rate of dune reddening in a humid tropical climate the formation of red beds has long interested geologists and pedologists1 3 it has been suggested that the nature and degree of reddening in dune sands can be a useful indicator of the relative age and environmental history of the sands several authors have concluded that dune sands undergo progressive reddening with time4 7 and james and stanley8 considered that coastal dunes might actually be mapped on the basis of colour however quantitative data regarding the rate of reddening in different environmental conditions are generally lacking i present here radiocarbon evidence from north east australia which suggests that red weathering profiles have developed in stabilized dunes of holocene age in humid tropical conditions within the past 7 500 yr

distribution and significance of novel low molecular weight sterenes in an immature evaporitic sediment from the jinxian sag north china abstract an unusual series of c 22 c 27 monounsaturated sterenes and c 24 c 30 tetracyclic terpanes 17 21 seco hopanes were detected in relatively high concentrations in an immature evaporitic marl sediment of the jinxian sag bohai bay basin north china the site of unsaturation in these novel sterenes is assigned tentatively to the d ring on the basis of mass spectral interpretation which also distinguishes them from reported unsaturated sterenes other hydrocarbon biomarker or stable isotope characteristics are indicative of microbial e g methyl hopanes phytoplankton or higher plant depleted 13 c values of isoprenoids and hopanes inputs and an anoxic carbonate depositional environment hexacyclic hopanes tetracyclic terpanes the hydrocarbon composition showed no obvious biodegradation and the relatively high concentration of unsaturated terpenoids e g gammacerene and low values of other established maturity parameters t s t m 0 23 r o 0 44 t max 417 c are consistent with sediments of low maturity the novel low molecular weight sterenes and the tetracyclic terpanes may be early diagenetic products of microbial sources in a carbonate environment

proxy dependence of the temporal pattern of deglacial warming in the tropical south china sea toward resolving seasonality abstract sea surface temperatures ssts reconstructed from two globigerinoides ruber white morphotypes g ruber sensu stricto s s g ruber sensu lato s l mg ca and alkenones uk 37 from core md01 2390 from the tropical south china sea scs during the last deglaciation reveal a proxy dependent discrepancy in the temporal pattern of the deglacial warming alkenone data suggest that the deglacial warming is punctuated by a decrease in temperature between 17 and 15 ka bp corroborating previously published alkenone uk 37 sst records from the southern scs within dating uncertainties this cooling is coeval with the heinrich event 1 h1 time interval in the north atlantic region underscoring the imprints of northern hemisphere forcing on tropical scs ocean temperatures the deglacial uk 37 sst minimum is also paralleled by a maximum in g ruber morphotype specific 18o g ruber mg ca sst estimates suggest a morphotype specific record of ssts during the time interval of h1 whereas g ruber s s imply a continuous warming starting around 18 ka bp without any marked response to h1 g ruber s l based mg ca sst estimates reveal a cooling around 17 15 ka bp similar to the h1 interval cooling seen in the alkenone sst record similar proxy dependent differences in deglacial surface water warming have been recorded in the eastern equatorial pacific implying a common pattern on both sides of the tropical pacific ocean we submit that this discrepancy could be due to differences in seasonality of planktonic foraminifera g ruber morphotypes and alkenone producing algae

shell weights from intermediate depths in the caribbean sea 1 whole foraminifera shell weights for g sacculifer and n dutertrei in caribbean sea cores covering a depth range of 680 to 3620 m show a decrease in weight of 3 6 0 4 g between glacial time and the holocene this difference likely reflects a thickening of foraminifera shells as a result of the higher carbonate ion concentration of glacial surface water the fact that the shells from the core at 680 m depth are considerably lighter than those from the core at 1030 m depth suggests either that there is an up water column increase in the offset between the pore water and the bottom water carbonate ion concentration or that factors other than surface water carbonate ion concentration influence the initial shell weight of particular interest is a strong preservation event corresponding to the deglacial interval at 680 m depth the present day core of the intermediate water mass

the benguela current and associated upwelling on the southwest african margin a synthesis of the neogene quaternary sedimentary record at dsdp sites 362 and 532

a tropical mechanism for northern hemisphere deglaciation 1 we investigate the role of the tropics in the melting and reforming of the laurentide ice sheet on glacial timescales using an atmospheric general circulation model it is found that warming of tropical sea surface temperatures ssts from glacial boundary conditions as observed at the end of glacial periods causes a large increase in summer temperatures centered over the ice sheet forming regions of canada this highlatitude response to tropical change is due to relatively small changes in the circulation of the extratropical atmosphere which lead to changes in the vertical profiles of temperature and moisture in the extratropical atmosphere the maximum perturbation in the summer radiative balance over the laurentide ice sheet 25 w m 2 due to the changes in the local atmospheric water vapor inventory is much larger than that induced by glacial to interglacial changes in atmospheric co2 these changes via an atmospheric bridge between the tropics and extratropics represent a mechanism for deglaciations which is consistent with timing constraints in contrast a cold perturbation to tropical sst for interglacial boundary conditions results in only very small changes in the delivery of water vapor to the laurentide region and therefore almost no cooling over the canadian region this implies that tropical ssts could play a more important role in melting ice sheets in the northern hemisphere than in reforming them possibly providing a mechanism which could help to explain the rapidity of deglaciation relative to glacial inception

geostrophic transport in the benguela current region historical data from the region between the greenwich meridian and the african continental shelf are used to compute the offshore geostrophic transport of the benguela current at 32 s the benguela current is located near the african coast transporting about 21 sv 1 sv 106 m3 s 1 of surface water toward the north relative to a potential density surface lying between the upper branch of circumpolar deep water and the north atlantic deep watar two warm core eddies of probable agulhas current origin an observed west of the benguela current at 32 s near 30 s the benguela current turns toward the northwest and begins to separate from the eastern boundary it carries about 18 sv of surface water across 28 s the current then turns mainly toward the west to flow over a relatively deep segment of the walvis ridge south of the valdivia bank a surface current with northward surface of about 10 cm s 1 flows along the western side of the valdivia bank while another northward surface current flows at about 20 cm s 1 some 300 km west of the bank about 3 sv of surface now do not leave the cape basin south of the vaidivia bank but instead drift northward as a wide sluggish flow out of the northern end of the cape basin because of the more southerly seaward extensions of most of the benguela current there are no deep reaching interactions observed between this current and the cyclonic gyre in the angola basin east of the greenwich meridian beneath the surface layer about 4 5 sv of antarctic intermediate water are carried northward across 32 and 28 s by the benguela current essentially all of which turns westward to cross the greenwich meridian south of 24 s

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

patterns of deglacial warming in the pacific ocean a review with emphasis on the time interval of heinrich event 1 abstract based on a compilation of currently available records of past sea surface temperature sst variability estimated from a variety of different proxies the regional scale deglacial sst development in the pacific ocean is tentatively classified into four endmember types the subtropical and tropical pacific is characterized by a continuous deglacial warming without marked interruption during the time interval of heinrich event 1 h1 whereas the subarctic north pacific exhibits centennial scale warm cold oscillations during this time interval sst records from marginal seas of the pacific show a deglacial warming interrupted by a cooling event coeval with h1 followed by a marked bolling sst increase a single sst record from the southwestern subantarctic pacific displays a continuous deglacial warming across h1 followed by an antarctic cold reversal type cooling during the allerod thus in contrast to the deglacial sst development in the atlantic which has been inferred to be overwhelmingly driven by the redistribution of heat through changes in the meridional overturning circulation moc none of the open oceanic pacific sst records reviewed here displays any obvious and or dominant response to the reduction of the moc and or the reorganization of atmospheric circulation during h1 within the limits of absolute chronologies all tropical and subtropical pacific sst records show an onset of deglacial warming at 19 1 ka coeval with the onset of the deglacial rise in sea level

holocene paleo climatic record from the south african namaqualand mudbelt a source to sink approach variations in the sediment input to the namaqualand mudbelt during the holocene are assessed using an integrative terrestrial to marine source to sink approach geochemical and sr and nd isotopic

plio pleistocene changes in the main biogenic silica carrier in the southern ocean atlantic sector abstract the interaction between biogenic silica export and burial paleoceanography diatom species succession and mats formation was examined based on relative abundances data of plio pleistocene diatoms from six cores recovered during odp leg 177 on a transect across the antarctic circumpolar current acc in the atlantic sector of the southern ocean fragilariopsis kerguelensis actinocyclus ingens and species of the genus thalassiothrix were the main contributors to the diatom assemblages three main steps marked the development of the silica system in the southern ocean step 1 at ca 2 77 ma establishment of increased biogenic silica burial in the antarctic circumpolar current area following the large scale oceanic reorganization connected to the increased northern hemisphere glaciation step 2 at ca 1 93 ma the antarctic polar front becomes the main biogenic silica sink diatom mats are widespread and are also found slightly to the north and south of the apf step 3 at ca 0 63 ma with the strong drop in abundance and later extinction at 0 38 ma of a ingens and the rise to dominance of f kerguelensis the system enters a glacial interglacial mode with diatom mats occurring during interglacials at the apf and in the antarctic zone but disappearing north of it

comparison of radiolarian and sedimentologic paleoproductivity proxies in the latest miocene recent benguela upwelling system abstract estimating past ocean productivity from ocean sediments often gives different results depending on the measurement used we have examined a suite of paleoproductivity proxies in latest miocene recent sediments from dsdp site 532 and odp site 1084 two deep sea sections underlying the benguela upwelling system off the atlantic coast of southern africa the productivity history of this system has been previously established via organic carbon concentration diatom floras and alkenone based estimates of surface water temperature and shows a change from low productivity in the early pliocene to sustain high productivity in the late pliocene recent each of our samples was split and simultaneously analysed for several proxies of ocean productivity including organic carbon toc carbonate abundance of opaline radiolarians accumulation rate of benthic foraminifera bfar the radiolarian faunal composition indices upwelling radiolarian index uri and the water depth ecology index wade other proxies for opal and carbonate dissolution plus stable isotopes of benthic foraminifera comparisons between proxies in the same measured samples between sites in downcore plots and to the published productivity record for this region suggest that toc and radiolarian faunal composition particularly the wade index are good indicators of past productivity albeit with different sensitivities log linear correlation wade toc r 0 78 n 65 p

geochemical evidence for variations in delivery and deposition of sediment in pleistocene light dark color cycles under the benguela current upwelling system abstract distinctive light dark color cycles in sediment beneath the benguela current upwelling system indicate repetitive alternations in sediment delivery and deposition geochemical proxies for paleoproductivity and for depositional conditions were employed to investigate the paleoceanographic processes involved in creating these cycles in three mid pleistocene intervals from odp sites 1082 and 1084 concentrations of total organic carbon toc vary between 3 5 and 17 1 concentrations of caco3 vary inversely to toc and al which suggests that both carbonate dissolution and terrigenous dilution contribute to the light dark cycles opal concentrations are independent of both toc and caco3 therefore eliminating diatom production and lateral transport of shelf material as causes of the light dark cycles 13corg and 15ntot values do not vary across light dark sediment intervals implying that the extent of relative nutrient utilization did not change the stable 15ntot values represent a balanced change in nitrate supply and export production and therefore indicate that productivity was elevated during deposition of the toc rich layers parallel changes in concentrations of indicator trace elements and toc imply that changes in organic matter delivery influenced geochemical processes on the seafloor by controlling consumption of pore water oxygen cu ni and zn are enriched in the darker sediment as a consequence of greater organic matter delivery redox sensitive metals vary due to loss mn and ba or enrichment mo under reducing conditions created by toc oxidation organic matter delivery impacts subsequent geochemical changes such as carbonate dissolution sulfate reduction and the concentration of metals thus export production is considered ultimately responsible for the generation of the color cycles

coupled primary production benthic foraminiferal assemblage and sulfur diagenesis in organic rich sediments of the benguela upwelling system abstract episodically deposited dark organic rich pleistocene and late pliocene sediments from the lower continental slope off southwest africa reveal complex interactions between changes in primary production benthic foraminiferal assemblage and anaerobic microbial processes the organic rich layers contain diatom assemblages characteristic of intense seasonal coastal upwelling whereas stratigraphically adjacent sediments reflect pelagic primary production coastal upwelling dominated depositional intervals coincide with periods of enhanced carbon flux to the seafloor enhanced organic carbon export during dark layer deposition was accompanied by decreases in the diversity of benthic foraminifera to few opportunistic species adapted to high phytodetritus accumulation rates and low o 2 conditions in all sediments the sulfur isotopic composition of pyrite indicates redox cycling of sulfide close to the sediment water interface the sulfur isotopic evidence and the permanent presence of abundant low o 2 adapted benthic foraminifera throughout the organic rich layers suggest an oxygenated benthic environment efficient oxidation of sulfide and removal of sulfide by sulfidization of organic matter inhibited buildup of toxic hydrogen sulfide from bacterial sulfate reduction at the sediment water interface these data imply that in continental slope sediments underneath productive surface waters benthic dysoxic conditions are maintained by the lateral advection of dissolved oxygen to support a small but well adapted benthic community

mg ca ratios of two globigerinoides ruber white morphotypes implications for reconstructing past tropical subtropical surface water conditions 1 tests of the planktonic foraminifer globigerinoides ruber white d orbigny have become a standard tool for reconstructing past oceanic environments paleoceanographers often utilize the mg ca ratios of the foraminiferal tests for reconstructing low latitude ocean glacial interglacial changes in sea surface temperatures sst we report herein a comparison of mg ca measurements on sample pairs n 20 of two g ruber white morphotypes g ruber sensu stricto s s and g ruber sensu lato s l from surface and downcore samples of the western pacific and indian oceans g ruber s s refers to specimens with spherical chambers sitting symmetrically over previous sutures with a wide high arched aperture whereas g ruber s l refers to a more compact test with a diminutive final chamber and small aperture the g ruber s s specimens generally show significantly higher mg ca ratios compared to g ruber s l our results from the mg ca ratio analysis suggest that g ruber s l specimens precipitated their shells in slightly colder surface waters than g ruber s s specimens this conclusion is supported by the differences in 18o and 13c values between the two morphotypes although it is still unclear if these two morphotypes represent phenotypic variants or sibling species our findings seem to support the hypothesis of depth and or seasonal allopatry within a single morphospecies

effects of seawater carbonate ion concentration and temperature on shell u mg and sr in cultured planktonic foraminifera we investigate the sensitivity of u ca mg ca and sr ca to changes in seawater co3 and temperature in calcite produced by the two planktonic foraminifera species orbulina universa and globige rina bulloides in laboratory culture experiments our results demonstrate that at constant temperature u ca in o universa decreases by 25 7 per 100 mol co3 k g 1 as seawater co3 increases from 110 to 470 mol kg 1 results from g bulloides suggest a similar relationship but u ca is consistently offset by 40 at the same environmental co3 in o universa u ca is insensitive to temperature between 15 c and 25 c applying the o universa relationship to three u ca records from a related species globigerinoides sacculifer we estimate that caribbean and tropical atlantic co3 was 110 70 mol kg 1 and 80 40 mol kg 1 higher respectively during the last glacial period relative to the holocene this result is consistent with estimates of the glacial interglacial change in surface water co3 based on both modeling and on boron isotope ph estimates in settings where the addition of u by diagenetic processes is not a factor down core records of foraminiferal u ca have potential to provide information about changes in the ocean s carbonate concentration below ambient ph ph 8 2 mg ca decreased by 7 5 o universa t o 16 6 g bulloides per 0 1 unit increase in ph above ambient ph the change in mg ca was not significant for either species this result suggests that mg ca based paleotemperature estimates for the quaternary during which surface ocean ph has been at or above modern levels have not been biased by variations in surface water ph sr ca increased linearly by 1 6 0 4 per 0 1 unit increase in ph shell mg ca increased exponentially with temperature in o universa where mg ca 0 85 exp 0 096 t whereas the change in sr ca with temperature was within the reproducibility of replicate measurements copyright 2004 elsevier ltd

eastern tropical pacific hydrologic changes during the past 27 000 years from d h ratios in alkenones 1 the tropical pacific plays a central role in the climate system by providing large diabatic heating that drives the global atmospheric circulation quantifying the role of the tropics in late pleistocene climate change has been hampered by the paucity of paleoclimate records from this region and the lack of realistic transient climate model simulations covering this period here we present records of hydrogen isotope ratios dd of alkenones from the panama basin off the colombian coast that document hydrologic changes in equatorial south america and the eastern tropical pacific over the past 27 000 years a and the past 3 centuries in detail comparison of alkenone dd values with instrumental records of precipitation over the past 100 a suggests that dd can be used as a hydrologic proxy on long timescales our records indicate reduced rainfall during the last glacial period that can be explained by a southward shift of the mean position of the intertropical convergence zone and an associated reduction of pacific moisture transport into colombia precipitation increases at 17 ka in concert with sea surface temperature sst cooling in the north atlantic and the eastern tropical pacific a regional coupled model forced by negative sst anomalies in the caribbean simulates an intensification of northeasterly trade winds across central america increased evaporative cooling and a band of increased rainfall in the northeastern tropical pacific these results are consistent with the alkenone sst and dd reconstructions that suggest increasing precipitation and sst cooling at the time of heinrich event 1

paleo sea surface temperature calculations in the equatorial east atlantic from mg ca ratios in planktic foraminifera a comparison to sea surface temperature estimates from u37k oxygen isotopes and foraminiferal transfer function we present two 270 kyr paleo sea surface temperature sst records from the equatorial divergence and the south equatorial current derived from mg ca ratios in the planktic foraminifer globigerinoides sacculifer the present study suggests that the magnesium signature of g sacculifer provides a seasonal sst estimate from the upper 50 m of the water column generated during upwelling in austral low latitude fall winter common to both down core records is a glacial interglacial amplitude of 3 3 5 c for the last climatic changes and lower holocene and glacial oxygen isotope stage 2 temperatures compared with interglacial stage 5 5 and glacial stage 6 temperatures respectively the comparison to published sst estimates from alkenones oxygen isotopes and foraminiferal transfer function from the same core material pinpoints discrepancies and conformities between methods

sedimentation rates off sw africa since the late miocene deciphered from spectral analyses of borehole and gra bulk density profiles odp sites 1081 1084 abstract sedimentation rates srs off sw africa were calculated by performing spectral analyses in the depth domain on borehole and gamma ray attenuation gra bulk density data from odp sites 1081 1084 inversion and integration of srs versus depth from spectral analysis yielded detailed sr profiles in the time domain our technique allowed the detection of excursions in calculated srs that not only often differed from those established through coarse scaled biostratigraphic data but also revealed a greater regional variability in the sediment accumulation over time high resolution bulk density data exhibited distinct periodicity in the waveband of milankovitch cycles precession at 19 23 kyr obliquity at 41 kyr eccentricity at 100 kyr the pronounced milankovitch cyclicity suggests that climate variability and trends in srs along the benguela current system bcs were responding to insolation patterns during the past 6 myr we find relatively low srs when evolutive amplitude spectra are dominated by obliquity and eccentricity periods in contrast significant sr peaks at all sites often occur when strong precessional amplitudes coexist with obliquity and eccentricity cycles episodes of high srs often coincide with peaks in organic carbon mass accumulation rates mar c org and reduced sea surface temperature sst in the southern walvis basin which have been associated with increased regional upwelling this suggests that the high srs reflect high productivity high mar c org attributed to strong wind and upwelling intensity during cool climate periods low ssts in accordance with orbital forcing patterns observed in our spectra

paleoclimate history of galapagos surface waters over the last 135 000 yr abstract records of planktonic and benthic foraminiferal 18 o and planktonic mg ca from core tr163 22 just northwest of the galapagos islands reveal a detailed 250 450 year resolution climate history of the region over the last 135 thousand years kyr sea surface temperatures ssts reconstructed from g ruber mg ca averaged 24 3 0 4 c during the holocene 22 6 0 6 c during marine isotope stage mis 2 3 and 4 and 26 0 0 9 c during mis 5e changes in sst lead changes in both planktonic and benthic 18 o by an average 3 kyr suggesting that sst changes in this region predated continental ice volume changes changes in sst display clear millennial scale variability especially in marine isotope stage 3 with behavior somewhat similar to antarctic proxy air temperature and south pacific sst records removal of the temperature component from the planktonic 18 o record demonstrates that glacial interglacial 18 o water changes at this site were 1 0 0 2 similar to estimates for mean ocean shifts implying that salinity changes due to regional hydrological variation between the last glacial maximum and holocene in the galapagos region were minimal comparison between the tr163 22 sst record and an sst record from core tr163 19 north of the equatorial front reveals a largely similar broad scale climate history suggesting that changes in the galapagos region were caused by large scale forcing rather than by local or regional dynamical changes changes in atmospheric greenhouse forcing are the most plausible explanation for the observed large scale climate changes in the eastern equatorial pacific

opal sedimentation shifts in the world ocean over the last 15 myr biogenic silica opal accumulation records were used to trace mechanisms consequence and geographic pattern of shifts in the main locus of opal deposition of the world ocean over the last 15 myr over this time interval the main opal sink seems to have moved from the north atlantic to the pacific equatorial pacific eastern equatorial pacific eastern boundary current upwelling systems california namibia peru and finally to the southern ocean the interplay between opal deposition and a series of climatic tectonic oceanographic and biologic events has been analyzed and discussed these events include the cenozoic global cooling trend intensified glaciation in antarctica late miocene early pliocene biogenic bloom development of northern hemisphere glaciation nhg closing of the panama seaway transition of the climate system from a monopolarto a bipolar glaciated world mid pleistocene revolution mpr nutrient availability evolution of diatoms and c4 plants and changes in continental weathering rates while the observed shifts are mostly traceable to oceanic reorganizations and global climatic evolution conditions favorable to opal deposition involve the above mentioned complex mix of processes for this reason the interpretation of opal deposition records might not always be straightforward we however believe that it can still provide clear indications of large scale oceanographic reorganizations in the geological past d 2004 elsevier b v all rights reserved

organic rich sediments in ventilated deep sea environments relationship to climate sea level and trophic changes sediments on the namibian margin in the se atlantic between water depths of 1000 and 3600 m are highly enriched in hydrocarbon prone organic matter such sedimentation has occurred for more than 2 million years and is geographically distributed over hundreds of kilometers along the margin so that the sediments of this region contain a huge concentrated stock of organic carbon it is shown here that most of the variability in organic content is due to relative dilution by buried carbonates this reflects both export productivity and diagenetic dissolution not differences in either water column or bottom water anoxia and related enhanced preservation of organic matter these observations offer a new mechanism for the formation of potential source rocks in a well ventilated open ocean in this case the south atlantic the organic richness is discussed in terms of a suite of probable controls including local wind driven productivity upwelling trophic conditions transfer efficiency diagenetic processes and climate related sea level and deep circulation the probability of past occurrences of such organic rich facies in equivalent oceanographic settings at the edge of large oceanic basins should be carefully considered in deep offshore exploration

the early matuyama diatom maximum off sw africa benguela current system odp leg 175 abstract several sites of ocean drilling program leg 175 between 20 and 30 s 1081 1082 1083 1084 and 1085 in the benguela current system show a distinct opal and diatom maximum within the late pliocene and early quaternary spanning the lower half of the matuyama reversed polarity chron mdm matuyama diatom maximum this maximum is centered around 2 0 2 6 ma and follows a rapid increase of diatom deposition near 3 1 ma within the mdm we recognized intervals dominated by the antarctic subantarctic species thalassiothrix antarctica which have the aspect of diatom mats the mdm and the mats developed during a time of sustained southern ocean influence 3 2 1 6 ma probably reflecting a period of seasonally pulsed continuous advection of subantarctic waters into the benguela oceanic current the onset and cessation of the mdm raises questions about modes in the operation of the silica cycle and the relation of these to major oceanographic events a depositional model for the late pliocene is proposed which involves positional changes in a longshore system of fronts substantial equatorward excursions of subantarctic waters during mdm time and subsurface waters greatly enriched in silicate

incorporation and preservation of mg in globigerinoides sacculifer implications for reconstructing the temperature and 18o 16o of seawater using bathymetric transects of surface sediments underlying similar sea surface temperatures but exposed to increasing dissolution we examined the processes which affect the relationship between foraminiferal mg ca and 18o we found that globigerinoides saccculifer calcifies over a relatively large range of water depth and that this is apparent in their mg content on the seafloor foraminiferal mg ca is substantially altered by dissolution with the degree of alteration increasing with water depth selective dissolution of the chamber calcite formed in surface waters shifts the shell s bulk mg ca and 18o toward the chemistries of the secondary crust acquired in colder thermocline waters the magnitude of this shift depends on both the range of temperatures over which the shell calcified and the degree to which it is subsequently dissolved in spite of this shift the initial relationship between mg ca and 18o determined by their temperature dependence is maintained we conclude that paired measurements of 18o and mg ca can be used for reconstructing 18owater though care must be taken to determine where in the water column the reconstruction applies

on the reconstruction of upwelling history namibia upwelling in context abstract eastern boundary upwelling is an important aspect of the modern ocean despite the relatively small area involved consequences of increased upwelling during the neogene as a result of intensifying trade winds include increased heat transport by the ocean increased mixing increased fractionation of phosphate from silicate and opportunities for evolution of new species coastal upwelling has been studied since the first decade of the 20th century the processes involved are complex and differ depending on geographic setting off namibia upwelling history has been studied by a number of drilling expeditions the last of these was odp leg 175 which occupied seven sites on the continental slope between walvis ridge and cape town during september and october of 1997 productivity proxies all along southwestern africa suggest the presence of increased upwelling and organic matter supply to the sea floor during glacial periods at the same time there is a decrease in the supply of diatoms and other siliceous plankton remains this is the walvis opal paradox established through the contrasting results of studies by diester haass 1985 and oberhansli 1991 we propose that the walvis opal paradox is fundamental to the understanding of glacial interglacial productivity fluctuations on a global scale furthermore a central feature of the history of late neogene upwelling off namibia is the matuyama opal maximum centered between gauss and olduvai magnetic chrons wefer et al proc odp 175 1998 it is due to the fact that diatom supply first increases during the gauss when the planet cools and then decreases again during additional cooling on entering the quaternary on a 400 000 year scale peak productions are coincident with or slightly lag maximum seasonal contrast potential in the high latitude insolation curve we suggest that this is further evidence that the nutrient content of thermocline waters was diminished during glacial periods the reasons why this should be so remain to be discovered

variations in mg ca and sr ca ratios of planktonic foraminifera caused by postdepositional dissolution evidence of shallow mg dependent dissolution a comparative study has been made of two species of planktonic foraminifera g tumida and g sacculifer in a depth transect on the ontong java plateau western equatorial pacific g tumida tests from core top sediments showed decreasing mg ca 2 65 1 25 mmol mol and sr ca 1 50 1 16 mmol mol ratios with increasing water depth 1600 4400 m while no such variation was found in g sacculifer tests in excess of 355 m average mg ca 3 6 mmol mol sr ca 1 4 mmol mol artificial dissolution of g tumida tests led to a decrease in both mg ca and sr ca but in g sacculifer there was no significant change in the ratios analyses by electron microprobe revealed that mg ca of the inner chamber calcite in g tumida tests was much higher than that of the calcite crust keel whereas sr ca was only slightly elevated there were no consistent spatial differences in either mg ca or sr ca for g sacculifer tests dissolution in the oceans gives rise to the removal of the chamber calcite in g tumida about 30 of the total calcite leaving the keel calcite although g tumida is thought of as a dissolution resistant form the majority of mg ca and sr ca depletion and chamber loss occurs above the lysocline it is also possible that much of the mg enriched gametogenic calcite has been lost by dissolution from g sacculifer above 1600 m mg content has a significant effect on the dissolution susceptibility of planktonic foraminifera calculations show that the saturation horizon for mg rich parts of tests may be elevated by several hundred meters compared with normal calcite

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

production of giant marine diatoms and their export at oceanic frontal zones implications for si and c flux from stratified oceans from a synthesis of recent oceanic observations and paleo data it is evident that certain species of giant diatoms including rhizosolenia spp thalassiothrix spp and ethmodiscus rex may become concentrated at oceanic frontal zones and subsequently form episodes of mass flux to the sediment within the nutrient bearing waters advecting towards frontal boundaries these species are generally not dominant but they appear selectively segregated at fronts and thus may dominate the export flux ancient thalassiothrix diatom mat deposits in the eastern equatorial pacific and beneath the polar front in the southern ocean record the highest open ocean sedimentation rates ever documented and represent vast sinks of silica and carbon several of the species involved are adapted to a stratified water column and may thrive in deep chlorophyll maxima thus in oceanic regions and or at times prone to enhanced surface water stratification e g during meltwater pulses they provide a mechanism for generating substantial biomass at depth and its subsequent export with concomitant implications for si export and c drawdown this ecology has important implications for ocean biogeochemical models suggesting that more than one diatom functional type should be used in spite of the importance of these giant diatoms for biogeochemical cycling their large size coupled with the constraints of conventional oceanographic survey schemes and techniques means that they are undersampled an improved insight into these key species will be an important prerequisite for enhancing our understanding of marine biogeochemical cycling and for assessing the impacts of climate change on ocean export production

pliocene variations in the position of the antarctic convergence in the southwest atlantic middle to late pliocene 4 1 1 9 ma variations in the positions of surface water masses and migrations of the polar front in the southwest atlantic are inferred from a factor analysis of radiolarian assemblages from dsdp site 514 faunal results suggest that surface water masses underwent progressive cooling as the polar front zone pfz advanced northward during the latest gilbert to late gauss chron the late gilbert chron 4 12 3 86 ma was the waning phase of a mid gilbert warm interval northern subantarctic surface water prevailed between 4 12 and 3 97 ma indicative of surface water temperatures warmer than those during the succeeding pliocene a long term sea surface cooling trend began between 3 97 and 3 86 ma which moved the pfz northward and closer to site 514 bringing cooler southern subantarctic surface waters to the site this movement northward of cooler surface waters is inferred to be related to the initial growth of sea ice and ice shelves throughout regions of west antarctica which were deglaciated or unglaciated during the prior warming interval of the gilbert chron a major late gilbert early gauss chron increase in the production of antarctic bottom water aabw resulted in an erosional or nondepositional hiatus at site 514 spanning 3 86 to 3 18 ma increased aabw activity at this time is linked to continued growth of expansive ice shelves and sea ice in the west antarctic region in the east antarctic margin and possibly in the marine embayments of east antarctica decreased aabw production led to a 3 2 ma resumption of sedimentation at site 514 and elsewhere in the southern ocean antarctic surface water assemblages above the hiatus 3 18 3 16 ma suggest that the pfz first passed over site 514 during the 3 86 3 18 ma interval of the hiatus following this initial invasion of antarctic surface waters between 3 16 and 2 94 ma the pfz retreated to a position near or south of the site this slight retreat of the pfz with a corresponding decrease in aabw activity is possibly related to a significant reduction in the area of shelf and sea ice as grounded ice expanded in the west antarctic region we interpret the widespread global enrichment of 18o at approximately 3 2 ma to be partially related to a cooling of surface waters the production of cooler bottom waters and an expansion of west antarctic ice volume associated with its grounding phase between 3 5 and 2 7 ma based on surface water mass migrations at site 514 the west antarctic ice volume increased significantly slightly prior to or at approximately 3 2 ma decreased between 3 14 and 2 7 ma and then increased by 2 67 ma to a more stable configuration with a volume at least as great as that at 3 2 ma during the late gauss 2 94 2 47 ma four northward advances of the pfz led to the migration of antarctic surface waters over the site by 2 67 ma and continued dominance of antarctic surface water through the remainder of the pliocene we suggest that this permanent change from subantarctic to antarctic surface water mass dominance was linked indirectly to the initial growth of northern hemisphere ice and a reduction of sea level we propose a model of simultaneous northern and southern hemisphere ice volume growth induced by interhemisphere positive feedback which is responsible for the major late gauss advance of antarctic surface waters and the global enrichment of 18o at 2 5 ma

carbon isotopic compositions of 28 30 bisnorhopanes and other biological markers in a monterey crude oil abstract an immature tar like oil api 3 13 c 23 6 vs pdb from the miocene monterey formation offshore california was selected for a study of carbon isotopic signatures of individual biomarkers the three principal stereoisomers of 28 30 bisnorhopane c 28 have within analytical precision identical carbon isotopic compositions average 13 c 32 3 0 4 and are considerably depleted in 13 c compared to the whole oil these 28 30 bisnorhopanes bnh differ isotopically from c 29 and c 30 17 h hopanes 25 8 and 26 1 and c 31 c 35 extended hopanes 13 c 27 7 and suggest different precursors for the c 28 hopanes than for c 29 c 35 hopanes the relative depletion of bnh of almost 9 compared to the isotopic composition of the whole oil suggests that these hopanes derive from chemoautotrophic bacteria possibly not yet identified h 2 s oxidizers which utilize 13 c depleted substrates the c 29 and c 30 hopanes are within analytical precision isotopically identical 26 and similar to algal derived compounds e g c 27 steranes 25 9 which is consistent with a cyanobacterial source for these hopanes an archaebacterial biomarker 1 1 biphytane 13 c 25 5 likely derived from methanogens is also isotopically similar to c 27 sterane norpristane pristane and phytane liberated by desulfurization of the aromatic and polar maltene fractions show isotopic compositions similar to the same isoprenoids in the free lipids of the bitumen total range from 24 5 to 27 5 this isotopic similarity supports a common origin for the free and sulfur bound forms of these isoprenoids this origin could be algal and or archaebacterial lipids which both show isotopic compositions within the range of the c 18 c 20 isoprenoids like other marine derived organic matter this monterey oil does not show the strong 13 c depletion typical for methylotroph derived compounds characteristically found in organic matter of lacustrine origin this may indicate fundamental differences of methane recycling processes in marine sulfate dominated as compared to lacustrine environments

a late pliocene diatom ge si record from the southeast atlantic abstract as a result of both culture and sediment core studies the ratio of germanium ge to silicon si in diatom shells has been proposed as a proxy for monitoring whole ocean changes in seawater ge si a ratio affected by changes in continental weathering however because of the difficulties of extracting and cleaning diatom frustules from deep sea sediments only samples from highly pure diatom oozes in the antarctic region have been previously analyzed here we present data on diatom ge si ratios ge si opal for the time interval between 3 1 and 1 9 ma from a mid latitude coastal upwelling area where significant terrigenous sediment input complicated the sample processing and analyses in general our ge si opal values show the same decreasing trend after 2 6 ma than previously measured in antarctic sediments shemesh et al 1989 paleoceanography 4 221 231 but with a noisier background that may reflect the local imprint of proximal continental input superimposed upon global changes in the ocean reservoir the time of initiation of large scale north hemisphere glaciation at 2 6 ma is characterized by a declining pattern of diatom ge si ratios which could have resulted from a global increase in the input of riverine si due to enhanced silica weathering and or equatorward northward intrusions of subantarctic waters enriched in silica high ge si opal ratios are associated with high opal contents from the same sediment samples and with warm climate as indicated by depleted benthic foraminiferal 18 o values from the north and equatorial atlantic cold periods signified by enriched benthic 18 o values on the contrary are associated with lower ge si opal ratios we interpret diatom ge si values to reflect the prevailing weathering state on the continents with greater chemical weathering during warm and wet periods of the pliocene and less during cooler and drier intervals

a laminated sediment sequence from the northern north atlantic ocean and its climatic record a remarkable 3 m thick sequence of laminated diatom ooze ldo has been recovered in the north atlantic ocean the ldo is monospecific and consists of the pennate diatom thalassiothrix longissima biostratigraphy and benthic oxygen isotope stratigraphy indicate that the ldo was deposited during substage 5e eem in analogy to recent observations of massive surface concentrations of diatoms in the equatorial pacific and neogene examples we suggest that the ldo represents numerous depositional events of thalassiothrix mats that were physically accumulated at a subarctic convergence front the occurrence of the ldo combined with other climate proxies indicates substantial geographic stability of ocean fronts in the north atlantic during substage 5e

the early matuyama diatom maximum off sw africa a conceptual model abstract an important discovery during ocean drilling program leg 175 when investigating the record of upwelling off namibia was the finding of a distinct late pliocene diatom maximum spanning the lower half of the matuyama reversed polarity chron mdm matuyama diatom maximum and centered around 2 6 2 0 ma this maximum was observed at all sites off southwestern africa between 20 s and 30 s and is most strongly represented in sediments of site 1084 off luderitz namibia the mdm is characterized by high biogenic opal content high numbers of diatom valves and a diatom flora rich in southern ocean representatives with thalassiothrix antarctica forming diatom mats as well as coastal upwelling components before mdm time diatoms are rare until ca 3 6 ma after the mdm in the pleistocene the composition of the diatom flora points to increased importance of coastal upwelling toward the present but is accompanied by a general decrease in opal and diatom deposition here we present a simple conceptual model as a first step in formalizing a possible forcing mechanism responsible for the record of opal deposition in the upwelling system off namibia the model takes into account southern ocean oceanography and a link with deepwater circulation and deepwater nutrient chemistry which in turn are coupled to the evolution of north atlantic deep water nadw the model proposes that between the mdm and the mid pleistocene climate revolution opal deposition off namibia is not directly tied to glacial interglacial fluctuations as seen in the global 18o record but that instead a strong deepwater link exists with increased nadw production as seen in the deepwater 13c record accounting for higher supply of silicate to the thermocline waters that feed the upwelling process the opal record of site 1084 shows affinity to eccentricity on the 400 kyr scale but not for the 100 kyr scale this points toward long term geologic processes for delivery of silica to the ocean

organic geochemical changes in pliocene sediments of odp site 1083 benguela upwelling system the intensification of the northern hemisphere glaciation inhg was a major event in the development of the current climate state and as one of the most productive regions in the world s oceans the behaviour of the benguela upwelling system bus following the inhg is of wide interest to investigate post inhg changes in productivity and organic matter accumulation total organic carbon and biomarker accumulation rates were determined for sediments from cop site 1083 and compared to alkenone derived sea surface temperatures and nitrogen isotopic compositions these data indicate that the interval between 2 6 and 2 4 ma was characterized by dramatic changes in upwelling intensity and organic carbon export on the northern edge of the modern bus the upwelling is reflected by significant changes in alkenone derived sst estimates between glacial and interglacial intervals with a total variability of 16 degrees c the studied interval is also characterized by large changes in organic matter export as reflected by changes in toc and biomarker accumulation rates which show maxima during ois 98 and during the transition from ois 97 to 96 intervals of elevated toc are also characterized by elevated concentrations of sedimentary microbial biomarkers and lower caco 3 suggesting that enhanced delivery of labile organic matter to the seafloor resulted in enhanced remineralisation with released co 2 being consumed by caco 3 dissolution however in apparent contrast to recent pleistocene sediments at the same site organic matter export after the inhg was not solely driven by upwelling intensity of the three pliocene glacial interglacial cycles examined ois 101 to 96 each is unique with respect to the timing and magnitude of changes in organic matter accumulation each is also characterized by different algal assemblages as inferred from biomarker distributions with ois 97 and 96 particularly dominated by diatoms we suggest that these differences reflect the important but evolving role of southern ocean waters in the pliocene bus nutrient depletion of so waters occurred during parts of pliocene glacial intervals such that even intense upwelling did not persistently result in enhanced organic matter accumulation rates c 2009 elsevier b v all rights reserved

accumulation of organic and inorganic carbon in pliocene pleistocene sediments along the sw african margin the ocean drilling program leg 175 recovered a unique series of stratigraphically continuous sedimentary sections along the sw african margin an area which is presently affected by active coastal upwelling the accumulation rates of organic and inorganic carbon are a major component of this record four leg 175 sites 1082 1084 1085 1087 are chosen as part of a latitudinal transect from the present northern to southern boundaries of the benguela current upwelling system to decipher the pliocene pleistocene history of biogenic production and its relationship with global and local changes in oceanic circulation and climate the pattern of caco3 and corg mass accumulation rates mars over 0 25 myr intervals indicates that the evolution of carbon burial is highly variable between the northern and the southern benguela regions as well as between sites that have similar hydrological conditions this as well as the presence over most locations of high amplitude rapid changes of carbon burial reflect the partitioning of biogenic production and patterns of sedimentation into local compartments over the benguela margin the combined mapping of caco3 and corg mars at the study locations suggests four distinct evolutionary periods which are essentially linked with major steps in global climate change the early pliocene the mid pliocene warm event a late pliocene intensification of northern hemisphere glaciation and the pleistocene the early pliocene spatially heterogeneous patterns of carbon burial are thought to reflect the occurrence of mass gravitational movements over the benguela slope which resulted in disruption of the recorded biogenic production this was followed 3 5 3 ma by an episode of peak carbonate accumulation over the whole margin and subsequently by the onset of benguela provincialism into a northern and a southern sedimentary regime near 2 ma this mid and late pliocene evolution is interpreted as a direct response to changes in the ventilation of bottom and intermediate waters as well as to dynamics of the subtropical gyral circulation and associated wind stress

the late miocene onset of high productivity in the benguela current upwelling system as part of a global pattern abstract we have examined the history of the elevated primary productivity associated with the benguela current upwelling system off southwest africa using sediments from 7 5 to 4 8 ma at ocean drilling program site 1085 in the middle cape basin sedimentation rates are low until 6 9 ma low accumulation rates of benthic foraminifers and organic carbon indicate that biological productivity was also low paleoproductivity dramatically increased at 6 7 6 5 ma and was highly variable until 4 8 ma with productivity maxima during cooler periods the presence of radiolarian opal only between 5 8 and 5 2 ma suggests an interlude of silica rich intermediate water in the cape basin the onset of heightened productivity under the benguela current is mirrored by similar increases reported between 6 9 and 6 7 ma in the tropical eastern pacific the western and northern pacific and the indian ocean the similarity between the patterns at site 1085 and in the pacific and indian oceans suggests that the dramatic productivity increase off southwest africa is part of a global response to paleoceanographic changes

a 350 ky radiolarian record off luderitz namibia evidence for changes in the upwelling regime abstract the study of radiolarian assemblages from core md 962086 provides new information on the variability in the upwelling intensity and origin of upwelled water masses over the past 350 ky in one of the major filamentous regions of the benguela upwelling system bus located off luderitz namibia the use of key radiolarian species to trace the source of upwelled waters and the use of a radiolarian based upwelling index uri to reconstruct the upwelling intensity represent the first use of radiolarians for paleoceanographic reconstructions in the bus these radiolarian based proxies indicate strongest upwelling during marine isotope stages mis 3 5 and 8 which compares well with other studies while during mis 3 and 8 the radiolarian based proxies indicate the influx of waters of southern ocean origin they also point to the increased influence of tropical waters during the lower portion of mis 5 during mis 2 4 and 6 the radiolarian assemblages indicate generally lower upwelling intensities although this signal is complicated by the increased occurrence of organic carbon in the sediments during these intervals during mis 2 there appears to be less of an input of southern ocean waters to the bus although during the also glacial mis 4 and 6 there is evidence for an increased influence of cold antarctic waters the comparison of the results from core md 962086 with other studies in the bus area indicates a non uniform pattern of upwelling intensity and advection of cold southern waters into this system during mis 2 weaker upwelling signaled by the radiolarian based proxy in mis 4 is in contrast to other studies that indicate higher productivity during this time period in general the data show that there is a strong spatiotemporal complexity in upwelling intensity in the bus and that the advection of water into it is not strongly tied to glacial interglacial variations in climate

high resolution elemental records from the south china sea and their paleoproductivity implications 1 the biogenic related elements ca sr ba p cd scavenged al and ti were analyzed by inductively coupled plasma mass spectrometry icp ms and inductively coupled plasma atomic emission spectrometry icp aes for core ns93 5 from the west slope of the south china sea terrestrial input as estimated from the accumulation of ti was higher during glacials than during interglacials carbonate accumulation rates are inversely related to those of terrestrial input suggesting higher production of calcareous phytoplankton during interglacials the accumulation patterns of authigenic sr ba p and cd match that of carbonate further indicating higher calcareous phytoplankton production during interglacials scavenged al and excess sio2 which is related to biogenic opal exhibit higher accumulation rates during glacials and correspond with changes in terrestrial input this indicates that terrestrial input driven is important to siliceous phytoplankton production but not for calcareous phytoplankton production as calcareous phytoplankton is the dominant component of the biogenic sediments in the south china sea particularly during interglacials previous inference of higher productivity in the south china sea during glacials based on only the biogenic opal proxy needs to be reconsidered

the interplay between the surface and bottom water environment within the benguela upwelling system over the last 70 ka the benguela upwelling system bus located between 30 and 20 s is one of the fundamental high productivity systems of the world ocean the bus has previously been studied in terms of primary productivity and ecology over glacial interglacial timescales however the response and coupling with the benthic environment have received little attention here for the first time we present a high resolution reconstruction of the bus highlighting the link between surface and benthic productivity and their response to climatic and oceanographic changes over the last 70 ka the study is based on benthic foraminiferal faunal analysis together with analyses of diatom assemblages grain size of the terrigenous fraction and stable o and c isotopic and bulk biogenic components of core geob3606 1 we reveal significant shifts in benthic foraminiferal assemblage composition tight coupling existed between the surface and bottom water environment especially throughout marine isotope stages 4 and 3 mis4 and mis3 due to the high export production the site has essentially experienced continuous low oxygen conditions however there are time periods where the hypoxic conditions were even more notable two of these severe hypoxic periods were during parts of mis4 and mis3 where we find an inverse relationship between diatom and benthic foraminifera accumulation meaning that during times of extremely high phytodetritus export we note strongly suppressed benthic productivity we also stress the importance of food source for the benthos throughout the record shifts in export productivity are attributed not only to upwelling intensity and filament front position but also regional global climatic and oceanographic changes had significant impact on the bus dynamics

late pliocene vegetation and climate in namibia southern africa derived from palynology of odp site 1082 the present day condition of bipolar glaciation characterized by rapid and large climate fluctuations began at the end of the pliocene with the intensification of the northern hemisphere continental glaciations the global cooling steps of the late pliocene have been documented in numerous studies of ocean drilling program odp sites from the northern hemisphere however the interactions between oceans and between land and ocean during these cooling steps are poorly known in particular data from the southern hemisphere are lacking therefore i investigated the pollen of odp site 1082 in the southeast atlantic ocean in order to obtain a high resolution record of vegetation change in namibia between 3 4 and 1 8 ma four phases of vegetation development are inferred that are connected to global climate change 1 before 3 ma extensive rather open grass rich savannahs with mopane trees existed in namibia but the extension of desert and semidesert vegetation was still restricted 2 increase of winter rainfall dependent renosterveld like vegetation occurred between 3 1 and 2 2 ma connected to strong advection of polar waters along the namibian coast and a northward shift of the polar front zone in the southern ocean 3 climatically induced fluctuations became stronger between 2 7 and 2 2 ma and semiarid areas extended during glacial periods probably as the result of an increased pole equator thermal gradient and consequently globally enhanced atmospheric circulation 4 aridification and climatic variability further increased after 2 2 ma when the polar front zone migrated southward and the influence of atlantic moisture brought by the westerlies to southern africa declined it is concluded that the positions of the frontal systems in the southern ocean which determine the locations of the high pressure cells over the south atlantic and the southern indian ocean have a strong influence on the climate of southern africa in contrast to the climate of northwest and central africa which is dominated by the saharan low pressure cell

geochemical characterization of tarballs on beaches along the california coast part i shallow seepage impacting the santa barbara channel islands santa cruz santa rosa and san miguel tarballs are common along the southern california coastline this study investigates tarballs from beaches along this coastline with a focus on santa cruz santa rosa and san miquel islands in the santa barbara channel the tarballs were fingerprinted using biomarker and stable carbon isotope parameters and then grouped according to genetic similarities the data show that the tarballs are of natural and not anthropogenic origin and that all originate from source rock within the miocene monterey formation via shallow seeps offshore sterane biomarker parameters were found to vary widely in the sample set biodegradation especially of the regular steranes is the primary process impacting the biomarker distributions in a large group of samples the most common tarball occurrences appear to come from offshore seepage near the west end of santa cruz island another major group most likely was transported north from near santa monica bay several individual occurrences of some of these tarball groups also were found on beaches as far north as pt reyes and as far south as san diego indicating significant long distance dispersal by ocean currents this study begins a library of tarball fingerprints to be used as a database to help distinguish between natural and anthropogenic tar occurrences all along the california coast and to compare shallow seepage with future samples of deeper production oils from the same area

environmental history of the south eastern south atlantic since the middle miocene evidence from the sedimentological records of odp sites 1088 and 1092 during leg 177 of the ocean drilling program odp well preserved middle miocene to pleistocene carbonate rich sediment records were recovered on a north south transect through the south eastern atlantic sector of the southern ocean at site 1088 on the agulhas ridge and site 1092 on meteor rise both sites were dominated by the deposition of calcareous nannofossil oozes through the miocene indicating low biological productivity in warm to temperate surface waters a continuous increase in the proportions of foraminifera since the latest miocene 6 5 ma points to enhanced nutrient supply possibly related to the global biogenic bloom event across the miocene pliocene boundary since the late pliocene different styles of biological productivity developed between the sites enhanced deposition of biosiliceous constituents at the southern site 1092 particularly in the early pleistocene is consistent with the formation of the circum antarctic opal belt since 2 5 ma in a setting near the polar front whereas carbonate deposition still prevailed at the northern site 1088 situated near the subtropical front clay mineral tracers of water mass advection together with the pattern of sedimentation rates and hiatuses reflect distinct pulses in the development of regional ocean circulation between 14 and 12 ma around 8 ma and since 2 8 ma these pulses can be related to antarctic ice sheet extension that mediates the production and flow of southern source water and stepwise increases in north atlantic deep water production that drives global conveyor circulation at site 1088 illite chemistry and silt clay ratios of the terrigenous sediment fraction reflect the history of terrestrial climate in southern africa with humid conditions prior to the early late miocene 9 7 ma followed by a dry episode until 7 7 ma the latest miocene and early pliocene were characterized by a humid episode until modern aridity was established in the late pliocene between 4 0 and 2 8 ma these climate changes were related to the latitudinal migration of climate belts in response to tectonically caused reorganizations in atmospheric and ocean circulation

norcholestane in miocene onnagawa siliceous sediments japan abstract a significant amount of 24 norcholestane with 20r 5 h 14 h 17 h stereochemistry is often found in marine siliceous sediments of the middle miocene onnagawa formation japan some onnagawa siliceous sediments are abnormally abundant in 24 norcholestane the primary production in the northeastern japan sea during the middle miocene was markedly increased due to the invasion of nutrient rich cold seawater from the north accompanied by the tectonic opening of the japan sea 24 norcholestane in high relative abundance is derived mainly from the marine diatoms which were enhanced during this event the drastic ecological change caused by rapid tectonic opening of the japan sea and global climatic deterioration during middle miocene time is suggested to be influential in the formation of 24 norcholestane rich onnagawa siliceous sediments

oscillations of the siliceous imprint in the central benguela upwelling system from mis 3 through to the early holocene the influence of the southern ocean based on a high resolution analysis of the diatom signal and biogenic bulk compo nents at site geob3606 1 25 s off namibia we describe rapid palaeoceanographic changes in the benguela upwelling system bus from early mis 3 through to the early holocene 55 000 to 7 000 14 c yr bp coastal upwelling strongly varied at 25 s from mis 3 through to mis 2 the abrupt decrease in the accumulation rate of biogenic silica and diatoms from mis 3 into mis 2 records rapid oceanographic changes in the bus off namibia during mis 3 leakage of excess h4sio4 acid from the southern ocean into low latitude surface waters as indicated by the occurrence of antarctic dia toms enhanced the production of spores of chaetoceros at the expense of calcareous phytoplankton furthermore shallower antarctic intermediate water aaiw would have enriched the thermocline off namibia with silicate transported from the southern ocean the strong decrease of the siliceous signal throughout mis 2 represents a decrease in the nutrient input to the bus even though the dia tom assemblage is still dominated by spores of the upwelling associated diatom genus chaetoceros depletion of silicate in the thermocline from the onset of mis 2 through to the early holocene reflects the shutdown of aaiw injection from the southern ocean into the bus causing upwelled waters to become reduced in silicate hence less favourable for diatom production the deglaciation and early holocene are characterised by the replacement of the upwelling associated flora by a non upwel ling related diatom community reflecting weakened upwelling retraction of the seaward extension of the chlorophyll filament off luderitz and dominance of warmer waters copyright 2003 john wiley sons ltd

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

a novel sterane 27 nor 24 methyl 5α cholestane in sediments a novel sterane 27 nor 24 methyl 5 alpha cholestane has been identified in sedimentary hydrocarbon mixtures by coinjection with an authentic standard the c sub 27 sterane occurs in silica rich sediments from the monterey formation usa the onnagawa formation japan and the menilite shale poland and in bituminous marls from the vena del gesso basin italy the compound seems to be biosynthetically related to 24 norcholestanes which co occur in sometimes relatively high amounts the sup 13 c content of the sterane in the monterey formation indicates an algal source similar to other steranes present in this sediment a diatom or a dinoflagellate source is suggested for this compound

late pliocene climate in the southeast atlantic preliminary results from a multi disciplinary study of dsdp site 532 abstract site 532 on the walvis ridge was sampled at 4000 to 800 year intervals from 2 24 to 2 60 ma spanning the three large glacial advances of the late pliocene an age model was created by correlating the oxygen isotope record to site 607 with linear interpolations between tie lines the resultant age model differs from that in the site reports by more than 800 000 years due to misidentification of a magnetic boundary sedimentation rates varied by an order of magnitude at this site with minimum accumulation during glacial events interglacial intervals were charactrized by high marine production and high summer precipitation on land while glacials had very low production and arid continental climate during the large glacial events stages 96 100 conditions of low production and continental aridity reached their greatest intensity but there is no evidence of a permanent mode shift in either marine or terrestrial records calcite concentration has a strong variation at obliquity frequencies with maxima during interglacials but occasionally shows a large amplitude at precessional frequencies as well so that high concentrations occur in a few glacial intervals as a result color variation is not a reliable guide to glacial scale cycles at this site composition of the phytoplankton assemblage is diverse and highly variable and we have not been able to distinguish a clear indicator of upwelling related production spectral analysis reveals obliquity and precessional signals in the pollen data while several diatom records contain combination tones indicating that these data represent a complicated response to both local and high latitude forcing

late pliocene to early pleistocene 2 4 1 25 ma paleoproductivity changes in the bering sea iodp expedition 323 hole u1343e abstract late pliocene to early pleistocene paleoproductivity changes in the bering sea were reconstructed using geochemical concentrations and mass accumulation rates mars of caco 3 biogenic opal and total organic carbon toc and sedimentary nitrogen isotope ratios 15 n at iodp expedition 323 hole u1343e drilled in the northern slope area 1956 m deep of the bering sea caco 3 concentration is generally low but prominent caco 3 peaks occur intermittently due to subseafloor authigenic carbonate formation rather than biogenic accumulation regardless of glacial interglacial variations biogenic opal concentrations reflect orbital scale glacial interglacial variations however toc concentration did not show clear glacial interglacial variation probably due to poor preservation the sedimentary 15 n values vary synchronously with biogenic opal concentration on orbital timescales the co varying pattern of opal productivity and 15 n values at hole u1343e is a result of nutrient utilization controlled by diatom productivity in the bering slope area where fe is not a limiting factor biogenic opal and toc mars showed a temporal shift at around 1 9 ma from a high productivity period under nutrient enriched conditions to a low productivity period under relatively nutrient depleted conditions high diatom productivity with low 15 n values before 1 9 ma is associated with abundant nutrient supply by upwelling in relation to strong surface current system this productivity decrease at about 1 9 ma was also found in the southern bering sea site u1341 and may be related to global opal reorganization

paleoenvironmental implications of novel c30 steranes in precambrian to cenozoic age petroleum and bitumen petroleums and bitumens from early proterozoic 1800 ma to miocene 15 ma age marine strata contain 24 isopropylcholestanes a novel group of c30 steroids the abundance of these compounds relative to 24 n propylcholestanes varies with source rock age late proterozoic vendian and early cambrian oils and or bitumens from siberia the urals oman australia and india have a high ratio of 24 isopropylcholestanes to 24 n propylcholestanes 1 while younger and older samples have a lower ratio 0 4 temporal changes in this parameter may reflect the relative abundance of certain porifera sponges and certain marine algae through time geochemical indicators such as this which can constrain the source rock age of a migrated oil are useful in source rock identification during petroleum exploration

phosphorite deposits on the namibian shelf abstract phosphorite deposits provide a source of fertilizer to feed an increasingly populated world and they provide a record of paleoceanographic changes in upwelling systems linked to climate the benguela upwelling system bus is among the most productive today and is associated with major phosphorite deposits exposed over an area of 24 700 km 2 on the namibian shelf analyses of cores associated with recent offshore mineral exploration provide new insights into the age and origin of these phosphorite deposits the deposit consists of coarsening upward muddy to gravelly pelletal phosphorite sand up to several meters thick on the middle to outer shelf 190 and 350 m water depth offshore of luderitz and walvis bay less extensive and less continuous deposits occur offshore of walvis bay as far north as the kunene river mouth on the inner to middle shelf 50 and 250 m water depth pelletal phosphorite sand some concentrically banded and concretionary phosphorite pebbles are the dominant grain types consisting of up to 90 wt carbonate fluorapatite francolite cement and inclusions of organic matter pyrite and terrigenous mud strontium isotope stratigraphy and foraminiferal biostratigraphy indicate that phosphogenesis was initiated in the latest miocene but that most phosphorite formed in the plio pleistocene during early burial diagenesis of organic rich mud as it does today in the holocene diatomaceous mud belt the highly condensed coarsening upward succession reflects increasingly high amplitude pleistocene sea level fluctuations phosphorite formation correlates to terrestrial aridification as well as to marine proxies of intensified coastal upwelling in the 600 m thick equivalent successions on the upper slope repeated phosphorite formation and reworking over pleistocene glacial to interglacial cycles resulted in the economic concentration of phosphorite with an estimated total resource of 7800 million tons of phosphate rock at an average grade of 19 wt p 2 o 5 on the namibian shelf

a molecular stable carbon isotope study of organic matter in immature miocene monterey sediments pismo basin the 300 m section of the miocene monterey formation outcropping at shell beach pismo basin ca 15 11 ma is composed of calcareous phosphatic 15 1 14 5 ma and siliceous facies 14 5 11 o ma an objective of this paper is to document lateral paleoenvironmental changes in the miocene monterey formation by comparing the shell beach sb profile with the naples beach nb section in the santa barbara ventura basin schouten et al 1997 which is 80 km to the south eight samples one sample representing on average a time period of ca 2000 y from this section were analyzed for variations of extractable biomarkers and their carbon isotopic signatures as indicators for paleoenviron mental change during the miocene saturated hydrocarbons present include 28 30dinorhopane phytane n alkanes c c3r lycopane and 17 21p h homohopane the biomarkers released after desulfur ization of the polar fractions predominantly consist of phytane 2 6 10 14 tetramethyl 7 3 methylpen tyl pentadecane c c3 n alkanes regular 5a and sd steranes dinosteranes and 22r 17 21 h pentakishomohopane steranes have similar carbon isotopic compositions 25 to 27 0 throughout the section and are isotopically similar at both sites indicating laterally similar and vertically stable environmental conditions for algae living in the upper part of the photic zone free and s bound n alkanes at sb mainly originate from marine organisms and not from terrestrial sources as in the nb section s bound pentakishomohopane is ca l 4 0 depleted compared to the steranes and is thought to be derived from the deeper water dwelling cyanobacteria these findings are consistent with stable carbon isotopic data obtained for these compounds from middle miocene monterey sediments at naples beach and indicates similar environmental conditions in the depositional environments of the santa barbara ventura and the pismo basin s bound highly branched isoprenoids have at both sites different isotopic compositions indicating the presence of different diatom species special growth conditions or different bloom periods in the pismo basin the carbon isotopic composition of 28 30dinorhopane shifts to more depleted values up section suggesting that the dinorhopane synthesizing organism or organisms live on c02 which is isotopically influenced by methane production and oxidation the cs hopane is enriched by l 4 0 in 13c compared to other hopanes and steranes specific bacteria possibly heterotrophs may have been the organisms producing this compound copyright 0 1997 elsevier science ltd

the late pliocene benguela upwelling status revisited by means of multiple temperature proxies as compared to the late pleistocene alkenone based sea surface temperature sst in the benguela region revealed relatively warm and stable sst recorded between approximate to 3 5 and 2 0 ma and coincide with a period of increasing biological productivity as revealed by increasing deposition of biogenic opal we assess how the hydrological patterns recorded in sst proxies are embedded in the geological record by performing a proxy proxy comparison we used laser ablation inductively coupled plasma mass spectrometry to measure the mg ca on the planktonic foraminifera species globigerina bulloides allowing in situ measurements of mg ca on individual foraminiferal tests mg ca derived temperatures provide much colder temperatures than alkenone derived sst by up to 10 degrees c we build a scenario involving contrasting sensitivities of paleothermometers upon the annual cycle namely alkenones preferentially capturing sst when the surface ocean is warmer than the mean annual average sst and g bulloides capturing sst when upwelling intensifies multichamber analysis also suggests that g bulloides migrates below the sea surface while calcifying its last chambers prior to gametogenesis allowing the extraction of both surface and subsurface temperature from mg ca measured on different chambers the range of temperatures recorded between our multiple sst proxies is supported by the range of temperatures simulated with a general circulation model when different seasons different water depth and different orbital configurations occurring during the late pliocene are considered a greater seasonal cycle in sst during the pliocene can account for alkenone and mg ca derived temperature contrast pointing to a radically different mode of upwelling activity in the benguela region compared to today

linking desert evolution and coastal upwelling pliocene climate change in namibia a late pliocene high resolution pollen record from the southeast atlantic ocean drilling program site 1082 registers vegetation development in southwest africa the marine record is continuous ranges from 3 5 to 1 7 ma and has a millennial resolution between 2 9 and 1 9 ma changes in climate and vegetation correspond to the matuyama diatom maximum of the namibian upwelling system and seem to be highly susceptible to latitudinal shifts in the polar front zone of the southern ocean a northward advance of the polar fronts is connected with an increase in winter rainfall in southwest africa rapid desiccation in namibia at 2 2 ma is associated with increasing upwelling and decreasing sea surface temperatures along the coast

nutrient leakage from the north pacific to the bering sea iodp site u1341 following the onset of northern hemispheric glaciation 1 intergrated ocean drilling program expedition 323 recovered a sediment record covering the last 4 3 ma from the bering sea integrated ocean drilling program site u1341 bowers ridge 2177 m water depth to resolve pliocene pleistocene paleoenvironmental changes in this marginal basin 190 sediment samples were analyzed for their bulk element composition aluminium contents in bowers ridge sediments are variable but overall higher toward younger sediments probably related to the intensification of the northern hemispheric glaciation and increasing sea ice transport in the bering sea the gradual increase of terrigenous input is mirrored by decreasing sio2 and excess si sixs contents but the overall si enrichment of the deposits reflects continuous opal deposition since the pliocene at bowers ridge unlike in the north pacific the sixs record at site u1341 does not support a dramatic decrease in opal export following the onset of the northern hemispheric glaciation around 2 7 ma but sio2xs have higher accumulation rates up to 8 g cm2 ka between 2 6 and 1 8 ma bp during this period the major oceanic opal deposition centers shifted globally from open marine high latitude regions to upwelling areas we here discuss how the onset of north pacific stratification at 2 7 ma bp may have caused leakage of nutrient rich deep intermediate north pacific water into the bering sea via the deep kamtchatka strait leading to increased opal deposition and likely reactive organic matter export at bowers ridge as a result magnetic and geochemical records were overprinted by intensified diagenesis significantly affecting their applications as paleoceanographic proxies

dinosterane and other steroidal hydrocarbons of dinoflagellate origin in sediments and petroleum abstract the steroidal alkanes of a selection of sediments and oils have been examined by gc ms with multiple metastable reaction monitoring specific 4 methyl sterane isomers have been identified by comparison with isomers synthesized from sterols isolated from dinoflagellates an immature marine oil shale and two mature marine oils of triassic to early cretaceous age contained high concentrations of c30 steranes comprising desmethyl 24 ethyl 4 methylcholestane and 4 23 24 trimethylcholestane dinosterane isomers an immature non marine oil shale and two non marine oils of cretaceous to eocene age contained stereoisomers of 24 ethyl 4 methylcholestane as the dominant c30 steranes reaction monitoring analyses in gc ms are particularly suited to unravelling complex distributions of homologous and stereoisomeric steroids encountered in oils and their source rocks

upwelling intensification as part of the pliocene pleistocene climate transition a deep sea sediment core underlying the benguela upwelling system off southwest africa provides a continuous time series of sea surface temperature sst for the past 4 5 million years our results indicate that temperatures in the region have declined by about 10 c since 3 2 million years ago records of paleoproductivity suggest that this cooling was associated with an increase in wind driven upwelling tied to a shift from relatively stable global warmth during the mid pliocene to the high amplitude glacial interglacial cycles of the late quaternary these observations imply that atlantic ocean surface water circulation was radically different during the mid pliocene

biomarker geochemistry of a foreland basin the oligocene menilite formation in the flysch carpathians of southeast poland black shales of the menilite formation the source rock for oils in the carpathian overthrust belt display a large variability in their bulk and molecular geochemical parameters biomarker and stable carbon isotope analyses indicate a variable contribution from different algae particularly dinoflagellates and diatoms and cyanobacteria this is reflected by specific predominantly sulfurised biomarkers e g c35 homohopanoids c25 highly branched isoprenoids and marine n alkanes and by particular distributions of steranes and 4 methylsteranes comprising 24 nor and 24 methyl 27 norcholestanes and related novel steranes with a methylation at c 23 the presence of hopanoids of methanotrophic origin 13c up to 57 implies a temporarily enhanced full methane cycle in a marine environment which affected the isotopic composition of organisms dwelling in the upper photic zone the presence of isorenieratene derivatives indicate periods of euxinic conditions within the photic zone in all investigated sub basins

intensification of the walker and hadley atmospheric circulations during the pliocene pleistocene climate transition when comparing new sea surface temperature sst records between the western and eastern equatorial pacific spanning the last 3 2 ma we found that the zonal temperature gradient over the entire tropical pacific irreversibly increased by 3 to 4 degrees c from 2 2 to 2 0 ma here we suggest a pronounced increase in atmospheric circulation from a weak to a strong zonal walker circulation wc during the early pleistocene evidence from other oceanic areas also suggests a strengthening in the meridional hadley circulation hc during the same time period therefore we also suggest that the invigoration of both atmospheric circulation patterns was intimately coupled during the plio pleistocene transition and likely linked to a shrinkage in the zonal extension of the tropical to subtropical warm sphere associated with a prominent increase in the pole to equator temperature gradient our conclusion refutes assumptions that the intensification of atmospheric circulation in the tropics and subtropics significantly contributed to the initiation of continental ice sheet formation at high latitudes since the onset of extensive northern hemisphere glaciation nhg occurred similar to 2 75 ma ago in the late pliocene instead the development of a stronger atmospheric circulation similar to 2 2 2 0 ma ago could have significantly contributed to the plio pleistocene climate cooling c 2010 elsevier b v all rights reserved

steps in the intensification of benguela upwelling over the walvis ridge during miocene and pliocene upwelling is a significant part of the ocean circulation controlling largely the transport of nutrient rich cold waters to the surface and therefore influencing ocean productivity and global climate the benguela upwelling system bus is one of the major upwelling areas in the world previous reconstructions of the bus mainly focused on the onset and intensification in southern and central parts but changes of the northern part have been rarely investigated in detail using the late miocene to pliocene organic walled dinoflagellate cyst record of odp site 1081 we reconstruct and discuss the early upwelling history over the walvis ridge with a special focus on the movement of the angola benguela front abf we suggest that during the late miocene the angola current flowed southwards over the walvis ridge more frequently than today because the abf was probably located further south as a result of a weaker meridional temperature gradient a possible strengthening of the meridional gradient during the latest miocene to early pliocene in combination with uplift of south western africa intensified the upwelling along the coast and increased the upwelling s filaments over the walvis ridge an intermediate period from 6 2 to 5 5 ma is shown by the dominance of habibacysta tectata cysts of a cool tolerant dinoflagellate known from the northern atlantic indicating changing oceanic conditions contemporaneous with the messinian salinity crisis from 4 3 ma on the upwelling signal got stronger again and waters were well mixed and nutrient rich our results indicate a northward migration of the abf as early as 7 ma and the initial stepwise intensification of the bus

comparison of foraminiferal cleaning procedures for mg ca paleothermometry on core material deposited under varying terrigenous input and bottom water conditions a down core comparison of two commonly applied foraminiferal cleaning procedures for mg ca paleothermometry has been conducted using well preserved globigerinoides ruber white 250 300 mm from core material deposited under varying terrigenous input and bottom water conditions this study demonstrates that in the majority of investigated core materials both cleaning methods yield fairly comparable results of mg ca ratios however fe and mn phases are effectively removed by the cleaning procedure containing a reductive step in a core interval indicating gradual transition of terrigenous deposition and pore water conditions the cleaning procedure without a reductive step results in anomalously higher mg ca ratios accompanied by high fe ca and mn ca ratios indicating the presence of high mg contaminants considering that the mg ca deviation of the comparison study is the cumulative sum of 1 the difference in cleaning efficiency of the applied methods 2 the cleaning method dependent partial dissolution of mg and 3 the heterogeneity of subsamples we suggest that selective mg loss from well preserved globigerinoides ruber shells caused by the reductive sample treatment is not substantial enough to significantly bias paleotemperature estimation thus for core material deposited under varying sources and amounts of terrigenous material and bottom water conditions favorable for formation of authigenic mineral phases the use of cleaning methods that do include a reductive step yields more effective cleaning results by successful removal of mineral phases that may contain high mg

pliocene pleistocene variability of upwelling activity productivity and nutrient cycling in the benguela region in this study we present combined high resolution records of sea surface temperature sst phytoplankton productivity and nutrient cycling in the benguela upwelling system bus for the past 3 5 ma the sst record provided evidence that upwelling activity off namibia mainly intensified ca 2 4 2 0 ma ago in response to the cooling of the southern ocean and the resultant strengthening of trade winds as revealed by productivity related proxies bus intensification led to a major transition in regional biological productivity when considering the termination of the matuyama diatom maximum a diatom high production event major oceanic reorganization in the benguela was accompanied by nutrient source changes as indicated by a new nitrogen isotopic delta n 15 record that revealed a stepwise increase at ca 2 4 and ca 1 5 ma ago the change in source region likely resulted from significant changes in intermediate water formation tied to the reorganization of oceanic conditions in the southern ocean which may have in turn mainly controlled the global ocean n cycle and therefore the n isotopic composition of nutrients since 3 5 ma ago

oceanic atmospheric and ice sheet forcing of south east atlantic ocean productivity and south african monsoon intensity during mis 12 to 10 variations in the strength of coastal upwelling in the south east atlantic ocean and summer monsoonal rains over south africa are controlled by the regional atmospheric circulation regime although information about these parameters exists for the last glacial period little detailed information exists for older time periods new information from odp site 1085 for marine isotope stages mis 12 10 shows that glacial interglacial productivity trends linked to upwelling variability followed a pattern similar to the last glacial cycle with maximums shortly before glacial maxima and minimums shortly before glacial terminations during the mis 11 10 transition several periodic oscillations in productivity and monsoonal proxies are best explained by southwards shifts in the southern sub tropical high pressure cells followed by abrupt northwards shifts comparison to coeval sea surface temperature measurements suggests that these monsoonal cycles were tightly coupled to anti phased hemispheric climate change with an intensified summer monsoon during periods of northern southern hemisphere cooling warming the timing of these events suggests a pacing by insolation over precession periods a lack of similar regional circulation shifts during the mis 13 12 transition is likely due to the large equatorwards shift in the tropical convection zone that occurred during this extreme glaciation

orbital and suborbital climate variability in the sulu sea western tropical pacific 1 a detailed record of planktic 18o from a sediment core in the sulu sea located between the south china sea and the western pacific warm pool reveals that for the past 400 kyr 1 kyr 1000 years 18o variability on orbital timescales is similar to that caused by changes in ice volume alone this result indicates that in the sulu sea temperature driven changes in planktic 18o on orbital times scales were generally compensated for by the effects of sea level and changes in seasonal monsoon intensity on the local freshwater budget as well as by other changes in the tropical hydrologic cycle and their attendant effects on surface water 18o increased freshening of the western tropical pacific warm pool is reminiscent of la nina conditions however we argue that the mean tropical climate state was not more la nina like than today on broader spatial scales suborbital variability occurred in the sulu sea throughout the past 400 kyr suggesting little sensitivity to ice volume or to glacial interglacial changes in tropical hydrology variations on 4 10 kyr timescales appear to be linked to those in the north atlantic region suggesting a common forcing of that variability we suggest that sulu sea salinity variations were a response to suborbital climate variability in the north atlantic region transmitted via changes in the intensity of the east asian summer monsoon we suggest that a north atlantic origin of that tropical suborbital variability can be reconciled with weak glacial amplification in the tropics if the tropical response is nonlinear

persistent warmth across the benguela upwelling system during the pliocene epoch a feature of pliocene climate is the occurrence of permanent el nino like or el padre conditions in the pacific ocean from the analysis of sediment cores in the modern northern benguela upwelling we show that the mean oceanographic state off southwest africa during the warm pliocene epoch was also analogous to that of a persistent benguela el nino at present these events occur when massive southward flows of warm and nutrient poor waters extend along the coasts of angola and namibia with dramatic effects on regional marine ecosystems and rainfall we propose that the persistent warmth across the pliocene in the benguela upwelling ended synchronously with the narrowing of the indonesian seaway and the early intensification of the northern hemisphere glaciations around 3 0 3 5 ma the emergence of obliquity related cycles in the benguela sea surface temperatures sst after 3 ma highlights the development of strengthened links to high latitude orbital forcing the subsequent evolution of the benguela upwelling system was characterized by the progressive intensification of the meridional sst gradients and the emergence of the 100 ky cycle until the modern mean conditions were set at the end of the mid pleistocene transition around 0 6 ma these findings support the notion that the interplay of changes in the depth of the global thermocline atmospheric circulation and tectonics preconditioned the climate system for the end of the warm pliocene epoch and the subsequent intensification of the ice ages

diatom inferred salinity changes from the yushe paleolake indicate an aridification during the pliocene pleistocene transition in north china abstract the global climate changed significantly during the pliocene pleistocene transition and a worldwide aridification occurred in order to investigate the influence of the aridification during the pliocene pleistocene transition in the east asian interior diatom assemblages from the upper zhangcun formation north china deposited during 2 7 2 5 ma bp were analyzed and the lake salinity was reconstructed using diatom environment transfer functions a total of 74 diatom taxa were found in the sediments belonging to 21 families and 32 genera four zones were established from the bottom to the top based on the changes in the diatom assemblages over the 15 7 m sediment sequence in zone 1 cyclotella iris dominated in assemblage while caloneis westii and staurosira construens were less presented among representative species in zone 2 c iris dominated which indicates carbonate rich water but in zone 3 benthic pennate taxa such as c westii and anomoeoneis sphaerophora became more abundant indicating a significant increase in water salinity from carbonate type to sulfate type caused by climatic change in zone 4 c iris became dominant again with abundant gomphonema intricatum and rare pinnularia rathsbergiana and martyana martyi species the salinity inferred by conductivity reconstruction increased from 1 9 ppt in zone 2 to 4 1 ppt in zone 3 the significant changes of anion ratio alk cl so42 indicate an abrupt change from carbonate rich to a sulfatic type water the increase of salinity reflects changes in the precipitation evaporation balance the change from carbonate to sulfatic water inferred from the diatom assemblages could indicate a significant aridification around ca 2 6 ma bp on the eastern edge of the loess plateau this is the most easterly record of aridification across the eastern asian interior and may be related with the global cooling and the development of the northern hemisphere glaciation

effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation the late cenozoic closure of the seaway between the north andsouth american continents is thought to have caused extensive changes in ocean circulation and northern hemisphere climate1 2 but the timing and consequences of the emergence of the isthmus of panama which closed the seaway remain controversial1 2 3 4 5 here we present stable isotope and carbonate sand fraction records from caribbean sediments which when compared to atlantic and pacific palaeoceanographic records indicate that the closure caused a marked reorganization of ocean circulation starting 4 6 million years ago shallowing of the seaway intensified the gulf stream and introduced warm and saline water masses to high northern latitudes these changes strengthened deep water formation in the labrador sea over the next million years as indicated by an increased deep water ventilation and carbonate preservation in the caribbean sea and favoured early pliocene warming of the northern hemisphere the evaporative cooling of surface waters during north atlantic deep water formation would have introduced moisture to the northern hemisphere although the pronounced intensification of northern hemisphere glaciation between 3 1 and 2 5 million years ago substantially lagged the full development of north atlantic deep water formation we propose that the increased atmospheric moisture content was a necessary precondition for ice sheet growth which was then triggered by the incremental changes in the earth s orbital obliquity

east asian monsoon forcing of suborbital variability in the sulu sea during marine isotope stage 3 link to northern hemisphere climate 1 we have generated a new high resolution record of variations in planktonic foraminiferal oxygen isotopes 18o and mg ca from a sediment core images 97 2141 in the sulu sea located in the philippine archipelago of western tropical pacific this record reveals distinct suborbital scale 18o changes most notably during marine isotope stage 3 mis3 30 000 to 60 000 years b p the amplitudes of these 18o fluctuations 0 4 to 0 7 exceed that which can be attributed to sea level changes and must be due to changes in sea surface conditions in the same interval variations in planktonic foraminifera mg ca suggest that suborbital surface ocean temperature variations of 1 to 1 5 c in the sulu sea were not in phase with 18o combined this evidence indicates that the mis3 millennial 18o events in the sulu sea were primarily the result of changes in surface water salinity which today is directly related to the east asian monsoon eam and its influence on the balance between surface water contributions from the south china sea and western pacific warm pool wpwp within dating uncertainties the mis3 sulu sea 18o suborbital variability indicates that times of fresher surface conditions in the sulu sea coincide with similar conditions in the wpwp stott et al 2002 and also with intensifications of the summer eam as recorded in the u th dated chinese hulu cave speleothem 18o record wang et al 2001 and thus by inference with interstadials in the greenland ice core records combined these results indicate that pronounced suborbital variability in the summer eam and intertropical convergence zone itcz during mis3 was tightly coupled with climate conditions in the northern high latitudes

carbonate crash and biogenic bloom in the late miocene evidence from odp sites 1085 1086 and 1087 in the cape basin southeast atlantic ocean 1 middle late miocene to early pliocene sedimentary sequences along the continental margin of southwest africa have changes that correspond to the carbonate crash 12 9 ma and biogenic bloom events 7 4 ma described in the equatorial pacific by farrell et al 1995 to explore the origins of these changes we analyzed the carbon and coarse fraction contents of sediments from odp sites 1085 1086 and 1087 at a time resolution of 5 to 30 kyr several major drops in caco3 concentration between 12 and 9 ma are caused by dilution from major increases in clastic input from the oranje river during global sea level regressions abundant pyrite crystals and good preservation of fish debris reflect low oxygenation of bottom pore waters regional productivity was enhanced during the time equivalent to the carbonate crash period higher benthic planktic foraminiferal ratios indicate that caco3 dissolution at site 1085 peaked between 9 to 7 ma which was after the global carbonate crash this period of enhanced dissolution suggests that site 1085 was located within a low oxygen water mass that dissolved caco3 more easily than north atlantic deep water which began to bathe this site at 7 ma at 7 to 6 ma the onset of the biogenic bloom increases and variations in total organic carbon and benthic foraminiferal accumulation rates show that paleoproductivity increased significantly above values observed during the carbonate crash period and fluctuated widely we attribute the late miocene paleoproductivity increase off southwest africa to ocean wide increases in nutrient supply and delivery1

biogeochemical changes within the benguela current upwelling system during the matuyama diatom maximum nitrogen isotope evidence from ocean drilling program sites 1082 and 1084 1 the matuyama diatom maximum mdm is a time of peak opal accumulation from 2 6 to 2 0 ma within the benguela current upwelling system that was initiated by increased influence of southern ocean water on the eastern south atlantic we measured opal total organic carbon toc and caco3 fluxes and c and n stable isotopes in sediments deposited from 2 4 to 1 95 ma at sites 1082 and 1084 to explore the biogeochemical dynamics within the benguela region the infusion of southern ocean water delivered dissolved nutrients and southern ocean flora and fauna resulting in local opal accumulation increasing up to 8 g cm2ky and the production of diatom mats some 15n measurements of diatom bound organic matter indicate that the mats grew within the benguela region the bulk sediment 15n records are taken to reflect changes in the 15n of nitrate in the incoming water where lower values at 2 4 ma reflect less nitrate utilization in the antarctic a long term increase in relative nitrate uptake in the southern ocean is evidenced by the gradual increase in 15n toward 1 9 ma

an evaluation of 14c age relationships between co occurring foraminifera alkenones and total organic carbon in continental margin sediments 1 radiocarbon age relationships between co occurring planktic foraminifera alkenones and total organic carbon in sediments from the continental margins of southern chile northwest africa and the south china sea were compared with published results from the namibian margin age relationships between the sediment components are site specific and relatively constant over time similar to the namibian slope where alkenones have been reported to be 1000 4500 years older than co occurring foraminifera alkenones were significantly similar to 1000 years older than co occurring foraminifera in the chilean margin sediments in contrast alkenones and foraminifera were of similar age within 2 sigma error or better in the nw african and south china sea sediments total organic matter and alkenone ages were similar off namibia age difference toc alkenones 200 700 years chile 100 450 years and nw africa 360 770 years suggesting minor contributions of preaged terrigenous material in the south china sea total organic carbon is significantly 2000 3000 years older owing to greater inputs of preaged terrigenous material age offsets between alkenones and planktic foraminifera are attributed to lateral advection of organic matter physical characteristics of the depositional setting such as seafloor morphology shelf width and sediment composition may control the age of co occurring sediment components in particular offsets between alkenones and foraminifera appear to be greatest in deposition centers in morphologic depressions aging of organic matter is promoted by transport age offsets are correlated with organic richness suggesting that formation of organic aggregates is a key process

glacial interglacial indian summer monsoon dynamics the modern indian summer monsoon ism is characterized by exceptionally strong interhemispheric transport indicating the importance of both northern and southern hemisphere processes driving monsoon variability here we present a high resolution continental record from southwestern china that demonstrates the importance of interhemispheric forcing in driving ism variability at the glacial interglacial time scale as well interglacial ism maxima are dominated by an enhanced indian low associated with global ice volume minima in contrast the glacial ism reaches a minimum and actually begins to increase before global ice volume reaches a maximum we attribute this early strengthening to an increased cross equatorial pressure gradient derived from southern hemisphere high latitude cooling this mechanism explains much of the nonorbital scale variance in the pleistocene ism record