the role of caco3 compensation in the glacial to interglacial atmospheric co2 change the only viable explanations put forth to date for the glacial to interglacial change in atmospheric co2 content suggested from measurements of the co2 content of gas extracted from ice cores involve changes in the ocean s nutrient cycles any nutrient change capable of creating the 80 atm changes in atmosphere co2 pressure suggested by the ice core results also creates significant change in the deep ocean s co3 content evidence from deep sea sediments suggests that these co3 changes are compensated on the time scale of a few thousand years by reductions or increases in amount of caco3 accumulating in deep sea sediments this compensation process has two important consequences first it significantly increases the magnitude of the co2 change per unit of nutrient forcing second it causes a delay in the response of the atmospheric co2 change while the first of these consequences is a boon to those seeking to explain the co2 change the second may prove to be a curse the ice core co2 record shows no evidence of a significant lag between the co2 response and the polar warming in any case it is important that we improve our knowledge of the magnitude and timing of the caco3 preservation events which mark the close of episodes of glaciation and of the dissolution events which mark the onset of these episodes

seawater ph pco2 and co2 3 variations in the caribbean sea over the last 130 kyr a boron isotope and b ca study of planktic foraminifera abstract here a new analytical methodology is described for measuring the isotopic composition of boron in foraminifera using multicollector inductively coupled plasma mass spectrometry mc icpms this new approach is fast 10 samples analysed in duplicate per analytical session and accurate to better than 0 25 at 95 confidence with acceptable sample size requirements 1 3 mg of carbonate a core top calibration of several common planktic and two benthic species from geographically widespread localities shows a very close agreement between the isotopic composition measured by mc icpms and the isotopic composition of b oh 4 in seawater as predicted using the recently measured isotopic equilibrium factor of 1 0272 at the depth of habitat a down core and core top investigation of boron concentration b ca ratio shows that the partition coefficient is influenced by co2 3 complicating the application of this proxy nevertheless it is demonstrated that these two proxies can be used to fully constrain the carbonate system of surface water in the caribbean sea odp site 999a over the last 130 kyr this reconstruction shows that during much of the holocene and the last interglacial period surface water at site 999a was in equilibrium with the atmosphere with respect to co2 during the intervening colder periods although the surface water pco2 was lower than the holocene it was a minor to significant source of co2 to the atmosphere possibly due to either an expansion of the eastern equatorial atlantic upwelling zone or a more local expansion of coastal upwelling in the southern caribbean such reorganisation of the oceanic carbonate system in favour of a larger source of co2 to the atmosphere from the equatorial ocean may require mechanisms responsible for lowering atmospheric co2 during glacial periods to be more efficient than previously supposed

millennial scale changes in north atlantic circulation since the last glaciation ocean circulation is closely linked to climate change on glacial interglacial and shorter timescales extensive reorganizations in the circulation of deep and intermediate depth waters in the atlantic ocean have been hypothesized for both the last glaciation1 2 3 4 5 6 and the subsequent younger dryas cold interval3 6 7 8 9 10 but there has been little palaeoceanographic study of the subtropical gyres11 12 13 these gyres are the dominant oceanic features of wind driven circulation and as such they reflect changes in climate and are a significant control on nutrient cycling and possibly atmospheric co2 concentrations here we present cd ca ratios in the shells of benthic foraminifera from the bahama banks that confirm previous suggestions11 12 that nutrient concentrations in the north atlantic subtropical gyre were much lower during the last glacial maximum than they are today up to 50 lower according to our data these contrasting nutrient burdens imply much shorter residence times for waters within the thermocline of the last glacial maximum below the glacial thermocline nutrient concentrations were reduced owing to the presence of glacial north atlantic intermediate water a high resolution cd ca record from an intermediate depth indicates decreased nutrient concentrations during the younger dryas interval as well mirroring opposite changes at a nearby deep site3 9 together these observations suggest that the formation of deep and intermediate waters north atlantic deep water and glacial north atlantic intermediate water respectively wax and wane alternately on both orbital and millennial timescales

tropical atlantic coral oxygen isotopes glacial interglacial sea surface temperatures and climate change abstract we have generated a detailed oxygen isotope time series from the fossil coral reefs from offshore barbados the barbados coral based record is a unique paleoceanographic data set with an equivalent sedimentation rate in excess of 600 cm kyr where not only is the annual signal uniquely preserved but seasonality as well oxygen isotope values during the late glacial and lgm 16 20 14c kyrs 19 24 calendar kyrs are 2 3 heavier than corresponding living specimens and indicate a regional cooling on the order of 4 5 c there is also an isotopic expression of the bolling pre boreal climate oscillation with values reflecting a cooling during the younger dryas seasonality a key diagnostic of the state of the climate system remained the same or slightly less than present and indicates that the observed coolings were a change in the mean state of the western tropical atlantic pan tropic cooling during the last glaciation is best explained by a change in the radiative balance of the tropics variable tropical sea surface temperatures during climate oscillations such as the younger dryas challenge the paradigm that climate change only cascades from variations in north atlantic deep water production

banktop responses to quaternary fluctuations in sea level recorded in periplatform sediments periplatform sediment from a 12 m core recovered from northwest providence channel bahamas contains a geochemical and paleontological record of sea surface temperatures ice volumes and the response of banktops to highstands of sea level a comparison of these data suggests that fluctuations of carbonate mineralogy in periplatform sediments result from fluctuations of sea level and from patterns of banktop sedimentation highstands of sea level that flood carbonate platforms are recorded in periplatfonn sediments as abrupt increases of exported sr rich aragonite derived from banktop orgiuiisms superposed on a background of sr poor aragonite pteropods and calcite foraminifera and coccoliths derived from planktonic sources the pulses of banktop sediment coincide with increases of water temperature determined from foraminiferal assemblages and with decreases in ratios of oxygen isotopes indicating decreased ice volume and rising sea level following these abrupt changes is a more gradual decline in bank derived sediment although paleotemperatures from foraminiferal assemblages and oxygen isotopic data clearly show that warm conditions and a highstand of sea level persist we suggest that this decrease of offbank transport is part of autocyclic sedimentation patterns of shallow water carbonate environments offbank transport is restricted as reefs sand shoals and islands reach sea level also green algal production may decline because progradation of tidal flats decreases lagoon area and the hydrologic and ecologic conditions change as lagoons are filled

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

carbon isotopic changes in benthic foraminifera from the western south atlantic reconstruction of glacial abyssal circulation patterns oxygen and carbon isotopic analyses have been performed on the benthic foraminifer planulina wuellerstorfi in seven late quaternary cores from the vema channel rio grande rise region the cores are distributed over the water depth interval of 2340 to 3939 m which includes the present transition from north atlantic deep water nadw to antarctic bottom water aabw the carbon isotopic records in the cores vary as a function of water depth the shallowest and deepest cores show no significant glacial interglacial difference in 13c four of the five cores presently located in the nadw have benthic foraminiferal 13c that is lower during glacial isotopic stages based on bathymetric gradients in 13c we conclude that like today there were two water masses present in the vema channel during glacial intervals a water mass enriched in 13c overlying another water mass depleted in 13c the largest gradient of change of 13c with depth however occurred at 2 7 km 1 km shallower than the present position of this gradient on the basis of paleontologic and sedimentologic evidence we consider it unlikely that the nadw aabw transition shallowed to this level reduced carbon isotopic gradients between the deep basins of the north atlantic and pacific oceans during the last glaciation suggest that production of nadw was reduced lower production of nadw may have modified the local abyssal circulation pattern in the vema channel region

florida straits density structure and transport over the last 8000 years 1 the density structure across the florida straits is reconstructed for the last 8000 years from oxygen isotope measurements on foraminifera in sediment cores the oxygen isotope measurements suggest that the density contrast across the florida current increased over this time period the magnitude of this change corresponds to an increase in the geostrophic transport referenced to 800 m water depth of 4 sverdrups sv over the last 8000 years the spatial and seasonal distribution of incoming solar radiation due to changes in the earth s orbit has caused systematic changes in the atmospheric circulation including a southward migration of the intertropical convergence zone over the last 8000 years these changes in atmospheric circulation and the associated wind driven currents of the upper ocean could readily account for a 4 sv increase in the strength of the florida current we see no evidence in our data for dramatic changes in the strength of the atlantic meridional overturning circulation over this time period

deep pacific caco 3 compensation and glacial interglacial atmospheric co 2 abstract benthic foraminiferal 13c suggests that there was a net shift of isotopically light metabolic co2 from the upper ocean into the deep ocean during the last glacial period according to the caco3 compensation hypothesis this should have caused a transient drop in deep ocean co32 that was eventually reversed by seafloor dissolution of caco3 the resulting increase in whole ocean ph may have had a significant impact on atmospheric co2 compounding any decrease that was due to the initial vertical co2 shift the opposite hypothetically occurred during deglaciation when co2 was returned to the upper ocean and atmosphere and deep ocean co32 temporarily increased followed by excess burial of caco3 and a drop in whole ocean ph the deep sea record of caco3 preservation appears to reflect these processes with the largest excursion during deglaciation as expected but various factors make quantification of deep sea paleo co32 difficult here we reconstruct deep equatorial pacific co32 over the last glacial interglacial cycle using benthic foraminiferal zn ca which is strongly affected by saturation state during calcite precipitation our data are in agreement with the caco3 compensation theory including glacial co32 concentrations similar to or slightly lower than today and a termination i co32 peak of 25 30 mol kg 1 the deglacial co32 rise precedes ice sheet melting consistent with the timing of the atmospheric co2 rise a later portion of the peak could reflect removal of co2 from the atmosphere ocean system due to boreal forest regrowth caco3 compensation alone may explain more than one third of the atmospheric co2 lowering during glacial times

field examination of the oceanic carbonate ion effect on stable isotopes in planktonic foraminifera we determined the 18o and 13c of individual globigerinoides ruber and pulleniatina obliquiloculata from sediment traps located from 5 n to 12 s along 140 w in the pacific ocean to evaluate the effects of varying co3 on shell 18o and 13c variations in the offset between shell 13c and 13cdic 13cs dic are attributed to differences in co3 temperature and shell size between sample sites when 13cs dic of g ruber was corrected for variations in co3 using the experimental slope of bijma et al 1998 the residual 13cs dic was correlated with mixed layer temperature 0 10 0 04 c 1 the slope of this temperature effect is consistent with experimental results in p obliquiloculata 13cs dic and temperature were strongly anticorrelated 0 14 0 03 c 1 we are unable to separate the influences of co3 and temperature in this species without independent experimental data correcting for co3 variability on 18os of g ruber improves the accuracy of estimated sea surface temperatures

southwest atlantic water mass evolution during the last deglaciation the rise in atmospheric co2 during heinrich stadial 1 hs1 14 5 17 5 kyr b p may have been driven by the release of carbon from the abyssal ocean model simulations suggest that wind driven upwelling in the southern ocean can liberate 13c depleted carbon from the abyss causing atmospheric co2 to increase and the 13c of co2 to decrease one prediction of the southern ocean hypothesis is that water mass tracers in the deep south atlantic should register a circulation response early in the deglaciation here we test this idea using a depth transect of 12 cores from the brazil margin we show that records below 2300 m remained 13c depleted until 15 kyr b p or later indicating that the abyssal south atlantic was an unlikely source of light carbon to the atmosphere during hs1 benthic 18o results are consistent with abyssal south atlantic isolation until 15 kyr b p in contrast to shallower sites the depth dependent timing of the 18o signal suggests that correcting 18o for ice volume is problematic on glacial terminations new data from 2700 to 3000 m show that the deep sw atlantic was isotopically distinct from the abyss during hs1 as a result we find that mid depth 13c minima were most likely driven by an abrupt drop in 13c of northern component water low 13c at the brazil margin also coincided with an 80 decrease in 14c our results are consistent with a weakening of the atlantic meridional overturning circulation and point toward a northern hemisphere trigger for the initial rise in atmospheric co2 during hs1

pelagic sedimentation on an inactive gullied slope northwest providence channel bahamas abstract the southern flank of little bahama bank is a deep water carbonate slope into which a series of closely spaced canyons 10 200 m deep have been cut it is similar in morphology to many other slopes in the bahamas and these slopes are generally considered to be created by the erosion of downslope sediment gravity flows however little evidence for downslope sediment movement or associated erosion were found in the holocene or latest pleistocene sediments of the slope reported on here the sediments from water depths below 260 m consist of a uniform pelagic drape covering both the gullies and inter gully ridge tops high resolution seismic reflectors are not truncated along individual gully walls and the fine scale stratigraphy of the sediments recorded in glacial interglacial changes in the aragonite calcite ratio of the sediments is preserved in sediments from gullies and ridge tops it appears that for the last two to three glacial cycles there has been only minor downslope transport of sediment despite the gullied morphology erosion is not presently occurring on the slope

improved oxygen isotope temperature calibrations for cosmopolitan benthic foraminifera abstract despite decades of use as a paleoceanographic proxy considerable uncertainty still surrounds the temperature dependence of benthic foraminiferal 18o widely applied paleotemperature equations may mix non equilibrium foraminifera with equilibrium synthetic calcite resulting in temperature sensitivities that are too large warm water foraminiferal calibrations may give temperature sensitivities that are too small for very cold waters here we combine new core top measurements from the florida straits and the arctic ocean with published data to derive new 18o temperature relationships for three groups of benthic foraminifera we derive a quadratic equation for cibicidoides and planulina that agrees well with equilibrium synthetic calcite and that should be applicable over all oceanographic temperatures we find that uvigerina is not at equilibrium and is isotopically heavier than cibicidoides and planulina by 0 47 in contrast to the historically used 0 64 hoeglundina elegans is further enriched and appears to be slightly heavier than equilibrium aragonite finally we discuss the implications of the florida straits observations for the hypothesis that benthic foraminifera precipitate their shells from a ph dependent mixture of bicarbonate and carbonate ions

depth profiles of δ13c in bottom water and core top c wuellerstorfi on the ontong java plateau and emperor seamounts we have measured the carbon isotopic composition of dissolved inorganic carbon in bottom waters of the ontong java plateau western equatorial pacific and on the northern emperor seamounts northwest pacific each of these locations is several hundred miles from the nearest geochemical ocean sections study geosecs stations and the observed 13c values at each site differ substantially from regionally averaged geosecs 13c profiles we discuss the possible causes of these differences including horizontal variability near bottom effects and problems with the pacific geosecs 13c data we also measured the isotopic composition c and o of core top c wuellerstorfi from a depth transect of cores at each location the 18o data are used to verify that our samples are holocene comparison of foraminiferal and bottom water 13c values shows that this species faithfully records bottom water 13c at both sites and demonstrates that there is no depth related artifact in the dissolved inorganic carbon c wuellerstorfi 13c relationship at these sites

thermodynamic influences on the marine carbon isotope record air sea exchange represents an important controlling factor for the distribution of carbon isotopes in the modern ocean even below the surface mixed layer here we show that this thermodynamic influence varies between water masses with a magnitude which is large relative to the amplitude of typical deep sea sediment 13c records thus changes in air sea exchange processes must be regarded as a significant source of variability for any marine 13c signal

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

enhanced ventilation of the north atlantic subtropical gyre thermocline during the last glaciation the ocean s intermediate1 6 and deep7 8 circulation are both known to have differed during the last glaciation from those of today but little is known about the history of the subtropical gyres variations in gyre processes should be closely linked to variations in global climate as gyre circulation is driven by air sea interactions and reflects the climate at the ocean surface the gyres are also a significant reservoir of carbon and nutrients so that gyre processes affect the distribution of carbon and nutrients in the oceans and thus atmospheric co2 here we use measurements of 13c and 18o in foraminifera from the bahamas to produce a detailed reconstruction of nutrient and temperature profiles in the thermocline during the last glaciation the thermocline of the glacial north atlantic subtropical gyre lacked the oxygen minimum that is characteristic of the modern ocean and was depleted in nutrients indicating greater more uniform thermocline ventilation at that time thus not only intermediate waters1 5 but the entire upper water column within the glacial north atlantic was depleted of nutrients moreover glacial thermocline waters were cooler had a steeper temperature gradient and a shallower base both the ventilation and the thermal structure of the glacial thermocline are consistent with what is known of the glacial climate9 14

glacial versus interglacial sedimentation rates and turbidite frequency in the bahamas the southern tongue of the ocean is a 1300 m deep flat floored basin in the bahamas that receives large amounts of sediment from the carbonate platforms surrounding it on three sides we have examined five 8 13 m long piston cores and determined bulk sedimentation rates turbidite frequency and turbidite accumulation rates for the past two glacial and interglacial periods the mean of bulk sedimentation rates is four to six times higher in interglacial periods average accumulation rates of recognizable turbidites are higher by a factor of 21 to 45 and interglacial turbidite frequency is higher by a factor of 6 to 14 sediment composition indicates that increased interglacial rates are due to higher accumulation of platform derived material additional data from other bahamian basins as well as published material from the caribbean strongly suggest that highstand shedding is a general trend in pure carbonate depositional systems carbonate platforms without a siliciclastic component export more material during highstands of sea level when the platform tops are flooded and produce sediment the response of carbonate platforms to quaternary sea level cycles is opposed to that of siliciclastic ocean margins where sediment is stored on the inner shelf during highstands and passed on to continental rises and abyssal plains during lowstands of sea level

deepwater circulation on blake outer ridge western north atlantic during the holocene younger dryas and last glacial maximum three depth transects containing a total of 33 sediment cores were investigated along the blake outer ridge in the western subtropical north atlantic sortable silt mean grain size and stable isotope records were used to assess the position and relative intensity of the western boundary undercurrent wbuc during the holocene the last glacial maximum lgm and the younger dryas yd intervals the holocene reconstruction is consistent with modern physical and chemical hydrographic measurements in the area suggesting a deep position for the fast flowing core of the wbuc 3000 4000 m deepening to 4500 m water depth on the ridge flanks and a water column dominated by north atlantic deep water nadw the lgm and yd reconstructions show that a comparable hydrographic regime was present during both these intervals suggesting a similar mode of circulation that was appreciably different from the holocene reconstruction the wbuc s zone of maximum flow speed during these intervals is suggested to have shifted above 2500 m water depth consistent with nutrient depleted glacial north atlantic intermediate water formation with an increasing influence of southern source water ssw beneath below 4000 m water depth results hint at increased ssw flow vigor during both the lgm and yd with higher flow speeds than during the holocene this study provides a framework for aiding the interpretation of time series records of paleocurrent flow speed changes in the region of the wbuc

topographic modification of the florida current by little bahama and great bahama banks abstract the effect of local topography in modifying the structure and variability of the florida current is examined using shipboard acoustic doppler and pegasus acoustic current profiler data pegasus absolute velocity data were obtained during 16 cruises in the florida current at 27 n as part of the subtropical atlantic climate studies stacs program the ensemble average of all pegasus velocity data shows that the effect of the constriction imposed on the mean florida current by little bahama bank can be detected up to 30 km into the straits of florida a simple model is proposed to explain how this effect can produce the subsurface maximum of northward flow commonly observed in the eastern straits pegasus and acoustic doppler data obtained during the march 1984 stacs cruise are used to describe the temporal and spatial variability of the flow it is shown that intermittent southward flow can exist in a band 10 15 km wide off little bahama bank one such event was detected during this cruise the p

oxygen isotope constraints on surface ocean temperatures published oxygen isotope results from benthic and planktonic foraminifera are used to constrain the extent to which surface ocean temperatures in the tropics changed between glacial and interglacial time the possible impacts of bioturbation and of the redistribution of 18o16o ratios within the sea putting aside the oxygen isotope results are consistent with the climap project conclusion that tropical ocean temperatures remained within 2 c of their present value

quantitative interpretation of atmospheric carbon records over the last glacial termination 1 the glacial interglacial rise in atmospheric pco2 is one of the best known changes in paleoclimate research yet the cause for it is still unknown forcing the coupled ocean atmosphere biosphere box model of the global carbon cycle bicycle with proxy data over the last glacial termination we are able to quantitatively reproduce transient variations in pco2 and its isotopic signatures 13c 14c observed in natural climate archives the sensitivity of the box model of the isotopic carbon cycle bicycle to high or low latitudinal changes is comparable to other multibox models or more complex ocean carbon cycle models respectively the processes considered here ranked by their contribution to the glacial interglacial rise in pco2 in decreasing order are the rise in southern ocean vertical mixing rates 30 ppmv decreases in alkalinity and carbon inventories 30 ppmv the reduction of the biological pump 20 ppmv the rise in ocean temperatures 15 20 ppmv the resumption of ocean circulation 15 20 ppmv and coral reef growth 5 ppmv the regrowth of the terrestrial biosphere sea level rise and the increase in gas exchange through reduced sea ice cover operate in the opposite direction decreasing pco2 during termination i by 30 ppmv according to our model the sequence of events during termination i might have been the following a reduction of aeolian iron fertilization in the southern ocean together with a breakdown in southern ocean stratification the latter caused by rapid sea ice retreat trigger the onset of the pco2 increase after these events the reduced north atlantic deep water nadw formation during the heinrich 1 event and the subsequent resumption of ocean circulation at the beginning of the bolling allerod warm interval are the main processes determining the atmospheric carbon records in the subsequent time period of termination i we further deduce that a complete shutdown of the nadw formation during the younger dryas was very unlikely changes in ocean temperature and the terrestrial carbon storage are the dominant processes explaining atmospheric 13c after the bolling allerod warm interval

the mean circulation east of the bahamas as determined from a recent measurement program and historical xbt data abstract observational evidence from a two ship synoptic survey from one year long current measurements at four sites and from two independent long term expendable baththermograph xbt data sets is combined to describe the circulation east of the bahamas the results indicate that a weak antilles current actually exists at mid depths about 300 100 m with a northward transport along this boundary of about 4 106 m3 s 1 however both the dynamic height fields and water mass distributions suggest that this current does not represent return flow from the gyre wire sverdrup recirculation but instead is part of the northwestern gulf stream recirculation system west of about 50 w the near surface flow east of the bahamas is more complicated and consists of two isolated anticyclonic circulation cells along the boundary the most intense of these is centered just northeast of abaco island in the northern bahamas the southern weaker cell is centered at about 24 n 71 w in the area just north of puerto r

the ventilation of the world s oceans maps of the potential vorticity field abstract maps of potential vorticity q within four different density layers are presented for the north and south atlantic north and south pacific and indian oceans potential vorticity is evaluated as f 0 z a prescription that is valid for large slow scales and that allows its mapping from hydrographic data alone here f is the coriolis frequency p0 the potential density and z the vertical coordinate it is shown that the character of a layer within the thermocline of a subtropical gyre will vary greatly depending on the extent to which the layer is isolated from surface boundary conditions and forcing fluid particles recirculating within ventilated layers have their potential vorticity and other properties reset with virtually every circuit round the gyre when they pass through the outcrop zone by contrast particles within unventilated or dynamically isolated layers have time to share their properties with neighboring particles and approach a common homogenized state the north

deep sea ostracode species diversity response to late quaternary climate change late quaternary ostracode assemblages from the north atlantic ocean were studied to establish the effect of climatic changes of the past 210 000 yr marine oxygen isotope stages 7 1 on deep sea benthic biodiversity and faunal composition two hundred and twenty five samples from thechain 82 24 core 4pc 41o43 0 n 32o51 0 w 3427 m water depth on the western mid atlantic ridge revealed high amplitude fluctuations in ostracode abundance and diversity coincident with orbital and suborbital scale climate oscillations measured by several paleoceanographic proxy records during the past 210 000 yr ostracode biodiversity as measured by species number s and the shannon weaver index h s oscillated from h s d 0 4 during glacial periods marine isotope stages 6 5d 5b 4 and 2 to h s d 1 1 during interglacial and interstadial periods stages 7 5e 5c 5a 3 and 1 a total of 23 diversity peaks could be recognized eleven of these signify major periods of high diversity h s 0 8 sd 10 21 occurring every 15 20 ka twelve were minor peaks which may represent millennial scale diversity oscillations the composition of ostracode assemblages varies with krithe dominated assemblages characterizing glacial intervals and argilloecia cytheropteroncharacterizing deglacials and trachyleberid genera poseidonamicus echinocythereis henryhowella oxycythereis abundant during interglacials diversity and faunal composition changes can be matched to independent deep sea paleoceanographic tracers such as benthic foraminiferal carbon isotopes krithe trace elements mg ca ratios and to north atlantic region climate records such as greenland ice cores when interpreted in light of ostracode species ecology these faunal and diversity patterns provide evidence that deep sea benthic ecosystems experience significant reorganization in response to climate changes over orbital to millennial timescales published by elsevier science b v

testing the utility of paleonutrient proxies cd ca and zn ca in benthic foraminifera from thermocline waters 1 reconstruction of oceanic nutrient concentrations in the past provides information about nutrient cycling and physical circulation and the role these processes have played in past climate changes the cd ca and zn ca of benthic foraminifera have been used successfully to reconstruct past deep ocean nutrient concentrations in this study we test the ability of benthic foraminiferal cd ca and zn ca to detect changes in thermocline nutrient concentrations using a set of 31 multicores collected in the florida straits multicore sites span depths of 173 751 m estimated seawater cd concentrations of 0 02 0 42 nmol kg 1 and estimated seawater zn concentrations of 0 3 3 1 nmol kg 1 cd ca in several taxa of benthic foraminifera captures the regional differences and general shape of the nutricline on either side of the florida straits indicating that it is capable of resolving small changes in upper ocean nutrient concentrations in the past we estimate that the upper ocean partition coefficient for calcitic cd ca may be slightly higher than the established value low seawater zn concentrations combined with low partition coefficients and slight laboratory contamination severely complicated the evaluation of benthic foraminiferal zn ca however at least one species c pachyderma incorporates zn with a relatively high partition coefficient 22 minimizing these complications c pachyderma zn ca reflects the regional differences and general shape of the nutricline on either side of the florida straits and demonstrates potential for thermocline paleoceanography

13c record of benthic foraminifera in the last interglacial ocean implications for the carbon cycle and the global deep water circulation the 13c 12c ratios of upper holocene benthic foraminiferal tests genera cibicides and uvigerina of deep sea cores from the various world ocean basins have been compared with those of the modern total carbon dioxide tco2 measured during the geosecs program the 13c difference between benthic foraminifera and tco2 is 0 07 0 04 for cibicides and 0 83 0 07 for uvigerina at the 95 confidence level 13c analyses of the benthic foraminifera that lived during the last interglaciation isotopic substage 5e about 120 000 yr ago show that the bulk of the tco2 in the world ocean had a 13c value 0 15 0 12 lower than the modern one at the 95 confidence level reflecting a depletion compared to the present value of the global organic carbon reservoir regional differences in 13c between the various oceanic basins are explained by a pattern of deep water circulation different from the modern one the antarctic bottom water production was higher than today during the last interglaciation but the eastward transport in the circumpolar deep water was lower

distribution and circulation of labrador sea water abstract labrador sea water is the final product of the cyclonic circulation of subpolar mode water in the open northern north atlantic mccartney and talley 1982 the temperature and salinity of the convectively formed subpolar mode water decrease from 14 7 c 36 08 to 3 4 c 34 88 on account of the cumulative effects of excess precipitation and cooling the coldest mode water is labrador sea water which spreads at mid depths and is found throughout the north atlantic ocean north of 40 n and along its western boundary to 18 n a vertical minimum in potential vorticity is used as the primary tracer for labrador sea water labrador sea water is advected in three main directions out of the labrador sea 1 northeastward into the irminger sea 2 southeastward across the atlantic beneath the north atlantic current and 3 southward past newfoundland with the labrador current and thence westward into the slope water region crossing under the gulf stream off cape hatteras the labrador sea water core is

parameter study of a continuously stratified model of the ideal fluid thermocline the parameter sensitivity of a continuously stratified model of the ideal fluid thermocline in the subtropical gyre interior is studied a one dimensional advection diffusion model is used to set up a background stratification that can provide both the potential vorticity function for the unventilated thermocline and the mixed layer depth used in the ideal fluid thermocline model the wind driven circulation is treated as a perturbation to this background stratification although the perturbation solution excludes mixing diffusion the dynamic effect of diapycnal mixing is included in the unperturbed solution therefore the ideal fluid solution should correspond to a nonzero diffusion solution for the wind driven and thermohaline circulation in the ocean it is shown that the model can reproduce the thermocline structure which corresponds to either finite or infinitely weak mixing under the extreme weak diffusion limit the model produces a thermocline that looks like a step function in the stratification which separates the wind driven gyre above it and the stagnant abyssal water underneath it it is shown that the subduction rate and production of mode water with low potential vorticity are closely related to the stratification or the potential vorticity of the unventilated thermocline the geometry of the mixed layer the ekman pumping rate and the orientation of the intergyre boundary changes in the structure of the thermocline in response to different upper boundary conditions are explored it is found that cooling and southward migration of the jet stream induce the production of low potential vorticity mode water while changes in the vertical density profile have an appearance like the second baroclinic mode

glacial interglacial differences in circulation and carbon cycling within the upper western north atlantic we investigated glacial interglacial changes in the circulation and carbon cycling in the western north atlantic subtropical gyre using hydrographic data and downcore records of the stable isotopic compositions of individual shells of bahamian benthic foraminifera potential temperature salinity depth relations show that modern thermocline 200 1000 m and deep 1000 2000 m waters in the providence channels bahamas originate in the sargasso sea and are typical of the subtropical gyre gradients in the stable isotopic compositions of late holocene planulina and cibicidoides species from the bank margins 400 to 1500 m depth reflect temperature nutrient and isotopic gradients of modern subtropical gyre waters the difference between the 18o of glacial maximum and late holocene foraminifera is 2 1 for the upper 900 m of the water column and 1 6 for deeper waters indicating that these waters were 4 c and 2 c cooler respectively during glacial time the glacial temperature gradient dt dz was similar to today while the base of the thermocline was 100 m shallower these results differ significantly from our earlier results from multiple shell 18o analyses which implied upper thermocline waters were only 1 c cooler and dt dz was greater during the glacial maximum the difference occurs because bioturbation adversely affects multiple shell analyses of glacial aged samples from shallow water depths at all depths above 1500 m foraminiferal 13c are greater during the glacial maximum than the late holocene by at least 0 1 to 0 2 as much as 0 6 in the lower thermocline indicating that nutrient concentrations throughout the thermocline were reduced and there was no oxygen minimum zone during the glacial maximum this suggests greater more uniform ventilation of the thermocline results of single and multiple shell 13c analyses of glacial age foraminifera compare favorably because samples most affected by mixing correspond to water depths where the glacial interglacial change of 13c was small cooler upper ocean waters during the glacial maximum reflect cooler temperatures at the ocean surface where isopycnal surfaces outcrop including large areas of the subtropical ocean a shallower thermocline base is consistent with southward migration of the northern edge of the subtropical gyre or increased mode water production enhanced thermocline ventilation is consistent with more vigorous winds and all isopycnal surfaces outcropping in the area of ekman downwelling

u and th concentrations and isotope ratios in modern carbonates and waters from the bahamas the short residence times of th and pa in seawater make them very responsive to changes in the ocean environment we use a new multi ion counting technique to make th and pa isotope measurements in seawaters from a near shore environment in which oceanic chemical tracers are not overwhelmed by terrestrial inputs the bahamas an unusual feature of the bahamas setting is the shallow depth of water residing on the bank tops these waters have significantly lower 232th 230th 10 000 than those immediately adjacent to the banks 24 000 31 000 and a 231pa 230th near the production ratio 0 1 the change in 232th 230th and 231pa 230th on the bank tops is explained by almost quantitative removal of th and pa by scavenging and their replacement with a mixture of 230th and 231pa alpha recoiled from the underlying carbonates together with th from dust dissolution analysis of a water profile in the tongue of the ocean which separates the great and little bahama banks allows us to trace the movement of bank top water to depth a distinct minimum in both 232th 230th 13 000 and 231pa 230th 0 5 is observed at 430 m and is interpreted to reflect density cascading of bank top water with entrained carbonate sediment these results suggest that th and pa can be used as water mass tracers in near shore environments uranium concentration measurements on the same waters demonstrate that u is conservative across a range in salinity of 2 psu with a concentration of 3 33 ppb at a salinity of 35 the incorporation of u and th isotopes into marine carbonates has also been assessed by analyzing carbonate samples from the same location as these bahamas waters such incorporation is critical for u th geochronology u isotope analyses demonstrate that seawater 234u averages 146 6 and does not vary by more than 2 5 o and that carbonates capture this value additional high precision measurements 1 o on modern carbonates confirm that all oceans have identical 234u modern marine carbonates are shown to have 232th 230th ratios that reflect the local seawater in which they formed

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

a tritium box model of the north atlantic thermocline abstract a box model of 1972 tritium observations on isopycnal surface in the main thermocline of the north atlantic subtropical gyre is used to estimate the time scales and volume of exchange of the thermocline with respect to surface waters the flux of water between the surface and the thermocline implied by this model 40 106 m3 s 1 greatly exceeds the downward ekman pumping 8 106 m3 s 1 this suggests that mixing and convective overturning are the dominant mechanisms for exchange between surface waters and the interior geostrophic flow the flux rate is approximately the same size as conventions estimates of the sverdrup transport this suggests that ventilation of the thermocline may occur by recirculation combined with a very efficient exchange across the poleward boundary of the gyre

a geostrophic transport estimate for the florida current from the oxygen isotope composition of benthic foraminifera we present a new method for the quantitative reconstruction of upper ocean flows for during times in the past for the warm t 5 c surface ocean density can be accurately reconstructed from calcite precipitated in equilibrium with seawater as both of these properties increase with decreasing temperature and increasing salinity vertical density profiles can be reconstructed from the oxygen isotopic composition of benthic foraminifera the net volume transport between two vertical density profiles can be calculated using the geostrophic method using benthic foraminifera from surface sediment samples from either side of the florida straits florida keys and little bahama bank we reconstruct two vertical density profiles and calculate a volume transport of 32 sv using this method this agrees well with estimates from physical oceanographic methods of 30 32 sv for the mean annual volume transport we explore the sensitivity of this technique to various changes in the relationship between temperature and salinity as well as salinity and the oxygen isotopic composition of seawater

quaternary glacial and deglacial ostracoda in the thermocline of the little bahama bank nw atlantic palaeoceanographic implications abstract we determined faunal and oceanographic changes during the last glacial and deglacial in the providence channel little bahama bank lbb using modern ocean from lbb florida hatteras slope and blake plateau western north atlantic and late quaternary lbb distributions of the benthic ostracode genus krithe from the mid depth 300 1600 m subtropical north atlantic ocean nine species of krithe are limited in their bathymetric distribution by warm bottom water temperatures or a temperature related parameter in the thermocline of the modern atlantic during the last glacial interval in the northwest providence channel of the little bahama bank five species of krithe k aequabilis k dolichodeira k gr minima k reversa and k trinidadensis migrated upslope conversely during the deglaciation most krithe species migrated downslope re occupying their deeper niches these vertical species migrations are attributed to decreased glacial bottom water temperatures and perhaps increased dissolved oxygen during the last glacial and warmer water temperatures during the deglacial based upon thermal values of recent depth ranges of selected species of krithe we estimate that glacial waters cooled about 4 c shallower than 900 m and about 2 c deeper than 900 m and deglacial waters warmed about the same values in shallow and mid depth water masses comparing to modern temperatures the discovery of common halocypris a mesopelagic ostracode in little bahama bank glacial and deglacial sediments also suggests greater oxygenation relative to the late holocene

carbon and oxygen isotopic disequilibria of recent deep sea benthic foraminifera abstract the carbon and oxygen isotopic compositions of 149 samples of benthic foraminifera from deep sea core tops indicate that none of the nine species studied secrete calcium carbonate in isotopic equilibrium with ambient bottom water uvigerina pyrgo murrhina and oridorsalis tener are the closest to 18o equilibrium with average deviations about 0 4 while planulina wuellerstorfi and p murrhina are the closest to 13c equilibrium with average deviations about 1 p wuellerstorfi shows the most systematic relationship between 13c and bottom water apparent oxygen utilization the intraspecific variabilities in 18o and 13c suggest that estimates of bottom water paleotemperatures can be made to a precision of 0 7 c while estimates of past apparent oxygen utilization aou can be made to 35 mol kg based on intraspecific comparisons of the recent samples with fossils no temporal changes in the degree of either 18o or 13c disequilibrium have been detected for planulina wuellerstorfi uvigerina oridorsalis tener and globocassidulina subglobosa

thermohaline instability in the north atlantic during meltwater events stable isotope and ice rafted detritus records from core so75 26kl portuguese margin a benthic isotope record has been measured for core so75 26kl from the upper portuguese margin 1099 m water depth to monitor the response of thermohaline overturn in the north atlantic during heinrich events evaluating benthic 18o in ts diagrams in conjunction with equilibrium c fractionation implies that advection of mediterranean outflow water mow to the upper portuguese margin was significantly reduced during the last glacial 15 compared to 30 today the benthic isotope record along core so75 26kl therefore primarily monitors variability of glacial north atlantic conveyor circulation the 14c accelerator mass spectrometry ages of 13 54 07 and 20 46 12 ka for two ice rafted detritus ird layers in the upper core section and an interpolated age of 36 1 ka for a third ird layer deeper in the core are in the range of published 14c ages for heinrich events h1 h2 and h4 marked depletion of benthic 13c by 0 7 1 1 during the heinrich events suggests reduced thermohaline overturn in the north atlantic during these events close similarity between meltwater patterns inferred from planktonic 18o at site 609 and ventilation patterns inferred from benthic 13c in core so75 26kl implies coupling between thermohaline overturn and surface forcing as is also suggested by ocean circulation models benthic 13c starts to decrease 1 5 2 5 kyr before heinrich events hl and h4 fully increased values are reached 1 5 3 kyr after the events indicating a successive slowdown of thermohaline circulation well before the events and resumption of the conveyor s full strength well after the events benthic 13c changes in the course of the heinrich events show subtle maxima and minima suggesting oscillatory behavior of thermohaline circulation a distinct feature of thermohaline instability in numerical models inferrred gradual spin up of thermohaline circulation after hl and h4 is in contrast to abrupt wanning in the north atlantic region that is indicated by sudden increases in greenland ice core 18o and in marine faunal records from the northern north atlantic from this we infer that thermohaline circulation can explain only in part the rapid climatic oscillations seen in glacial sections of the greenland ice core record

regional and global benthic δ18o stacks for the last glacial cycle although detailed age models exist for some marine sediment records of the last glacial cycle 0 150 ka age models for many cores rely on the stratigraphic correlation of benthic 18o which measures ice volume and deep ocean temperature change the large amount of data available for the last glacial cycle offers the opportunity to improve upon previous benthic 18o compilations such as the lr04 global stack not only are the age constraints for the lr04 stack now outdated but a single global alignment target neglects regional differences of several thousand years in the timing of benthic 18o change during glacial terminations here we present regional stacks that characterize mean benthic 18o change for 8 ocean regions and a volume weighted global stack of data from 263 cores age models for these stacks are based on radiocarbon data from 0 to 40 ka correlation to a layer counted greenland ice core from 40 to 56 ka and correlation to radiometrically dated speleothems from 56 to 150 ka the regional 18o stacks offer better stratigraphic alignment targets than the lr04 global stack and furthermore suggest that the lr04 stack is biased 1 2 kyr too young throughout the pleistocene finally we compare global and regional benthic 18o responses with sea level estimates for the last glacial cycle

reduced north atlantic central water formation in response to early holocene ice sheet melting central waters of the north atlantic are fundamentalfor ventilation of the upper ocean and are also linked tothe strength of the atlantic meridional overturning circula tion amoc here weshowbasedonbenthic foraminiferalmg ca ratios that during times of enhanced melting fromthe laurentide ice sheet lis between 9 0 8 5 thousandyears before present ka the production of central watersweakened the upper amoc resulting in a cooling overthenorthernhemisphere centeredat8 54 0 2kaand8 24 0 1 ka our dataset records two 150 year coolingevents in response to the drainage of lake agassiz ojibway indicating early slow down of the upper amoc in responseto the initial freshwater flux into the subpolar gyre spg followed by a more severe weakening of both the upperand lower branches of the amoc at 8 2 ka these resultshighlight the sensitivity of regional north atlantic climatechange to the strength of central water overturning andexemplify the impact of both gradual and abrupt freshwaterfluxes on eastern spg surface water convection in light ofthe possible future increase in greenland ice sheet meltingdue to global warming these findings may help us to betterconstrain and possibly predict future north atlantic climatechange

the north atlantic tritium distribution in 1972 the distribution of tritium in the north atlantic in 1972 is compared with the distribution of salinity and the first order potential voracity as mapped on six constant potential density surfaces in the north atlantic the picture presented suggests an advective transport regime which is consistent with currently developing notions of the large scale gyre structure lateral mixing along isopycnals appears to be important in the northwestern region of the subtropical gyre and vertical cross isopycnal mixing needs to be invoked only in near surface layers

glacial deep water carbonate chemistry inferred from foraminiferal mg ca a case study from the western tropical atlantic we explore using changes in planktonic foraminiferal mg ca with water depth in a single region to infer relative changes in deep water carbonate chemistry the mg ca ratio in foraminiferal calcite is quantitatively lowered by dissolution we exploit this dissolution effect to generate a profile of carbonate ion concentration co32 for the deep waters of the tropical atlantic during the last glacial maximum we generated mg ca data for three species g ruber g sacculifer and n dutertrei from three cores located along a depth transect 2 8 to 4 0 km on the ceara rise in the western equatorial atlantic we attribute lower mg ca in glacial intervals from the shallow core to changes in sea surface temperature sst the even lower glacial mg ca values in the deeper cores are attributed to dissolution and are used to reconstruct a paleo co32 profile our down core mg ca data for g ruber and g sacculifer confirm that these species are more resistant to mg loss due to dissolution than n dutertrei the greater susceptibility of n dutertrei s mg content to dissolution limits the utility of this species in thermocline temperature reconstructions to cores above the lysocline but significant to this study makes n dutertrei useful in quantifying changes in deep water co32 our paleo co32 reconstruction based on n dutertrei suggests the last glacial maximum co32 gradient in the atlantic was much steeper than today implying that the boundary between deepwater masses in the atlantic was shallower during the last glacial maximum our results suggest comparison of mg ca from multiple cores from one region could similarly provide constraints on changes in carbonate chemistry in other basins and other time periods

3h and 3he in the beta triangle observations of gyre ventilation and oxygen utilization rates abstract isopycnal maps of 3h 3he age with about 100 km resolution have been obtained for a 1000 km scale area in the eastern subtropical north atlantic the midscale texture of the maps is consistent with isopycnal diffusivities of order 500 m 2 s 1 analysis of the distributions within the context of advection diffusion equations reveals that the larger scale 3h 3he age gradients observed within the area are not seriously affected by mixing on those surfaces that outcrop in the region of ekman downwelling thus isopycnal velocities can be estimated from 1 but record only the velocity component normal to the outcrop the velocities thus obtained agree well with geostrophic estimates although the comparison is flawed by the fundamental mismatch in timescales between the two techniques backward extrapolation of the maps to zero age outcrop positions indicate that the contribution of unventilated older recirculated water to the gyre flow above 600 m depth is small in this area no more than 20

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

modeling the water masses of the atlantic ocean at the last glacial maximum 1 we produced gridded monthly sea surface boundary conditions for the atlantic ocean at the last glacial maximum lgm based on the sea surface temperature reconstruction of the glamap project we used an ocean general circulation model ogcm subject to these sea surface boundary conditions and a corresponding wind stress field from an atmospheric general circulation model to study the differences in the distribution of the main water masses between the lgm and the present our global ogcm is characterized by high vertical resolution low vertical diffusion and isopycnal mixing and hence allows for a realistic representation of the hydrology and circulation of the modern atlantic ocean according to a series of lgm experiments with an increasing sea surface salinity anomaly in the weddell sea the ventilated thermocline was colder than today by 2 3 c in the north atlantic ocean and in the experiment with the largest anomaly 1 0 beyond the global anomaly by 4 5 c in the south atlantic ocean its depth was reduced by 50 m on average most notably in the tropics in the north atlantic ocean the outcrop locations of the thermocline isopycnal surfaces migrated southward by 5 10 and the ventilation increased in the south atlantic ocean the mixed layer and thermocline water masses were dominated by cold water originating from drake passage and the import of warm water from the indian ocean was reduced to about 4 sv or 40 of its modern value antarctic intermediate water was colder by 3 4 c and could be traced as far as 10 n the meridional overturning rates of north atlantic deep water nadw and antarctic bottom water aabw in the atlantic ocean were similar to those of the present day experiment 9 10 sv and 4 sv respectively however nadw cooled by 2 5 c and aabw by 1 c aabw was near the freezing point of seawater at the surface and the saltiest water mass in the atlantic ocean even saltier than nadw we show that the differences between the lgm and the present day experiments can be traced back to the changes in the subpolar and interhemispheric sea surface density gradients

quaternary aragonite cycles and oxygen isotope record in bahamian carbonate ooze carbonate ooze in bahamian troughs displays cyclic variation in the content of aragonite a 10 m core devoid of turbidites shows 3 5 cycles each defined by a sharp increase followed by a gradual decrease of aragonite the aragonite curve matches closely the oxygen isotope curve of planktic foraminifera from the same core aragonite highs correspond to light oxygen isotope values and thus to interglacial stages content of terrigenous material is low during interglacials and higher during glacial periods intermittent flooding and exposure of the bahama banks is most probably not the cause of the cycles because the latest increase in aragonite precedes bank flooding by 8 000 yr and because the cycles are distinctly asymmetric with rapid increase and gradual decrease of aragonitic content carbonate dissolution cycles tied to the glacial rhythm of earth9s climate are a more likely explanation of the variations in aragonite content

response of eastern tropical atlantic central waters to atlantic meridional overturning circulation changes during the last glacial maximum and heinrich stadial 1 shows a mg ca temperature sensitivity of 0 19 mmol mol perc estimates of the lgm and hs1 thermocline temperatures are comparable to the present day values between 200 and 400 m water depth but were 1 2 1 5 c warmer at 550 570 m depth the hs1 thermocline waters 200 570 m depth did not show any warming relative to the lgm this is in contrast to previous climate model studies which concluded that tropical atlantic thermocline waters warmed significantly when atlantic meridional overturning circulation was reduced however our results suggest that thermocline temperatures of the northeastern tropical atlantic show no pronounced sensitivity to changes in the thermohaline circulation during glacial periods in contrast we find a significant increase in thermocline water salinity during the lgm 200 550 m depth and hs1 200 400 m depth with respect to the present day which we relate to changes in the wind driven circulation we infer that the lgm thermocline 200 550 m depth and the hs1 upper thermocline 200 400 m depth in the northeastern tropical atlantic was ventilated by surface waters from the north atlantic rather than the southern sourced waters this suggests that the frontal zone between the modern south atlantic and north atlantic central waters was probably shifted southward during the lgm and hs1

changes in north atlantic deep sea temperature during climatic fluctuations of the last 25 000 years based on ostracode mg ca ratios 1 we reconstructed three time series of last glacial to present deep sea temperature from deep and intermediate water sediment cores from the western north atlantic using mg ca ratios of benthic ostracode shells although the mg ca data show considerable variability scatter that is common to single shell chemical analyses comparisons between cores between core top shells and modern bottom water temperatures bwt and comparison to other paleo bwt proxies among other factors suggest that multiple shell average mg ca ratios provide reliable estimates of bwt history at these sites the bwt records show not only glacial to interglacial variations but also indicate bwt changes during the deglacial and within the holocene interglacial stage at the deeper sites 4500 and 3400 m water depth bwt decreased during the last glacial maximum lgm the late holocene and possibly during the younger dryas maximum deep sea warming occurred during the latest deglacial and early holocene when bwt exceeded modern values by as much as 2 5 c this warming was apparently most intense around 3000 m the depth of the modern day core of north atlantic deep water nadw the bwt variations at the deeper water sites are consistent with changes in thermohaline circulation warmer bwt signifies enhanced nadw influence relative to antarctic bottom water aabw thus maximum nadw production and associated heat flux likely occurred during the early holocene and decreased abruptly around 6500 years b p a finding that is largely consistent with paleonutrient studies in the deep north atlantic bwt changes in intermediate waters 1000 m water depth of the subtropical gyre roughly parallel the deep bwt variations including dramatic mid holocene cooling of around 4 c joint consideration of the mg ca based bwt estimates and benthic oxygen isotopes suggests that the cooling was accompanied by a decrease in salinity at this site subsequently intermediate waters warmed to modern values that match those of the early holocene maximum of 7 c intermediate water bwt changes must also be driven by changes in ocean circulation these results thus provide independent evidence that supports the hypothesis that deep ocean circulation is closely linked to climate change over a range of timescales regardless of the mean climate state more generally the results further demonstrate the potential of benthic mg ca ratios as a tool for reconstructing past ocean and climate conditions

mid pliocene deep sea bottom water temperatures based on ostracode mg ca ratios abstract we studied magnesium calcium mg ca ratios in shells of the deep sea ostracode genus krithe from a short interval in the middle pliocene between 3 29 and 2 97 ma using deep sea drilling sites in the north and south atlantic in order to estimate bottom water temperatures bwt during a period of climatic warmth results from dsdp and odp sites 552a 610a 607 658a 659a 661a and 704 for the period ma reveal both depth and latitudinal gradients of mean mg ca values shallower sites 552a 610a and 607 have higher mean mg ca ratios 10 3 9 7 10 1 mmol mol than deeper sites 661a 6 3 mmol mol and high latitude north atlantic sites 552a 610a 607 have higher mg ca ratios than low latitude 658a 9 8 mmol mol 659a 7 7 mmol mol 661a 6 3 mmol mol and southern ocean 704 8 0 mmol mol sites converting mg ca ratios into estimated temperatures using the calibration of dwyer et al 1995 dwyer g s cronin t m baker p a raymo m e buzas j s correge t 1995 north atlantic deepwater temperature change during late pliocene and late quaternary climatic cycles science 270 1347 1351 suggests that mean middle pliocene bottom water temperatures at the study sites in the deep atlantic were about the same as modern temperatures however brief pulses of elevated bwt occurred several times between 3 29 and 2 97 ma in both the north and south atlantic ocean suggesting short term changes in deep ocean circulation

suborbital intermediate water variability inferred from paired benthic foraminiferal cd ca and δ13c in the tropical west atlantic and linking with north atlantic climates abstract paired benthic cd ca and 13c records have been generated along core m35003 in the western tropical atlantic decreased glacial water column dissolved cadmium cdw and increased benthic 13c indicate enhanced ventilation with nutrient deplete intermediate waters in line with similar inferences from other north atlantic mid depth records an abrupt early deglacial 13c collapse that is associated with a marked positive cdw anomaly indicates a transient collapse of mid depth ventilation from north atlantic sources conceivably in conjunction with the h1 meltwater anomaly the cdw record displays fine scale fluctuations that mimic the greenland dansgaard oeschger d o cycles and show decreased cdw during stadials this pattern is opposite to cdw variations in a deep water record from bermuda rise that display increased cdw concentrations during stadials the divergent pattern between mid depth and deep water cdw records indicates millennial scale switches between deep and shallow convection in the glacial north atlantic at the pace of the d o climatic cycles several high amplitude anomalies occur in the cdw record that reach levels similar to those observed today in the north pacific while a substantial nutrient increase in the mid depth north atlantic cannot be ruled out during these events changes of pore water chemistry and cd p fractionation during biological uptake offer alternative scenarios to explain the peak cdw maxima

the dynamics of the oceanic subtropical gyres recent theoretical advances in physical oceanography have produced plausible models for the structure of the circulation in the oceans subtropical gyres these theoretical ideas are reviewed and assessed in the light of present observational evidence the dominant role of potential vorticity is emphasized in describing the strong interplay between three dimensional distributions of density and velocity in particular the complementary processes of subduction and recirculation jointly act to shape the circulation pattern of the subtropical gyre

the future of earth s oceans consequences of subduction initiation in the atlantic and implications for supercontinent formation subduction initiation is a cornerstone in the edifice of plate tectonics it marks the turning point of the earth s wilson cycles and ultimately the supercycles as well in this paper we explore the consequences of subduction zone invasion in the atlantic ocean following recent discoveries at the sw iberia margin we discuss a buoyancy argument based on the premise that old oceanic lithosphere is unstable for supporting large basins implying that it must be removed in subduction zones as a consequence we propose a new conceptual model in which both the pacific and the atlantic oceans close simultaneously leading to the termination of the present earth s supercycle and to the formation of a new supercontinent which we name aurica our new conceptual model also provides insights into supercontinent formation and destruction supercycles proposed for past geological times e g pangaea rodinia columbia kenorland

a simulation of bomb tritium entry into the atlantic ocean abstract tritium is used in a model calibration study that is aimed at developing three dimensional ocean circulation and mixing models for climate and geochemical simulations the north atlantic tritium distribution is modeled using a three dimensional advective field predicted by a primitive equation ocean circulation model the effect of wintertime convection is parameterized by homogenizing the tracer to the observed march mixed layer depth mixing is parameterized by horizontal and vertical fickian diffusivities of 5 10 6 cm2 s 1 and 0 5 cm2 s 1 respectively the spreading of tritium in the model is dominated by advection in the horizontal and by wintertime convection and advection in the vertical the horizontal and vertical mixing provided by the model have negligible effect a comparison of the model tracer fields with observations shows that most of the basic patterns of the tritium field are reproduced the model s mean vertical penetration of 543 m in 1972 is comparable to the 592 m penetra

florida current surface temperature and salinity variability during the last millennium surface water d 18 ow near dry tortugas increased 0 4 during the course of the little ice age lia 1200 1850 a d equivalent to a salinity increase of 0 8 1 5 on the great bahama bank where surface waters are influenced by the north atlantic subtropical gyre d 18 ow increased by 0 3 during the last 200 years although a portion 0 1 of this shift may be an artifact of anthropogenically driven changes in surface water sco2 the remaining d 18 ow signal implies a 0 4 1 increase in salinity after 200 years b p the simplest explanation of the d 18 ow data is southward migration of the atlantic hadley circulation during the lia scaling of the d 18 ow records to salinity using the modern low latitude d 18 ow s slope produces an unrealistic reversal in the salinity gradient between the two sites only if d 18 ow is scaled to salinity using a high latitude d 18 ow s slope can the records be reconciled variable atmospheric 14 c paralleled dry tortugas d 18 ow suggesting that solar irradiance paced centennial scale migration of the inter tropical convergence zone and changes in florida current salinity during the last millennium citation lund d c and w curry 2006 florida current surface temperature and salinity variability during the last millennium paleoceanography 21 pa2009 doi 10 1029 2005pa001218

weaker gulf stream in the florida straits during the last glacial maximum as it passes through the florida straits the gulf stream consists of two main components the western boundary flow of the wind driven subtropical gyre and the northward flowing surface and intermediate waters which are part of the global conveyor belt compensating for the deep water that is exported from the north atlantic ocean1 the mean flow through the straits is largely in geostrophic balance and is thus reflected in the contrast in seawater density across the straits2 here we use oxygen isotope ratios of benthic foraminifera which lived along the ocean margins on the boundaries of the florida current during the last glacial maximum to determine the density structure in the water and thereby reconstruct transport through the straits using the geostrophic method a technique which has been used successfully for estimating present day flow3 our data suggest that during the last glacial maximum the density contrast across the florida straits was reduced with the geostrophic flow referenced to the bottom of the channel at only about two thirds of the modern value if the wind driven western boundary flow was not lower during the last glacial maximum than today these results indicate a significantly weaker conveyor belt component of the gulf stream compared to present day values whereas previous studies based on tracers suggested that deep waters of north atlantic origin were not widespread during glacial times indicating either a relatively weak or a shallow overturning cell our results provide evidence that the overturning cell was indeed weaker during glacial times

sea level and surface water change in the western north atlantic across the oligocene miocene transition a palynological perspective from iodp site u1406 newfoundland margin abstract the oligocene miocene transition omt 23 1 ma terminates the late oligocene warming trend and is marked by a transient large amplitude expansion of antarctic ice sheets the associated glacial maximum which is expressed by a 1 positive shift in benthic foraminiferal oxygen isotope values is commonly referred to as the mi 1 isotope event whereas the causes for the glacial maximum at the omt are intrinsically connected to southern hemisphere ice sheet dynamics the behavior of the surface ocean in the northern hemisphere during this time is poorly known to contribute to a better understanding of the paleoceanographic evolution during the omt in the higher latitude north atlantic we have analysed both marine and terrestrial palynomorphs from integrated ocean drilling program iodp site u1406 offshore newfoundland this site has yielded a complete omt section and exhibits a high quality magnetostratigraphy that provides precise age control and allows reliable correlation to other records beyond newfoundland our palynological data which span the interval from 23 3 to 22 5 ma and have a mean temporal resolution of 11 9 kyrs show strong 110 kyr eccentricity paced oscillations during the earliest miocene these oscillations are in phase with similar cyclicity identified in previously published benthic foraminiferal oxygen isotope records more specifically a pronounced sea level variability is documented by the abundances of neritic dinoflagellate cysts dinocysts and terrigenous palynomorphs which both reach maxima during peak glacial intervals as inferred from previously published south atlantic benthic oxygen isotope data a decline in the abundance of warmer water dinocysts suggests a surface water cooling offshore newfoundland from the latest oligocene onwards surface water productivity as derived from the ratio between heterotrophic and autotrophic dinocysts remained generally low throughout the studied interval notably this ratio does not exhibit any correlation with changes in surface water temperature which is estimated from the ratio of warm water over cold water dinocysts together with the consistently low surface water productivity the lack of a correlation between surface water productivity and temperature makes it highly unlikely that the observed paleoceanographic change was caused by a southward migration of the arctic front instead we argue that our data may document an enhanced influence of the proto labrador current on surface waters offshore newfoundland during the earliest miocene that suppressed the influence of the gulf stream in this region of the northwest atlantic we speculate that the enhanced influence of the proto labrador current was triggered by cooling of the northern hemisphere and possibly modulated by high latitude sea ice expansion

determination of the lithium isotopic composition of planktic foraminifera and its application as a paleo seawater proxy to investigate the potential use of li isotopes in foraminifera as a paleo lithium seawater proxy the li isotopic compositions of planktic foraminifera orbulina universa globigerinoides sacculifer globorotalia menardii a ndgloborotalia truncatulinoides were determined by thermal ionization mass spectrometry tims using phosphate as an ion source and multi collector inductively coupled plasma mass spectrometer mc icp ms rigorous cleaning procedures were employed to purify foraminiferal tests of detrital metal oxide and organic phases in single species analyses data generated using both methods reveal that d 7 li in planktic foraminifera resemble seawater such that the isotopic fractionation from the precipitation of foraminiferal calcite appears to be minimal down core measurements indicate that the d 7 li of o universa has remained constant over the last 44 ka in the north atlantic suggesting little change of li isotopic composition of ocean water during the last glaciation consistent with the long mean residence time of li results suggest that planktic foraminifera may provide a reliable record of the lithium isotopic composition of ocean water in the past the first measurements of seawater d 7 li from the indian ocean average 33 0f1 2x 2r throughout the water column this value is within error of values previously reported for the atlantic and pacific oceans as is expected based on the long mean residence time of li in the ocean there is no evidence for a significant decrease in li cl ratios as reported by some workers with indian ocean waters averaging 9 10f0 11 ag g d 2005 elsevier b v all rights reserved

glacial deep water geometry south atlantic benthic foraminiferal cd ca and δ13c evidence a depth transect of cores from 1268 to 3909 m water depth in the western south atlantic are ideally situated to monitor the interocean exchange of deep water and variations in the relative strength of northern and southern sources of deep water production benthic foraminiferal cd ca and 13c data suggest that glacial north atlantic intermediate water gnaiw extended at least as far south as 28 s in the western south atlantic the core of nutrient depleted water was situated at 1500 m above and below water masses with higher nutrient concentrations when examined in conjunction with published paired cd ca and 13c from intermediate depth cores from other basins it appears that the extent of gnaiw influence on the intermediate waters of the world s oceans was less than suggested previously differentiating among possible pathways for the glacial deep ocean 3 km requires a better understanding of the controls on cd ca and 13c values of benthic foraminifera

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

temperature control on the incorporation of magnesium strontium fluorine and cadmium into benthic foraminiferal shells from little bahama bank prospects for thermocline paleoceanography surface sediments from little bahama bank lbb intersecting the subtropical thermocline were used to assess the influence of temperature on the incorporation of mg sr f and cd into shells of benthic foraminifera samples were obtained from twelve cores along the southern slope of lbb covering a temperature range of 18 4 5 c between 301 and 1585 m we studied the composition of ten calcitic and one aragonitic species which are often used in paleochemical reconstructions mg ca ratios decrease with increasing water depth in all benthic species both with calcitic and aragonitic mineralogy showing a strong correlation with water temperature similar decrease is seen in sr ca but with no correlation with temperature none of the benthic species studied here exhibits a depth or temperature related change in f ca similar trends are observed when using an ocean wide dataset which includes shallow and deep core tops 300 5000 m we suggest that temperature is the primary control on the mg content of benthic foraminifera based on inorganic precipitation experiments and thermodynamic considerations presented here a 30 40 decrease in the mg distribution coefficient in calcite may be expected as a result of a temperature change from 25 c to 5 c which is about half the observed change in lbb a calibration curve applied to c pachyderma data from core tops along the slope of little bahama bank suggests that water temperature may be inferred from mg ca ratios with an uncertainty of about 0 8 c therefore the mg content of benthic foraminifera may provide a new independent temperature proxy for studying shallow waters paleoceanography the linear decrease in sr ca with increasing depth is not correlated with temperature the trend is constant from the ocean surface down to 5 km suggesting that pressure related effects on the calcification process are a more likely explanation than post depositional dissolution mg ca ratios in aragonitic shells of h elegans covary with temperature in accord with recent observations from corals in contrast the sr and f chemistry of h elegans is very different than that of corals and inorganically precipitated aragonites the disparities between the elemental composition of biogenic and inorganic phases and the large intergeneric and interspecific differences observed both in planktonic and benthic foraminifera implicate temperature related physiological processes in regulating the coprecipitation of elements in foraminiferal shells our work demonstrates that cd ca ratios of shallow calcitic species reflect the vertical distribution of nutrients no significant influence of temperature on the partitioning of cd into the shells was found our data extend the previous deep water calibration boyle 1992 thereby allowing for the reconstruction of the nutrient chemistry of shallow thermocline waters

the subpolar mode water of the north atlantic ocean abstract the warm waters of the subtropical and subpolar basins of the north atlantic have tight regional temperature salinity relationships and are conventionally called the regional central waters a volumetric census of the temperature salinity characteristics of the north atlantic by wright and worthington 1970 shows that waters characterized by certain segments of the t s relationships have large volumes compared to those of other segments volumetric mode waters such mode waters appear as layers with increased vertical separation between isopycnals pycnostads the present study reports on the existence of pycnostads in the central and eastern north atlantic these subpolar mode waters are formed by deep winter convection in the subpolar north atlantic and participate in the upper water circulation of the northern north atlantic the seasonal outcropping of the pycnostads occurs within and adjacent to the north atlantic current the irminger current the east and west greenland currents and

the influence of continental ice sheets on the climate of an ice age the climate influence of the land ice that existed 18 000 years before present 18k b p is investigated by use of a general circulation model of the atmosphere coupled with a static mixed layer ocean simulated climates are obtained from two versions of the model one with the land ice distribution of the present and the other with that of 18k b p in the northern hemisphere the tropospheric flow field is strongly influenced by the laurentide ice sheet and features a split flow straddling the ice sheet with a strong jet stream forming the southern branch the northern branch of the flow brings very cold air over the north atlantic ocean where thick sea ice is maintained the distribution of sea surface temperature sst difference between the two experiments in the northern hemisphere resembles the difference between the sst at 18k b p and at present as estimated by the climap project 1981 the 18k b p ice sheets have very little influence upon atmospheric temperature and sst in the southern hemisphere this is because the interhemispheric heat transport hardly changes as the loss of heat energy due to the reflection of solar radiation by continental ice sheets in the northern hemisphere is almost completely counterbalanced by the in situ reduction of upward terrestrial radiation hydrologic changes in the model climate are also found with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in north america and eurasia these findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum

the position of the gulf stream during quaternary glaciations ocean general circulation theories predict that the position of the boundary between subtropical and subpolar gyres and therefore the position of the gulf stream north atlantic current system and the subpolar subtropical front is set by the line of zero ekman pumping where there is no convergence or divergence of water in the directly wind forced surface layer of the ocean in the present day north atlantic ocean this line runs southwest to northeast from off the carolinas to off ireland however during the last ice age 18 000 years ago the subpolar subtropical boundary ran more zonally directly toward gibraltar a numerical atmospheric general circulation model indicates that the field of ekman pumping 18 000 years ago was modified by the presence of a continental ice cap more than 3 kilometers thick such that the line of zero ekman pumping overlaid the paleogyre boundary these results demonstrate that the presence of a thick continental ice sheet could have caused changes in sea surface temperatures in the north atlantic during quaternary glaciations by altering wind patterns

core top evaluation of benthic foraminiferal isotopic ratios for paleo oceanographic interpretations abstract the benthic foraminifera cibicides wuellerstrofi oridforsalis tener and pyrgo rotalaria from twelve core tops in the norwegian greenland sea and c wuellerstorfi o tener and o umbonatus from four core tops on the rio grande rise were analysed for oxygen and carbon isotopes the norwegian greenland sea data yield statistically discrete means for both 18o and 13c for each species the interregional comparison of our data to published data from the east pacific rise shows that c wuellerstorfi 18o and 13c variations reflect oceanographic differences between sites whereas the data on oridorsalis and pyrgo do not we conclude that c wuellerstorfi is a reliable sensor of bottom water conditions whereas other taxa are of unproven utility supportive biological studies and the lack of positive covariance of 18o to 13c among deep sea benthic taxa lead us to reject models calling for incorporation of metabolic co2 to explain the isotopic variation among deep sea benthic foraminifera we propose a within sediment microhabitat hypothesis to explain the 13c variations among taxa

a secondary ionization mass spectrometry calibration of cibicidoides pachyderma mg ca with temperature an evaluation of c pachyderma mg ca using a new suite of warm water multicores from the florida straits shows that the slope of mg ca with temperature is shallower than previously thought using secondary ionization mass spectrometry we have documented that the distribution of magnesium within the polished walls of foraminiferal tests is gaussian suggesting that the mg ca in these samples is not affected by the addition of a secondary high magnesium calcite in the walls the mg ca within a typical c pachyderma test varies by about 20 1 100 and the variability increases slightly in tests with higher mg ca the regression of c pachyderma mg ca with temperature has a slope of 0 13 0 05 mmol mol 1 per c indistinguishable from the slope observed in inductively coupled plasma mass spectrometry measurements from a different subset of the same multicores but about one half the slope of previously published calibrations the largest differences between the calibrations comes at the warm water end of the regression where previously published c pachyderma mg ca values from little bahama bank are at least 3 mmol mol 1 higher than observed in these new cores the reasons for this difference are not fully known but are most likely related to diagenesis at little bahama bank

how much did glacial north atlantic water shoal observations of 13c and cd ca from benthic foraminifera have been interpreted to reflect a shoaling of northern source waters by about 1000 m during the last glacial maximum with the degree of shoaling being significant enough for the water mass to be renamed glacial north atlantic intermediate water these nutrient tracers however may not solely reflect changes in water mass distributions to quantify the distribution of glacial north atlantic water we perform a glacial water mass decomposition where the sparsity of data geometrical constraints and nonconservative tracer effects are taken into account and the extrapolation for the unknown water mass end members is guided by the modern day circulation under the assumption that the glacial sources of remineralized material are similar to that of the modern day we find a steady solution consistent with 241 13c 87 cd ca and 174 18o observations and their respective uncertainties the water mass decomposition indicates that the core of glacial north atlantic water shoals and southern source water extends in greater quantities into the abyssal north atlantic as previously inferred the depth of the deep northern southern water mass interface and the volume of north atlantic water however are not grossly different from that of the modern day under this scenario the vertical structure of glacial 13c and cd ca is primarily due to the greater accumulation of nutrients in lower north atlantic water which may be a signal of the hoarding of excess carbon from the atmosphere by the glacial atlantic

gyres driven by combined wind and buoyancy flux abstract the combined effects of buoyancy forcing and wind in a gyre scale steady ocean circulation are modeled using discrete layers with an interfacial flux not necessarily vertical the equations for vorticity conservation of the geostrophic flow in this system are fully nonlinear involving a jacobian for the layer thicknesses these equations are written in a form which can be solved by the method of characteristics the form of these equations invites the interpretation that the geostrophic baroclinic flow is driven by buoyancy and steered by the wind two examples are solved and discussed a subtropical gyre with heating and a subpolar gyre with cooling in each case there are distinct regimes of flow depending upon whether the characteristics originate at the eastern or western boundaries of the model a simple geometrical argument illustrates that the difference between these two regimes the direct and indirect cells depends upon the sign of the true vertical velocity relative to the interf

glacial deep ocean sequestration of co2 driven by the eastern equatorial pacific biologic pump abstract the potential influence of low latitude ocean primary productivity on glacial atmospheric carbon dioxide levels has proven challenging to deduce using mass accumulation rates mars of biogenic particulates in deep sea sediment cores benthic foraminiferal b ca serves as a proxy for past seawater calcite saturation state and thereby provides a fresh perspective on this outstanding paleoceanographic problem here we employ cibicidoides wuellerstorfi b ca in the panama basin region of the eastern equatorial pacific eep to investigate the nature of deep tropical pacific carbon storage over the past 50 ka bp we present evidence for persistently lower deep panama basin calcite saturation state reflecting an increase in total carbon dioxide storage during the last ice age relative to the holocene these results reflect the modification of inflowing deep waters by overlying export productivity and support the concept of an invigorated glacial eep soft tissue pump possibly driven by oceanic nutrient iron and silica redistribution benthic cibicidoides spp carbon 13 is consistent with this conclusion by exhibiting substantially lighter values during glacial time reflecting the accumulation of metabolic carbon dioxide in the deep tropical pacific counterintuitively downcore application of the globorotalia menardii calcite fragmentation index mfi reveals enhanced glacial sedimentary calcite preservation in the panama basin together these results point towards a systematic decoupling of bottom water chemistry from biogenic burial fluxes the crux of the aforementioned traditional paleoproductivity problem

deglacial variability in the surface return flow of the atlantic meridional overturning circulation 1 benthic foraminiferal cd ca from a florida current sediment core documents the history of the northward penetration of southern source waters within the surface return flow of the atlantic meridional overturning circulation amoc cd seawater estimates cdw indicate that intermediate depth southern source waters crossed the equator and contributed to the florida current during the bolling allerod warm period of the last deglaciation consistent with evidence of only a modest amoc reduction compared to today the cdwestimates also provide the first paleoceanographic evidence of a reduction in the influence of intermediate depth southern source waters within the florida current during the younger dryas a deglacial cold event characterized by a weak north atlantic amoc our results reveal a close correspondence between the northward penetration of intermediate depth southern source waters and the influence of north atlantic deep water suggesting a possible link between intermediate depth southern source waters and the strength of the atlantic amoc

micron scale intrashell oxygen isotope variation in cultured planktic foraminifers abstract in this study we show that the rate of shell precipitation in the extant planktic foraminifer orbulina universa is sufficiently rapid that 12 h calcification periods in 18 o labeled seawater can be resolved and accurately measured using secondary ion mass spectrometry sims for in situ 18 o analyses calcifying o universa held at constant temperature 22 c were transferred every 12 h between ambient seawater 18 o w 0 4 vsmow and seawater with enriched barium and 18 o w 18 6 vsmow to produce geochemically distinct layers of calcite separated by calcite precipitated with an ambient geochemical signature we quantify the position of the ba labeled calcite in the shell wall of o universa via laser ablation icp ms depth profiling of trace element ratios and then measure intrashell 18 o calcite in the same shells using sims with a 3 m spot and an average precision of 0 6 2 sd measured 18 o calcite values in o universa shell layers are within 1 1 of predicted 18 o calcite values elemental and oxygen isotope data show that la icp ms and sims measurements can be cross correlated within the spatial resolution of the two analytical techniques and that 18 o calcite and elemental tracers appear to be precipitated synchronously with no measurable spatial offsets these results demonstrate the capability of sims to resolve daily growth increments in foraminifer shells and highlight its potential for paleoceanographic and biomineralization applications on microfossils