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Late Pleistocene ventilation history of the North Pacific as seen through delta carbon-13 records of the Southern California borderland

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Late Pleistocene ventilation history of the North Pacific as seen through delta carbon-13 records of the Southern California borderland

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Content INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type o f computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. 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LATE PLEISTOCENE VENTILATION HISTORY OF THE NORTH PACIFIC AS SEEN THROUGH 5I3C RECORDS OF THE SOUTHERN CALIFORNIA BORDERLAND Copyright 1998 Michael James Neumann A Thesis Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Earth Sciences August 1998 Michael James Neumann Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 1393180 Copyright 1998 by Neumann, Michael James All rights reserved. UMI Microform 1393180 Copyright 1999, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. U N IV E R SIT Y O F S O U T H E R N C A L IF O R N IA TH E G R A D U A T E S C H O O L U N IV E R S IT Y AARK LOS A N G E L E S . C A L IF O R N IA 80CI07 This thesis, written by M ich ael James Neumann under the direction of h.i®. Thesis Committee, and approved by all its members, has been pre sented to and accepted by the Dean of The Graduate School, in partial fulfillment of the requirements for the degree of Master of Science, Geology u s t 1 8 , 1998 Date. THESIS COMMITTEE katrmax Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Dedicated to my Mom, who also happens to be my best friend. Thanks for the love, support, and strength you have given me throughout my life. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS DEDICATION ii LIST OF FIGURES v LIST OF TABLES xi ABSTRACT xii INTRODUCTION 1 GEOLOGY OF THE SOUTHERN CALIFORNIA BORDERLAND 10 Inner Basins 1 1 Descanso Plain 1 1 Central Basins 14 Animal Basin 14 San Clemente Basin 14 San Nicolas Basin 14 Outer Basins 15 East Cortez Basin 15 No Name Basin 15 Tanner Basin 16 OCEANOGRAPHY OF THE SOUTHERN CALIFORNIA BORDERLAND 17 California Current 17 California Countercurrent 18 California Undercurrent 18 METHODS 24 Sediment Sampling/Analysis 24 Isotopes: Methods and Interpretation 24 AGE MODELS 33 Animal Basin 36 No Name Basin 39 San Nicolas Basin 45 Descanso Plain 45 East Cortez Basin 50 San Clemente Basin 50 Tanner Basin 57 Summary 57 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RESULTS 65 Stage 6 66 Stage 6 Summary 70 Stage 5 71 Stage 5 Summary 72 Stage 4 73 Stage 4 Summary 78 Stage 3 79 Stage 3 Summary 81 Stage 2 81 Stage 2 Summary 85 DISCUSSION 88 CONCLUSIONS 97 REFERENCES 99 APPENDIX A 103 APPENDIX B 106 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. V LIST O F FIGURES FIGURE 1 - Map of the Southern California Borderland showing positions of silled marine basins and locations of piston cores (black dots) used in this study.............................................................. 2 FIGURE 2 - Relationship between dissolved oxygen and the 81 3 C of dissolved inorganic carbon (DIC). We utilize this relationship in reconstructing changes in dissolved oxygen concentrations for the Southern California Borderland into Stage 6........................................... .4 FIGURE 3 - Schematic cross section of the SCB, after Gorsline and Emery (1959), modified from Gorsline and Teng (1989). Cores for this study were recovered from each of the basin categories: inner, central and outer............................................................................................ 12 FIGURE 4 - Schematic drawing of flow for the California Current and California Countercurrent over the silled marine basins of the SCB. The California Current is one of four major eastern boundary currents in the world. The California Countercurrent defines surface circulation in the SCB and can be thought of as a semi-permanent eddy of the California Current (Modified from Hickey, 1993).......................................................... 19 FIGURE 5 - Schematic drawing of flow for the California Undercurrent. The Undercurrent flows from the southeast and supplies deep water to the marine basins of the SCB. The source region of the undercurrent is poorly understood, but evidence indicates it is of southerly (possibly the Eastern Equatorial Pacific) rather than sub-arctic origin. (Modified from Hickey, 1993).............................................................................. 20 FIGURE 6 - As waters enter the SCB through the California Undercurrent flow is progressively impeded by a series of shallower sills as waters travel from southeast to northwest. Water exchange is regulated by horizontal diffusion with water just below the depth of each sill. In this manner, individual basins act as “traps” and sample the water column at their respective sill depth................................................................. 22 FIGURE 7 - Waters below sill depth are nearly uniform in temperature and salinity. This is an effect of the basin acting as a “trap” for water at sill depth. Waters in the basins are of uniform property as sampled by the sill (From Emery, 1960) 23 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. FIGURE 8 - Typical profile of 81 ;,C of DIC for the SCB. Plotted points indicate core top analyses of various benthic foraminifera. C. makanii appears to most accurately record the isotopic composition of the water................................... 26 FIGURE 9 - Relationship between dissolved oxygen and the S1 3 C of dissolved inorganic carbon (DIC). We utilize this relationship in reconstructing changes in dissolved oxygen concentrations for the Southern California Borderland into Stage 6................................................................................................................................... 30 FIGURE 10 - 81 3 C record from ODP Site 849. ODP Site 849. located west of the East Pacific Rise, offers a nearly continuous stable isotopic record of Pacific variability, which approximates the global oceanic signal (Mix et a i , 1995)...................................................................................................... 31 FIGURE 11 - Comparison of 5I80 records from SPECMAP and ODP Site 849. Note the approximate 10 kyr phase lag between the two records. Because of the discrepancy, an adjustment was made to the Site 849 age model to bring the two records into agreement........................................................................... 37 FIGURE 12 - Age model for Animal Basin. Age control for the upper 40 kyr of the sequence is based on l4C dates. Beyond 40 kyr, age control is based on correlation to of the benthic and planktonic S1 8 0 records to global references; SPECMAP for the planktonic records and ODP Site 849 for the benthic records.........................................................................................................38 FIGURE 13 - Comparison of the age model based benthic SlsO record for Animal Basin and ODP Site 849. ODP Site 849 acts as a monitor of changes in the global 5I80 signal as seen in the deep Pacific. Horizontal lines indicate horizons at which I4C samples were analyzed. The approximate 1. \%c shift at 120 kyr was used as the 8lsO tie-point for the age model..........................................40 FIGURE 14 - Comparison of the age model based planktonic S1 8 0 record for Animal Basin and SPECMAP. SPECMAP provides a 51 8 0 record that reflects changes in the global 5 I80 pool due to changes in ice volume. Horizontal lines indicate horizons at which l4C samples were analyzed..................... 41 FIGURE 15 - Age model for No Name Basin. Age control for the upper 40 kyr of the sequence is based on l4C dates................................................................... 42 FIGURE 16 - Comparison of the age model based benthic 5 I80 record for No Name Basin and ODP Site 849. ODP Site 849 acts as a monitor of changes in the global 8lsO signal as seen in the deep Pacific. Horizontal lines indicate horizons at which 1 4 C samples were analyzed..........................................43 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. vii FIGURE 17 - Comparison of the age model based planktonic 81 8 0 record for No Name Basin and SPECMAP. SPECMAP provides a 5 1 8 0 record that reflects changes in the global 5 I80 pool due to changes in ice volume. Horizontal lines indicate horizons at which l4C samples were analyzed......................44 FIGURE 18 - Age model for San Nicolas Basin. Age control for the upper 40 kyr of the sequence is based on 1 4 C dates. Beyond 40 kyr, age control is based on correlation to of the benthic and planktonic 8lsO records to global references; SPECMAP for the planktonic records and ODP Site 849 for the benthic records.............................................................................................................46 FIGURE 19 - Comparison of the age model based benthic 5I80 record for San Nicolas Basin and ODP Site 849. ODP Site 849 acts as a monitor of changes in the global S1 8 0 signal as seen in the deep Pacific. Horizontal lines indicate horizons at which l4C samples were analyzed. The approximate 1.1 %c shift at 120 kyr was used as the 51 8 0 tie-point for the age model.................................................... 47 FIGURE 20 - Comparison of the age model based planktonic 51 8 0 record for San Nicolas Basin and SPECMAP. SPECMAP provides a 51 8 0 record that reflects changes in the global 5 1 8 0 pool due to changes in ice volume. Horizontal lines indicate horizons at which l4C samples were analyzed....................48 FIGURE 21 - Age model for Descanso Plain. Age control for the upper 40 kyr of the sequence is based on 1 4 C dates. Beyond 40 kyr, age control is based on correlation to of the benthic and planktonic 8lsO records to global references; SPECMAP for the planktonic records and ODP Site 849 for the benthic records 49 FIGURE 22 - Comparison of the age model based benthic 8lsO record for Descanso Plain and ODP Site 849. ODP Site 849 acts as a monitor of changes in the global 8lsO signal as seen in the deep Pacific. Horizontal lines indicate horizons at which I4C samples were analyzed. The approximate 1.1 %c shift at 120 kyr was used as the S1 O tie-point for the age model.............................................51 FIGURE 23 - Comparison of the age model based planktonic 8lsO record for Descanso Plain and SPECMAP. SPECMAP provides a 8lsO record that reflects changes in the global 8lsO pool due to changes in ice volume. Horizontal lines indicate horizons at which 1 4 C samples were analyzed. The gap in the record represents an interval in which numbers of G. bulloides were not abundant enough for analysis.............................................................................................................. 52 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. viii FIGURE 24 - Age model for East Cortez Basin. Age control for the upper 40 kyr of the sequence is based on l4C dates. Beyond 40 kyr, age control is based on correlation to of the benthic and planktonic 5 I80 records to global references; SPECMAP for the planktonic records and ODP Site 849 for the benthic records............................................................................................................... 53 FIGURE 25 - Comparison of the age model based benthic Sl80 record for East Cortez Basin and ODP Site 849. ODP Site 849 acts as a monitor of changes in the global 8I80 signal as seen in the deep Pacific. Horizontal lines indicate horizons at which l4C samples were analyzed. The approximate l.l%o shift at 120 kyr was used as the 51 O tie-point for the age model...................... 54 FIGURE 26 - Comparison of the age model based planktonic S1 8 0 record for East Cortez Basin and SPECMAP. SPECMAP provides a 5lsO record that reflects changes in the global 8 I8 0 pool due to changes in ice volume. Horizontal lines indicate horizons at which l4C samples were analyzed...................... 55 FIGURE 27 - Age model for San Clemente Basin. Age control for the upper 40 kyr of the sequence is based on 1 4 C dates. Beyond 40 kyr, age control is based on correlation to of the benthic and planktonic 8lsO records to global references; SPECMAP for the planktonic records and ODP Site 849 for the benthic records................................................................................56 FIGURE 28 - Comparison of the age model based benthic 8lsO record for San Clemente Basin and ODP Site 849. ODP Site 849 acts as a monitor of changes in the global 8lsO signal as seen in the deep Pacific. Horizontal lines indicate horizons at which 1 4 C samples were analyzed................ 59 FIGURE 29 - Comparison of the age model based planktonic 8lsO record for San Clemente Basin and SPECMAP. SPECMAP provides a Sl80 record that reflects changes in the global 8lsO pool due to changes in ice volume. Horizontal lines indicate horizons at which 1 4 C samples were analyzed........................................................................................................................60 FIGURE 30 - Age model for Tanner Basin. Age control for the upper 40 kyr of the sequence is based on 1 4 C dates. Beyond 40 kyr, age control is based on correlation to of the benthic and planktonic Sl80 records to global references; SPECMAP for the planktonic records and ODP Site 849 for the benthic records..........................................................................................61 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IX FIGURE 31 - Comparison of the age model based benthic 8I80 record for Tanner Basin and ODP Site 849. ODP Site 849 acts as a monitor of changes in the global 8 I80 signal as seen in the deep Pacific. Horizontal lines indicate horizons at which 1 4 C samples were analyzed. The minimum value at 120 kyr was used as the 8lsO tie-point for the age model................................. 62 FIGURE 32 - Comparison of the age model based planktonic 5I80 record for Tanner Basin and SPECMAP. SPECMAP provides a SlsO record that reflects changes in the global 8I80 pool due to changes in ice volume. Horizontal lines indicate horizons at which 1 4 C samples were analyzed........................................................................................................................63 FIGURE 33 - Plot showing variation in A8)3 C for Descanso Plain. AS1 3 C represents changes in 8I3 C in excess of global S1 3 C variation. We assume that these variations are primarily driven by changes in dissolved oxygen, and hence A8I3C acts as a monitor of dissolved oxygen content..................................................................................................................... 67 FIGURE 34 - Plot showing variation in A81 3 C for East Cortez Basin. A8I3C represents changes in 8 I3 C in excess of global S1 3 C variation. We assume that these variations are primarily driven by changes in dissolved oxygen, and hence A81 3 C acts as a monitor of dissolved oxygen content......................................................................................................................68 FIGURE 35 - Plot showing variation in A8I3 C for Animal Basin. ASI3C represents changes in S1 3 C in excess of global 8 I3 C variation. We assume that these variations are primarily driven by changes in dissolved oxygen, and hence A8I3C acts as a monitor of dissolved oxygen content.................................................................................................................... 69 FIGURE 36 - Plot showing variation in A8I3C for San Nicolas Basin. A81 3 C represents changes in 8 I3 C in excess of global 81 3 C variation. We assume that these variations are primarily driven by changes in dissolved oxygen, and hence ASI3C acts as a monitor of dissolved oxygen content..................................................................................................................... 74 FIGURE 37 - Plot showing variation in A8I3C for Tanner Basin. A8I3C represents changes in S1 3 C in excess of global SI3C variation. We assume that these variations are primarily driven by changes in dissolved oxygen, and hence A8I3C acts as a monitor of dissolved oxygen content.................................................................................................... 75 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. X FIG U RE 38 - Plot showing variation in A81 3 C for San Clemente Basin. A8I3 C represents changes in 51 3 C in excess of global 8I3C variation. We assume that these variations are primarily driven by changes in dissolved oxygen, and hence A81 3 C acts as a monitor of dissolved oxygen content..................................................................................................................... 76 FIGU RE 39 - Plot showing variation in A8I3C for No Name Basin. A81 3 C represents changes in 8I3C in excess of global 8I3C variation. We assume that these variations are primarily driven by changes in dissolved oxygen, and hence A81 3 C acts as a monitor of dissolved oxygen content..................................................................................................................... 82 FIG U RE 40 - A8I3C for the seven basins of the study....................................................87 FIG U RE 41 - 1 4 C plot of benthic and planktonic foraminifera from the same sediment horizon. Decreases in the age gradient are coincident with intervals in which the AS1 3 C signal suggests that dissolved oxygen was increased....................................................................................................................... 90 FIGU RE 42 - 1 4 C plot of benthic minus planktonic age based on analysis of foraminiferal tests from the same sediment horizon. Note that for certain horizons in San Clemente and San Nicolas Basins the age difference exceeds 2 kyr. This possibly indicates reworking or down-slope transport of sediment at these horizons................................................................................................................... 91 FIGU RE 43 - A8I3C plot for East Cortez Basin. The excursion of approximately 0.8% o at 80 kyr represents peak low oxygen conditions for the SCB for the last 200 kyr. This excursion corresponds to an approximate drop in dissolved oxygen of 150pmol/kg...................................................................................95 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES TABLE 1 - Occurrence of Live Assemblages of M. pompiliodes..................................7 TABLE 2 - SCB Basin Descriptions and Data................................................................13 TABLE 3 - Core Top Analyses of Various Benthic Foraminifera...............................29 TABLE 4 - l4C Summary Data..........................................................................................34 TABLE 5 - Sedimentation Rate Summary Data............................................................ 64 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. XII ABSTRACT The Southern California Borderland (SCB). due to its location on the eastern margin of the North Pacific, and unique geology and oceanography, provides an ideal setting for study of North Pacific geochemical cycling during the Pleistocene. The SCB is ventilated by waters which originate in the equatorial Pacific. Changes in the concentration of oxygen and nutrients in these source waters, resulting from biogeochemical changes in the source water region, are transmitted to the SCB via deep-water circulation. Deep waters that fill the basins today are low in oxygen and rich in nutrients. Changes in the amount of oxygen entering the basins, via deep water circulation, affects the geochemical gradients within the Borderland Basins. Such changes are recorded in the geochemistiy and fossil assemblages within basin sediments. We have investigated changes in geochemical gradients within the SCB basins by isotopically analyzing the fossil assemblages of 7 piston cores located along a north-south transect through the SCB. The carbon and oxygen isotopic compositions of both benthic and planktonic foraminifera were measured in each core. Choice of benthic species was based on ability to record the isotopic composition of the surrounding dissolved inorganic carbon (DIC) pool. We define a parameter A51 3 C that is a measure of 5I3C changes in excess of global variation and interpret it as a measure of changes in dissolved oxygen. Using a relationship between 5I3C of DIC and dissolved oxygen, relative changes in oxygen concentrations are reconstructed by Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. xiii assuming a constant Redfield relationship between 8I3 C, phosphate, and oxygen during the Pleistocene. All cores exhibit temporally coincident trends in A8I3C, 8I3C, and SlsO. The A8I3C record shows that during Stage 2 to Stage 5, the ventilation condition of the SCB has varied from being relatively less ventilated to relatively more ventilated than during the Holocene. There appears to be no correlation of ventilation condition to glacial versus interglacial periods. We interpret these results as stemming from two possible mechanisms: 1) a decrease/increase in the oxygen content of source waters entering the SCB, and/or 2) an decrease/increase in the “travel time” of the source water to the SCB, allowing more/less time for oxidation of organic matter. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INTRODUCTION The Southern California Borderland i'SC.B > encompasses an area from south of the I .S-Mexico border to Point Conception. California. Due to its unique ecology and oceanography, the area offers an ideal setting in which to study North Pacific biogeochemicai cycles. Because of this, in May of 19P5. during an Ocean Drilling Program tODPt site survey cruise aboard the R/V Manner Ewing, seven piston cores were recovered from basins within the SCB. Cores were collected to assess the paleoceaDography of the region and elucidate climate-induced environmental changes along the eastern margin of the North Pacific. Cores were recovered along a southeast to northwest transect from 31' 15.52' North latitude (Animal Basin') to 32'' 51.51' North latitude (Tanner Basin) (Figure U. Tins study focuses on the stable isotopic records from six of the cores collected on the survey and an additional core collected on a previous cmise. This study investigates the temporal variability in downeore < V V as recorded in benthic foraminiferal tests to reconstruct the ventilation history of the SCB and North Pacific to marine glacial Stage 6. The SCB provides a sensitive region in which to study North Pacific geochemical cycling due to its high sedimentation rates, series of silled marine basins, and location on the eastern margin of the North Pacific (Sec Oceanography section). Benthic foraminiferal tests are unique paleo-environmental recorders because certain species secrete their tests in isotopic equilibrium with the surrounding water. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 34° c > v 1 v- 1 - 4 . \ ^ ' ’ C b ' V c k ~ / \\Vi • * 32° r \ A i \ 3 K 4F N ^ . _ _ ^ ^ - V . X \ i n g o 117° 1 K ey • - Core Location 02 - Anim al Basin 03 - Descanso Plain 04 - East C ortez Basin 05 — San Clem ente Basin 08 - San N icolas Basin 09 - T anner Basin A H F - No Nam e Basin FIGURE 1 - Map of the Southern California Borderland showing positions of silled marine basins and locations of piston cores (black dots) used in this study. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 while others more directly record the isotopic composition of dissolved inorganic carbon (DIC) in the surrounding water (McCorkle and Keigwin, 1994; Sarnthein, 1994). We rely on this phenomena to reconstruct past changes in DIC by isotopically analyzing the fossil assemblage of benthic foraminiferal tests. Grossman (1982) and Broeker and Peng (1982) have shown that a direct relationship exists between 81 3 C of DIC and dissolved oxygen concentrations (Figure 2). This relationship has been demonstrated for the SCB, as well as for the world’s oceans (Grossman, 1982, Broeker and Peng, 1982). We utilize the relationship between DIC 8I3C and dissolved oxygen to reconstruct relative changes in bottom water dissolved oxygen for the North Pacific from the present to Stage 6. In using this relationship to reconstruct relative changes in dissolved oxygen we assume that the slope of the relationship between 81 3 C of DIC and dissolved oxygen has not varied through time. In reconstructing the ventilation history of the California Margin we further define a parameter, A81 3 C, which is a monitor of changes in 8I3C in excess of global changes, and, we purport, is primarily a function of changes in dissolved oxygen levels, For marine glacial Stages 1 through mid-Stage 3, changes in the benthic- planktonic radio-carbon (l4C) age gradient are also investigated in support of the 8I3 C and A81 3 C data. Previous work suggests that intermediate water oxygen levels in the SCB have varied dramatically on glacial to interglacial timescales (Kennett and Ingram, 1995). Today, water that enters the SCB is low in oxygen and rich in nutrients. This, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 Dissolved Oxygen vs 33 C of DIC 200 u > £ E 150 3 I 100 •o 4 ) > I 50 C O Q A A a m SCB GEOSECS Sta.201 GEOSECS Sta.226 GEOSECS Sta.326 -1.5 -1 -0.5 0 0.5 1 1.5 2 6 3C of DIC(%.) FIGURE 2 - Relationship between dissolved oxygen and the 81 3 C of dissolved inorganic carbon (DIC). We utilize this relationship in reconstructing changes in dissolved oxygen concentrations for the Southern California Borderland into Stage 6. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 coupled with a high rain of organic matter, which consumes oxygen as it is oxidized, can drive basins toward anoxia. Santa Barbara Basin is an example. Today, Santa Barbara Basin is anoxic, producing conditions under which laminated sediments are deposited. Sediment records from the basin indicate that anoxic conditions have dominated throughout the Holocene (Kennett and Ingram, 1995; Behl and Kennett, 1996). It has been found, however, that the laminations are punctuated by periods of bioturbated sediments (Kennett and Ingram, 1995; Behl and Kennett, 1996). This finding suggests that, at times, Santa Barbara Basin had dissolved oxygen concentrations above lOpmol/kg, allowing for bioturbation. Kennett and Ingram (1995) and Behl and Kennett (1996) found that the intervals of bioturbated sediments (indicating high bottom water oxygen concentrations) temporally coincide with characteristically cold time intervals (glacials and stadials), and conversely, intervals of laminated sediments coincide with characteristically warm time intervals (inter-glacial and inter-stadials). Similar sedimentological patterns have been reported for basins in the Gulf of California (Keigwin and Jones, 1990). Kennett and Ingram (1995), and Behl and Kennett (1996), interpret this finding as an indication that during Stage 2, bottom water within the SCB had higher levels of dissolved oxygen, and that during Stage 3, low oxygen conditions dominated as evidenced by a return to laminated sediments (Behl and Kennett, 1996). In addition to the sedimentological evidence, Kennett and Ingram (1995) investigated changes in the benthic-planktonic radiocarbon (l4C) age gradient. In Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 principle, changes in the apparent age difference between surface and deep water, a proxy for ventilation, can be reconstructed by !4C dating of benthic and planktonic foraminifera from the same sediment horizon (Broeker ct a l. 1990). They found that young bottom waters were associated with cool intervals, and conversely, older bottom waters were associated with warm intervals. They interpret this to indicate that during cold intervals bottom waters reaching Santa Barbara basin are relatively more ventilated and most likely sourced in the proximal intermediate waters of the North Pacific (Kennett and Ingram, 1995). The increased age of bottom waters during warm intervals is interpreted to reflect increased contribution of low oxygen waters from more distal sources. The findings of Kennett and Ingram (1995) and Behl and Kennett (1996) are not without complication. Today, the sill depth of Santa Barbara basin coincides with the core of the oxygen minimum zone (OMZ), and. thus, bottom water oxygen levels are heavily influenced by fluctuations in both the thickness and depth of the OMZ. It is possible that the periods of bioturbated sediments are actually manifestations of changes in the thickness and depth of the OMZ and are not indicative of source waters with higher concentrations of dissolved oxygen. The record from Santa Barbara Basin is not the only record that supports the notion of higher dissolved oxygen levels in the SCB during the last glacial. Blake and Douglas (1981) reported the presence of fossil assemblages of Melonis pompiliodes in glacial sediments in numerous SCB basins. Live assemblages of M. pompiliodes have been reported throughout the world’s oceans under varying Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 TABLE 1 Occurence of Live Assemblages of M. Pompiliodes Location Depth (m) Oxygen (gmol/kg) Pot. Temp. (°C) Salinity (PPt) Reference North Atlantic 1,995 240 3.2 35.00 Phleger et. al, 1953 Circumpolar Current 3,000 210 1.0 34.66 Bandy and Echols, 1964; Echols, 1971 Antarctica 3,000 220 -0.2 34.68 Bandy and Echols, 1964; Echols, 1971 North Pacific 2,300 100 1.4 34.66 Kulm and Fowler, 1974; Bandy and Chierici, 1966 California Margin 2,300 100 1.7 34.63 Bandy and Chierici, 1966 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 oceanographic conditions (Table 1). It is significant, however, that although salinity, temperature, depth, and nutrient concentrations vary between locations, dissolved oxygen levels are above 100 pmol/kg. Blake and Douglas (1981) further note the presence of live assemblages of M. pompiliodes in the SCB in North San Quintin Basin, which has a dissolved oxygen concentration above the 100 pmol/kg threshold. Today, dissolved oxygen concentrations in the SCB are, on average, 45 pmol/kg. If the distribution of M.pompiliodes is controlled by a dissolved oxygen threshold, it is significant to note that numerous basins of the SCB contain fossil assemblages of M.pompiliodes during Stage 2. Basins with glacial fossil assemblages of M. pompiliodes then indicate that dissolved oxygen concentrations across the SCB were substantially higher during Stage 2. In addition to finding fossil assemblages of M. pompiliodes in numerous SCB basins during Stage 2, Blake and Douglas note that the species disappeared first from the northern basins (shallowest sills) at approximately 16 kyr and progressively, over the next 6 kyr, from the southern basins (deeper sills). This pattern of disappearance compares with the route of deep water circulation in the SCB (Blake and Douglas, 1980). We interpret this finding as possibly signaling a retreat of a water mass with high dissolved oxygen content at the end of Stage 2. In addition to the work of Kennett, Ingram, Behl, Keigwin, Jones, Blake and Douglas, other studies indicate that dissolved oxygen concentrations of the North Pacific have varied on glacial to interglacial timescales. In 1996, using the 1 4 C age difference between benthic and planktonic foraminifera, Ca/Cd ratios, as well as benthic S1 8 0 and SI3C records, Van Geen et al. investigated sediment records from two cores along the California margin, north of the SCB, to reconstruct the ventilation Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 history of the North Pacific. In their study, they find that the California margin cores record reduced ventilation during intervals coinciding with periods of reduced ventilation (periods of laminated sediments) in Santa Barbara Basin and Gulf of California Basins. They conclude that the records from Santa Barbara Basin and the Gulf of California records are indicative of larger scale ocean circulation changes and that the California margin is a region sensitive to changes in the North Pacific. In this study we reinvestigate the notion set forth, in part, by Kennett and Ingram (1995), Behl and Kennett (1996), Keigwin and Jones (1990), Blake and Douglas (1980), and Van Geen et al. (1996), that the North Pacific may have been relatively more ventilated during Stage 2 and relatively less ventilated from the middle of Stage 3 to the beginning of Stage 2. We further extend the investigation beyond mid-Stage 3 to Stage 6. Through analyzing downcore changes in the A51 3 C record of seven SCB basins, we reconstruct the ventilation history of the SCB, and the North Pacific, through the late Pleistocene. Unlike Santa Barbara Basin and the basins of the Gulf of California, the basins of this study have sill depths well below the OMZ, eliminating any physiographic effects on dissolved oxygen concentrations. We hold that oxygen levels within the basins of this study are primarily a function of source water dissolved oxygen and are not driven by fluctuations in the thickness and depth of the OMZ. Furthermore, the southeast-northwest transect of the seven basins provides a comprehensive record of change within the SCB. Possible driving mechanisms, and associated implications, are also considered. Following is a brief introduction to the geology and oceanography of the SCB, followed by the results, analysis and findings of the study. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 0 GEOLOGY OF THE SCB The west coast of North America is characterized by a morphology typical of a convergent plate boundary. Narrow shelves (average of 25km) grading to steep continental slopes, terminating in deep trenches, and high relief coastal ranges are all common features along the margin (Dailey et al., 1993). The exception, however, is the SCB. The SCB is characterized by a broad shelf (up to 300km) and a series of silled marine basins that resemble a checker-board pattern (Howell et a l, 1980). The checker-board morphology of the SCB is a product of transform motion along the Pacific and North American plate. Over the past 5-6 Ma the characteristic right-slip motion along the margin has been concentrated in the San Andreas fault zone and has controlled the structural development of the SCB (Gorsline and Teng, 1989). This lateral motion has shifted a series of blocks producing 24 “pull apart” silled marine basins (Atwater, 1989). Basins are oriented along southeast to northwest trends and are further arranged in approximately three parallel rows from east to west. Basin floors range from approximately 1,000 meters deep to greater than 2,500 meters deep. Sill depths generally decrease form south to north, and range in depth from as shallow as 425 meters to as deep as 2,000 meters. Although the physiography of basins within the SCB varies dramtically, basins can be grouped into three categories, 1) inner basins, 2) central basins, and 3) outer basins (Gorsline, 1980). Inner basins are considered to be those basins that lie leeward of the inner-most row of islands. Inner basins are dominated by terrigenous sedimentation and serve as a barrier for terrigenous input to central and outer basins. Sedimentation rates drop two-fold moving from inner basins to central basins, and by Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 11 another factor of two moving from central basins to outer basins (Gorsline and Teng, 1989). Central and outer basins are dominated by hemipelagic sedimentation. A schematic cross section of the SCB is presented as Figure 3. In this study, cores from seven different basins, including inner, central, and outer basins, are investigated. A brief description of each basin follows. A summary data table is presented in Table 2. Complete core descriptions are in Appendix C. Inner Basins Descanso Plain Descanso Plain is located in the southern portion of the SCB and composes the southern end of the San Diego Trough. Depth to bottom ranges from 915 to 1,370 meters. Depth of the deepest sill is approximately 1,200 meters. Descanso Plain does not fit the classical description of a marine basin, and is more a depression than a basin (Emery, 1960). Descanso Plain, essentially, is a marine basin that has been nearly completely filled with sediment. Descanso Plain covers an area of 1,880 square kilometers between 32° and 32° 45' North latitude, and 117° 15' and 118° West longitude. On May 21, 1995, a piston core, measuring 6.70 meters was recovered from Descanso Plain at a depth of 1,299 meters. The core was recovered from 32° 04.39' North latitude, 117° 21.85' West longitude, and consisted of hemipelagic, dark olive gray, silty clay. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 12 South & West North & East Coastal Rangas Tarrlg. & Homlpol. Sill ’ / Oapositional Plain Sill Sill Sediment Fill Outer Basin Figure 3 - Schematic cross section of the SCB, after Gorsline and Emery (1959), modified from Gorsline and Teng (1989). Cores for this study were recovered from each of the basin categories: inner, central and outer. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. TABLE 2 SCB Basin Descriptions and Data Name Basin Category Bottom Depth (m) Deepest Sill (m) Basin Area (km2) D ate of Core Recovery Lattilude Longitude C ore ID Core Length (m) Lithology D escanso Plain Inner 915-1,370 1,200 1,880 5/21/95 32° 04 .3 9 ' 117° 21 .8 5 ' EW 9504-03PC 6.70 H em ipelagic, dark olive gray, silty-clay Anim al Basin Central - 2,000 2,500 5/21/95 31° 25.92' 117° 35.09' EW 9504-02PC 7.67 H em ipelagic, dark olive gray, silty-clay San C lem ente Basin Central 2,100 1,815 1,595 5/23/95 32° 28.55' 118° 07 .4 9 ' EW 9504-05PC 6.74 H em ipelagic, dark olive gray, silty-clay San Nicolas Basin Central 1,830 1,100 2,850 5/26/95 32° 48 .0 5 ' 118° 48 .0 0 ' EW 9504-08PC 7.00 H em ipelagic, dark olive, silty-clay E ast C ortez Basin O uter 1,980 1,400 1,130 5/22/95 32° 17.01' 118° 23.73' EW 9504-04PC 8.74 H em ipelagic, dark olive, marl No Nam e Basin O uter 1,915 1,550 1,130 - 310 4 0 .1 1 ' 118° 11.32' AHF16832 - - T anner B asin O uter 1,550 1,160 1,350 5/27/95 32° 51.51' 119° 57.48' EW 9504-09PC 7.19 H em ipelagic, dark olive, marl 14 Central Basins Animal Basin On May 21, 1995 a piston core, measuring 7.67 meters was recovered from Animal Basin at a depth of 2,042 meters. Animal basin covers approximately 2,500 square kilometers and has a sill depth of 2,000 meters. The core was recovered from 31° 25.92' North latitude, 117° 35.09' West longitude, and consisted of hemipelagic, dark olive gray, silty clay. San Clemente Basin San Clemente Basin lies in the central region of the SCB, bounded by 31° 45' and 32° 30' North latitude, and 117° 45' and 118° 15' West longitude. The basin encompasses 1,595 square kilometers in area and has a maximum depth of 2,100 meters. San Clemente has one of the deeper sills of marine basins in the SCB at 1,815 meters. On May 23, 1995, a piston core measuring 6.74 meters was recovered from San Clemente Basin at a depth of 1,818 meters. The core was recovered from 32° 28.55' North latitude, 118° 07.49' West longitude, and consisted of hemipelagic, dark olive gray, silty clay. San Nicolas Basin San Nicolas Basin, is located in the northern region of the SCB. Depth to the bottom is 1,830 meters. Sill depth is 1,100 meters. San Nicolas covers an area of 2,850 square kilometers between 32° 30’ and 33° 15' North latitude, and 118° 30' and 119° 30' West longitude. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 15 On May 26, 1995 a piston core measuring 7.00 meters was recovered from San Nicolas Basin at a depth of 1,442 meters. The core was recovered from 32° 48.05' North latitude, 118° 48.00' West longitude, and consisted of hemipelagic, dark olive, silty clay. Outer Basins East Cortez Basin East Cortez Basin lies south of the United States/Mexico border and is considered to lie in the southern portion of the SCB. East Cortez has an intermediate sill depth at a depth of 1,400 meters. Depth to bottom is 1,980 meters. East Cortez covers an area of 1,130 square kilometers, and is bounded by 32° 15' and 32° 45' North latitude, and 118° 15' and 118° 45' West longitude. On May 22, 1995, a piston core, measuring 8.74 meters was recovered from East Cortez Basin at a depth of 1,759 meters. The core was recovered from 32° 17.01' North latitude, 118° 23.73' West longitude, and consisted of a hemipelagic, dark olive, marl. No Name Basin Like East Cortez, No Name Basin lies in the southern portion of the SCB. It is bounded by 31° 45' and 32° North latitude, and 118° and 118° 15' degrees West longitude, and covers an area of 1,130 square kilometers. Sill depth is at 1,550 meters, and depth to bottom is 1,915 meters. A core measuring 3.5 meters was recovered from 32° 17.01' North latitude, 118° 23.73' West longitude. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 16 Tanner Basin Tanner Basin, is located in the northern region of the SCB. Depth to bottom is 1,550 meters. Sill depth is 1,160 meters meters. Tanner Basin covers an area of 1,350 square kilometers between 32° 30' and 33° 15' degrees North latitude, and 119° 30' and 120° 15'West longitude. On May 27, 1995, a piston core, measuring 7.19 meters was recovered from Tanner Basin at a depth of 1,194 meters. The core was recovered from 32° 51.51' North latitude, 119° 57.48' West longitude, and consisted of a hemipelagic, dark olive, marl. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 17 OCEANOGRAPHY OF THE SCB The oceanography of the SCB is a product of the interplay between three current systems: the California Current, the California Countercurrent, and the California Undercurrent. The SCB is located on the eastern margin of the North Pacific Basin, bounded on its west by the equatorward-flowing California Current. Surface circulation in the region, however, does not follow the path of the California Current and is generally to the northwest. This pattern comes from complex interaction between the topography of the region and the California Current. As with surface flow, deep water flow, known as the California Undercurrent, is to the northeast. Following is a brief description of the oceanography of the SCB. California Current The California current is one of four major eastern boundary currents in the world and forms the western oceanographic boundary of the SCB. It is a slow, northwest to southeast-flowing current that is characterized by low temperatures and relatively low salinities (as compared to salinities in the North Pacific). The current originates as the West Wind Drift bifurcates near 45° North latitude along the western margin of North America, forming the southward-flowing California Current and the northward-flowing Sub-Arctic Current. Strong northwesterly winds, generated by the interactions of the North Pacific High, Aleutian Low, and North American Low, drive the current (Gardner et al., 1997). The Current has significant seasonal variation, reaching a maximum seasonal flow during the summer when the North Pacific High is most strongly developed. Average flow during the month of July is 7.8 Sv (Hickey, 1993). Seasonal low flow is reached during January, with a flow of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 18 approximately 5.8 Sv. Maximum current velocities are reached approximately 300 km offshore (Hickey, 1979; Lynn and Simpson, 1987). As the current flows equatorward, interactions with the morphology of the southern California coast cause large scale eddies to spin off (Hickey, 1993). These large-scale, semi-permanent eddies, known as the California Countercurrent, bathe the SCB and drive surface circulation in the SCB. California Countercurrent The California Countercurrent is a product of the interaction between the California Current and the coastline of southern California. The Countercurrent can be thought of as a semi-permanent large scale eddy caused by the southward-flowing California Current (Hickey, 1993) (Figure 4). The Countercurrent is a poleward- flowing current with seasonal maximum flows during the summer and winter (Hickey, 1993). During the summer months the Countercurrent is most eddy-like with flow rejoining the California Current (Hickey, 1979). During the winter months flow from the current is near continuous through the Santa Barbara channel, rejoining the California Current north of Point Conception (Hickey, 1979). During spring, the Countercurrent appears to be nearly absent, with flow entering the SCB and turning equatorward rather than poleward (Hickey, 1993). California Undercurrent The California Undercurrent comprises the deep-water circulation cell for the SCB, and as with the California Countercurrent, the Undercurrent is a poleward- flowing current (Figure 5). The Undercurrent flows through the SCB below the main pycnocline to as far north as Vancouver Island (Hickey, 1979). The Undercurrent Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 19 121 ° 119° 117° 34° 33° 32° Q ] Silled M arine Basin J Island C alifornia C ountercurrent FIGURE 4 - Schematic drawing of flow for the California Current and California Countercurrent over the silled marine basins of the SCB. The California Current is one of four major eastern boundary currents in the world. The California Countercurrent defines surface circulation in the SCB and can be thought of as a semi-permanent eddy of the California Current (Modified from Hickey, 1993). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20 121 ° 119° 117° 34° 33° 32° [ ] S illed M arine B asin ^ Island FIGURE 5 - Schematic drawing of flow for the California Undercurrent. The Undercurrent flows from the southeast and supplies deep water to the marine basins of the SCB. Source region of the undercurrent is poorly understood, but evidence indicates it is of southerly (possibly the Eastern Equatorial Pacific) rather than sub arctic origin. (Modified from Hickey, 1993). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 21 generally flows shoreward of the California Current with a high speed core located over the continental slope (Hickey 1979; 1989; 1992). The Undercurrent reaches a seasonal maximum flow during the summer, and a seasonal low during the spring (Hickey, 1993). Source water regions for the Undercurrent are poorly understood. Today, water entering the SCB, through the Undercurrent, is low in oxygen and rich in nutrients. Evidence suggests that this water is of southern origin rather than sub arctic origin and is likely a mix between southerly-sourced waters, possibly the Eastern Equatorial Pacific, and North Pacific Intermediate waters (Tsuchiya 1980, Liu and Kaplan 1989, Talley, 1993). As this southerly-sourced deep water enters the SCB, it is impeded by a series of progressively shallower sills as it moves from southeast to northwest (Figure 6). As the water encounters the sill, it fills the basin, giving the basin a temperature and salinity characteristic of the water mass. Below sill depth, basins have nearly unchanging water mass properties (Emery 1960) (Figure 7). In this manner, individual basins act as “traps” and sample the water column at each respective sill depth. We utilize this relationship, as well as the S1 3 C versus dissolved oxygen relationship, in reconstructing past dissolved oxygen changes in the SCB. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. N o rth S o u th Silt Sill FIGURE 6 - As waters enter the SCB through the California Undercurrent flow is progressively impeded by a series of shallower sills as waters travel from southeast to northwest. Water exchange is regulated by horizontal diffusion with water just below the depth of each sill. In this manner, individual basins act as “traps” and sample the water column at their respective sill depth. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. T E M P E R A T U R E IN 5 0 0 •SANTA BARBARA BASIN VSAN PEDRO BASIN ’SANTA MONICA BASIN •SANTA CATALINA BASIN TANNER B A S IN S A N NICO LAS BA SIN 1500 - S A N T A CRUZ B A SIN E A S T CO RTES B A SIN 2 00 0 FIGURE 7 - Waters below sill depth are nearly uniform in temperature and salinity. This is an effect of the basin acting as a “trap” for water at sill depth. Waters in the basins are of uniform property as sampled by the sill (From Emery, 1960). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 24 METHODS Sediment Sampling/Analysis Sediment cores were obtained using a 4 inch inner diameter piston core. On the ship, cores were split, described, sampled for pore water fluids, and archived in a refrigerated storage. Once the cores were returned to the University of Southern California, one half of each core was slabbed and x-radiographed. Individual sediment samples were obtained from the “working” half of the core liner. Cores were sampled continuously with samples covering an interval of two centimeters. Samples were weighed and placed in an oven for drying (T=80°C). Subsequent to drying, samples were reweighed and placed in sodium hexametaphosphate for deflocculation. Once deflocculated, samples were washed over a 63pm sieve. The coarse fraction (>63pm) was placed in a filter, washed with deionized water, and placed in an oven for drying. Subsequent to drying, samples were weighed and placed in glass vials. Individual samples for isotopic analysis were selected at eight centimeter intervals from core top to core bottom. Samples were picked for both benthic and planktonic foraminifera. Selection of foraminiferal species will be addressed in the following section. Isotopes: Methods and Interpretation Samples were analyzed for both 5I3C and 5 I8 0 an a Prism VG Isotech Mass Spectrometer. 8 values were calculated as follows: R — R ^13 ^ i S a m p le S tan (lurd ^ j Q O O D S ta n d u rd where R=1 3 C/I2C of sample or standard. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 25 The standard used was an internal standard (ULTISS) calibrated to the National Bureau of Standards standard NBS-19. Precision of analyses is ±0.01%c for carbon and ±0.09%c for oxygen. Accuracy is ±0.170%c for carbon and ±0.139%c for oxygen. Work by McCorkle and Keigwin (1994), Samthein (1994), and Grossman (1980), suggest that calcium carbonate tests of many species of foraminifera accurately record both the 8I3C and 8I80 of surrounding water during test formation. Their work also suggests that certain species closely record the isotopic composition of DIC in the surrounding water. In this study, we analyze the planktonic foraminifera Globigerina bulloides (G. bulloides), a commonly used planktonic species, and the benthic species Cibicides makanii (C. makanii). C. makanii provides benthic 8I3C and 8lsO records for the basins of the study. G. bulloides provides a 8I80 record for the surface ocean, but does not accurately record the SI3C of the surface ocean due to effects of photosymbionts. Interpretation of both the benthic and planktonic 5lsO signal is discussed in the following section addressing Age Models. In selecting a species for benthic 8I3C and 8I80 analyses, we turned to the work of Grossman (1982) who extensively investigated which foraminiferal species accurately record 8 1 3 C of DIC in the SCB. Based, in part, on the work of Grossman (1982) we chose the species C. makanii. Further analysis of core-top samples of C. makanii and other benthic species was conducted. Of the species analyzed, C. makanii most accurately recorded bottom water 8 I3 C values for DIC. Figure 8 presents a plot of typical DIC values for the SCB with the 8I3 C values for the core top Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 26 CORE TOP ANALYSES OF BENTHIC FORAMINIFERA AND S13C OF DIC FOR THE SCB s ' 3C(%o) - 3 - 2 - 1 0 1 2 3 0 500 E . e 1000 CL LU a 1500 2000 FIGURE 8 - Typical profile of SBC of DIC for the SCB. Plotted points indicate core top analyses of various benthic foraminifera. C. makanii appears to most accurately record the isotopic composition of the water. “ 1 — I — I — I — — I — I — I — I — — I — I — I — I — — I — I — I — 1 — — I — I — I — T -L /H — I — 1 — T < > - o o o o o o ♦ o • C. makanii ♦ E. smithi ► C. delicata ■ H. elegans o d13C of DIC Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 27 analyses of this study. Table 3 presents a summary data table for the core top analyses. Having found a species that accurately records the 8I3C of DIC, we utilized the relationship between SI3 C of DIC and dissolved oxygen concentrations (Figure 9) to reconstruct the ventilation history of the SCB and North Pacific into Stage 6. Similar relationships between S1 3 C of DIC and dissolved oxygen concentration have been demonstrated for the worlds’ oceans by Broeker and Peng (1982). We further utilize the relationship between sill depth and bottom water flow, as discussed in Chapter 3, to reconstruct the temporal and spatial patterns of ventilation through the water column. In order to interpret the SCB 8I3C records as a recorder of changes in dissolved oxygen concentrations, global 81 3 C changes were removed by comparing the SCB records to those at ODP Site 849. ODP Site 849 (Approx. 0.2°N, 110°W), located west of the East Pacific Rise (3,851 m), offers a nearly continuous stable isotopic record of Pacific variability (Figure 10), which approximates the global oceanic signal (Mix et al., 1995). The suitability of ODP Site 849 as a global reference site is extensively discussed by Mix et al. (1995). The time resolution of the SCB and ODP Site 849 records, and therefore precise age/8l3C comparison, however, was markedly different, making direct subtraction difficult. To obviate this artifact, a running average was taken through the SCB records, bringing the sampling resolution in line with ODP Site 849. Using ODP Site 849 as a reference for global 8I3 C changes, we removed 81 3 C variation due to changes in the oceanic carbon pool from the SCB records. This was Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 28 done by defining a parameter, A8I3 C, which represents changes in 8 1 3 C along the Eastern Pacific in excess of the global changes as recorded at ODP Site 849. We assume that the variability seen in the parameter ASi3C is driven by fluctuations in the dissolved A8I3C differences between ODP Site 849 and the SCB. Using Grossman’s (1982) relationship (Figure 9), the variations in A81 3 C are used to calculate temporal changes in relative dissolved oxygen concentrations to Stage 6. Today, the 8I3C gradient between Site 849 and the SCB is approximately 0.4%c for the southerly basins and 0.2%c for the northern basins (Tanner and San Nicolas), with the SCB displaying lower SI3 C values as compared to ODP Site 849. This difference in 8 I3C between the northern and southern basins is most likely due to greater influence of North Pacific intermediate water which has higher dissolved oxygen concentrations than the southerly sourced waters entering the SCB. The parameter A8I3C is a measure of the 81 3 C gradient between ODP Site 849 and the SCB, and variations in this gradient reflect changes in bottom water dissolved oxygen concentration. A shift to lower ASI3C values signals a decrease in the Site 849-SCB gradient and vice versa. The gradient can be affected through multiple mechanisms: 1) a decrease/increase in “travel time” between the source region and the SCB, 2) a decrease/increase in levels of dissolved oxygen in either the source region or SCB, 3) decrease/increase in the rain rate of organic carbon in either the SCB or source Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE 3 Core-Top Analyses of Various Benthic Foraminifera Species Basin Core M easured 5 n C (%o ) M easured 5 1 8 0 (% «,) C.Delicala C atalina A H F267I4 -2.367 0.701 C.Delicata San Nicolas AHF25844 -2.140 1.942 C.Delicata Tanner AHF25997 -1.909 2.125 C.Delicata Tanner AHF26023 -1.887 2.277 E.Smithi Catalina A H F26714 -0.805 2.427 E.Smithi San Nicolas AHF26322 -0.982 2.333 E.Smithi Tanner AHF26023 -1.012 2.435 E.Smithi San Nicolas AHF26325 -0.983 2.596 E.Smithi San Nicolas AHF26325 -1.086 2.649 C.McKannai Tanner Berclson -0.136 2.78 C.McKannai Tanner Berelson -0.079 2.325 C.McKannai San Clem ente A H F29481 -0.179 2.515 C.McKannai San Nicolas AHF26035 -0.189 2.357 C.M cKannai San Clem ente AHF25894 -0.214 3.106 C.McKannai San Clem ente Berelson -0.957 2.704 H.Elegans San Clem ente Berelson 1.524 3.72 H.Elegans Tanner Berelson 1.621 3.944 H .Elegans Tanner Berelson 1.720 3.477 H .Elegans San Clem ente A H F29481 1.669 3.754 H.Elegans San Nicolas AHF26035 1.497 3.55 H.Elegans San Clem ente AH F25894 1.857 4.183 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 30 Dissolved Oxygen vs $3 C of DIC 200 CD ▲ A o E 3 . 150 A ■ C 0 ) O ) I* 100 O " O 0 ) > ° 50 at a • • SCB G EO SEC S Sta.201 G EO SEC S Sta.226 G EO SEC S Sta.326 1.5 1 -0.5 0 0.5 5 1 3 C of DIC(%.) 1 1.5 2 FIGURE 9 - Relationship between dissolved oxygen and the SI3C of dissolved inorganic carbon (DIC). We utilize this relationship in reconstructing changes in dissolved oxygen concentrations for the Southern California Borderland into Stage 6. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. BENTHIC 81 3 C RECORD ODP Site 849 31 S1 3 C ( % « ) 0 .5 0 -0.5 -1 5 0 — 100 — tr > LU C5 < 5 0 — 200 — C. wueilerstorfi FIGURE 10 - SI3C record from ODP Site 849. ODP Site 849, located west of the East Pacific Rise, offers a nearly continuous stable isotopic record of Pacific variability, which approximates the global oceanic signal (Mix et al., 1995). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 32 region, and 4) a shift in source water region location. In this study we focus on the first two mechanisms. To better understand which mechanism is in play, we investigate changes in the benthic-planktonic radiocarbon age gradient. In principle, changes in the apparent age difference between surface and deep water, a proxy for ventilation and residence time, can be reconstructed by l4C dating of benthic and planktonic foraminifera from the same sediment horizon (Broeker et al., 1990). A decrease in the benthic- planktonic radio-carbon age gradient, coincident with a decrease in A8I3C, would possibly indicate that “travel time” between the source region and the SCB decreased. Conversely, a decrease in the A81 3 C signal with no change in the benthic-planktonic radio carbon age gradient could indicate that “travel time” remained constant, but levels of oxygen were increased in either the SCB or source region. The following two sections present results and discussion of the study. In the discussion, a mass balance approach is used to better quantify changes in dissolved oxygen levels and shed light on the processes involved. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 33 AGE MODELS Before relative changes in bottom water oxygen levels could be reconstructed, age models were developed to facilitate chronostratigraphic correlation between the SCB basins and ODP Site 849. Age models were derived from benthic and planktonic 8lsO records correlated to SPECMAP and radiocarbon (l4C) dates of planktonic foraminifera. In addition, percent carbonate and alkenone index UK37 were used to further refine the age models. Age models for the upper 40 kyr of each sequence were derived from 1 4 C dates of planktonic foraminifera. Approximately four planktonic foraminiferal samples were taken from each core for analysis. Sediment samples covered an interval of two centimeters. Sediment samples were dried, weighed, deflocculated, and then washed over a 63pm sieve. The coarse fraction (>63pm) was then dried and weighed. Subsequent to drying, the coarse fraction was picked for planktonic foraminifera. Approximately 3-5mg of mixed planktonic foraminifera were picked for analysis. Analyses were performed at Lawrence Livermore Nuclear Laboratory on an Accelerator Mass Spectrometer. Subsequent to analyses, age data for each basin was linearly curve fit to obtain an average sedimentation rate for the upper 40 kyr of the sequence. In calculating the average sedimentation rate, we assumed no compaction, constant accumulation rates, and no change in porosity. Individual l4C ages were calculated, and corrected for reservoir effects, following the conventions of Stuiver and Polach (1977). Uncertainty in the age models, for the upper 40 kyr, is on the order of 0.5-2 kyr. Table 4 presents a summary of 1 4 C data. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 34 TABLE 4 1 4 C Data Summary Identification (Sill Depth) Interval (cm) Planktonic 14C Age (Ka) Benthic 14C Age (Ka) Benthic-Planktonic Difference EW9504-02PC 30-32* 6.50 ±0.06 — — Animal Basin 31-33 5.89 ±0.07 — — (2,000m) 108-110 25.04 ± 0.39 — — 190-192 42.80 ± 2.50 — - EW9504-03PC 45-47 9.27 ± 0.07 _ _ Descanso Plain 81-83 13.89 ±0.21 — — (1,200m) 160-162 35.60 ± 1.40 - - EW9504-04PC 25-27 6.03 ±0.05 5.49 ± 0.05 0.54 ± 0.07 East Cortez Basin 96-98 12.17 ±0.07 13.55 ±0.07 0.62 ± 0.09 (1,400m) 184-186 20.55 ±0.12 21.51 ±0.11 1.04 ± 0.15 256-258 30.14 ±0.37 30.23 ± 0.28 0.09 ± 0.50 EW9504-05PC 40-42 8.50 ± 0.06 9.70 ± 0.05 1.20 ±0.07 San Clemente Basil 108-110 16.65 ±0.14 18.45 ±0.11 1.80 ±0.16 (1,815m) 138-140 19.81 ±0.14 20.84 ± 0.45 1.03 ±0.50 220-222 31.60 ± 1.35 35.80 ±0.56 4.20 ± 1.50 EW9504-08PC 38-40 6.78 ±0.05 11.38 ±0.07 4.60 ± 0.08 San Nicolas Basin 121-123 12.87 ± 0.16 15.59 ±0.08 2.72 ±0.18 (1,100m) 151-153 19.74 ±0.12 20.51 ±0.15 0.77 ±0.18 240-242 31.90 ±0.69 32.31 ±0.50 0.41 ±0.90 EW9504-09PC 8-10 1.95 ±0.05 _ _ Tanner Basin 104-106 10.79 ±0.06 — — (1,160m) 248-250 22.77 ±0.15 — — AHF16832 95-97 10.69 ±0.08 _ _ No Name Basin 142-144 14.73 ±0.12 — — (1,550m) 255-257 23.19 ±0.22 — — 355-357 36.20 ±0.88 - - * - Sample actually from EW9504-02TC, 30-32cm Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 35 Beyond 40 kyr, age models were derived from 51 8 0 stratigraphies of benthic and planktonic foraminifera correlated to the SPECMAP model. The 8lsO signal is primarily a monitor of ice sheet volume, but is also affected by changes in temperature and salinity. A change in Sl80 of 0.5%c can represent a change in temperature of 2°C, a change in salinity of l%c, and/or a change in the oceanic pool of l60 due to ice volume effects. Higher 8lsO values could reflect local changes in temperature, increases in salinity, and/or an increase in ice sheet volume. In order to mitigate the temperature and salinity effects, and establish a depth-age correlation based on the benthic and planktonic 8 lsO stratigraphies, it was necessary to correlate the SCB 8lsO records to global S1 8 0 reference records. The global references, SPECMAP for the planktonic records and ODP Site 849 for the benthic records, provide a SlsO record which primarily monitors changes in ice sheet volume. As ice sheets expand during glaciations, isotopically light oxygen (l60 ) is preferentially taken up in the ice sheets due to Rayleigh fractionation processes (Hoefs, 1997). This enriches the remaining oceanic oxygen pool in isotopically heavier oxygen (lsO), which subsequently drives the SI80 signal more positive. The timing of interglacial to glacial transitions, and the associated Sl80 variations are well constrained. Interglacial to glacial variability is thought to be driven by orbital forcing which affects solar insolation and global temperatures. The period of changes in orbital parameters is well constrained, and hence, through correlating the Borderland 8lsO records and global Sl80 reference records, a depth-age correlation is established. Uncertainty in the age models beyond 40 kyr is estimated to be 5 kyr. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 36 ODP Site 849, located in the deep Pacific, has a well defined, nearly continuous, benthic 8lsO record. Site 849 is therefore used as a reference for global changes in 5I80 on glacial to interglacial timescales (Mix et ai, 1995). The suitability of ODP Site 849 as a global reference site is thoroughly discussed by Mix et al. (1995). The Site 849 record, however, showed a lag of approximately 10 kyr when compared to the SPECMAP record (Figure 11). In light of this discrepancy, an adjustment was made in the Site 849 age model to bring into agreement the records from SPECMAP and Site 849. Based on linear extrapolation of average sedimentation rates, bottom ages for the 7 basins of the study ranged from as old as 198 kyr in East Cortez Basin to as young as 48 kyr in No Name Basin. All but one record (No Name Basin) extends into Stage 5, with three records (Animal Basin, East Cortez Basin, and Descanso Plain) extending into Stage 6. A brief description of each age model follows. Anim al Basin 767 centimeters of sediment was recovered from Animal basin. Samples for radiocarbon age dating were obtained from the top 190 centimeters of the core. The upper-most sample (30-32cm) yielded an age of 6.50 kyr. The bottom-most sample (190-192cm) yielded an age of 42.80 kyr. A linear extrapolation between the data points (Figure 12) yields an average sedimentation rate of 4cm/ kyr for the upper 40 kyr. A minimum in the benthic 5I80 record is present at 465 cm, which is interpreted as oxygen isotope stage 5e. Values in the planktonic 8I80 stratigraphy exhibit a decrease in the same interval. Linear extrapolation between 40 kyr and the excursion at 5e yield an average sedimentation rate of 3.5cm/ kyr (Figure 12). Extrapolating to Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 37 518 o g l o b a l r e f e r e n c e r e c o r d s SPECMAP and ODP Site 849 1 gO SPECMAP (% o) 100 — G ) o > < 150 — 200 SPECMAP 5 '8 0 Record ODP Site 84951 8 0 Record 250 4.5 5 4 3.5 3 S,80 Site 849 (% o ) FIGURE 11 - Comparison of 5lsO records from SPECMAP and ODP Site 849. Note the approximate lOkyr phase lag between the two records. Because of the discrepancy, an adjustment was made to the Site 849 age model to bring the two records into agreement. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 38 AGE vs. DEPTH Animal Basin EW 9504-02PC 0 100 § 2 0 0 X S 300 400 500 0 20 40 60 80 100 120 140 AGE (Kyr) FIGURE 12 - Age model for Animal Basin. Age control for the upper 40kyr of the sequence is based on 1 4 C dates. Beyond 40kyr, age control is based on correlation to of the benthic and planktonic § lsO records to global references; SPECMAP for the planktonic records and ODP Site 849 for the benthic records. Ave. Sed. Rate = 4 “"/Kyr Ave. Sed. Rate = 3.5 °7Kyr 5 180 Based Date 1 4 C Based Date Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 39 the bottom of the core gives a terminal age of 194 kyr. The benthic and planktonic 5lsO records correlate well with the global 5I80 reference records (Figures 13 and 14). The benthic 5lsO record from Animal basin appears to be shifted in respect to ODP Site 849 at the Stage 1-2 boundary. Peak glacial benthic 8lsO values for Animal Basin precede peak glacial values for ODP Site 849 by approximately 5 kyr. This is most likely due to a hiatus, or missing material, in the Animal record, or may be an artifact of low accumulation rates due to sea level rise. A further excursion is noted from approximately 165 kyr to 180 kyr. Sl80 values for Animal Basin during this interval are near Holocene values. It is possible that the age model needs to be adjusted, pushing this interval into Stage 7. We feel however, upon review of the data, that this is an unlikely scenario as sedimentation rates would decrease to near 2 cm/ kyr. The excursion may be a product of temperature and/or salinity effects and warrants further study. No Name Basin Five samples were obtained from the upper 300 centimeters for radiocarbon dating. Samples covered intervals of two centimeters. The upper-most sample (95- 97cm) yielded an age of 10.69 kyr, and the lower-most sample (355-357cm) an age of 36.20 kyr. Linear extrapolation between the data points gives an average sedimentation rate of 10cm/ kyr (Figure 15). Both the benthic and planktonic 5I80 records correlate well with global 51 8 0 records and suggest the record extends into Stage 3 (Figures 16 and 17). Linear extrapolation of the average sedimentation rate to the bottom of the core gives a terminal age of 48 kyr. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 40 BENTHIC 51sO RECORD Animal Basin E W 9 5 0 4 -0 2 P C 5 ,eO (% o ) 5 4 3 2 6.50 Kyr 25.04 Kyr 42.80 Kyr 5 0 — f 100 — 150— EW9504-02PC 200 - s it e 849 FIGU RE 13 - Comparison of the age model based benthic Sl80 record for Animal Basin and ODP Site 849. ODP Site 849 acts as a monitor of changes in the global 5 lsO signal as seen in the deep Pacific. Horizontal lines indicate horizons at which l4C samples were analyzed. The approximate 1.1 % o shift at 120kyr was used as the 5 1 8 0 tie-point for the age model. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 41 PLANKTONIC 8 1sO RECORD Animal Basin E W 9504-02P C 5,80 (% o ) 3 1.5 0 - 1 . 5 -3 6.20 Kyr 25.04 Kyr 4 2 .8 0 Kyr 50 s 100— 150 — 200 EW9504-02PC SPECMAP FIGURE 14 - Comparison of the age model based planktonic 8lsO record for Animal Basin and SPECMAP. SPECMAP provides a SlsO record that reflects changes in the global 5i80 pool due to changes in ice volume. Horizontal lines indicate horizons at which l4C samples were analyzed. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. D E P T H (cm) 42 AGE vs. DEPTH No Name Basin AH F16832 0 50 100 150 Ave. Sed. Rate = 10c n 7Kyr 200 250 300 350 C Based Date 400 20 25 30 35 40 AGE (Kyr) FIGURE 15 - Age model for No Name Basin. Age control for the upper 40kyr of the sequence is based on l4C dates. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 43 BENTHIC 81sO RECORD No Name Basin AHF 16832 5'80 (% o ) 5 4 3 2 10.69 Kyr 14.73 Kyr 23.19 Kyr 36.20 Kyr 50 — AHF16832 §E 1 0 0 — L L I 150— 2 0 0 — SITE 849 FIGURE 16 - Comparison of the age model based benthic Sl80 record for No Name Basin and ODP Site 849. ODP Site 849 acts as a monitor of changes in the global SI80 signal as seen in the deep Pacific. Horizontal lines indicate horizons at which 1 4 C samples were analyzed. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 44 PLANKTONIC S180 RECORD No Name Basin AHF 16832 SlaO (% « ) 3 1.5 0 -1.5 -3 10.69 Kyr 14.73 Kyr 23.19 Kyr AHF 16832 5 0 O ) 15 0 - - 2 0 0 — SPECMAP FIGURE 17 - Comparison of the age model based planktonic 8 lsO record for No Name Basin and SPECMAP. SPECMAP provides a SI80 record that reflects changes in the global 8lsO pool due to changes in ice volume. Horizontal lines indicate horizons at which ,4C samples were analyzed. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 45 San Nicolas Basin A 560 centimeter piston core was recovered from San Nicolas Basin. Four radiocarbon samples were obtained between 38 and 240 centimeters. Based on linear extrapolation of l4C ages, the average sedimentation rate for the upper 40 kyr is 7cm/ kyr (Figure 18). The benthic 5 1 8 0 record shows an abrupt change of approximately 1.2%o at a depth of 509 centimeters and is interpreted as Stage 5e (120 kyr). Based on linear extrapolation between 40 kyr and 120 kyr, the terminal age of the core is 130 kyr, with an average sedimentation rate of 3cm/ kyr covering the interval from 40 kyr to core bottom (Figure 18). The benthic Sl80 record correlates well with the global 5lsO record (Figure 19). The planktonic record also correlates well with the global 5I80 record and suggests that the record extends through Stage 5 (Figure 20). Holocene planktonic §l80 values show a positive excursion from approximately 7 kyr to core top. This excursion is not present in any of the other records. We feel that the excursion may be a product of temperature and/or salinity effects and warrants further study. However, if the benthic foraminiferal age determination was used to define the uppermost age, the Stage 1-2 boundary in San Nicolas would be consistent with ODP Site 849. Descanso Plain Descanso Plain yielded a sediment record 454 centimeters long. Radiocarbon samples were taken from between 45 and 160 centimeters. The upper-most sample (45-47cm) yielded an age of 9.27 kyr, the lower-most (160-162) an age of 35.60 kyr. Linearly extrapolating between data points gives a sedimentation rate of 4cm/ kyr for the upper 40 kyr of the core (Figure 21). An approximate 1. l%o shift is present in the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 46 AGE vs. DEPTH San Nicolas Basin EW 9504-08PC 100 Ave. Sed. Rate = 7 “"/Kyr 200 Ave. Sed. Rate = 3 c m /Kyr 300 400 500 5 1 8 0 Based Date 14C Based Date 600 80 100 120 140 60 20 40 AGE (Kyr) FIGURE 18 - Age model for San Nicolas Basin. Age control for the upper 40kyr of the sequence is based on 1 4 C dates. Beyond 40kyr, age control is based on correlation to of the benthic and planktonic 8lsO records to global references; SPECMAP for the planktonic records and ODP Site 849 for the benthic records. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 47 BENTHIC 51 8 0 RECORD San Nicolas Basin E W 9504-08P C 5 1 8 0 (% .) 6.78 Kyr 10.50 Kyr 12.87 Kyr 19.74 Kyr 31.90 Kyr 50 — § E 100— U J a < 5 0 — 2 0 0 - site 849 FIGURE 19 - Comparison of the age model based benthic 5I80 record for San Nicolas Basin and ODP Site 849. ODP Site 849 acts as a monitor of changes in the global 8lsO signal as seen in the deep Pacific. Horizontal lines indicate horizons at which l4C samples were analyzed. The approximate 1.1 % o shift at 120kyr was used as the 8ibO tie-point for the age model. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 48 PLANKTONIC 5 180 RECORD San Nicolas Basin E W 9504-08P C 5 iaO (% o) 6.78Kyr 12.87 Kyr 19.74 Kyr 31.90 Kyr 5 0 s 100— - EW9504-08PC 1 5 0 — 200 — SPECMAP FIGURE 20 - Comparison of the age model based planktonic 81 8 0 record for San Nicolas Basin and SPECMAP. SPECMAP provides a 8lsO record that reflects changes in the global 8I80 pool due to changes in ice volume. Horizontal lines indicate horizons at which l4C samples were analyzed. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 49 AGE vs. DEPTH Descanso Plain EW 9504-03PC 50 Ave. Sed. Rate = 4 c m /Kyr 1 0 0 -g - 150 £ 200 a. UJ Q 250 Ave. Sed. Rate = 3 c m /Kyr 300 8 0 Based Date 14C Based Date 350 400 80 100 120 140 0 20 40 60 AGE (Kyr) FIGURE 21 - Age model for Descanso Plain. Age control for the upper 40kyr of the sequence is based on l4C dates. Beyond 40kyr, age control is based on correlation to of the benthic and planktonic 5lsO records to global references; SPECMAP for the planktonic records and ODP Site 849 for the benthic records. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 50 benthic 5I80 record at a depth of 360 centimeters and is interpreted as Stage 5e (120 kyr). Linear extrapolation between 40 kyr and 120 kyr yields an average sedimentation rate of 3cm/ kyr (Figure 21). Extrapolation to the bottom of the core gives a terminal age of 170 kyr. The planktonic record, as well as the benthic record, correlate well with the global 51 8 0 reference records (Figures 22 and 23). East Cortez Basin Five samples were taken from the upper 256 centimeters for radiocarbon dating. Samples covered an interval of two centimeters. The upper-most sample (25- 27cm) yielded an age of 6.03 kyr, and the lower-most (256-258cm) an age of 30.14 kyr. Linear extrapolation between the data points gives an average sedimentation rate of 9cm/ kyr (Figure 24). Linear extrapolation between 40 kyr and 120 kyr (Stage 5e), as interpreted from a minimum in the benthic 8lsO record at 608 centimeters, yields an average sedimentation rate of 4 cm/ kyr (Figure 24). Extrapolation to the bottom of the core gives a terminal age of 198 kyr. Both the benthic and planktonic age model based records correlate well with the global Sl80 reference records and suggests that the sequence extends through Stage 6 (Figure 25 and 26). San Clemente Basin 540 centimeters of sediment was recovered from San Clemente Basin. Samples for radiocarbon age dating were obtained from the top 220 centimeters. The upper-most sample (20-22cm) yielded an age of 6.01 kyr, and the bottom-most (220- 222cm) an age of 35.80 kyr. A linear extrapolation between the data points (Figure 27) yields an average sedimentation rate of 7cm/ kyr. Based on the benthic 8lsO data, it does not appear that the record extends into Stage 5e. However, based on the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 51 BENTHIC S180 RECORD D escanso Plain E W 9504-03P C S taO (% o) 5 4 3 2 9.27 Kyr 13.89 Kyr 35.60 Kyr 5 0 § E 1 0 0 - - 1 5 0 - - EW9504-03PC 200- - s it e 849 FIGURE 22 - Comparison of the age model based benthic S1 8 0 record for Descanso Plain and ODP Site 849. ODP Site 849 acts as a monitor of changes in the global Sl80 signal as seen in the deep Pacific. Horizontal lines indicate horizons at which l4C samples were analyzed. The approximate 1.1 % c shift at 120kyr was used as the 8lsO tie-point for the age model. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 52 PLANKTONIC 5 180 RECORD D e sc an so Plain E W 9 5 0 4 -0 3 P C S ,aO (% o ) 3 1.5 0 -1.5 -3 9.27Kyr 13.89 Kyr 35.60 Kyr 50 — £ 100 — o > 150 EW9504-03P] 200 — SPECMAP FIGURE 23 - Comparison of the age model based planktonic 51 8 0 record for Descanso Plain and SPECMAP. SPECMAP provides a SlsO record that reflects changes in the global 8I80 pool due to changes in ice volume. Horizontal lines indicate horizons at which 1 4 C samples were analyzed. The gap in the record represents an interval in which numbers of G. bulloides were not abundant enough for analysis. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 53 AGE vs. DEPTH East Cortez Basin E W 95 04-0 4P C 0 100 200 I 300 X Si 400 Q 500 600 700 0 20 40 60 80 100 120 140 AGE (Kyr) FIGURE 24 - Age model for East Cortez Basin. Age control for the upper 40kyr of the sequence is based on l4C dates. Beyond 40kyr, age control is based on correlation to of the benthic and planktonic 8 lsO records to global references; SPECMAP for the planktonic records and ODP Site 849 for the benthic records. Ave. Sed. Rate = 9 c m /Kyr Ave. Sed. Rate = 4 cm /Kyr 8 1sO Based Date 14C Based Date Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 54 BENTHIC S180 RECORD E ast Cortez Basin E W 9 5 0 4 -0 4 P C 51 8 0 (% o ) 5 4 3 2 6.03 Kyr 12.17 Kyr 20.55 Kyr 30.14 Kyr 50 - - § E 100— H i U < 5 0 — 200 — EW9504-04PC FIGURE 25 - Comparison of the age model based benthic 8lsO record for East Cortez Basin and ODP Site 849. ODP Site 849 acts as a monitor of changes in the global 51 8 0 signal as seen in the deep Pacific. Horizontal lines indicate horizons at which 1 4 C samples were analyzed. The minimum at approximately 120kyr was used as the 8I80 tie-point for the age model. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 55 PLANKTONIC 5 1 a O RECORD East Cortez Basin E W 9504-04P C 51sO (% o ) 6.03 Kyr 12.17 Kyr 20.55 Kyr 30.14 Kyr 5 0 — -g ; 100— O ) 1 5 0 — EW9504-04PC 200 — SPECMAP FIGURE 26 - Comparison of the age model based planktonic 8lsO record for East Cortez Basin and SPECMAP. SPECMAP provides a 51 8 0 record that reflects changes in the global 51 8 0 pool due to changes in ice volume. Horizontal lines indicate horizons at which 1 4 C samples were analyzed. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 56 AGE vs. DEPTH San Clemente Basin EW 9504-05PC 100 — Ave. Sed. Rate = 7 "’ ’ /Kyr 200 — E O 300 — Ave. Sed. Rate = 4 "7Kyr a. L U Q 400 — 8 1 8 0 Based Date 1 4 C Based §ate 500 — 600 0 80 1 0 0 20 40 60 120 AGE (Kyr) FIGURE 27 - Age model for San Clemente Basin. Age control for the upper 40kyr of the sequence is based on l4C dates. Beyond 40kyr, age control is based on correlation to of the benthic and planktonic 8lsO records to global references; SPECMAP for the planktonic records and ODP Site 849 for the benthic records. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 57 planktonic 8I80 record, it appears as though the record extends to Stage 5d. Extrapolation between 40 kyr and 5d gives an average sedimentation rate of 4cm/ kyr from 40 kyr to 110 kyr (Figure 27). Extrapolating to the bottom of the core gives a terminal age of 110 kyr. Both the benthic and planktonic age model based records correlate well with the global 8lsO reference records (Figures 28 and 29). Tanner Basin Tanner Basin yielded a sediment record 710 centimeters long. Three radiocarbon samples were taken between 8 and 248 centimeters. The upper-most sample (8- 10cm) yielded an age of 1.95 kyr, the lower-most (248-250cm) an age of 22.77 kyr. Linear extrapolation between data points gives an average sedimentation rate of 11cm/ kyr for the upper 40 kyr (Figure 30). A minimum in the benthic 8lsO record is present at 662 centimeters, and is interpreted as oxygen isotope stage 5e (120 kyr). Planktonic S1 8 0 values exhibit a decrease in the same interval. Linear extrapolation between 20 kyr and the excursion at 5e yield an average sedimentation rate of 4cm/ kyr covering that interval (Figure 30). Extrapolating to the bottom of the core gives a terminal age of 135 kyr. The planktonic record, as well as the benthic record, correlates well with the global SlsO reference records (Figures 31 and 32). Based on both the isotope stratigraphies and l4C data, the 710 centimeter section appears to extend through Stage 5. Summary Age models were developed to facilitate chronostratigraphic correlation between the SCB basins and ODP Site 849. Age models were derived from benthic and planktonic 81 8 0 records correlated to SPECMAP and radiocarbon (,4C) dates of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 58 planktonic foraminifera. In addition, percent carbonate and alkenone index UK37 were used to further refine the age models. Three basins have records that extent into Stage 6: Descanso Plain, East Cortez Basin, and Animal Basin. San Nicolas, Tanner, and San Clemente Basins have records that extend into Stage 5, while the record from No Name Basin terminates in Stage 3. In developing the age models, we assumed an age of zero kyr at core top. This assumption, however, may not be valid as core material may have been lost during recovery due to suction caused by the piston core. In light of this, we may have underestimated sedimentation rates for the upper portions of some cores. All basins exhibit decreases in sedimentation rate at approximately 30 kyr. Rates decrease from an average value of 7.5cm/ kyr, for the upper 30 kyr, to 4.5cm/ky, for 30-120 kyr. This decrease could be driven by numerous mechanisms. Compaction, changes in sea level, decreased productivity, a hiatus, or winnowing, are all mechanisms by which the sedimentation rate could be changed. It is also significant to note that in both San Nicolas and San Clemente Basins the sediments appear to have undergone some reworking. This is evidenced in the benthic-planktonic 1 4 C age difference (Table 4). The presence of old benthic foraminifera at a relatively shallow sediment depth may indicate that the sediments have been reworked or that sediment has been transported down-slope. Table 5 presents a summary of accumulation rates. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 59 BENTHIC 51 8 0 RECORD San Clemente Basin E W 9504-05P C 5,80 ( % o ) 8.50 Kyr 16.65 Kyr 19.81 Kyr 31.60 Kyr 50 — § E 1 0 0 — EW9504-05PC 150— 20 0 — SITE 849 FIGURE 28 - Comparison of the age model based benthic 5 I8 0 record for San Clemente Basin and ODP Site 849. ODP Site 849 acts as a monitor of changes in the global 5 I80 signal as seen in the deep Pacific. Horizontal lines indicate horizons at which l4C samples were analyzed. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 60 PLANKTONIC 8 1sO RECORD San Clemente Basin E W 95 04-05P C 5,80 (%o) 3 1.5 0 - 1 . 5 -3 8.50 Kyr 16.65 Kyr 19.81 Kyr 31.60 Kyr 5 0 — ? ; 100 — O ) - EW9504-05PC 1 5 0 — 200 SPECMAP FIGURE 29 - Comparison of the age model based planktonic 8lsO record for San Clemente Basin and SPECMAP. SPECMAP provides a 5 lsO record that reflects changes in the global 5lsO pool due to changes in ice volume. Horizontal lines indicate horizons at which 1 4 C samples were analyzed. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 61 AGE vs. DEPTH Tanner Basin EW 9504-09PC 1 0 0 Ave. Sed. Rate = 11 “7 K yr 200 I 300 x 400 Ave. Sed. Rate = 4 “"/Kyr i- Q . L U Q 500 S1 8 0 Based Date ,4C Based Date 600 700 80 100 120 140 60 20 40 AGE (K yr) FIGU RE 30 - Age model for Tanner Basin. Age control for the upper 40kyr of the sequence is based on l4C dates. Beyond 40kyr, age control is based on correlation to of the benthic and planktonic S1 8 0 records to global references; SPECMAP for the planktonic records and ODP Site 849 for the benthic records. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 62 BENTHIC 51sO RECORD Tanner Basin E W 9504-09P C 5 ,80 (% o ) 1.95 Kyr 10.79 Kyr 22.77 Kyr 5 0 - - § E 1 0 0 — LU s EW9504-09PC 5 0 — 200 SITE 849 FIGURE 31 - Comparison of the age model based benthic 5 lsO record for Tanner Basin and ODP Site 849. ODP Site 849 acts as a monitor of changes in the global 8lsO signal as seen in the deep Pacific. Horizontal lines indicate horizons at which l4C samples were analyzed. The minimum value at 120kyr was used as the SlsO tie- point for the age model. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 63 PLANKTONIC 81 8 0 RECORD Tanner Basin E W 9504-09P C 5'80 (% » ) 3 1.5 0 - 1 . 5 -3 1.95 Kyr 10.79 Kyr 22.77 Kyr 5 0 — ^ 100 — C D EW9504-09PC 5 0 — 2 0 0 — SPECMAP FIGURE 32 - Comparison of the age model based planktonic Sl80 record for Tanner Basin and SPECMAP. SPECMAP provides a 81 8 0 record that reflects changes in the global 8lsO pool due to changes in ice volume. Horizontal lines indicate horizons at which l4C samples were analyzed. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 64 TABLE 5 Sedimentation Rate Summary Core Identification (Sill Depth) 14C Ages (Kyr) Sedim entation Rate for Upper 40K yr 5e Present? Sedim entation Rate beyond 40K yr (cm /K yr) Core Bottom (Kyr) E W 9504-02PC A nim al Basin 5.89-42.80 4 cm /K yr Y es 3.5 cm /Kyr 200 EW 9504-03PC D escanso Plain 9.27-35.60 4 cm /K yr Yes 3 cm /K yr 170 EW 9504-04PC East C ortez Basin 6.03-30.14 9 cm /K yr Y es 4 cm /K yr 200 EW 9504-05PC San C lem ente Basin 8.50-31.60 7 cm /K yr N o 4 cm /K yr 110 EW 9504-08PC San N icolas Basin 6.78-31.90 7 cm /K yr Y es 3 cm /K yr 130 EW 9504-09PC T anner Basin 1.95-22.77 11 cm /K ry Yes 4 cm /K yr 140 A H F16832 No Nam e Basin 10.69-36.20 10 cm /K yr N o 10 cm /K yr 50 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 65 RESULTS As the primary focus of this study is investigating the ventilation history of the SCB and North Pacific as seen through the parameter A5I3 C, both the raw and average benthic 5 1 3 C stratigraphies will not be discussed here. Plots of the raw and average benthic 5,3C are included in Appendix A. Both the raw and average benthic 8I3C stratigraphies are plotted against 51 3 C data from ODP Site 849. As was previously discussed, ODP Site 849 was used as a global reference site to facilitate the removal of global 81 3 C changes from the SCB records. Once the global signal is removed, the remaining SI3C signal functions as a monitor of changes in 8I3C in excess of the global signal, which we have defined as the parameter ASI3C. Here, we evaluate both spatial, and temporal variations in the parameter ASI3C. We assume, via Grossman’s relationship between 81 3 C of DIC and dissolved oxygen (Figure 9), that these changes are primarily due to changes in dissolved oxygen content. Finally, we assume that the dissolved oxygen concentration at ODP Site 849 has remained constant with time. Results are presented chronologically beginning with Stage 6 and progressing to Stage 2. Results are also presented spatially with results from the shallowest silled basins presented first, progressing to the deeper silled basins. Here we are using the relationship between water mass and sill depth (Figure 6) to present a “snapshot” of what is happening through the water column. It is important to note that uncertainty in the age models makes some of the presented correlations tenuous. Age uncertainty past 120 kyr is on the order of 20 kyr and from 40 kyr to 120 kyr on the order of 10 kyr. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 66 Stage 6 Only three basins have records that extent into Stage 6: Descanso Plain, East Cortez Basin, and Animal Basin. The beginning of Stage 6 finds the three basins with AS1 3 C values slightly less than Holocene values. This suggests that the contrast in oxygen concentrations were reduced at the end of Stage 7/beginning of Stage 6 as compared to today. Across the Stage 6-7 boundary the records from Descanso Plain, East Cortez, and Animal Basin show initial decreases in AS1 3 C, and hence increases in dissolved oxygen content (Figures 33, 34 and 35). The basins exhibit similar trends in A81 3 C until approximately 165 kyr, where the records begin to diverge. At this point it appears as though the upper water column becomes decoupled from the deeper (> 1,400 meters) water column. This interpretation is tentative, however, as age uncertainty during this interval is on the order of 20 kyr. Descanso Plain, from approximately 165 kyr, exhibits increasing values of ASI3 C, suggesting that oxygen concentrations are decreasing in the upper water column. A8I3C values reach a Stage 6 maximum at approximately 140 kyr, with values of 0.7%c (Figure 33). From 140 kyr, A81 3 C trends toward lower values suggesting that upper water column oxygen concentrations begin to recover. By the end of Stage 6, ASI3C values in Descanso Plain are near Holocene values. This suggests that from the 140 kyr minimum in oxygen, oxygen levels increase, reaching Holocene values by the close of Stage 6. The record from East Cortez Basin, from 165 kyr, exhibits decreasing values of A8I3 C. A8I3C values reach a minimum at approximately 140 kyr, suggesting that Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 67 BENTHIC A513C D e s c a n s o Plain E W 9 5 0 4 -0 3 P C A513C (%.) 0.2 0.6 1 50 — 00 — Ss. 5 0 — 200 Sill = 1,200m More Oxygen Less Oxygen FIGURE 33 - Plot showing variation in A8I3 C for Descanso Plain. A8 l3C represents changes in SI3C in excess of global 81 3 C variation. We assume that these variations are primarily driven by changes in dissolved oxygen, and hence A8 l3C acts as a monitor of dissolved oxygen content. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 68 BENTHIC AS13C E a st C ortez B asin E W 9 5 0 4 -0 4 P C A8’3C (% ») 0 0.4 0.8 50 £ 1 0 0 — $ L U 1 _ O < 5 0 — 200 - Sill = 1 ,400m More Oxygen Less Oxygen FIGU RE 34 - Plot showing variation in AS1 3 C for East Cortez Basin. A8l3C represents changes in SI3C in excess of global 8I3C variation. We assume that these variations are primarily driven by changes in dissolved oxygen, and hence A8I3C acts as a monitor of dissolved oxygen content. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 69 BEN TH IC AS13C Anim al B asin E W 9 5 0 4 -0 2 P C A81 3 c (% •) A _ I I I I I U - f 1 - 1 2 5 0 - - / 3 . ^ 4 - Sa - / 5b £ 1 0 0 - 5c $ of - 5d o < - 5e 1 5 0 - - — _ 6 - 2 0 0 - Sill = 2,000m ^ ----- More Oxygen L ess Oxygen FIGURE 35 - Plot showing variation in A8 I3 C for Animal Basin. A8i3C represents changes in SI3 C in excess of global 8 I3C variation. We assume that these variations are primarily driven by changes in dissolved oxygen, and hence A8i3C acts as a monitor of dissolved oxygen content. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 70 intermediate depth waters of the SCB were relatively more ventilated as compared to Holocene conditions (Figure 34) during Stage 6. A8I3C values return to Holocene values at approximately 130 kyr and continue to increase across the Stage 5-6 boundary. This trend suggests that from the A8I3C minimum at approximately 140 kyr dissolved oxygen concentrations decreased at intermediate depths in the SCB reaching Holocene values at the Stage 5-6 boundary. It is significant to note that from 140 kyr oxygen concentrations in the upper water column appear to be increasing, while oxygen concentrations in the intermediate water column appear to be decreasing. This is consistent with a pattern of decoupling between the upper and intermediate to deep water column that is seen in Stages 3 and 4. The Stage 6 record from Animal Basin shows rapidly changing values of ASI3C across the Stage 6-7 boundary. Values decrease rapidly, plateauing at approximately 165 kyr. From 165 kyr, values remain relatively constant to approximately 155 kyr, where values begin to rapidly increase (Figure 35). This suggests that from 1170 kyr to 155 kyr Animal Basin was relatively more ventilated as compared to Holocene conditions. ASI3 C values for Animal Basin reach Holocene •S 1 3 C values at approximately 150 kyr and continue to increase toward the Stage 5-6 boundary. Stage 6 Summary Stage 6 is characterized by a decoupled relationship between the upper and intermediate to deep water column. In the upper water column A8I3C values suggest that ventilation was decreased through Stage 6, reaching a minimum at approximate 140 kyr before oxygen concentrations began to recover. In the intermediate depths, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 71 however, the A8I3C record suggests that intermediate waters of the SCB were relatively more ventilated throughout Stage 6 as compared to Holocene conditions. Peak ventilation occurrs at approximately 140 kyr. From 140 kyr oxygen concentration appear to decrease, reaching Holocene levels near the end of Stage 6. Stage 5 The beginning of Stage 5 finds the SCB with A8i3C values substantially higher than Holocene values. This suggest that at the beginning of Stage 5 oxygen concentrations across the entire SCB were significantly decreased relative to Holocene values. It also appears as though the entire water column is coupled, unlike the beginning of Stage 6, and as will be seen, Stages 3 and 4. After a sharp increase in A8I3 C, A8 I3C values generally decrease from the beginning of Stage 5e to Stage 5c. This suggests that from the beginning of Stage 5e to Stage 5c oxygen concentrations, after an initial decrease, increased across the SCB. From Stage 5c to the Stage 4-5 boundary, oxygen concentrations decrease throughout the SCB, setting the stage for the lowest oxygen levels that occur in Stage 4. Both San Nicolas and Tanner Basin show minimum values of ASI3C in Stage 5 at approximately 102 kyr , which corresponds to the beginning of Stage 5c (Figures 36 and 37). Similar trends are seen in the record from Descanso Plain which shows a minimum ASI3 C value, and hence highest oxygen conditions, in Stage 5c (Figure 33). The intermediate depth basin of East Cortez exhibits similar trends, with minimum A8I3C values in Stage 5c (Figure 34). The record from San Clemente Basin resembles that of East Cortez Basin and exhibits a Stage 5 AS1 3 C minimum in Stage 5c (Figure Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 72 38). These A8I3C records indicate that oxygen conditions during late Stage 5 were higher than during the Holocene. From the end of Stage 5c and to the Stage 4-5 boundary, A8I3C values for all of the basins increase. This suggests that from the Stage 5c oxygen maximum, to the Stage 4-5 boundary, oxygen concentrations across the SCB decreased. The three basins representing the upper water column (San Nicolas, Tanner, and Descanso) exhibit maximum post Stage 5c AS,3C values in Stage 5a. The record from East Cortez basin is similar to the shallower records showing a post Stage 5c A8I3C maximum in Stage 5a, with ASI3C then slightly decreasing to the Stage 4-5 boundary. The record from San Clemente basin begins in Stage 5d, and as with the record from East Cortez basin exhibits maximum A81 3 C values in Stage 5a. The record from Animal Basin stands in contrast to the other records in late Stage 5. The record shows decreasing trends in A8I3C at the Stage 4-5 boundary (Figure 35). This suggests that oxygen concentrations in Animal Basin are increasing at the end of Stage 5. The increase begins near the Stage 5a-5b boundary and continues to the Stage 4-5 boundary where A8I3C values near Holocene values. From the Stage 4-5 boundary trends are similar to that of the other SCB records for Stage 4, with oxygen concentrations generally increasing through Stage 4. Stage 5 Summary In general Stage 5 can be seen as a Stage in which oxygen concentrations cycled from a minimum, through a maximum, back to a minimum. Throughout Stage 5 the water column appears to be in phase, unlike the pattern seen in Stage 6, and as Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 73 will be seen in Stages 3 and 4. Conditions at the end of Stage 5, across the SCB, appear to be relatively less ventilated than Holocene conditions. The difference, however, is approximately 0.1 %c, which corresponds to a relative decrease of approximately 15pM of dissolved oxygen. Stage 4 The beginning of Stage 4 finds the basins of the SCB in a comparatively reduced state of ventilation as compared to Holocene conditions. The upper water column exhibits ASI3C values approximately 0.3%c lighter than Holocene values, suggesting that oxygen concentrations were decreased at the beginning of Stage 4 as compared to Holocene conditions. From the Stage 4-5 boundary, A8i3C values for all the basins show general decreasing trends toward the Stage 3-4 boundary. The AS1 3 C records from the shallower basins suggest that oxygen concentrations remained relatively less ventilated from the Stage 4-5 boundary to approximately 65 kyr. The record from San Nicolas basin shows significant increases in A81 3 C from the Stage 4-5 boundary, reaching a maximum at approximately 65 kyr. Oxygen concentrations then appear to increase from mid-Stage 4 (65 kyr) to the Stage 3-4 boundary. Tanner Basin exhibits relatively constant AS1 3 C values from the beginning of Stage 4 to mid-Stage 4 (65 kyr) and does not record similar changes in AS1 3 C as San Nicolas Basin, despite being at similar depth. The A8I3C record from Tanner Basin suggests that oxygen concentrations remained relatively low throughout Stage 4 (Figure 37). Descanso Plain exhibits similar patterns to that of Tanner Basin. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 74 B E N T H IC A 81 3 C San Nicolas Basin E W 9 5 0 4 -0 8 P C AS13 C (%.) 0 0.4 0.8 50 - - H I l a 5 0 -- 200- - Sill = 1,100m < ------ M ora O x y g e n L a s s O x y g e n FIGURE 36 - Plot showing variation in A8i3C for San Nicolas Basin. A8I3C represents changes in 81 3 C in excess of global S1 3 C variation. We assume that these variations are primarily driven by changes in dissolved oxygen, and hence AS1 3 C acts as a monitor of dissolved oxygen content. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 75 B E N T H IC AS13C Tanner Basin E W 9 5 0 4 -0 9 P C A513C (% » ) 0 0.4 0.8 0 F 1 0 0 - - $ lii a < ~ T T 'I | 1 IQ I 1 1 1 j 1 1 1 | 1 1 1 J 1 1 1 [ 1 L 2 - r 3 . - > 5a - 5b 5c - \ 5d - 5a - 6 - Sill = 1,160m O x y g e n L e s s O x y g e n FIGURE 37 - Plot showing variation in ASI3C for Tanner Basin. ASI3 C represents changes in Sl3C in excess of global 8I3C variation. We assume that these variations are primarily driven by changes in dissolved oxygen, and hence A51 3 C acts as a monitor of dissolved oxygen content. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 76 BENTHIC A51 3 C San Clemente Basin EW9504-05PC a s ,3c (%•) 0.2 0.6 1 50 00 — U l 50 2 00 - Sill = 1,815m L e s s O x y g e n M ore O x y g e n FIGURE 38 - Plot showing variation in A8I3 C for San Clemente Basin. ASI3 C represents changes in 8l3C in excess of global 8l3C variation. We assume that these variations are primarily driven by changes in dissolved oxygen, and hence A8l3C acts as a monitor of dissolved oxygen content. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 77 From mid-Stage 4, the shallower silled basins (San Nicolas, Tanner, and Descanso) exhibit significant decreases in A81 3 C (Figures 3 5 , 3 6 , and 3 7 ). This suggests that oxygen concentrations in the upper water column increased rapidly from mid-Stage 4 to the Stage 3-4 boundary. A8i3C values decrease, from a maximum in San Nicolas and Tanner Basin of approximately 0.8% c at 7 0 kyr, to near Holocene values at approximately 6 0 kyr. Descanso Plain exhibits a similar decrease in A81 3 C, from a maximum near 7 0 kyr, to Holocene values at 6 0 kyr. The magnitude of the decrease, however, is not as large as seen in the records from San Nicolas and Tanner. Unlike the shallower basins, the record from East Cortez, during late Stage 4, exhibits increases in A8i3 C. This suggests that oxygen concentrations at intermediate depths decreased slightly at the end of Stage 4. Values increase from a A81 3 C minimum at approximately 65 kyr, approximately the same time the shallower basins were experiencing lowest oxygen conditions, and continue to increase through the Stage 3-4 boundary (Figure 34). The record from San Clemente Basin shows similar trends to those of East Cortez Basin. Oxygen concentrations at the outset of Stage 4 are relatively lower than Holocene values. However, oxygen concentrations appear to initially decrease at the beginning of Stage 4 reaching a minimum at approximately 65 kyr (Figure 38). As with the East Cortez record, from approximately 65 kyr to near the Stage 3-4 boundary oxygen concentrations appear to increase significantly. A81 3 C values decrease from a maximum of approximately l%c at 7 0 kyr to approximately 0.8%o at the Stage 3-4 boundary. The value of approximately 1 % o is somewhat suspect as it is Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 78 constrained by a single data point. A more likely scenario is that San Clemente reaches a A8I3C maximum similar to that of East Cortez Basin of 0.8%o. Late Stage 4 finds the basins of the SCB in varying states of ventilation. At the close of Stage 4, San Nicolas Basin has A81 3 C values that indicate a relative oxygenation as compared to Holocene values (Figure 36). In contrast to the upper water column, records for the intermediate and deep basins have A8i3C values that indicate oxygen concentrations were less than Holocene values. As with Stages 5 and 6, the record from Animal Basin is different than the other deep Stage 4 record of San Clemente Basin. Animal Basin has AS,3C values at the end of Stage 4 near Holocene values, suggesting relatively higher oxygen concentrations in Animal Basin as compared to San Clemente Basin. Stage 4 Summary As with the beginning of Stage 5, and unlike the beginning of Stage 6, records of A8I3 C find the shallow, intermediate, and deep ocean in phase. A81 3 C values appear to indicate that the SCB was relatively less ventilated, as compared to Holocene conditions, at the outset of Stage 4. All the records appear to be in phase to mid-Stage 4, showing maximum A8i3C values and lowest oxygen conditions at approximately 70 kyr. By late Stage 4, however, the deeper water column apparently becomes decoupled from the upper water column. Records from the intermediate and deep basins suggest that oxygen concentrations in the SCB begin to increase at approximately 70 kyr, reaching highest levels just before the Stage 3-4 boundary. The shallower sites, however, experience highest oxygen conditions at the Stage 3-4 boundary. This is similar, as will be seen, to patterns in Stage 2 in which the deeper Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 79 basins show increased ventilation with subsequent thickening of the ventilated zone ultimately encompassing the shallower basins. Stage 3 As we move into Stage 3, A81 3 C values in the basins begin to increase, signifying decreases in dissolved oxygen across the SCB. As with Stage 5, the shallow records of San Nicolas, Tanner, and Descanso first exhibit changes. The records begin to exhibit higher ASI3C values, as compared to Holocene values, at the Stage 3-4 boundary (Figures 33, 36, and 37). In San Nicolas Basin, the decrease in A8I3C slightly precedes the Stage 3-4 boundary and begins to diverge at approximately 60 kyr. A81 3 C values of the three basins show an approximate 0.2% c increase through Stage 3. Maximum values of ASI3C, for all three basins, are reached at approximately 4 0 kyr, and then decrease to the Stage 2-3 boundary where values return to Holocene values. San Nicolas Basin further shows a spike in the A8I3 C signal, reaching a maximum value of approximately 0.6% c at 30 kyr. This spike is possibly noise as it is constrained by a single point. It is likely that A8i3C across this interval remains constant at 0.4% c. The records from the three basins seem to indicate that dissolved oxygen levels for the shallower depths of SCB initially deceased during Stage 3, reaching a minimum at approximately 40 kyr. From 40 kyr the records suggest that oxygen levels increased (decreasing ASI3C values), reaching Holocene levels near the Stage 2-3 boundary. This would indicate that dissolved oxygen values in the SCB, through Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 80 Stage 3, cycled through a minimum and returned to Holocene values at the Stage 2-3 boundary. The records from the intermediate and deep silled basins seem to be decoupled from the shallower records during Stage 3. ASI3C values from the intermediate silled basins indicate that intermediate waters of the SCB were relatively more ventilated from mid-Stage 3 and into Stage 2 (Figures 34, 38 and 39). A81 3 C values decrease from the Stage 3-4 boundary, reaching Holocene values at approximately 40 kyr. The change to Holocene values signals the end of a long decrease in A8I3C from maximum values (minimum oxygen) in Stage 4. From 40 kyr the intermediate silled basins continue to exhibit decreasing A8I3C values (more oxygen). Similarly, from 40 kyr, the shallower silled basins begin to exhibit decreases in A81 3 C (more oxygen). The record from San Clemente Basin appears to be decoupled from the shallower records of San Nicolas and Tanner, similar to the records from the intermediate basins. AS1 3 C values for San Clemente Basin decrease from the Stage 3- 4 boundary, reaching Holocene values at approximately 45 kyr. A8I3 C values continue to decrease to the Stage 2-3 boundary, suggesting increasing levels of dissolved oxygen at approximately 1,800 meters (Figure 38). The Stage 3 A8I3 C record for Animal Basin shows no similarity to the record from San Clemente Basin, the other deep silled record. The record from Animal Basin more closely resembles the records from shallower depth basins. The Animal basin record shows little A8I3 C decrease during Stage 3 until near the Stage 2-3 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 81 boundary where values decrease by approximately 0.2%c (Figure 35). Maximum A81 3 C values (lowest oxygen levels) are observed in Stage 3 at approximately 40 kyr. However, again, A8I3C values are only slightly elevated as compared to Holocene values. From 40 kyr to the Stage 2-3 boundary, ASI3 C values for Animal Basin decease (increasing oxygen), reaching Holocene values near the Stage 2-3 boundary (Figure 34). Stage 3 Summary In general A8n C trends through Stage 3 indicate that waters in the SCB were relatively less ventilated as compared to the Holocene, with lowest oxygen levels near the beginning of Stage 3. It appears, however, the intermediate basins, as well as the deep record from San Clemente Basin, are decoupled from the shallower records of San Nicolas and Tanner Basin. The shallower sites exhibit lowest oxygen levels during the latter half of Stage 3, whereas the intermediate sites exhibit lowest oxygen levels during the beginning of Stage 3. The record from San Clemente Basin shows similar trends to that of intermediate depth records. As with Stage 4, the record from Animal Basin appears markedly different from other records of the SCB. This may indicate that Animal Basin does not record and, hence, is not “seeing” the same magnitude of change in ventilation as the rest of the SCB Basins. This would indicate that the changes in ventilation are restricted to the upper 2,000 meters of the water column. Stage 2 The records of ASI3C from Stage 2 show similar results as previous work (Kennett and Ingram, 1995; Behl and Kennett, 1996) in the SCB. At the beginning of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 82 BENTHIC A 813C No N am e B a sin AHF 16832 A81 3 C ( % o ) 5 0 - - £a 00 — t m a < 5 0 — 200 Sill = 1,550m L a s s O x y g e n M ore O x y g e n FIGURE 39 - Plot showing variation in A8I3 C for No Name Basin. A81 3 C represents changes in 8l3C in excess of global Sl3C variation. We assume that these variations are primarily driven by changes in dissolved oxygen, and hence A8I3C acts as a monitor of dissolved oxygen content. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 83 Stage 2 the intermediate and deeper silled basins appear to be relatively more ventilated, and the shallower basins relatively less ventilated, as compared to Holocene conditions. Basins show initial decreases in A81 3 C indicating higher levels of oxygen across the SCB throughout Stage 2, with subsequent increases in ASI3C to Holocene values. From the Stage 2-3 boundary, through mid-Stage 2, A81 3 C values of the three shallow silled basins decrease, reaching a minimums near the Stage 1-2 boundary (Figures 33, 36, and 37). From the Stage 2 minimums at approximately 12 kyr, the shallower basins exhibit increasing ASI3C values through the Stage 1-2 boundary. The increase from minimum A81 3 C values begins at approximately 9 kyr in San Nicolas Basin and at approximately 12 kyr in the records from Descanso Plain and Tanner Basin (Figures 34, 36, and 37). The increase in A81 3 C coincides with the Stage 1-2 boundary in the three basins. The trend toward higher values of ASI3C, indicating lower levels of dissolved oxygen, continues through mid-Stage 1 reaching a minimum at approximately 5 kyr. The intermediate silled basins of East Cortez and No Name, with sills of approximately 1,400 and 1,550 meters respectively, show decreases in A8I3C beginning at the Stage 2-3 boundary (Figures 34 and 39). This is similar to the shallower silled basins which also exhibit decreasing A8I3C values across the Stage 2- 3 boundary. The timing of the decrease in the intermediate records, however, precedes the decrease in the shallower records. This suggests that waters with higher oxygen concentrations first reached the SCB at intermediate depths and the zone of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 84 increased ventilation progressively thickened, affecting shallower depths. The timing of the AS1 3 C increase in San Nicolas and Tanner, from the minimum at approximately 12 kyr, may possibly indicate that the zone of ventilation retreated from the intermediate waters and progressively from shallower waters. A81 3 C values for the intermediate silled basins remain relatively low through Stage 2 and, similar to the shallow silled basins, AS1 3 C values remain relatively light through the Stage 1-2 boundary. This suggests that the intermediate waters of the SCB remained relatively more ventilated through Stage 2 and into Stage 1. The ASI3C transition from lighter values (increased oxygen) to Holocene values in the intermediate silled basins begins at the Stage 1-2 boundary and continues to approximately 5 kyr were it reaches a minimum, indicating lowest oxygen conditions (Figures 34 and 39). If dissolved oxygen levels at Site 849 were not different during this period as today, a 0. l%o difference would indicate that dissolved oxygen levels were near zero at 5 kyr. The two deep silled basin of this study, San Clemente Basin (sill depth of 1,815m) and Animal Basin (sill depth of 2,000m), exhibit records through Stage 2 that are not necessarily consistent with each other. The record from San Clemente Basin exhibits A8I3 C trends similar to those of the intermediate silled basins. Values for A5i3C begin to show a decline shortly after the Stage 1-2 boundary and continue to decline through Stage 2, reaching a minimum at approximately 12 kyr (Figure 38). AS1 3 C values remain relatively low through the Stage 1-2 boundary and into Stage 1. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 85 The record from Animal Basin exhibits A8I3C trends, through Stage 2, that are not consistent with the San Clemente record, as well as the other records of this study. The record from Animal basin exhibits AS1 3 C values similar to present day values throughout Stage 2. Values begin to diverge to higher values (less oxygen) approaching the Stage 1-2 boundary (Figure 35). It is possible that Animal Basin, due to its deep sill, is “sampling” water that remains relatively unchanged during Stage 2, and hence the ASI3C shows little divergence from contemporary values. Stage 2 Summary The ASI3 C records of the basins of this study indicate that waters within the SCB were relatively more ventilated through Stage 2. The records suggest that the ventilated waters first entered the SCB at depths near 1,400 meters, as seen through the records of East Cortez and No Name basin, and progressively thickened as evidenced in the shallow records of San Nicolas basin, Tanner Basin, and Descanso Plain. The temporal extent of the increased ventilation, as well as the magnitude of the ASI3C decrease, is greatest in the two intermediate records. This suggests that the core of increased ventilation, during Stage 2, occurs in the intermediate depths of the SCB. The magnitude of the A8i3C decrease, across the SCB is fairly consistent between all basins with a value of approximately 0.3%o (The implications of a 0.3%o decrease in ASi3C are explored in the next chapter using a mass balance approach). The spatial extent of increased ventilation in Stage 2 seems to be defined at depth by the AS1 3 C record from Animal Basin. It is possible that the lack of change in AS1 3 C during Stage 2 in Animal Basin is an artifact of the water mass at 2,000 meters being Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 86 relatively unchanged. This notion is supported through the dissimilarity between the records from Animal basins and the other basins of the SCB for Stage 3 and beyond. Figure 40 presents A8I3C for all basins. Stage boundaries were picked based on dates from Martinson et al. (1987). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 87 2 « 1 1 " I < ® 2 a • : X 6 t - a U l zzx Si- o O v is IS 5 :> •o" u X X h i « FIGURE 40 - A51 3 C for the seven basins of the study. The vertical line represents the approximate Holocene A5I3 C value. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 88 DISCUSSION Records of A5I3C suggest that oxygen concentrations across the SCB have varied from relatively less ventilated to relatively more ventilated, as compared to the Holocene, on glacial to inter-glacial timescales. We feel that there are two possible mechanisms that could have affected changes in the ventilation of the SCB, 1) increase/decrease the oxygen content of source waters entering the SCB, and/or 2)increase/decrease the “travel time” of the source water to the SCB, allowing more/less time for oxidation of organic m atter. It is difficult to assess whether Mechanism 1 is primarily responsible for the variability seen in the A8i3C signal. This is due to poor understanding of the source region for deep waters entering the SCB and because multiple processes can be called on to drive changes in source water oxygen content. Changes in productivity in the waters overlying the source region could drive oxygen concentrations in either direction. Increased productivity would cause source water oxygen values to decrease, and, conversely, decreases in productivity would cause increases in oxygen. Another mechanism by which source water oxygen values could be changed is through a recent ventilation event, or by mixing of the source water mass with a water mass high in oxygen content. It is the uncertainties in the driving mechanism for changing source water oxygen content that makes assessing Mechanism 1 difficult. Mechanism 2, increasing/decreasing the “travel time” of source waters to the SCB, is more readily assessed. The amount of time it takes water to reach the SCB can be addressed in relative terms by reconstructing the deep water-surface water age gradient. The age gradient between the surface and deep ocean is a function of deep Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 89 water flow. Today the gradient between the surface North Pacific and deep North Pacific is on the order of 1,700 years (Van Geen et al, 1995). A reduction in this gradient would signify that the “travel time” of waters to the deep North Pacific decreased, assuming that productivity remained constant. Reducing the “travel time” may increase oxygen content because deep waters experience less oxidation, if the rain of carbon to the deep ocean remains constant. Reconstruction of relative changes in the deep-water/surface-water age gradient can be accomplished through down-core l4C dating of benthic and planktonic foraminifera from the same sediment horizon. Data from the SCB (Figure 41, Table 4) suggests that, at least during Stage 2, the “travel time” mechanism may be in play. I4 C data from San Nicolas, East Cortez, and San Clemente Basin all show decreases in the benthic-planktonic age gradient during coincident intervals that the A81 3 C signal suggests that the SCB was relatively more ventilated (Figures 41 and 42). The data sets are somewhat suspect, however, as the benthic-planktonic age gradient at several intervals exceeds 2,000 years, the age of the oldest known deep waters today. This discrepancy may be due to reworking of the sediments, or downslope transport of sediments. The records do, however, show decreases in the benthic-planktonic age gradient across the same intervals as A8I3C indicates increased oxygen content. The two data sets, when considered together, are consistent with the assumption that “travel time” for deep waters from the source region to the SCB was decreased during Stage 2. To this point, analysis of the A8i3C signal and its implications has been mostly qualitative. Here, we shift focus and take a more quantitative approach in analyzing the A8I3C signal. To gain a first order understanding of the ASi3C signal we utilize a Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 90 ,4C BENTHIC-PLANKTONIC GRAOIENT S an N icolas B asin E W 9504-08PC 50 Plank. "C Banthie '*C _ 100 § 5 150 a. L il o 200 250 300 40 20 30 50 0 10 "CAGE (K yr) ,4C BENTHIC-PLANKTONIC GRADIENT E a st Cortez Basin E W 9504-04PC O xyganaiad Interval 50 100 P 150 200 250 300 50 30 40 0 10 20 "CAGE (K yr) ,4C BENTHIC-PLANKTONIC GRAOIENT S an C lem ente B asin E W 9504-05P C 5 0- - 100- - 5 1 50-;- 2 0 0 - - 2 5 0 - - Plank. "C Benthic "C 3 0 0 - f 0 50 40 30 10 20 ,4 C AGE (K yr) FIGURE 41 - 1 4 C plot of benthic and planktonic foraminifera from the same sediment horizon. Decreases in the age gradient are temporally coincident with intervals in which the A8|:,C signal suggests that dissolved oxygen was increased. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 91 BENTHIC-PLANKTONIC 14C AGE GRADIENT Benthic-Planktonic Age Difference (kyr) San Clemente Basin O East Cortez Basin San Nicolas Basin FIGURE 42 - l4C plot of benthic age minus planktonic age based on analysis of foraminiferal tests from the same sediment horizon. Note that for certain horizons in San Clemente and San Nicolas Basins the age difference exceeds 2kyr. This possibly indicates reworking or down-slope transport of sediment at these horizons. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 92 mass balance. The mass balance is set up such that the 8I3C signal of the SCB is a function of the initial SI3C signal as seen in the deep Pacific, plus a term accounting for oxidation of organic matter as waters travel from the source region to the SCB. The balance is set up as follows: 51 3 Cscb(Cd.p.+Cox.)= §I3Cd.p.Cd.p.+( §l3CsU ri.-20%o) Cox. Where: 5I3 CS C b= S1 3 C signal of the SCB 8 ,3 C d .p .= 5,3C signal of the Deep Pacific § l3C su rf.= § '3 C signal of the Surface Ocean Cd.p.=TC02 concentration of the Deep Pacific in (imol/kg Co x .=TC02 concentration of carbon oxidized, in (imol/kg, as source water travels to SCB ( 8 l3Csurf.-20%o)=Isotopic composition of organic matter oxidized Rearranging gives: C (6"C - 6 U C ) Q — n p W n n u (< 5 L ,C -< 5 'r +20) v S C B S u r j . As previously discussed in the methods section, the parameter A81 3 C was obtained by subtracting the SCB 8I3C records from ODP Site 849. This is 8 I3C d .p .- 8 i3C s c b - Rewriting the mass balance gives: C = _____C np(A6"C)____ - ( ^ - ^ ^ + 20) A litmus test for the validity of this formulation is to determine if the balance accurately models present conditions. In investigating the mass balance and the implications of the parameter ASI3C we will focus on the record from East Cortez basin as it is the most complete record and shows the largest variation in AS1 3 C. Today, waters Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 93 entering the SCB at 1,400 meters, the approximate sill depth of East Cortez Basin, have dissolved oxygen values of approximately 50pmol/kg. Assuming the source water region for the SCB has a dissolved oxygen concentration of 1 lOpmol/kg (average value of dissolved oxygen for Pacific Intermediate waters near ODP Site 849), it implies that 60pmol/kg of oxygen is lost as waters travel from the source region to the SCB. Today, the A§I3C value for East Cortez Basin is approximately 0.4%o. The test for the mass balance is: Does a 0.4%c A5I3 C value account for a decrease in oxygen of 60pmol/kg? Substituting values into the mass balance gives: q _ 2400umol/ke (0.4%*) °X (0.3%c-2%e+20%o) Cox.=52 jj.mol/kg Assuming a Redfield ratio of 106:16:1150 for Carbon:Nitrate:Phosphate:Oxygen (Martin et al. 1987), the corresponding decrease in dissolved oxygen equals approximately 70pmol/kg. This compares well, as a first order approximation, to the presently observed value of 60pmol/kg. Now, using the mass balance as a first order approximation to quantify dissolved oxygen changes, we can explore the implications of the A8I3C signal. Using the A8I3C record from East Cortez Basin, we now investigate the largest excursion in A81 3 C seen in the A8I3C records of this study. The record from East Cortez Basin shows an approximate 0.8%o excursion in ASI3C at approximately 80 kyr, the end of Stage 5a (Figure 43). This excursion represents minimum oxygen conditions for East Cortez, and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 94 for the SCB. Using the mass balance to quantify dissolved oxygen, this AS1 3 C shift represents a difference between ODP Site 849 and the SCB of 140pmol/kg of dissolved oxygen. Today, Pacific Intermediate water has a dissolved oxygen concentration of approximately 1 lOpmol/kg. If Pacific Intermediate waters had relatively similar dissolved oxygen concentrations during Stage 5a as today, this suggests that East Cortez Basin should have gone anoxic during Stage 5a (oxygen deficit of approximately 46pmol/kg). There is, however, no evidence that East Cortez basin was anoxic during this interval. We feel there are multiple scenarios in which a 156pmol/kg drop in dissolved oxygen could be accommodated. Three scenarios are presented. Scenario 1: The dissolved oxygen concentration at ODP Site 849 was near Holocene concentrations (Approx. llOpmol/kg). With this scenario, the approximate 0.8%c shift in the A8I3C parameter is accommodated by changes in the SCB or source water region of the SCB. Here, the SCB needs to have a higher dissolved oxygen concentration to keep the basins from going anoxic. Several possible mechanisms by which to increase SCB oxygen content are: • Source water dissolved oxygen concentration was higher during Stage 5a. Several possible mechanisms to increase source water oxygen content are, but not limited to: 1) decreased rain rate of organic matter in the source region caused by a decrease in productivity, 2) a ventilation of the water of the source region, or 3) mixing of the source region water with a water mass high in dissolved oxygen, creating a new source water mass higher in dissolved oxygen. • Shift in the source water region to a region with higher dissolved oxygen content. This mechanism requires a change in physical oceanography, and could be accommodated by changes in deep water circulation patterns. • A decrease in the “travel time” of source water to the SCB. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 95 BENTHIC A513C East Cortez Basin EW 9504-04PC A 5 13C (*■) 0 0.4 0.8 >. LU o < 1 0 0 150 200 M o r e O x y g e n L e s s O x y g e n FIGURE 43 - A8i;iC plot for East Cortez Basin. The excursion of approximately 0.8%c at 80kyr represents peak low oxygen conditions for the SCB for the last 200kyr. This excursion corresponds to an approximate drop in dissolved oxygen of 150pmol/kg. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 96 • Decrease productivity in the SCB. This would increase dissolved oxygen concentration in the SCB, allowing for greater amounts of oxidation to occur before anoxia. Scenario 2: ODP Site 849 had higher dissolved oxygen concentrations during Stage 5a as compared to the Holocene. In this scenario the oxygen gradient, and hence the A8i3C gradient, between the SCB and ODP Site 849 is increased, allowing for more oxidation to occur between ODP Site 849 and the SCB before waters become anoxic. Scenario 3: The foraminiferal species used in the study have vital effects and have not accurately recorded bottom water 8 I3C. Another mechanism by which the ASI3C signal may be affected is through authigenic calcium carbonate precipitation. A calcium balance for pore waters indicates that Calcium Carbonate precipitation on existing foraminiferal tests should shift the S1 3 C signal by approximately -0.05% o, although some assumptions required could underestimate this effect (Hammond, pers. com.). The magnitude of AS1 3 C shifts seen in the SCB records is approximately five times greater than this effect, and should produce only a modest influence on the signal. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 97 CONCLUSIONS • The ASI3C parameter exhibits somewhat temporally coherent variability across the SCB. Authigenic calcium carbonate precipitation may contribute to the variability. The contribution, however, is approximately 5 times less than the variation in the signal. • Ventilation conditions of the SCB, in comparison to ODP Site 849, as seen through the parameter A81 3 C, have varied from relatively more ventilated to relatively less ventilated, as compared to Holocene conditions, on glacial to interglacial timescales over the last 170 kyr. We interpret this to be driven by changes in the dissolved oxygen gradient between the SCB and ODP Site 849. • The records for Stage 2 and Stage 3 agree with previous work (Kennett and Ingram 1995; and Behl and Kennet 1996), suggesting that conditions were relatively more ventilated during Stage 2 and less so during Stage 3. This suggests that the changes in ventilation seen in the SCB records are not merely a local signal, but a monitor of conditions in the North Pacific. • During Stage 2 it appears as though the intermediate water column becomes relatively more ventilated with the zone of ventilation thickening, in time, to shallower depths. The zone of increased oxygen does not appear to extend to greater than 2,000 meters. • During Stage 3, the end of Stage 4, and Stage 6, the upper water column (<1,000 meters) appears to be decoupled from the deep water column (1,000 to 2,000 meters). During periods in which the upper water column appears more ventilated, the deep water column appear to be less ventilated, and vise versa. This is similar to a pattern reported by Van Geen et al. (1995) for the Northern California Margin. It is important to note, however, that age control during this interval is on the order of 20 kyr, making correlation tenuous. • There does not appear to be a close correlation between the ventilation condition of the SCB and glacial versus interglacial periods as previously suggested by Kennett and Ingram (1995) and Behl and Kennet (1996). • Changes in oxygen, assuming that the SCB and ODP Site 849 have the same dissolved oxygen to 81 3 C relationship (Figure 9), we feel, can be driven by two separate mechanisms: 1) decrease/increase the oxygen content of source water for the SCB 2) decrease/increase the “travel time” of source water to the SCB • Using a mass balance calculation it appears as though oxygen concentrations dropped by approximately 150pmol/kg during Stage 5a, which corresponds to minimum oxygen conditions across the SCB. A drop of this magnitude would have driven many of the basins anoxic, however, there is no evidence of anoxia. We feel there are three scenarios Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 98 by which a drop of this magnitude could be accommodated without driving the basins anoxic. Scenarios are as follows: Scenario 1: The dissolved oxygen concentration at ODP Site 849 was near Holocene concentrations (Approx. 1 lOpmol/kg). With this scenario, the approximate 0.8%o shift in the A8I3 C parameter is accommodated by changes in the SCB or source water region of the SCB. Here, the SCB needs to have a higher dissolved oxygen concentration to keep the basins from going anoxic. Several possible mechanisms by which to increase SCB oxygen content are: • Source water dissolved oxygen concentration was higher during Stage 5a. Several possible mechanisms to increase source water oxygen content are, but not limited to: 1) decreased rain rate of organic matter in the source region caused by a decrease in productivity, 2) a ventilation of the water of the source region, or 3) mixing of the source region water with a water mass high in dissolved oxygen, creating a new source water mass higher in dissolved oxygen. • Shift in the source water region to a region with higher dissolved oxygen content. This mechanism requires a change in physical oceanography, and could be accommodated by changes in deep water circulation patterns. • A decrease in the “travel time” of source water to the SCB. • Decrease productivity in the SCB. This would increase dissolved oxygen concentration in the SCB, allowing for greater amounts of oxidation to occur before anoxia. Scenario 2: ODP Site 849 had higher dissolved oxygen concentrations during Stage 5a as compared to the Holocene. In this scenario the oxygen gradient, and hence the AS1 3 C gradient, between the SCB and ODP Site 849 is increased, allowing for more oxidation to occur between ODP Site 849 and the SCB before waters become anoxic. Scenario 3: The foraminiferal species used in the study have vital effects and have not accurately recorded bottom water 81 3 C. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 99 References Atwater, T., 1989. Plate tectonic history of the northeast Pacific and western North America. DNAG vol. N. Eastern Pacific Ocean and Hawaii. Denver, Geological Society of America, p. 21-71. Bandy, O.L. and M. Chierici,1966. Depth-temperature evaluation of selected California- Mediterranean bathyl foraminifera: Marine Geology, v. 4, p. 254-271. Bandy, O.L. and R. Echols, 1964. Antarctic foraminiferal zonation: Antarctic Research Series, American Geophysical Union, v. 1, p. 73-91. Behl, R.J. and J.P. Kennett, 1996. Brief interstadil events in the Santa Barbara basin, NE Pacific, during the past 60 kyr: Nature, v. 379, p. 243-246. Blake, G.H. and R.G. Douglas, 1981. Pleistocene occurrence of Melonis pompiliodes in the California Borderland and its implication for foraminiferal paleocology: Cushman Foundation Special Publication, no. 19, p.59-67. Broeker and Peng, 1982. Tracers in the Sea. Lamont-Doherty Earth Observatory, Columbia University, New York. 690p. Broeker, W.S., T.H. Peng, S, Trumbore, G. Bonani, and W. Wolfli, 1990. The distribution of radiocarbon in the glacial ocean: Global Biogeochemical Cycles, v.4, p. 103-117. Dailey, M.D., J.W. Anderson, D.J. Reish, and D.S. Gorsline, 1993. The Souther California Bight: Background and Setting. In Dailey, M.D.. D.J. Reish, and J.W. Anderson, Eds. Ecology of the Southern California Bight. Berkeley, University of California Press, p. 1-18. Echols, R.J., 1971. Distribution of foraminifera in sediments of the Scotia Sea area, Antarctic waters: Antarctic Oceanology I: Antartic Research Series, v. 15, p. 93- 168. Emery, K.O., 1960. The Sea off Southern California. John Wiley and Sons Inc., New York. 366p. Gardner, J.V., W.E. Dean, P. Dartnell, 1997. Biogenic sedimentation beneath the California Current system for the past 30 kyr and its paleoceanographic significance: Paleoceanography, v. 12, p. 207-226. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 0 0 Gorsline, 1980. Depositional patterns of hemipelagic Holocene sediments in borderland basins on an active margin. In Field, M.E.; A.H. Bouma; I.P. Colbum, R.G. Douglas; and J.C. Ingle, Eds. Proceedings of the Quaternary depositional environments of the Pacific Coast. Pacific Coast Paleogeography Symposium, n. 4, p. 185-200. Gorsline, D.S. and K.O. Emery, 1959. Turbidity-current deposits in San Pedro and Santa Monica basins off southern California: Geological Society of America Bulletin, v. 70, n. 3, p. 279-290. Gorsline, D.S. and L. S.-Y. Teng, 1989. The California Continental Borderland. DNAG vol. N. Eastern Pacific Ocean and Hawaii. Denver, Geological Society of America, p. 471-487. Grossman, E.L., 1982. Stable isotopes in live benthic foraminifera from the southern California borderland: Thesis or dissertation, University of Southern California. Hickey, B.M., 1979. The California Current system-Hypotheses and facts: Progress in Oceanography, v.8, p. 191-279. Hickey,B.M., 1989. Patterns and processes of circulation over the Washington continental shelf and slope. In Landy, M. and B.M. Hickey, Eds. Coastal Oceanography of Washington and Oregon. Amsterdam, Elsevier Science, p. 41- 109. Hickey, B., 1993. Physical Oceanography. In Dailey, M.D., D.J. Reish, and J.W. Anderson, Eds. Ecology of the Southern California Bight. Berkeley, University of California Press, p. 19-70. Hoefs, J.H., 1997. Stable Isotope Geochemistry. Springer, New York. 201p. Howell, D.G., J.K. Crouch, H.G. Greene, D.S. McCulloch, and I.G Veder, 1980. Basin development along the late Mesozoic and Cenozoic California margin: A plate tectonic margin of subduction, oblique subduction, and transform tectonics: International Association of Sedimentology Special Publication, v. 4, p. 43-62. Keigwin, L.D. and G.A. Jones, 1990. Deglacial climatic oscillations in the Gulf of California: Paleoceanography, v. 5, p. 1009-1023. Kennett, J.P. and B.L. Ingram, 1995. A 20,000-year record of ocean circulation and climate change from the Santa Barbara Basin: Nature, v. 377, p. 510-513. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 0 1 Kulm, L.D. and G.A. Fowler, 1974. Oregon continental margin structure and stratigraphy: a test of the imbricate thrust model. In Burk, C.A., and C.L. Drake, Eds. The Geology of Continental margins. New York, Spinger-Verlag, p. 261- 283. Liu, K.K. and I.R. Kaplan, 1989. The eastern tropical Pcific as a source of 15N-enriched nitrate in seawater off southern California: Limnology and Oceanography, v. 34, p. 820-830. Lynn, R.S. and J.J Simpson, 1987. California Current system-The seasonal variability of its physical characteristics: Journal of Geophysical Research, v. 92, p. 12947- 12966. Martin, J.H., G.A. Knauer, D.M. Karl, and W.W. Broenkow, 1987. VERTEX: Carbon Cycling in the northeast Pacific: Deep Sea Research, v. 34, p. 267-285. Martinson, D.G., N.G. Pisias, J.D. Hayes, J. Imbrie, T.C. Moore, and K. Brookforce, 1987. Age dating and the orbital theory of the Ice Ages: Development of a high resolution 0 to 300,000 year chronostratigraphy: Quaternary Research, v. 27, p. 1 - 29. McCorkle, D.C. and L.D. Keigwin, 1994. Depth profiles of delta 13C in bottom water and core top C. wuellerstorfi on the Ontong Java Plateau and Emperor Seamounts: Paleoceanography, v. 9, n. 2, p. 197-208. Mix, A.C., N.G. Pisias, W. Rugh, J. Wilson, A. Morey, and T.K. Hagelberg, 1995. Benthic foraminifer stable isotpe record from ODP site 849 (0-5 MA):Local and global climate changes: Procedeing of the Ocean Drilling Program, Scientific Results, v. 138, p. 371-412. Phleger, F.B., F.L. Parker, and J.F. Peirson, 1953. North Atlantic core foraminifera: Sweedish Deep Sea Expedition Reports, v. 7, p. 1-122. Samthein, M., W. Kyaw; J. Simon; J.C. Duplessy, L. Labeyrie, H. Erlenkeuser, and H. Ganssen, 1994. Changes in East Atlantic deepwater circulation over the last 30,000 years; eight time slice reconstructions: Paleoceanography, v. 9, n. 2, p. 209-267. Stuiver, M. and H.A. Polach, 1977. Discussion; reporting of C-14 data: Radiocarbon, v. 19, p. 355-363. Talley, L.D., 1993. Distribution and formation of North Pacific intermediate water: Journal of Physical Oceanography, v. 23, p. 517-537. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 0 2 Tsuchiya, M., 1980. Inshore circulation in the Southern California Bight, 1974-1977: Deep Sea Research, v. 27(2A), p. 99-118. Van Geen, A., R.G. Fairbanks, P. Dartnell, M. McGann, J.V. Gardner, and M. Kashgarian, 1996. Ventilation changes in the northeast Pacific during the last deglaciation: Paleoceanography, v. 11, no. 5, p. 519-528. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 103 APPENDIX A Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 104 “= S g • I ?<S » ■ £ = 2 I 8 B iU tfW * o |!=.^vvVZb B B S T -- I APPENDIX A .l - 5I3 C plots for the seven SCB basins of the study. Sampling interval is approximately every 8 centimeters. Resolution is on the order of lkyr. The records were compared to the global reference record of ODP Site 849. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 105 o o ( U U t f M W o ttuiiw APPENDIX A.2 - Average 81 3 C plots for the seven SCB basins of the study. Average 81 3 C was obtained by taking a running average through the raw 8I3C records for the SCB. The Average SI3 C records were then subtracted from the ODP Site 849 record, leaving a record of 8I3C changes in excess of global variation. We define this parameter as »8I3C. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 106 APPENDIX B Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 107 O 2 Os ■*f 'i f p - O s c o p - r*- 0 T f — i n i n 0 CO SO i n r - ■o- r~- — i n i n sO t o r-; s q c o O CO i n 0 cn p — 0 — - J — — CN CN CN cn cn —- —- CN — '■ £ & c o CQ c o O n S O c o r - s o _ cn O s c o r - T f n 0 CN — O n c o "vf ■*f C O * i n SO c o 00 00 CO SO "Cf O p - 0 ON CO CN 0 0 O ) p ^ i n i n s q s q T f CO CO CO c o c o c o c o c o CQ U NO m Os _ CN CN CN p - CN 0 CN p - 0 0 O n 0 'f - i n ^ f T f T f i n p - O 0 O O O 0 0 0 6 S U > c - < O to CQ SO «n Os CN CN CN p - 0 0 c o sO P - 0 CN 0 r - NO SO i n NO O O 0 O O O 0 O l — O ' t O h ’ — fO — ^"O O ininoocoONcocot'O Tpinsop-oosop-p-sOso 0 0 0 0 0 0 0 0 0 0 0 0 0 C O 0 0 S O C O cn — O 0 0 p - * — CO IT) O ' ' t s o r-» m m 0 0 0 0 C O 0 0 O 0 0 c-- so rr r* " T f i n c o 0 0 0 0 CQ •s < ; § C J ' ■ CQ 2 O c 0 O O X ) ' a JjA c r ) tsd C u o o O O S m 0 0 s d i n o o o o s 0 0 — r- ^ ” t ^ ^ — ^ sd so 00 o c n c o c o s q T f ^ - c i o n i o r ^ P ' o d o ' MI/IIO-O'ONOSOO-OIO^^COCO o s -h N i/ i v q c j h C O ^ o o o 'O N n i r i ‘ ocNcOTt^r^oocNcoiosdr^od N(NN(S(slMNCOCOcOfOCOCO C L o Q |0 c o -o o U * 0 * O •* O * O m * r T i n * 0 * O OO * O CN sf) P - 00 O O CN O CO O r f 'd- 0 i n 0 sO O P - 0 00 S o . . 0, o o o O s UOOOOOOOIOO^OOVOO * Q - ( N N t ^ ' n ' O s O h Reproduced with permission of the copyright owner. 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Further reproduction prohibited without permission. 1 1 0 o C O To PI O ' cn SO sO p - o p - s o p - o p i sO p i o o O ' SO O ' O sO OO p - sO P I p - i n p i oo m P l SO p SO P i i n O rj- O ) r r SO cn OO OO cn cn O * — O ' — o p i p i d o d d o d — o Tf sO p - P - O in oo _ oo rj* p i SO P l O ' oo oo cn sO oo s ^ r o P I cn cn cn in SO p» p- O ' r f in oo O O s q p^ O O r-; in O Tf cn r r cn in p^ in p i p i c n cn cn cn cn p i p i p i p i p i p i p i p i p i p i cn CQ CQ gg U w O ' p i t o o o o oo © r f O ' 00 O ' c n p i tj- ■^r p i P l p~ cn i n oo — c n cn m tj* cn p i o d © ~ © O © © © © u -5 U > c 2 ) < u to 9 CQ O — * — — cn 00 © — tj- O ' P l oo cn SO cn p» Tf p © — P l pi r f in —1 — © d © © © U lb CQ O ' — n o ' t o o Is - O n lO SO CN i n OO O P - no O n O ' O O — O O O O — — — : oo oo c n — i n O ' p i — O ' P - P l O ' n O — O ' CO o — c n — n n m - o d d © © o d d p - 'rj- © d u o •= W ) ^ ■5 <1 o U C CQ 2 o 0 1 ) <! 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I ll fe§ TP oo p - _ NO o o C M N O O N o O N N O m oo N O m TP oo lO OO oo o CN TP cn in CN oo N O p- C N O N TP cn O N c n oo 00 r-; P-; N O CN C N in cn oo p - O N o cn cn cn —• — ■ —• — — • — — d — P - t p N O cn CN O cn p- Tp c n CN o O in in c n cn T p p- m NO N O o O n cn m oo N O CN o Tf cn in in CN C N 00 O n p^ Ti cn in C N in Tf Tf —• cn On CN o CN O O cn O cn e n cn cn c n cn cn c n c n c n cn C N cn cn cn CN cn cn cn i n cn t p r - in (N O O O n O oo cn O ffl ^ u w in — O n O N C N cn TP cn T f N O d O d o N O o' n (N o no n O n m Tp c n cn n n no o h o o o © d :> •£ U 5 = - < o t o 03 O n T p © — O n O N p - O n p» in <N cn N O <N oo N O p - O O C N o s IN Tp Tf in in in in NO in in in o © o o o o o O o o O C Q O c n r- n p- oo oo n o c n n o cn — cn in cn n © oo oo m m o cn n o in tp in rr Tt cs in n o in © d o o d d d d o d o O M o o i n ^ N D r i M o o ^ m M t — o o c N o o i n O T p c n c N i n T p c n r - - p^oofnin'Oin'tooiniOTrin d d d d d d d d d d d d d oo < , CQ 00 >> < ^ o m i n o o r - * * o d cnocnenor-oooooineNenincNr-cNp--ONOOcNTpNOooo i n r '! ( N f '] ! > n N q f n q N c r n q o p P O ,tP;(NC\inh;&~Nqin CNd(Ni(NNrninod--c,'irndiriini*'odoNON«doN^: dNd't — cn cn cn cn cn c N C N c n c n c n c n c n e n m e n c n c n T p i n i n i n N o r - P - o o O . s Q 3 in «n oo - © r N T p p - * o c n © c N i n — p» m on in — cn in p-- cn © © © © — c N c n T p T p i n i n N O N O N o r - p ' - o o o o o N © —« n n in p C-vJfSjfvJCNjCNJCVj t O fO N O O O O N O N O N ^ ^ ^ ” ^ o u Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 112 o 00 ~ 0 O U e o .2 o OO Ov p*« P-* in 00 in Tp CN in P-* p- p- vo 00 On m ON vO m — — — CN — — d O cn ^ ^ O N ' r t ' O N i r i - ^ N S O S S — -^pcn — p - o m o N — O H — O c n eN cn r - T p f n d d Q o d d d d d d d d c o CQ cn oo __ P - in NO in O n cn in O O cn vO in O n s s P-* NO C N O n O O 00 cn c n m m o p- CN o T f NO e' NO VO O n cn -^p "3- m m cn c n cn CN CN cn en cn cn CN (pi CN CN C N CN cn c n c n cn c < u CQ U 00 OV 00 CN p - cn r - oo r* oo r - i n ^ T f i n m cn o d o o d d o c n i n o vo S « in n 'O i n o t t >n d o d o d cn d o m d o rr "3 ’ d > C — ) < § to g CQ oo On OO N Is M P - O n P - no vO O m m i n \ o d d d d o ‘ d © c n i n © vo r r © cn o oo ov on o oo d o — d d o o o o m m O N p - CN cn m m o o o o U to ° S c o CQ o — p-- m i n o vo © cn o v i n i n i n c n cn t p i n vo d d o d d d T p V O 00 — — cn cn cn t p no cn oo © i n d —: d — : d oo cn cn OO — <N — m rt in n- — < N m cn Ov in d P— Ov Ov oo on i n i n i n oo o d d •= oo i < ■ § u 1 CQ 2 O Ov s < ca ^ k> O cn o vd o i- 00 ;n < £4 cn i n O n ' : - ^ 2 O' O' ^ ov m m vo in ^ o - oo cn d d i n « cn cn c n cn Ov I — Ov O 1 — n n n n n d ^ i n ' t ^ vO cn oo p - no — i n <n - o o oo — • cn cn cn t p t p O oo cn o r- o Ov O O — o c n oo ov 2 — z: — i n © © o o o i n v o p - O N O O N O p - ooocnTpvor-'p^ooovoinvo c N c n m c n c n c n c n c n c n - ^ j - T f T p w M Tt m (N - co vo ^ n - o o v o S C N 3° — cNcNcnTf-^rinvop^ooooovdi c o *o o V U u Qu cu cn ■TP © •rt* © s m s m O n O n £ £ ui L U Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 113 O g, J2 i n i r i M v C ' t i ' i n n m - - oop-*soo©ascNso©p*»p--© « ^ 00 (S — h- C S O N 10 M V O CN 00 sO o o ^p Os SO Tf SO cn cn sO o CN m c n i n oo OS oo oo © o cn O o s m Ov sO i C N 3 SO r-- oo Os o 00 — — — — — — o — — o — — o o o 3 C 00 ^ O o ' ■ s 2. e o C D p - un CN «n «n C N m Os sO 00 _ m m — cn r~- Os __ in r - cn o C N i n CN «n t p TP n - sO c n SO Os so o CN sO oo Os P - o c CN sO 0 0 CN s q O O p oo p oo 00 o o p p 00 p oo p p s o sO sO Tp SO in in in cn cn cn cn c n cn cn c n c n cn cn cn cn cn cn cn cn cn cn cn cn cn cn 03 U o o o m O "3 - (N © ' O T f C N d o o T f o i) ■ £ U ' > c 2 < o <0 03 o o o o © © sO cn sO C N c n cn CN CN CN C N © o o © © © O C N o* T f O ’t O ' M N r l ' t M W oocNoocn^psocnp- — — cncncncnTpcncncN^fcn d d d d d d d d o d p - » m — CNSOOO^OOOSOCN— ’ • 3 ’ ^ O - 0'ffi ' O0' w ^ N f n - oo — — cn — cncn — cncN — cncN cn o d d d d d o d d d d d o' CQ o o •= 0 1 ) ^ *5 <! « o U * CQ 2 C J c o a> 00 - r c C ) -T C L o n- 00 5n < ^ m i n c n c N — © © o o p - s o - s j - m c n c N — o © ls;P^irj,^ n ( N M ^ 0 0 l s|in'O^;fntN-;-; c n T t - i n s o p - - o d o s O s d — e N c n — cn N (N fN p'-cnoocnosrpp-^cNoqcn ’t i r i o S o o o d o ' d d - — c n c n sd os cn cNCNCNcNCNCNCNcncncncncncncncnTf D * £ & * C N — O O S O rf C N — 00 S O rf — — 00 vO — c ^ r ^ c n ^ > n v D v O P ^ o o O N O O — ^ C N — O O \D C N O O O N - O O vo Tf O J c N c n - ’t f - T p i n P ^ o o o s — cn cn c n t p i n cNCNCNcNCNcNcNcNcnmcnmcnm o u Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 114 © NO r-* to T f CO NO — to © 00 to On CO On 00 ON rq 00 3 oo r-; r-* I ■rf —m — © © — — © © © o s c t o CQ — o o i o n o o n o — c o o v t — < n — t o t o o o © — ^ c ^ f N O N c o t — —■ vo ro ro — — so — oo \o so ro — co r-- co oo cn © ~ o < n o o ^ ^ M \ O h N O N - ^ co v O T f ^ r ^ v o v o ' O i n T f T t ( ^ T t f s a \ o o - ; — © o n o . c > N D r - ^ r - ^ c N c N c N N © n r l n n ^ r n r n M n n n f N n c N r i n ^ r i f v i f ' i f n r i c N r i r i o i c i t N CQ U © © © o © © © © © © ON r- vo — NO 00 00 © On t o r- oo r- 00 t o CO d © © © © © © © © © o o f- © 6 S V ' > c 2 ‘ K o t< o ro >o © o oo to o o co \ o VO tO © o o s o © © © © © © r- 00 t o 0 0 n O r f CO t o © © © © © © U To CQ ONCNNON©r,-coioONCNONr--r',-co — cnno — cNooco^oor-NOcocNNor-* » o r - - t o i o v o i o < N T f c N a v r - - m ’' 3 - m ( N o o v o o o i r i © r ,- < N T i - < o v o o v v o — Tt^fr^vO’ ^ftor'-tnvO’ ^-mOfnsoiocsr^m^rtO'^frntosqtoiovooo d d d d d o d d d d d — d d d d d d d d d d d d d d d © O X J < 2 <J .- •g U * a ~t oo > ■ » < ^ On ^ O d © * 3 * K Tf to to »o vp — : — no 3 oo — ; — T f OO t o (N ON sd on w o ^ tt © co d oo — co n o © -rf oo — n to ^ S S S ooocx^OnO n^ S E S T T T - - - Cl £ < 3 * OO VO ’t fNJ « OO NO ^ N - 0 0 NO ^ CN — NO T f CN —• OO N Nj- n - OO T f ( S N O N O r - O O O N © © — C N c O T f r T t - t O N O r - O O O N © — C N C N O O O O O N © © C N C O m f n n m n ^ t t ^ ^ t t ^ t ^ t f T f i o i o t o i n m i o i O ' O O ' O y o o u Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 115 ES CN to Os © sO Tf CN O' to ro SO to so OO to ro ro 00 © p- so © © to to ro CN ro ro - — “ — — o oe ~ i o sO sO CN ro sO ro CN oo to © to CN p- CN to © CN oo „ © ro sO oo © sO ro sO oo tj- Os CN CN oo SO Os p- © 00 CN os Os so Os P- P- Os p- CN CN to to to to Os © 00 OC p- r— | p^ P-; Os SO to to tj; ro ■^r CN CN CN ro ro CO ro ro ro ro ro ro ro ro* ro ro ro ro ro ro ro CO ro ro ro ro ro* ro CQ u & ro © © o CN CM © © © © © © O ' © 1 > -5 u CQ © © o © © © © © o © © to © P- CN © r o Os Os CN © p- sO so sO P- 0 0 Os OO OO Os 00 © © © © O © © © © © © u t+i "to — C N c O © T l - t / - > a s t / - ) r O o o n N o o - i n - O ' O ' ' O ^ o o ^ O ' O i n v o ^ ' O © © * © ‘ © © d © © © tocNCNtosop-cscNtooo — oo — ^ vo - — ' D r - o r ,> ‘ 0 0 N ^ - “ ~ , (r i 0 ' ,t ^ t r s , O ( N r s s o p - p - p - s o o s o s o s o s o o o o o s o c o s o o p » o o ■ © © © © © o o d o o o * ©*©©©©© CQ < y ou , < , CQ £ < 3 O il > > < U H . g o o o o o o o o o o o o o o o o o o o o - o o i n N O j y q n o P ’t © ’ ro sO oo — ^ p o\ oi 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 " _ c o i r i ( N O \ ^ i r n q P ’t ~ c c i / ] r i a \ € r n i n p d f ^ i n o d - ’t'OC'riTfr^dpi'Aco i o u - j s o s o s o s o p - p - p - p - o o o o o o o s o s o s o s — OO sO r f CN — OO vO T}- N — 00 vO T f vO ’t O l — OO SO ^ — .. _ _ oo oo o\ o - ( N N W T r i n \ o ^ p o o - c n r o tj - tj - t/-> \ o p - y O ^ ^ V O \ 0 \ O P P P P h P P P P P P O O O O M O O O O O O M O O - OO O ’T (N j in 'O o u Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 116 o oo *tb o SO d cn 00 CN Os Os sO sO — oo tp O sO o so SO 00 p-* r- Os •— * cn t-» o Os Tp p- Os Os cn — Os rf r~- Os — Os Os so in to Tp OS Os o o o d o o o — o o — CN CN CN — — sO Os in r- o o Os Tf CN SO o r- o s r» Os O OS r-- r - r - i P-* _ ■Tp o Os r- CN Os cn cn sO p“ 00 CN 00 cn o s cn o 00 cn ^3- CN m sO in OO SO rp OO o cn Os sq in Os — — sq in in in in ■^p cn CN CN CN CN CN CN CN CN cn cn CN cn cn cn cn •*P Tp rp Tp ^p Tp ” ^p’ aa o cn o o * -> -5 < § CQ Os sO ■ ^p SO c n sO c n i n CN c n i n sO i n c n O o o O o O U 'cb CQ — c s i o o s r - r n ^ t c N i n c n O s r p s O O s O — ' t N O N - i n r f ' T d o d d d d d d os — r - - n ' — c N s o m — in os so oo — ^ © s o o o o c N c n o o ,^i-'^t 10 vo i/^ in iT/ i— in vo vo oi i/i cn d d o d d d d d d o d d © ^p cn © — Os Os O in m m Tf d o d d % a *1 < ■ § u 1 CQ 2 O o r-» Os O IT i o Tp ’S ° g BO is cu o o in 00 o m sO sd o 00 os M M n ' t T f i O s O s O h O O O O O s i ^ ^ ' J o o o o o o o o — — r - r n o o i n o o o o r - sOP^ooosoqosoooocNcnooTpinsqp^Os © — ri ro sf in sd O' O O - n m ^ _ — — cn cn cn cn cn cn cn J= - n. E < 3 ^ * * * S 0 0 2 s o o CN 28 o c n CN o O CN o c n O O oo m so -3- ti- w m 3 ^ f t r t - f C S O O s O s O ^ O O C N O O O O O O o u Reproduced with permission of the copyright owner. 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O n oo r- o o — CN © © — — CN sO c o — O tn in oo cn — O n — — CN — CN CN o D C To CQ Tf — CN O Tf r - CN NO NO — m m in NO CN NO oo c n cn Tf c n On i n 0 0 m m O n NO Tf CN o © CN m c n m c n NO Tf ON in CN Tf CN Tf Tf NO 00 c n CN CN CN c n c n c n CN c n CN c n c n CN cn c n c n c n c n CQ u CN CN Tf Tf c n r - NO CN Tf © ON 00 — c n CN © © © © © © d © o *J s u > e - < a> CO 5j CQ C N 3 © CQ rsi O c o »0 O OO ~ ° s ^ - o — rn n CN © O n — CN CN O NO © o o o ’ vO T f © — in sO O c n cn S O Tf Tf O O O cn tt m o d o o o ■ £ < * ' « g U £ CQ 2 O O N in in o C N 2 < * o r - r- N O o Tf ON O i) > » < i4 Tf C N O cn © r- oo O O — m m m o r - T f o r - ' — Tf — TfcNO — — c n cn cn o n Tf in O — cNcnTfvivop^r^ooos*® r - r f T f — o o in o o — m cN cN *ONOTfinvnoin — Tfincn o — Cl £ < 3 ^ c o •o o U T f CN O OO O — CN CN in m m in rs, - ^ , T f C N O O O s O T f O O C N O i n O O N O r ' l n c o " M n n T f i n i n ' C h h h o o O N « ^ U O h o oo on — t"- r — in — o o — ' cn n n Tf n ON £ U J Reproduced with permission of the copyright owner. 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NO 1 _ „_ cn CN Tt r-» cN cn Tt Tt 00 CN NO t— CN NO NO On in r- cn 00 oo NO O CN On CO Tt NO NO r-; oo cn r-; Tt O' — r- On (N o o r- On oo On in — — — — — — — d — d d —• — — d d o o —* O X To ^ O * c o CO T t r ^ r ^ w - j p ' - T f o c s o v o — T t c N O c n — o i c n c n m Is ; r>i i n \o in in t|- ^ o c n c n c n c n c n c n c n c n c n r t On O O in O n O oo On On CN nO tt (Nj (Nj rn y£5 M cn cn cn cn cn cn — sO O O OO — r* » n in Tt cn cn cn cn cn cn cn cn cn oo — r-- ON T t 00 fS Nt - cn cn cn U w in in r~- cn Tt OO O n CN Tf o r-- Tf NO in r- NO in ON O Tf CN n On cn cn NO cn cn cn CN cn cn — Tt 00 o d d o d o d o o d o o 6 -c U > C 2 H £ o OO H CQ n in r-- cn Tt oo O' CN Tt o r-» o o m NO o cn OO cn NO On in cn NO cn CN cn cn CN CN cn in >n o O © o O o o O o o o o U CQ T f o o c n ^ N o o O N i o O ' O O' CN On N© sO — OO nO n © Tt ^ ' O c n N c n M M M T f ^ o o o o o o o o o o N N OO OO Is* O' in no vo v> oo o ^ (N (N n cn cn 0 0 0 ) 0 0 0 r t ’T OO — h — SO NO o NO N M cn N 0 0)0)0*0 (N h- (N oo cn ' t m t-- in 0)0 0 cj t> ■5 «' S u £ pa 2 w <* C O * r i * 00 < ooinMONinNON'ONmooooinooinooinNooviNootrtMiftoeinN rfmmNor^p^oqoN»nONONNqoNNqONNOcnONNqcnONNqcnNOONNqcn *— C N c n r f i O N d r ^ o d o N - - - - c N c n « o o d o N C S i r j p ^ O c n t n o 6 — c n c n N o r ^ * N N M M N M M n N c n f n m f n c n f n f n ' j ^ ’t i o ^ ' n ' n ' O ' O ' O ' O ' O o. £ <s ^ ONp^uncn-— ONp^mcnmocntncMOrtcNOooNOTtc^iooomNOTrso u - i N o r - o o o N O N O — c s c n ^ ^ f ^ m N O N O t ^ - o o o o O N O — c N c s c n c n r j - r j - — — — — — c N C N C N C N C N C N C N C N c N c N c N c N c N c N c n c n c n c n c n c n c n c n o u Reproduced with permission of the copyright owner. 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Further reproduction prohibited without permission. 1 2 2 m o ~ c n 9 o Tf 00 ro — o o d o NO o co in oo CN O n «n CN Tf CN o o r- NO r- «n u-> oo co r-* o «n lO oo NO NO lO o O o —« m Tf co r- IT) NO Tf OO m r-; o o o d d o o o d o — — —’ d d ~ c 0) CQ — >n O n O n CN CN O p - p - r o NO NO NO O' CN r - r - O n O n r o 00 NO Tf O n r o NO s i n r - in NO p - CN O T f NO cn CO T f Tf (O — Tf Tf O T f ON p oo T f Tf oo rO oo in CN CN CN CN CN CN CN CN r o cn CN CN r o CN r o r o r o r<N r o r o r o CQ U o CN o cn CN o d O s s o o d a -5 U > c - < <U CO CQ T f oo — o CN CN (N in O O CN ro o o O O O vo to o — m S O O S d o © it) r- oo 'O ^ o (N oo ^ on in iX <o © cn © oc o oo on on co © P O P § - - - O O (N CN © d o ® © d d d d d d d O n NO o O n O n Tf 00 NO ON O OO f " — *— — m Tf — o o o d d d I ^ o o 1 CQ 2 00 < 00 > ■ * < m in on — m cs v O' Tf CN On -- n £ d - f N i N n n t i n i r i ' d K S - .© ^ T frN O o oo cN m r-O N — r o in r -. — oomroor-Tf — onnoco© on — ro so oo ooovncNONmr^- ^ - .................. ................................................................: O O •— cn ro oo w O' w u “ lN r i f n ^ f i o i r i ' O h o o o o o. £ CN OO i : T f C N O O O N O T f C N O O O N O T f C N O C - ~ N M r i T f i n ^ ^ h x o N C C J cu On O s O u U J Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 123 o CN o OO o 00 CN oo cn r-* NO p- O' cn O n CN On NO r- ON m On in CN m NO OO O' VO in CN CN r- in Tf ON o r» CN cn r~- CN CN o Tf r- in o in r-; CN Tf Tf cn CN O' oo nO CN CN cn in p r-» Tf in oo r-* — — — — — — —’ — — —’ — O o o — — d — o o d d d o X "cO o jc c u CQ n c n • o O n c n CN o Tf NO ON NO Tf 0 0 00 CN O n O n in O n m CN NO oo oo ON OO CN m CN ON 0 0 in oo in oo m NO c n c n CN 0 0 OO r- in no in s q in s o Tf Tf in CN Tf c n CN CN Ti in in NO s q Tf c n CN c n c n c n c n c n c n c n c n c n c n c n c n c n c n c n cn c n e n c n c n c n c n c n c n c n c n c n sJ _c o ' ’o ' CQ U CO c n r-* CN O n NO r-> c n no NO in oo NO O n NO in oo u n — c n c n c n c n c n c n cn — d o o O o O d o d < o co CQ ro o ON NO o\ — cm cn m no S O C N c n cn U n i T l M M O O C N - n O ' C O l O C N P ^ T f C N N O v O r - O — m c N c n c n c n c N c n e n T f e n d o d d d d d d o o \ O O O O N i n T f O O O C N N O O N i n N O O O N O © N O © v o o N c n N O i n i n o o c N © — in t"- in no e n c n c N e n c N c n e n e n e n c N e n e n e n e n c n c n d<oc><Dd<z5d<odo<oc^dcScicS 03 o o •5 <? ' r t g 5 * 03 2 O 2 00 < U n 'O oo oo co O' C\ CN ON NO ON © ON 00 d d - N r ^ - o ' d o ' d - r i ^ ' b C N N M N N M M N f O r t r t m f n T j - r t O N » n t O N O N O N D r > - r - - o o o o o N O N O ©ONoooor^NpinTfcncN — ©onoooo O cn Tf d oo on —V i in S on - D . E a * ' O o o ' O T t c s O o o ' O ^ w - ' i n o N h i n m - O N h i n c o - on p-- in cn — on © © — c N c n T f ^ i n N o r - o o o o o o o N © — c N c N c n T f i n N O N O r - - o o O N © © c N c N C N C N C N c N c N c N c N c N c N c N C N C N c n e n c n c n c n e n e n c n c n c n e n e n T f T f o u Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 124 o x To WO co T f NO T f 00 CO O n NO CN o wo CO o CO NO T f T f O n OO w o O n CN CO wo CN p - NO CN p - CO p - o o CO CO Os n CN Q — n OO p - 00 oo oo ON O n W O o CO wo T f NO CN CN T f r*^ CN © CO T f o CO p NO © © © O © — ~ ■ * — — — — — © * — *— © o 30 To ^ ■ 5 ^ c i> CQ j \ i n T j , \ O ' O n o \ N 0 0 N i n o \ - ' 0 0 v o O ' n n o c n c o o o p - - — — r - T f p - © © w o p - — CN CN CN © — n i n n N r i f S f S n - ; N O « 0 \ 0 \ 5 ; O ; O On © On n f ^ i r n ^ n n n n n r ,i^r<ir^rnnfn(ri(NfsH(N co c n co c n O N (N IT) vo - O oo - Is* N ON VO 00 CN — — CN CN CN © co co co cn © no T f CO CN O n O ON 2 c — CO CO CO p- _ p- NO CN Tf 00 p- ON NO W O Tf — wo o u OO wo © CO CO CO © Tf CN On o p- NO wo NO wo CQ CN p» NO r- wo P- oo p- r- wo NO Tf co CN Tf Tf W0 p- U © © © © © © © © © © © © © © © © © © To o CO CO CO p- p- NO CN Tf 00 p- ON NO wo Tf wo si E CJ ' ON wo p- oo NO oo co ON CO oo p» p- On © 3 CN > < c o T o ? co p Tf © Tf © Tf © wo © NO © wo © wo p wo p Tf © p CO p co p CO © CO p CO p Tf © W O © CQ U To CO CO CO CN co CO Tf p- CO CN On oo CO Tf wo o o Tf oo oo cn ON CN Tf o © »n © oo CN CN 00 wo NO © T f © wo Tf CO © wo NO NO co p- CN CN wo © CN NO wo wo co Tf W O Tf Tf wo NO nO NO W O W O wo wo Tf wo Tf CO co Tf co CO ■ " 3 - co Tf CO co Tf wo -C c o © o © o' o' © ' o' © p * p © p ©■ ©■ © ' o' p p p* p © © ' o* p p o' o' cn 1 < o u CQ 2 3 < . . N > c cj oo > % < *4 w o c N C N c o c O T f T f w o w o N O N O N O r ^ T f c o c N — o o N o o r ^ ’s O i n T f S N O o d © C N T f W O P - * © N — no no r— t t ■ t c o r N — o o n o o o o — . ^ T . . .....................................................................NO ON CN CO c o w ' i p - © — c o T f N O o o © r ^ O O C O O O C O O O O N O N O N O N O N O N ^ X — — — — — — On ON 00 _ _ ici iri O O — — — — — — •£ H . o Q © OO NO Tf CN O OO NO Tf CN O CN CO CO Tf l O ' O h h M O N O - T f T f T f T f T f T f T f T f - T f T f i n i A O O n O tJ - C N O O O N D vO C N O O O n O Tf CN OO no — c N c o T f m u o N o r - . o o o N O N O — ri co ^ i / i i o i c i i n i / i i n > n i f i i n i n i n \ 0 ' 0 \ 0 \ 0 N 0 u a, s o u U Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 125 0 00 To 0 c 0 0 g Si c C 3 C U 0 0 0 0 0 0 00 co sO 1 — . 0 0 Tf O' CO 0 CO 0 — 0 0 d d 0 o o os Tf CN Tf © o o o o o O' in - - Tf CN CO O d • o — - o o o o o o — — C O Tf — O co co oo cn Tt so — : — — : cn — d co ^ ■ £ c o CQ r-« 0 0 — 0 0 cn 00 P-* 0 0 SO co 00 00 0 0 O Tf Tf Tf wo — 0 0 O wo O' CN cn Os _ CO 00 W) CN Os r - CO 00 Os Os W0 O' O P - Tf 0 0 O wo W0 r- wo sO W 0 sO r- Os r-» CN co CN Os O p O 0 p CO CO CN CN CN CN CN CN CN CN co CO CO CO Tf Tf T f Tf Tf Tf Tf ca yg U w CN O CO CN W O Tf d d Tf d o r-» o d CQ JJ To O CN O 0 0 CN CN Tf W0 wo wo co O CN WO wo so 00 CN r- W0 Tf 0 O O O O 0 O O JU To ^ o ^ c o CQ CN © Os sO sO © sO O sO 00 Os O m in m m h os o o o d d o W O C O O s c O T f s O C N T f © O ' — c n w o 00 w o — w o t t CN CN CN CN Tf CO sO sO OO d o d d d d d d d 0 0 00 r - cn Tf — © — in m in Tf d o o d Tf Tf o cn r - — co co co r-* © co Tf in o ^ in «n d o o o o o CQ Z c 0 0D C3 c C ) T a . © O ' 0 d r-; Tf >n n 'O Is — sc so wo cn 0 0 o CO — CO Tf wo sc — Tf os wo co — co co Tf wo so r * * ^ 00 O' x — - M ro T f 00 CN © d — T f s O r ^ - O O O s O — OSTfWO O s O T f O O C N — O ' CN W O CO o i co Tf Tf wo sd sd 0 0 0 0 os CL £ Q 3 c o es o IQ O U Tf CN O Tf CN O wo s o r-* o s © — s o s o s o s o r - r - o o 00 o s o CN Uh 33 < Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 126 o oe "oo o o o o o o o o © O © o NO ON NO ON ON CN CN ON Tf i n 0 0 OO NO Tf c n Tf c n O n Tf in oo o —« ‘ o CN CN o O — — o C o CQ NO T f m o T f in o CN NO o O n T f CN ON CN CN r- ON ON t— c n 0 0 O n T f NO T f < n i n 0 0 o in O n o CN oo NO T f T f ON oo c n c n NO O n in CN r - in oo Ov — O n ON oo OO 0 0 c n — OO e' T f NO m r-; r-^ NO NO NO in n NO NO T f in T f c n T f c n c n c n c n c n T f T f c n e n c n c n c n c n c n c n c n c n c n c n c n c n c n c n c n a o CQ (J c n © O n 0 -1 © C N © 6 ■ £ U > c 2 C o c o CQ O r- T f © r-* C M © on C N CN © Tf i n T f o C J r« i 60 CQ O ' o o m « v o in o o v o - r, v o > n ^ 't © © © © o © c n o o —« e n i n r - » © © e n N O T f o v —' © i n o o r - m T f — mcN — — m o c N 0 0 0 0 0 0 0 O O O O N in r- *Tf in© CNO NT fON en o o v o c n t t - c n m © c n r- T f O M - n M m t N i n n O M d d d d d d d d d d d d <! e « 5 u 5 £ . CQ 2 W) < U o ON 00 > > < w Q . O D ■ v o r - O N C N — c N c N r j - i n v o r ^ o o o — c N m O u - j v o r - o o o — cNm«r>sor^ — O v in rt c o cj © o o n o T f c n — ^ ^ o v r n - ovh;vp,tcsovoqvq^; o d - c N f n c n T ) : i n i n v o ^ o 6 o v o i d - - n i n r n ' t i n v d ^ h o 6 o v d cNCNCNeNCNrNCNcNcNCNcNcNcNcNcncnenencnenenenencncnencnTf c o -o o U O O O O n O i t > O O O O O O O O O O n u - ) O O O O O O O O n O O O — cNcncnininNor--ooaN© — cNcnTfTfinNot--oooN©— « m c n t >o 'O c N c N c N c N c N C N C N C N C N C N c n c n e n c n c n c n c n c n c n c n c n T f T f T f T f T t T f T f Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Core Identification Depth (cm) Age (Kyr) Planktonic M C Age (Ka) Benthic IJC Age (Ka) Benthic 5 l:,C ( % c ) /\ve. Benthic 8 UC ir.t \ •8i3C Benthic (*<■ ) Benthic 5 lsO ( 7 c o ) Planktonic 5 I80 (7 o o ) A H F 16832 470 41.28 -0.441 3.521 480 42.09 -0.430 3.686 510 44.53 -0.597 -0.553 0.577 3.579 520 45.34 -0.632 3.647 530 46.16 -0.540 3.728 550 47.78 -0.680 3.597 560 48.59 -0.675 -0.678 0.745 3.738 * - Indicates sample was taken from trigger core. Value in () indicates depth in trigger core. N ) Core Identification D epth (cm) A djusted Age (Kyr) Benthic 8 IJC (%•) B enthic 5 lsO (%o) OD P Site 849 0.07 -1.364 0.21 3.66 0.17 1.578 0.08 3.49 0.28 4.815 0.19 3.31 0.45 9.816 -0.15 4.17 0.55 12.759 -0.27 4.69 0.69 16.878 -0.26 4.92 0.89 22.763 -0.08 4.55 0.89 22.763 -0.16 4.80 1.09 28.647 0.02 4.59 1.18 31.295 0.05 4.55 1.28 34.238 0.02 4.72 1.39 37.474 0.10 4.36 1.50 40.711 0.05 4.46 1.61 43.947 -0.02 4.63 1.85 51.009 0.07 4.47 1.94 53.657 -0.04 4.45 2.17 60.424 -0.21 4.54 2.31 64.543 -0.11 4.57 2.43 68.074 0.30 4.27 2.49 69.839 0.13 4.14 2.56 71.899 0.25 4.10 2.62 73.664 -0.03 4.23 2.73 76.901 0.12 3.95 2.80 80.201 0.22 3.83 2.89 83.501 0.21 4.00 2.92 86.801 0.21 3.90 3.06 90.101 0.10 3.85 3.15 93.401 0.17 4.00 3.24 96.701 0.09 3.95 3.33 100.000 -0.06 3.91 3.38 103.300 -0.11 3.73 3.44 106.600 0.06 3.70 3.44 109.900 0.10 3.79 3.55 113.200 0.05 3.78 3.66 116.500 0.23 3.30 3.77 119.800 0.12 3.23 3.88 123.100 -0.02 3.15 3.98 126.400 -0.02 3.27 4.08 129.700 -0.23 4.19 4.18 133.000 -0.30 4.42 4.28 136.300 -0.30 4.85 4.37 139.600 -0.39 4.75 4.47 142.900 -0.38 4.98 4.56 146.200 -0.45 4.70 4.67 149.500 -0.33 4.74 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. C ore Depth A djusted Age Benthic S'^C Benthic 5 I80 Identification (cm) (Kyr) (*») (%o) O D P Site 849 4.98 152.800 -0.46 4.38 5.08 156.100 -0.39 4.72 5.28 159.400 -0.45 4.81 5.38 162.700 -0.49 4.52 5.58 166.000 -0.37 4.26 5.68 169.300 -0.22 3.98 5.78 172.600 -0.35 4.38 5.89 175.900 -0.34 4.39 5.99 179.200 -0.41 4.16 6.08 182.500 -0.42 4.46 6.28 185.800 -0.45 4.49 6.38 189.100 -0.16 4.10 6.47 192.400 0.05 3.97 6.57 195.700 -0.01 3.91 6.67 199.000 -0.16 3.66 6.77 202.300 -0.02 3.61 6.88 205.600 -0.13 3.76 6.98 208.900 0 .1 1 3.89 7.08 212.200 -0.04 3.61 7.18 215.500 -0.03 3.64 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 130 C ore C om posite Identification Age (Kyr) 8 d l8 0 (%o) SPEC M A P 0 -2.09 2 -1.91 4 -1.74 6 -1.41 8 -1.02 10 -0.44 12 0.29 14 1.01 16 1.58 18 1.81 20 1.78 22 1.65 24 1.38 26 1.14 28 1.02 30 0.96 32 0.94 34 0.94 36 0.96 38 0.94 40 0.85 42 0.77 44 0.67 46 0.59 48 0.56 50 0.5 52 0.38 54 0.37 56 0.41 58 0.5 60 0.68 62 0.89 64 1 66 0.93 68 0.66 70 0.22 72 -0.24 74 -0.53 76 -0.69 78 -0.88 80 -0.98 82 -0.77 84 -0.48 86 -0.45 88 -0.47 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Core Identification SPEC M A P e (Kyr) Com posi 8 d l8 0 90 -0.46 92 -0.52 94 -0.71 96 -0.8 98 -0.91 100 -0.96 102 -0.8 104 -0.69 106 -0.59 108 -0.51 110 -0.5 112 -0.73 114 -1.19 116 -1.53 118 -1.72 120 -1.98 122 -2.12 124 -1.89 126 -1.19 128 -0.26 130 0.51 132 1.05 134 1.33 136 1.35 138 1.28 140 1.32 142 1.33 144 1.26 146 1.26 148 1.41 150 1.57 152 1.58 154 1.45 156 1.3 158 1.07 160 0.85 162 0.6 164 0.4 166 0.25 168 0.15 170 0.11 172 0.12 174 0.18 176 0.27 178 0.47 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 132 Core C om posite Identification Age (K yr) 5 d l8 0 ( % o ) SPEC M A P 180 0.71 182 0.83 184 0.62 186 0 .1 1 188 -0.42 190 -0.88 192 -1.31 194 -1.62 196 -1.62 198 -1.41 200 -1.17 202 -0.99 204 -0.88 206 -0.88 208 -1 210 -1.12 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IMAGE EVALUATION TEST TARGET (Q A -3 ) I.O >- iiia --------- i- na [r LI it 1 L . | I.25 1 .4 I I ____ I I 150mm IIVUGE.Inc 1653 East Main Street Rochester, NY 14609 USA Phone: 716/482-0300 Fax: 716/288-5989 < 0 1 9 9 3 . A p p lie d I m a g e . I n c .. A l l R ig h ts R e s e r v e d Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

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Creator Neumann, Michael James (author)

Core Title Late Pleistocene ventilation history of the North Pacific as seen through delta carbon-13 records of the Southern California borderland

Degree Master of Science

Degree Program Earth Sciences

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

Tag biology, oceanography,geochemistry,Geology,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c16-25566

Unique identifier UC11342131

Identifier 1393180.pdf (filename),usctheses-c16-25566 (legacy record id)

Legacy Identifier 1393180.pdf

Dmrecord 25566

Document Type Thesis

Rights Neumann, Michael James

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