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

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

could deep subantarctic convection feed the world deep basins during the last glacial maximum simple box model calculations are used to simulate the oceanic circulation during the last glacial maximum lgm these experiments show that the main features of the 13c and 14c distributions and of the lysocline depth may be explained by a circulation pattern very different from the modem one intermediate and upper deep waters were produced in the north atlantic ocean whereas deep waters of subantarctic mode type forming at the northern edge of the subantarctic convergence invaded the main oceanic basins the southern ocean mainly self ventilated had a reduced deep component that flew southward along the east pacific ridge and the australian west cost the thermodynamic fractionation that occurs during air sea exchange has only contributed slightly to the glacial deep 13c distribution through surface water temperature variations

glacial holocene biogenic sedimentation patterns in the south china sea productivity variations and surface water pco2 a bathymetric transect of cores in the south china sea extending from 4200 m to less than 1000 m water depth has been examined for glacial interglacial changes in carbonate and organic carbon sedimentation typical pacific carbonate cycles high carbonate content during glacials and low carbonate content during interglacials characterize cores from water depths deeper than 3500 m in contrast atlantic carbonate cycles low carbonate during glacials and high carbonate during interglacials are observed in cores from depths shallower than 3000 m as a result of increased dilution of carbonate by terrigenous material during glacial low stands of sea level glacial interglacial changes in the carbonate chemistry of south china sea intermediate and deep waters resulted in significant changes in the positions of the carbonate compensation depth ccd and the aragonite compensation depth acd during the last glacial the ccd and acd were at least 400 and 1200 m deeper respectively than at present organic carbon accumulation rates in the south china sea were approximately 2 times higher during the last glacial than the holocene carbon isotopic analyses and c n ratios of the organic matter indicate that only a small fraction of the increase in glacial organic carbon accumulation can be attributed to input of terrestrial carbon on the basis of this we conclude that surface water productivity in the south china sea was approximately 2 times higher during the last glacial maximum this is consistent with previous studies which have demonstrated that glacial productivity was higher in low to mid latitude regions of the atlantic and eastern pacific the deglacial decrease in organic carbon accumulation is accompanied by a decrease in 13corg using the relationship between 13corg and co2 aq developed by popp et al 1989 we estimate that surface water pco2 values in the south china sea during the last 25 000 years were very similar to atmospheric co2 concentrations

ba distribution in surface southern ocean sediments and export production estimates 1 we present excess ba baxs data i e total ba corrected for lithogenic ba for surface sediments from a north south transect between the polar front zone and the northern weddell gyre in the atlantic sector and between the polar front zone and the antarctic continent in the indian sector focus is on two different processes that affect excess ba accumulation in the sediments sediment redistribution and excess ba dissolution the effect of these processes needs to be corrected for in order to convert accumulation rate into vertical rain rate the flux component that can be linked to export production in the southern ocean a major process affecting ba accumulation rate is sediment focusing which is corrected for using excess 230 th this correction however may not always be straightforward because of boundary scavenging effects a further major process affecting excess ba accumulation is barite dissolution during exposure at the sediment water column interface export production estimates derived from excess 230 th and barite dissolution corrected baxs accumulation rates i e excess ba vertical rain rates are of the same magnitude but generally larger than export production estimates based on water column proxies 234 th deficit in the upper water column particulate excess ba enrichment in the mesopelagic water column we believe export production values based on excess ba vertical rain rate might be overestimated due to inaccurate assessment of the baxs preservation rate barite dissolution has in general been taken into account by relating it to exposure time before burial depending on the rate of sediment accumulation however the observed decrease of excess ba content with increasing water column depth or increasing hydrostatic pressure illustrates the dependence of barite preservation on degree of saturation in the deep water column in accordance with available thermodynamic data therefore correction for barite dissolution would not be appropriate by considering only exposure time of the barite to some uniformly undersaturated deep water but requires also that regional differences in degree of undersatuation be taken into account index terms 1050 geochemistry marine geochemistry 4835 4850 4835 oceanography biological and chemical inorganic marine chemistry keywords excess ba sediment southern ocean export production

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

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

late quaternary paleochemistry of high latitude surface waters recent studies have stressed the role of high latitude nutrient levels and productivity in controlling the carbon isotopic composition of the deep sea and the co2 content of the atmosphere we undertook a study of the chemical composition of the polar planktonic foraminifer neogloboquadrina pachyderma s sinistral coiling from 30 late holocene samples and 49 down core records from the high latitude north and south atlantic oceans to evaluate the history of sea surface chemical change from glacial to interglacial time stable isotopic analysis of coretop samples from the atlantic pacific and southern oceans shows no significant correlation between the 13c of n pachyderma and either 13c or po4 in seawater conversely cd ca ratios in planktonic foraminifera are consistent with the po4 content of surface waters the level of maximum glaciation 18 000 yr b p identified by climap and 18o was chosen for mapping isopleths of 18o on n pachyderma s in the north atlantic reveal a pattern largely influenced by sea surface temperature s s t and generally support the s s t reconstruction of climap differences between the two suggest significantly lower salinity in north atlantic surface waters at high latitudes than in lower latitudes down core 13c records of n pachyderma confirm that low 13c values occurred in the northeast atlantic during the latest glacial maximum labeyrie and duplessy 1985 however a map of 13c for the 18 000 yr b p level for a much larger region in the north atlantic shows that minimum n pachyderma 13c occurred in temperate waters n pachyderma 13c decreased toward the southwest reaching a minimum of 1 at 37 n despite the variability seen in 13c records of n pachyderma none of our cores show significant temporal variability in cd ca from the combined cd ca and 13c data we can see no evidence for an upwelling gyre in the eastern north atlantic during the latest glacial maximum nor evidence that the southern and northern oceans had significantly different levels of preformed nutrients than today

the effect of vertical nutrient redistribution on surface ocean δ13c processes that shift nutrients from mid to lower ocean depths may or may not increase the ocean s vertical carbon pump redistribution of 13c produced by these processes is compared in two box models a vertical three box ocean and a thirteen box ocean in the former there is no 13c fractionation laterally between surface waters and the ocean nutrient and 13c distributions are linearly correlated this correlation is not changed when these tracers become redistributed and if the model surface ocean is nutrient limited the surface 13c cannot change in the 13 box ocean there is a transfer of negative 13c from the cold surface water through the atmosphere into the warm ocean its 13c is therefore lower than it would be as a result of the carbon pump by itself if a middepth nutrient depletion occurs because of lower nutrients in antarctic waters the warm surface 13c increases if the vertical nutrient shift occurs because of ocean circulation or biological recycling changes the warm surface water 13c change depends on the ratio of its vertical co2 fluxes i e exchange of atmospheric co2 versus upwelling total co2 and net biological production if this ratio remains about the same then little change occurs in surface 13c and the 13c of pacific deep water decreases about 0 3 in this case no change in the average ocean 13c is required to explain observations from sediment data this would imply that the ice age land biota carbon mass was about the same as that of today the vertical co2 flux ratio could be an important consideration if greater wind driven upwelling is a factor in the nutrient redistribution

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

on the late pleistocene ocean geochemistry and circulation a box model of the atmosphere and ocean was developed to investigate how geochemical distributions extant during the late pleistocene may have come about the model simulates the regional distribution of calcium carbonate dissolution as well as the chemical oceanography and atmospheric co2 13c and radiocarbon if the downward biological flux of particulate carbon increases by a factor of 2 to 3 in the antarctic and if this increase is combined with a relative increase of the atlantic sector antarctic bottom water aabw versus north atlantic deep water nadw source ratio from 1 3 to about 2 1 then the model predicts several changes that seem to be recorded in the sedimentary record as follows 1 a global redistribution of nutrients and 12c from the intermediate to deep water takes place with the atlantic intermediate water phosphate decreasing 0 6 mole kg 1 and the 13c increasing 0 3 to 0 5 2 the dissolved oxygen level of the deep sea is reduced from an average of about 180 to 70 mole kg 1 but the intermediate water oxygen declines only a small amount 3 the decrease in intermediate water nutrient concentration results in lower average organic carbon and calcium carbonate production in the warm surface ocean 4 the atmospheric co2 decreases by 90 to 110 ppm 5 initially a global increase in calcium carbonate dissolution occurs which is followed by a relaxation toward better preservation than exists for the present ocean in the model in this paper the reduction of nadw by itself does not produce these effects rather the nutrient decrease that does occur is found mostly in north pacific intermediate water and the model atmospheric co2 decrease is only 10 to 30 ppm it is observed that 92 of the atmospheric co2 change takes place according to a 200 year time constant in the model this corresponds to the response time of the upper ocean and atmosphere to a change in the stationary state atmospheric pco2 thus according to this model the time lag between the nutrient based cause and the atmospheric co2 response is not expected to be particularly large

the isotopic composition of diatom bound nitrogen in southern ocean sediments treatment of diatom microfossils from southern ocean sediments with hot perchloric acid leaves a diatom bound n fraction which is 0 4 lower in 15n than the bulk sediment typically 3 lower in recent antarctic diatom ooze results from southern ocean surface sediments indicate that early diagenetic changes in bulk sediment n content and 15n are not reflected in diatom bound n suggesting that diatom bound n is physically protected from early diagenesis by the microfossil matrix a meridional transect of multicores from the indian sector of the southern ocean shows a northward increase in the 15n of diatom bound n suggesting that diatom bound 15n like bulk sedimentary 15n varies with nitrate utilization in the overlying surface waters the 15n of diatom bound n is 3 4 higher in glacial age antarctic sediments than in holocene sediments supporting the hypothesis previously based on bulk sediment 15n that nitrate utilization in the surface antarctic was higher during the last ice age while there are important uncertainties the inferred range of utilization changes could potentially explain the entire 80 ppm amplitude of observed glacial interglacial variations in atmospheric co2

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

seasonal changes in the isotopic composition of planktonic foraminifera collected in panama basin sediment traps abstract isotopic analyses have been made on five species of planktonic foraminifera collected in two deployments of parflux mark ii time series sediment traps in the panama basin the automated sampling system on the traps provided 4 one month samples from 29 july to 16 november 1979 and 6 two month samples from december 1979 to november 1980 the 18o values of globigerinoides ruber and globigerinoides sacculifer in this region are primarily affected by a low salinity surface layer that forms during the early winter these species each show a 1 total range in 18o the 18o values of the colder water species globorotalia menardii neogloboquadrina dutertrei and globorotalia theyeri show smaller seasonal changes in 18o the 13c values of g ruber and g sacculifer exhibit small seasonal changes 0 35 and 0 4 respectively despite large seasonal changes in surface water productivity the colder water species exhibit only slightly larger changes in 13c up to 0 55 throughout the year all colder water species exhibit minimum or near minimum 13c values during february and march which is the period of maximum upwelling and primary productivity seasonal variations in the flux of foraminifera in the water column at this location will have only a small effect on the isotopic composition of the sediment assemblage extreme values of 18o and 13c do not occur during the periods which are associated with the high flux of foraminiferal tests

biogenic sediments in the west caroline basin the western equatorial pacific during the last 330 000 years abstract primary productivity as well as new production have played an important role in the global carbon cycle during the late quaternary the mean organic carbon nitrogen atomic ratio was 8 3 from the c4402 sediments in the west caroline basin which indicates a limited contribution of terrigenous organic carbon to the organic matter in the sediments the fluctuation of carbonate preservation shows that the accumulation rate of organic carbon has reflected primary productivity the results from sediment trap experiments which were carried out at site c4402 indicate that plankton bloom was characterized by a large influx of siliceous plankton when organic carbon was effectively removed palaeoproductivity estimates calculated by using the formula of sarnthein et al 1988 would be plausible because the fluctuation pattern of such estimates correlates closely with changes in the accumulation rate of biogenic opal in the sediments the primary productivity in the west caroline basin increased during stage 2 stage 3 late stage 6 stage 6 7 boundary and stage 8 at a glance the results are similar to other studies that have reported higher glacial productivity in low latitude regions however some leads and lags are found between the west caroline basin and other areas of the equatorial pacific and atlantic the spectral analysis of mar organic indicates that the western equatorial pacific reaches a maximum in mar organic approximately 7000 years before the maxima in the eastern pacific a regional variation of the response of mar organic to the orbital forcing climatic condition suggests that the efficiency of the organic carbon pump may vary with longitude in the equatorial pacific

global variations of surface ocean productivity in low and mid latitudes influence on co2 reservoirs of the deep ocean and atmosphere during the last 21 000 years based on detailed reconstructions of global distribution patterns both paleoproductivity and the benthic 13c record of co2 which is dissolved in the deep ocean strongly differed between the last glacial maximum and the holocene with the onset of termination i about 15 000 years ago the new export production of low and mid latitude upwelling cells started to decline by more than 2 4 gt carbon year this reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric co2 as recorded in ice cores and with a slight delay of more than 1000 years to a large scale gradual co2 depletion of the deep ocean by about 650 gt c this estimate is based on an average increase in benthic 13c by 0 4 0 5 the decrease in new production also matches a clear 13c depletion of organic matter possibly recording an end of extreme nutrient utilization in upwelling cells as shown by sarnthein et al 1987 the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades which in turn was linked via a shrinking extent of sea ice to a massive increase in high latitude insolation i e to orbital forcing as primary cause

response of global deep water circulation to earth s climatic change 135 000 107 000 years ago the response of deep ocean circulation to major climatic events of the past 135 000 years is inferred using carbon 13 analyses of benthic foraminifera from the major ocean basins the results demonstrate that the circulation of the world ocean deep water is very sensitive to climate and that it changes drastically during climatic transitions

vertical distribution and isotopic fractionation of living planktonic foraminifera from the panama basin a model1 2 which explains the vertical and seasonal distribution of planktonic foraminifera was developed using data from the western north atlantic and is comprised of three tenets 1 the conditions in the photic zone upper 80 100 m exclusively dictate planktonic foraminifera species composition and abundance throughout the water column 2 species are vertically stratified within the photic zone according to their temperature preference depth distribution according to temperature preference has been proposed by several authors3 based on isotope analyses of sediments due to seasonal temperature variations seasonal variations in the 18o composition of seawater and species specific isotope fractionation rigorous proof of this hypothesis cannot be provided from sediment analyses alone 3 the chlorophyll maximum is a major food source zone which is preferentially exploited by foraminifera our data from the panama basin which are presented here are confirmation of this model the panama basin in the eastern equatorial pacific which has a shallow and steep thermocline was sampled for living planktonic foraminifera a multiple opening closing net and environmental sensing system mocness 4 was used to collect 13 sets of eight vertically stratified oblique samples we report here the quantitative distribution and stable isotopic composition of planktonic foraminifera from four mocness tows taken over 5 days during august 1979 rv knorr cruise 73 at 5 20 n 8 50 w each tow consisted of eight samples which integrated 12 5 m intervals from 0 to 100 m for moc 126 25 m intervals from 0 to 200 m for moc 127 100 150 m intervals from 0 to 1 000 m on moc 128 and 250 m intervals from 0 to 2 000 m on moc 131

chironomid record of late quaternary climatic and environmental changes from two sites in central asia tuva republic russia local regional or global causes abstract sediment cores from two mountain lakes lake grusha at 2413 m a s l and ak khol at 2204 m a s l situated in the tuva republic southern siberia russia just north of mongolia were studied for chironomid fossils in order to infer post glacial climatic changes and to investigate responses of the lake ecosystems to these changes the results show that chironomids are responding both to temperature and to changing lake depth which is regarded as a sensitive proxy of regional effective moisture the post glacial history of this mountain region in central asia can be divided into seven successive climatic phases the progressive warming during the last glacial interglacial transition ca 15 8 14 6 cal kyr bp the warm and moist bolling allerod like interval ca 14 6 13 1 cal kyr bp the cool and dry younger dryas like event ca 13 1 12 1 cal kyr bp warmer and wetter conditions during ca 12 1 8 5 cal kyr bp a warm and dry phase ca 8 5 5 9 cal kyr bp cold and wet conditions during ca 5 9 1 8 cal kyr bp as well as cold and dry climate within the last 1800 years the chironomid records reveal patterns of climatic variability during the late glacial and holocene which can be correlated with abrupt climatic events in the north atlantic and the asian monsoon dominated regimes apparently the water balance of the studied lakes is controlled by the interrelation between the dominant westerly system and the changing influence of the summer monsoon as well as the influence of alpine glacier meltwater supply it is possible that monsoon tracks could have reached the southwest tuva resulting in an increase in precipitation at ca 14 6 13 1 and ca 12 1 8 5 cal kyr bp whereas cyclonic westerlies from the north atlantic were likely responsible for considerable moisture transport accompanying the global neoglacial cooling at ca 5 9 1 8 cal kyr bp these events suggest the changes of the regional pattern of atmospheric circulation which could be in turn induced by the global climatic shifts some discrepancies compared with other reconstructions from central asia may be associated with regional spatial differences between the changing predominant circulation mechanisms and with local differences in uplift and descent of air masses within the complicated mountain landscape in this paper we also discuss the possibilities and perspectives for using chironomids in reconstructions of past temperatures and climate induced changes in water depth of lakes in central asia

the cause of the glacial to interglacial atmospheric co2 change a polar alkalinity hypothesis in an attempt to create a scenario for the cause of the glacial to interglacial co2 change recorded in air trapped in polar ice we call on an increase in the alkalinity of polar surface waters in this way we circumvent a major deficiency of the polar nutrient scenarios of sarmiento and toggweiler 1984 siegenthaler and wenk 1984 and knox and mcelroy 1984 namely our scenario does not require a drop in the nutrient content of polar surface waters in conformity with the demonstration by boyle 1988a b that the cadmium content of planktonic foraminifera from polar regions did not decrease from late glacial to holocene time the rise in alkalinity required by our model is a natural consequence of the demise during glacial time of north atlantic deep water as a major force in ocean circulation and of the nutrient maximum deepening of boyle 1988b rather than being original our hypothesis builds on the concept basic to the polar nutrient hypotheses namely that the co2 partial pressure in polar waters controls that for both the atmosphere and warm surface ocean it also requires the alkalinity increase in surface waters produced by boyle s nutrient deepening

the δ13c of equatorial atlantic surface waters implications for ice age pco2 levels carbon isotopic records of nutrient depleted surface water place constraints on the past fertility of the oceans and on past atmospheric pco2 levels the best records of nutrient depleted 13c are obtained from planktonic foraminifera living in the thick mixed layers of the western equatorial and tropical atlantic ocean we have produced a composite stacked globigerinoides sacculifer 13c record from the equatorial atlantic which exhibits significant spectral power at the 100 000 and 41 000 year milankovitch periods but no power at the 23 000 year period similar to the record presented by shackleton and pisias 1985 surface deep ocean 13c produced with the g sacculifer record leads the 18o ice volume record however the glacial interglacial amplitudes of 13c differ between our record and shackleton and pisias 1985 record although large changes in 13c occur in the equatorial atlantic during early stages of the last three glacial cycles surface deep 13c at glacial maxima 18o stage 2 late stage 6 and late stage 8 was only about 0 2 greater than during the subsequent interglacial our results imply that nutrient driven pco2 changes account for about one third of the pco2 decrease observed in ice cores and consequently 13c should not be used as a proxy pco2 index enough variance in the ice core pco2 records remains to be explained that conclusions about pco2 and ice volume phase relationships should also be reexamined as much as 40 ppm pco2 change still has not been accounted for by models of past physics and chemistry of the ocean

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

timing of late quaternary productivity pulses in the panama basin and implications for atmospheric co2 high resolution percent corg and 18oforam records obtained from panama basin core atlantis ii 54 25pc and additional data from nearby core p7 show that enhanced burial of organic carbon has characterized every major glacial period for the last 500 kyr in that area both corg concentration and mass accumulation rate profiles exhibit a sawtooth pattern with maxima occurring typically in the later stages of glacial periods comparison with dust records suggests that the carbon accumulation rate profile reflects both the upwelling history and a variable rate of iron input during the late quaternary the sawtooth character may derive from increased wind velocities and rates of upwelling during glacials which are indirectly related to ice volume sarnthein et al 1988 the rapid decline in export production at the end of glacials in the equatorial pacific may be attributed to the retreat of ice sheets thus reduced wind velocities and upwelling coupled with a coincident decline in atmospheric dust load and or delivery rate the corg accumulation rate profiles do not correlate well with atmospheric co2 records for example atmospheric co2 was already at a minimum 40 kyr ago when production in the panama basin began increasing dramatically commensurate with an increase in global dust levels using the relationship between the degree of photosynthetic fractionation and the concentration of free co2 in the surface ocean postulated by popp et al 1989 13corg measurements made on core p7 show that panama basin surface waters have been supplying co2 to the atmosphere continually for at least the last 50 kyr there is no evidence for a flux of co2 into the surface ocean in this area at any time during this period despite the higher production if the panama basin cores are representative of the eastern and central equatorial pacific then these observations weaken the influence on co2 drawdown postulated for increased glacial productivity at low latitudes

sedimentary iron records from the cape basin abstract the iron hypothesis suggests that dust derived fe delivered to the southern ocean during glacial intervals fueled primary productivity and led to co 2 drawdown clear support for a dustier glacial atmosphere comes from ice core records of dust concentrations furthermore there is unequivocal proof from open ocean fe fertilization experiments that primary productivity in the modern day southern ocean is limited by fe however substantial hemipelagic detrital sources dilute and obscure the eolian signal here we present records of fe concentrations total and reducible and fe fluxes to highlight the importance of hemipelagic fe sources to the cape basin we illustrate that on average only 7 of the fe flux to site 1089 can be accounted for by particle settling indicating that redistribution by bottom currents accounts for an order of magnitude more fe than particulate scavenging processes distribution by surface currents or eolian deposition we also find that on average only 7 of the fe content is easily reducible furthermore we speculate that a significant source of dissolved fe to the bottom waters may come from re suspended bottom sediments

remineralization of particulate authigenic trace metals in the middle atlantic bight implications for proxies of export production abstract samples collected by time series sediment traps deployed in the middle atlantic bight were studied to better understand the formation and preservation of particulate authigenic forms of trace metals cu ni ba that hold potential to serve as proxies in the sedimentary record of past changes in the flux of biogenic detritus sinking from the surface ocean into the deep sea export production particulate biogenic and authigenic phases are extremely labile as evidenced by the observation that as much as 70 of the particulate fluxes of organic carbon and of certain metals cu ni and mn and up to 25 of the particulate fluxes of authigenic ba and of opal collected by sediment traps are released rapidly into solution during the time period between particle collection and trap retrieval further remineralization on the seabed reduces concentrations of authigenic cu and ni in surface sediments below the limit of detection approximately 80 of authigenic ba is remineralized during early diagenesis on the seabed much more than is expected for conditions of high sediment mass accumulation rate that exist in the study area extensive remineralization during early diagenesis combined with large corrections required to remove the aluminosilicate contribution to the concentrations of cu ni and ba in sediments preclude the successful use of down core profiles of these trace metals to reconstruct past changes in export production of the middle atlantic bight similar problems are likely to plague paleoproductivity reconstructions in other ocean margin regions or wherever high fluxes of aluminosilicate phases occur

reconstructing the ocean carbon system variation during the last 150 000 years according to the antarctic nutrient hypothesis in this study the vostok ice core co2 record and the 13c difference between the deep atlantic and pacific a p are used in combination with model simulations to analyze the history of the ocean carbon pump and the sources of atlantic deep water during the last 150 kyr it is assumed that the mechanism by which the glacial atmospheric co2 decreased is an increase in the ratio of antarctic net carbon production to upwelling in that region results from a wide range of circulations and antarctic net carbon productions input into a 14 box ocean atmosphere model show that similar distributions of phosphate 13c atmospheric co2 content and surface versus deep radiocarbon age are produced once the following parameters are fixed 1 the ratio of net carbon production to upwelling in the antarctic region 2 the ratio of northern component water to antarctic bottom water input into the atlantic and 3 the total upwelling into the low latitude surface waters therefore rather arbitrary circulations and antarctic net production values can be used to map model simulated geochemical properties as a function of these parameters decrease in atmospheric co2 and atlantic to pacific 13c difference are calculated from the model for constant low latitude upwelling and these are mapped as a function of the ratios 1 and 2 above the isolines of these two geochemical properties tend to be orthogonal and one can position any pco2 a p pair on an overlay of the two maps this is done for coeval ice core co2 and marine sedimentary 13c data for the last 150 kyr one finds that the history of the antarctic carbon pump efficiency varies with the same pattern as that of the atmospheric co2 the fraction of northern component water entering the atlantic tends to vary with the same shape function as the global marine 18o curve

radiocarbon age of last glacial pacific deep water one of the most important projects envisaged ever since the possibility emerged of making tandem accelerator mass spectrometric radiocarbon determinations has been that of investigating changes in the radiocarbon age of the deep ocean1 initial attempts to achieve this2 were thwarted by difficulties imposed by bioturbation because these workers used core v28 238 with an accumulation rate of only 1 5 cm kyr 1 thus emphasizing the need to work in a core with a higher accumulation rate working in the glacial section of core tr163 31b with an accumulation of 10 cm kyr 1 we show here that the ventilation age of pacific deep water was about 500 years greater in last glacial times than it is today

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

the carbon isotopic record of the c37 2 alkenone in the south atlantic last glacial maximum lgm vs holocene the carbon isotopic fractionation ep of the c37 2 alkenone was analysed for 19 south atlantic sediment samples from the last glacial maximum lgm our study covers the equatorial and subtropical ocean including the coastal upwelling regions off south africa the equatorial upwelling and the oligotrophic western basins the results were compared to the holocene ep records from the respective core locations andersen n muller p j kirst g schneider r r 1999 alkenone 13c as a proxy for past pco2 in surface waters results from the late quaternary angola current in fischer g wefer g eds use of proxies in paleoceanography examples from the south atlantic springer berlin pp 469 488 benthien a andersen n schulte s muller p j schneider r r wefer g 2002 carbon isotopic composition of the c37 2 alkenone in core top sediments of the south atlantic ocean effects of co2 and nutrient concentrations glob biogeochem cycles 16 10 1029 2001gb001433 generally alkenone ep was lower during the lgm compared to the holocene higher glacial ep values were only found in sediments from the angola basin and in one sample from the eastern crest of the walvis ridge considering present understanding of lgm holocene changes in surface water conditions i e nutrient level primary productivity phytoplankton assemblages the observed glacial interglacial difference in ep indicates that multiple factors controlled the isotopic fractionation in alkenone producing algae depending on the regional setting in the oligotrophic areas of the south atlantic the lower than holocene glacial ep values can be partly explained with a decrease in surface water pco2 during the lgm in contrast the holocene to lgm decrease in ep values in the coastal upwelling areas as well as in the eastern tropical atlantic most probably reflects much higher glacial haptophyte growth rates induced by an increase in surface water nutrient concentrations the exceptional opposite trend of the ep differences in the angola basin can be explained by a shift in the phytoplankton community towards a greater dominance of diatoms under glacial conditions thus leaving less nutrients available for haptophytes in this way the isotopic record of alkenones indicate lower haptophyte growth rates during the lgm although other palaeoceanographic proxies point to enhanced productivity and higher nutrient levels

an atlas of the distribution of calcium carbonate in sediments of the deep sea historical observations of the concentration of calcium carbonate in global deep sea sediments are compiled and compared with a new gridded field of seawater co3 concentration to reveal regional variations in the calcite lysocline the most obvious mode of variability of the calcite lysocline is the thickness of the lysocline defined here as the difference in overlying water carbonate saturation co3 between high and low calcite sediments with a thicker lysocline in the atlantic than in the pacific i attribute this variation to differences in the delivery rate of terriginous material a recent model for the lower glacial atmospheric pco2 proposed to change the relationship between the depth of the lysocline and the co3 of the water column by changing the rain rate ratio of organic carbon to calcite production the rain ratio model archer and maier reimer 1994 i search the data set for analogs to the proposed glacial world by looking for a link between the regional climate at the sea surface and the depth of the lysocline below the co3 at the carbonate compensation depth ccd in the tropics appears to be 10 20 mol kg 1 co3 more undersaturated than in high latitudes but this is smaller than the 40 mol kg 1 shift required by the model in addition the general resemblance of the glacial lysocline to the present day requires that the proposed shift in co3 at the ccd be globally uniform rather than locally variable as climate forcing would probably generate i conclude that the rain ratio model would probably require some globally uniform perturbation during glacial time such as a change in ocean si content if it is to explain the entire pco2 decrease observed in the glacial atmosphere finally i grid the sedimentary data to estimate that the inventory caco3 which is available to neutralize fossil fuel co2 is approximately 1600 gt carbon a quantity which may be exceeded by fossil fuel release in the next several centuries

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

preliminary estimates for the radiocarbon age of deep water in the glacial ocean radiocarbon ages for benthic and planktonic foraminifera from the late glacial sections of two atlantic and two pacific cores are reported the differences for benthic planktonic pairs suggest that the radiocarbon age for deep atlantic water was somewhat larger than today s i e 600 250 as opposed to 400 years and that the radiocarbon age for deep pacific water was also slightly larger than today s 2100 400 as opposed to 1600 years our results suggest that during glacial time the deep pacific was as it is today significantly depleted in radiocarbon relative to the deep atlantic as many questions remain unanswered regarding the reliability of this approach these conclusions must be considered to be preliminary

changes in the oceanic 13c 12c ratio during the last 140 000 years high latitude surface water records detailed records of the carbon and oxygen isotopic ratios of neogloboquadrina pachyderma are compared between nine high latitude sediment cores from the northern and southern hemispheres covering the last 140 000 yrs the strong analogies between the 13c records permit to define a 13c stratigraphic scale with three clear cut transitions simultaneous with the oxygen isotopic transitions 65 125 kyrs 54 65 kyrs and 21 13 kyrs the 13c records of n pachyderma in the high latitude cores which follow the changes in 13c of the surface water tco2 near areas of deep water formation present trends similar to the benthic foraminifera 13c records in cores v19 30 and m12 392 although amplitudes of the isotopic shifts are different this implies that a large part of the observed variations represents global changes in the carbon distribution between biosphere and ocean the 13c12c ratios of n pachyderma in the north atlantic cores display larger regional variations at 18 kyrs b p than at present to explain these differences we have plotted the 18 kyrs b p 13c values of n pachyderma from 17 cores distributed n of 40 n comparison with published surface water temperature distribution at 18 kyrs b p indicates that a strong divergent cyclonic cell centered approximatively 55 n and 15 w was active during most of the last ice age maximum this hydrology analogous to the present weddell sea explains the published evidences of bottom water formation if located on the northern flank of the gyre and the strong polar front on the southern flank probable location of intermediate water formation

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

late quaternary paleoproductivity changes off the congo deduced from stable carbon isotopes of planktonic foraminifera a detailed record 2 kyr intervals of the difference in stable carbon isotopes 13c between globigerina bulloides and globigerinoides ruber pink is used to reconstruct changes in upwelling intensity off the congo river for the last 190 000 yr comparisons of the oxygen and carbon isotope data from this core with records from the niger fan and from pelagic cores in the eastern equatorial south atlantic indicate that the congo fan isotope records do not contain a strong freshwater signal as is described off other major rivers the temporal pattern of the 13c signal correlates with the marine organic carbon record from the congo fan thus the planktonic 13c record reflecting past changes in upwelling intensity and nutrient content corroborates the signal provided by sedimentary organic carbon which is presumed to indicate changes in the amount of biological productivity and export flux to the seafloor the planktonic 13c signal is characterized by a dominant 23 kyr periodicity which provides evidence for a strong response of upwelling fluctuations off the congo to precessional forcing minima in the 13c record are aligned with periods of minimum boreal summer insolation over central africa reflecting an increase of upwelling and biological productivity off the congo at periods of enhanced zonal intensity of southeast trades and corresponding weak southeast monsoon over the eastern south atlantic a strong response to changes in river discharge probably did not occur indicating that fertilization by river derived nutrients has played only a minor role with respect to late quaternary changes in the total amount of primary productivity off the congo

evidence for a bathyal front at 2000 m depth in the glacial pacific based on a depth transect on ontong java plateau data on oxygen and carbon isotope compositions of the benthic foraminifer planulina wullerstorfi from 18 cores 17 box cores and one piston core from ontong java plateau provide proxy depth profiles for temperature water mass and nutrient content for the late holocene the last transition and the last glacial the 18o profile during glacial time shows an increased gradient at a depth near 2000 m the corresponding 13c data suggest that a bathyal nutricline existed close to the same depth level the 13c values provide limits on the global change in carbon content of the glacial ocean which may be estimated as distinctly less than 1 atmospheric carbon mass 1 acm 700 gtc the greater co2 content of glacial deep waters which is reflected in the more negative 13c values may be at least in part due to a more sluggish renewal of abyssal deep waters if so the water of the deep pacific was up to 400 years older than now in turn ventilation in the upper waters above 2000 m may have been more vigorous than today

understanding the causes and consequences of past marine carbon cycling variability through models abstract on geological time scales the production and degree of recycling of biogenic carbon in the marine realm and ultimately its removal to sediments exerts a dominant control on atmospheric co 2 and hence variability in climate this is a highly complex system involving a myriad of inter connected biological chemical and physical processes for this reason alone linking observations often highly abstracted in the form of proxies to the primary processes involved and ultimately to explanatory hypotheses for specific geological events and transitions is challenging the past few decades have seen a progressive improvement in theoretical and process based understanding of the various components that make up the marine carbon cycle and hand in hand with this the development of numerical model representations of the complete system models have also been designed and or adapted with paleoclimate questions in mind and applied to quantitatively explore the role of the marine carbon cycle in both perturbations and long term geologic evolutionary trends in global climate and possible feedbacks between them however we must ask whether paleoclimate models incorporate sufficiently appropriate representations of the dynamics and sensitivities of the marine carbon cycle and indeed whether in the geological context we really know what these dynamics are here we provide a comprehensive overview of how marine carbon cycling and the biological carbon pump is treated in available paleoclimate models with the aim of critically evaluating their ability to help interpret past marine carbon cycle and climate dynamics to this end we first provide an overview of commonly used paleoclimate models and some of their associated paleo applications drawing from a wide range of global carbon cycle box models and earth system models of intermediate complexity emics secondly we review and evaluate the three dominant processes involved in the cycling of organic and inorganic carbon in the marine system and how they are represented in models namely biological productivity at the ocean surface remineralisation dissolution of particulate carbon within the water column and the benthic pelagic coupling at the seafloor we generate and employ illustrative examples using the model genie to show how different parameterisations of water column and sediment processes can lead to significantly different model projections our compilation reveals the prevalence of static parameterisations of marine carbon cycling among existing paleoclimate models which are commonly empirically derived from present day observations although such approaches tend to represent carbon transfer in the modern ocean well they are potentially compromised in their ability to reflect the true degree of freedom and strength of feedbacks with respect to past climate events particularly those characterised by environmental boundary conditions that differ fundamentally from today finally we discuss the importance of using models of different complexities and how questions of model uncertainty may start to be addressed

enhanced scavenging of 231pa relative to 230th in the south atlantic south of the polar front implications for the use of the 231pa 230th ratio as a paleoproductivity proxy abstract the fractionation of 230th and 231pa was investigated throughout the atlantic sector of the southern ocean published scavenging models generally assume that the 231pa 230t ratio of surface sediments is primarily determined by the mass flux of particles this relationship holds north of the polar front where low primary productivity coincides with ratios of unsupported 231pa 230th xs 231pa 230th in surface sediments below the production ratio of both radionuclides in the water column however we observed high xs231pa 230th ratios conventionally interpreted as a high productivity signal in surface sediments south of the polar front especially throughout the weddell sea in contradiction with the low particle flux of this region measurements of both dissolved and particulate fractions of 231pa and 230th in the water column revealed a strong n s decrease in the th pa fractionation factor from typical open ocean values around 10 north of the polar front to values between 1 and 2 south of 60 s this observation clearly indicates that the high xs231pa 230th ratios in surface sediments south of the antarctic circumpolar current are produced by a n s increase in the relative scavenging efficiency of 231pa relative to 230th most probably due to a change in the chemical composition of particulate matter and not by a high mass flux it is speculated that biogenic opal suggested not to significantly fractionate231pa and 230th may explain the enhanced scavenging of 231pa to the south this assumption is further supported by extremely high 231pa 230th ratios up to 0 34 in material collected with sediment traps south of the polar front where fluxes are primarily determined by biogenic opal based on these results we conclude that in regions where the sedimenting flux is dominated by biogenic opal the 231pa 230th ratio is not a reliable indicator for the mass flux of particles thus limiting its use as a paleoproductivity proxy in the southern ocean

deep circulation of the north atlantic over the last 200 000 years geochemical evidence variations in the cadmium calcium ratio of north atlantic deep water are recorded in the fossil shells of benthic foraminifera the oceanic distribution of cadmium is similar to that of the nutrients hence the cadmium calcium ratio in shells records temporal variations in nutrient distributions data from a north atlantic sediment core show that over the past 200 000 years there has been a continuous supply of nutrient depleted waters into the deep north atlantic the intensity of this source relative to nutrient enriched southern waters diminished by about a factor of 2 during severe glaciations this evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested

co 2 record in the byrd ice core 50 000 5 000 years bp the analysis of air in polar ice cores revealed 30 lower co2 values during glacial periods than during interglacial periods at present this is confirmed by results from six different ice cores two from greenland and four from antarctica1 5 in all cores the co2 change coincides with the change in the isotopic composition of the ice expressed as either the 18o or d ratio both are indicators for the mean annual surface temperature6 to investigate the relationship between atmospheric co2 concentration changes with changes in climate the atmospheric co2 concentration during and at the end of the last glaciation has to be known in detail to achieve this we have studied a great number of samples from the deep ice core from byrd station westantarctica drilled in 1968 these measurements allow us to reconstruct the atmospheric co02 concentration in the time period 50 000 15 000 yr bp in great detail

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

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

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

a new approach to paleoclimatic research using linear programming abstract one of the most frequently attempted correlations in quaternary research is between insolation and paleoclimatic data yet there are a large number of insolation time series that could potentially explain a quaternary dataset individually or in combination we computed 342 insolation time series varying by latitude time of year and time of day for fitting to four different paleoclimatic records foraminiferal 18 o from specmap temperatures inferred from vostok antarctica ice cores marine accumulation rates of a freshwater diatom melosira originating from tropical africa lakebeds and 18 o variations in calcite at devil s hole nevada we developed two inductive linear programming models that solve for the weighted combination of insolation curves that minimize either the average or maximum residual from the proxy curve each of the four proxy records lagged and unlagged was solved by both model types on average our composite insolation curves fit the proxy records 48 76 better than does june daily insolation at 60 n the key insolation curve of the milankovitch paradigm globally high latitude insolation 60 70 n and s and insolation at specific times of day noon or non noon as opposed to daily dominated the results regionally the model tended to select insolation curves from absolute latitudes similar to those of the proxy records the fact that these results are plausible given known biophysical processes combined with the fact that a small number of curves repeatedly accounted for a disproportionate share of the explanation suggest strongly that the correlations found are not happenstance despite the inductive method used

sensitivity of the ocean atmosphere carbon cycle to ice covered and ice free conditions in the nordic seas during the last glacial maximum a global carbon cycle box model forced by an ocean general circulation model ogcm is used to investigate how different sea surface reconstructions for the northern north atlantic ocean nordic seas for the last glacial maximum lgm affect the ocean atmosphere carbon cycle via changes in the large scale thermohaline circulation for perennial sea ice cover in the nordic seas climap chart ser geol soc am mc 36 1981 the model predicted deep water formation areas d 13 c distribution and 14 c ventilation ages are partly inconsistent with palaeoceanographic data for the glacial atlantic ocean considering ice free conditions during lgm summer in the nordic seas weinelt et al palaeoclimatology 1 1996 283 brings the model results in better agreement with palaeoceanographic findings thus supporting this particular sea surface reconstruction for both lgm scenarios the ocean circulation model simulates a reduction in the export of north atlantic deep water nadw to the southern ocean by 50 compared to today the effect of changes in the intensity of the thermohaline circulation on atmospheric co2 content alone is rather small accounting for approximately 20 of the net co2 lowering during the lgm d 2004 elsevier b v all rights reserved

sporadic shutdown of north atlantic deep water production during the glacial holocene transition pulsations in the production of north atlantic deep water nadw have been implicated in generating drastic climatic fluctuations during the glacial holocene g h transition1 3 the stable isotope record of benthic foraminifera in high resolution cores from the norwegian sea suggests that such pulsations did occur4 although the question of exact timing and mechanism is still open there is little doubt that nadw pulsations were important in climatic history because the rate of nadw production influences the rate of advection of heat to the northern north atlantic5 here we report that a sporadic shutdown of nadw may be recognizable in deep sea carbonates with normal low sedimentation rates hence the possibility arises that relatively short lived events 1 000 2 000 yr in deep circulation can be mapped over large areas of the sea floor despite the detrimental effects of bioturbation on signal resolution

stable carbon isotopes in marine porewaters abstract we present centimeter scale porewater 13 c profiles from four sites in the central equatorial pacific ocean which reveal steep porewater 13 c gradients up to 1 0 cm 1 at the deep sea sediment water interface we describe the processes controlling porewater carbon isotopic composition and incorporate them into a model of the deep sea benthic carbon cycle our measured 13 c profiles are then used to estimate carbon rain rates at two of these sites manop sites c and s the 13 c data yield organic carbon rain rates of 10 mol c cm 2 yr 1 at site c and 3 mol c cm 2 yr 1 at site s these carbon rain rates agree with recent carbon rain estimates based on sediment trap data and porewater nitrate profiles but are a factor of 2 lower than estimates based on millimeter scale porewater oxygen profiles our model results indicate that changes of the same magnitude in organic carbon rain rate and bottom water composition o 2 co 2 and 13 c have comparable effects on the carbon isotopic composition of surficial porewaters this suggests the need to consider the effects of benthic carbon cycling on the stable carbon isotope record preserved in deep sea benthic foraminifera tests

benthic isotope evidence for changes of the mediterranean outflow during the late quaternary a suit of sediment cores close to and south of the strait of gibraltar 12 36 n 500 2800 m water depth were analyzed for stable isotopes in epibenthic foraminifers cibicidoides wuellerstorfi and planulina ariminensis during peak glacial times the data exhibit higher 13c values of up to 1 6 at intermediate depths near the strait of gibraltar 36 n the values decrease to the south as evidenced by our data but also to the north as revealed by data of intermediate depth cores north of 38 n in duplessy et al 1987 thus the distribution pattern of 13c provides crucial evidence for an increased influence of nutrient depleted mediterranean outflow water mow on the glacial northeast atlantic hydrography during oxygen isotope terminations i and ii the meridional carbon isotope gradient indicates a significantly decreased but still active mow as deduced from the 18o fluctuations the temperatures of the mow in the atlantic were lower during glacial times by as much as 5 c during glacial times and during termination i the maximum 13c values of the mow correlate with minimum values of the north atlantic deep water nadw and vice versa this inverse response to climatic change of the carbon isotope signals of both water masses indicates that the supply of saline mow to the north atlantic may be less important for the formation of nadw than previously assumed

ice core sample measurements give atmospheric co 2 content during the past 40 000 yr recent measurements1 2 on ice samples from camp century greenland 77 10 n 61 08 w byrd station antarctica 80 01 s 110 31 w and dome c 74 40 s 125 10 e suggest that during the late part of the last glaciation the atmospheric co2 concentration was significantly lower than during the holocene further investigation of this natural increase of the atmospheric co2 concentration in the past should aid our understanding of the climatic implications of the man made co2 increase since the beginning of industrialization3 here we report new and precise measurements of the co2 concentration of the air occluded in bubbles of ice samples from camp century and byrd station using a new dry extraction technique the extracted gases were analysed with an ir laser spectrometer irls samples from 22 different depths were analysed from each core the samples are distributed over a depth interval corresponding approximately to the past 40 000 yr in addition results for ice samples from selected depth horizons from a colder region north central greenland 74 37 n 39 36 w and from a warmer region dye 3 greenland 65 11 n 43 50 w are given based on these results we estimate the trend of the atmospheric co2 concentration during the past 40 000 yr

reconstruction of atmospheric co2 from ice core data and the deep sea record of ontong java plateau the milankovitch chron we provide a reconstruction of atmospheric co2 from deep sea sediments for the past 625000 years milankovitch chron our database consists of a milankovitch template of sea level variation in combination with a unique data set for the deep sea record for ontong java plateau in the western equatorial pacific we redate the vostok ice core data of barnola et al 1987 to make the reconstructions we employ multiple regression between deep sea data on one hand and ice core co2 data in antarctica on the other the patterns of correlation suggest that the main factors controlling atmospheric co2 can be described as a combination of sea level state and sea level change for best results squared values of state and change are used the square of sea level rule agrees with the concept that shelf processes are important modulators of atmospheric co2 e g budgets of shelf organic carbon and shelf carbonate nitrate reduction the square of change rule implies that on short timescales any major disturbance of the system results in a temporary rise in atmospheric co2

the internal structure of rock glaciers and recently deglaciated slopes as revealed by geoelectrical tomography insights on permafrost and recent glacial evolution in the central and western alps italy france abstract ground ice of permafrost origin and sedimentary ice of glacial origin can coexist in locations where rock glaciers and glaciers interacted as well as in glacigenic sediments abandoned by a retreating glacier and subsequently exposed again to atmospheric cooling some of these geomorphological settings in the central foscagno rock glacier and western alps marinet and schiantala rock glaciers schiantala debris covered glacier maledia glacier were explored by means of geoelectrical tomographies the aim was that of inferring the presence of ice and cryologically interpreting electrical stratigraphies in order to test whether or not the internal structure of these landforms can be used for the reconstruction of recent permafrost and glacier evolution geomorphological data assisted these reconstructions and available borehole stratigraphies were used to calibrate the resistivities along with the ice debris mixture massive ice has also been found as lenses both at the apex and the front of the studied rock glaciers these lenses of sedimentary origin are thought to be transferred from a glacier snout to sectors of rock glacier and eventually embedded into the permafrost creep the scarcity of frozen debris in the mid upper part of the rock glaciers as revealed by low resistivity values can be due to the disruptive effect of the over riding glacier over the permafrost the near surface sedimentary ice masses detected along the slopes of the studied glacial cirques are interpreted as or debris covered terminations of the glaciers still visible upward or as fragments of it detached by the main bodies these ice masses are locally associated to medium high resistive sediments consistent with permafrost occurrence this indicates that the non glacial environment established during the deglaciation allowed the onset of frozen sediments formation overall the results indicate that internal structure of rock glaciers and recent deglaciated slopes can store the different climate related episodes occurred in a specific area such as those linked to the shifting between glacial to criotic condition and vice versa

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