langmuir cells on San Pedro shelf. Width of sand ribbons should be about two to three times the wave length of Langmuir cells or about four to - s- i - x- times the depth of water. Dimensions of sand ribbons represented herein range from about ^0 to 120 m, with most ribbons being about 100 m and these occur in depths of about 25 m. Any asymmetry in helical flow cells will 21^ Figure 52. Schematic diagram depicting the rela tionship of Langmuir circulations (three-dimensional helical flow cells) in the overlying water to mesoscale current lineations on the sea-floor. 215 INTENSE D0WNWELL1NG DIFFUSE UPWELLING (HIGH VELOCITY) (LOW VELOCITY) I r DIVERGENCE CONVERGENCE 7 ^ a r e a o f D ^ E E R A 6 E °F C E / ^ — SAND RIBBON EROSIONAL 100m FURROW 50 m produce asymmetric bedforms. Longitudinally-directed flows form normal to crests of surface waves. Waves generally approach San Pedro Bay from the south and southwest. These would generate helical flows elongated in a north-south direc tion. Current lineations on San Pedro shelf are oriented NNE-SSW to NE-SW, which is consistent with an origin from Langmuir circulations produced by surface waves. Meteorological Driving Forces General Atmospheric variables strongly influence nearshore surface currents on the continental margin. Meteorologi cal forces driving oceanic motions include transfer through wind stress, wind stirring of the water column, pressure adjustments, heat transfer and mass water trans fer through evaporation and precipitation (Mooers, 1976). Winds are the most important forces imparting motion to surface waters off California (Pirie e_t al. , 1975) • Of the variables above, then, only wind stress and wind stir ring are considered for discussion of sediment transporta tion on the southern California shelf. The others may well be important to the physical oceanographer, but are beyond the scope of this dissertation. Wind patterns over the southern California shelf 217 change diurnally (offshore-onshore breezes), weekly (peri odic passage of high and low pressure cells every few days) and seasonally. Episodic severe storms add another component to these normal events. The role of seasonal atmospheric systems has been discussed earlier, but a short summary is useful at this point. From spring to fall, winds generally blow from the north. Surface water flows toward the south and a north westerly countercurrent exists in the subsurface. For part of this time (March-August) upwelling occurs along the coast. During winter the northerly winds either weak en or reverse, and the southerly-flowing California Cur rent moves offshore permitting the northwesterly-flowing Davidson Current to develop at the surface. This winter system should produce Ekman coastal downwelling and bottom waters over the continental margin would exhibit an off shore component. Relatively shallow water over the con tinental shelf will be affected more by localized winds, tides, local bathymetry and coastline topography. More frequent atmospheric phenomena (daily offshore-onshore breezes and periodic passage of pressure cells) also ex ercise influence over magnitude and direction of sediment transport on the shelf. On the shelf off Washington and Oregon, Smith and Hopkins (1972) have demonstrated that periodic storms move 218 significantly greater amounts of sediment than fair- weather events which prevail a larger percentage of time. Highly turbid waters and well-developed bedforms observed on San Pedro shelf during or shortly after storms suggest that these events are also important off southern Califor nia. Since storms play a major role in depositional pro cesses on the continental shelf, it behooves us to examine the effects of storms in some detail. Shelf Hydraulic Regime The complex hydrodynamics of the inner shelf (and nearshore portions of the central shelf) may be simplified by conceptualizing this region to consist of three hy draulic provinces and three flow fields (Fig. 53); for a detailed discussion see Swift (1976, p. 263-26^). Wave orbital motion and momentum transfer of wind stress (Ekman spiral) dominate velocity components in the upper boundary layer (1). A core flow (2) extends below this layer to the top of the bottom layer (3)- Because the shelf pressure field is in a constant state of flux, the nature of the core cell vacillates between true geo- strophic, rotary tidal current and inertial current flow. Frictional retardation of the core flow produces the bot tom boundary layer and causes this layer to flow to the left of the core flow; a reverse Ekman spiral. Wave-driven flow dominates close to shore where the 219 Figure 53- Schematic diagram showing conceptual ized flow fields on the inner and central shelf (a), hydraulic provinces on the inner and central shelf (h), and the velocity structure during intense storms (c). (After Swift, 197 6, p. 263, Fig. 6). 2 2 0 Is ZONE OF WAVE DRIVEN FLOW. 2: ZONE OF FRICTION-DOMINATED FLOW. 3: ZONE OF GEOSTROPHIC FLOW. UPPER BOUNDARY LAYER CORE FLOW LOWER BOUNDARY LAYER two boundary layers overlap. Seaward of this zone, a frictional-driving mechanism prevails, and the boundary layers separate, but still occupy most of the water column. The geostrophic zone occurs farther seaward where the two boundary layers widely diverge. Storms modify flow fields on the shelf by expanding the upper and lower boundary layers (at the expense of the geo strophic core) and displacing the three provinces seaward (Fig. 53)• The zone of friction-dominated flow prevails over a greater proportion of the shelf. Storm-induced Bottom Features As wind stress increases during severe storms (high winds), the surface zone of Ekman transport intensifies; that is, it thickens and when the mixed layer (depth of thermocline) is sufficiently deep, the former becomes ful ly developed. Above a critical Reynolds number, horizon tal flow fields of helical cells (Langmuir circulation) develop (are superimposed) on the Ekman spiral (Faller, 1971). Assaf et al. (1971) found this transition to occur when wind speeds reached 10 knots (50 cm/sec). High winds produce conditions which simultaneously erode the thermo cline and generate Langmuir cells (Faller, 1969). Build ing upon this premise, one can imagine a situation in which the shallow waters of the shelf become completely mixed; that is, there exists no thermal stratification so 222 that a zone of friction-dominated flow (momentum trans ferred downward by wind stress at the surface) extends from the surface of the water to the sea-floor (Swift, 1975)• In this case, Langmuir circulation occupies the total flow field. If a lower Ekman layer exists, helical flow may occur in it. During strong storms, the lower and upper layer could overlap, producing compound helical flow structure from surface to sea-bed (Swift, 1976). Mesoscale Current Lineations Assuming that Langmuir circulation fills the entire flow field, helical vortices would then impinge upon the bottom. As discussed in the previous chapter, the scale of any bedforms would be related to the dimensions of Lang muir cells, the size of which depends upon the thickness of the convective layer in which they form (Fig. 5 2). However, this relationship may not hold if pre-existing patterns in the wind field or sea-bed bathymetry force a different scale to the cell dimensions (Faller, 1969)• Thus, once formed, current lineations may be self-sus taining by influencing the size and position of Langmuir circulations. Of course, inordinately intense storms probably generate helical cells randomly offset to patterns of alternating sand ribbons and erosional furrows. Such events would tend to diffuse boundaries between adjacent 223 ribbons and furrows by causing erosion in a normally depositional site and sedimentation in a scoured trough. As stated previously, current lineations are ori ented approximately NNE-SSW. Local storms frequently generate northwesterly wind fields. Langmuir cells may or may not form at an angle to wind stress (Faller, 1969)• If the cells on San Pedro shelf are oblique to storm winds, then Ekman theory indicates that Langmuir cells could have the appropriate orientation necessary to account for current lineations in the substrate, and the horizontal (forward) velocity component of the helical flow regime should be directed offshore (SSW). Therefore, storm-induced helical flow cells can account for current lineations on San Pedro shelf in the same way as wave-induced Langmuir circulations. Probably both processes work simultaneously, with one or the other dominating under a given set of conditions. Small-scale bedforms associated with these features support an origin from complex currents. Small-scale Bedforms Storms generate three-dimensional flow fields in waters overlying San Pedro shelf. These helical cells have a unidirectional component in an offshore direction and they may dominate over normal oscillatory surge from 22^ waves. Current lineations are mesoscale bedforms gener ated by this hydraulic regime. Type A, B and B' ripples appear to be the small-scale features characteristic of higher energy conditions. Several lines of evidence support this conclusion; 0 Examination of many photographs indicates that Type A, B and B' bedforms, rather than true end-members, seem to be well-formed members in a series of ripples grading from long-crested oscillatory ripples to very complex forms. 0 In support of the above, consider Transect A-A', Figures 11 and 12. No ripples exist at the deepest station (7)* Progressing landward symmetrical ripples are encountered at Station 5* Closer to shore the ripples become more sinuous and occasionally ex hibit incipient secondary crests (junctures) oblique to the main ripple. These junctures become more common and better developed in shallower water. These types are very well developed along Transect III-IV and at station Cm (Figs. 12 and 50). 0 Ripple orientation corresponds with flow 225 oblique to the shelf edge and with the sense of transport indicated by mesoscale current lineations. ° Systematic transition from simple ripple types to more complex types seems typical of intensifying unidirectional flow, which in this case, reflects flow regimes pro duced by strong meteorological forces. Since energy imparted by winds is trans ferred downward, the effects are greater in shallower water. Lack of asymmetry in ripple form poses a problem in that unidirectional flow generates asynmetrical ripples. I can offer four lines of reasoning to account for the absence of asymmetry. (1) A weak, unidirectional current flowing opposite to the direction of wave propagation would form symmetri cal instead of asymmetrical ripples (Reineck and Singh, 1973; P. 41). (2) It is possible that these ripples are not responses to unidirectional currents. If not, then oscil latory surge generated by surface waves must form these structures. Possible mechanisms responsible for ripples of this type were discussed in the previous section on Surface Waves. Although Type A, B and B* ripples differ 226 from wave-induced ripples reported in the literature, it is possible that they are small-scale hierarchal bedforms associated with ameliorating storm conditions on the continental shelf. (3) Vertical and oblique (almost parallel with the bottom) views of ripples observed on 6 October, 1975 sug gest an alternate explanation. When viewed from above (Fig. 12f) the bedforms appear symmetrical. However, views almost parallel with the sea-floor evidence a slight asymmetry (Fig. 12e). Development and possible migration of smaller-scale ripples on the stoss side of larger ripples may "erode" the gradual slope of the stoss side in such a way as to steepen it, making its slope more nearly equal to that of the lee side. This would tend to produce a symmetrical ripple. Because dimensions of the ripples are similar, not much material would have to be removed or "shifted" from the larger ripple to modify its shape. (*0 These ripples most certainly reflect very intense and complex flow regimes. Obviously, severe storms generate strong surface waves as well as a variety of wind-induced currents. Thus, wave surge is superim posed on helical flow or vice versa. Such unusual flow fields drastically alter flow in the bottom boundary lay er. Any laminar flow is destroyed and normal turbulence 227 in the BBL increases "by orders of magnitude. Packages of turbulent vortices and eddies possibly create the compound bedforms observed on the shelf under such conditions. In summary, I conclude that small-scale bedforms of Type A, B and B* characterize intense and complex flow fields induced by strong winds (and differential pressure fields) associated with localized storms. (Strong surge reaching San Pedro from slightly more distant storms pos sibly exercised greater influence in the genesis of bed forms observed in shallow water on 6 October, 1975-) While satisfied that these features form in response to storm conditions, I cannot, with available data, relate their origin to a specific mechanism. Suspended Sediment Intense flow conditions, with consequent break down in density stratification, may be responsible for characteristic structures of the substrate, but normal stratification of the water column accounts for typical patterns of suspended particulate matter. Variance in general trends of turbidity isopleths at the surface and bottom probably reflects divergence in currents above and below the seasonal thermocline. Wind stirring of surface water keeps material in suspension, and it disperses seaward under the influence of wind, waves and tides. Meteorological events probably generate near 228 bottom currents with net flow directed offshore. These currents resuspend fines deposited on the sea-bed carrying them across the shelf to the slope and ocean basins. Often tongues of very turbid water extend toward heads of submarine canyons (Fig. 22). Changes in profiles in the vicinity of San Gabriel Submarine Canyon suggest that sub marine canyons modify flow patterns on the shelf. Thus, currents from other forces, in addition to those induced by winds, influence dispersal of suspended sediment. A discussion of possible driving mechanisms follows. Internal Waves Internal waves propagate along density interfaces within the water column and are common in the main and seasonal thermocline in the world's oceans (LaFond, 1962; Wunsch, 1971). These waves may influence transportation of sediment in the marine environment (Emery, 1956; LaFond, 196I; 1962). Under certain conditions, as inter nal waves move across a sloping bottom, they break and generate internal surf analogous to surface waves (Wunsch, 1968; Cacchione and Wunsch, 197*0* Laboratory experiments have demonstrated that breaking internal waves can entrain and transport sediment (Southard and Cacchione, 1972), and Cacchione and Southard (197*0 have argued theoretically that waves with frequencies and amplitudes commonly found 229 in the ocean should he capable of moving fine-grained sediment covering the continental shelf. To date, how ever, no studies have supported their conclusions with definitive field evidence. Numerous studies have shown that internal waves are common along the southern California coast (see sum mary in LaFond, 1962). These waves propagate shoreward and occur over a wide range of frequencies from a few min utes to tidal periods (Summers and Emery, 19&3; Emery and Gunnerson, 1973)- Several investigators suggest that shoaling and breaking internal waves move or suspend sediment on the southern California shelf (LaFond, 19^2; Emery and Gunnerson, 1973; Karl, 1975)* The following paragraphs develop this hypothesis from data collected during the course of my field work. Monitoring of light transmission and temperature at particularly steep gradients in the seasonal thermo- cline evidences periodic and systematic fluctuations in these two variables. Visual inspection of the records reveals that perturbations occur as sinusoidal waves hav ing periods as short as 5 to 15 minutes (Fig. 37)• In shallow water, these wave-forms often have flattened crests and droughts (Fig. 37)* Oscillations of the sea sonal thermocline, having a period of hours (Fig. 38), probably correlates with internal waves of tidal period 230 (Gains and LaFond, 1966; Cains, 1968). Flattened crests and troughs are characteristic of internal bores (pers. commun., D. A. Cacchione, U. S. Geo logical Survey, Menlo Park, California, 1976). When the wave enters shallow water, crests flatten as the wave ap proaches the sea surface and troughs flatten as the wave impinges upon the sloping bottom (LaFond, 1966). Asym metry in the wave-form indicates steepening of the wave; eventually it breaks and generates internal surf (Lee, 1961; LaFond, 1962; Cains, 1967; Emery and Gunnerson, 1973)• Internal waves progressing along a sloping bottom will break when (Cacchione and Wunsch, 197^0* //c<l (28) where ^ is the bottom slope and c is the wave character istic slope given by: 2 (5" 2 = ____ N2 - (T2 (29) where (p is the wave frequency and N is the Brunt-Vaisala ■'"Equation (29) ordinarily includes the Coriolos term, f, and should be written : p 2 = ’<T N2 - O'2 but f is of such low frequency relative to the frequency, , of internal waves observed in this study that it be comes insignificant and does not effect the calculation of C. frequency, a function of depth, z which determines the highest possible frequency of internal waves (the lower limit is a function of latitude). The following equation defines the Brunt-Vaisala frequency: n2 _ . _k_ (30) p dz where g is the acceleration of gravity and p is the densi ty of the medium. Using CALCOFI data (Table XI) from the vicinity of San Pedro Bay, I calculated representative Brunt-Vaisala frequencies for depth zones coincident with the summer and winter thermocline (CALCOFI, 1957-196*0 . Estimates of N are, of course, rough approximations, because N changes continuously in time and space and should be calculated for each specific case. Values indicate that very high frequency internal waves can occur off this coast in sum mer and winter. Inserting N and various values of O ' in equation (29) gives the wave characteristic slope. I measured the gradient of portions of the shelf and upper slope along five transects across San Pedro shelf (Fig. 5b). Table XII shows that high frequency internal waves theoretically break as they converge upon the bottom. Thus, I think the results of this study and other studies referenced above leave no doubt that internal waves shoal and break on the continental shelf off southern Califor- 232 TABLE XI Representative Temperature, Salinity and Sigmat Data for Depths of the Summer and Winter Thermocline Depth(m) Temp.(°q) Sal./0/ \ ( /oo) Sigma^ June , 1956 0 16.93 33.66 2^.52 9 15.95 33.58 2k. 69 27 12.52 33.56 25.39 z ' * January, I960 29 Ik. 57 33.55 2k. 98 50 12. 7k 33.5^ 25.33 60 11.8k 33.58 25.5^ *Data from CALCOFI (1957-196^) stations 87.35 and 87.36, water depth 518 m. Average sigma, for June is 2^.86 and for January is 25.19. 233 TABLE XII Values of //c for Internal Waves of Various Frequencies (l/T) over Typical Slopes on San Pedro Shelf Slope 5 7.5 15 30 360 f/c, January , I960 Period (Tmin) * 1 . 004 0, . 01 0.02 0. 04 0. 08 >1 2 . 01 0. , 02 0. 04 0.10 0. 20 3 . 04 0, ,11 0.16 o.4o 0. 80 71 4 . 04 0, ,11 0.16 0.40 0. 80 71 5 .18 0, .51 0.72 >1 71 71 X/c, June, 1957 l . 004 0, .01 0. 02 0.05 0.10 >1 2 . 01 0, . 04 0.06 0.13 0.25 71 3 . 04 0., 16 0. 22 0.50 1.00 71 4 . 04 0.,16 0. 22 0. 50 1. 00 71 5 .18 0..72 1. 00 >1 71 71 * Transects on Figure 3b N = 0.82 min._?" for June (0-27 m) N = 0.59 min. for January (30-60 m) Assuming an insignificant vertical density gradient over 100 m, N = 0.05-0.16 min.”l (3-10 cycles/hour). When Jr/e < 1 the waves break on the slope. 234 nia. However, how effective are they in transporting sediment? Laboratory experiments of Southard and Cacchione (1972) have shown that breaking internal waves produce a characteristic zonation of bedforms on the sea-floor and suspend sediment in the water column. In the zone of breaking, asymmetrical ripples advance downslope and fine sediment entrained in the water column moves offshore. I have speculated that internal waves migrate vertically with the seasonal thermocline (Karl, 1975)• Thus, the point at which the seasonal thermocline intersects the shelf defines the zone of breaking. In summer steep temperature gradients exist at about 10 to 30 m, and in winter less steep gradients occur at about ^0 to 60 m (Fig. 39; Table XIII). While I have observed internal waves within the spring, summer and fall thermoclines, I have not had opportunity to monitor the deeper thermocline in winter. However, there is no reason to doubt the existence of internal waves at this time of year. The zone of transitory ripple fields (35-^0 rn) cor responds with the depth at which the winter thermocline intersects the shelf. Sediment size in this area, the oretically, is capable of being moved by internal waves of frequencies and amplitudes observed off southern Calif 235 ornia (Cacchione and Southard, 197*0- Breaking internal waves, then, might ripple the bottom. As the seasonal thermocline migrates upward with the coming of summer, in ternal waves would break in shallower water. This period of quiesence would allow biogenic reworking of the sub strate. This mechanism could account for the lack of rip ples in this depth range in summer months. However, I have shown that seasonal fluctuations in surface wave energy can produce the same phenomenon. While this is the more likely explanation, it does not rule out the pos sible influence of internal surf. Transmission profiles along transects from shore to the head of San Gabriel Canyon show interesting patterns of turbidity. In January and December, 197*^ sediment moved offshore in turbid layers near the bottom and higher in the water column (Fig. and b). In addition, the Dec ember profile shows an isolated patch of highly turbid near-bottom water at the shelf break. Areas of concen trated suspended particulate matter correlate with steep gradients in the winter thermocline. I conjecture that internal waves, propagating along these density discontin uities, impinge upon the sea-floor in the zone where the thermocline intersects the bottom. As these waves break, they resuspend fines from the bottom. Resuspended material moves seaward with the return flow, breaking off into dis- 236 Figure 5^* Transmission profiles during January, December and August, 197^ showing zones of turbid water, possibly generated by internal waves propagating along the seasonal thermocline and breaking where it intersects the shelf. 237 20033 20034 20035 20037 20036 1900 m 0m — 50 % TRANSMISSION JAN. 1974 ty AHF S T A ■ <20 II 20-40 W i 40-60 KD 60-80 □ >80 100 — 150 21660 21678 21677 21676 — 200 1900 m 50 % TRANSMISSION DEC. 1974 100 150 20867 20868 20670 20672 20871 AUG. 1974 — 50 crete layers at density discontinuities within the water column. These observations are consistent with the re sults of laboratory experiments conducted by Southard and Cacchione (1972). A profile in August, 197*+ along the December, 197*+ transect shows no turbid layers at these depths, but does show exceedingly high near-bottom concentrations at about 20 m (Fig. 5^c). This is around the depth of the summer thermocline. Again, surface waves create enough energy to entrain sediment at this depth, but, perhaps, internal surf is responsible for the offshore horizontal flow of water and suspended particulate matter. Similar patterns have not been observed on other portions of the shelf. The association with San Gabriel submarine canyon may be significant. Average velocities of internal waves propagating shoreward across the shelf are on the order of 15 cm/sec (Lee, 1961; Summers and Emery, 1963)• Canyons exhibit an up and down "pumping- action" of water. Internal waves probably influence cur rents in canyons where they attain phase velocities of 50 cm/sec (Shepard and Marshall, 19&9; Shepard et_ al., 197*0 • Thus, submarine canyons may focus or augment the affects of internal waves on shelf sediments. Net down- canyon flow may also act as a drain for suspended particu late matter resuspended by currents (caused by internal waves, surface waves, etc.). Longitudinal and transverse 239 sections shown in Figures 27 through 31 provide evidence for this conjecture. Edge waves trapped over submarine canyons also in fluence shelf circulation and, therefore, sediment trans port (Inman et al. , 1976) . Inman ejt al. (1976) suggest that water flowing across canyons (parallel to the coast) loses energy, while currents transverse to the shore re main unimpeded by the canyon. Thus, internal waves and edge waves (body waves) contribute to currents and circu lation patterns which, in part, account for various tur bidity phenomena associated with submarine canyons ob served in transmission profiles and discussed earlier (see Figs. 22, 3^ and 5^)• Field observations reported herein agree well with experimental predictions and results. Still, I cannot define conclusively the role body waves play in transport ing sediment. This area requires, and deserves, more study as body waves, particularly internal waves, may be important agents for resuspending fine sediment, causing it to by-pass the shelf for eventual deposit on the slope and deep basins. Near-bottom Currents Nature of Currents Although near-bottom currents on the central shelf 2^0 usually flow towards the open ocean, the four records ob tained so far show variability within this general trend (Figs. 55-58). As pointed out earlier, several inputs contribute to flow fields on the shelf. Progressive vec tor diagrams for 17-21 December, 1973 suggest that meteor ological events probably influence current systems on the central shelf (20-50 m) more strongly than other factors. Mr. Noel Plutchak, from work on the East coast and Oregon coast, has observed that high and low pressure cells pass over coastal regions with a frequency of three to four days. Current meters have been left on the bottom only three to four days. Unfortunately, these records are not long enough to correlate confidently with atmospheric fluc tuations. Nonetheless, short term events in these records are very interesting and lead to intriguing speculation. During 17-21 December, 1973 the current meter em- placed in a depth of 27 m. evidences more meteorological (?) noise than does the deeper current meter. Tidal cur rents generally increase in velocity as they progress from shallow to deep water (Fleming and Revelle, 1939)* Strong tidal periodicity observed in records from the deeper meter suggests that tidal flow augments residual near bottom currents in the outer portion of the central shelf. Abrupt reversal in flow direction about half way 241 through the shallow station record correlates roughly with a change in wind speed and direction from light west and northwest winds to strong (^-10 knots) north and north east winds. Strong northerly winds would push surface water offshore causing localized onshore upwelling. An onshore component added to net southerly flow could ac count for the shift to an easterly direction. This is speculation and a totally different mechanism may be responsible for current reversal. Steep gradients in the winter thermocline probably intersect the shelf somewhere between the shallow (27 m) and deep (51 m) stations. The thermocline could represent an obstacle to downward transfer of momentum imparted to surface water by winds. In this case, the depth at which the thermocline impinges upon the sea bed could mark a significant boundary between two major current systems. Recent coastal upwelling experiments (CUEA program under IDOE) also indicates that the thermocline plays a domin ant role in continental margin dynamics. Results from March and April, 1976 current meter records are the reverse of those of December (Figs. 57 and 56)> and this leads to speculation not only of dis tinct inshore and offshore flow fields, but also of dif ferent winter and spring current systems. The current meter emplaced at 27 m (April) was close to the seasonal 2k2 thermocline -- only 10 to 12 m below it, whereas the deep meter at ^5 m (March) was up to 30 m below the bottom of the mixed surface layer. If we assume that the shallow meter was in a transition zone where the thermocline did not block wind-induced currents, northwesterly winds dur ing April could produce southeasterly transport near the sea-floor. In spring the northerly flowing current in San Pedro Channel becomes better developed and pushes the inshore southerly flowing current closer to the outer shelf. This boundary current may influence hydraulic systems on the outer shelf, thereby accounting for net southwesterly flow over the outer portion of the central shelf in March. Periodicity within monthly tidal cycles offers an alternate, and more probable, explanation to account for differences among current meter records. Neap and spring tides must influence net water mass transport on the shelf. December records were obtained at the end of a neap cycle shortly before, and just as, tidal range began increasing. In contrast, both March and April meters measured currents during strong spring tides (around the peak of the spring tidal cycle). Records are too short to determine conclusively which of the above mechanisms exercises greatest control over current systems on the central shelf. 2^3 Because I lack sufficient data to deduce driving mechanisms of bottom currents, additional discussion is only an intellectual exercise. Sediment Transport and Substrate Response Determination of Particle Transport History Noel Plutchak and I have collaborated to devise a technique for tracing the transport history of grains of a given size class across the shelf (Karl and Plutchak, 1976; Plutchak and Karl, in preparation; Karl ejt al. , in preparation). Our original premise was to determine sort ing effects and we have not yet incorporated mass trans port into our calculations. However, we can approximate the maximum transport distance of a particle with our existing program. Assumptions requisite to our method follow: o Oscillatory currents generated by surface waves and tides produce little net transport. A unidirectional current superimposed on oscillatory surge, if sufficiently strong, will move sediment in a preferred direction, o High velocity currents transport coarse and fine particles, but successively lower vel ocity currents move only progressively finer grains. (Actually, grains move when 244 shear stress at the bottom generated by a current of a certain speed exceeds the critical shear stress of that particle. For an understanding of the concepts in volved, see the previous section on Principles of Sediment Transport.) Table XIII gives critical shear stresses ) and cor responding velocities (U po(P required to initiate movement of grains of diameter used in our investigation, o If currents of different speeds have pre ferred directions, they will transport vari ous size grains in divergent directions, thereby sorting the bedload population, o For now we hold that a measurement at a single point is representative of currents everywhere on the central shelf. Further experiments will enable us to determine over what regional scale we can assume non-divergence of the water mass, o We may be able to recognize these effects in patterns of textural variables of sur- ficial sediment on the continental shelf. San Pedro shelf is essentially a closed deposition- al system with limited sediment sources. Hence, it is an 2kS TABLE XIII Critical Shear Stresses (*TC ) and Corresponding Velocities (Uiooc) Required to Move Grains of a Given Diameter Grain x- q (mm) Diameter xD( j Z f ) U100c <Tr- a c try 8 J 0 Coarse Silt 0.0^ ^.5 0.0664 6.28 0.1213 0.0517 Very Fine Sand 0.09 3*5 0.1494 9.73 0.2912 0.1242 Fine Sand 0.18 2.5 0.2988 13.33 0.5467 0.2332 Medium Sand 0.3 5 1*5 0.5810 18.59 1.0633 0.4536 Coarse Sand 0.71 0.5 1.1786 25.44 1.9912 0.8496 Very Coarse Sand 1.50 -0.5 2.5000 39-53 4.8078 2.0513 1.66D/ \ from Graf, 1971> P* 9^; also can he calculated from equation (7) > where C = ( jToO^. based on drag coefficient assumed by Stermberg (1972); C = 0.003* " I d* ^ J ' ' based on drag coeefficient assumed by Smith and Hopkins (1972); C = 0.00128, c ro ON ideal area to test our hypothesis. Textural variables most sensitive to selected transport are skewness and standard deviation (sorting). Sediment enters the shelf system only over a limited and well-known range of sizes. We define a nor mal grain size population by constructing a histogram which includes all size classes observed on San Pedro shelf. We compare each sample to this reference distri bution. Deviation from our standard results from the in teraction of the substrate with dynamic processes operat ing on the shelf. Figures 55 through 58 illustrate that currents sort sediment on the central shelf. Resultant vectors show the directions and maximum possible distances of transport for coarse silt, very fine, fine, medium, coarse and very coarse sand (Fig. 59; Table XIV). Since we assume non-divergence of the water mass, we can trace the route a sediment particle follows through time by sorting out current speeds and associated directions. We represent this as a progressive vector diagram for each size class (Figs. 55~58)• These show the complex path a grain takes in its journey across the shelf. Three out of four records indicate that all grain classes move offshore. The shallow December, 1973 record suggests transport parallel with bathymetric contours. 2^7 Figure 55- Partial progressive vector diagrams showing the transport history of vari ous diameter grains and resultant net displacement for December, 1973 at a depth of 51 m- 2kQ DEC. 1973 (5lmeters) coarse sand (0.71mm) medium sand (0.35mm) fins sand ( 0.18 mm) — T — 5 0 0 5 0 0 caarsa silt (0.04 mm) very fine sand (0.09m m ) Figure 56. Partial progressive vector diagrams showing the transport history of var ious diameter grains and resultant net displacement for December, 1973 a depth of 27 m. 250 DECEMBER 1973 (27m ) 0.04 mm • o o • 4 0 0 1104 vory flno sand 0.09 mm •1000 tlOO •• - 1 1 0 0 modium sand 0.18 mm Figure 57* Partial progressive vector diagrams showing the transport history of var ious diameter grains and resultant net displacement for March, 197& at a depth of ^5 m. 252 MARCH 1976 (45 m) 0.04 mm 500 cm - 8 0 0 -900 0.09 mm 500 c -500. 900 cm -5 0 0 2000 500 0.35mm -5 0 0 -500 500 cm 0.18 mm 500 -5 00 , -5 00 Figure 58. Partial progressive vector diagrams showing the transport history of var ious diameter grains and resultant net displacement for April, 1976 at a depth of 28 m. 254 APRIL 1976 very fine s a n d (2 8 m ) -500 0.09 m m -500 300 1500 couse silt 0.0,4 m m -200 2000 500 TABLE XIV Approximate Maximum Net Transport Distance (m/Day) for Grains of a Given Diameter* Grain (xDmm) Diameter (xD^) A (27 m) B (51 m) C (45 m) D (28 m) *a *b Coarse Silt 0.04 4.5 6 6 7 7 6.5 6.5 Very Fine Sand 0.09 3.5 6 6 4 2 4.0 5.0 Fine Sand 0.18 2.5 3 4 3 0 1.5 3.5 Medium Sand 0.35 1.5 0.1 3 1 0 0.0 2.0 Coarse Sand 0.71 0.5 0 0.4 0 0 0 2.0 Very Coarse Sand 1.50 -0.5 0 0 0 0 0 0 A = December, 1973; B = December, 1973; C = March, 1976; D = April 1976. # Net transport does not necessarily indicate that total distance a grain travelled in this time. Refer to Figures 55 through 5^ for an estimate of that distance, and to Figure 59 for representation of transport direction. Figure 60 illustrates vectorally summed transport directions and distance for shallow and deep stations. xo = average net transport for shallow stations, a , = average net transport for deep stations. r v > o\ Figure 59- Resultant vectors for each grain class compiled on one diagram for December, 1973 deep (a); December, 1973 shallow (b); April, 1976 (c) and March, 1976 (d). 257 A. B. 0 C & IT - I I , l* T » • M lla a I T * NC IT-Il.wri u- V* 0 . M « r*k l* T « 4 9 * V- The reader must keep in mind that these are short-term measurements; consequently, net transport directions may differ from long-term trends. For example, if the shallow December record ended after only about 1.5 days instead of 3*5 days, net transport would have been southerly and in agreement with all other measurements. To get an idea of longer term trends, I vectorially summed results from deep and shallow stations (Fig. 60). Near shore, sands move eastward, while silt is carried shorter distances southwesterly. Farther offshore, all grain classes trav el in a southwesterly direction. Data presented in this way reinforces conclusions of sorting, and concepts of separate shallow and deep current regimes on the central shelf. Fortunately, many short-term records and other data collected during this study permit me to deduce dom inant transport trends which I will summarize in the con cluding chapter. Moreover, in two instances (deep and shallow, December, 1973) large separation occurs between 0.09 mm and 0.18 mm size classes. In all cases at indi vidual stations, 0.04 mm and 0.09 mm diameter grains are carried the greatest distance (Figs. 55-59)- Grains are transported most efficiently as suspended load. This sug gests that sizes smaller than 0.18 mm travel frequently in a suspended mode. Currents transport particles in suspension when 259 Figure 60. Resultants vectorally summed for both deep stations, December, 1973 and March, 1976 (a) and both shallow sta tions, December, 1973 and April, 1976 (b). 260 3GOa the ratio between settling velocity and drag velocity for a grain of a given diameter lies below 1.0. Table XI shows velocities required to move grains of sizes chosen for this investigation in a suspended mode. Anything greater than very fine sand necessitates currents much stronger than those normally encountered on San Pedro shelf. Fine sand (0.125 mm) might be carried as suspended load when storms generate near-bottom flows of 75 cm/sec and greater, but in fair-weather periods currents must transport grains 0.125 mm as bedload. Coarse silt (0.0^ mm) and finer grain classes move frequently as suspended load. These ratios approximate conditions necessary to suspend grains from the bedload population and to trans port those grains in a completely suspended mode. Such calculations do not take into account normal turbulence which prevails over much of the shelf. Sporadic high velocity bursts probably supply enough background energy to allow lower velocity currents to carry relatively large grains short distances in suspension. For example, eddies in the lee of ripple marks suspend grains within centimeters of the sea-floor. Furthermore, photographs reveal that grains exist in suspension within a few meters of the bottom, even when measured currents rarely exceed 10 cm/sec 1 m above the sea bed. Such situations suggest 262 TABLE XV Ratio Between Settling Velocity (w ) and Frictional Drag Velocity (U*) for Selected Grain Diameters, with (U^qqc) Required to Transport Grains in Suspended Mode Grain Diameter xD(cm) xD( j Z f ) a w s U b C P c c u* c U100c P c Coarse Silt 0.004 4.5 0.12 0.25 1.2 >0.30 >7.42 1 Very Fine Sand 0.009 3.5 0. 65 0.39 4.12 >1.63 5>4o.28 1 Fine Sand 0.018 2.5 2.60 0.54 12.04 >6.50 ^160.89 1 Medium Sand 0.035 1.5 10. 42 0.75 34.73 Coarse Sand 0.071 0.5 39.40 1.03 95.63 Very Coarse Sand 0.150 -0.5 180.90 l. 60 282.66 £ 1 Calculated according to equation (17), where^ = 0.011. ^Calculated according to equation (8), where C = 0.04o4. c-n ~ P„ = w c s [k(U*) \ where k = 0.4. ro o\ ' u J that solids remain in suspension for significant lengths of time (days) after events sufficiently intense to sus pend them have ended. In addition to turbulence, strong stratification during quiet intervals inhibits fine grained material from settling out of the water column. Thus, particles are carried more easily in suspension than implied by data in Table XV. Grains^0.04 mm (coarse silt) probably always move in suspended mode; those 0.250 mm (coarse sand) move, except on rare occasions, as bedload. Particles between these sizes travel sometimes in partial suspension and other times as bedload depending upon conditions prevailing on the shelf. Records from March and April, 197& not only show strong separation in direction between coarse silt and very fine sand, but also demonstrate shorter distances of transport for very fine sand as opposed to coarse silt (Fig. 59c, d). In contrast, distance and direction of transport are equal for these grain classes on deep (December, 1973) plots with barely perceptible separation in shallow December diagrams (Fig. 59a, "b). Speeds in March and April are lower than those measured in December (Fig. ^0). Such observations suggest that coarse silt moved often as suspended load in March and April, whereas very fine sand and coarser particles travelled as bedload. Evidently, In December, 1973 sediment coarser than very 26^ fine sand could not be carried in total suspension, with very fine sand probably moving infrequently in total suspension. All records, except for April, 1976 which shows no consistent sorting trends, demonstrate that progressively coarser particles have a stronger onshore component, and as one would expect, are transported successively shorter distances from their origin. While sorting occurs throughout the central shelf region, it is more systematic and uniform in deeper water. This reflects decreasing "noise" from sporadic meteorological events with increas ing depth. Regional Patterns of Textural Variables Areal patterns of skewness and standard deviation on San Pedro shelf are evidence for selected transport of various size grains by near-bottom currents. On the basis of skewness, calculated by comparison to a reference dis tribution described on pages 2^+5 a^d 2^+7 > 'the shelf can be partitioned into three major zones: (1) a central area of normal to fine skewed samples flanked by (2) inner and (3) outer bands of coarse skewed (relative to central shelf) distributions (Fig. 6l). On hand-contoured maps, these zones correspond roughly with subdivisions of the shelf based on bathymetry. They also exist in fifth degree trend surfaces, but do not correlate as closely to 265 Figure 6l. Areal patterns of skewness (using values calculated by comparison to a standard reference distribution) surfi- cial sediment, San Pedro shelf; pat terned area highlights the central region of values greater than 1 flanked by zones of coarser skewed sediment. 266 WILMINGTON LONG BEACH SAN PEDRO' BREAKWATER PT. FERMIN SKEWNESS depth zones (Fig. 62). By and large, sorting trends parallel those of skewness; sorting tends to decrease away from the middle portion of the shelf. In this case, trend surfaces better define these broad patterns than do hand-contoured maps. Mean and median grain size patterns agree with those of skewness and standard deviation; bands of relatively coarser sediment occur nearshore and at the shelf edge (Figs. 6, 7 and 61). These observations of regional effects pertain primarily to portions of the shelf between San Pedro Sea Valley and San Gabriel Canyon. East and west of these boundaries, I lack sufficient data to deduce trends with confidence. Strongly unimodal, very fine sand comprises most of the central shelf (Fig. 63)• Inner shelf sediment consists of sands with less pronounced fine and medium sand classes. Coarser size classes occur in frequency distributions of samples from the shelf edge. Samples from progressively deeper stations lose coarser fractions, gradually gaining finer fractions with a consequent shift in the modal class from fine to very fine sand to coarse silt (AHF 225^2-225^5). Shelf Parallel Hydrodynamic Provinces Although we recognize that a complex system of cur rents comprises shelf flow fields, diagnostic changes in 268 Figure 62. Fifth degree trend surface maps of skewness (a), sorting (b) and mean grain diameter (c) surficial sediment, San Pedro shelf (from Grant, 1973)- 269 PHI SKEWNESS M SORTING STANDARD D E V IA TIO N ) 10 K M MEAN GRAIN SIZE ON MICRONS) I N 10 K M Figure 63. Histograms of samples collected along a north-south transect across San Pedro shelf. 271 WEIGHT PERCENT 100-1 50* 0 100 50- 1 0 0 Y/W yyy/s/s/yfl/ss/ji 2 3 A S C / 6 y Z t f 7 7 7 7 1 A S C PHI 2 3 4 S C 3 4 S C 2 3 4 S C 2 3 4 S C 2 3 A S C 2 3 A S C - 50 L0 AHF 21A01 21A02 21A03 21A0A 21A05 21A06 21388 AHF 21375 CENTRAL SHELF INNER SHELF MM 1 0.5 0.25 .125 062 CLAY I 1 1 1 h—I I PHI 0 1 2 3 A SILT r 1 0 0 0 1 2 3 . A S C 1 2 3 A S C 1 2 3 A S C 50 0 1 2 3 . A S C 1 2 3 A S C 1 2 3 A S C 2 3 A S C 0 1 2 3 A S C i 2 3 A S C q 12 34 s C 225A5 22SAA 225A3 21398 21399 21A14 21A13 UPPER SLOPE OUTER SHELF Figure 64. Conceptualized diagrams depicting the hydrodynamic processes contributing to complex current systems of the contin ental shelf (a) and the seasonal and shorter term fluctuation in relative energy levels. 273 SHELF HYDRODYNAMIC SYSTEM SHELF PARALLEL PROVINCES OUTER SHELF Shelf Edge CENTRAL SHELF INNER SHELF Beach 30CJNDARY CURRENTS, TICES ■METEOROLOGICA LLY-INDUCED CURRENTS SURFACE WAVE- INDUCED CURRENTS U pweILina Edge waves Internal waves Storm-induced Currents Tides Surface Waves iurface Waves Tides 3reaking Internal Waves Surface Waves W ind—induced Currents Tides Breaking Surface Waves SHELF TRANSVERSE PROVINCE T R A N S V E R S E S U B M A R IN E C A N Y O N P R O J E C T IO N Currents, generated by progressive internal waves trapped edge waves, etc., in submarine canyons influence sediment dispersal on the adjacent con tinental shelf within a narrow zone transverse to and superimposed on shelf parallel provinces SUMMER FAIR-WEATHER FAIR-WEATHER skewness, sorting and frequency distributions suggest three distinct hydraulic provinces approximately parallel with the shoreline characterized by specific processes. Inner shelf: Oscillatory currents, generated by shoaling sur face waves, dominate inner shelf water dynamics. Beaches supply coarser particles to this region via rip currents (Cook, 1969; Cook and Gorsline, 1972). Particles finer than medium sand tend to escape the inner shelf under the influence of net offshore surge asymmetry. Medium sand and coarser sediment essentially remain trapped in the nearshore system, only rarely breaking free to the cen tral shelf. Thus, a restricted range of size classes reach the central shelf. Central shelf: On the central shelf, wind-driven surface waves and tides generate near-bottom currents which move sedi ment particles to-and-fro, resulting in little net dis placement. Surface waves tend to override the effects of tidal currents nearshore, whereas tides become increas ingly important components in deeper water. Atmospheric events trigger unidirectional currents of variable direc tion and duration which are overprinted on surface wave currents and tidal currents. Although the fluctuating 275 nature of wind-induced currents causes grains to move in semi-randomized patterns, these currents transport sedi ment net distances along shore in shallow water and off shore in the outer portion of the province. Thus, central shelf current systems, dominated hy meteorologically- induced currents, further sort already limited grain size populations introduced from the inner shelf. Outer shelf: Less well-sorted and coarser-skewed populations on the outer shelf and upper slope suggest it to he an area of increased turbulence. Processes contributing energy at the shelf break include boundary currents in San Pedro Channel, upwelling, and various body waves (internal wave, edge wave, etc.). Body waves, along with other pro cesses, not only probably cause sufficient turbulence to keep fine-grained material in suspension, allowing parti cles to disperse and escape the shelf, but also winnow out mud from the bedload population on the seaward margin of the outer shelf and the upper shope. As suspended particulate matter moves to quieter environments, it set tles out over the slope and deep ocean floor, accounting for fine modal classes in these areas. Anomalies in Regional Textural Trends Tertiary rocks cropping out on the sea-floor, 6 to 276 8 km south of the Los Angeles "breakwater produce major anomalies in regional trends of all textural variables plotted in this study. Relict sediments (Pleistocene beach deposits) are associated with this area and are revealed by increasing median grain diameter, lower standard deviation (improved sorting) (on hand-contoured maps), coarser skewness, greater percent sand, lower per cent silt, and larger sand/mud ratios. (Figs. 6, 7> 8, 9, 61 and 62). Another smaller patch of relict sediment occurs 3 km south of Platform EVA. Other major perturbations in contour patterns do not readily correlate with obvious physical features of the sea-floor, but are evidence instead for localized depositional processes transverse to and superimposed upon regional shelf parallel hydrodynamic provinces. Extend the axis of San Gabriel Canyon shoreward and consider the area adjacent to this imaginary line as it projects across the shelf. Note that anomalies, some times subtle, but always distinct, characterize this re gion in each hand-contoured map. A narrow strip on the eastern half of this line marks an area of slightly finer-grained and poorer-sorted sediment (Figs. 6 and 7)« In this band, percent sand decreases and percent silt increases forming closures in contour patterns. Closures to the west of these showing 277 opposite trends occur near the head of San Gabriel Canyon. Meager control prevents me from establishing whether or not these western anomalies are continuations of anoma lous isopleths south of Platform EVA; in which case they could be related to relict deposits. A broad zone of low sand/mud ratios intrudes well into the shelf at this point. High sand/mud values to the north mark relict sediments straddling the inner-central shelf boundary (Fig. 9)• This protrusion coincides with a tongue of relatively skewed to the coarse material extending sea ward. An elongated lobe of less coarsely skewed sediment, aligned with the nearshore tongue, projects across the shelf break. Shelf Transverse Hydrodynamic Province The strong association with the projection of San Gabriel Canyon onto the shelf suggests that the canyon is influencing processes of physical sedimentation. Submar ine canyons function as pumps, alternately drawing water from the shelf down canyon and forcing water from the deep basins up canyon. The anomalous patterns in textural variables on the shelf in the vicinity of San Gabriel Canyon reflect this pumping action. The axis of the canyon as it projects onto the shelf is analogous to a busy highway cutting across a 278 network of less frequently used surface streets. Sediment moving in suspension over the shelf takes all roads, hut often enters the faster freeway. Fine-grained particles settle out of suspension everywhere on the shelf, hut be cause more grains travel the major thoroughfare, more of them settle out over this area, thus accumulating in the bottom sediment at a higher rate. This accounts for the anomalies in grain size, sorting, percent sand, percent silt, and sand/mud ratio. Gyral currents, produced by the up-and-down axis flushing of water , disperse parti cles around the canyon head, forming a halo in contour patterns open on the seaward side. Large grains escaping the inner shelf also are drawn to the canyon, thereby contributing coarse material to the fine-grained bedload population of the central and outer shelf. Histograms illustrate the input of coarser material and reveal how fine-grained sediments increasing mask coarse material progressively offshore by diluting the coarse fraction (Fig. 63)• This mechanism is responsible for the tongue of relatively coarse skewed sediment extending from the nearshore region seaward. A recent investigation of living foraminiferal populations demonstrates that shelf species are displaced downslope where San Gabriel Canyon incises the shelf (pers. commun., G. Blake, Department of Geological 279 Sciences, University of Southern California). This sup ports the conclusion that San Gabriel Canyon siphons water from the shelf and acts as a conduit for the preferential transport of sediment across the shelf. 280 CONCLUSIONS Conceptual Model of Shelf Processes Numerous processes interact to produce a complex and intricate system of currents which transport, erode and deposit sediment over the continental shelf. Results of this study allow me to recognize four hydrodynamic provinces; each of which is characterized by a diagnostic process or association of processes (Fig. 64a). Three zones (inner, central and outer shelf) are aligned approx imately parallel to the shoreline. A fourth transverse zone, defined in regions where submarine canyons incise the shelf, is superimposed on the other provinces, cutting across them normal to the coastline. The seaward bound aries of shelf parallel provinces occur at about 20 to 25 m water depth (inner), 60 to 70 m (central) and at the shelf break (outer). Shelf transverse zones correspond approximately with the width of the head of associated sub marine canyons and extend from the canyon head to shore. As energy input to the shelf varies, these bound aries shift or disappear. Rigorous winter conditions intensify hydraulic regimes which decrease in strength 281 during summer months. Shorter period weather fluctuations (intermittent storms disrupting a dominant fair-weather system) are overprinted on these primary seasonal regimes (Fig. 6^b). Bedforms and suspended sediment respond most quickly to regular and sporadic changes in the strength and position of shelf flow fields (Figs. 65-6?), whereas textural patterns change and equilibrate more slowly to shelf hydrodynamic processes (Fig. 68). Grains enter the shelf system from the beach via rip currents (Fig. 69)* Oscillatory currents dominate the inner shelf zone. A narrow range of particles escapes this province to the intricate central shelf system. The limits of vertical migration of the seasonal thermocline (about 20-60 m) coincide with the shallow and deep bound aries of the central zone, and separate current systems may occur shallower and deeper than the point at which the thermocline intersects the shelf floor. Thus, the central zone may be divided into two subprovinces. Meteorologically-induced currents, surface wind wave generated currents and tidal currents are more impor tant than other processes influencing transportation of sediment everywhere in the central province, but the rela tive contribution of each differs progressively from shore seaward (Fig. 6^). Surface waves and tides are subordin ate currents in a sediment dispersal system dominated by 282 Figure 65. Schematic diagram illustrating bedform zonation on the shelf under summer fair-weather (a) and storm (b) condi tions . 283 SUMMER FAIR-WEATHER RIPPLING 3I0TURBATI0N RIPPLING 3I0TVRSATI0N TRANS ITION 3I0TUR3ATT0N 3IC7UR3ATIQN SUBMARINE CANTON SHELF EDGE SUMMER STORM CONDITIONS RIPPLING > 3IOTURBATION RIPPLING > 3IOTURBATION RIPPLING 9IOTURBATION RIPPLING 3ICTUR3ATTCN SUBMARINE CANYON iSHELF EDGE Jians Figure 66. Schematic diagram illustrating bedform zonation on the shelf under winter fair-weather (a) and storm (b) condi tions . 285 WINTER FAIR WEATHER A RIPPLING > 3IOTVRflATION RIPPLING ^ 3IOTURBATION TRANSITION £ r 2 n ~ j — - 3 ■ * 1 > 3IOTUR3ATION > RIPPLING 3 IQTUP.BATION SUBMARINE CANYON s 3 7 3 -3 — 7 3 pSHELF £002 B WINTER STORM CONDITIONS BEACH rippling •3IOTUR3A7ION TRANSITION w V 2 2 _ _ _ — £ 2 ^ TIPPLING > 3I0TUF3ATI0N > 3 :otur3ATicn SUBMARINE CANYON SHELF 2DG2 Figure 67. Schematic profile depicting the dis persion of suspended particulate matter across the shelf in summer (a) and winter (b). 287 CONCENTRATIONS DECREASE FROM WINTER CONDITIONS AND ZONE II OVERLAPS ,?) WITH ZONE III BECOMING INDISTINGUISHABLE STORMS INCREASE TUR3IBITY TO LEVELS EQUAL TO OR GREATER THAN WINTER CONDITIONS SUMMER ^ ^^IN T R O D U C T T O N FINES FROM resuspession T y SURFACE WAVES AND WIND- INDUCSD CURRENTS. DIS PERSAL SEAWARD ALONG DENSITY INTERFACES . POSSIBLE ZONE OF RESUSPENSION FROM 3REARING INTERNAL WAVES WINTER Figure 68. Conceptualized textural patterns on the shelf resulting from the interac tion of the substrate with the complex hydrodynamic processes characterizing overlying waters. 289 A SUBSTRATE RESPONSE Z ' \ \ ) / M = 1 SD » 1 M>L SD^>L S>L / ______ S>L _ MCI 3D>L S * ■ 1 — 7 / / iSHELF EDGE CENTRAL SHELF 'STANDARD REFERENCE) MEDIAN GRAIN DIAMETER !M) : f:ne 1 COARSE) SORTING , SD) = 1 'BETTER I POORER! SKEWNESS (S) = ■ 1 'FINER L COARSER! B CUTER SHELF M = i-» -M S L SD=rI-^5D>I S = i-fco > 1 SHELF TRANSVERSEiI) ( a ) n e a r s h o r e SD=1-»SD»1 S = L-*S»1 ,b) offshore M«I-»M«1 SD^L-^SD^I PALIMPSFST GRADING ' II' SEWi-^SD-i S*L-»S=i S = i-»-S#l Figure 69- Schematic diagrams showing the concep tualized movement of bedload across the shelf (a) where large arrows repre sent coarser grains, and the concep tualized dispersion of near-bottom suspended particulate matter (b). 291 3 EDLOAD TRANSPORT / SUBMPRIN CAivTOM 3HSI*F ZZQ c DISPERSION OF NEAR BOTTOM SUSPENDEND SEDIMENT meteorologically-induced events. In the nearshore region, surface waves move grains to-and-fro, but their effects decrease further offshore where tides are increasingly important components. Meteorologically-induced currents superimposed on tidal and surface wave currents move sedi ment net distances in preferred directions. These cur rents sort particles, moving grains along shore in shallow water and towards the shelf edge in deeper water (Fig. 69); increasingly coarser grains have progressively stronger onshore directional components and travel pro portionately shorter distances over a comparable time interval. Suspended particulate matter moves seaward near the bottom, along density interfaces within the water column, and at the surface (Figs. 67 and 69)• Some particles set tle out only to be resuspended by strong surface wave surge, storm-induced currents, and breaking internal waves which migrate vertically with the seasonal thermocline. In this way fine-grained material undergoes repeated de position and resuspension before reaching the shelf edge. Upwelling, boundary currents, and various body waves contribute to turbulence at the shelf break which rapidly diffuses concentrated plumes of suspended matter passing over the outer shelf. Boundary currents carry suspensates to quieter depositional environments where 293 they accumulate on the bottom. On narrow shelves of southern California, submarine canyons appear to exercise considerable influence on shelf circulation patterns. Canyons enhance the effects of progressive internal waves propagating shoreward. Trapped edge waves in the heads of canyons produce conditions im peding cross-canyon flow, but do not inhibit on-offshore flow (Inman et al. , 1976) • Events in canyons generate transverse hydrodynamic processes on the shelf which not only act as preferential conduits for suspended sediment down canyon (Fig. 69)» but also form a transition zone overprinted on shelf parallel provinces which may divide the shelf into, or connect, separate circulation cells. Major Implications o Four hydrodynamic provinces, characterized by specific associations of depositional pro cesses, occur on the shelf. Three zones trend parallel (shelf parallel) to the shore line. The fourth (shelf transverse), present where submarine canyons incise the shelf, cuts perpendicularly across shelf parallel pro vinces . o Major current systems apparently occur above and below the seasonal thermocline; 29^ hence, the thermocline may define an important boundary between flow fields on the central shelf. o Internal waves propagating along the sea sonal thermocline break where it intersects the sea-floor. These waves resuspend fine grained sediment, disperse it horizontally and carry it seaward. o Surface waves and high winds generate Lang- muir circulations. Mesoscale current linea- tions are evidence for these three-dimensional helical flow cells, where they impinge on the sea-floor. o Small-scale bedforms respond to varying energy levels in the overlying water column. Ripple marks on the central and outer shelf are ephemeral features erased by biogenic reworking during periods of relative qui- esence. Compound bedforms indicate strong flow conditions produced by storms and large surface waves. o Trends in isopleths of several textural variables correlate with shelf hydrodynamic provinces. Of these, skewness (as calculated by comparison to a reference distribution) 295 seems to be the most sensitive. Histograms reflect skewness trends, and, thus, hydro- dynamic processes. Submarine canyons exercise great control over circulation patterns and sediment dispersal on narrow continental shelves. Modern sediment appears to be texturally mature and relict sediments are being re worked by processes operating on the shelf (palimpsest sediment). Although the sub strate is not completely graded in the sense of Swift (1970), surficial deposits appear to be in dynamic equilibrium with depositional processes operating on southern California shelves. REFERENCES REFERENCES Adeymo, M. D., 1970, Velocity fields in the wave breaker zone: Am. Soc. Civil Engineers, Proc. 12th Conf. on Coastal Eng., p. ^35-^60. Allen, J. R. L., 19^3» The classification of cross-strati fied units, with notes on their origin: Sedimentology, v. 2, p. 93-11^. _______ , 1966, on bedforms and paleocurrents: Sedimento logy, v. 6, p. 153-190. _______ , 1968, Current Ripples, North-Holland Publ., Amsterdam, ^ 3 P- Anonymous, 1976, Nucleopore membranes and hardware for the laboratory, catalog Lab 20: Nucleopore Comp., Pleasanton, California, 32 p. Assaf, G. R. Gerard and A. L. Gorden, 1971 Some mechan isms of oceanic mixing revealed in aerial photographs: Geophy. Res., v. 76, p. 6550-6572. Atwater, T., 1970, Implications of plate tectonics for Cenozoic evolution of western North America: Geol. Soc. American Bull., v. 81, p. 3513-3536. Bagnold, R. A., 19^1» The Physics of Blown Sand and Desert Dunes, Methuen, London, 265 p. _______ , 19^6, Motion of waves in shallow water: Inter action between waves and sand bottoms: Royal Soc. (London) Philos. Trans. Ser. A, v. 187, p. 1-15* _______ , 1963, Mechanics of marine sedimentation: In M. N. Hill (ed.), The Sea, v. 3> Wiley - Interscience, New York, N. Y., p. 507-582. _______ , 1966, An approach to the sediment transport problem from general physics: U. S. Geological Survey Prof. Paper ^22, 37 P- 2 9 8 Barnes, P. N., 1970, Marine Geology and Oceanography of Santa Cruz Basin, Calif.: unpub. Ph.D. dissertation, Univ. Southern Calif., Los Angeles, Calif. Barrel, J., 1906, Relative geological importance of con tinental, littoral and marine sedimentation: Jour. Geol., v. 16, p. 336-35^, A30-457, 52^-568. _______ , 1912, Criteria for the recognition of ancient delta deposits: Geol. Soc. America Bull., v. 23. p. 377-AA7. Belderson, R. H., Kenyon, N. H., Strede, A. H. and Stubbs, A. R., 1972, Sonographs of the Sea-Floor: a picture atlas; Elsevier Publishing Co., Amsterdam, 185 P- Bird, E. C. F., 1970, Coasts, M.I.T. Press, Cambridge, Mass., 2A6 p. _______ and Isaacs, B. (eds.), 1972, Plate Tectonics, Selected papers from the Jour. Geophys. Res., Am. Geophys. Union, Washington, D. C., 951 P* Blatt, H., Middleton, G. and Murray, R., 1972, Origin of sedimentary rocks; Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 63A p. Booth, J. S., 1973 > Textural changes as an indicator of sediment dispersion in the Northern Channel Island passages, Calif.: Jour. Sed. Petrology, v. A3, p. 238-250. _______ and Gorsline, D. S., 197A, Thoughts on new areas for research in shelf sediment transport studies: Mem. Inst. Geol. Bassin Aquitaine, no. 7» P« 1A5-1A8. Bunnell, V. D., 1969* The water structure of the San Pedro Basin, California Borderland: unpub. M.S. thesis, Univ. Southern Calif., Los Angeles, Calif., 127 p. Cacchione, D. A. and Southard, J. B., 197^» Incipient sed iment movement by shoaling internal gravity waves: Jour. Geophys. Res., v. 70 , p. 2237-22A2. Cacchione, D. A. and Wunsch, C., 197^» Experimental study of internal waves over a slope: Jour. Fluid Mech., v. 66, p. 223-239. 299 Cains, J. L., 1967, Asymmetry of internal tidal waves in shallow coastal waters: Jour. Geophys. Res., v. 72* p. 3563-3565. _______ , 1968, Thermocline strength fluctuations in coastal waters: Jour. Geophys. Res., v. 73* P* 2591- 2595. _______ and LaFond, E. C., 1966, Periodic motions of the seasonal thermocline along the southern California coast: Jour. Geophys. Res., v. 71* P* 3903-3915* Caldwell, J. M., 1956, Wave action and sand movement near Anaheim Bay, California: U. S. Army Corps of Engineers, Beach Erosion Board, Tech. Memo. 68, 21 p. California Cooperative Oceanic Fisheries Investigations (CALCOFI), 1957-1964, Cruise Date, 1953-1963, Data Reports: Physical and Chemical Data Reports: Physical and Chemical Data: Univ. of California, Scripps In stitute of Oceanography. Chamberlain, T. C., 1897* The method of multiple working hypotheses: Jour. Geology, v. V, p. 837-848. Chesterman, W. D., Clynich, P. R. and Stride, A. H., 1958, An acoustic aid to sea bed survey: Acustica, v. 8, p. 285-290. Christiansen, R. L. and Lipman, P. W., 1972, Cenozoic vol- canism and plate-tectonic evolution of the western United States II. Late Cenozoic: Royal Soc. (London) Philos. Trans., ser. A., v. 271, P- 249-284. Clay, C. S., Eses, J. and Weisman, J., 1964, Lateral echo- sounding of the ocean bottom on the continental rise: Jour. Geophys. Res., v. 69, p. 3823-3825* Clifton, H. E., 1976, Wave-formed sedimentary structures - a conceptual model: In Davis, R. A. and Ethington, R. L. (eds.), Beach and nearshore sedimentation, Soc. Econ. Palien and New Spec. Pub. 24, p. 126-148. _______ , Hunter, R. E. and Phillips, R. L., 1971* Depositional structures and processes in the non barred high energy nearshore: Jour. Sed. Petrology, v. 41, p. 65I-67O. Cook, D. 0., 1969, Calibration of the Univ. Southern 300 Calif, automatically recording settling tube: Jour. Sed. Petrology, v. 39, P- 781-786. _______, 1989, Sand transport by shoaling waves: unpub. Ph.D. dissertation, Univ. Southern Calif., Los Angeles, Calif., 1^8 p. _______ and Gorsline, D. S., 1972, Field observations of sand transport by shoaling waves: Marine Geol., v. 13, p. 31-56. Cotton, C. A., 1952, Criteria for the classification of coasts: Proc. 17th Conference of the International Geographical Union, p. 315-319- Creager, J. S. and Sternberg, R. W., 1972, Some specific problems in understanding bottom sediment distribution and dispersal on the continental shelf: In Swift, D. J. P., Duane, D. B. and Pilkey, 0. H. Teds.), Shelf Sediment Transport and Process and Pattern, Dowden, Hutchinson and Soss, Inc., Stroudsburg, Pa., p. 3^7-362. Curray, J. R., i960, Sediments and history of the Holocene transgression, continental shelf northwest Gulf of Mexico: In Shepard, F. P., Phleger, F. B. and van Andel, T. H. (eds.), Recent sediment, northwest Gulf of Mexico, Am. Assoc. Petroleum Geologists, p. 221- 226. _______ , 1965, Late Quaternary history, continental shelves of the United States: In Wright, Jr., H. E. and Frey, D. G. (eds.), The Quaternary of the United States, Princeton University Press, Princeton, New Jersey, p. 723-735- Davis, C. C., in preparation, Observations of circulations and suspended sediment transport over a portion of the southern California borderland from satellite imagery: unpub. M.S. thesis, Univ. Southern Calif., Los Angeles, Calif. Dingle, J. R., 197^> Wave-formed ripples in nearshore sands, unpub. Ph.D. dissertation, Univ. of Calif., San Diego, Calif., 136 p. Drake, D. E., 1972, Distribution and transport of sus pended matter, Santa Barbara Channel, Calif.: unpub. Ph.D. dissertation, Univ. Southern Calif., Los Angeles, Calif., 358 p. 301 _______ , 1976, Suspended sediment transport and mud deposition on continental shelves: In Stanley, A. J. and Swift, D. J. P. (eds.), Marine Sediment Transport and Environmental Management, John Wiley and Sons, New York, p. 127-158. Duane, D. B., Field, M. E., Meisburger, E. P., Swift., D. J. P. and Williams, S. J., 1972, Linear shoals on the Atlantic inner continental shelf, Florida to Long Islands In Swift, D. J. P., Duane, D. B. and Pilkey, 0. H. {eds.), Shelf Sediment Transport: Pro cess and Pattern, Dowden, Hutch, Hutchenson & Ross, Inc., Strousburg, Pa., p. 447-^98. Eckart, C., 1952, The propagation of waves from deep to shallow water: In Gravity Waves, Natl. Bur. Standards Circ. 521, p. 1S5-173 Emery, K. 0., 1952, Continental shelf sediments off southern California: Am. Assoc. Petroleum Geologists Bull., v. 63, p. 1105-1108. _______ , 1956, Deep standing internal waves in California basins: Limnol. Oceanogr., v. 1, p. 35-^1- _______ , 1958, Shallow submerged marine terraces of southern California: Geol. Soc. America Bull., v. 69, p. 39-60. _______ , i960, The Sea Off Southern California: John Wiley and Sons, Inc., New York, 366 p. _______ , 1968, Relict sediments on continental shelves of the world: Am. Assoc. Petroleum Geologists Bull., v. 52, p. Ah5-^6^. _______ and Gunnersen, C. G., 1973* Internal swash and surf: U. S. Natl. Acad. Sci. Proc., v. 70, p. 2379- 2380. Emery, K. 0. and Uchupi, E., 1963> Western North Atlantic Ocean: Topography, rocks, structure, water, life and sediments, Am. Assoc. Petroleum Geologists, Memo. 17» 532 p. Faller, A. J., 1969* The generation of Langmuir circula tions by the eddy pressure of surface waves: Limnol. Ocean., v. 14, p. 50^-518. 302 _______ , 1971» Oceanic turbulence and the Langmuir circu lation: Ann. Rev. Ecol. System, v. 2, p. 201-233* _______ and Woodcock, A. H., 1964, The spacing of windows of sargasm in the ocean: J. Marine Res., v. 22, p. 22-29* Felix, D. W., 1961, An inexpensive recording settling tube for analysis of sands: Jour. Sed. Petrology, v. 39, p. 777-780. _______ and Gorsline, D. S., 1971, Newport Submarine Can yon, Calif.: an example of the effects of shifting loci of sand supply upon canyon position: Marine Geol., v. 10, p. 177-198. Fisher, R. L., 1974, Pacific-type, continental margins: In Burk, C. R. and Drake, C. L. (eds.), The Geology of Continental Margins, Springer Yerlog, Inc., New York, p. 25-41. Fleming, R. H. and Revelle, R., 1939, Physical processes in the oceans: In Trask, P. D. (ed.), Recent Marine Sediments, Am. Assoc. Petroleum Geologists, p. 48- l4l. Folk, R. L., 1988, Petrology of sedimentary rocks: Hemphil's, Austin, Texas, 170 p. _______ , 1971, Genesis of longitudinal and oghurd dunes elucidated by rolling upon grease: Geol. Soc. America Bull., v. 82, p. 3461-3468. Gorsline, D. S., 1958, Marine geology of San Pedro and Santa Monica Basins and vicinity, Calif.: unpub. Ph.D. dissertation, Univ. Southern Calif., Los Angeles, Calif., 301 p. _______ and Grant, D. J., 1972, Sediment textural patterns on San Pedro shelf, Calif. (1951-1971) Reworking and transport by waves and currents: In Swift, D. J. P., Duane, D. B. and Pilkey, 0. H. (eds.), Shelf Sediment Transport: Process and Pattern, Dowden, Hutchinson and Ross, Inc., Stroudsbourg, Pa., p. 575-600. Graf, W. H., 1971, Hydraulics of Sediment Transport, McGraw-Hill, New York, 513 P« 303 Grant, D. J., 1973» Sediment of the San Pedro shelf: unpub. M.S. thesis, Univ. Southern Calif., Los Angeles, Calif., 120 p. Hamilton, W., 19^9» Mesozoic California and the underflow of Pacific mantle: Geol. Soc. America Bull., v. 80., p. 2409-2430. Heezen, B. C., 1974, Atlantic-type continental margins: In Burk, C. A. and Drake, C. L. (eds.), The Geology of Continental Margins, Springer-Verlag, Inc., New York, p. 13-24. Hendricks, T., 1976a, Current velocities required to move sediments: In Southern California Coastal Water Re search Project Annual Report 1976, p. 71-76. _______ , 1976b, Measurements of subthermocline currents: In Southern California Coastal Water Research Project Annual Report 1976, p. 63~70. Hjulstrom, F., 1939. Transportation of detritus by moving water: In Trask, P. D. (ed.), Recent Marine Sediments, Am. Assoc. Petroleum Geologist, Tusla, p. 5-31- Horrer, P. L., 1950, Southern hemisphere swell and waves from a tropical storm at Long Beach, Calif.: U. S. Army Corps of Engineers, Beach Erosion Board, Bull., v. 4, no. 3. P* 1-18. Howard, J. D. and Reineck, H. E., 1975» Comparison of physical and biogenic sedimentary structures of a marine high energy and a marine "zero energy" coast; IXth International Congress of Sedimentology, Nice, 1975, Theme 6, p. 73-76. Howell, D. G. (ed.), 1976, Aspects of the geologic history of the California continental borderland: Pacific Section Am. Assoc. Petroleum Geologists, Misc. Pub. 24, 561 p. Ingle, Jr., J. C., 1966, The movement of beach sand: Dev elopments in sedimentology, Elsevier, Amsterdam, v. 5, 221 p. Inman, D. L., 1963. Sediments: physical properties and mechanics of sedimentations. In Shepard, F. P., Sub marine Geology, 2nd ed., Harper and Row, New York, p. 101-151. 304 Inman, D. L. and Nordstrom, C. E., 1971, On the tectonic and morphologic classification of coasts: Jour. Geo logy, v. 79, p. 1-21. _______ and Flick, R. E., 1976, Currents in submarine can yons: An air-sea-land interaction: Annual Rev. Fluid Mechs., v. 8, p. 275-310. Isaacs, J. D. and Schick, G. B., i960, Deep-sea free in strument vehicle: Deep-Sea Research, v. 7, P- 61-67. _______ , Reid, Jr. , J. L. and Schwartzlose, R. A. , 1966, Near-bottom currents measured in 4 kilometers depth off the Baja Calif. Coast: Jour. Geophys. Res., v. 7, p. ^297-^303. Johnson, D. W., 1919, Shore processes and development, Wiley, New York, New York, 58^ P- Kachel, N. B. and Sternberg, R. W., 1971, Transport of bedload as ripples during an ebb current: Marine Geol. , v. 10, p. 229-2^. Karl, H. A., 1975, Agents of sediment dispersal, San Pedro continental shelf, southern Calif, (abs.): Sed iment transport section, Oceanography session, In vited late abstracts, 1975 Fall Annual Meeting, Am. Geophys. Union. _______ , 1975, Distribution and significances of sedi mentary structures and bedforms on the continental shelf, southern Calif, (abs.): Geol. Soc. America Abstracts with programs, v. 7, P- 331-332. _______ , 1976, Box core liner system developed at the Sed- imentology Research Laboratory, Univ. Southern Calif. Marine Geol., v. 20, p. M1-M6. _______ and Plutchak, 1976, Sediment patterns as indica tors of transport mechanisms, San Pedro shelf, Calif, (abs.): Geol. Soc. America Abstracts, v. 8, p. 9^6. _______ and Gorsline, D. S., in preparation, Some deposi- tional processes affecting sediment textures on the continental shelf, southern Calif. Kelly, J. C. and McManus, D. A., 1970, Hierarchal analysis of variance of shelf sediment texture: Jour. Sed. Pet- rology, v. 4o, p. 1335-1339- 305 Kenyon, N. H., 1970, Sand ribbons of European tidal seas: Marine, Geol., v. 9, p. 25-39* Kline, S. L., Reynolds, W. C., Schraub, F. A. and Rum- stadler, P. W. , 19^7» The structure of turbulent boundary layers: Jour. Fluid Mech., v. 30, p. 7Al- 773* Komar, P. D., 1973, An occurrence of "brick pattern" oscillatory ripple marks at Mono Lake, Calif.: Jour. Sed. Petrology, v. A3, p. 111-1113* _______ , 197A, Oscillatory ripple marks and the evolution of ancient wave conditions and environments: Jour. Sed. Petrology, v. AA, p. 169-180. _______, 1978a, Boundary layer flow under steady unidirec tional currents: In, Stanley, D. J. and Swift, D. J. P. (eds.), Marine Sediment Transport and Environmental Management, John Wiley and Sons, Inc., New York, 602 p. _______ , 1976b, The transport of cohesionless sediments on continental shelves: In Standly, D. J. and Swift, D. J. P. (eds.), John Wiley and Sons, New York, p. 107-125* Marine Sediment Transport and Environmental Management. _______ , 1976c, Beach Process and Sedimentation: Pren- tice-Hall, Inc., Englewood Cliffs, New Jersey, A29 p. _______ and Miller, M. C., 1973* The threshold of sediment movement under oscillatory water waves: Jour. Sed. Petrology, v. A3, p. 1101-1110. _______ , 1975a, Sediment threshold under oscillatory waves: Am. Soc. Civil Engineers, Proc. lA"^^1 Conf. on Coastal Eng., p. 756-775* _______ , 1975h, on a comparison of the threshold of sedi ment motion under waves and unidirectional currents with a discussion of the practical evaluation of threshold: Jour. Sed. Petrology, v. A5, P* 362-367. _______ , 1975c, The initiation of oscillatory ripple marks and the development of plane-bed at high shear stresses under waves: Jour. Sed. Petrology, v. A5, p. 697-703. 306 Komar, P. D., Neudeck, R. H. and Kulm, L. D., 1972, Ob servations and significance of deep-water oscillatory ripple marks on the Oregon continental shelf: In Swift, D. J. P., Duane, D. B. and Pilkey, 0. H. (eds.)» Shelf Sediment Transports Process and Pattern; Dowden, Hutchinson and Ross, Inc., Stroudsbourg, Pa., p. 601- 619. Kulm, L. D., Roush, R. C., Harlett, J. C., Neudeck, R. H., Chambers, D. M. and Runge, E. J., 1975» Oregon contin ental shelf sedimentation: interrelationships of facies distribution and sedimentary processes: Jour. Geology, v. 83, p. 1^5-175* La Fond, E. C., 1961, Internal wave motion and its geo logical significance: In "Mahodevan Volume," Osmania University Press, p. 61-77* _______ , 1962, Internal waves: In Hill, M. N. (ed.), The Sea, v. 1, Wiley-Interscience, New York, p. 731-755* _______ , 1966, Internal waves: In Fairbridge, R. W. (ed.), Reinhold Publishing Corp., New York, p. 402-^08. Lee, 0. S., 1961, Observations on internal waves in shal low water: Limnol Oceanogr., v. 6, p. 312-321. Liepper, D. F., 1955» Sea temperature variations associ ated with tidal currents in stratified shallow water over an irregular bottom: Jour. Marine Res., v. 1^, p. 23^-252. Longuet-Higgins, M. S., 1953» Mass transport in water waves: Royal Sec. (London) Philos. Trans., ser. A, v. 2^5, p. 535-581. Ludwick , J. C. , 1975, Variation in boundary drag coeffi cient in the tidal entrance to Chesapeake Bay, Vir ginia: Marine Geol., v. 19» P* 19-28. Manohar, M., 1955» Mechanics of bottom sediment movement due to wave action: U. S. Army Corps of Engineers, Beach Erosion Board, Tech. Memo. No. 57. 121 p. McCave, I. N., 1972, Transport and escape of fine-grained sediment from shelf areas: In Swift, D. J. P. , Duane, D. B. and Pilkey, 0. H. (eds.), Shelf Sediment Trans port: Process and Pattern, Dowden, Hutchinson and Ross, Inc., Stroudsbourg, Pa., p. 225-2^8. 307 McKinney, T. F. , Stubblefield, W. L. and Swift, D. J. P. , 197^» Large-scale current lineations on the central New Jersey shelf: investigations by side-scan sonar: Marine Geol., v. 17, p. 79-102. Meade, R. H., 1972, Sources and sinks of suspended matter on continental shelves: In Swift, D. J. P., Duane, D. B. and Pilkey, 0. H. (eds.), Shelf Sediment Transport: Process and Pattern, Dowden, Hutchinson and Ross, Inc., Stroudsbourg, Pa., p. 249-262. Migniot, C. 1968, Etude des proprietes physiques et dif- ferents sediments tres fins et de leur comportement sous des actions hydrodynamiques: La Houille, Blanche, v. 7, p. 591-620. Mitchell, A. H. and Reading, H. G., 1969» Continental margins; geosyncline and ocean floor spreading: Jour. Geology, v. 77. P- 629-646. Mooers, C. N. K., 1976, Wind-driven currents on the con tinental margins: In Stanley, D. J. and Swift, D. J. P. (eds.), Marine Sediment Transport and Environmental Management, John Wiley & Sons, New York, p. 29-52. Moore, D. G., 1951. Submarine geology of San Pedro shelf, Calif.: unpub. M.S. thesis, Univ. Southern Calif., Los Angeles, Calif. _______ , 1954, Submarine geology of San Pedro shelf: Jour. Sed. Petrology, v. 24, p. 162-181. _______ , 1957. Acoustic sounding of Quaternary marine sediments off Point Loma, Calif.: U. S. Navy Electron ic Lab. Retp. 815, 17 P* Murray, S. M., 1975. Accumulation rates of sediment and metals off southern Calif, as determined by Pb210 method: unpub. dissertation, Univ. Southern Calif., Los Angeles, Calif., 145 p. Nikuradse, J., 1933. Laws of Flow in Rough Pipes: Natl. Advisory Comm. Aeronautics Tech. Memo. 1292 (trans. from German, 1950). Norris, R. M., 1964, Dams and beach-sand supply in south ern Calif.: In Miller, R. L. (ed.), Papers in Marine Geology, MacMillan, New York, p. 154-171. 308 O'Brien, M. P., 1950, Wave refraction at Long Beach and Santa Barbara, Calif.: U. S. Army Corps of Engineers, Beach Erosion Board Bull., v. no. 1, p. 1-11. Petzold, T. H. and Austin, R. W., 1968, An underwater transmissometer for ocean survey work: Tech. Rept. Scripps Inst. Oceangr., Ref. 68-69, 5 P» Pirie, D. M., Murphy, M. J. and Edmiston, J. R., 1975, California nearshore surface currents; Shore and Beach, Oct., 1975, p. 23-24. Plutchak, N. and Karl, H. A., in preparation, Skewness as an indicator of sorting and transport of sediment on the continental shelf. Prandtl, L. and Tietjen, 0. G., 1934, Applied Hydro- and Aeromechanics: J. P. Den Hartog (trans.), Dover Pub lications, Inc., New York, 311 p. Rao, K. N., Narasimha, R. and Narayanon, M. A. B., 1971, The "bursting" phenomenon in a turbulent boundary layer: Jour. Fluic Mech., v. 48, p. 339-352. Reid, J. L. Jr. , Roden, G. I. and Wylie, J. G. , 1958, Studies of the California Current System: Calif. Cooperative Fisheries Investigations, Calif. Dept. Fish and Game, p. 27-56. Reineck, H. E. and Singh, I. B., 1973, Depositional Sedi mentary Environments, Springer-Verlag, Berlin, 439 p. Rodolfo, K. S., 1970, Annual suspended sediment supplied to the California continental borderland by the south ern California watershed: Jour. Sed. Petrology, v. 40 , p. 666-671. Royse, C. F., Jr., 1970, An introduction to sediment analysis: Sediment Analysis, Tempe, Ariz., 180 p. Schick, G. B. and Isaacs, J. D., 1961, Underwater remote programming: Undersea Technol., Nov. -Dec., p. 29-32. Schubel, J. R. and Okubo, A., 1972, Comment on the dis persal of suspended sediments across continental shelves: In Swift, D. J. P., Duane, D. B. and Pilkey, (eds.), Shelf Sediment Transport: Process and Pattern, Dowden, Hutchinson and Ross, Inc., Stroudsbourg, Pa., p. 333-346. 309 Scott, J. T. , Myer, G-. E. , Stewart, R. and Walker, E. G. , 1969, On the mechanism of Langmuir circulations and their role in Empilimion mixing: Limnol. Ocean., v. 1^, P. ^93-503. Shapiro, A. 1961, Shape and Flow: Doubleday & Co., Inc., Garden City, New York, 186 p. Shepard, F. P., 1932, Sediments on the continental shelves: Geol. Soc. of America Bull., v. ^3» P* 1017- 1039. _______ , 19^8, Submarine Geology, Harper and Row, New York. _______ , 1963, Submarine Geology, Harper and Row, New York, 557 P. _______ , and Dill, 1966, Submarine Canyons and Other Sea Valleys, Rand McNally, Chicago. Shepard, F. P. and Emery, K. 0., 19^1> Submarine topo graphy off California Coast: Canyons and tectonic implications: Geol. Soc. America, Special Paper 31» 171 P. Shepard, F. P. and LaFond, E. C., 19^0, Sand movement along the Scripps Institution pier: Am. Jour. Sci., v. 238, p. 272-285. Shepard, F. P. and Marshall, M. N., 1969, Currents in LaJolla and Scripps Submarine Canyons: Science, v. 165, p. 177-178. Shepard, F. P. and Marshall, N. F., 1973 > Currents along floors of submarine canyons: Am. Assoc. Petroleum Geologists Bull., v. 57» P« 2^-264. _______ and McLoughlin, P. A., 197^> Currents in submarine canyons: Deep-Sea Research, v. 21, p. 691-706. Shields, A., 1936, Anwendung der Ahnlichheits Mechanik und der Turbuleneforschung auf die Geschiebe Bewegring: Preuss: Versuchanstalt fur Wasserbau und Schiffbau, Berlin, 20 p. Simons, D. B., Richardson, E. V. and Nordin, C. F., Jr., 1965, Sedimentary structures generated by flow in alluvial channels: In Middleton, G. V. (ed.), Primary 310 Sedimentary Structures and their Hydrodynamic Inter pretation, Soc.. Econ. Paleon. and Min. Spec. Pub. 12, p. 3^-52. Smith, J. D. and Hopkins, T. S., 1972, Sediment transport on the continental shelf off of Washington and Oregon in light of recent current measurement: In Swift, D. J. P., Duane, D. B. and Pilkey, 0. H. (eds.), Shelf Sediment Transport: Process and Pattern, Dowden, Hutchinson and Ross, Inc., Stroudsbourg, Pa., p. 1^3“ 180. Southard, J. B. and Cacchione, D. A., 1972, Experiments on bottom sediment movement by breaking internal waves: In Swift, D. J. P., Duane, D. B. and Pilkey, 0. H. (eds.), Shelf Sediment Transport: Process and Pattern, Dowden, Hutchinson and Ross, Inc., Strouds bourg, Pa., p. 83-97* Stanley, D. J. and Swift, D. J. P. (eds.), 1976 Marine Sediment Transport and Environmental Management, John Wiley and Sons, Inc., New York, 602 p. Sternberg, R. W., 1968, Friction factors in tidal chan nels with differing bed roughness: Marine Geol., v. 6, p. 2^3-260. _______ , 1971» Measurements of incipient motion of sedi ment particles in the marine environment: Marine Geol., v. 10, p. 113-119* _______ , 1972, Predicting initial motion and bedload transport of sediment particles in the shallow marine environment: In Swift, D. J. P., Duane, D. B. and Pilkey, 0. H. Teds.), Shelf Sediment Transport: Pro cess and Patterns, Dowden, Hutchinson and Ross, Inc., Stroudsbourg, Pa., p. 61-82. Stevenson, R. E. and Gorsline, D. S., 1956, A shoreward movement of cool subsurface water: Am. Geophys. Union Trans., v. 37» P* 553-557* Suess, E., 1906, The Face of the Earth (Sollas, W. J., trans.), Oxford. Summers, H. J. and Emery, K. 0., 1963, Internal wave of tidal period off southern California: Jour. Geophys. Res., v. 68, p. 827-839. 311 Sundborg, 0., 1956, The river Klaroolvan, a study in fluvial processes: Geografiska Annaler, v. 38, P* 125-316. Sverdrup, H. N. and Fleming, R. H., 19^1, The waters off the coast of southern California, March to July, 1937: Scripps Inst. Oceanogr., Bull., v. h, p. 261- 378. Swift, D. J. P., 1970, Quaternary shelves and the return to grade: Marine Geol., v. 8, p. 5~30. _______, 1972, Implications of sediment dispersal from bottom current measurements, some specific problems in understanding bottom sediment distribution and dispersal on the continental shelf - a discussion of two papers: In Swift, D. J. P., Duane, D. B. and Pilkey, 0. H. (eds.), Shelf Sediment Transport: Pro cess and Pattern, Dowden, Hutchinson and Ross, Inc., Stroudsbourg, Pa., p. 363-375* _______ , 1975» Response of the shelf floor to geostrophic storm currents, Middle Atlantic Bight of North Amer ica: Proceedings IXth International Congress of Sedi- mentology, Nice, 1975* Theme 6, p. 193-198. _______ , 1976, Coastal sedimentation: In Stanley, D. J. and Swift, D. J. P. (eds.), Marine Sediment Transport and Environmental Management, John Wiley & Sons, New York, p. 255-310. _______ , Duane, D. B. and Pilkey, 0. H. (eds.), 1972a, Shelf Sediment Transport: Process and Pattern, Dowden, Hutchinson and Ross, Inc., Stroudsbourg, Pa., 6h8 p. Swift, D. J. P., Kofoed, J. W., Saulsbury, F. P. and Sears, P., 1972b, Holocene evolution of the shelf surface, central and southern Atlantic shelf of North America: In Swift, D. J. P., Duane, D. B. and Pilkey, 0. H. (eds.), Shelf Sediment Transport: Process and Pattern: Dowden, Hutchinson and Ross, Inc., Strouds bourg, Pa., p. 499-57h. Swift, D. J. P., Ludwick, J. C. and Boehmer, W. R., 1972c, Shelf sediment transport: a probability model: In Swift, D. J. P., Duane, D. B. and Pilkey, 0. H. Teds.), Shelf Sediment Transport: Process and Pattern, Dowden, Hutchinson and Ross, Inc., Stroudsbourg, Pa., p. 195-221. 312 Swift, D. J. P. and Ludwick, J. C., 1976, Substrate re sponse to hydraulic processes: grain-size frequency distributions and bedforms: In Stanley, D. J. and Swift, D. J. P. (eds.)» Marine Sediment Transport and Environmental Management, John Wiley and Sons, New York, p. 159-196. Swift, D. J. P., Stanley, D. J. and Curray, J. R., 1971. Relict sediments or continental shelves: Jour. Geo logy, v. 79, p. 322-3^6. Tucker, M. J., 1966, Sideways-looking sonar for marine geology: Geo-marine Technology, v. 2, p. 18-21. Valentin, H., 1952, Die Kusten der Erde: Supplement to Petermanns Geogr. Mitl., No. 246. van Andel, Tj. H. and Postma, H., 195^, Recent sediments of the Gulf of Persia: In Reports of the Orinoco shelf expedition, v. 1: Kon. Nedrl. Akad. Wetensch Verk., v. 20, n. 5, 245 p. Wimbush, M. and Munk, W., 1970, The benthic boundary lay er: In Maxwell, A. E. (ed.), The Seas, v. pt. 1, B. Wiley, Interscience, New York, p. 731-758. Wunsch, C., 1968, on the progression of internal waves up a slope: Deep-Sea Research, v. 25, P- 251-258. ________, 1971, Internal waves: Am. Geophys. Union Trans., v. 56, p. 233-235. Young, R. A. and Southard, J. B., 1975, Erodability of cohesive marine sediments: field and laboratory ex periments (abs.): Geol. Soc. Amer. Abstracts with programs, v. 7, p. 1325- Zenkovich, V. P., 1967, Processes of Coastal Development, Steers, J. A. and King, C. A. M. (eds.), Fry, D. G. (trans.), Wiley-Interscience, New York, 738 p. 313 APPENDICES A p p e n d ix A Box core, Shipek grad and current meter station locations on Figure 6a keyed to AHF station numbers Fig.6a AHF Fig.6a AHF Fig.6a AHF Fig.6a AHF 1 19973 29 21A15 53 21A0A 81 19982 2 21730 30 21A1A 21537 * 82 213A9 3 21729 31 21A13 CM , 2 8m , VT 22555 A 225^6 32 21A12 5A 21A05 83 19892 5 19885 33 19979 22536 8A 19868 6 225^7 3A 21A11 55 20829 21380 7 20825 35 21A10 56 21A06 86 19983 8 20826 36 21A09 22535 87 21381 9 20827 37 21A08 57 2253A 88 19890 10 19880 38 20830 58 22533 89 1998A 11 225^8 39 21A07 59 21389 90 22556 12 19881 Ao 19871 60 21390 91 216A2 13 19867 Al 19869 .61 21391 92 22557 CM, 51m V IV CM,27m V VI3 62 21392 93 216A3 lA 19976 A2 19872 63 21393 9A 216AA 15 19882 A3 19873 6A 2139A 95 216A5 16 19977 AA 225A5 65 21395 96 19985 17 19883 A5 21397 66 21396 97 216A6 18 19978 225AA 67 21397 22558 19 225A9 A6 21398 68 21382 98 22559 20 19975 0 225A3 69 21383 99 226A7 21 Shipekll A7 21399 70 2138A 100 226A8 22 ShipekI 225A2 2255^ 101 22650 23 Shipeklll A8 21A00 71 21385 102 226A9 2A 1997A 225A1 72 21386 103 22651 25 19878 A9 21A01 73 21387 10A 22652 26 ShipekIV 225A0 7 A 21388 105 22653 27 22550 50 21A02 75 21375 106 19986 28 20828 22539 76 21376 107 19987 22552 . 19980 108 19988 CM,A5m VT 77 21377 51 22531 78 19981 52 21A03 79 21378 22538 80 19893 ^Current meter emplaced during Cruise 1271. Shipek grab samples collected during R/V VANTUNA cruise, ^12-15. April, 1976. ^Current meter emplaced during Cruise 1271. Current meter emplaced during R/V VANTUNA cruise, 15-19» ..March, 1976. ^Current meter emplaced during R/V VANTUNA cruise, 12-16, April, 1976. A p p e n d ix A ' Box core, Shipek grab and current meter stations keyed to1 location numbers on Figure 6a Cruise 1271 Cruise 1294 Cruise 1310 Cruise 1335 AHF Fig.6a AHF Fig.6a AHF Fig.6a AHF Fig.6a 19867 13 20825 7 21404 53 22538 52 19868 84 20826 8 21405 54 22539 50 19869 41 20827 9 21406 56 22540 49 19871 40 20828 28 21407 39 22541 48 19872 42 20829 55 21408 37 22542 47 19873 43 20830 38 21409 36 22543 46 19878 25 21410 35 22544 45 19880 10 Cruise 1310 21411 34 22545 44 19881 12 21412 32 22546 4 19882 15 21375 75 21413 31 22547 6 19883 17 21376 76 21414 30 22548 11 19890 88 21377 77 21415 29 22549 19 19891 85 21378 79 22550 27 19892 83 21379 82 Cruise 1316 22551 34 19893 80 21380 84 22552 50 21381 87 21642 91 22553 63 Cruise 1273 21382 68 21643 93 22554 70 21383 69 21644 94 22555 82 19973 1 21384 70 21645 95 22556 90 19974 24 21385 71 21646 97 22557 92 19975 20 21386 72 21647 99 22558 97 19976 14 21387 73 21648 100 22559 98 19977 16 21388 74 21649 102 19978 18 21389 59 21650 101 VANTUNA.March 19979 33 21390 60 21651 103 19980 76 21391 61 21652 104 Shipek Fig.6a 19981 78 21392 62 21653 105 19982 81 21393 63 21729 3 I 22 19983 86 21394 64 21730 2 II 21 19984 89 21395 65 III 23 19985 96 21396 66 Cruise 1335 IV 26 19986 106 21397 67 19987 107 21398 46 22531 51 uurrenx 19988 108 21399 47 22533 58 iviexer rlg.oa 21400 48 22534 57 I8967 13 21401 49 22535 56 I8969 4l 21402 50 22536 54 3/76 50 21403 52 22537 53 k/76 53 316 A p p e n d ix B Camera station locations of Figure 10a keyed to AHF station numbers F ig . 1 0 a 1 2 3 k 5 6 7 8 9 10 11 12 13 lA 15 16 17 21 22 23 2k 25 26 27 28 29 30 31 32 33 3k 35 36 AHF 199^0 199^1 19909 20 7k5 20767 21723 1992^ 19977 19976 , 11> 3/76 18,3/76 17,3/76 19932 19933 19^75 16,3/76 19,3/76 20cm, 3/76 21,3/76 2171^ 21715 19923 19921 20912 19922 ? k3,k/?6 kk,k/7&o 10,^-GW k5,k/?6 13,3/76 20 7k6 Ik,3/76 15,3/76 19975 IV,k/76 g. 10a l AHF Fig.10a AHF 37 20910 , 69 2256^ 38 6cm,12/75 70 22560 39 IV, k/76 71 22563 ko 19568 72 3cm,12/75 kl 20911 28,^-GW k2 13,3/76 73 ^cm,12/75 k3 k6,k/76 7k 27,3/76 kk 2,^-GW 75 26,3/76 k5 9,k-GW z 39,10-GW-^ 76 25,3/76 k6 77 19916 k7 19920 78 19919 k8 19915 79 19917 k9 1991^ 80 19898 50 38,10-GW 81 19899 51 19913^ 19979? 1,k-GW 82 22 436 52 83 22k37 53 8k 1,10-GW 5k 6,A-GW 1,k/76 55 5,k-GW 85 li,k/76 56 21705 22^40 86 2,10-GW 2,k/76 k,k-GW 87 2i,k/76 37,10-GW 88 3, V76 57 5cm,12/75 89 k,k/76 58 16,4-GW 22k3 5 59 A,3/76 90 5,k/76 60 B,3/76 91 6,10-GW 61 32,3/76 6,k/76 62 cm, k/ 7 6 92 7,k/76 63 cm , k/ 7 6 93 19897 6k 30,3/76 <pk 20681 65 1cm,12/75 95 19896 66 29,3/76 96 19955 67 68 I?,k-GW 2cm,12/75 97 1995^ (1)3/76 refers to VANTUNA cruise 15-19 March, 1976; see log for station coordinates; (2)k/76 refers to VANTUNA cruise 12-16 April, 1976; (3)4-GW refers to Golden West cruise 25 April, 197^; (4)12/75 refers to VANTUNA cruise 8-12 December, 1975; (5)10-GW refers to Golden West cruise 6 October, 1975; (6)AHF 19979 and 1, ^-GW represent the same station reoccupied in winter and spring. A p p e n d ix B Camera stations keyed to location numbers on Figure 10a GOLDEN WEST Cruise 12 56 4/2 5/74 AHF Fig.10a GW Fig.10a 19^75 lA 1 53 2 AA Cruise 1260 A 56 5 55 19568 AO 6 5A 9 A 5 Cruise 1271 10 30 13 A2 19896 95 16 58 19897 93 17 67 19898 80 19899 81 Cruise 1292 19913 51 1991^ A9 AHF Fig.10a 19915 A8 19915 77 207^5 A 19919 78 207A6 32 19920 A7 19921 25 Cruise 129A 19922 27 19923 2A 20909 3 1992A 6 20910 37 19932 12 20911 Al 19933 13 20912 26 199^0 2 199^1 1 Cruise 1316 19954 97 19955 96 21681 9A 21705 56 Cruise 1273 2171A 22 21715 23 19975 35 19976 8 Cruise 1330 19977 7 19979 52 22A35 89 22^36 82 22^37 83 22AA0 56 VANTUNA Cruise 1335 3/15-19/76 AHF Fig.10a 3/76 Fig.10a 22560 70 17 11 22563 71 18 10 2256A 69 19 16 cm 20 17 GOLDEN WEST A 59 10/6/75 B 60 32 61 GW Fig.10a 31 62 30 6A 1 8A 29 66 2 86 28 72 6 91 27 7 A 37 56 26 75 38 50 25 76 39 A6 VANTUNA VANTUNA 4/12-16/76 12/8-12/75 4/76 Fig.10a 21/7 5 Fig.10a 1 8A 1cm 65 ii 85 2 cm 68 2 86 3 cm 72 p— ^ 2 87 A cm 73 3 88 5 cm 55 A 89 6 cm 38 5 6 90 91 VANTUNA 7 92 3/15-19/76 A3 28 AA 29 3/76 Fig.lOa A6 ^3 cm 63 11 9 IV 36 12 21 IV 39 13 31 1A 33 15 3A 16 15 318 A p p e n d ix C Cruise 1250 TRANSMISSION TRANSMISSION AHF SUR W BOT w DEPTH (m) AHF SUR W EOT W 19148 42 71 159 19164 57 69 19149 31 56 22 19165 — — 19150 4o 53 37 19166 19151 85 70 299 19167 — 19152 49 80 367 19168 60 80 19153 41 48 2k 19169 - - — 19154 42 55 32 19170 44 55 19155 48 82 395 19171 — 19156 52 69 208 19172 50 31 19157 33 30 31 19173 59 51 19158 38 29 20 19174 19159 56 78 111 19175 — — 19161 — — --- 19176 — — 19162 — — --- 19177 63 65 19163 22 80 96 19178 - - SUR: Percent transmission 5 f i i "below the surface. BOT: Percent transmission 1 m above the bottom. DEPTH . . I tlL , 205 235 234 228 169 246 319 A p p e n d ix G ( C o n tin u e d ) Cruise 1273 TRANSMISSION TRANSMISSION AHF SUR BOT DEPTH AHF SUR BOT DEPTH W W (m) w W (m) 19972 23 3 19 19997 44 14 19 19973 50 45 36 19998 53 51 23 19974 44 33 18 19999 58 86 126 (040)19975 52 59 28 20000 64 87 84 19976 57 4o 47 20001 65 88 229 19977 60 77 64 20002 60 89 192 (038)19978 55 77 181 20003 55 50 60 19979 ----- — --- 20004 46 24 22 (037)19980 A9 3 19 20005 61 48 24 (036)19981 53 2 2 6 20006 59 75 447 (035)19982 54 7 36 20007 69 82 229 (034)19983 50 59 71 20008 64 72 74 (033)19984 53 63 227 20009 56 25 37 19985 — — -------- 20010 32 1 29 (032)19986 1 1 11 20011 69 25 54 (031)19987 3 43 36 20012 58 35 71 (030)19988 9 4l 225 20013 62 64 78 (029)19989 22 25 42 20014 55 72 85 (028)19990 28 43 76 20015 58 71 159 (027)19991 51 78 212 20016 61 57 79 (026)19992 20 3 29 20017 32 52 29 (025)19993 50 49 69 20018 25 31 4o 19994 54 61 241 20019 65 54 73 19995 65 82 189 20020 50 33 25 19996 I 4 . 9 57 49 20021 57 42 60 SUR: Percent transmission 5 m below the surface. BOT: Percent transmission 1 m above the bottom. Numbers in parentheses refer to transmissometer stations. 320 Appendix C (Continued) Cruise 1273 Suspended (mg/l) SUSPENDED SEDIMENT SUSPENDED SEDIMENT AHF SUR BOT DEPTH AHF SUR BOT DEPTH (mg/l) (mg/l) (m) (mg/l) (mg/l) (m) 19972 1.8 1.1 19 19997 2.2 1.7 19 19973 1.6 2.2 36 19998 0.9 2.7 23 199974 2.0 2.1 18 19999 0.5 0.9 126 19975 2.0 1.1 28 20000 0.5 1.3 84 19976 1.1 1.9 47 20001 0.4 0.4 229 19977 0.7 0.9 64 20002 0.8 0.4 192 19978 1.0 0.7 181 20003 1.4 0.8 60 19979 1.1 0.8 -- 20004 2.0 1.7 22 19980 1.3 3.1 19 20005 1.6 1.0 24 19981 0.9 2.1 26 20006 1.0 1.0 447 19982 0.4 0 . 6 36 20007 0.9 0.7 229 19983 0. 6 0.3 71 20008 1.8 0.8 74 19984 1.0 1.0 227 20009 1.2 2.0 37 19985 1.3 5.8 -- 20010 1.6 6.2 29 19986 9.0 7.3 11 20011 0.6 2.6 54 19987 5. 6 4.3 36 20012 6. 2(?) 0.7 71 19988 3.4 Contam. 225 20013 2.2 0.8 78 19989 3.4 4.3 42 20014 1.2 0.5 85 19990 2.7 1.1 76 20015 1.3 0.9 159 19991 1.7 Contam. 112 20016 1.8 5.4 79 19992 1.4 1.4 29 20017 2.7 1.3 29 19993 1.4 1.6 69 20018 1.8 2.5 40 1999A 1.2 1.2 241 20019 1.4 0.8 73 19995 0.8 1.6 I89 20020 0.7 3.2 25 19996 6.4 2.5 49 20021 0.5 2.3 60 SUR: Concentration (mg/l) of suspended sediment from the surface. BOT: Concentration (mg/l) of suspended sediment 1 m above the bottom. 321 A p p e n d ix C ( C o n tin u e d ) C r u is e 1294 TRANSMISSION AHF SUR BOT DEPT3 W w (m) 20831 59 72 30 20832 62 83 30 20833 70 76 53 20834 75 81 54 20835 82 81 59 20836 83 77 68 20837 85 — 116 20838 83 — 120 20839 81 45 65 20840 78 71 50 20841 71 7 4 45 20842 70 75 37 20843 70 81 24 20844 72 75 19 20845 66 71 22 20846 55 52 23 20847 65 68 23 20848 70 72 26 20849 73 75 28 20850 70 71 36 20851 78 77 42 SUR: Percent transmission 1 BOT: Percent transmission 1 TRANSMISSION AHF SUR BOT DEPTH w W (m) 20852 80 70 48 20853 82 — 83 20854 81 — 171 20855 82 — 83 20856 80 68 53 208 57 7 4 65 45 20858 73 64 38 20859 71 51 32 20860 68 44 28 20861 68 39 25 20862 73 53 26 20863 69 57 36 20864 77 61 44 20865 81 — 77 20866 83 — 239 20867 79 — 166 20868 79 56 60 20869 71 66 34 20870 68 48 29 20871 68 23 23 20872 60 53 18 m below the surface, m above the bottom. 322 A p p e n d ix C ( C o n tin u e d Cruise 1310 AHF BOT DEPTH AHF BOT DEPTH AHF BOT DEPTI W (m) W (m) W (m) 21381 66 106 21^56 15 20 21^79 73 52 21382 82 65 21^57 10 31 21^80 ^5 ^0 21388 23 21 21^58 3 ^ ^7 21^81 31 29 21389 20 23 21^59 33 37 21^82 22 2h 21^06 16 21 21^60 20 27 21^83 27 33 21^07 10 23 21^61 20 25 21^84 k7 50 21^18 82 55 21^62 25 32 21^85 20 37 21^20 5^ k2 21^63 38 21^86 17 26 ^1^22 25 21 21^6^ 79 8^ 21^87 22 21^2^ 18 19 21^65 52 ^6 21^88 ^0 32 21^25 10 20 21^66 32 39 21^89 58 ^5 21^27 ^7 23 21^67 8 27 21^90 82 86 21^29 61 ^5 21^68 13 26 21^91 57 50 21^31 82 65 21^69 16 31 21^92 56 35 21^35 77 57 21^70 ^6 AA 21^93 39 21 21^37 kk 21^71 83 83 21^9^ ^0 38 21^39 A9 27 21^72 58 ^6 21^95 7^ 53 21^0 15 26 21^73 37 39 21^96 87 80 21^41 35 30 21^7^ 6 59 21^97 8^ 72 21^3 73 ^5 21^75 20 27 21^98 77 61 21^5 71 66 21^76 29 32 21^99 55 31 21^7 87 10 6 21^77 53 ^5 21500 65 ^ 3 21^55 1^ 32 21^78 79 75 21502 86 10^ BOT: Percent transmi s si on 1 m above the bottom 323 AHF 21655 21656 21657 21658 21659 21660 21661 21662 21663 21664 21665 21666 21667 21668 21669 21670 21671 21672 21673 21674 21675 21676 21677 21678 21679 21680 A p p e n d ix C C r u is e TRANSMISSION SUR BOT DEPTH 42 57 63 67 — 193 64 75 7 4 60 28 42 52 27 24 58 31 41 69 55 58 81 — 180 82 — 188 76 85 56 56 35 41 47 17 21 47 35 23 55 40 30 76 53 41 82 50 65 84 80 114 77 58 46 63 46 32 51 15 26 16 5 19 41 10 25 66 10 27 52 51 37 74 20 65 83 - - 175 (Continued) 1316 TRANSMISSION AHF SUR BOT DEPTH 21681 75 __ 188 21682 64 45 33 21683 63 50 30 21684 55 44 25 21685 19 12 22 21686 15 9 16 21687 54 29 26 21688 71 5 38 21689 81 72 102 21690 36 10 51 21691 67 10 33 21693 25 7 20 21694 42 6 23 21695 52 16 29 21696 63 43 35 21697 64 55 53 21698 77 — 162 21699 67 84 81 21700 61 37 41 21701 58 4 5 32 21702 32 23 28 21703 52 29 27 21704 44 29 31 21705 63 33 4o 21706 53 64 46 324 A p p e n d ix D Textural Variables A B C D E F Q G H I J AHF Med. Mean S.D. Skew. _£ Kurtosis $ Sa $ Si Sa/Mud Cruise 1271 19867 0.085mm 0.078mm 0.86^ 2.97 1.45 13.57 80. 73 17.18 4.19 19868 0.075 0.065 0.94 2.75 1.37 10.20 67.20 30.98 2.05 19869 0.097 0.095 0.91 2.29 1.43 13.10 91.33 7.53 10.53 19871 0.102 0.099 0.88 2.58 1.28 11.70 90.85 8.33 9.94 19872 0.091 O.O87 0.080 3.57 1.45 18.84 91.56 7.28 10.86 19873 0.095 0.094 0.81 2.^2 1.45 12.49 91.36 7.9 8 10.56 I9878 0.191 0.197 0.78 1.95 1.44 19.87 99.18 O.36 122.44 19880 0.080 0.068 0.98 3.0^ 1.45 10.70 75.37 22.50 3.06 19881 0.086 0.083 0.72 2.86 1.48 19.36 86.97 12.12 6.69 19882 0.076 0.065 1.00 2. 25 1.43 7.67 64.73 33.58 1.84 19883 0.080 O.O69 0.98 2.72 1.47 9.67 72.90 25.30 2. 69 19890 O.O63 0.054 1.12 2.03 1.47 5.91 50.51 46. 39 1.02 19891 0.720 0.060 1.09 2.07 1.48 5.96 61.64 36.27 1. 61 19892 0.081 0.073 0.84 3.15 1.48 13.86 78.20 20.53 3.59 19893 0.076 0.067 0.90 2.72 1.50 10.46 67.69 30.83 2.09 Cruise 1273^ 19973 0.023 0.015 1.69 -0.^1 1.21 -0.88 23.18 45.18 0.30 19974 0.384 0.386 0.68 0.16 -0.11 -0.80 100.00 0.00 0.00 19975 0.363 0.248 2.01 2.23 0.06 4.02 90.48 1.27 9.50 19976 0.083 0.061 1.34 2.26 1.38 3.55 84.54 7.46 5.47 19977 0.075 0.042 1.63 1.1^ 1.43 -0.22 67. 67 20.00 2.09 LO r \ 3 A p p e n d ix D ( C o n t in u e d ) , T e x t u r a l V a r ia b le s AHF Med. Mean S.D. Skew. fR Kurtosis $ Sa fo Si Sa/Mud 19978 0.044 0.027 1. 61 0.12 0.16 -1.05 40.75 46.88 0.69 19979 , , 19980A7 19980B4 0.104 0.091 1.29 2.7^ 1.10 7.33 93.47 0.00 14.32 0.067 0.034 1.66 0.69 0.48 -0.94 55-98 31.10 1.27 0.102 0.099 1.4l 2.22 1.00 5.45 92.72 0.66 12.73 19982 0.077 0.047 1.59 1.34 1.28 0.28 71.96 16.75 2.57 19983 0.064 0.032 1.62 0.52 0.41 -1.06 51.18 36.77 1.05 19984 0.017 0.011 0.95 0.49 1.50 0.56 1.29 72.99 0.01 19985 0.075 0.042 1. 67 1.09 0.86 -0.32 67.32 19.56 2.06 19986 O.O87 0.056 I.83 0.87 0.36 -0.32 70.14 19.42 2.35 19987 0.024 0.015 I.29 -0.42 1.42 0.32 13.74 67.07 0.16 19988 0.020 0.011 0.90 0.84 Cruise 1.50 12942 0.28 0.86 75-59 0.01 20825 0.291 0.257 1.41 1.99 -0.18 5. 60 94.90 3.43 18. 62 20826A 0.157 0.123 1-59 1.32 0.55 1.64 85.87 11.34 6.08 20826B 0.204 0.160 I.89 1.20 0.24 0.91 84. 61 11.77 5.50 20827A 0.620 0.547 0.67 2.04 1.21 4.20 100.00 0.00 0.00 20828A 0.088 0.078 1.08 2.05 1.45 5.85 89-55 7.92 8.57 20828B 0.086 O.O76 0.86 3.22 1.47 10.74 91.50 6.88 10.77 20829A 0.085 0.071 0. 94 3.03 1.45 8.44 89.34 8.44 8.38 20829B 0.085 0.070 0.96 2.86 1.44 7-39 88.43 9.37 7. 64 20830A 0.156 0.140 0.76 2.83 1.09 26.29 98.50 0.23 65-53 20830B 0.097 0.097 0.71 3.42 1.26 20.87 97. 64 I.25 41.45 V o O o\ Appendix D (Continued), Textural Variables AHF Med. Mean S.D. Skew. 21375 0.228 0. 21376 0.283 0. 21377 0.075 0. 23178 0.01^ 0. 21379 0.08^ 0. 21380 0.020 0. 21382 0.072 0. 21383 0.072 0. 2138^ O.O67 0. 21385 0.06^ 0. 21386 O.O67 0. 21387 0.092 0. 21388 0.173 0. 21390 0.085 0. 21391 0.081 0. 21392 0.076 0. 21393 0.078 0. 2139^ 0.079 0. 21395 0.075 0. 21396 0.086 0. 21397 0.069 0. 21398 O.O63 0. 21399 0.078 0. ro Cruise 0. 7^ 1. >57 0. 95 0. .89 1. 3^ 0. , 9^ 1. 37 -0, .07 1. 0. '91 1.k2 1,'38 1.^1 0,,80 1.^0 0.,86 1. ^3 0.'52 1. z j4 0,, k2 1.k2 0,,5k 1.2k 1,-58 1.08 2, .67 1.08 2. '07 1.26 1, • 35 1. 33 1, .15 1. 29 1.'38 1. 25 1. .51 1. 37 1.,02 1.58 0. '77 1.56 0. '53 1.50 0, .^3 1.i+8 0., 62 22? 263 04-9 031 060 055 043 ow 038 035 038 078 154 069 059 049 053 055 047 064 040 035 056 fa Kurtosi 13102 0.^1 7.55 0.21 2. 60 1.09 -0.32 0.81 -1.17 1.16 -0.03 1.53 0.89 1.03 -0.6^ 1.09 -0.55 0.79 -1.01 0.72 -1.09 0.81 1.00 1.52 2. 60 0.70 9.31 1.73 k. 72 1.58 1.6^ 1. 32 0.0^ 1.^6 0.66 1.52 1.08 1.22 -0.2^ 0.99 -0.17 0.86 -0.67 0.70 -1.03 1.31 0.3^ % Sa % Si 98.72 1. 29 98.06 1.9^ 67.19 29.71 ^1.30 5^. 92 72.k$ 2k. 50 7^.91 19.35 61.68 33. 60 62.86 32. k8 5^. 98 ^0.26 51. 11 ^3.37 55. ky 39. 88 85. 00 12. 55 9k. 83 3. 76 85- 98 11.58 77.59 19. 30 69.15 27. 06 73. 11 23. 12 75. k7 21.18 66. 59 29. 2k 71.99 2k.20 57.67 35. 30 51. 0^ ^1. 87 70.81 25.k? Sa/Mud 76.82 50.67 2.04 1.4-9 2.88 2.95 1.61 1. 69 1.22 1.05 1.25 5.67 18.33 6.13 3.46 2.24 2. 71 3.08 1.99 2.57 1.36 1.04 2.43 A p p e n d ix D ( C o n t in u e d ) , T e x t u r a l V a r ia b le s AHF Med. Mean S.D. Skew 21401 0.088 0.069 1.02 2.34 21402 0.078 0.052 1.29 1.37 21403 0.082 0.06l 1.18 1.85 21404 0.088 0.075 1.00 2.53 21405 0.084 0.068 1.04 2.31 21406 0.091 0.074 1.26 1.61 21407 0.157 0.134 0.96 3-37 21408 0.150 0.135 0.72 3.57 21409 0.089 0.086 0.57 3.90 21410 0.094 0.089 0.88 2.83 21411 O.O83 0.065 1.10 2.36 21413 0.176 0.153 1.98 0.93 21414 0.118 0.092 1.64 1.05 21415 0.084 0.059 1.48 1.10 Cruise 21642 0.080 0.056 1.40 1.03 21643 0.081 0.056 1.48 1.08 21644 0.027 0.017 1.20 -0.55 21645 0.073 0.045 1.45 0.69 21646 0.219 21648 0.077 0.051 1.33 1.11 21650 0.038 0.025 1.41 -0.25 21651 0.088 0.064 1. 56 1.01 21652 0.057 0.031 1.59 0.33 V j j ro 00 _R Kurtosis $ Sa $ Si Sa/Mud 1. 72 4. 90 86.22 11.89 6.26 1.45 0.61 72.81 23.48 2. 68 1. 64 2.38 80.39 16. 61 4.10 1.73 6. 74 89.29 8.66 5.68 1.48 4.68 85. 71 12.15 6.00 1.47 2.15 83.02 14.31 4.89 O.78 13.19 95.38 3.04 20.66 0.86 19.16 98.03 1.30 49.84 1. 78 22.21 95.45 3.11 27.89 1. 66 9.69 95.16 4.84 19. 66 1. 72 4.55 84. 74 12.16 15.26 0. 60 0.41 85.32 10.61 5.81 0.71 0.40 79.64 17.06 3.91 I.29 0.33 73-57 21. 68 2.78 13162 1.35 0.26 76.50 23.86 2..78 1.50 0.43 73.02 21. 70 2. • 71 1.59 0.86 14.84 73.25 0. .17 0.99 -0.68 61.95 33.69 1. ,63 0.74 98.87 1.13 87..58 1.32 0.00 69.62 27.00 2. .29 1.10 -0.73 32.19 60.34 0. . 27 1.05 0.13 73-56 21.75 2..78 0.62 -1.06 47.54 42.26 0. ■ 91 Appendix D (Continued), Textural Variables AHF Med. Mean S.D. Skew. 21653 0.480 0 21729 0.084 0 21730 0.029 0 22531 0.082 0. 22533 0.073 0. 2253A 0.128 0. 22535 0.125 0. 22536 0.104 0. 22537B 0.030 0. 22538 O.O83 0. 22539 0.085 0. 22540 0.091 0. 22542 0.135 0. 225A3 0.082 0. 22544 0.062 0. 225A5 0.051 0. 22546 0.074 0. 225^7 O.O78 0. 225A8 0.083 0. 225^9 0.086 0. 22550 0.102 0. 22551 0.099 0. 22552 0.082 0. V u o ru MD 1.54 0.08 1.68 1.10 1.66 -0.17 Cruise 0.092 3.15 1. 35 1.41 1. 39 1.61 1.32 1. 55 0. 97 2.56 0.88 3. 68 1. 03 2.28 0. 99 3.07 0. 97 2. 45 1. 75 0. 77 1.56 1.61 1.48 1.46 1. 65 0. 99 1. 25 2. 31 1. 05 2. 85 1.02 1. 17 1.10 2.74 1. 25 2.41 0. 97 2. 69 1.02 3. 24 030 056 019 072 062 107 109 092 082 069 075 O87 120 064 0A7 040 059 066 077 076 090 096 070 Kurtosis $ Sa f o Si -0.99 42.65 ^9.17 1.30 0.11 72.53 18.22 0.55 -1.06 28. 61 48.08 1 —1 13 12.81 78.79 19.37 2.68 59-24 37.39 3-99 81.14 16.48 4.89 85-53 12.64 IO.96 88.62 10.14 18.06 89.52 8.44 6.09 80.95 18.02 12.12 83.06 19.40 12.33 86.87 11.24 1.26 76.44 21.25 2.46 67.81 25.9^ 2.38 49.39 43.40 0.73 40.12 50.72 5.80 63. 85 31.25 9.69 73.09 23.93 9.58 78. 32 19.70 9.90 82.86 14.06 3.17 84.87 11. 63 12.19 89.63 8.63 11.55 80. 64 16. 65 Sa/Mud 0. 74 2. 64 0.40 3.71 1.45 A. 30 6.13 7.79 8.55 A. 25 3.80 6.62 3.24 2.11 0. 98 0. 67 1.77 2. 72 3.61 A. 83 5.62 8.64 4.14 A p p e n d ix D (C o n tin u e d ) , T e x t u r a l V a r ia b le s AHF 22553 2255^ 22555 22556 22557 22558 22559 Med. Mean S.D. Skew. ! 3 r Kurtosis f Sa $ Si Sa/Mud 0.077 0.065 1.04 3.01 10.46 70.91 25. 84 2.44 0.073 0.060 1.0? 2.65 7.67 63. 64 33-35 1.75 0.080 0.070 0.92 3.12 12.43 76.00 22.04 3.17 0.124 0.105 1.26 1.96 5.84 83.02 14.68 4. 89 0.14-3 0.114 1.25 0.30 0.06 62.46 37.13 1. 66 0.171 0.144 1.46 1.33 3.78 80.20 17.17 4.05 0.071 0.061 1.03 2.30 7.57 61.21 36.45 1. 58 A: AHF Station number; B: median grain diameter in mm; C: mean grain diameter in mm; D: standard deviation in phi units; E: skewness; Fs skewness calculated according to method discribed in text, p. 2^7; G: kurtoses; H: percent sand; Is percent silt; J: sand/mud ratio. In calculating textural variables for samples collected during Cruises 1271 and 1335 the fractional weight of the total sample was determined for each whole phi interval down to 80 (sand through silt); the clay fraction (9-110) was not differentiated into whole phi units and the total clay weight assigned to the 8-90 class. In calculating textural variables for samples collected during Cruises 1273, 129^, 1310 and 1316 the fractional weight of the total sample was determined for each whole phi interval down to ^0 (sand portion); the total silt fraction (5-80) was assigned arbi trarily to the 6-70 class and the total clay fraction (9-110) was assigned to the 8-90 class. V jJ V jO o 331 3 -'Samples from Cruise 1335 were analyzed using both methods described above. All data presented in Table III were calculated according to the procedure described under footnote 2. ^These stations were misidentified in labelling. AHF 19980A is probably 19981 and 19980B is probably 19980. Isopleths of textural variables shown on maps in the text are based largely on data from Cruises 1271» 129^» 1310 and 1316. Cruises 1273 and 1335 were used to fill-in gaps in regional coverage.

Asset Metadata

Creator Karl, Herman Adolf (author)

Core Title Processes influencing transportation and deposition of sediment on the continental shelf, Southern California

Contributor Digitized by ProQuest (provenance)

Degree Doctor of Philosophy

Degree Program Geological Sciences

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

Tag Marine Geology,OAI-PMH Harvest,Sedimentary Geology

Language English

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c29-343607

Unique identifier UC11219104

Identifier DP28544.pdf (filename),usctheses-c29-343607 (legacy record id)

Legacy Identifier DP28544.pdf

Dmrecord 343607

Document Type Dissertation

Rights Karl, Herman Adolf

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA