silicic acid dynamics in the glacial sub antarctic implications for the silicic acid leakage hypothesis 1 the silicic acid leakage hypothesis salh purports that changes in silicon and nitrogen depletion ratios in the glacial antarctic created a large pool of unused silicic acid that was transported to lower latitudes in subantarctic mode water samw where it enhanced diatom productivity lowering atmospheric pco2 however increased opal accumulation beneath the sub antarctic during glacial times implies significant consumption of silicic acid in subantarctic surface waters that may have significantly diminished or eliminated si leakage to test how nutrient dynamics in the sub antarctic affected the si oh 4 content of samw during the last glacial period we produced 30si opal records for cores from the subantarctic and subtropical zones of the indian ocean spanning the last 50 000 years comparison with diatom bound 15n records shows that subantarctic surface waters were enriched in si relative to n during the last glaciation consistent with the salh the record from the subtropics does not show this enrichment in si during the last glacial period suggesting that subantarctic surface waters were mainly incorporated into samw rather than being transported across the subtropical front isotope mass balance calculations were used to test for si leakage from the sub antarctic the results show that silicic acid concentration in samw would more than double during the last glaciation if upwelling and northward ekman drift in the antarctic were similar to the present day circulation calculations that assume increased stratification in the glacial antarctic eliminate si leakage but they do not produce the known increase in opal burial in the glacial sub antarctic reconciling the isotope data and opal burial records with a highly stratified antarctic requires the addition of a large local source of silicic acid in the glacial sub antarctic that is inconsistent with present day circulation and nutrient distributions including such a source in our calculations results in significant opal burial in the sub antarctic but it does not enhance si leakage over that occurring in the holocene resolving past changes in the circulation of the southern ocean is clearly vital to future tests of the salh

antarctic intermediate water properties since 400 ka recorded in infaunal uvigerina peregrina and epifaunal planulina wuellerstorfi benthic foraminifera reconstruction of intermediate water properties is important for understanding feedbacks within the ocean climate system particularly since these water masses are capable of driving high low latitude teleconnections nevertheless information about intermediate water mass evolution through the late pleistocene remains limited this paper examines changes in antarctic intermediate water aaiw the most extensive intermediate water mass in the modern ocean through the last 400 kyr using the stable isotopic composition 18o and 13c and trace element concentration mg ca and b ca of two benthic foraminiferal species from the same samples epifaunal planulina wuellerstorfi and infaunal uvigerina peregrina our results confirm that the most reasonable estimates of aaiw temperature and co2 3 are generated by mg cau peregrina and b cap wuellerstorfi respectively we present a 400 kyr record of intermediate water temperature and co2 3 from a sediment core from the southwest pacific dsdp site 593 40 30 s 167 41 e 1068 m water depth which lies within the core of modern aaiw our results suggest that a combination of geochemical analyses on both infaunal and epifaunal benthic foraminiferal species yields important information about this critical water mass through the late pleistocene when combined with two nearby records of water properties from deeper depths our data demonstrate that during interglacial stages of the late pleistocene aaiw and circumpolar deep water cpdw have more similar water mass properties temperature and 13c while glacial stages are typified by dissimilar properties between aaiw and cpdw in the southwest pacific our new co2 3 record shows short time scale variations but a lack of coherent glacial interglacial variability indicating that large quantities of carbon were not stored in intermediate waters during recent glacial periods

pushing the boundaries glacial interglacial variability of intermediate and deep waters in the southwest pacific over the last 350 000 years glacial interglacial changes in southern ocean s air sea gas exchange have been considered as important mechanisms contributing to the glacial interglacial variability in atmospheric co2 hence understanding past variability in southern ocean intermediate to deep water chemistry and circulation is fundamental to constrain the role of these processes on modulating glacial interglacial changes in the global carbon cycle our study focused on the glacial interglacial variability in the vertical extent of southwest pacific antarctic intermediate water aaiw we compared carbon and oxygen isotope records from epibenthic foraminifera of sediment cores bathed in modern aaiw and upper circumpolar deep water ucdw 943 2066 m water depth to monitor changes in water mass circulation spanning the past 350 000 years we propose that pronounced freshwater input by melting sea ice into the glacial aaiw significantly hampered the downward expansion of southwest pacific aaiw consistent with climate model results for the last glacial maximum this process led to a pronounced upward displacement of the aaiw ucdw interface during colder climate conditions and therefore to an expansion of the glacial carbon pool

equatorial subthermocline currents across the pacific recent sections crossing the equator at nine longitudes from 146 e to 86 w show zonal currents below 400 m similar to those found in a 16 month mean section on 159 w from the pacific equatorial ocean dynamics pequod program in 1982 1983 most of the new measurements were made with a lowered acoustic doppler current profiler eastward current extrema north and south intermediate countercurrents are found in all sections about 2 from the equator in the depth range 500 1500 m with the possible exceptions of 146 e where topography complicates the picture south of the equator and 150 e where the sections extend only from 1 s to 2 n poleward of the intermediate countercurrents westward flow is found near 3 from the equator in most of the sections on the equator from 250 500 m depth a westward equatorial intermediate current is found in many but not all of the sections similarly it is present in the pequod mean but not in all synoptic sections below the intermediate currents and countercurrents an eastward current near 3000 m was found at and south of the equator in the pequod mean and in the new sections from 150 e to 110 w near 4000 m there is westward flow south of the equator in the pequod mean and near the equator in the new sections from 179 e to 135 w geostrophic currents calculated from an 8 year mean hydrographic section at 165 e also resemble the pequod mean although not conclusive the evidence presented here indicates that these currents are basin scale components of the general circulation perhaps involving vigorous horizontal recirculation in a set of basin wide elongated gyres within a few degrees of the equator

northward intrusion of antarctic intermediate water in the western pacific abstract the northward intrusion of antarctic intermediate water aaiw is examined using historical data combined with synoptic observations from a repeated hydrographic section in the western pacific ocean the results of this analysis suggest that aaiw is traced as a salinity minimum to only about 15 n via the new guinea coastal undercurrent and the mindanao undercurrent there is no northward extension of aaiw farther to the north along the western boundary although relatively high oxygen water does exist in the okinawa trough it is connected with high oxygen water in the south china sea scs through the luzon strait but not from the south as an extension of aaiw local circulation seems to play an essential role in localizing the oxygen maximum in the scs evidence exists to suggest that high oxygen water enters the scs as part of the pacific deep water around the still depth 2000 m of the luzon strait from there part of it upwells and is entrained into shallower isopycnal surfaces by vertica

consistent relationship between global climate and surface nitrate utilization in the western subarctic pacific throughout the last 500 ka 1 the open subarctic pacific is at present a high nitrate low chlorophyll hnlc region where nitrate is perennially abundant at the surface theoretically the hnlc status of this region is subject to modification by ocean circulation and or micronutrient supply with implications for the effectiveness of the biological pump and hence carbon sequestration in the ocean interior records of biogenic detritus in sediments from throughout the subarctic pacific indicate that export production was generally lower during glacial maxima while nitrogen isotope measurements from the bering sea have shown that nitrate consumption there was more complete during the last glacial period than it is today here nitrogen isotopic analyses of bulk sediments 15nbulk from three deep water sites in the open subarctic pacific are evaluated in terms of regional nitrate isotopic composition and local relative nitrate utilization the eastern subarctic pacific 15nbulk record bears great similarity to 15nbulk records from the western margin of north america over the last glacial cycle suggesting that variability in the isotopic composition of subeuphotic zone nitrate the growth substrate is reasonably coherent throughout the northeast pacific and dominates at these sites however the two western subarctic pacific records which lie at the heart of the hnlc region display a different pattern implying that significant changes in local relative nitrate utilization overlie the regional background variability after a novel correction intended to remove the background signal associated with denitrification in the eastern tropical north pacific these nitrate utilization records are correlated with a benthic oxygen isotope stack reflecting global deep ocean temperature and ice volume r2 0 65 the correlation implies a strong link between global climate and subarctic pacific nitrate utilization with nearly complete nitrate consumption during glacial periods when export production was low

the cause of carbon isotope minimum events on glacial terminations the occurrence of carbon isotope minima at the beginning of glacial terminations is a common feature of planktic foraminifera carbon isotopic records from the indo pacific sub antarctic and south atlantic we use the 13 c record of a thermocline dwelling foraminifera neogloboquadrina dutertrei and surface temperature estimates from the eastern equatorial pacific to demonstrate that the onset of 13 c minimum events and the initiation of southern ocean warming occurred simultaneously timing agreement between the marine record and the 13 c minimum in an antarctic atmospheric record suggests that the deglacial events were a response to the breakdown of surface water stratification renewed circumpolar deep water upwelling and advection of low 13 c waters to the convergence zone at the sub antarctic front on the basis of age agreement between the absolute 13 c minimum in surface records and the shift from low to high 13 c in the deep south atlantic we suggest that the 13 c rise that marks the end of the carbon isotope minima was due to the resumption of north atlantic deep water influence in the southern ocean

variability in tropical thermocline nutrient chemistry on the glacial interglacial timescale abstract the organic carbon to calcite rain ratio in the tropical ocean may play a role in regulating global climate through its influence on co 2 draw down in the upper ocean the rain ratio may be altered by changes in the nutrient chemistry of the thermocline such changes in the tropical pacific are revealed by the carbon isotope values of thermocline dwelling planktonic foraminifera neogloboquadrina dutertrei the tropical pacific record over the last 30 kyr in the region south or along the equator which is fed by upwelling of deeper equatorial undercurrent water euc shows a carbon isotope signal distinct from any other in global mixed layer or benthic environments this unique record is consistent across the pacific unlike carbon isotope data from other basins and oceanic habitats the tropical pacific thermocline tracer shows last glacial values more positive than those of post glacial times the isotopic shift occurs in the early deglacial 20 17 kyr and leads to a deglacial carbon isotope minimum whose timing differs from that seen elsewhere the deglacial record of the pacific seems best interpreted as the progressive development of the modern nutrient rich thermocline under high nutrient low chlorophyll hnlc conditions the eastern tropical atlantic also has a unique glacial to modern carbon isotope record that is essentially opposite to that seen in the pacific strongly negative values in glacial times differ from those of the standard stratified ocean indicating higher nutrient concentrations a large shift to more positive values occurs rapidly at about 13 14 kyr this indicates a marked reduction in thermocline nutrients the implication is that nutrient flow to the tropics from the deep ocean via sub antarctic sources was stronger for the atlantic during the glacial but was weaker in the pacific transformation to modern conditions occurred in two steps at 17 18 and 13 14 kyr a timing that matches shifts in atmospheric co 2 concentrations and which would be compatible with driving those concentrations higher over deglacial time the mechanism could be an inherent difference in production regimes between the tropical pacific and atlantic

glacial interglacial changes in subarctic north pacific stratification since the first evidence of low algal productivity during ice ages in the antarctic zone of the southern ocean was discovered there has been debate as to whether it was associated with increased polar ocean stratification or with sea ice cover shortening the productive season the sediment concentration of biogenic barium at ocean drilling program site 882 indicates low algal productivity during ice ages in the subarctic north pacific as well site 882 is located southeast of the summer sea ice extent even during glacial maxima ruling out sea ice driven light limitation and supporting stratification as the explanation with implications for the glacial cycles of atmospheric carbon dioxide concentration

increased glacial age ventilation of the chilean margin by antarctic intermediate water antarctic intermediate water is an oxygen rich water mass that spreads throughout the southern hemisphere oceans marine sediment chemistry indicates that the water mass was produced at higher rates and had higher oxygen concentrations during the last glacial maximum antarctic intermediate water is at present a water mass that brings oxygen to intermediate depths throughout the southern hemisphere oceans models have suggested that intermediate waters had higher concentrations of oxygen during the last glacial period1 2 consistent with globally reduced denitrification3 and increased production of antarctic intermediate water4 however some palaeoceanographic reconstructions5 6 have indicated that production decreased in the southeast pacific ocean at this time here we analyse the concentrations of re and mn the sedimentary concentrations of which are controlled by the amount of dissolved oxygen at the sea floor from three sediment cores located along the chilean margin for the past 30 000 years our results from the cores which bracket the present day water column extent of antarctic intermediate water show that the depth range of well oxygenated antarctic intermediate water increased off chile during the last glacial maximum dissolved oxygen content began to decrease approximately 17 000 years ago coincident with rapid antarctic warming and a poleward shift of the southern westerly winds7 our estimates of productivity from accumulation rates of organic carbon and opal do not co vary with the seafloor oxygen variations ruling out local control of seafloor oxygenation we conclude that the data are best explained by a combination of increased oxygenation and increased flux of antarctic intermediate water during the last glacial maximum

intermediate water ventilation on the northeastern pacific margin during the late pleistocene inferred from benthic foraminiferal δ13c late pleistocene intermediate water ventilation history in the northeastern pacific has been inferred from benthic foraminiferal carbon isotopic data from seven california margin basins secular variations in oceanic 13c recorded at north pacific odp site 849 were subtracted from each basin record leaving a residual 13c history that reflects variations in ventilation during the previous interglacial intermediate waters above 2000m contained less oxygen than they do today or pacific deep water at site 849 was better ventilated intermediate water ventilation began to improve during oxygen isotope stage 4 and continued to improve throughout stages 3 and 2 this enhanced ventilation was not contemporaneous at all depths and appears to have progressed upwards through the water column the diachronous nature of these changes suggest that there was not simply an on off mechanism which resulted in higher or lower ventilation in the north pacific during the last glacial cycle

millennial scale deep water oscillations reflections of the north atlantic in the deep pacific from 10 to 60 ka northeast pacific benthic foraminiferal 18o and 13 reveal repeated millennial scale events of strong deep sea ventilation associated with nutrient depletion and or high gas exchange during stadial cool high ice volume episodes from 10 to 60 ka opposite the pattern in the deep north atlantic two climate mechanisms may explain this pattern north pacific surface waters chilled by atmospheric transmission from a cold north atlantic and made saltier by reduced freshwater vapor transports could have ventilated the deep pacific from above alternatively faster turnover of pacific bottom and mid depth waters driven by southern ocean winds may have compensated for suppressed north atlantic deep water production during stadial intervals during the younger dryas event 11 6 13 0 cal ka ventilation of the deep ne pacific 2700 m lagged that in the santa barbara basin 450 m by 500 years suggesting that the ne pacific was first ventilated at intermediate depth from above and then at greater depth from below this apparent lag may reflect the adjustment time of global thermohaline circulation

water mass conversion in the glacial subarctic pacific 54 n 148 w physical constraints and the benthic planktonic stable isotope record benthic uvigerina spp cibicidoides spp gyroidinoides spp and planktonic n pachyderma sinistral g bulloides stable isotope records from three core sites in the central gulf of alaska are used to infer mixed layer and deepwater properties of the late glacial subarctic pacific glacial interglacial amplitudes of the planktonic 18o records are 1 1 1 3 less than half the amplitude observed at core sites at similar latitudes in the north atlantic these data imply that a strong negative w anomaly existed in the glacial subarctic mixed layer during the summer which points to a much stronger low salinity anomaly than exists today if true the upper water column in the north pacific would have been statically more stable than today thus suppressing convection even more efficiently this scenario is further supported by vertical i e planktic versus benthic 18o and 13c gradients of 1 which suggest that a thermohaline link between pacific deep waters and the subarctic pacific mixed layer did not exist during the late glacial epibenthic 13c in the subarctic pacific is more negative than at tropical subtropical pacific sites but similar to that recorded at southern ocean sites suggesting ventilation of the deep central pacific from mid latitude sources e g from the sea of japan and sea of okhotsk still convection to intermediate depths could have occurred in the subarctic during the winter months when heat loss to the atmosphere sea ice formation and wind driven upwelling of saline deep waters would have been most intense this would be beyond the grasp of our planktonic records which only document mixed layer temperature salinity fields extant during the warmer seasons also we do not have benthic isotope records from true intermediate water depths of the subarctic pacific

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

glacial marine nutrient and carbon redistribution evidence from the tropical ocean the nature and timing of marine nutrient and carbon redistribution through a glacial cycle remains unclear understanding transfers to and from the surface and deep ocean reservoirs is important to explaining pleistocene variation in atmospheric co2 content observations in the modern ocean show that the nutrient supply to the tropical upwelling regions depends on content of deep reservoirs and vertical mixing in the southern and subantarctic oceans previous work in the pacific demonstrated that nutrient supply to the tropics was reduced during the glacial consonant with reduced vertical mixing in the southern ocean we examine the glacial record of the tropical atlantic with the same methods used in the pacific n dutertrei carbon isotope data combined with export production estimates to evaluate changes in thermocline nutrient content in contrast to the pacific we find evidence for an increase in tropical atlantic nutrient supply under glacial conditions the source of nutrients can be traced to subantarctic surface waters and ultimately to an enriched abyssal reservoir bathymetrically forced vertical mixing could account for the transfer of nutrients from this reservoir in the s atlantic the enriched reservoir developed in early mis 4 75 ka and persisted until about 14 5 ka bolling allerod this timing corresponds to shifts in atmospheric co2 content from intermediate to minimum full glacial levels at 75 ka and from intermediate to holocene concentrations near 14 5 ka

nitrogen isotopic evidence for deglacial changes in nutrient supply in the eastern equatorial pacific 1 the eastern equatorial pacific eep is a high nutrient low chlorophyll region of the ocean downcore nitrogen isotope records from the eep have been previously interpreted as a direct reflection of changes in nutrient consumption however the observed changes in sedimentary 15n since the last glacial maximum have no coherent relationship with export productivity or an inferred variation in the iron to nitrate ratio of the surface waters rather downcore n isotope records in the eep strongly resemble changes in the extent of water column denitrification as recorded in nearby sedimentary 15n records along the western margin of the americas this similarity is attributed to the overprinting of the n isotopic composition of nitrate in the eep through the advection of nitrate westward from the margins in the subsurface a local nitrogen isotope record of changes in the degree of nutrient consumption is extracted from the bulk sedimentary record by subtracting two different sedimentary 15n records of denitrification changes from two new eep 15n records tr163 22 and odp site 1240 the denitrification records used are from 1 the central american margin odp site 1242 and 2 the south american margin geob7139 2 the degree of consumption in the surface waters declines rapidly from elevated values during the last glacial maximum to a pair of minima around 15 and 11 13 ka and finally it increases into the holocene the derived eep nitrogen isotope record indicates that the regional peak in export productivity occurred when the supply of nutrients exceeded the apparently high demand the influx of nutrients during the deglaciation is attributed to the resumption of intense overturning in the southern ocean and the release of sequestered co2 and nutrient rich o2 poor waters from the deep ocean this has important implications for understanding the glacial interglacial scale variation in intermediate water suboxia and water column denitrification

southern ocean influence on the eastern tropical north pacific s intermediate depth circulation during the last glacial maximum the oxygen and carbon isotopic compositions of benthic foraminiferal tests were measured on sedimentary sequences retrieved on the magdalena margin off southern baja california mexico we reconstruct the hydrographic changes along the water column that occurred in the northeastern tropical pacific since the last glacial maximum lgm and compare those changes to the ones that occurred in the northwest pacific nwp i e off japan and russia in the northeast pacific along the californian margin as well as in the southeast pacific off chile the foraminiferal 18 o depth profiles across the north and southeast pacific show similar trends between the lgm and the holocene indicating that changes in the oceanographic conditions between 400 and 2000 m depth were very similar changes in the isotopic composition of dissolved inorganic carbon 13 c dic in the baja california margin since the last glacial maximum were reconstructed using the 13 c of shallow endobenthic foraminifers u peregrina and the epibenthic cibicides mckannai the most striking result is a marked shift toward more positive 13 c values below 1200 m depth in the northeast pacific nep during the holocene relative to the lgm this observation suggests that a nutrient rich water mass ventilated the nep during the lgm at a basin scale the 13 c values of nep waters at intermediate depths were more negative relative to the nwp and southeast pacific during the lgm suggesting that the nutrient rich water column along the nep i e baja california margin was confined in that area as observed today

strong thermodynamic imprint on recent bottom water and epibenthic δ13c in the weddell sea revealed implications for glacial southern ocean ventilation abstract paleonutrient proxies are widely used to reconstruct the geometry of deep water masses during the last glacial maximum lgm epibenthic 13 c provides best spatial coverage and artifacts are well investigated discrepancies between reconstructed lgm circulation patterns derived from models or different benthic nutrient proxies can partly be resolved by varying air sea signatures of 13 c i e 13 c as however there are very few data available to calculate a 13 c as of modern bottom water dissolved inorganic carbon dic 13 c and to document how this signal is recorded in benthic foraminiferal 13 c here i show that today bottom water in the atlantic sector of the southern ocean is 13 c enriched with 13 c dic values between 0 4 and 1 0 and 13 c as values 0 4 and that this signal is recorded in live and dead epibenthic 13 c this is in contrast to a uniform modern antarctic circumpolar 13 c dic of rather 0 4 which hitherto is used as modern framework to compare to low lgm 13 c dic of southern sourced bottom water and glacial inter basin differences i conclude that a potential reduction of the strong recent thermodynamic imprint during bottom water generation in glacial times could explain depleted circum antarctic 13 c dic without associated co 2 enrichment and anoxia in antarctic bottom waters the present synoptic compilation of 13 c dic and live benthic foraminifera 13 c is in support of hypotheses that explain low lgm 13 c by a depletion of southern end member 13 c dic due to extensive sea ice formation with low 13 c as brine rejection and diminished air sea gas exchange

silicic acid leakage from the southern ocean a possible explanation for glacial atmospheric pco2 1 using a simple box model we investigate the effects of a reduced si n uptake ratio by antarctic phytoplankton on the marine silica cycle and atmospheric pco2 recent incubation experiments demonstrate such a phenomenon in diatoms when iron is added hutchins and bruland 1998 takeda 1998 franck et al 2000 the southern ocean may have supported diatoms with reduced si n uptake ratios compared to today during the dustier glacial times petit et al 1999 a similar reduction in the uptake ratio may be realized with an increased production of nondiatom phytoplankton such as phaeocystis our model shows that reduced si n export ratios in the southern ocean create excess silicic acid which may then be leaked out to lower latitudes any significant consumption of the excess silicic acid by diatoms that leads to an enhancement in their growth at the expense of coccolithophorids diminishes caco3 production and therefore diminishes the carbonate pump in our box model the combination of a reduced carbonate pump and an open system carbonate compensation draw down steady state atmospheric co2 from the interglacial 277 to 230 242 ppm depending on where the excess silicic acid is consumed by comparison the atmospheric pco2 sensitivity of general circulation models to carbonate pump forcing is 3 5 fold greater which combined with carbonate compensation can account for peak glacial atmospheric pco2 we discuss the importance of the initial rain ratio of caco3 to organic carbon on atmospheric pco2 and relevant sedimentary records that support and constrain this silicic acid leakage scenario

carbon isotope composition of tropical surface water during the past 22 000 years carbon isotope values of many species of planktonic foraminifera are size dependant values of 13c of individual size fractions are therefore an integration of low 13c values of calcite precipitated in the juvenile growth stage and high values precipitated in later stages in general the selection of a particular size fraction for downcore studies has been subjective analysis of different size fractions of planktonic foraminifera however yields different time series in downcore studies by measuring the 13c of many size fractions the 13c precipitated throughout the growth of the foraminifera can be calculated time series of the 13c of calcite precipitated in the late growth stages of planktonic foraminifera from two nearby cores from the caribbean sea result in a better correlation than time series of constant size fractions these 13c records indicate similar 13c values during the last glaciation and the late holocene and a broad deglacial minimum approximately synchronous with a minimum in the 13c records of benthic foraminifera from intermediate depth atlantic cores the deglacial minimum may be a reflection of the isotopic composition of the underlying intermediate water which may be affected by circulation changes or changes in preformed 13c values and or of the flux of water upwelled into the surface layer the small 0 2 to 0 0 glacial interglacial 13c difference in tropical surface water is also believed to be affected by the chemistry of the underlying source water

changes in eastern pacific ocean ventilation at intermediate depth over the last 150 kyr bp the circulation patterns of the deep glacial pacific ocean are still debated difficulties arise due to the scarcity of reliable paleoceanographic records that can document the past movements and properties of pacific ocean water masses here we jointly use delta 13 c and delta 18 o measured on the epibenthic foraminifer cibicidoides wuellerstorfi from the md02 2529 sediment core collected at 1619 m water depth in the eastern equatorial pacific to monitor changes in water mass circulation spanning the past 150 kyr bp after the extraction of short term centennial to millennial scale delta 13 c and delta 18 o changes which were similar to 1 0 and 0 5 parts per thousand respectively we observed that these rapid delta 13 c and 8180 shifts were closely interrelated during the last 150 kyr bp a comparison of md02 2529 with other benthic delta 13 c records localized to the north and south of the core location revealed that md02 2529 was alternately bathed by a northern nutrient rich and a southern nutrient poor water mass the comparison provided a diagnostic for the latitudinal movements of a sharp water mass front that was particularly evident during marine isotope stages 4 and 3 on the millennial timescale by considering that delta 13 c is an indicator of the northern vs southern origin of the water that bathed the md02 2529 coring site in the past we found that a north pacific water mass that occasionally spreads to the eastern pacific ocean as deep as 1600 m and as far south as 8 degrees n was responsible for shifts toward the positive delta 18 o we observed in the past we then used the delta 13 c delta 18 o relationship to reconstruct latitudinal temperature and or salinity gradients of the water mass that were linked to changes in the northern and or the southern water mass end members evolution of the delta 13 c delta 18 o relationship spanning the past 150 kyr bp has shed light on how hydrological processes occurring at northern and southern high latitudes are transmitted to the ocean s interior through water mass advection c 2010 elsevier b v all rights reserved

intermediate zonal jets in the tropical pacific ocean observed by argo floats abstractargo float data in the tropical pacific ocean during january 2003 august 2011 are analyzed to obtain lagrangian subsurface velocities at their parking depths maps of mean zonal velocities at 1000 and 1500 m are presented at both depths a series of alternating westward and eastward zonal jets with a meridional scale of 1 5 is seen at the basin scale from 10 s to 10 n these alternating jets with mean speeds about 5 cm s 1 are clearly present in the western and central parts of the basin but weaken and disappear approaching the eastern coast they are stronger in the southern hemisphere along the equator at both 1000 and 1500 m a westward jet is seen the jets closer to the equator are remarkably zonally coherent across the basin but the jets farther poleward appear broken in several segments in the western half of the basin the 1000 m zonal jets appear to slant slightly poleward from east to west at the western boundary in the south east of solomon islands and papua new guinea the al

rapid shifts in subarctic pacific climate between 138 and 70 ka during the past decades remarkable changes in sea surface temperature sst and sea ice extent have been observed in the marginal seas of the subarctic pacific however little is known about natural climate variability at millennial time scales far beyond instrumental observations geological proxy records such as those derived from marine sediments offer a unique opportunity to investigate millennial scale natural climate variability of the artic and subarctic environments during past glacial interglacial cycles here we provide reconstructions of sea ice variability inferred from ip25 ice proxy with 25 carbon atoms sea ice biomarker and sst fluctuations based on alkenone unsaturation index graphic of the subarctic pacific realm between 138 and 70 ka warmest sea surface conditions were found during the early eemian interglacial 128 to 126 ka exceeding modern ssts by 2 c the further north pacific climate evolution is marked by pronounced oscillations in sst and sea ice extent on millennial time scales which correspond remarkably well to short term temperature oscillations known from greenland and the north atlantic these results imply a common forcing which seems to be closely coupled to dynamics of the atlantic meridional overturning circulation however immediate propagation of such climate fluctuations far beyond the north atlantic basin suggests a rapid circumpolar coupling mechanism probably acting through the atmosphere a prerequisite to explain the apparent synchronicity of remote climatic reorganizations in the subarctic pacific

using silicon isotopes to understand the role of the southern ocean in modern and ancient biogeochemistry and climate abstract the growth of siliceous phytoplankton mainly diatoms in the southern ocean influences the preformed nutrient inventory in the ocean on a global scale silicic acid use by diatoms and deep circulation combine to trap dissolved si in the southern ocean resulting in high levels of silica production and expansive diatom oozes in southern ocean sediments the analysis of the silicon isotope composition of biogenic silica or opal and dissolved silicic acid provide insight into the operation of the global marine silicon cycle and the role played by the southern ocean in nutrient supply and carbon drawdown both in the modern and in the past silicon isotope studies of diatoms have provided insight into the history of silica production in surface waters while the analysis of spicules from deep sea sponges has defined both the spatial and the temporal variability of silicic acid concentrations in the water column together these and other proxies reveal variations in the northward flow of southern ocean intermediate and mode waters and how changes in southern ocean productivity altered their preformed nutrient content we present a new hypothesis the silicic acid ventilation hypothesis savh to explain the geographical variation of opal based proxy records in particular the contrasting patterns of opal burial change found in the low and high latitudes by understanding the silicon isotope systematics of opal and silicic acid in the modern we will be able to use opal based proxies to reconstruct past changes in the southern ocean and so investigate its role in global carbon cycling and climate

deglacial whole ocean δ13c change estimated from 480 benthic foraminiferal records terrestrial carbon storage is dramatically decreased during glacial periods due to cold temperatures increased aridity and the presence of large ice sheets on land most of the carbon released by the terrestrial biosphere is stored in the ocean where the light isotopic signature of terrestrial carbon is observed as a 0 32 0 7 depletion in benthic foraminiferal 13c the wide range in estimated 13c change results from the use of different subsets of benthic 13c data and different methods of weighting the mean 13c by volume we present a more precise estimate of glacial interglacial 13c change of marine dissolved inorganic carbon using benthic cibicidoides spp 13c records from 480 core sites more than 3 times as many sites as previous studies we divide the ocean into eight regions to generate linear regressions of regional 13c versus depth for the late holocene 0 6 ka and last glacial maximum 19 23 ka and estimate a mean 13c decrease of 0 38 0 08 2 for 0 5 5 km estimating large uncertainty ranges for 13c change in the top 0 5 km below 5 km and in the southern ocean we calculate a whole ocean change of 0 34 0 19 this implies a terrestrial carbon change that is consistent with recent vegetation model estimates of 330 694 gt c additionally we find that a well constrained surface ocean 13c change is essential for narrowing the uncertainty range of estimated whole ocean 13c change

glacial age hydrography of the far northwest pacific ocean stable isotope data on benthic foraminifera from more than 30 cores on the northern emperor seamounts and in the okhotsk sea are synthesized in paleohydrographic profiles spanning the depth range 1000 4000 m holocene core top benthic foraminiferal 18o and 13c data are calibrated to modern hydrographic properties through measurements of 13c of co2 and 18o of seawater cibicidoides stable isotope ratios are close to the 13c and equilibrium 18o of seawater whereas uvigerina 18o and 13c are variably offset from cibicidoides glacial maximum 13c of cibicidoides displays a different vertical profile than that of the holocene when results are adjusted by 0 32 to account for the secular change in 13c during the last glacial maximum the data coincide with the modern seawater and foraminiferal curves deeper than 2 km however at shallower depths 13c gradually increases by as much as 1 above the modern value furthermore above 2 km the benthic 18o decreases by 0 5 these results are consistent with a benthic front at 2 km in the north pacific see herguera et al 1992 but they differ from interpretations based on trace metal data which indicate a source of nutrient depleted deep water during glaciation the isotopic data suggest that during glaciation there was a better ventilated watermass at intermediate depths in the far northwestern pacific it was relatively fresher than deep waters there and deep waters were as nutrient rich as today

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

el nino southern oscillation like variability during glacial terminations and interlatitudinal teleconnections interannual decadal variability in the equatorial pacific el nino southern oscillation enso induces climate changes at global scale but its potential influence during past global climate change is not yet well constrained new high resolution eastern equatorial pacific proxy records of thermocline conditions present new evidence of strong orbital control in enso like variability over the last 275 000 years recurrent intervals of saltier thermocline waters are associated with the dominance of la nina like conditions during glacial terminations coinciding with periods of low precession and high obliquity the parallel dominance of 13c depleted waters supports the advection of antarctic origin waters toward the tropical thermocline this oceanic tunneling is proposed to have reinforced orbitally induced changes in enso like variability composing a complex high and low latitude feedback during glacial terminations

alternating influence of northern versus southern sourced water masses on the equatorial pacific subthermocline during the past 240 ka the eastern equatorial pacific eep is a key area to understand past oceanic processes that control atmospheric co2 concentrations many studies argue for higher nutrient concentrations by enhanced nutrient transfer via southern ocean intermediate water soiw to the low latitude pacific during glacials recent studies however argue against soiw as the primary nutrient source at least during early marine isotope stage 2 mis 2 as proxy data indicate that nutrients are better utilized in the southern ocean under glacial conditions new results from the subarctic pacific suggest that enhanced convection of nutrient rich glacial north pacific intermediate water gnpiw contributes to changes in nutrient concentrations in equatorial subthermocline water masses during mis 2 however the interplay between soiw versus gnpiw and its influence on the nutrient distribution in the eep spanning more than one glacial cycle are still not understood we present a carbon isotope 13c record of subthermocline waters derived from deep dwelling planktonic foraminifera globorotaloides hexagonus in the eep which is compared with published 13c records around the pacific results indicate enhanced influence of gnpiw during mis 6 and mis 2 compared to today with largest contributions of northern sourced intermediate waters during glacial maxima these observations suggest a mechanistic link between relative contributions of northern and southern intermediate waters and past eep nutrient concentrations a switch from increased gnpiw decreased soiw to diminished gnpiw enhanced soiw influence on equatorial subthermocline waters is recognized during glacial terminations and marks changes to modern like conditions in nutrient concentrations and biological productivity in the eep

disparities in glacial advection of southern ocean intermediate water to the south pacific gyre highlights surface mg ca temperatures and salinities show comparable glacial conditions subsurface mg ca temperatures suggest that lgm is 3 to 2 c colder than mis 6 relative to holocene subsurface salinities suggest fresher lgm and saltier mis 6 thermal gradients suggest stratified lgm and well mixed mis 6 water column contrasting glacial scenarios suggest variable formation and advection of soiws abstract the intermediate waters formed in the southern ocean are critical for ventilating the thermocline in the southern hemisphere gyres and transporting climatic signals from high to low latitudes on glacial interglacial time scales despite the importance of the southern ocean intermediate waters soiws information on past changes in soiws formation is fragmentary and its impact on the south pacific gyre spg s thermocline largely unknown here we present a 200 kyr record of paired mg ca ratios and stable oxygen isotope from surface and deep dwelling planktonic foraminifera from the spg on average the globigerina bulloides mg ca derived sea surface temperatures show similar conditions during the lgm and marine isotope stage mis 6 9 4 c versus 9 8 c in contrast the subsurface temperatures derived from the mg ca values of globorotalia inflata and globorotalia truncatulinoides suggest that lgm is 3 to 2 c colder than mis 6 furthermore at subsurface depths the reconstructed 18osw ivc record proxy for relative local salinity changes suggests opposite glacial conditions with slightly saltier than holocene waters during mis 6 and fresher than holocene waters during lgm contrasting glacial scenarios plausibly due to changes in the presence of soiws at the study site suggest variable formation and or advection of soiws to the spg during different glacial stages the variability in soiws is probably driven by the changes in the intensity of the southern westerly winds

paleoproductivity in the southern peru chile current through the last 33 000 yr abstract based on a multiparameter approach including organic carbon biogenic opal carbonate and the species composition of planktic foraminifera this paper provides the first qualitative assessment of the history of paleoproductivity on glacial interglacial time scales in the southern peru chile current pcc off chile which belongs to the least studied parts of the world ocean during the last glacial maximum lgm highest relative paleoproductivity of the last 33 kyr indicated by high accumulation rates of organic carbon biogenic opal and carbonate has been found contrasted by lowest values during the early and middle holocene this shift from high to low productivity is accompanied by a major change in the species composition of planktic foraminifera from a dominance of neogloboquadrina pachyderma sin to the dominance of n pachyderma dex the temporal pattern of paleoproductivity off chile is very similar to the history of the continental paleoclimate in the region which is supposed to be driven by the position of the southern westerlies this observation points to a functional relationship between the position of the southern westerlies and the history of paleoproductivity off chile assuming that atmospheric and oceanographic circulation are closely linked a northward displacement of the antarctic circumpolar current during the lgm in line with the northward movement of the southern westerlies would bring the main nutrient source closer to our core sites resulting in increased productivity however based on the available data it is not clear if the higher productivity in the southern pcc during the lgm reflects generally higher productivity during this time or only a regional displacement of the main productivity centers

a switch from si oh 4 to no 3 depletion in the glacial southern ocean 1 phytoplankton in the antarctic deplete silicic acid si oh 4 to a far greater extent than they do nitrate no3 this pattern can be reversed by the addition of iron which dramatically lowers diatom si oh 4 no3 uptake ratios higher iron supply during glacial times would thus drive the antarctic towards no3 depletion with excess si oh 4 remaining in surface waters new 30si and 15n records from antarctic sediments confirm diminished si oh 4 use and enhanced no3 depletion during the last three glaciations the present low si oh 4 water is transported northward to at least the subtropics we postulate that the glacial high si oh 4 water similarly may have been transported to the subtropics and beyond this input of si oh 4 may have caused diatoms to displace coccolithophores at low latitudes weakening the carbonate pump and increasing the depth of organic matter remineralization these effects may have lowered glacial atmospheric pco2 by as much as 60 ppm

paleonutrient and productivity records from the subarctic north pacific for pleistocene glacial terminations i to v our study addresses fundamental questions of the mode and timing of orbital and millennial scale changes in the meridional overturning circulation moc of the subarctic north pacific particular concerns are the vertical mixing the present and past abundance of nutrients in surface waters despite strong stratification and the north pacific north atlantic seesaw of oscillations in sea surface temperature sst we do this by generating and interpreting multiple records for glacial terminations i v down two long piston cores one each from the western and eastern subarctic pacific chlorins and biogenic opal are proxies for surface water productivity delta 13 c of epibenthic foraminifera is a record of deepwater ventilation and the delta 13 c of n pachyderma sin is a tracer of nutrients in subsurface waters that extend up to the sea surface during times of vertical mixing the degree of mixing is traced by pairing sst and delta 18 o records of planktic surface and subsurface pycnocline dwellers tight age control is deduced from a suite of age calibrated 14 c plateau boundaries for termination i and benthic delta 18 o and geomagnetic events for the last 800 ka carbon 14 paleoreservoir ages record the ages of surface and deep waters to uncover short term changes in moc over termination i we have defined a standard sequence of short term productivity events for termination i also evident during terminations ii to v and subsequent interglacials over the last 450 ka the peak glacial regime of stable stratification and low productivity terminated together with the end of ice rafting and melting near 17 ka similar to 2000 years after the onset of termination i pulses of vertical mixing and incursion of warm surface waters from the subtropics followed convected young water masses finally penetrated down to 3600 m water depth at 17 0 to less than 14 5 ka significantly improving bottom water ventilation through the late deglacial and earliest interglacial mixing with upwelled nutrients from the pycnocline induced short term maxima in algal production of chlorins and biogenic opal near 17 15 and 15 12 ka respectively deglacial meltwater incursions in the aleutian current and silica input from north american rivers also promoted east pacific productivity after 15 5 ka productivity decreased during the late deglacial and early interglacial coeval with an exceptional peak in caco 3 preservation caused by both low organic flux and well ventilated deepwater subsequently low salinity and cool surface waters and in turn stratification were gradually restored a second opal dominated productivity maximum marked the ends of interglacials the deglacial pulses of vertical mixing around 17 11 ka imply an important contribution of the north pacific to the coeval release of oceanic co 2 into the atmosphere and support the east west seesaw model of climate change

the changing roles of iron and vertical mixing in regulating nitrogen and silicon cycling in the southern ocean over the last glacial cycle the southern ocean plays a critical role in the air sea co2 balance through biological and physical mechanisms vertical supply of deep waters returns nutrients and co2 to the surface and stimulates phytoplankton growth photosynthesis in the southern ocean is limited by iron and only a fraction of the carbon and nutrients that return to the surface are consumed for potential sequestration in the deep sea here we present the most spatially extensive data set of silicon and nitrogen isotope measurements from diatom frustules to date to examine the controls on nutrient drawdown during the last glacial period and across the glacial termination in both the antarctic and subantarctic zones the new data confirm existing views that differing silicon and nitrate consumption patterns in the antarctic zone are likely the result at least in part of iron addition during the last glacial maximum lgm however earlier in the glacial a more coordinated response in the two proxy records with both reflecting enhanced consumption during episodes of increased iron accumulation and export production implies a different system response than observed for the lgm a collapse of the expected equatorward gradient in silicon isotope values and contraction of the nitrogen isotope gradient during the deglaciation suggests that nutrient supply increased not only in the antarctic zone but also in the subantarctic perhaps due to enhanced deep mixing locally enhanced deep water ventilation across the southern ocean likely increased the nutrient content of mode waters during the deglaciation

patterns of export production in the eastern equatorial pacific over the past 130 000 years 1 productivity at six core locations in the eastern equatorial pacific eep was reconstructed with a benthic foraminiferal transfer function the core records show strong regionality especially where affected by peru margin upwelling of deeper equatorial undercurrent water euc originally coming from the subantarctic this peru margin record differs from that seen along the equator where divergence leads to shallow upwelling and it is generally inverse to that seen in cores outside the areas of equatorial upwelling principal components analysis shows that the main productivity pattern correlates well to the global oxygen isotope record and has lowest values during isotope stages 2 and 4 in addition to this equatorial cores show a higher frequency pattern of variation which becomes much more pronounced during mis 3 and 2 the reconstructions based on benthic foraminifera were tested against those from nonaccumulation rate based inorganic chemical proxies of export production these were found to correlate well in the region influenced by peru upwelling and also to share common features for sites along the equator all the nonaccumulation rate based paleotracers are consistent with one another and differ from accumulation rate derived proxies the differences between the two classes of paleotracers may result from uncertainties in calculating actual biogenic fluxes since 230th normalized results conform more to those we obtained analysis of planktonic carbon isotope values for the eep and their comparison to the record of the pacific subantarctic indicates that the subantarctic contribution to the euc was reduced during mis 3 and 2

thorium 230 normalized particle flux and sediment focusing in the panama basin region during the last 30 000 years 1 application of the 230 th normalization method to estimate sediment burial fluxes in six cores from the eastern equatorial pacific eep reveals that bulk sediment and organic carbon fluxes display a coherent regional pattern during the holocene that is consistent with modern oceanographic conditions in contrast with estimates of bulk mass accumulation rates mars derived from core chronologies two nearby sites less than 10 km apart which have different mars show nearly identical 230 th normalized bulk fluxes focusing factors derived from the 230 th data at the foot of the carnegie ridge in the panama basin are 2 in the holocene implying that lateral sediment addition is significant in this part of the basin new geochemical data and existing literature provide evidence for a hydrothermal source of sediment in the southern part of the panama basin and for downslope transport from the top of the carnegie ridge the compilation of core records suggests that sediment focusing is spatially and temporally variable in the eep during oxygen isotope stage 2 ois 2 from 13 27 ka bp focusing appears even higher compared to the holocene at most sites similar to earlier findings in the eastern and central equatorial pacific the magnitude of the glacial increase in focusing factors however is strongly dependent on the accuracy of age models we offer two possible explanations for the increase in glacial focusing compared to the holocene the first one is that the apparent increase in lateral sediment redistribution is partly or even largely an artifact of insufficient age control in the eep while the second explanation which assumes that the observed increase is real involves enhanced deep sea tidal current flow during periods of low sea level stand

deep dwelling planktonic foraminifera of the northeastern pacific ocean reveal environmental control of oxygen and carbon isotopic disequilibria abstract we assess the utility of four species of living planktonic foraminifera as tracers of thermocline and intermediate water masses in the northern pacific ocean based on their water column distribution and shell isotopic composition assuming oxygen isotopic equilibria with the water column we infer apparent calcification depths this allows an estimate of apparent carbon isotopic disequilibria we then relax the assumption of oxygen isotopic equilibrium to examine habitat effects on kinetic disequilibrium processes in the california current left coiling neogloboquadrina pachyderma and globigerina calida calcify in the upper thermocline globorotalia scitula resides within the shallow salinity minumum potential density 25 1 26 7 while globoquadrina hexagona is associated with the deeper north pacific intermediate water 26 7 26 9 apparent carbon isotopic disequilibria corrected for oxygen isotopic disequilibria range from 1 0 1 9 in these asymbiotic species the carbon isotopic disequilibrium can be modeled as a single exponential function of temperature or a logarithmic function of potential food supply we infer that carbon isotopic disequilibrium increases with metabolic rate related to temperature and or food supply kinetic processes of oxygen and carbon isotopic disequilibria yields reasonable depth habitats if the slope of the oxygen carbon isotopic shift is about 0 35 consistent with culture data our finding of a link between environment metabolism and isotopic disequilibrium observed in oceanic settings suggests the potential to better reconstruct the structure and biological processes of the upper water column from geologic data

intermediate and deep water mass distribution in the pacific during the last glacial maximum inferred from oxygen and carbon stable isotopes intermediate ocean circulation changes during the last glacial maximum lgm in the north pacifi ch ave been linked with northern hemisphere climate through airesea interactions although the extent and the source of the variability of the processes forcing these changes are still not well resolved the ventilated volumes and ages in the upper wind driven layer are related to the wind stress curl and surface buoyancy fluxes at mid to high latitudes in the north pacific in contrast the deeper thermohaline layers are more effectively ventilated by direct atmosphere sea exchange during convective formation of subantarctic mode waters samw and antarctic intermediate waters aaiw in the southern ocean the precursors of pacific intermediate waters piw in the north pacific results reported here show a fundamental change in the carbon isotopic gradient between intermediate and deep waters during the lgm in the eastern north pacific indicating a deepening of nutrient and carbon rich waters these observations suggest changes in the source and nature of intermediate waters of southern ocean origin that feed piw and enhanced ventilation processes in the north pacific further affecting paleoproductivity and export patters in this basin furthermore oxygen isotopic results indicate these changes may have been accomplished in part by changes in circulation affecting the intermediate depths during the lgm 2010 elsevier ltd all rights reserved

carbon isotope evidence for changes in antarctic intermediate water circulation and ocean ventilation in the southwest pacific during the last deglaciation 1 deep sea sediment core fr1 97 gc 12 is located 990 mbsl in the northern tasman sea southwest pacific where antarctic intermediate water aaiw presently impinges the continental slope of the southern great barrier reef analysis of carbon 13c and oxygen 18o isotope ratios on a suite of planktonic and benthic foraminifera reveals rapid changes in surface and intermediate water circulation over the last 30 kyr during the last glacial maximum there was a large 13c offset 1 1 between the surface dwelling planktonic foraminifera and benthic species living within the aaiw in contrast during the last deglaciation termination 1 the 13cplanktonic benthic offset reduced to 0 4 prior to an intermediate offset 0 7 during the holocene we suggest that variations in the dominance and direction of aaiw circulation in the tasman sea and increased oceanic ventilation can account for the rapid change in the water column 13cplanktonic benthic offset during the glacial interglacial transition our results support the hypothesis that intermediate water plays an important role in propagating climatic changes from the polar regions to the tropics in this case climatic variations in the southern hemisphere may have led to the rapid ventilation of deep water and aaiw during termination 1 which contributed to the postglacial rise in atmospheric co2

crustal thicknesses and poisson s ratios in the eastern tibetan plateau and their tectonic implications 1 crustal thicknesses and poisson s ratios in the eastern tibetan plateau were estimated using the h k stacking method on teleseismic receiver functions the data came mainly from the regional seismic networks in 2006 2008 results show that the crust thickens from east to west with a thickness difference of 30 km a sharp change of crustal thickness from 41 5 to 52 5 km is observed across the longmen shan crustal thickness predictions based on the airy type isostasy are consistent with the estimations from h k stacking implying that the topography is approximately compensated the study area can be divided into three parts according to the poisson s ratios 1 the northern songpan garze terrane and the western qinling orogenic belt with low ratios 0 26 2 the southern songpan garze terrane the sanjiang fold system and the sichuan basin with high to intermediate ratios 0 27 0 30 and 3 the southwestern yangtze platform with low to intermediate ratios 0 27 joint interpretation of the low average vp values from deep seismic sounding profiles and the low vp vs ratios from receiver function analysis favors the presence of felsic crust rather than significant volumes of partial melts in the northern songpan garze terrane and the western qinling orogenic belt the junction of the longmen shan fault zone the xianshuihe fault zone and the anninghe fault zone has an ultrahigh poisson s ratio 0 30 which could be considered as an evidence of local partial melt we propose that the eastward movement of upper and middle crustal material in the southern songpan garze terrane is obstructed by the more rigid sichuan basin resulting in strain accumulation along the longmen shan fault zone

evidence from the high latitude north atlantic for variations in antarctic intermediate water flow during the last deglaciation we present evidence that the characteristic chemical signature based on coupled benthic foraminiferal cd ca and d13c of antarctic intermediate waters aaiw penetrated throughout the intermediate depths of the atlantic basin to the high latitude north atlantic during the abrupt cooling events of the last deglaciation heinrich 1 and the younger dryas aaiw may play the dynamic counterpart to the bipolar seesaw when near freezing salty bottom waters from the antarctic aabw sluggishly ventilate the deep ocean our data reinforce the concept that interglacial circulation is stabilized by salinity feedbacks between salty northern sourced deep waters nadw and fresh southern sourced waters aabw and aaiw further the glacial ocean may be susceptible to the more finely balanced relative densities of nadw and aaiw due to either freshwater input or a reversal of the salinity gradient such that the ocean is poised for nadw collapse via a negative salinity feedback the unstable climate of the glacial period and its termination may arise from the closer competition for ubiquity at intermediate depths between northern and southern sourced intermediate waters

the influence of air and sea exchange on the carbon isotope distribution in the sea we explore here the influence of the temperature dependence of isotope fractionation between atmospheric co2and ocean co2 on the distribution of carbon isotopes in the ocean this is accomplished by an analysis of departures from the expected redfield tie between po4 and 13c we find that for the surface ocean the temperature influence largely compensates for the biologic influence in the deep ocean the temperature influence imprinted at the sites of deepwater formation reduces somewhat the biologically induced difference between the carbon isotope ratios for deep waters produced in the northern atlantic and in the antarctic these same features are reproduced in the hamburg ocean model in order to assess the impact of changes in the ratio of ocean mixing rate to wind speed we have made a model run in which co2 exchange rates between air and sea were everywhere doubled as expected the influence of the thermodynamic effect on the oceanic carbon isotope distribution is magnified

origin and pathway of equatorial 13 c water in the pacific identified by a simulated passive tracer and its adjoint abstract the origin and pathway of the thermostad water in the eastern equatorial pacific ocean often referred to as the equatorial 13 c water are investigated using a simulated passive tracer and its adjoint based on circulation estimates of a global general circulation model results demonstrate that the source region of the 13 c water lies well outside the tropics in the south pacific some 13 c water is formed northeast of new zealand confirming an earlier hypothesis on the water s origin the south pacific origin of the 13 c water is also related to the formation of the eastern subtropical mode water estmw and the sub antarctic mode water samw the portion of the estmw and samw that eventually enters the density range of the 13 c water 25 8 26 6 kg m 3 does so largely by mixing water formed in the subtropics enters the equatorial region predominantly through the western boundary while its interior transport is relatively small the fresher north pacific estmw and central mode wate

millennial scale climate change and intermediate water circulation in the bering sea from 90 ka a high resolution record from iodp site u1340 1 millennial scale climate events in the north pacific are thought to be related to changes in the circulation of north pacific intermediate water which may have formed in the bering sea in the past to advance our understanding of the mechanisms that underlie millennial scale events bering sea sediment cores from the integrated ocean drilling program site u1340 were used to construct high resolution multiproxy climate records of the last 90 000 years sediment density records show millennial scale events resembling dansgaard oeschger events several of which are laminated interstadials were characterized by 3 5 c warming increased productivity driven by upwelling and reduced benthic oxygenation bering sea intermediate water also changed over longer timescales our records show the presence of intermediate water with lower salinity and higher oxygen content than modern beginning around 60 ka and persisting until the beginning of the deglaciation the bolling allerod was characterized by high productivity laminated sediments and strong denitrification signature our data support the idea that productivity derived changes in oxygenation at intermediate water source regions may have contributed to the intensification of the north pacific wide oxygen minima during the bolling allerod

okhotsk sea ice coverage and kamchatka glaciation over the last 350ka evidence from ice rafted debris and planktonic δ18o high resolution records of ice rafted debris ird and oxygen isotope records spanning an e w trending transect across the okhotsk sea unravel the marine and terrestrial cryogenic history of ne siberia over the last 350 kyr ird predominantly dispersed basin wide by sea ice shows lowest fluxes during interglacial periods implying a reduced and seasonal sea ice coverage highest ird accumulation rates are observed during glacial and deglacial periods with a more extended but highly dynamic ice cover although being rather synchronous ird fluxes are on average higher in the western okhotsk sea than in the eastern part pointing to a persistent but mobile particle supplying sea ice cover even during full glacial conditions presumably less dense in the eastern parts mis 6 is exceptional in this respect asynchronous fluxes of ird which vary spatially reflect rapid paleoclimatic and paleo glaciomarine changes ird accumulation rates were by factor 2 3 higher during mis 6 as compared to the last glacial maximum and the ird depositional center shifted from the western okhotsk sea early mis 6 toward kamchatka late mis 6 synchronous to a distinct change in the ird mineral composition both the characteristic composition of late mis 6 ird originating from the sredinny mountain range of kamchatka and their significantly enhanced accumulation rates refer to intensified iceberg dispersal across the eastern part of the okhotsk sea at 138 ka 135 ka 129 ka and 128 ka bp this scenario affords the presence of extended mountain glaciers protruding down to sea level on the western side of kamchatka anomalously light planktonic stable oxygen isotopes during mis 6 3 termination ii and mis 5 5 5 4 suggest significant freshwater supply related to the westward drainage of kamchatka glaciers the intensified kamchatka glaciation observed during late mis 6 was repeated during mis 3 iceberg discharges into the eastern okhotsk sea are observed at 60 ka 51 ka 42 ka 38 ka 36 ka and 31 ka and may partly correspond to n atlantic heinrich events

glacial interglacial changes in nutrient supply and stratification in the western subarctic north pacific since the penultimate glacial maximum abstract in piston cores from the open subarctic pacific and the okhotsk sea diatom bound 15n 15ndb biogenic opal calcium carbonate and barium were measured from coretop to the previous glacial maximum mis 6 glacial intervals are generally characterized by high 15ndb 8 and low productivity whereas interglacial intervals have a lower 15ndb 5 7 6 3 and indicate high biogenic productivity these data extend the regional swath of evidence for nearly complete surface nutrient utilization during glacial maxima consistent with stronger upper water column stratification throughout the subarctic region during colder intervals an early deglacial decline in 15ndb of 2 at 17 5 ka previously observed in the bering sea is found here in the open subarctic pacific record and arguably also in the okhotsk and a case can be made that a similar decrease in 15ndb occurred in both regions at the previous deglaciation as well the early deglacial 15ndb decrease best explained by a decrease in surface nutrient utilization appears synchronous with southern hemisphere associated deglacial changes and with the heinrich 1 event in the north atlantic this 15ndb decrease may signal the initial deglacial weakening in subarctic north pacific stratification and or a deglacial increase in shallow subsurface nitrate concentration if the former it would be the north pacific analogue to the increase in vertical exchange inferred for the southern ocean at the time of heinrich event 1 in either case the lack of any clear change in paleoproductivity proxies during this interval would seem to require an early deglacial decrease in the iron to nitrate ratio of subsurface nutrient supply or the predominance of light limitation of phytoplankton growth during the deglaciation prior to bolling allerod warming

trends in thermal maturity indicators for the organic sulfur rich eagle ford shale abstract thermal maturity is critical to evaluate petroleum systems and to interpret biomarker results for paleoenvironmental and geobiology studies many thermal maturity indices were developed for marine source rocks containing type ii kerogen but their behavior in organic sulfur rich source rocks requires more investigation here we present geochemical analyses of whole and extracted rock isolated kerogen and extractable organic matter across a natural thermal maturity sequence of the upper cretaceous eagle ford shale to evaluate the behavior of maturity parameters in organic sulfur rich source rocks the samples have similar mineralogy and trace element composition minimizing potential facies effects on thermal maturity parameters atomic h c ratios of isolated kerogen extractable organic matter yield and programmed pyrolysis results show that the samples range from the pre oil through dry gas generation windows programmed pyrolysis data and kerogen elemental ratios show that the immature samples host both type iis atomic sorg c 0 04 and sulfur rich type ii kerogen kerogen sorg c 0 03 0 04 while samples with lower kerogen sorg c ratios kerogen sorg c

abrupt changes of intermediate water properties on the northeastern slope of the bering sea during the last glacial and deglacial period 1 millennial scale variability in the behavior of north pacific intermediate water during the last glacial and deglacial period and its association with dansgaard oeschger d o cycles and heinrich events are examined based on benthic foraminiferal oxygen and carbon isotopes 18obf and 13cbf and caco3 using a sediment core recovered from the northeastern slope of the bering sea a suite of positive 18obf excursions at intermediate depths of the bering sea which seem at least in part associated with increases in the 18obf gradients between the bering and okhotsk seas suggest the bering sea as a proximate source of intermediate water during several severe stadial episodes in the last glacial and deglacial period absence of such 18obf gradients during periods of high surface productivity in the bering and okhotsk seas which we correlate to d o interstadials suggests a reduction in intermediate water production in the bering sea and subsequent introduction of nutrient rich deep waters from the north pacific into intermediate depths of the bering sea we argue that a reorganization of atmospheric circulation in the high latitude north pacific during severe cold episodes in the last glacial and deglacial period created favorable conditions for brine rejection in the northeastern bering sea the resulting salinity increase in the cold surface waters could have initiated intermediate and deep water formation that spread out to the north pacific

reduced ventilation and enhanced magnitude of the deep pacific carbon pool during the last glacial period it has been proposed that the ventilation of the deep pacific carbon pool was not significantly reduced during the last glacial period posing a problem for canonical theories of glacial interglacial co2 change however using radiocarbon dates of marine tephra deposited off new zealand we show that deep 2000 m 2000 m and shallow sub surface ocean atmosphere 14c age offsets i e reservoir or ventilation ages in the southwest pacific increased by 1089 and 337 yrs respectively reaching 2689 and 1037 yrs during the late glacial a comparison with other radiocarbon data from the southern high latitudes suggests that broadly similar changes were experienced right across the southern ocean if like today the southern ocean was the main source of water to the glacial ocean interior these observations would imply a significant change in the global radiocarbon inventory during the last glacial period possibly equivalent to an increase in the average radiocarbon age 2 km 2 km of 700 yrs 700 yrs simple mass balance arguments and numerical model sensitivity tests suggest that such a change in the ocean s mean radiocarbon age would have had a major impact on the marine carbon inventory and atmospheric co2 possibly accounting for nearly half of the glacial interglacial co2 change if confirmed these findings would underline the special role of high latitude shallow sub surface mixing and air sea gas exchange in regulating atmospheric co2 during the late pleistocene

surface nitrate utilization in the bering sea since 180 ka bp insight from sedimentary nitrogen isotopes we present high resolution records of sedimentary nitrogen 15nbulk and carbon isotope ratios 13cbulk from piston core so201 2 85kl located in the western bering sea the records reflect changes in surface nitrate utilization and terrestrial organic matter contribution in submillennial resolution that span the last 180 kyr the 15nbulk record is characterized by a minimum during the penultimate interglacial indicating low nitrate utilization 62 80 despite the relatively high export production inferred from opal concentrations along with a significant reduction in the terrestrial organic matter fraction mterr this suggests that the consumption of the nitrate pool at our site was incomplete and even more reduced than today 84 15nbulk increases from marine isotope stage mis 5 4 and culminates during the last glacial maximum which indicates that nitrate utilization in the bering sea was raised during cold intervals mis 5 4 5 2 4 and almost complete during mis 3 and 2 93 100 this is in agreement with previous hypotheses suggesting that stronger glacial stratification reduced the nutrient supply from the subeuphotic zone thereby increasing the iron to nutrient ratio and therefore the nitrate utilization in the mixed surface layer large variations in 15nbulk were also recorded from 180 to 130 ka bp mis 6 indicating a potential link to insolation and sea level forcing and its related feedbacks millennial scale oscillations were observed in 15nbulk and 13cbulk that might be related to greenland interstadials

planktonic foraminifera stable isotopes and water column structure disentangling ecological signals differential carbon and oxygen stable isotope 13c and 18o fractionation between planktonic foraminifera test calcite and sea water related to ecology and life stage confound the potential for reconstructing palaeo water column temperature and carbon gradients multi species analysis and strict selection of test sizes are useful methods for identifying these fractionation processes also known as vital effects in fossil taxa however there are a limited number of species with adequate size controlled data sets needed for ground truthing the approach in the modern here we report 13c and 18o measurements made on twelve species of modern planktonic foraminifera across a range of fourteen tightly constrained size windows from a tropical indian ocean core top sample this data set includes more test size windows per species especially from the smallest identifiable test size classes and a wider range of species than previously attempted we use the size controlled 18o calcite trajectories to infer depth habitats and calculate species specific calcification temperatures the temperatures are then used to constrain species specific calcification depths along the modern vertical temperature profile in the western tropical indian ocean by overlaying the per species 13c calcite trajectories on local water column 13cdic profiles we estimate if and when i e at which test sizes the planktonic foraminifera species investigated approach ambient 13cdic values the profiling shows significant size controlled 13c deviation from seawater values in all species at some life growth stage which we attribute to i metabolic fractionation in tests 300 m of mixed layer photosymbiotic taxa for most species there is a size window where these effects appear to be at a minimum and or in balance exceptions are globigerinita glutinata a small 200 m surface living species globigerina bulloides which is highly opportunistic and deep living globorotalia tumida and globorotaloides hexagonus the latter two species being affected by various unexplained 13c vital effects use of our refined guidelines for test size selection should improve the potential for making realistic reconstructions of water column 13cdic in a modern tropical stratified setting and potentially in the distant geological past when there are no living analogues present

hemispheric roles of climate forcings during glacial interglacial transitions as deduced from the vostok record and lln 2d model experiments the vostok ice contains fingerprints of atmospheric greenhouse trace gases antarctic temperature northern hemisphere temperature and global ice volume sea level changes during the last glacial interglacial cycles and thus allows us to investigate the sequences of these climatic events in particular during the transitions from full glacial to interglacial conditions the use of the updated co2 record presented here and a reexamination of the sea level proxy confirm that the succession of changes has been similar through each of the four marked transitions found at vostok antarctic air temperature and co2 increase in parallel and almost synchronously while the rapid warmings over greenland take place during the last half of their change and coincide with the marked decay in continental ice volume the vostok results thus emphasize a fundamental difference between south and north in terms of climate dynamics our results confirm the role of co2 as an important amplifier of the glacial interglacial warming in the south it appears also that the marked warming observed at high northern latitudes lagging behind the co2 increase by several thousand years is roughly synchronous with the decay of the northern ice sheets suggesting a major role of climatic feedback due to this decay such a climatic scenario is supported by sensitivity experiments performed with the lln 2 d model forced by the northern hemisphere insolation and co2 model results indicate that the decay of the northern ice sheets and the northern hemisphere temperature depend primarily on the northern summer insolation these results nevertheless could be affected if mechanisms specific to the southern hemisphere appear to play a major role in driving the northern hemisphere climate the model also helps to constrain the time response of ice volume to insolation and co2 changes

decreased influence of antarctic intermediate water in the tropical atlantic during north atlantic cold events abstract antarctic intermediate water aaiw is a key player in the global ocean circulation contributing to the upper limb of the atlantic meridional overturning circulation amoc and influencing interhemispheric heat exchange and the distribution of salinity nutrients and carbon however the deglacial history of aaiw flow into the north atlantic is controversial here we present a multicore top neodymium isotope calibration which confirms the ability of unclean foraminifera to faithfully record bottom water neodymium isotopic composition e nd values in their authigenic coatings we then present the first foraminifera based reconstruction of e nd from three sediment cores retrieved from within modern aaiw in the western tropical north atlantic our records reveal similar glacial and interglacial contributions of aaiw and a pronounced decrease in the aaiw fraction during north atlantic deglacial cold episodes heinrich stadial 1 hs1 and younger dryas yd our results suggest two separate phases of reduced fraction of aaiw in the tropical atlantic during hs1 with a greater reduction during early hs1 if a reduction in aaiw fraction also reflects reduced amoc strength this finding may explain why in many regions there are two phases of hydrologic change within hs1 and why atmospheric co2 rose more rapidly during early than late hs1 our result suggesting less flow of aaiw into the atlantic during north atlantic cold events contrasts with evidence from the pacific where intermediate depth e nd records may indicate increased flow of aaiw into the pacific during the these same events antiphased e nd behavior between intermediate depths of the north atlantic and pacific implies that the flow of aaiw into atlantic and pacific seesawed during the last deglaciation

reconstruction of past climate variability and enso like fluctuations in the southern gulf of california alfonso basin since the last glacial maximum abstract nannofossil assemblages from core md02 2510 provide a 22 ka record of past oceanographic variability in alfonso basin gulf of california east subtropical pacific in this area environmental conditions depend on a monsoonal system heavily influenced by changes in the location of the itcz and nearby atmospheric pressure centers to reconstruct nutricline depth and enso like variability two ecological indexes were calculated based on the relative abundance of the three dominant coccolith species the late glacial period is characterized by intensified wind driven upwelling high primary productivity and la nina like conditions an environmental shift occurs during the glacial interglacial transition el nino like conditions intensify nutricline deepens and surface productivity declines the late holocene is characterized by a persistent increase in nutricline depth and dominance of el nino like conditions the fluctuations in the composition of the coccolith assemblages can be related to orbital scale fluctuations in the average position of the itcz however while the enso like signal that overprints the record varies in response to orbital forcing on suborbital time scales the relation between enso like conditions and the average position of the itcz and the north pacific high changes suggesting that the development of persistent el nino like conditions is strongly dependent on the specific climatic background

influence of equatorial diatom processes on si deposition and atmospheric co2 cycles at glacial interglacial timescales 1 the causes of the glacial cycle remain unknown although the primary driver is changes in atmospheric co2 likely controlled by the biological pump and biogeochemical cycles the two most important regions of the ocean for exchange of co2 with the atmosphere are the equatorial pacific and the southern ocean so the former a net source and the latter a net sink under present conditions the equatorial pacific has been shown to be a si oh 4 limited ecosystem a consequence of the low source si oh 4 concentrations in upwelled water that has its origin in the so this teleconnection for nutrients between the two regions suggests an oscillatory relationship that may influence or control glacial cycles opal mass accumulation rate mar data and 15n measurements in equatorial cores are interpreted with predictions from a one dimensional si oh 4 limited ecosystem model cosine for the equatorial pacific the results suggest that equatorial pacific surface co2 processes are in opposite phase to that of the global atmosphere providing a negative feedback to the glacial cycle this negative feedback is implemented through the effect of the so on the equatorial si oh 4 supply an alternative hypothesis that the whole ocean becomes si oh 4 poor during cooling periods is suggested by low opal mar in cores from both equatorial and antarctic regions perhaps as a result of low river input terminations in this scenario would result from blooms of coccolithophorids triggered by low si oh 4 concentrations

ventilation of the deep southern ocean and deglacial co2 rise past glacial interglacial increases in the concentration of atmospheric carbon dioxide co2 are thought to arise from the rapid release of co2 sequestered in the deep sea primarily via the southern ocean here we present radiocarbon evidence from the atlantic sector of the southern ocean that strongly supports this hypothesis we show that during the last glacial period deep water circulating around antarctica was more than two times older than today relative to the atmosphere during deglaciation the dissipation of this old and presumably co2 enriched deep water played an important role in the pulsed rise of atmospheric co2 through its variable influence on the upwelling branch of the antarctic overturning circulation

evidence from southern ocean sediments for the effect of north atlantic deep water flux on climate evidence from southern ocean sediments for the effect of north atlantic deep water flux on climate

spatial reorganization in the equatorial divergence in the eastern tropical pacific during the last 150 kyr 1 high resolution downcore records of bulk sediment nitrogen isotopes 15n and organic carbon corg contents from multiple eastern tropical pacific sites show remarkable uniformity during the last glacial stage whereas during the holocene and the last interglacial period they diverge significantly the close covariation of 15n records during glacial stages points toward regional changes in the background isotopic signal of the inorganic nitrate pool likely caused by variations in the denitrification rates in the nearby suboxic zones on the other hand we attribute the divergence of the 15n and corg records during interglacial periods to a spatial reorganization in the equatorial divergence we posit a southward displacement of the zone of strongest upwelling in the south equatorial current to explain the reduced productivity and higher nitrate consumption recorded at the equator during warmer intervals