oxygen and carbon isotope record of east pacific core v19 30 implications for the formation of deep water in the late pleistocene north atlantic abstract a detailed oxygen and carbon isotope record has been obtained from benthic foraminifera in core v19 30 from the carnegie ridge on the south side of the panama basin expressing these records and the oxygen and carbon isotope records previously published for atlantic core m 12392 on a common timescale it is apparent that the oxygen isotope records are very similar but that the carbon isotope records are quite different by obtaining the carbon isotope gradient between the two sites as a function of time we show that the production of north atlantic deep water has varied over a wide range during the late pleistocene and that the pattern of variation is not simply related to the well known oxygen isotope record although the two oxygen isotope records are very similar changes in the interoceanic gradient are detectable and support the hypothesis that in the glacial mode the north atlantic was colder and less oxygenated than it is today shackleton s 1 1977 interpretation whereby the carbon isotope record from the atlantic core reflects changes in the terrestrial biomass is an over simplification however the record from the pacific core v19 30 probably can be explained in these terms since it probably approximates the carbon isotope record of global mean oceanic dissolved co 2

high resolution i ca ratios of benthic foraminifera from the peruvian oxygen minimum zone a sims derived assessment of a potential redox proxy oceanic oxygen decline due to anthropogenic climate change is a matter of growing concern tropical oxygen minimum zones omzs are the most important areas of oxygen depletion in the modern oceans a quantitative oxygen proxy in omzs is highly desirable in order to identify and monitor recent dynamics as well as to reconstruct pre anthropocene changes in amplitude and extension of oxygen depletion a previous study revealed that there are significant correlations between i ca ratios of foraminiferal bulk samples for different benthic foraminiferal species from the peruvian omz nevertheless species for which less specimens were available showed a higher variability between i ca ratios in different badges to test if this might be related to intra or inter shell heterogeneity we focused on microanalyses of i ca ratios within these species in our present study we developed a method for measuring benthic foraminiferal i ca ratios a potential proxy for the reconstruction of marine oxygen concentrations we applied 92 spot analyses in individual foraminiferal specimens from the peruvian omz using secondary ion mass spectrometry sims the i ca ratios on 8 of 11 cleaned uvigerina striata and planulina limbata specimens determined with sims showed no significant difference to previous icp ms measurements on bulk samples from the same species this indicates that both techniques are suited to the analysis and that the applied cleaning protocols efficiently removed the strong iodine contaminations nevertheless despite the highly significant correlation between bulk icp ms i ca ratios and bottom water oxygen concentrations for u striata no significant correlation was observed for the sims derived individual i ca ratios this indicates that icp ms bulk analyses on pooled bulk samples might be more suitable for reliable oxygen reconstructions using i ca ratios on the contrary the strong intra test e g shell variations could be induced by the oxygen variability in the habitats of foraminifera therefore the high resolution findings provide the perspective for tracking relative short term oxygen fluctuations by measuring ontogenetic changes in i ca ratios within individual foraminiferal tests measurements on cross sections of uncleaned u striata specimens revealed a strong contaminant iodine phase within the massive centre of the foraminiferal test walls which usually would be considered to be free of contamination the contaminant iodine is probably associated to organic matter and located inside a microporous framework within the foraminiferal calcite this might be related to microtubular structures which have been revealed in previous studies during early dissolution states of foraminiferal test walls

was deep water formed in the north pacific during the late quaternary cadmium evidence from the northwest pacific abstract a benthic foraminifera cd ca record dating from the last glacial period to the holocene for a high sedimentation rate core recovered from the northwest pacific is reported it shows that the deep water water depth of 2700 m cadmium concentration was about 50 lower in the last glacial period than in the holocene at 15 kyr b p the beginning of deglaciation a minimum cd ca is recorded which is almost the same as that of the modern north atlantic considering previously obtained cadmium records from the northwesternmost and western equatorial pacific a steep gradient in the deep water cadmium concentration between the western equatorial pacific and the northwest pacific from the last glacial to deglacial periods has been estimated in contrast to cadmium records benthic foraminifera 13 c records in these regions showed similar increasing trends during this time span and no large difference in 13 c can be observed between these two regions this discordance between these two nutrient tracers may come from the change in the 13 c phosphate relationship in the ocean during the late quaternary although we cannot absolutely rule out other possibilities we suggest that there was a convection cell in the northwest pacific during the last glacial period and at the beginning of deglaciation period the turnover rate of this cell increased and cadmium concentration in the northwest pacific significantly decreased

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

an oceanographic explanation for the apparent carbon isotope cadmium discordancy in the glacial antarctic the seeming discordance between the glacial to interglacial changes in the carbon isotope ratio and cadmium content of benthic foraminifera from the deep antarctic has cast a shadow on the reliability of these proxies as valid of paleocirculation indicators the problem is that while cadmium content shows little glacial to interglacial change lea and boyle 1990 boyle 1992 the carbon isotope change is larger than at any other place in the ocean curry et al 1988 innu et al 1990 charles and fairbanks 199o even after correction for the 0 35 glacial to interglacial change in the isotope ratio for mean ocean atmosphere carbon a difference of 0 5 to 0 6 remains on the basis of redfield ratios for today s ocean this is equivalent to a 25 increase in cadmium content which is not seen this puzzle has been with us for several years

effect of mg ca ratio in seawater on shell composition in shallow benthic foraminifera 1 the ratio of magnesium to calcium mg ca in caco3 shells of foraminifera is widely used to determine paleotemperatures however mg ca is highly variable within and between species suggesting a strong physiological influence on the incorporation of mg2 into the shells while most field and laboratory calibrations have focused on the effect of temperature we chose to study the effect of ambient mg ca on the calcification process and the final shell composition we cultured two species of symbiont bearing benthic foraminifera amphistegina lobifera and amphistegina lessonii in seawater with different mg ca ratios electron probe analysis of the shell mg ca revealed a positive but not entirely linear correlation with mg ca in the culturing media with slightly different curves for each species partition coefficients of mg2 dmg in the calcite shells showed a decrease by a factor of roughly 2 between the lowest and highest mg ca in the ambient water this was previously demonstrated in inorganic calcite precipitation experiments however the biogenic dmg was significantly lower than the inorganic one suggesting a physiological mechanism that reduces mg ca at the calcification site unlike inorganic experiments that display a dependence of dmg on the kinetics of precipitation the biogenic dmg is not correlated with the rate of calcification both dmg and calcification rates in our experiment were sensitive to the mg ca ratio rather than the concentration of either ca2 or mg2 the largest addition of caco3 was obtained at mg ca of 1 and not at present day seawater ratio mg ca 5 this may reflect the mg ca that prevailed during the eocene mg ca 1 5 when this genus evolved

water isotopes in precipitation data model comparison for present day and past climates abstract variations of hdo and h2 18 o concentrations are observed in precipitation both on a geographical and on a temporal basis these variations resulting from successive isotopic fractionation processes at each phase change of water during its atmospheric cycle are well documented through the iaea wmo network isotope concentrations are in middle and high latitudes linearly related to the annual mean temperature at the precipitation site paleoclimatologists have used this relationship to infer paleotemperatures from isotope paleodata extractable from ice cores deep groundwater and other such sources for this application to be valid however the spatial relationship must also hold in time at a given location as the location undergoes a series of climatic changes progress in water isotope modeling aimed at examining and evaluating this assumption has been recently reviewed jouzel et al 1997 with a focus on polar regions and more specifically on greenland we extend this review in comparing the results of two different isotopic agcms nasa giss and echam and in examining with a more global perspective the validity of the above assumption i e the equivalence of the spatial and temporal isotope temperature relationships these results confirm the dominating role of local temperature changes on the paleo isotope signal in most regions however the exact calibration of this valuable paleothermometer is biased by for example the seasonality of precipitation and other factors we forced the two models by the climatic boundary conditions of the mild holocene at 6 kyr bp which only slightly differs from today s climate the isotope response on this weak forcing is quite heterogeneous the only robust common response is the intensification of the hydrological cycle in low latitudes and therefore isotopically more depleted precipitation in the tropics and subtropics we also examine recent progress made in modeling the relationship between the conditions prevailing in moisture source regions for precipitation and the deuterium excess of that precipitation

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

linkages between east antarctic ice sheet extent and southern ocean temperatures based on a pliocene high resolution record of ice rafted debris off prydz bay east antarctica 1 ice rafted debris mass accumulation rates ird mar at a drill site on the antarctic continental margin are investigated to evaluate the linkages between east antarctic ice sheet extent and southern ocean temperatures in the early to mid pliocene odp site 1165 is within 400 km of the antarctic coastline and in the direct pathway of icebergs released by the amery ice shelf the amery ice shelf is the largest ice shelf in east antarctica and it buttresses the lambert glacier drainage system which accounts for 14 of the outflow from the east antarctic ice sheet ird mar were low during peak southern ocean warming in the early pliocene after a brief precursor a tenfold increase in ird mar at 3 3 ma marks the termination of the early pliocene ice sheet minimum coincident with the m2 glacial for the mid pliocene a strong correlation exists between the high amplitude signal in the lr04 benthic stack and ird mar suggesting linkages between east antarctic ice extent global ice volume and deep water temperatures the ird record at site 1165 provides evidence of greater sensitivity of the lambert glacier amery ice shelf system to southern ocean warming than is currently predicted by ice sheet models which may relate to uncertainties in the understanding of ocean heat uptake poleward heat transport and ice sheet ocean interactions

cadmium chemical tracer of deepwater paleoceanography the oceanic distribution of cadmium resembles that of phosphorus because the cadmium content of foraminiferal shells is governed by the cadmium content of seawater planktonic and benthic fossil shells can be used to infer nutrient distributions within ancient oceans empirical studies demonstrate that cadmium in benthic foraminiferal shells is related to the bottom water composition through a proportionality constant d 2 9 this constant is the same for each of the species studied cibicidoides wuellerstorfi cibicidoides kullenbergi nuttallides umbonifera and uvigerina spp downcore cadmium data from high quality pacific and atlantic sediment cores suggest that the cadmium inventory of the ocean did not change significantly between the most recent glacial maximum and the present hence changes in the cadmium content of fossils at a site directly reflect changes in nutrient distributions due to altered oceanic circulation patterns studies of cadmium in pleistocene sediments show that deep ocean circulation patterns were significantly different during the most recent glacial maximum in the western north atlantic ocean the nutrient content of waters from 2500 to 3500 m was twice as high during glacials as during interglacial periods signifying an increase in the proportion of waters of antarctic origin in this depth interval and a decrease but not a cessation in the flux of north atlantic deep waters through this depth range below 3500 m the nutrient increase was greater indicating a higher proportion of antarctic bottom water above 2500 m the nutrient content was lower during glacial periods than it has been during interglacial times the cd content of high latitude north atlantic and southern ocean surface waters does not show a significant glacial interglacial change which argues against theories for changes atmospheric carbon dioxide that require changes in high latitude nutrient concentrations

changes in redox conditions in deep sea sediments of the subarctic north pacific ocean possible evidence for the presence of north pacific deep water cores of upper quaternary and holocene sediment from the subarctic north pacific north of about 48 n contain one or more layers of oxidized brown sediment interbedded within predominantly reduced green sediment the brown layers are enriched in several trace elements especially mn mo ni and co relative to the green layers where multiple oxidized layers are present the intensity of the brown coloration and the magnitude of trace element enrichment often decrease with depth suggesting that the oxidized layers are unstable and are being chemically reduced at depth the oxidized layers represent a change in redox conditions between the north pacific red clay province and the subarctic biosiliceous green clay province the redox change may have been caused by an increase in supply of dissolved oxygen to bottom waters during glacial interglacial transitions as the result of the periodic formation of a seasonal bottom water mass in the northeastern pacific ocean

intensification of the northeast pacific oxygen minimum zone during the bolling allerod warm period although climate records from several locations around the world show nearly synchronous and abrupt changes the nature of the inferred teleconnection is still poorly understood on the basis of preserved laminations and molybdenum enrichments in open margin sediments we demonstrate that the oxygen content of northeast pacific waters at 800 m depth during the bolling allerod warm period 15 13 kyr was greatly reduced existing oxygen isotopic records of benthic and planktonic foraminifera suggest that this was probably due to suppressed ventilation at higher latitudes of the north pacific comparison with ventilation records for the north atlantic indicates an antiphased pattern of convection relative to the north pacific over the past 22 kyr perhaps due to variations in water vapor transport across central america

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

deep sea temperature and ice volume changes across the pliocene pleistocene climate transitions earth has undergone profound changes since the late pliocene which led to the development 2 7 million years ago ma and intensification 0 9 ma of large scale northern hemisphere ice sheets recorded as transitions in the benthic foraminiferal oxygen isotope 18ob record here we present an orbitally resolved record of deep ocean temperature derived from benthic foraminiferal magnesium calcium ratios from the north atlantic which shows that temperature variations are a substantial portion of the global 18ob signal the record shows two distinct cooling events associated with the late pliocene lpt 2 5 to 3 ma and mid pleistocene mpt 1 2 to 0 85 ma climate transitions whereas the lpt increase in ice volume is attributed directly to global cooling the shift to 100 000 year cycles at the mpt is more likely to be a response to an additional change in ice sheet dynamics

comparison of atlantic and pacific paleochemical records for the last 215 000 years changes in deep ocean circulation and chemical inventories abstract detailed cd ca and 13 c data have been obtained for benthic foraminifera from western north atlantic and equatorial pacific sediment cores in the modern ocean both tracers are closely linked to nutrient distributions the sedimentary records for both tracers indicate that bottom waters overlying the atlantic site have been nutrient depleted relative to those at the pacific site over the last 215 000 years from this evidence it is reasonable to infer that there has been a continuous net flux of nutrient depleted water from the western north atlantic into the pacific this exchange has undergone significant fluctuations with the export of nutrient depleted atlantic water diminishing by about a factor of two relative to the inflow from southern ocean sources over the last 215 000 years carbon isotope fluctuations in both regions are dominated by variable storage of isotopically light carbon on continents with a lesser contribution from these deep ocean circulation changes the cadmium signal in the north atlantic is dominated by changes in deep ocean circulation patterns cadmium shows less variability in the pacific which may reflect changes in the global average cadmium content or minor changes in deep pacific circulation patterns using these records to estimate global averages it appears that glacial ocean water had 22 more cd and 0 46 less 13 c than the modern ocean these numbers are estimates which may be revised as more data become available although they are not likely to be as much as 20 in error for cd or 0 2 for 13 c relative north atlantic deep water nadw formation rates are modulated with a significant 41 kyr periodicity linked to obliquity induced variations in high latitude insolation nadw lags 8 2 kyr behind insolation however

antarctic role in northern hemisphere glaciation earth s climate underwent a major transition from the warmth of the late pliocene when global surface temperatures were 2 to 3 c higher than today to extensive northern hemisphere glaciation nhg 2 73 million years ago ma we show that north pacific deep waters were substantially colder 4 c and probably fresher than the north atlantic deep water before the intensification of nhg at 2 73 ma the atlantic pacific temperature gradient was reduced to

pliocene pleistocene ice rafting history and cyclicity in the nordic seas during the last 3 5 myr a continuous 3 5 myr ird record was produced from ocean drilling program odp site 907 a timescale based on magnetic polarity chrons oxygen isotope stratigraphy for the last 1myr and orbital tuning was developed the record documents a stepwise inception of large scale glacial cycles in the nordic seas region the first being a marked expansion of the greenland ice sheet at 3 3 ma a second step occurred at 2 74 ma by an expansion of large scale ice sheets in the northern hemisphere ice sheet variability around the nordic seas was tightly coupled to global ice volume over the past 3 3 myr between 3 and 1 ma most of the variance of the ird signal is in the 41 kyr band whereas the last 1 myr is characterized by stronger 100 kyr variance the gamma ray porosity evaluator grape density record is closely linked with ird variations and documents sub orbital variability resembling the late quaternary heinrich bond cycles

paired carbon isotope and cadmium data from benthic foraminifera implications for changes in oceanic phosphorus oceanic circulation and atmospheric carbon dioxide abstract the carbon isotope and cadmium content of foraminiferal shells from oceanic sediments provides information on past chemical distributions in the ocean starting from reasonable assumptions it can be shown that paired data on both tracers provides more information than does either separately the slope of paired isochronous 13c and cd ca data from fossil benthic foraminifera depends on oceanic p cd and gd 13c p ratios the zero cd ca intercept of this line depends on mean oceanic 13c p and the 13c p ratio given data sufficient to define oceanic mean 13c and cd contents it is possible to place quantitative constraints on the product of the c p redfield ratio and mean oceanic phosphorus and to estimate a circulation parameter which is independent of changes in ocean chemical inventories with the limited available data no significant changes in oceanic p cd can be detected between the holocene and most recent glacial maximum if this data is taken to be representative of the whole ocean then the p and cd contents of the ocean were about 17 higher during the last glacial maximum than at present ocean box models indicate that this change in oceanic p and a 2 c deep ocean cooling during glacials would cause a 47 ppmv reduction in atmospheric pco2 during glacial intervals

a complete high resolution paleocene benthic stable isotope record for the central pacific odp site 1209 1 we have compiled the first stratigraphically continuous high resolution benthic foraminiferal stable isotope record for the paleocene from a single site utilizing cores recovered at pacific odp site 1209 the long term trend in the benthic isotope record suggests a close coupling of volcanic co2 input and deep sea warming over the short term the record is characterized by slow excursions with a pronounced periodic beat related to the short 100 kyr and long 405 kyr eccentricity cycle the phase relationship between the benthic isotope record and eccentricity is similar to patterns documented for the oligocene and miocene confirming the role of orbital forcing as the pace maker for paleoclimatic variability on milankovitch time scales in addition the record documents an unusual transient warming of 2 c coeval with a 0 6 carbon isotope excursion and a decrease in carbonate content at 61 75 ma this event which bears some resemblance to eocene hyperthermals marks the onset of a long term decline in 13c the timing indicates it might be related to the initiation of volcanism along greenland margin

deep time foraminifera mg ca paleothermometry nonlinear correction for secular change in seawater mg ca 1 the mg ca ratio of foraminifera tests is increasingly being utilized as a paleotemperature proxy deep time pre pleistocene mg ca paleothermometry is complicated by the fact that the mg ca ratio of seawater mg casw has undergone considerable secular variation over the cenozoic previous studies have corrected for this by assuming an invariant mg distribution coefficient dmg with mg casw more recent laboratory culturing has shown that this is not the case demonstrating that a power relationship best describes the variation in test mg ca mg catest with mg casw therefore previous corrections are likely to have led to inaccurate temperature reconstructions here we show how the systematics of such a correction should be applied and demonstrate why this provides good evidence that the mg ca ratio of paleogene seawater was lower than previously implied by foraminiferal constraints in agreement with the majority of the proxy mg casw evidence we also demonstrate how it is indirectly possible to constrain the value of h the power component of a mg catest mg casw calibration potentially enabling the appropriate correction of results derived from species where this relationship has not been calibrated however this technique should not be treated as a substitute for culturing the previous erroneous assumptions regarding both 1 the relationship between mg catest and mg caswand 2 the mg ca ratio of seawater at a given time in the past may counteract each other to differing extents as a result previous absolute pre pleistocene paleotemperature estimates derived from mg ca ratios in foraminifera should be treated with caution although relative temperature changes over short 1 ma timescales are likely to be reliable

paired analyses of oxygen isotope and elemental ratios within individual shells of benthic foraminifera genus uvigerina abstract we compare different methodologies in situ and bulk for obtaining oxygen isotope 18o and elemental ratios in the benthic foraminifera genus uvigerina from odp site 1015 california margin to assess what new information can be obtained with high resolution in situ techniques specimens were prepared in epoxy mounts and exposed in cross section such that multiple high resolution analyses could be completed on the same shells using both secondary ionization mass spectrometry sims and laser ablation inductively coupled mass spectrometry la icp ms we also measured elemental ratio data using la icp ms depth profile measurements on whole uncast foraminifera and elemental ratio and 18o with standard bulk techniques using the same species of benthic foraminifera from the same sediment sub samples comparison of the data collected by the different methodologies indicates that there is a consistent offset of 0 9 0 1 between sims and bulk analysis of 18o in these samples the in situ laser data studied in epoxy mount is correlated with the foraminifera bulk measurements for both mg and sr whereas the in situ depth profile laser measurements of mg and sr from whole foraminifera are less correlated with the bulk measurements we also observe that the intra shell variability for each of the proxies is larger than the analytical error and does not follow chamber number we propose that the 18o mg and sr variability within and between single specimens at this site is linked to some combination of measurement bias vital effects and variable environmental conditions in the pore water where the tests were precipitated this information can in turn be related to the regional setting of the site

a deeper respired carbon pool in the glacial equatorial pacific ocean article i nfo atmospheric pco2 was approximately 80 ppm lower during the last glacial period than during pre industrial times identifying the fate of that carbon has been one of the great challenges in paleoceanography we present evidence from ten equatorial pacific ocean sediment cores to show that the deep pacific ocean likely stored more carbon during the last glacial period than the holocene the concentration of the redox sensitive metal uranium u in sediments was systematically greater during the last glacial period than during the holocene indicating more reducing conditions in glacial age sediments reconstructions of biogenic opal flux indicate that changes in u distribution were not the result of changes in biological productivity and the ensuing rain of organic carbon to the sea floor which also affects the redox conditions of the sediments together these results lead to the interpretation that bottom water in the equatorial pacific during the glacial period had significantly lower oxygen concentration than during the holocene and a correspondingly greater level of respired co2 this conclusion is supported by evidence for greater preservation of brassicasterol a biomarker produced by diatoms in glacial age sediments of the eastern equatorial pacific the presence of additional respired co2 in the glacial deep ocean would have lowered atmospheric pco2 by 1 increasing the total storage of co2 in the glacial ocean and 2 increasing ocean alkalinity following a transient carbonate dissolution event our results are consistent with recently published data from the north pacific ocean this suggests that increased carbon storage in the glacial deep pacific ocean was a basin wide phenomenon consistent with a large scale transfer of carbon to the deep ocean during glacial periods

dynamic behaviour of the east antarctic ice sheet during pliocene warmth warm intervals within the pliocene epoch 5 33 2 58 million years ago were characterized by global temperatures comparable to those predicted for the end of this century1 and atmospheric co2 concentrations similar to today2 3 4 estimates for global sea level highstands during these times5 imply possible retreat of the east antarctic ice sheet but ice proximal evidence from the antarctic margin is scarce here we present new data from pliocene marine sediments recovered offshore of adelie land east antarctica that reveal dynamic behaviour of the east antarctic ice sheet in the vicinity of the low lying wilkes subglacial basin during times of past climatic warmth sedimentary sequences deposited between 5 3 and 3 3 million years ago indicate increases in southern ocean surface water productivity associated with elevated circum antarctic temperatures the geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the wilkes subglacial basin an area today buried beneath the east antarctic ice sheet we interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the east antarctic ice sheet was sensitive to climatic warmth during the pliocene

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

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

late quaternary changes in intermediate water oxygenation and oxygen minimum zone northern japan a benthic foraminiferal perspective 1 a strong oxygen minimum zone omz currently exists at upper intermediate water depths on the northern japanese margin nw pacific the omz results largely from a combination of high surface water productivity and poor ventilation of upper intermediate waters we investigated late quaternary history last 34 kyr of ocean floor oxygenation and the omz using quantitative changes in benthic foraminiferal assemblages in three sediment cores taken from the continental slope off shimokita peninsula and tokachi northern japan at water depths between 975 and 1363 m these cores are well located within the present day omz a region of high surface water productivity and in close proximity to the source region of north pacific intermediate water late quaternary benthic foraminiferal assemblages experienced major changes in response to changes in dissolved oxygen concentration in ocean floor sediments foraminiferal assemblages are interpreted to represent three main groups representing oxic suboxic and dysoxic conditions assemblage changes in all three cores and hence in bottom water oxygenation coincided with late quaternary climatic episodes similar to that known for the southern california margin these episodes in turn are correlated with orbital and millennial climate episodes in the greenland ice core including the last glacial episode bolling allerod b a younger dryas preboreal earliest holocene early holocene and late holocene the lowest oxygen conditions marked by dysoxic taxa and laminated sediments in one core occurred during the b a and the preboreal intervals suboxic taxa dominated mainly during the last glacial the younger dryas and most of the holocene dysoxic conditions during the b a and preboreal intervals in this region were possibly caused by high surface water productivity at times of reduced intermediate ventilation in the northwestern pacific remarkable similarities are evident in the late quaternary sequence of benthic foraminiferal assemblage change between the two very distant continental margins of northern japan and southern california the oscillations in omz strength reflected by these faunal changes were widespread and apparently synchronous over wide areas of the north pacific reflecting broad changes in intermediate water ventilation and surface ocean productivity closely linked with late quaternary climate change on millennial and orbital timescales

extinction of deep sea foraminifera as a result of pliocene pleistocene deep sea circulation changes in the south china sea odp sites 1143 and 1146 during the late pliocene middle pleistocene 56 species and 15 genera of elongate cylindrical benthic foraminifera disappeared from the deep sea in the south china sea odp sites 1143 and 1146 as part of the last global extinction in the deep sea this extinction group ext gp exhibited a pulsed decline in abundance and species richness mostly during glacials and often associated with periods of expansion of polar ice that resulted front increased cooling of the earth s climate since similar to 2 5 ma particularly during the mid pleistocene climate transition mpt 1 2 0 6 ma we infer that the ext gp decline in abundance and disappearance was a result of the increased glacial cooling and consequent increased ventilation of the deep sea water masses the detailed record of withdrawal of the ext gp differs between the two sites with far more disappearances occurring prior to the mpt in the deeper site 1143 2772m than in the shallower site 1146 2092 in the late pliocene and early pleistocene declines in deeper parts of the south china sea site 1143 may have resulted from enhanced glacial production of deep southern sourced water passing over the sill into the basin from the north west pacific during the mpt however the ext gp declines and disappearances were of similar timing and magnitude in both sites implying that both were influenced by the same deep water mass during glacials at this time this could have been north pacific deep water which many workers infer was formed in the northern pacific during the last glacial and may have begun forming during mpt glacials in association with the progressively enhanced cooling of the northern hemisphere c 2006 elsevier ltd all rights reserved

cadmium zinc copper and barium in foraminifera tests the concentrations of cadmium zinc copper and barium have been determined on 2 mg samples of single species foraminifera populations cleaning techniques were tested using north atlantic core tops and followed by a detailed downcore study for the last 30 000 years in south atlantic core v22 174 raw foram tests cleaned by crushing followed by ultrasonic removal of fine grained material and dissolved in a ph 5 5 acetate buffer contain appreciable amounts of trace elements associated with ferromanganese and alumino silicate contaminants a reductive complexing cleaning treatment reduces ferromanganese contamination by 1 2 orders of magnitude acetate buffers at ph 5 5 complex iron and raise the solubility of ferromanganese oxides these buffers are unsuitable for separating carbonate lattice bound trace elements from the fraction associated with ferromanganese phases improved mechanical and ultrasonic reductive cleaning combined with a mild dissolution in distilled water under 1 atm pco2 reduces contaminant levels another order of magnitude the cd and zn concentrations order 10 8 mole cd mole ca and 10 5 mole zn mole ca of species with low surface area show an increase with decreasing isotopic temperatures this increase is consistent with the increasing concentrations of these metals from low values in surface waters to higher values at depth the variance of cd and zn over the last 30 000 years in the central south atlantic is consistent with the probable variability of the dissolved trace elements at the calcification levels of the species analyzed cu and ba are irreproducible and probably sensitive to residual contaminant phases the trace element content of the tests differs from levels observed in a recent coprecipitation study foraminifera may be a significant vector in zinc cycling in the ocean

ventilation changes in the northeast pacific during the last deglaciation under present climate conditions convection at high latitudes of the north pacific is restricted to shallower depths than in the north atlantic to what extent this asymmetry between the two ocean basins was maintained over the past 20 kyr is poorly known because there are few unambiguous proxy records of ventilation from the north pacific we present new data for two sediment cores from the california margin at 800 and 1600 m depth to argue that the depth of ventilation shifted repeatedly in the northeast pacific over the course of deglaciation the evidence includes benthic foraminiferal cd ca 18o 16o and 13c 12c data as well as radiocarbon age differences between benthic and planktonic foraminifera a number of features in the shallower of the two cores including an interval of laminated sediments are consistent with changes in ventilation over the past 20 kyr suggested by alternations between laminated and bioturbated sediments in the santa barbara basin and the gulf of california keigwin and jones 1990 kennett and ingram 1995 behl and kennett 1996 data from the deeper of the two california margin cores suggest that during times of reduced ventilation at 800 m ventilation was enhanced at 1600 m depth and vice versa this pronounced depth dependence of ventilation needs to be taken into account when exploring potential teleconnections between the north pacific and the north atlantic

sub milankovitch cycles in periplatform carbonates from the early pliocene great bahama bank high resolution bulk sediment magnetic susceptibility and aragonite content and 18o records from two different planktonic foraminifera species were analyzed in an early pliocene core interval from the straits of florida ocean drilling program site 1006 the 18o record of the shallow dwelling foraminifera g sacculifer and the aragonite content are dominated by sub milankovitch variability in contrast magnetic susceptibility and the 18o record of the deeper dwelling foraminifera g menardii show precession cycles the relationship between the aragonite and the paleoproxy data suggests that the export of sediment from the adjacent great bahama bank was triggered directly by atmospheric processes rather than by sea level change we propose a climate mechanism that bears similarities with the semiannual cycle component of eastern equatorial pacific sea surface temperatures under present day conditions

comparison of water mass changes in the deep tropical atlantic derived from cd ca and carbon isotope records implications for changing ba composition of deep atlantic water masses eastern tropical atlantic benthic foraminiferal ba ca and cd ca data from core v30 49 3093 m reveal large inferred changes in nutrient concentrations of deep atlantic waters during the last 250 kyr relative changes in north atlantic deep water contribution to this site are estimated by scaling the v30 49 cd ca record to values of modern end member water masses these estimates agree well with the relative structure and timing of circulation changes in the eastern tropical atlantic reconstructed from a 13c record based mixing model raymo et al 1997 temporal differences between v30 49 cd ca and ba ca records suggest that the ba ca record reflects changes in circulation with an additional increase in the ba composition of deep atlantic water masses during glacial episodes possibly resulting from increased productivity similarity between the 13c and ba ca records suggests that carbon isotopes in the deep glacial atlantic also reflect productivity increases

north pacific deep water formation during the latest glaciation for at least 20 years palaeoceanographers have speculated about the existence of a source of young nutrient depleted deep water in the north pacific npdw during glaciations proof of its existence has eluded researchers because the present deep north pacific is very corrosive to calcium carbonate thus it has been difficult to obtain a long time series of oxygen isotope data on benthic foraminifera for dating the sediment and carbon isotope data for use as a proxy for deep water nutrient content i report here on a stable isotope record from a western subarctic pacific core taken at 3 km water depth the carbon isotope ratios in the benthic foraminifera cibicidoides show no evidence of nutrient depleted npdw from glacial to holocene time

comment on deep sea temperature and ice volume changes across the pliocene pleistocene climate transitions sosdian and rosenthal reports 17 july 2009 p 306 used magnesium calcium ratios in benthic foraminifera from the north atlantic to reconstruct past bottom water temperatures they suggested that both ice volume change and ice sheet dynamics played important roles during the late pliocene and mid pleistocene climate transitions we present evidence that their record of deep ocean temperature is not reliable thus raising doubts about their conclusions

the role of vertical chemical fractionation in controlling late quaternary atmospheric carbon dioxide the 30 decrease in atmospheric carbon dioxide during glacial maxima must be driven by some change in the chemical circulation of the ocean here a new model for late quaternary co2 variability is presented which resolves some problems occurring in previous models including the timing of carbon dioxide response and changes in the oxygen content of the deep ocean the primary driving factor in this model is a rearrangement of chemical distributions in the ocean whereby labile nutrients and metabolic co2 are concentrated in deep waters rather than in intermediate waters as observed in the modern ocean this new bottom heavy chemical structure does not affect atmospheric carbon dioxide directly instead co2 induced acidity lowers the deep ocean carbonate ion concentration and temporarily increases carbonate dissolution rates oceanic alkalinity then rises until the deep ocean carbonate ion is restored to its steady state value the resulting increase in oceanic alkalinity draws co2 out of the atmosphere into the ocean alkalinity and atmospheric co2 lag several thousand years behind the change in oceanic chemical structure this delayed response is determined by the limited rate of continental weathering and deep ocean carbonate dissolution relative to the oceanic alkalinity inventory it is proposed that characteristic deglacial and preglacial states of the ocean are leading factors driving glacial interglacial climate changes this concept reinterprets the carbon isotope contrast between surface water and deep waters 13c p b as due to a shift of light metabolic carbon from intermediate waters into deep waters the process is illustrated here by a simple equilibrium five box ocean model the observed intermediate depth nutrient depletion is not sufficient in itself to determine which of several possible mechanisms are operating and some mechanisms are not as effective in changing atmospheric co2 as others the largest response is seen from deepening the regeneration cycle of organic carbon the least response is seen from converting north atlantic deep water into intermediate water

evidence for northward expansion of antarctic bottom water mass in the southern ocean during the last glacial inception 1 we investigated deep water changes in the southern ocean during the last glacial inception in relationship to surface hydrology and global climatology to better understand the mechanisms of the establishment of a glacial ocean circulation changes in benthic foraminiferal 13c from three high resolution cores are compared and indicate decoupled intermediate and deep water changes in the southern ocean from the comparison with records from the north atlantic south atlantic and the southern ocean we show that the early southern deep water 13c drop observed at the mis 5 5 5 4 transition occurred before any significant reduction of north atlantic deep water ventilation we propose that this drop is linked to the northward expansion of poorly ventilated antarctic bottom water aabw mass in the southern ocean associated with an early cooling in the high southern latitudes the westerly winds and surface oceanic fronts would migrate equatorward thus weakening the upwelling of circumpolar deep waters reduced heat brought to antarctic surface waters would enhance sea ice formation during winters and the deep convection of cold and poorly ventilated aabw

control of north atlantic deep water circulation by the greenland scotland ridge coherent bathymetric features along the reykjanes ridge indicate that there were significant changes in the flux of buoyant material within the icelandic hot spot during the neogene the radial extent of the topographic swell associated with this hot spot is of the order of 1000 to 2000 km and therefore these changes affected the greenland scotland ridge gsr at present sill depths along the gsr are generally less than 500 m with the deepest passage being less than 1000 m making the overflow water sensitive to even small changes in the ridge depths reconstructions of neogene mantle plume activity correlate with the deepwater circulation patterns in the north atlantic times of high mantle plume activity caused northern component water ncw production to cease ncw fluxes resumed once this phase of high mantle plume activity slowed the long term climate change during the neogene must be controlled by factors other than ncw production however climatic optima during the late early miocene and early pliocene appear to have been augmented by high ncw fluxes while subsequent middle miocene and middle pliocene coolings correlate with uplifts on the gsr and reduced ncw flux we suggest that reductions in ncw may have contributed to both of these cooling events

carbon isotopic variations on glacial to interglacial time scales in the ocean modeling and implications downcore variations in the deep sea 13c signal as recorded in benthic foraminifera are a function of past changes in global organic carbon inventory and ocean circulation thus the carbon isotopic composition of fossil benthic foraminifera constitutes a valuable geochemical proxy for reconstructing paleooceanographic conditions this study examines the mean ocean 13c 12c variations due to the climatically induced changes in the size of the two organic carbon pools terrestrial biomass forest soil and continental shelf sediment through modeling the paired foraminiferal 13c 18o data in the literature it is estimated that during the past several hundred thousand years in late quaternary transfer of organic carbon between these two pools and the ocean in response to glacial interglacial climate and sea level changes has resulted in global oceanic 13c fluctuations with a mean amplitude of about 0 32 the transfer has accounted for about two thirds of the observed carbon isotopic shift in the deep eastern pacific ocean circulation accounting for the remaining one third of 13c amplitude variations in the deep north atlantic ocean it has accounted for about one third of the shift of the two organic carbon reservoirs forest soil is roughly 2 5 times more responsible than shelf sediment in altering the mean carbon isotopic composition of the quaternary oceans destruction of organic matter from the shelf sediment reservoir is responsible for raising the oceanic nutrient inventory during glacial times by about 4 relative to the present interglacial level a level which is difficult to be assessed by the cadmium proxy marine deposition of organic carbon in glacial oceans increased by 3 10 in spite of a reduction in terrestrial biomass during ice ages isolating out the global climatic signals in 13c records shows that since about 300 kyr ago there has been a trend of increasing organic carbon accumulation toward the present at least in the equatorial e pacific it also shows that the contrast between the 13c values hence nutrient content of deep water in the atlantic and pacific observed in today s ocean was smaller during glacial periods in the northwestern indian ocean the global climate corrected 13c results reveal interglacial intensification of the monsoon driven upwelling and productivity back to at least oxygen isotopic stage 11 circa 400 kyr b p

late quaternary sea ice and sedimentary redox conditions in the eastern bering sea implications for ventilation of the mid depth north pacific and an atlantic pacific seesaw mechanism abstract on glacial interglacial and millennial timescales sea ice is an important player in the circulation and primary productivity of high latitude oceans affecting regional and global biogeochemical cycling in the modern north pacific brine rejection during sea ice freezing in the sea of okhotsk drives the formation of north pacific intermediate water npiw that ventilates the north pacific ocean at 300 m 1000 m water depth glacial intervals of the late quaternary however experienced a deepening of glacial npiw to at least 2000 m with the strongest ventilation observed during cold stadial conditions of the last deglaciation however the origin of the shifts in npiw ventilation is poorly understood numerical simulations suggest an atmospheric teleconnection between the north atlantic and the north pacific in response to a slowdown or shutdown of the atlantic meridional overturning circulation this leads to a build up of salinity in the north pacific surface ocean triggering deep ventilation alternatively increased sea ice formation in the north pacific and its marginal seas may have caused strengthened overturning in response to enhanced brine rejection here we use a multi proxy approach to explore sea ice dynamics sedimentary redox chemistry and benthic ecology at integrated ocean drilling program site u1343 in the eastern bering sea across the last 40 ka our results suggest that brine rejection from enhanced sea ice formation during early heinrich stadial 1 locally weakened the halocline aiding in the initiation of deep overturning additionally deglacial sea ice retreat likely contributed to increased primary productivity and expansion of mid depth hypoxia at site u1343 during interstadial conditions confirming a vital role of sea ice in the deglacial north pacific carbon cycle

antarctic and southern ocean influences on late pliocene global cooling the influence of antarctica and the southern ocean on late pliocene global climate reconstructions has remained ambiguous due to a lack of well dated antarctic proximal paleoenvironmental records here we present ice sheet sea surface temperature and sea ice reconstructions from the andrill and 1b sediment core recovered from beneath the ross ice shelf we provide evidence for a major expansion of an ice sheet in the ross sea that began at 3 3 ma followed by a coastal sea surface temperature cooling of 2 5 c a stepwise expansion of sea ice and polynya style deep mixing in the ross sea between 3 3 and 2 5 ma the intensification of antarctic cooling resulted in strengthened westerly winds and invigorated ocean circulation the associated northward migration of southern ocean fronts has been linked with reduced atlantic meridional overturning circulation by restricting surface water connectivity between the ocean basins with implications for heat transport to the high latitudes of the north atlantic while our results do not exclude low latitude mechanisms as drivers for pliocene cooling they indicate an additional role played by southern high latitude cooling during development of the bipolar world

subarctic pacific evidence for a glacial deepening of the oceanic respired carbon pool abstract measurements of benthic foraminiferal cadmium calcium cd ca have indicated that the glacial interglacial change in deep north pacific phosphate po4 concentration was minimal which has been taken by some workers as a sign that the biological pump did not store more carbon in the deep glacial ocean here we present sedimentary redox sensitive trace metal records from ocean drilling program odp site 882 nw subarctic pacific water depth 3244 m to make inferences about changes in deep north pacific oxygenation and thus respired carbon storage over the past 150 000 yr these observations are complemented with biogenic barium and opal measurements as indicators for past organic carbon export to separate the influences of deep water oxygen concentration and sedimentary organic carbon respiration on the redox state of the sediment our results suggest that the deep subarctic pacific water mass was depleted in oxygen during glacial maxima though it was not anoxic we reconcile our results with the existing benthic foraminiferal cd ca by invoking a decrease in the fraction of the deep ocean nutrient inventory that was preformed rather than remineralized this change would have corresponded to an increase in the deep pacific storage of respired carbon which would have lowered atmospheric carbon dioxide co2 by sequestering co2 away from the atmosphere and by increasing ocean alkalinity through a transient dissolution event in the deep sea the magnitude of change in preformed nutrients suggested by the north pacific data would have accounted for a majority of the observed decrease in glacial atmospheric pco2

interior hydrography and circulation of the glacial pacific ocean abstract the deep water of the pacific ocean is a key component of the global climate system on the time scale of late pleistocene glaciation and deglaciation despite its importance the deep pacific during the last glacial maximum has received relatively little attention compared to the deep atlantic in part because the pacific poorly preserves carbonate sediments on the sea floor here we review the current state of knowledge of the deep hydrography and circulation of the glacial pacific by examining available nutrient proxy data including some new 13 c and 18 o data measured on benthic foraminifera planulina wuellerstorfi from the vicinity of japan available benthic 13 c and 18 o and radiocarbon data from the pacific support the presence of a deep hydrographic boundary at around 2000 m during the last glacial maximum paleoceanography 3 1988 343 paleoceanography 7 1992 273 paleoceanography 13 4 1998 323 the deep hydrographic divide in the glacial pacific is similar to what is inferred in the atlantic quaternary research 18 1982 218 paleoceanography 3 1988 317 paleoceanography 3 1988 343 annual reviews of earth planetary sciences 20 1992 245 science 259 1993 1148 the indian nature 333 1988 651 paleoceanography 13 1998 20 and the southern ocean paleoceanography 11 1996 191 suggesting that this is a global phenomenon during the glacial time the upper water mass has a distinctly enriched 13 c compared to the deeper water mass whose possible origins are discussed

north atlantic deep water collapse triggered by a southern ocean meltwater pulse in a glacial climate state 1 it is generally accepted that surface freshwater anomalies in the southern ocean drive increases in north atlantic deep water nadw formation via a bipolar density see saw we find that a southern ocean freshwater pulse of comparable magnitude to meltwater pulse 1a shuts down instead of strengthens nadw in a glacial climate simulation unlike the modern day simulation the glacial experiment is associated with a more fragile north atlantic thermohaline circulation whereby freshwater anomalies that propagate into the north atlantic are able to dominate the bipolar density see saw meltwater pulses over the north atlantic and subsequent nadw shut down are often invoked to explain cold heinrich events appearing in the paleoclimate record our results suggest that triggers for nadw collapse may also originate from the southern hemisphere in glacial epochs once nadw collapses north pacific deep water develops consistent with a north pacific north atlantic see saw triggered from the southern ocean

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

manganese carbonate overgrowths on foraminifera tests below the zone where manganese is remobilized as mn2 aq reductively cleaned foraminifera in deep sea sediments have much higher mnca than those in core tops and sediment traps mnca ranges from less than 20 10 6 in and above the mno2 maximum to as high as 700 10 6 in reducing panama basin sediments the most plausible explanation for this enrichment is that the tests are coated with mn carbonate overgrowths these coatings can account for a significant proportion of the mn in reduced deep sea sediments uptake of manganous ion by carbonate may explain the absence of mn nodules in areas of high carbonate accumulation extreme degrees of overgrowth can alter foram trace element values but this artifact can be avoided by avoiding foraminifera with high mn ca

late pleistocene nutrients and sea surface productivity in the south china sea a record of teleconnections with northern hemisphere events surface nutrient variations during the last 200 000 years have been reconstructed based on the cd ca ratios in the tests of planktonic foraminifera neogloboquadrina dutertrei and the biogenic opal content from two gravity cores retrieved from the northern and northwestern parts of the south china sea scs the cd ca ratios obtained from n dutertrei in recent sediments from fourteen box cores distributed over the scs basin reflect present nutrient levels in the overlying surface waters areas with relatively high cd ca values in the surface sediments are in the region of high chlorophyll a in the northern south china sea near the dongsha islands consistent with previous observation high values of cd ca found in sediments east of vietnam and east of the nansha islands may be a result of increased nutrients due to local upwelling induced by the summer monsoon core 17940 2 raised from the northern continental slope of the scs exhibits exceptional high sedimentation rates 25 85 cm kyr for the last 35 kyr the cd ca ratios in this core are relatively higher during the periods of late d 18 o stage 3 and the mid holocene core 17950 2 with an average sedimentation rate of 5 cm kyr offers a continuous long record back to d 18 o stage 7 in general cd ca values in the downcore records are higher during interglacials and progressively increase as the interglacials proceed values peak around the times of optimum climate conditions and correlate with periods of increased opal wt correlations in the interval of overlap between the two records support the interpretation that variations in cd ca ratios in core 17940 2 are not an individual signal but can be replicated of special interest in this study is the tentative correlation between cd ca peaks in the scs record and the timing of iceberg discharge events heinrich events in the north atlantic mass accumulation rate mar of opal data from core 17950 2 indicate high surface productivity during glacial intervals corresponding to oxygen isotope stages 6 4 and 2 the increase in surface productivity during glacials from the northern scs is contemporaneous with an intensified winter monsoon as recorded by the terrestrial loess deposits the agreement with wind strength recorded in the loess plateau from mainland china supports the

late neogene history of deepwater ventilation in the southern ocean we compiled carbon isotope records from the north atlantic south atlantic and pacific oceans to estimate changes in vertical and interbasinal 13c gradients for the last 9 myr benthic 13c values of deep water in the south atlantic decreased in a series of steps at 7 2 75 and 1 55 ma away from the north atlantic and toward the pacific the benthic 13c of intermediate water in the south atlantic evolved differently from deep waters resulting in an increase in the intermediate to deep 13c gradient 13cid the 13cid increased in steps at 2 75 and 1 55 ma marking the development and intensification of a chemical divide in the atlantic ocean between well ventilated intermediate water and poorly ventilated deep water we suggest these changes in interbasinal and vertical gradients resulted from decreasing northern component water and reduced ventilation of southern component water scw the latter was caused by several interrelated processes in antarctic sources areas including increased sea ice cover enhanced surface water stratification decreased ekman induced upwelling and reduced vertical mixing across the thermocline because antarctic surface water processes and deepwater ventilation rates ultimately influence atmospheric co2 concentration these processes may have acted as a positive feedback that contributed to the major cooling steps in late neogene climate

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

variability in the deep and intermediate water circulation of the atlantic ocean during the past 25 000 years northern hemisphere modulation of the southern ocean the relative flux of north atlantic deep water nadw out of the atlantic can be monitored in the southern ocean where high 13c nadw mixes rapidly with low 13c recirculated pacific water before forming antarctic bottom water aabw by using 13c measured in benthic foraminifera as a water mass tracer it is shown that the southern ocean was dominated by pacific water with little nadw contribution during the last glaciation these tracer results document the direct physical connection between insolation controlled northern hemisphere oscillations and changes in the chemical and physical properties of southern ocean water the 13c records from the deep tropical atlantic document the transition from an atlantic dominated by southern ocean water during the last glaciation to an atlantic dominated by nadw during the holocene with more southern ocean water in the deep atlantic during the last glaciation the boundary between nadw and southern ocean water was north of its modern position allowing more southern ocean water to enter the eastern atlantic through the romanche fracture zone carbon isotope records from the caribbean and mediterranean seas suggest that the influence of mediterranean overflow water mow extended to the caribbean during the last glaciation and therefore was a volumetrically much more important water mass in the intermediate depth atlantic than it is today

changes in the distribution of δ13c of deep water σco2 between the last glaciation and the holocene carbon isotopic measurements on the benthic foraminiferal genus cibicidoides document that mean deep ocean 13c values were 0 46 lower during the last glacial maximum than during the late holocene the geographic distribution of 13c was altered by changes in the production rate of nutrient depleted deep water in the north atlantic during the late holocene north atlantic deep water with high 13c values and low nutrient values can be found throughout the atlantic ocean and its effects can be traced into the southern ocean where it mixes with recirculated pacific deep water during the glaciation decreased production of north atlantic deep water allowed southern ocean deep water to penetrate farther into the north atlantic and across low latitude fracture zones into the eastern atlantic mean southern ocean 13c values during the glaciation are lower than both north atlantic and pacific 13c values suggesting that production of nutrient depleted water occurred in both oceans during the glaciation enriched 13c values in shallow cores within the atlantic ocean indicate the existence of a nutrient depleted water mass above 2000 m in this ocean

cadmium and delta13c paleochemical ocean distributions during the stage 2 glacial maximum changes in heat and salt transport by ocean currents have been implicated in ice age climate cycles weyl 1 968 newell 1 974 broecker et al 1 990b in addition to the direct physical effects of the ocean on climate the ocean carbon system controls atmospheric co2 and the co2 fluctuations documented in ice core bubbles barnola et a1 1 987 neftel et a1 1 988 are thought to be a significant factor in climate oscillations hansen et al 1 984 dramatic changes in oceanic circulation patterns and carbon system chemistry have occurred during the late quaternary glacial interglacial global climate cycles boyle keigwin 1 982 curry lohmann 1 983 shackleton pisias 1 984 boyle keigwin 1 987 duplessy et al 1 988 curry et al 1 988 broecker et al i 990a these changes in the ocean system may be significant driving forces in the progression of ice age co2 cycles toggweiler sarmiento 1 985 ennever mcelroy 1 985 wenk siegenthaler 1 985 boyle 1 988a b broecker peng 1 990 the oceanic distributions of c513c cd and other carbon system linked properties are controlled by the interaction between biological uptake and decomposition with the general circulation of the ocean because records of past oceanic cd and c5 1 3c are preserved in shells of planktonic and benthic foraminifera

magnetostratigraphy and tephrochronology of the upper quaternary sediments in the okhotsk sea implication of terrigenous volcanogenic and biogenic matter supply seven lithological units alternating between horizons enriched in biogenic opal diatoms and carbonate foraminifera and units composed largely of terrigenous sediment with very low biogenic admixture were distinguished in a series of late quaternary sediment cores from the sea of okhotsk sediments were characterised using on board visual description smear slides analyses grain size composition and magnetic susceptibility ms records five tephra marker layers identified as ko tr k2 k3 and k4 were distinguished using petrological mineralogical and geochemical analyses age models were developed by comparing lithological units tephra stratigraphy and ms records with oxygen isotope curves and with records of biogenic caco3 opal content and sediment grain size composition in three ams radiocarbon dated okhotsk cores this chronological framework allowed us to investigate climate control over the sedimentation regime and productivity and to clarify the formation times of the lithological and tephra units the data show that sediment ms variations in the south eastern area of the glacial okhotsk sea arose primarily from volcanic material input the sedimentation in all other parts of the sea was mainly controlled by the supply of terrigenous material the cores show a tight correlation between ms sediment grain size and climate change in the okhotsk sea coarse sediments with a high ms were accumulated during the cold period oxygen isotope stages mis 2 4 6 fine sediments with a low ice rafted debris ird content and ms were formed in the warm isotope stages according to the oxygen isotope stratigraphy and radiocarbon data the ko tr k2 k3 and k4 tephra were deposited at 7 7 8 0 26 0 kyr bp in mis 4 about 60 70 kyr ago and near mis 5 4 respectively comparison of tephra mineralogy petrology spatial distributions and ages with the history of kurile kamchatka volcanism allows us to identify likely candidates for the tephra source eruptions the combined use of ms records tephrochronology and lithological unit sequences provides a detailed basis for okhotsk sea sediment stratigraphy

stable isotope and lithologic evidence of late glacial and holocene oceanography of the northwestern pacific and its marginal seas abstract stable isotopes geochemical lithological and micropaleontological results from cores from the far northwest fnw pacific and the okhotsk and bering seas are used to reconstruct the regional environment for the last glaciation the deglacial transition and the holocene 18 o records of planktonic foraminifera of the region show two light shifts during deglacial time provoked by the freshening of the surface water and climate warming these north pacific terminal events t1anp and t1bnp with ages of 12 500 and 9300 yr b p respectively occur almost simultaneously with two episodes of accelerated glacier melting around the north atlantic along with the isotopic shifts the caco 3 content in regional sediments increased abruptly 1a and 1b carbonate peaks probably due to changes of productivity and pore water chemistry of surface sediments organic matter and opal concentration increased during the transition between t1anp and t1bnp events in the sediments of the fnw pacific and the southern part of the bering sea and opal content increased in the holocene in the bering and okhotsk seas 13 c records of cores from the okhotsk and bering seas and the fnw pacific do not contradict the hypothesis of increased intermediate water formation in the region during glaciation during deglaciation accumulation of the coarse terrigenous component decreased in sediments of the bering sea and the fnw pacific before the t1anp event probably as a result of rising sea level and opening of the bering strait

changes in caribbean surface hydrography during the pliocene shoaling of the central american seaway pliocene d18o records of shallow and deep dwelling planktonic foraminifers from the caribbean ocean drilling program sites 999 and 1000 the tropical east pacific sites 1241 and 851 and the atlantic site 925 ceara rise and site 1006 western great bahama bank were used to examine atlantic caribbean pacific atmospheric and oceanic linkages associated with the progressive closure of the central american seaway 5 5 3 ma comparisons indicate the development of an inner caribbean salinity gradient in the mixed layer and salinity changes on precessional periodicities after 4 4 ma site 1000 when the pacific caribbean throughflow became significantly restricted the high amplitude variability in salinity is also observed at site 1006 monitoring the caribbean outflow into the atlantic comparisons of caribbean and atlantic planktonic d18o records suggest the north atlantic subtropical gyre as a major source for high salinity surface waters precession induced variations in the volume transport of pacific surface water masses through the panamanian seaway are considered a main factor to explain the caribbean salinity minima results from a coupled climate model point to changes in the el nin o southern oscillation state as a potential trigger for changes in the amount of pacific inflow into the caribbean