north pacific halocline and cold climate induced by panamanian gateway closure in a coupled ocean atmosphere gcm 1 the influence of the closure of the panamanian gateway during the late cenozoic on climate in and around the north pacific is investigated by using a coupled ocean atmosphere general circulation model with an open and closed gateway in the case of an open closed gateway deep convection is present absent in the north pacific the deep convection is associated with surface saline water transported from the subtropical atlantic through the open gateway to the north pacific on the other hand with the closed gateway the lack of saline water transport from the atlantic induces halocline formation over the subarctic pacific with cold climate the deep convection in the north pacific leads to a vigorous thermohaline circulation with larger meridional heat transport and causes warmer climate in and around the north pacific these results are generally consistent with paleoceanographic and paleoclimatic estimates related to the closure of the panamanian gateway

the u series toolbox for paleoceanography the geochemistry of marine sediments is a major source of information about the past environment of the many measurements that provide such information those of the u series nuclides are unusual in that they inform us about the rate and timescales of processes oceanic processes such as sedimentation productivity and circulation typically occur on timescales too short to be assessed using parent daughter isotope systems such as rb sr or sm nd so the only radioactive clocks that we can turn to are those provided by cosmogenic nuclides principally 14c or the u series nuclides this makes the u series nuclides powerful allies in the quest to understand the past ocean climate system and has led to their widespread application over the last decade as in other applications of the u series those in paleoceanography rely on fractionation of the nuclides away from secular equilibrium in the oceanic setting this fractionation is generally due to differences in the solubility of the various nuclides the behavior of the u series nuclides in the ocean environment was widely researched in the middle decades of the twentieth century this work established knowledge of the concentrations of the nuclides in the various compartments of the ocean system and of their fluxes between these compartments such understanding was comprehensively summarized in the ivanovich and harmon u series volume 1992 particularly by cochran 1992 understanding of the behavior of the u series nuclides has not advanced very dramatically in the decade since that summary but a major theme of research has been the use of this geochemical understanding to develop u series tools to assess the past environment table 1 view this table table 1 summary of seawater data for u series nuclides with paleoceanographic applications s soluble i insoluble full descriptions of the paleoceanographic uses and references are provided in the text further details of the half

cyclic magnetite dissolution in pleistocene sediments of the abyssal northwest pacific ocean evidence for glacial oxygen depletion and carbon trapping the carbonate free abyss of the north pacific defies most paleoceanographic proxy methods and hence remains a blank spot in ocean and climate history paleomagnetic and rock magnetic geochemical and sedimentological methods were combined to date and analyze seven middle to late pleistocene northwest pacific sediment cores from water depths of 5100 to 5700 m besides largely coherent tephra layers the most striking features of these records are nearly magnetite free zones corresponding to glacial marine isotope stages miss 22 12 10 8 6 and 2 magnetite depletion is correlated with organic carbon and quartz content and anticorrelated with biogenic barite and opal content within interglacial sections and mid pleistocene transition glacial stages mis 20 18 16 and 14 magnetite fractions of detrital volcanic and bacterial origin are all well preserved such alternating successions of magnetic iron mineral preservation and depletion are known from sapropel marl cycles which accumulated under periodically changing bottom water oxygen and redox conditions in the open central northwest pacific ocean the only conceivable mechanism to cause such abrupt change is a modified glacial bottom water circulation during all major glaciations since mis 12 oxygen depleted antarctic bottom water aabw sourced bottom water seems to have crept into the abyssal northwest pacific below 5000 m depth thereby changing redox conditions in the sediment trapping and preserving dissolved and particulate organic matter and in consequence reducing and dissolving both biogenic and detrital magnetite at deglaciation a downward progressing oxidation front apparently remineralized and released these sedimentary carbon reservoirs without replenishing the magnetite losses

ordovician paleotopography as evidenced from original dips and differential compaction of dolostone and shale unconformably overlying precambrian basement on manitoulin island canada abstract the middle to basal upper ordovician lindsay formation unconformably overlies the paleoproterozoic bar river and lorrain formations on manitoulin island ontario canada representing a depositional hiatus of at least 1 7 billion years the paleoproterozoic inliers currently exposed as basement highs in the sheguiandah region comprised a 14 km2 area of quartz arenite archipelago during the middle to late ordovician inland sea transgression of north america the quartz arenite outcrop collectively covers an area of approximately 1 8 km2 high energy transport and reworking during wave and tropical storm activity along a high relief rocky shoreline is indicated by dolostone containing 2 5 m size rounded to subrounded quartz arenite boulders with percussion marks up to 4 5 m size subangular quartz arenite blocks consistent with mechanical breakage along joints fractures or bedding planes lenticular conglomerate beds and cracks in quartz arenite basement containing mixtures of dolostone quartz granules and fossiliferous debris with continued transgression organic rich carbonate muds were deposited under low energy conditions either on carbonate strata or directly on quartz arenite basement in restricted regions protected from the open sea clast size distribution in the dolostone clast rounding and the location of the shale quartz arenite unconformity relative to basement highs are all consistent with a longshore current running from the present northeast to southwest with the leeward sides of rocky islands protected from high wave and storm energy processes subsequent deposition of upper ordovician and silurian strata resulted in burial and differential compaction of the lindsay formation units the compaction may have been associated with fractures through which mg rich fluids migrated locally altering the lowermost lindsay formation to dolostone evidence for differential compaction is provided by bed thickening down dip of basement highs and boulder flanks and higher regional dips in shale beds proximal to basement highs compared with dolostone strata the relatively high angle strata of the lindsay formation are a result of the combined effects of paleotopography a high relief rocky shoreline and differential compaction

evidence from diatom bound nitrogen isotopes for subarctic pacific stratification during the last ice age and a link to north pacific denitrification changes higher diatom bound d 15 n 70 wt lower opal content and 1200 ppm lower biogenic barium taken together and with constraints on sediment accumulation rate these results suggest a reduced supply of nitrate to the surface due to stronger stratification of the upper water column of the bering sea during glacial times with more complete nitrate consumption resulting from continued iron supply through atmospheric deposition this finding extends the body of evidence for a pervasive link between cold climates and polar ocean stratification in addition we hypothesize that more complete nutrient consumption in the glacial age subarctic pacific contributed to the previously observed ice age reduction in suboxia and denitrification in the eastern tropical north pacific by lowering the nutrient content of the intermediate depth water formed in the subpolar north pacific in the deglacial interval of the bering sea record two apparent peaks in export productivity are associated with maxima in diatom bound and bulk sediment d 15 n the high d 15 n in these intervals may have resulted from greater surface nutrient consumption during this period however the synchroneity of the deglacial peaks in the bering sea with similar bulk sediment d 15 n changes in the eastern pacific margin and the presence of sediment lamination within the bering sea during the deposition of the productivity peaks raise the possibility that both regional and local denitrification worked to raise the d 15 n of the nitrate feeding bering sea surface waters at these times

productivity changes in the bering sea during the late quaternary changes in biological productivity of the bering sea have been evaluated for the late quaternary based on biogenic opal calcium carbonate and microfossils in two piston cores biological productivity increased during marine isotope stage mis 1 after the last glaciation during the last deglaciation two pronounced peaks of calcium carbonate content were observed at ca 2400 m water depth which can be explained by the caco3 compensation hypothesis and coccolithophore blooms simultaneous with the caco3 peaks oxygen poor deep water was apparently distributed in the aleutian basin based on benthic foraminiferal assemblages the low o2 events seem to be related to deep water circulation and or elevated productivity in the northwest pacific after the caco3 peak events biogenic opal contents and diatoms increased gradually associated with enhanced vertical mixing with an inflow of the alaskan stream through the eastern aleutian arc passes r 2005 elsevier ltd all rights reserved

a 15 000 year paleoenvironmental record from meiji seamount far northwestern pacific late glacial and holocene hemipelagic sediments from meiji seamount in the far northwest pacific contain common to abundant planktonic and benthic foraminifera for ams 14c dating for stable isotope analysis and for interpreting paleoclimate change we present here chronostratigraphic faunal and geochemical results from a piston core which indicate that during glacial times as young as 14 000 yrs bp the northwest pacific sea surface salinity was at least as low as today effectively inhibiting convective overturn between 12 000 and 13 000 yrs ago after a major flux of ice rafting there is faunal and 18o evidence of an abrupt decrease in surface ocean salinity coincident with this event was an increase in biological productivity shown by higher fluxes of calcium carbonate organic carbon opal and greater abundances and lower 13o of the benthic foraminifera uvigerina oxygen isotope ratios in uvigerina and cibicidoides show step like decreases at about 13 000 14 000 11 000 10 000 and 6000 8000 yrs bp these events may be analogous to steps in the north atlantic 18o record during meltwater events if this interpretation is correct then the temperature and salinity history of the deep pacific lags that of the north atlantic by about 1000 yrs consistent with the transport time of deep water from the north atlantic to the north pacific

anticyclonic rings in the gulf of mexico abstract using the historical data set this study describes the anticyclonic rings that separated from the loop current in the eastern gulf of mexico six quasi synoptic data sets are used to describe the evolving circulation of the gulf of mexico from october 1966 to september 1967 showing the separation and movement into the western gulf of three anticyclonic rings the historical data are used to determine that these rings typically translate to the west at a mean speed of 2 1 km day 1 their length scale as defined by their rms radii is 183 km an estimate of ring life span as defined by an e folding time is one year within the context of the gulf s water property distributions these rings appear as warm salty bodies the heat and salt added by one of these rings after separation are estimated to be 7 109 j m 2 and 17 g cm 2 respectively the heat and salt added by one of these features play an important role in the heat and salt budget of the western gulf the latter indicates that about one r

deep water formation in the north pacific and deglacial co2 rise deep water formation in the north atlantic and southern ocean is widely thought to influence deglacial co 2 rise and climate change here we suggest that deep water formation in the north pacific may also play an important role we present paired radiocarbon and boron isotope data from foraminifera from sediment core md02 2489 at 3640 m in the north east pacific these show a pronounced excursion during heinrich stadial 1 with benthic planktic radiocarbon offsets dropping to 350 years accompanied by a decrease in benthic 11 b we suggest that this is driven by the onset of deep convection in the north pacific which mixes young shallow waters to depth old deep waters to the surface and low ph water from intermediate depths into the deep ocean this deep water formation event was likely driven by an increase in surface salinity due to subdued atmospheric monsoonal freshwater flux during heinrich stadial 1 the ability of north pacific deep water npdw formation to explain the excursions seen in our data is demonstrated in a series of experiments with an intermediate complexity earth system model these experiments also show that breakdown of stratification in the north pacific leads to a rapid 30 ppm increase in atmospheric co 2 along with decreases in atmospheric 13 c and 14 c consistent with observations of the early deglaciation our inference of deep water formation is based mainly on results from a single sediment core and our boron isotope data are unavoidably sparse in the key hs1 interval so this hypothesis merits further testing however we note that there is independent support for breakdown of stratification in shallower waters during this period including a minimum in 15 n younging in intermediate water 14 c and regional warming we also re evaluate deglacial changes in north pacific productivity and carbonate preservation in light of our new data and suggest that the regional pulse of export production observed during the bolling allerod is promoted by relatively stratified conditions with increased light availability and a shallow potent nutricline overall our work highlights the potential of npdw formation to play a significant and hitherto unrealized role in deglacial climate change and co 2 rise

lower continental slope cyclonic eddies in the central gulf of mexico current meters an inverted echo sounder hydrography drifters and satellite imagery are used to characterize relatively small 100 to 150 km diameter cold cyclonic eddies in the central basin and on the lower louisiana slope of the gulf of mexico these cyclones are shown to be long lived 6 months or more have limited movements when compared with loop current anticyclones and be fairly vigorous with upper layer currents of 30 50 cm s 1 they usually have only small temperature differences with surrounding water masses in the upper 50 to 100 m of the water column and are therefore not readily apparent in satellite thermal imagery the largest isotherm displacements occur over depths of 200 800 m in one case a cyclone was traced from the deep basin near 92 w to the northern slope as a major anticyclone propagated southwestward through the gulf the presence of cyclones and anticyclones on the louisiana slope is consistent with observed current meter measurements in the upper half of the water column that have long several months periods and approximately equal variances in the cross slope and along slope directions

last glacial maximum to holocene sea surface conditions at umnak plateau bering sea as inferred from diatom alkenone and stable isotope records 1 the bering sea gateway between the pacific and arctic oceans impacts global climate when glacial interglacial shifts in shore line position and ice coverage change regional albedo previous work has shown that during the last glacial termination and into the holocene sea level rises and sea ice coverage diminishes from perennial to absent yet existing work has not quantified sea ice duration or sea surface temperatures sst during this transition here we combine diatom assemblages with the first alkenone record from the bering sea to provide a semiquantitative record of sea ice duration sst and productivity change since the last glacial maximum lgm during the lgm diatom assemblages indicate that sea ice covered the southeastern bering sea perennially at 15 1 cal ka b p the diatom assemblage shifts to one more characteristic of seasonal sea ice and alkenones occur in the sediments in low concentrations deglaciation is characterized by laminated intervals with highly productive and diverse diatom assemblages and inferred high coccolithophorid production at 11 3 cal ka b p the diatom assemblage shifts from one dominated by sea ice species to one dominated by a warmer water north pacific species simultaneously the sst increases by 3 c and the southeastern bering sea becomes ice free year round productivity and temperature proxies are positively correlated with independently dated records from elsewhere in the bering sea the sea of okhotsk and the north pacific indicating that productivity and sst changes are coeval across the region

evolution of a warm core ring in the gulf of mexico lagrangian observations during 1985 and 1986 a gulf of mexico ring shed by the loop current was observed to migrate toward the western gulf of mexico this movement across the gulf was well documented by observations that included drifter data within and outside the ring sea surface temperature at weekly intervals expendable bathythermograph surveys at various times one major hydrographic cruise when the ring was in the northwestern gulf and currents from moorings over which the ring passed the drifter data were used to infer the movement of the ring center as well as the eccentricity and orientation of the major axes the data from the drifters bridge the gaps between detailed surveys to the extent that a daily history of the position and shape of the ring can be constructed the synthesis of these diverse but complimentary data sources provides a detailed description of how the ring interacted with the bathymetry of the northern gulf of mexico as well as with previously and subsequently shed rings

regional variations in the influence of mesoscale eddies on near surface chlorophyll eddies can influence biogeochemical cycles through a variety of mechanisms including the excitation of vertical velocities and the horizontal advection of nutrients and ecosystems both around the eddy periphery by rotational currents and by the trapping of fluid and subsequent transport by the eddy in this study we present an analysis of the influence of mesoscale ocean eddies on near surface chlorophyll chl estimated from satellite measurements of ocean color the influences of horizontal advection trapping and upwelling downwelling on chl are analyzed in an eddy centric frame of reference by collocating satellite observations to eddy interiors as defined by their sea surface height signatures the influence of mesoscale eddies on chl varies regionally in most boundary current regions cyclonic eddies exhibit positive chl anomalies and anticyclonic eddies contain negative chl anomalies in the interior of the south indian ocean however the opposite occurs the various mechanisms by which eddies can influence phytoplankton communities are summarized and regions where the observed chl response to eddies is consistent with one or more of the mechanisms are discussed this study does not attempt to link the observed regional variability definitively to any particular mechanism but provides a global overview of how eddies influence chl anomalies

neodymium isotopic composition in foraminifera and authigenic phases of the south china sea sediments implications for the hydrology of the north pacific ocean over the past 25 kyr end and normalized rare earth elements ree patterns of benthic and planktonic foraminifera and fe mn coatings precipitated on sediments have been investigated for the south china sea scs to 1 assess the reliability of the extraction of past seawater end in the scs and to 2 reconstruct past hydrological changes during the last 25 kyr reductively cleaned mono specific planktonic foraminifera globigerinoides ruber and mixed benthic foraminifera in core top sediments from 1500 to 2400 m display similar end values to those of the modern pacific deep water pdw end of 3 9 to 4 4 furthermore the end of the reductive cleaning solutions shows similar end values to ones obtained on cleaned foraminifera combined with paas normalized ree patterns these results confirm that the oxidative and reductive cleaning procedure applied to foraminifera does not totally remove all of the fe mn coatings and that end values yielded by cleaned planktonic foraminifera retain the end imprint of the bottom and or pore water end values obtained from a leaching procedure carried out on the bulk non decarbonated sediments are comparable to the end values of the modern pdw whereas a similar leaching procedure applied to decarbonated sediments reveals a bias due to contamination with nd deriving from lithogenic particles in core md05 2904 seawater end reconstructed from planktonic foraminifera indicates that the last glacial period is characterized by lower end 5 2 0 2 to 6 4 0 3 than the late holocene 4 1 0 2 assuming that nd input from river does not change strongly the end of the pdw of the northern scs these end variations suggest a higher relative proportions of southern sourced water in the deep water of the western subtropical pacific ocean during the last glacial period

mid depth circulation in the northwest pacific during the last deglaciation evidence from foraminiferal radiocarbon ages 1 sediment cores mr01 k03 pc4 pc5 1366 m water depth collected from off northern japan were studied using coexisting planktonic and benthic foraminiferal radiocarbon measurements to reconstruct the history of mid depth circulation in the northwest pacific reconstructed ventilation ages indicate that consistent with data from a previous radiocarbon study at a shallower site there was significant variation in mid depth circulation during the last deglaciation especially in the bolling allerod 13 15 ka and younger dryas 11 5 13 ka intervals our record indicates that the ventilation changes in the north pacific were antiphase to those of the north atlantic suggesting that atmospheric moisture transport associated with the asian monsoon might have played a great role in millennium scale ventilation changes in the north pacific during the last deglaciation

analysis of bioerosion in clasts from a miocene rocky shore concepcion formation veracruz mexico abstract study of bioerosion traces in the geologic record of rocky shores is can establish the location of ancient shorelines and aid understanding of the evolution of marine communities in marginal environments as an example the ichnologic record associated with cobbles of the conglomerate that crops out along the east side of neovolcanic ridge near plan del rio village in veracruz state south central mexico is described and explained the conglomerate corresponds to the upper part of the concepcion formation deposited during the miocene the bivalves and gastropods included in the sandy matrix and the presence of oysters and bryozoans on the surfaces of clasts allowed interpretation of this conglomerate as an ancient rocky shore the present work deals with bioerosion recorded in the clasts six ichnogenera and ten ichnospecies were determined corresponding to the activity of polychaetes and or sipunculids caulostrepsis taeniola maeandropolydora sulcans and trypanites weisei echinoids circolites isp clionaid sponges entobia cateniformis e geometrica and e ovula and boring bivalves gastrochaenolites cluniformis g lapidicus and g torpedo the relative abundance of boring organisms allows these biota to be placed within the entobia ichnofacies which is characteristic of hard substrates with deep bioerosion the abundance and diversity of gastrochaenolites and entobia in the ichnoassociations studied indicate a shallow marine environment with a low sedimentation rate including episodes of removal or rolling of clasts this process is inferred from clast roundness and the presence of bioerosion traces on most clast surfaces on the other hand the presence of complete and eroded gastrochaenolites borings in the same clast shows different episodes of bioerosion results of this work allow for an understanding of the genetic history of the conglomerate confirming its deposition in a rocky shore palaeoenvironment and indicating the location of an ancient shoreline on the west margin of the gulf of mexico during the miocene

biogeography in 231pa 230th ratios and a balanced 231pa budget for the pacific ocean the ratio of unsupported protactinium 231 to thorium 230 in marine sediments pa th xs is potentially sensitive to several processes of oceanographic and climatological interest deep ocean circulation marine biological productivity as it relates to total particle flux and particle composition specifically biogenic opal and authigenic mn in order to attribute variations in pa th xs observed in sediment records to changes in specific processes through time a better understanding of the chemical cycling of these elements in the modern ocean is necessary to this end a survey was undertaken of pa th xs in surface sediments from the subarctic pacific so202 inopex expedition in combination with a pacific wide compilation of published data throughout the pacific pa th xs is robustly correlated with the opal content of sediments in the north and equatorial pacific simultaneous positive correlations with productivity indicators suggest that boundary scavenging and opal scavenging combine to enhance the removal of pa in the eastern equatorial pacific and subarctic pacific deep ocean water mass ageing 3 5 km 3 5 km associated with the pacific overturning appears to play a secondary role in determining the basin scale distribution of pa th xs a basin wide extrapolation of pa removal is performed which suggests that the pacific pa budget is nearly in balance we hypothesize that through time pa th xs distributions in the pacific could define the evolving boundaries of contrasting biogeographic provinces in the north pacific while the influence of hydrothermal scavenging of pa potentially confounds this approach in the south pacific

deepwater formation in the north pacific during the last glacial termination between approximately 17 500 and 15 000 years ago the atlantic meridional overturning circulation weakened substantially in response to meltwater discharges from disintegrating northern hemispheric glacial ice sheets the global effects of this reorganization of poleward heat flow in the north atlantic extended to antarctica and the north pacific here we present evidence from north pacific paleo surface proxy data a compilation of marine radiocarbon age ventilation records and global climate model simulations to suggest that during the early stages of the last glacial termination deep water extending to a depth of approximately 2500 to 3000 meters was formed in the north pacific a switch of deepwater formation between the north atlantic and the north pacific played a key role in regulating poleward oceanic heat transport during the last glacial termination

the influence of microhabitats on the carbon isotopic composition of deep sea benthic foraminifera we report 13c and 18o values for rose bengal stained benthic foraminifera from a set of box cores from continental margin environments in the atlantic and pacific oceans these isotopic results are compared with foraminiferal distribution data and pore water 13c profiles to evaluate the importance of environmental microhabitat effects on the carbon isotopic composition of benthic foraminifera the 13c values of infaunal taxa are consistently lower than those of epifaunal taxa suggesting that microhabitat effects on test composition do exist the 13c differences between foraminiferal carbonate and bottom water dissolved inorganic carbon are not correlated with the 18o differences between benthic foraminifera tests and equilibrium calcite but they do correlate with variations in the chemistry of sediment pore waters however interspecific 18o differences as well as 13c differences between species with similar vertical distributions in the sediments indicate that taxon specific vital effects also influence test composition

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

the deglacial history of surface and intermediate water of the bering sea the lithology of deglacial sediments from the bering sea includes intervals of laminated or dysaerobic sediments these intervals are contemporaneous with the occurrence of laminated sediments from the california margin and gulf of california which suggests widespread low oxygen conditions at intermediate depths in the north pacific ocean the cause could be reduced intermediate water ventilation increased organic carbon flux or a combination of the two we infer abrupt decreases of planktonic foraminifer d 18 o at 14 400 and 11 650 yr bp which may be a combination of both freshening and warming on the shirshov ridge the abundance of sea ice diatoms of the genus nitzschia reach local maxima twice during the deglaciation the latter of which may be an expression of the younger dryas these findings expand the extent of the expression of deglacial millennial scale climate events to include the northernmost pacific r 2005 elsevier ltd all rights reserved

230th normalization an essential tool for interpreting sedimentary fluxes during the late quaternary there is increasing evidence indicating that syndepositional redistribution of sediment on the seafloor by bottom currents is common and can significantly affect sediment mass accumulation rates notwithstanding its common incidence this process generally referred to as sediment focusing is often difficult to recognize if redistribution is near synchronous to deposition the stratigraphy of the sediment is not disturbed and sediment focusing can easily be overlooked ignoring it however can lead to serious misinterpretations of sedimentary fluxes particularly when past changes in export flux from the overlying water are inferred in many instances this problem can be resolved at least for sediments deposited during the late quaternary by normalizing to the flux of 230th scavenged from seawater which is nearly constant and equivalent to the known rate of production of 230th from the decay of dissolved 234u we review the principle advantages and limitations of this method notwithstanding its limitations it is clear that 230th normalization does provide a means of achieving more accurate interpretations of sedimentary fluxes and eliminates the risk of serious misinterpretations of sediment mass accumulation rates

intermediate water ventilation change in the subarctic northwest pacific during the last deglaciation 1 the laminated sediments suggest significant depletion in dissolved oxygen of intermediate water in the north pacific during the last deglaciation however the cause of depleted oxygen during deglaciation is still a matter of debate here we present foraminiferal mg ca based intermediate and surface temperatures and 18o of seawater 18ow a proxy of salinity in the oyashio region in order to investigate intermediate water circulation through the last deglaciation results indicate that the intermediate water temperature and 18ow increased in association with ventilation age at the bolling allerod period suggesting that the poor ventilation at that time the surface record shows that the decrease of salinity preceded the slowdown of intermediate ventilation the coupled variation of intermediate and surface water suggests that the supply of cold fresh intermediate water diminished because of poor ventilation at the high latitude due to surface freshening

foraminiferal end in the deep north western subtropical pacific ocean tracing changes in weathering input over the last 30 000 years abstract this study focuses on the neodymium isotopic composition end of mixed planktonic foraminifera species in sediment cores collected on the north western margin of the south china sea scs and in the western equatorial pacific the aim was to identify temporal changes in the end of the upper circumpolar deep water ucdw during its northward penetration in the western subtropical pacific and to re evaluate the significance of deep water end changes at the northern margin of the scs over the past 25 kyr the past seawater end record derived from sediments of the subtropical western pacific displays a narrow range from 2 9 0 3 to 1 6 0 4 this suggests that the end of the ucdw is greatly modified during its northward penetration through the process of boundary exchange along the western volcanic margin of the south pacific and that the unradiogenic end signature of the ucdw observed in the south pacific about 6 has not been propagated beyond the equatorial pacific at least not over the last 25 kyr seawater end values obtained from the northern scs display large variations with values that are lower 6 8 0 3 to 5 6 0 2 for the last glacial period than for the late holocene 5 7 0 3 to 4 1 0 2 such glacial end cannot be attributed to a higher proportion of southern sourced water ssw as end values of the ucdw in the equatorial western pacific are more radiogenic than those observed in the scs the evolution of the seawater end values of the northern scs during the last glacial period and the last climatic transition is coeval with variations in the contribution of sediments from the pearl river the low sea level stand of the last glacial period resulted in a more proximal position of the pearl river mouth relative to core md05 2904 which a higher input of freshwater and in particular detrital sedimentary particles originating from the pearl river that partially dissolved during sinking led to a decrease in the seawater end along the north western margin of the scs enhanced rainfalls associated with intensified monsoon and more frequent typhoon activities during the early holocene climatic optimum from 9 to 7 cal kyr bp are linked to a decrease in sea surface salinity lower 18o values of planktonic foraminifera and a decrease in end values 6 2 0 3 induced by lithogenic nd input from pronounced freshwater and sediment discharge from distal rivers

14c activity and global carbon cycle changes over the past 50 000 years a series of 14c measurements in ocean drilling program cores from the tropical cariaco basin which have been correlated to the annual layer counted chronology for the greenland ice sheet project 2 gisp2 ice core provides a high resolution calibration of the radiocarbon time scale back to 50 000 years before the present independent radiometric dating of events correlated to gisp2 suggests that the calibration is accurate reconstructed 14c activities varied substantially during the last glacial period including sharp peaks synchronous with the laschamp and mono lake geomagnetic field intensity minimal and cosmogenic nuclide peaks in ice cores and marine sediments simulations with a geochemical box model suggest that much of the variability can be explained by geomagnetically modulated changes in 14c production rate together with plausible changes in deep ocean ventilation and the global carbon cycle during glaciation

intensification of the oxygen minimum zone in the northeast pacific off vancouver island during the last deglaciation ventilation and or export production 1 the oxygen minimum zone omz off vancouver island was more oxygen depleted relative to modern conditions during the allerod 13 5 to 12 6 calendar kyr and again from 11 to 10 kyr the timing of omz intensification is similar to that seen throughout the north pacific although the onset appears to have been delayed by 1500 years off vancouver island radiocarbon dating of coeval benthic and planktonic foraminifera shows that between 16 0 and 12 6 kyr the age contrast between surface and intermediate waters 920 m depth off vancouver island was similar to or slightly less than that today there is no evidence of an increased age difference i e decreased ventilation during the deglaciation particularly during the allerod however sedimentary marine organic carbon concentration and mass accumulation rate increased substantially in the allerod suggesting that increased organic matter export was the principal cause of late pleistocene omz intensification off vancouver island

variability in north pacific intermediate and deep water ventilation during heinrich events in two coupled climate models the responses of north pacific intermediate and deep water ventilation and ocean biogeochemical properties to northern north atlantic glacial freshwater perturbations are evaluated with a coupled atmosphere ocean general circulation model miroc and an earth system model of intermediate complexity loveclim when the atlantic meridional overturning circulation amoc is weakened as a result of the north atlantic freshwater discharge both models simulate subthermocline and intermediate water warming in the pacific ocean the sensitivities of the pacific meridional overturning circulation pmoc to amoc weakening differ significantly between the two models miroc simulates a small enhancement of the deep sinking branch of the pmoc in the north pacific on the contrary the loveclim freshwater experiment exhibits intensified deep water formation in the north pacific associated with a maximum transport change of 19 sv despite the significant differences in ocean circulation response both models successfully reproduce high oxygen and low nutrient conditions of intermediate and deep waters in accordance with sediment core based paleoproxy reconstructions from the north pacific and bering sea during heinrich event 1 emergence of younger intermediate and deep water in the north pacific can be partly attributed to an overall enhanced mixing as well as intensified overturning circulation of the subpolar north pacific our models simulate broad features observed in several paleoproxy data of the pacific ocean biological production decrease in northern japan cooling in the western north pacific ocean and the southward shift of the pacific intertropical convergence zone

north pacific intermediate water circulation enhanced by the closure of the bering strait the bering strait provides a shallow connection that allows freshwater to flow from the north pacific into the north atlantic but this passage was closed during past glacials when sea level was at least 50 m lower than at present climate models investigating bering strait closure predict that this mechanism increases the salinity in the north atlantic and reduces the salinity in the north pacific inducing a pacific atlantic seesaw in meridional overturning circulation and poleward heat flux however the pacific circulation response to bering strait closure and thus the seesaw theory has not been tested by long paleoceanographic records we present long records of foraminiferal 18o and 13c from integrated ocean drilling program site u1342 in the bering sea which provide the first evidence of enhanced north pacific intermediate water when the bering strait was closed during each of the extreme glacials of the last 1 2 myr these results suggest that orbital scale variations in north pacific intermediate water are coherent and in phase with variations in upper north atlantic deep water but are unrelated to changes in lower north atlantic deep water together these results provide evidence for systematic orbital scale variability in north pacific ocean circulation and may challenge the idea of an orbital scale pacific atlantic seesaw

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

uranium removal in oceanic sediments and the oceanic u balance pore water uranium data from the nw atlantic ocean cariaco trench black sea and san clemente basin are used to calculate fluxes across the sediment water interface all samples were collected in situ and show depletions in pore water u relative to the overlying water concentration the uptake rate of u derived from pore water gradients reflects the redox environment with lowest fluxes 10 g cm 2 ky in oxic su ic sediments of the nw atlantic dominated by no 3 reduction and higher fluxes 25 70 g cm 2 ky in the anoxic sulfate reducing sediments of the cariaco trench black sea and san clemente basin the anoxic fluxes compare well with previous estimates based on solid phase data calculations indicate that the areally integrated removal of u into su ic hemipelagic sediments is of greater magnitude than that into anoxic sulfate reducing sediments these fluxes are discussed in the context of the oceanic u balance the removal of u in all oceanic sediments is estimated to account for about 65 of the riverine input and this sink plus removal of u in altered oceanic crust balances the most probable value for riverine input

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

productivity and sedimentary δ15n variability for the last 17 000 years along the northern gulf of alaska continental slope 1 biogenic opal organic carbon organic matter stable isotope and trace metal data from a well dated high resolution jumbo piston core ew0408 85jc 59 33 3 n 144 9 21 w 682 m water depth recovered from the northern gulf of alaska continental slope reveal changes in productivity and nutrient utilization over the last 17 000 years maximum values of opal concentration 10 occur during the deglacial bolling allerod b a interval and earliest holocene 11 2 to 10 8 cal ka bp moderate values 6 occur during the younger dryas 13 0 to 11 2 cal ka bp and holocene and minimum values 3 5 occur during the late glacial interval lgi when converted to opal mass accumulation rates the highest values 5000 g cm 2 kyr 1 occur during the lgi prior to 16 7 cal ka bp which points to a strong influence by lgi glacimarine sedimentation regimes similar patterns are also observed in total organic carbon and cadmium paleoproductivity proxies mid holocene peaks in the terrestrial organic matter fraction at 5 5 4 7 3 5 and 1 2 cal ka bp indicate periods of enhanced delivery of glaciomarine sediments by the alaska coastal current the b a and earliest holocene intervals are laminated and enrichments of redox sensitive elements suggest dysoxic to anoxic conditions in the water column the laminations are also associated with mildly enriched sedimentary 15n ratios indicating a link between productivity nitrogen cycle dynamics and sedimentary anoxia after applying a correction for terrestrial 15n contributions based on end member mixing models of terrestrial and marine organic matter the resulting b a marine 15n 6 3 0 4 ratios are consistent with either mild denitrification or increased nitrate utilization these findings can be explained by increased micronutrient fe availability during episodes of rapid rising sea level that released iron from the previously subaerial coastal plain iron input from enhanced terrestrial runoff and or the intermittent presence of seasonal sea ice resulting from altered ocean atmospheric circulation during the b a in the gulf of alaska

separation of warm core rings in the gulf of mexico abstract the separation of anticyclonic rings is studied using a 12 level primitive equation numerical model of the western north atlantic the gulf stream formation region model is based on the bryan cox semtner code and uses degree horizontal resolution the eastern boundary of the model near the mid atlantic ridge is forced by a pumps and baffles region to have the appropriate temperature and salinity structure vertical shear and total transport the model is closed by a solid northern wall at 36 n and is forced by steady winds in the results presented here large rings separate from the loop current in the gulf of mexico at periods near 30 weeks the separation of a single typical ring is shown in detail the most striking feature is that the separation is not a single spectacular event but a long gradual process involving recirculation between the ring and the main flow for many weeks after the time at which one would on the basis of standard observational evidence normally believe the

uniformitarianism as a guide to rocky shore ecosystems in the geological record literature on pleistocene and neogene rocky shores is reviewed from a uniformitarian perspective to assess the fidelity of physical and biological information entrained in the geological record through present day processes coverage by latitude spans tropical to subarctic shores variations in paleotopography are illustrated by unconformities between sedimentary accumulations and rocks of igneous or non igneous origin former rocky shores occur across a range of geographic scales that include i spot localities ii embayments with continuous transition from exposed outer to protected inner shores and iii entire islands with windward and leeward shores differences in rate and mag nitude of sea level change affect rocky shore physiography terrace deposits characterize the pleistocene but ramp de posits typify older neogene shores on average species with hard parts account for about 50 of the modern rocky intertidal fauna on a regional basis regardless of latitude biodiversity is highest in mid latitudes fixed organisms with encrusting wedging or boring habits corals barnacles oysters other bivalves and vermetid gastropods show high potential for fossilization in growth position mobile organisms that cling to rocks gastropods crabs and echinoids suffer post mortem transport but may be immured within neptunian dikes or interstices among cobbles and boulders at best localized fossil deposits from the pleistocene reflect 30 of the biodiversity of skeletonized organisms tabulated from modern rocky shores on a regional basis uniformitarianism provides little insight into the diversity of soft bodied organisms excluding stromatolites that joined the ecosystem in precambrian times and the extent to which soft bodied organisms dominated shore life through later times

erratum dynamics of rocky shores cretaceous pliocene pleistocene and recent baja california peninsula mexico rocky shorelines provide an excellent record that can be used to interpret the environmental conditions prevailing in a particular area in time and space former rocky shores are first rate indicators of sea level position and they provide important local to regional information on tectonics and neotectonics in this paper sedimentary units made of gravel size clasts interpreted as having been deposited on a rocky shore provide data for the interpretation of the hydrodynamic conditions under which the units were deposited a model is presented by which to evaluate the minimum wave height associated with rocky shore deposits located on the baja california peninsula both on the pacific and gulf of california margins for upper cretaceous and pliocene shoreface deposits and for a modern beach deposit elements considered under the application of the model are the average clast size and water depth assigned to each deposit based on an equation proposed by earlier workers in conjunction with airy s linear

main eddy vertical structures observed in the four major eastern boundary upwelling systems in the four major eastern boundary upwelling systems ebus mesoscale eddies are known to modulate the biological productivity and transport near coastal seawater properties toward the offshore ocean however little is known about their main characteristics and vertical structure this study combines 10 years of satellite altimetry data and argo float profiles of temperature and salinity and our main goals are i to describe the main surface characteristics of long lived eddies formed in each ebus and their evolution and ii to depict the main vertical structure of the eddy types that coexist in these regions a clustering analysis of the argo profiles surfacing within the long lived eddies of each ebus allows us to determine the proportion of surface and subsurface intensified eddies in each region and to describe their vertical structure in terms of temperature salinity and dynamic height anomalies in the peru chile upwelling system 55 of the sampled anticyclonic eddies aes have subsurface intensified maximum temperature and salinity anomalies below the seasonal pycnocline whereas 88 of the cyclonic eddies ces are surface intensified in the california upwelling system only 30 of the aes are subsurface intensified and all of the ces show maximum anomalies above the pycnocline in the canary upwelling system 40 of the aes and 60 of the ces are subsurface intensified with maximum anomalies extending down to 800 m depth finally the benguela upwelling system tends to generate 40 50 of weak surface intensified eddies and 50 60 of much stronger subsurface intensified eddies with a clear geographical distribution the mechanisms involved in the observed eddy vertical shapes are discussed

coastal evolution of late cretaceous and pleistocene rocky shores pacific rim of northern baja california mexico cretaceous on cretaceous and pleistocene on cretaceous unconformities are mapped throughout a 45 km 2 field area surrounding the village of erendira on the pacific coast of northern baja california mexico the unconformities represent a late pleistocene rocky shore 120000 130000 ka directly superimposed on a campanian early maastrichtian rocky shore 77 70 ma superb exposure and preservation of coastal features allow for precise paleogeographic restorations physical analysis includes a comparison of rocky shore composition configuration and overall length paleoecological analysis permits the recognition and comparison of preferred wave directions high intensity windward biotas during the late cretaceous included rock encrusting rudists and coralline red algae while low intensity leeward biotas were characterized by rock encrusting oysters scleractinian corals and bryozoans during the pleistocene the open coast was exploited by the byssate bivalve mytilus and boring bivalves including petricola and penitella while more protected settings were dominated by the gastropods olivella and saxidomus amino acid analysis of saxidomus nuttalli yielded an age estimate consistent with the last interglacial epoch oxygen isotope stage 5e wave impact was oblique to the paleoshore during the late pleistocene onshore winds were generated from the west in contrast wave movement was generated from the east to southeast and parallel to shore during the late cretaceous field data are integrated with paleogeographic reconstructions and predictive models including computer models for local and global oceanography where different paleogeographies and oceanographic models conflict field mapping of this sort adds a much needed element of ground truth

response of the bering sea to 11 year solar irradiance cycles during the bolling allerod previous studies find decadal climate variability possibly related to solar activity although the details regarding the feedback with the ocean environment and ecosystem remain unknown here we explore the feedback system of solar irradiance change during the bolling allerod period based on laminated sediments in the northern bering sea during this period well ventilated water was restricted to the upper intermediate layer and oxygen poor lower intermediate water preserved the laminated sediment an 11 year cycle of diatom and radiolarian flux peaks was identified from the laminated interval increased fresh meltwater input and early sea ice retreat in spring under the solar irradiance maximum follow the positive phase of arctic oscillation which impacted the primary production and volume of upper intermediate water production in the following winter strength of this 11 year solar irradiance effect might be further regulated by the pressure patterns of pacific decadal oscillation and or el nino southern oscillation variability

radiocarbon evidence for a possible abyssal front near 3 1 km in the glacial equatorial pacific ocean abstract we investigate the radiocarbon ventilation age in deep equatorial pacific sediment cores using the difference in conventional 14c age between coexisting benthic and planktonic foraminifera and integrate those results with similar data from around the north pacific ocean in a reconstruction for the last glaciation 15 to 25 conventional 14c ka most new data from both the equatorial pacific and the emperor seamounts in the northwestern pacific come from maxima in abundance of benthic taxa because this strategy reduces the effect of bioturbation although there remains considerable scatter in the ventilation age estimates on average ventilation ages in the equatorial pacific were significantly greater below 3 2 km 3080 1125 yrs n 15 than in the depth interval 1 9 to 3 0 km 1610 250 yrs n 12 when compared to the average modern seawater c 14 profile for the north pacific the equatorial pacific glacial data suggest an abyssal front located somewhere between 3 0 and 3 2 km modern water depth above that depth the data may indicate slightly better ventilation than today and below that depth glacial equatorial pacific data appear to be as old as last glacial maximum lgm deep water ages reported for the deep southern atlantic this suggests that a glacial reservoir of aged waters extended throughout the circumpolar southern ocean and into the equatorial pacific renewed ventilation of such a large volume of aged and by corollary carbon rich water would help to account for the rise in atmospheric pco2 and the fall in c 14 as the glaciation drew to a close

the relationship between variations in the gulf of mexico loop current and straits of florida volume transport abstract twelve years of monthly mean positions of the northern boundary of the loop current in the eastern gulf of mexico from satellite and in situ data have been compared with coincident 1977 1988 estimates of volume transport in the straits of florida in the subseasonal frequency band 15 1 to 5 1 cycles per month volume transport estimated from cuba minus florida sea level difference in this frequency band accounts for 69 of the variance in volume transport estimated from the florida grand bahama island submarine cable on average the loop current has a dominant period of 11 months whereas the volume transport is dominated by annual spectral energy little significant coherence squared occurs between them the maximum northward penetration of the loop current occurs on average in winter when the volume transport is a minimum but this is an artifact of the sampling epoch this negative relationship is most pronounced for 1979 1981 when transport is characterized as unimodal but for 1984 1985 and 1

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

deglacial variability in okhotsk sea intermediate water ventilation and biogeochemistry implications for north pacific nutrient supply and productivity highlights multi proxy multi site reconstruction of okhotsk sea palaeo productivity and mid depth ventilation changes from 8 to 18 ka link between hinterland river discharge and downstream okhotsk sea intermediate water osiw ventilation nutrient signatures surplus fe si oh 4 export in osiw during bolling allerod to pelagic pacific supported transient nutrient replete conditions subarctic and subtropical pacific gyres disconnected during bolling allerod with restricted osiw flow to lower latitudes deglacial osiw export and mid depth pacific biogeochemistry modulate millennial scale regional co2 source sink conditions the modern north pacific plays a critical role in marine biogeochemical cycles as an oceanic sink of co2 and by bearing some of the most productive and least oxygenated waters of the world ocean the capacity to sequester co2 is limited by efficient nutrient supply to the mixed layer particularly from deeper water masses in the pacific s subarctic and marginal seas the region is in addition only weakly ventilated by north pacific intermediate water npiw which receives its characteristics from okhotsk sea intermediate water osiw here we present reconstructions of intermediate water ventilation and productivity variations in the okhotsk sea that cover the last glacial termination between eight and 18 ka based on a set of high resolution sediment cores from sites directly downstream of osiw formation in a multi proxy approach we use total organic carbon toc chlorin biogenic opal and caco3 concentrations as indicators for biological productivity c n ratios and xrf scanning derived elemental ratios si k and fe k as well as chlorophycean algae counts document changes in amur freshwater and sediment discharge that condition the osiw stable carbon isotopes of epi and shallow endobenthic foraminifera in combination with 14c analyses of benthic and planktic foraminifera imply decreases in osiw oxygenation during deglacial warm phases from c 14 7 to 13 ka bolling allerod and c 11 4 to 9 ka preboreal no concomitant decreases in okhotsk sea benthic planktic ventilation ages are observed in contrast to nearby but southerly locations on the japan continental margin we attribute okhotsk sea mid depth oxygenation decreases in times of enhanced organic matter supply to maxima in remineralization within osiw in line with multi proxy evidence for maxima in primary productivity and supply of organic matter sedimentary c n and fe k ratios indicate more effective entrainment of nutrients into osiw and thus an increased nutrient load of osiw during deglacial warm periods correlation of palynological and sedimentological evidence from our sites with hinterland reference records suggests that millennial scale changes in osiw oxygen and nutrient concentrations were largely influenced by fluvial freshwater runoff maxima from the amur caused by a deglacial northeastward propagation of the east asian summer monsoon that increased precipitation and temperatures in conjunction with melting of permafrost in the amur catchment area we suggest that osiw ventilation minima and the high lateral supply of nutrients and organic matter during the allerod and preboreal are mechanistically linked to concurrent maxima in nutrient utilization and biological productivity in the subpolar northwest pacific in this scenario increased export of nutrients from the okhotsk sea during deglacial warm phases supported subarctic pacific shifts from generally fe limiting conditions to transient nutrient replete regimes through enhanced advection of mid depth nutrient and fe rich osiw into the upper ocean this mechanism may have moderated the role of the subarctic pacific in the deglacial co2 rise on millennial timescales by combining the upwelling of old carbon rich waters with a transient delivery of mid depth derived bio available fe and silicate

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

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

deglacial subarctic pacific surface water hydrography and nutrient dynamics and links to north atlantic climate variability and atmospheric co2 the glacial to holocene evolution of subarctic pacific surface water stratification and silicic acid si dynamics is investigated based on new combined diatom oxygen 18odiat and silicon 30sidiat isotope records along with new biogenic opal subsurface foraminiferal 18o alkenone based sea surface temperature sea ice diatom and core logging data from the ne pacific our results suggest that 18odiat values are primarily influenced by changes in freshwater discharge from the cordilleran ice sheet cis while corresponding 30sidiat are primarily influenced by changes in si supply to surface waters our data indicate enhanced glacial to mid heinrich stadial 1 hs1 ne pacific surface water stratification generally limiting the si supply to surface waters however we suggest that an increase in si supply during early hs1 when surface waters were still stratified is linked to increased north pacific intermediate water formation the coincidence between fresh surface waters during hs1 and enhanced ice rafted debris sedimentation in the north atlantic indicates a close link between cis and laurentide ice sheet dynamics and a dominant atmospheric control on cis deglaciation the bolling allerod b a is characterized by destratification in the subarctic pacific and an increased supply of saline si rich waters to surface waters this change toward increased convection occurred prior to the bolling warming and is likely triggered by a switch to sea ice free conditions during late hs1 our results furthermore indicate a decreased efficiency of the biological pump during late hs1 and the b a possibly also the younger dryas suggesting that the subarctic pacific has then been a source region of atmospheric co2

increased ventilation age of the deep northeast pacific ocean during the last deglaciation the amount of radiocarbon depleted carbon dioxide in the atmosphere rose dramatically during the last deglaciation estimates of the radiocarbon content of water at 2 7 km depth in the northeast pacific ocean over the past 24 000 years suggest that this water mass was not a significant source of this carbon

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

glacial to interglacial changes in nitrate supply and consumption in the subarctic north pacific from microfossil bound n isotopes at two trophic levels reduced nitrate supply to the subarctic north pacific snp surface during the last ice age has been inferred from coupled changes in diatom bound 15n db 15n bulk sedimentary 15n and biogenic fluxes however the reliability of bulk sedimentary and db 15n has been questioned and a previously reported 15n minimum during heinrich stadial 1 hs1 has proven difficult to explain in a core from the western snp we report the foraminifera bound 15n fb 15n in neogloboquadrina pachyderma and globigerina bulloides comparing them with db 15n in the same core over the past 25 kyr the 15n of all recorders is higher during the last glacial maximum lgm than in the holocene indicating more complete nitrate consumption n pachyderma fb 15n is similar to db 15n in the holocene but 2 2 higher during the lgm this difference suggests a greater sensitivity of fb 15n to changes in summertime nitrate drawdown and 15n rise consistent with a lag of the foraminifera relative to diatoms in reaching their summertime production peak in this highly seasonal environment unlike db 15n fb 15n does not decrease from the lgm into hs1 which supports a previous suggestion that the hs1 db 15n minimum is due to contamination by sponge spicules fb 15n drops in the latter half of the bolling allerod warm period and rises briefly in the younger dryas cold period followed by a decline into the mid holocene the fb 15n records suggest that the coupling among cold climate reduced nitrate supply and more complete nitrate consumption that characterized the lgm also applied to the deglacial cold events

influence of northwest pacific productivity on north pacific intermediate water oxygen concentrations during the bolling allerod interval 14 7 12 9 ka elevated productivity in the northwest pacific is suggested as a new possible control driving past intervals of low o2 intermediate water along the western continental margin of north america according to this mechanism o2 consumption would occur near the site of formation of north pacific intermediate water npiw due to increased respiration of organic carbon in response to a high productivity event evidence is provided for such a productivity increase during the bolling allerod interval 14 7 12 9 ka a time when laminated sediments were deposited along the northern california margin by this mechanism low o2 events in intermediate waters off the western north american margin could occur without significant changes in the rate of npiw ventilation

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

deepwater circulation variation in the south china sea since the last glacial maximum deepwater circulation plays a central role in global climate compared with the atlantic the pacific deepwater circulation s history remains unclear the luzon overflow a branch of the north pacific deep water determines the ventilation rate of the south china sea scs basin sedimentary magnetic properties in the scs reflect millennial scale fluctuations in deep current intensity and orientation the data suggest a slightly stronger current at the last glacial maximum compared to the holocene but the most striking increase in deep current occurred during heinrich stadial 1 h1 and to a lesser extent during the younger dryas yd results of a transient deglacial experiment suggest that the northeastern current strengthening at the entrance of the scs during h1 and the yd times of weak north atlantic deep water formation could be linked to enhanced formation of north pacific deep water

large climate driven changes of oceanic oxygen concentrations during the last deglaciation during the last glacial termination the solubility of gases in the ocean decreased as ocean temperatures rose however marine sediments have not unanimously recorded ocean deoxygenation throughout this time some records show increasing oxygenation since the last glacial maximum particularly in the deep sea while many document abrupt oxygenation changes often associated with apparent changes in the formation rate of north atlantic deep water here we present a global compilation of marine sediment proxy records that reveals remarkable coherency between regional oxygenation changes throughout deglaciation the upper ocean generally became less oxygenated but this general trend included pauses and even reversals reflecting changes in nutrient supply respiration rates and ventilation the most pronounced deoxygenation episode in the upper ocean occurred midway through the deglaciation associated with a reinvigoration of north atlantic deep water formation at this time the upper indo pacific ocean was less oxygenated than today meanwhile the bulk of the deep ocean became more oxygenated over the deglaciation reflecting a transfer of respired carbon to the atmosphere the observed divergence from a simple solubility control emphasizes the degree to which oxygen consumption patterns can be altered by changes in ocean circulation and marine ecosystems

pivoting analyses of the selective entrainment of sediments by shape and size with application to gravel threshold measured variations of pivoting angles with grain size shape reliability and angularity and imbrication are employed in analyses of grain threshold to examine how these factors influence selective grain entrainment and sorting with a bed of uniform grain sizes as employed experimentally to establish the standard threshold curves such as that of shields the threshold condition depends on grain shape and fabric the analysis demonstrates quantitatively that there should be a series of nearly parallel threshold curves depending on grain pivoting angles for a given grain size the order of increasing flow strength required for entrainment is spheres smooth ellipsoids depending on their reliability angular grains and imbricated ellipsoids depending on their imbrication angles the relative threshold values for these different grain shapes and fabric are predicted according to their respective pivoting angles but remain to be directly tested by actual threshold measurements the pivoting angle of a grain also depends on the ratio of its size to those it rests upon this dependence permits an evaluation of selective entrainment by size of grains from a bed of mixed sizes the condition generally found in natural sediments the pivoting model predicts systematic departures from the standard threshold curves for uniform grain sizes such departures have been found in recent studies of gravel threshold in rivers and offshore tidal currents the pivoting model is compared with those threshold data with reasonable agreement however more controlled measurements are required for a satisfactory test of the model it is concluded that variations in pivoting angles for grain entrainment are significant to the processes of selective sorting by grain size and shape

radiocarbon profiles of the nw pacific from the lgm and deglaciation evaluating ventilation metrics and the effect of uncertain surface reservoir ages during the last deglaciation the ventilation of the subarctic pacific is hypothesized to have changed dramatically including the rejuvenation of a poorly ventilated abyssal water mass that filled the deep ocean and fluctuations in the strength of north pacific intermediate and deep water formation at millennial timescales foraminiferal radiocarbon reconstructions of past ventilation changes in the pacific are valuable but are hampered by poor carbonate preservation low sediment accumulation rates bias from bioturbation and poorly constrained past surface reservoir age in this study we present paired benthic planktonic radiocarbon measurements from the okhotsk sea and emperor seamounts we take advantage of large contemporaneous peaks in benthic abundances from the last glacial maximum bolling allerod ba and early holocene to produce time slices of radiocarbon from 1 to 4 km water depth we explore the impact of uncertain surface reservoir age and evaluate several approaches to quantifying past ocean radiocarbon distribution using our nw pacific data and a compilation of published data from the north pacific both the calendar age and the absolute value of an ocean radiocarbon estimate depend on the assumed surface reservoir age but for a time slice from a small geographical area with radiocarbon independent stratigraphic correlation between cores the shape of a water column profile is independent of surface reservoir age the nw pacific profiles are similar in shape to the compilation profiles for the entire north pacific which suggests that deglacial surface reservoir age changes across the n pacific did not diverge dramatically across the areas sampled the last glacial maximum lgm profile 2 km spans a wide range of values ranging from values similar to today to lower than today however by the ba the profile has a similar shape to today ultimately local surface reservoir ages end member water mass composition and mixing ratios must each be constrained before a radiocarbon activity reconstruction can be used to confidently infer ventilation changes

deglacial weakening of the oceanic soft tissue pump global constraints from sedimentary nitrogen isotopes and oxygenation proxies abstract among the many potential explanations for the 80 ppm rise of atmospheric co2 concentrations at the end of the last ice age most involve a weakening of the oceanic soft tissue pump here we use global data compilations of sedimentary nitrogen isotopes and benthic oxygenation proxies to provide a synoptic global perspective on the deglacial soft tissue pump weakening the net change between the last glacial maximum and holocene shows a removal of respired carbon everywhere that proxy data is available with the exception of the upper 1 5 km of the north pacific while excess nitrate accumulated in polar oceans these observations could be explained by intensifying iron limitation a shoaling of organic matter remineralization and or a change in ocean circulation but are inconsistent with a change in the magnitude or position of the southern mid latitude westerlies the net soft tissue pump weakening was front loaded in the early deglaciation 17 5 14 ka when atmospheric 13c and 14c were changing rapidly and appears to have contributed little net change thereafter superimposed on the overall deglacial trend were pronounced transient changes that coincided with variability in the atlantic meridional overturning circulation amoc and bipolar seesaw the seesaw variability is most clearly expressed as anti phased oxygenation changes between the upper 1 5 km of the north pacific and the deep north atlantic consistent with an atlantic pacific ventilation seesaw but it dominated transient variability in records throughout the world although the soft tissue pump seesaw made little contribution to the contrast between the glacial and interglacial states it could have contributed to deglacial variability in atmospheric co2 and might have catalyzed the deglaciation

direct ventilation of the north pacific did not reach the deep ocean during the last deglaciation 1 despite its tremendous size the deep north pacific has received relatively little attention by paleoceanographers it was recently suggested that the deep north pacific was directly ventilated by dense waters formed in the subarctic pacific during heinrich stadial 1 hs1 of the early deglaciation here we present new redox sensitive trace metal data from a sediment core at 2393 m in the subarctic pacific in comparison with previously published data from elsewhere in the region the combined picture shows no sign of ventilation during the early deglaciation in any available core from water depths of 2393 m and deeper while the deepest core to display clear signs of enhanced ventilation during hs1 was raised from 1366 m water depth thus it appears likely that although the north pacific was well ventilated to intermediate depths during hs1 the deep ocean did not receive a significant input of dense waters from a local source but remained isolated from the surface waters above

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

millennial scale ocean dynamics controlled export productivity in the subtropical north pacific the integrated effects of ocean climate dynamics on export production in the north pacific have remained elusive we present a 91 k y export productivity ep record based on sedimentary reactive phosphorus from the western subtropical north pacific on a millennial time scale ep decreased during northern hemisphere cold events when atmospheric dust loading was high and increased during warm episodes the inferred antiphase relation between dust and ep suggests that the supply of macronutrients to the sunlit surface ocean modulated by the penetration depth of north pacific intermediate water and not eolian fe exerted a major control on ep in the subtropical north pacific a compilation of global ep records suggests that eolian fe most likely played a role in stimulating ep regionally only in the subantarctic zone of the southern ocean over the past 91 k y during the cold south warm north phase of the bipolar seesaw the biological pump in both hemispheres was enhanced synchronously yet by different drivers atmospheric fe input for the subantarctic and subsurface macronutrient supply for the north pacific including the tropical and or subtropical pacific and the antarctic zone of the southern ocean

aspects of the behavior of cold perturbations in the eastern gulf of mexico a case study abstract between 2 march and 13 may 1983 while using in situ and satellite data three cold perturbations were observed off the west florida shelf these perturbations moved southward along the boundary of the loop current at speeds of about 4 to 10 km day 1 geostrophic current and current meter data indicated a cyclonic circulation associated with the cold perturbations the geostrophic current indicated northward flow on the west side of the warm filaments that formed on the shoreward side of the cold perturbation and weak southward flow on the east side however the current meter data only gave indications of northward flow in the filaments the current meter array may not have been able to discriminate the entire flow pattern in the filaments

the southern ocean s role in carbon exchange during the last deglaciation changes in the upwelling and degassing of carbon from the southern ocean form one of the leading hypotheses for the cause of glacial interglacial changes in atmospheric carbon dioxide we present a 25 000 year long southern ocean radiocarbon record reconstructed from deep sea corals which shows radiocarbon depleted waters during the glacial period and through the early deglaciation this depletion and associated deep stratification disappeared by 14 6 ka thousand years ago consistent with the transfer of carbon from the deep ocean to the surface ocean and atmosphere via a southern ocean ventilation event given this evidence for carbon exchange in the southern ocean we show that existing deep ocean radiocarbon records from the glacial period are sufficiently depleted to explain the 190 per mil drop in atmospheric radiocarbon between 17 and 14 5 ka

benthic foraminiferal δ13c and accumulation rates of organic carbon uvigerina peregrina group and cibicidoides wuellerstorfi the glacial to interglacial 13c records of the benthic foraminifera cibicidoides wuellerstorfi and the uvigerina peregrina group from deep sea cores cannot be adjusted by a generally valid constant the 13c values of the u peregrina group largely correlate with the accumulation rates of organic carbon suggesting a local habitat effect those of c wuellerstorfi vary independently with respect to the carbon flux and record fluctuations in the 13c of the ambient bottom water isotopic composition

transient stratification as the cause of the north pacific productivity spike during deglaciation during the last deglaciation the north pacific ocean was characterized by a spike in primary productivity which has been attributed to iron input marine sediment analyses suggest that instead the productivity may have been fuelled by deep convection and subsequent stratification