globorotalia truncatulinoides growth and chemistry as probes of the past thermocline 1 shell size this work identifies features of the life history of the deep living planktonic foraminifer globorotalia truncatulinoides that offer possibilities for reconstructing characteristics of the past ocean s main thermocline part 1 considers two aspects of variation in shell size the predictability of growth related size changes which we need to calculate changes in shell chemistry and a model for environmentally forced changes in shell size frequency which suggests how shell size may be a direct source of paleoceanographic information even though size variation among shells of g truncatulinoides at the same stage of growth same number of chambers exceeds the size difference between successive growth stages growth related size changes are predictable because shells tend to grow at the same rate variation in initial shell size is sufficient to account for the large size variation found among shells at the same stage of growth several lines of evidence suggest that g truncatulinoides reproduces at 600 m in the water column and it appears that vertical mixing to that depth is required to return juvenile shells to the surface anything that prevents this such as shallowing of the thermocline can interfere with g truncatulinoides life history in such a way that its shell size frequency distributions are altered among shells falling to the seafloor from a reproducing population are large numbers of both juvenile and adult sizes and if reproduction is inhibited the frequencies of those sizes are reduced and the relative frequency of intermediate sized shells increases a paleoceanographically useful result of this is that the topography of the main thermocline tends to be reflected in the size frequency distribution of g truncatulinoides shells from the underlying sediments in areas where the top of the main thermocline is shallower than 600 m production of juveniles 125 177 m and reproductive adults 425 m is reduced leaving predominantly intermediate sized 212 355 m shells

oxygen isotopic composition of multiple species of planktonic foraminifera recorders of the modern photic zone temperature gradient abundances of 12 species of planktonic foraminifera collected in two plankton tows from the east tropical atlantic are compared to the chlorophyll content and the temperature of the sea water from which they were collected as expected from previous work in the tropics all dominant tropical species occur in greatest abundance within the photic zone many species occur in greatest abundances in the seasonal thermocline in association with the maximum chlorophyll concentration while a few algal symbiont bearing species occur in greatest abundance in the mixed layer the 18o measurements of planktonic foraminifera shells from core top sediment samples confirm the vertical stratification within the photic zone that is suggested by the relationship between hydrography and abundances found in the plankton tows and found in the statistical study by ravelo et al 1990 comparison between the measured 18o values of planktonic foraminifera with the predicted 18o profiles of the overlying water column at three core locations indicate that species abundances in the sediment record the seasonally integrated conditions of the photic zone and suggests that the abundance of a species in the sediment depends on whether the preferred ecological conditions of that species may be found within the photic zone of the overlying water column sometime during the year species which calcify below the photic zone have only trace relative abundances finally it appears that the total range of 18o values of the dominant species approximates the predicted annual 18o of calcite range in the upper 80 m of the water column

living planktic foraminifera in the central tropical pacific ocean articulating the equatorial cold tongue during la nina 1992 abstract in cold tongue conditions of august september 1992 living planktic foraminifera in the equatorial pacific tracked circulation featuresand phytoplankton abundance an equatorial assemblage associated with the cool and productive equatorial region contained g bulloides a species often associated with tropical coastal upwelling as well as the nonspinose herbivores g menardii g glutinata p obliquiloculata and n dutertrei previously associated with equatorial environments within surface subtropical waters poleward of 5 n and 5 s g sacculifer g ruber and g conglobatus dominated foraminiferal populations these species have successfully adapted to oligotrophic conditions by exploiting dinoflagellate endosymbionts high standing stocks of these species in equatorial regions suggest that they can also thrive within equatorial light levels and temperatures a deep southern assemblage dominated by nonspinose g conglomerata and g tumida and spinose g aequilateralis had a subsurface maximum at 80 200 m outside of active upwelling and outcropped to the surface at 1 s from el nino to cold tongue conditions equatorial fauna reflected higher primary productivity and an increase in the role of advection by the south equatorial current

calcitic foraminiferal data confirmed by cadmium in aragonitic hoeglundina application to the last glacial maximum in the northern indian ocean a core top study of cadmium uptake into the shells of the aragonitic benthic foraminifera hoeglundina elegans demonstrates that the hoeglundina cd ca partition coefficient is close to 1 0 throughout the ocean cd uptake by hoeglundina is far less depth dependent than that of calcitic benthic foraminifera furthermore manganese carbonate does not precipitate on these aragonitic shells allowing for the recovery of cd estimates in some samples where calcitic species are spoiled by contaminating overgrowths because cd incorporation into hoeglundina shows little depth dependence a comparison of calcitic and hoeglundina cd data can be used to verify the assumption that the depth dependence observed for calcitic benthic foraminifera is time invariant this comparison has been undertaken in downcore and last glacial maximum lgm samples from the northern indian ocean aragonitic and calcitic foraminiferal estimates for cd in the lgm ocean are in excellent agreement this result indicates upper ocean estimates of lgm cd are reliable despite a factor of two variation in cd uptake by calcitic species over this depth range cd and 13c data indicate that the uppermost waters of the lgm arabian sea were strongly nutrient depleted relative to today but that the deepest waters of the northern bay of bengal had nutrient concentrations at least as high as or higher than modern levels a strong vertical gradient of increasing nutrients with increasing depth existed in both basins during the lgm a west to east gradient of increasing nutrient concentrations also is evident at all depths in the bay of bengal there is evidence for an enhanced gradient of nutrients increasing from south to north the lgm deep arabian sea and intermediate depth bay of bengal were nutrient depleted compared to the modern ocean however cd and 13c data indicate that nutrient depletion in the northern indian ocean did not exceed that of the deep eastern tropical pacific except during the latest part of oxygen isotope stage 2 and according to cd data only the early stages of deglaciation during oxygen isotope stage 3 and early stage 2 cd in the northern indian ocean and cd in the eastern tropical pacific were indistinguishable although both regions have lower cd at these times compared to the holocene

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

paleoceanographic implications of the difference in deep sea sediment mixing between large and fine particles more and more paleoceanographic studies are performed on different size fractions of deep sea sediments although it has been a controversial issue for some time the bioturbation process depends on the particle size and can in principle decouple paleoceanographic records obtained in the same core this problem is studied by using a simple mixing model which allows the derivation of analytical equations for both the expected phase shift and relative attenuation of signals carried by different size fractions depending on several parameters the time shift and relative attenuation can be on the order of a few millenia and 50 respectively however high sedimentation rates 10 20 cm kyr minimize these potential complications allowing us to study millenium scale events in well chosen sedimentary environments

melting experiments on the enstatite diopside join at 70 224 kbar including the melting of diopside melting relations on the enstatite diopside en mg2si2o6 di camgsi2o6 join including the compositions of crystalline phases and melts coexisting along the solidi were experimentally determined in the pressure range 70 224 kbar with a split sphere anvil apparatus ussa 2000 melting is peritectic in enstatite rich compositions at 70 124 kbar 1840 2100 c and eutectic at higher pressures while the diopside rich clinopyroxene melts azeotropically at 70 165 kbar and up to 300 c lower temperatures than the eutectic orthopyroxene is replaced with enstatite rich clinopyroxene at 120 kbar and 2090 c first garnet with 17 mol di forms on the solidus at 158 kbar and 2100 c two garnets coexist on the solidus at 165 183 kbar and 2100 c garnet coexists with casio3 perovskite at 183 224 kbar 2100 2230 c and two coexisting perovskites are stable at higher pressures the melting curve of diopside was determined at 80 170 kbar the slope becomes negative at 140 kbar and 2155 c at 170 kbar and 2100 c diopside with 96 di breaks down to garnet with 89 di and casio3 perovskite the new data were used to calculate an improved temperature pressure phase diagram for the cmas system which can be useful for estimating the mineralogy of the earth s upper mantle

distribution of recent nannofossils beneath the benguela system southwest african continental margin abstract one hundred and forty eight surface samples recovered from the southwest african continental margin 35 17 s have been examined for their nannofossil content coccolith abundance is high in sediments from the deep water areas but declines toward the coast under the main areas of upwelling five distinct bathymetric oceanographic assemblages can be characterized by their nannofossil content coastal upwelling orange bank intermediate southern deep water and northern deep water angola current these distinctions are based on the distribution of eight ecologically significant taxa in order of decreasing abundance they are gephyrocapsa oceanica helicopontosphaera kamptneri cyclococcolithina leptopora coccolithus pelagicus syracosphaera div sp thoracosphaera div sp rhabdosphaera div sp and umbilicosphaera sibogae sea surface temperature and salinity variations which correlate with the extent and intensity of the main upwelling cells are thought to be the most important controls on coccolith distribution although nutrient availability and reduction of surface water transparency may be of local importance the exclusion of three stratigraphical index species for the quaternary emiliania huxleyi gephyrocapsa caribbeanica and g ericsonii from the quantitative analysis will permit the future application of these results to paleoceanographic reconstructions of the benguela system in pleistocene core sections

planktonic foraminifera calcareous nannoplankton and ascidian variations during the last 25 kyr in the southwestern atlantic a paleoproductivity signature micropaleontological and geochemical analyses from western south atlantic core san 76 off southeast brazil revealed changes in stable isotope values and in the assemblages of calcareous nannoplankton and planktonic foraminifera during the past 25 kyr that point to significant paleoceanographic and climatic changes leading to an increase in productivity during the last deglaciation the enhanced surface productivity was clearly indicated by increased relative abundances of the planktonic foraminifera globigerina bulloides and neogloboquadrina dutertrei and the decreased values of 13 c in planktonic foraminiferal tests a coeval shoaling of the nutricline and thermocline was indicated by decreased relative abundances of the calcareous nannoplankton florisphaera profunda and an increased relative abundance of the planktonic foraminifera globorotalia truncatulinoides right coiling we speculate that these changes are related to n s shifts of the atlantic intertropical convergence zone itcz a significant increase in the cd ca ratio and decrease in 13 c values in the benthic foraminifer hoeglundina elegans along with a significant increase in the relative abundance of ascidian spicules during the deglaciation suggest that benthic communities in this area strongly benefited from increased surface water productivity 2007 elsevier b v all rights reserved

the vitoria eddy and its relation to the brazil current in late austral summer 1991 a cyclonic thermocline eddy was detected in the subtropical western south atlantic off the brazilian shelf near the city of vitoria this vitoria eddy was tracked for 55 days by surface drifters drogued at 100 m depth the drifters had been deployed in the western boundary current regime by fs meteor as part of a basinwide surface current study the analysis of a combined ctd xbt section across the vitoria eddy together with drifter data and satellite images of the thermal surface structure revealed the unexpected complexity of the region the eddy interacted not only with the local topography and the brazil current located farther offshore but also with an extended upwelling regime north of cabo frio the hydrographic and kinematic properties and anomalies of the vitoia eddy are analyzed and compared with similar vortices described elsewhere in literature

simmax a modern analog technique to deduce atlantic sea surface temperatures from planktonic foraminifera in deep sea sediments we present a data set of 738 planktonic foraminiferal species counts from sediment surface samples of the eastern north atlantic and the south atlantic between 87 n and 40 s 35 e and 60 w including published climate long range investigation mapping and prediction climap data these species counts are linked to levitus s 1982 modern water temperature data for the four caloric seasons four depth ranges 0 30 50 and 75 m and the combined means of those depth ranges the relation between planktonic foraminiferal assemblages and sea surface temperature sst data is estimated using the newly developed simmax technique which is an acronym for a modern analog technique mat with a similarity index based on 1 the scalar product of the normalized faunal percentages and 2 a weighting procedure of the modern analog s ssts according to the inverse geographical distances of the most similar samples compared to the classical climap transfer technique and conventional mat techniques simmax provides a more confident reconstruction of paleo ssts correlation coefficient is 0 994 for the caloric winter and 0 993 for caloric summer the standard deviation of the residuals is 0 90 c for caloric winter and 0 96 c for caloric summer at 0 m water depth the sst estimates reach optimum stability standard deviation of the residuals is 0 88 c at the average 0 to 75 m water depth our extensive database provides sst estimates over a range of 1 4 to 27 2 c for caloric winter and 0 4 to 28 6 c for caloric summer allowing sst estimates which are especially valuable for the high latitude atlantic during glacial times an electronic supplement of this material may be obtained on adiskette or anonymous ftp from kosmos agu org login toagu s ftp account using anonymous as the username and guestas the password go to the right directory by typing cd append typels to see what files are available type get and the name of the file toget it finally type exit to leave the system paper 95pa01743 simmax a modern analog technique to deduce atlantic sea surfacetemperatures from planktonic foraminifera in deep sea sediments uwepflaumann josette duprat claude pujol and laurent d labeyrie diskette may be ordered from american geophysical union 2000florida avenue n w washington dc 20009 payment mustaccompany order

atlantic ocean circulation during the younger dryas insights from a new cd ca record from the western subtropical south atlantic author posting american geophysical union 2003 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in paleoceanography 18 2003 1086 doi 10 1029 2003pa000888

planktonic foraminiferal assemblages preserved in surface sediments correspond to multiple environment variables abstract here we investigate the relationships between modern planktonic foraminiferal species assemblages from atlantic and pacific core top sediment samples and 35 water column and preservation properties using canonical correspondence analysis cca cca finds two faunal dimensions axes that are most highly correlated to the environmental variables and describes each axis in terms of the best linear combination of environmental variables cca axis 1 30 4 of the faunal variance is related primarily to mean annual sea surface temperature sst r 0 96 cca axis 2 7 9 of the faunal variance is related to environmental variability associated with an inverse relationship between sst and surface salinity as well as pycnocline phosphate concentrations the seasonal range in nitrate concentrations water depth and chlorophyll concentrations at the sea surface based on this clustering of nutrient and chlorophyll on axis 2 we infer an ecological response to oceanic fertility no evidence is found for a unique dissolution influence suggesting that sea floor carbonate ion concentration cannot be estimated reliably from planktonic foraminiferal assemblages our results support the use of foraminiferal assemblages to estimate mean annual sst

the last 100 000 years in the western mediterranean sea surface water and frontal dynamics as revealed by coccolithophores a quantitative analysis was carried out on coccolith assemblages from two pleistocene cores k1 and k10 from the western mediterranean the distribution of selected coccolithophore species provides new paleoclimatic and paleoceano graphic data a continuous sequence from the top of isotope stage 5 to the holocene was recorded the reversal in dominance between gephyrocapsa muellerae and emiliania huxleyi was dated in both cores at ca 73 ka at about 47 ka e huxleyi shows a regular increase whereas g muellerae progressively decreases in abundance during interglacial periods high concentrations of coccoliths are observed whereas in glacial times coccoliths are more diluted and the percentage of reworked forms increases as a consequence of the higher terrigenous input after taking careful account of the dilution factor we conclude that the production of coccolithophores was higher during warm periods maxima in coccolith concentrations coincide with highstand episodes probably as a result of the intensification of the atlantic flux into the mediterranean across the gibraltar strait this intensification could have produced an increase in nutrient content in the surface mediterranean waters during cold periods the western mediterranean front underwent a reduction in activity probably due to an increase in the saline and or thermal gradients between the superficial waters and intermediate waters in the liguro provencal basin

paleoceanographic interpretations of coccoliths and oxygen isotopes from the sediment surface of the southwest indian ocean abstract the distribution of forty four coccolithophore species in one hundred deep sea core tops from the southwest indian ocean is described three coccolith assemblages have been recognised maputo agulhas current and deep water by the relative abundances of four ecologically significant coccolithophore species gephyrocapsa oceanica emiliania huxleyi calcidiscus leptoporus and umbilicosphaera sibogae their biogeographical distribution appears to be related to water temperature nutrient concentration and dissolution the degree of preservation of coccoliths and foraminifera indicates that the carbonate lysocline lies somewhere between 3500 and 4000 m resulting in the concentration of dissolution resistant microfossils below this depth stable oxygen isotope ratios of the planktonic foraminiferal species globigerinoides sacculifer range between 1 5 to 1 0 pdb equal to 22 8 25 1 c and occur in a narrow band on the sea floor beneath the a route of the agulhas current these values are about 0 5 per mil pdb lighter than samples analyzed on either side of this band and can be explained by the agulhas current s elevated temperature at the ocean surface of 2 3 c thus an oxygen isotope imprint of the agulhas current exists beneath it on the sea floor the agulhas current is probably the major factor influencing sedimentation sediment distribution patterns and geological features in the study area at present it is voluminous and fast flowing possibly eroding sediments up to 2500 m below the surface the oxygen isotope ratios and nannoplankton counts obtained in this study indicate however that the majority of samples are most probably recent or at least not older than 85 000 years this implies that sediments are accumulating on the ocean floor and that the agulhas current does not have a pronounced erosional influence at least in areas from which cores were retrieved for this study

globorotalia truncatulinoides as indicator of upper ocean thermal structure during the quaternary evidence from the south china sea and okinawa trough abstract globorotalia truncatulinoides is shown to be indicative of upper ocean thermal structure and sensitive to the thermocline fluctuations and the thickness of the north pacific subtropical mode water npstmw thermostads for the quaternary in the south china sea scs and okinawa trough during the last 1 5 ma the relative abundance percentage of g truncatulinoides displayed long term oscillations on a time scale longer than the glacial interglacial cycle but with two major changes around 550 400 ka and 115 55 ka bp it decreased to near zero during 550 400 ka bp and then disappeared from the equatorial indian and pacific oceans this suggests that the thermocline depth and the scale of winter deep mixing decreased at that time interval and since then the linkage between the scs and the equatorial oceans at intermediate depths remarkably weakened and the npstmw strongly influenced the scs the predominance of left coiling g truncatulinoides together with the occurrence of globoquadrina conglomerata in the western north pacific between 115 and 55 ka bp indicates a deep thermocline and very thick npstmw thermostads a decreasing trend in the relative abundance of g truncatulinoides from marine isotopic stages 7 to 1 is evident in the scs indicating a progressive reduction of the npstmw thermostads after the last glacial maximum g truncatulinoides increased in abundance but abruptly disappeared between 8 and 4 ka bp from the scs and okinawa trough implying a mid holocene reduction in the npstmw thermostad thickness

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

late pleistocene palaeocenography of the tasman sea implications for the dynamics of the warm pool in the western pacific quantitative analyses of planktonic foraminifera from 47 core top samples spatially distributed through the tasman sea and cores rc12 113 e36 23 dsdp sites 588 592 593 and odp site 828a from a n s transect supplemented with stable isotope analyses indicate that three planktonic foraminiferal assemblages defined by factor analysis on core top material correlated with three hydrographic modes defined on the basis of sea surface temperatures temperature profiles seasonal changes in temperature and mixed layer depth similar assemblages were found in down core material along the tasman sea transect that combined with semi quantitative analyses of foraminiferal assemblages provinces and the coiling ratio of globorotalia truncatulinoides allows reconstruction of the position of the tasman front or the subtropical divergence during the late brunhes chron the results indicate that the tasman front migrated from its present position at 30 s to 26 s during the last glacial maximum the northward migration of the tasman front may indicate a reduction in volume of the equatorial warm pool and or an increase in the strength of cool subtropical water masses the late pleistocene distribution of g truncatulinoides left coiling from appears to be related to the formation of subantarctic mode water thermostads this relationship may explain the evolutionary origin of this species in the southwest pacific at 2 4 ma simultaneously with the onset of late pliocene glaciations the past position of the subtropical convergence is reconstructed by means of coilingv directions in neogloboquadrina pachyderma the convergence apparently migrated slightly north of 43 s core e36 23 during glacial stages 6 10 and 12

astronomical forcing of contrasting rainfall changes in tropical south america between 12 400 and 8800 cal yr b p abstract today precipitation over tropical south america is largely controlled by the seasonal movements of the inter tropical convergence zone itcz during the summer the itcz is shifted southward due to the warming of the continent paleoclimate data from southeastern amazonia and the central andes indicate that these two areas evolved similarly during the last 30 000 yr however between 12 400 and 8800 cal yr b p eastern amazonia received substantial moisture whereas the bolivian altiplano was arid this suggests that the itcz during summer was then farther north than it is today

the deglacial history of the western tropical atlantic as inferred from high resolution stable isotope records off northeastern brazil abstract the western south atlantic boundary currents represent a sensitive system within the global thermohaline circulation thc we investigated the impact of deglacial thc changes on the western tropical atlantic studied in six high resolution sediment cores from the upper continental slope of brazil the stratigraphy of the cores is mainly based on 14c ams dating of monospecific foraminiferal samples changes in the upper layer tropical ocean during the deglaciation are inferred from stable oxygen isotope measurements on planktic and benthic foraminifera variations in the 18o residuals are assumed to be mainly temperature related during the oldest and younger dryas cooling periods two major deglacial thc disturbances are reported from north atlantic sediment cores concomitant to the repeated thc slowdown we observe an upper layer warming in the tropical ocean a reduced northward heat export from the tropical areas during these periods weak north brazil current is additionally reflected by low meridional gradients in the stable oxygen records this generally agrees with results from coupled ocean atmosphere models

building icelandic igneous crust by repeated melt injections observations of microseismicity provide a powerful tool for mapping the movement of melt in the crust here we record remarkable sequences of earthquakes 20 km below the surface in the normally ductile crust in the vicinity of askja volcano in northeast iceland the earthquakes occur in swarms consisting of identical waveforms repeating as frequently as every 8 s for up to 3 h we use template waveforms from each swarm to detect and locate earthquakes with an automated cross correlation technique events are located in the lower crust and are inferred to be the result of melt being injected into the crust during melt intrusion high strain rates are produced in conjunction with high pore fluid pressures from the melt or exsolved carbon dioxide these cause brittle failure on high angle fault planes located at the tips of sills moment tensor solutions show that most of the earthquakes are opening cracks accompanied by volumetric increases this is consistent with the failure causing the earthquakes by melt injection opening new tensile cracks analysis of the magnitude distribution of earthquakes within a swarm reveals a complicated relationship between the imposed strain rates and the fluids that cause brittle failure the magnitude of the earthquakes is controlled by the distance fluids can migrate along a fault whereas the frequency of the events is controlled by the strain rate faults at the tips of sills act to focus melt transport between sills and so must be an important method of transporting melt through the lower crust

sea surface temperatures in the equatorial and south atlantic ocean during the last glacial maximum 23 19 ka 1 we used planktic foraminiferal assemblages in 70 sediment cores from the tropical and subtropical south atlantic ocean 10 n 37 s to estimate annual mean sea surface temperatures ssts and seasonality for the last glacial maximum with a modified version of the imbrie kipp transfer function method iktf that takes into account the abundance of rare but temperature sensitive species in contrast to climap project members 1981 the reconstructed ssts indicate cooler glacial ssts in the entire tropical subtropical south atlantic with strongest cooling in the upwelling region off namibia 7 10 c and smallest cooling 1 2 c in the western subtropical gyre in the western atlantic our data support recent temperature estimates from other proxies in the upwelling regions in the eastern atlantic our data conflict with sst reconstructions from alkenones which may be due to an environmental preference of the alkenone producing algae or to an underestimation of foraminiferal ssts due to anomalous high abundances of n pachyderma sinistral

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

spatial and temporal offsets between proxy records in a sediment drift chronologies for late quaternary marine sediment records are usually based on radiocarbon ages of planktonic foraminifera signals carried by other sedimentary components measured in parallel can provide complementary paleoclimate information a key premise is that microfossils and other indicators within a given sediment horizon are of equal age we show here that haptophyte derived alkenones isolated from bermuda rise drift sediments are up to 7000 years older than coexisting planktonic foraminifera this temporal offset which is apparently due to lateral transport of alkenones on fine grained particles from the nova scotian margin markedly influences molecular estimates of sea surface temperatures more broadly the observation raises questions about both the temporal and the geographic fidelity of paleoenvironmental records encoded by readily transported components of sediments

distribution of coccoliths in surface sediments of the south eastern south atlantic ocean ecology preservation and carbonate contribution abstract recent coccoliths from 52 surface sediment samples recovered from the south eastern south atlantic were examined qualitatively and quantitatively in order to assess the controlling mechanisms for their distribution patterns such as ecological and preservational factors and their role as carbonate producers total coccolith abundances range from 0 2 to 39 9 coccoliths 109 g 1 sediment four assemblages can be delineated by their coccolith content characterising the northern benguela the middle to southern benguela the walvis ridge and the deeper water distinctions are based on multivariate ordination techniques applied on the relative abundances of the most abundant taxa emiliania huxleyi calcidiscus leptoporus gephyrocapsa spp coccolithus pelagicus and subtropical to tropical species the coccolith distribution seems to be temperature and nutrient controlled co varying with the seaward extension of the upwelling filament zone in the benguela a preservation index cex based on the differential dissolution behaviour of the delicate e huxleyi and gephyrocapsa ericsonii versus the robust c leptoporus is applied in order to detect the position of the coccolith lysocline although some samples were recognised as dissolution affected the distribution of the coccoliths in the surface sediments reflects the different oceanographic surface water conditions mass estimations of the coccolith carbonate reveal coccoliths to be only minor contributors to the carbonate preserved in the surface sediments the mean computed coccolith carbonate content is 17 wt equivalent to a mean contribution of 23 to the bulk carbonate

an evaluation of 14c age relationships between co occurring foraminifera alkenones and total organic carbon in continental margin sediments 1 radiocarbon age relationships between co occurring planktic foraminifera alkenones and total organic carbon in sediments from the continental margins of southern chile northwest africa and the south china sea were compared with published results from the namibian margin age relationships between the sediment components are site specific and relatively constant over time similar to the namibian slope where alkenones have been reported to be 1000 4500 years older than co occurring foraminifera alkenones were significantly similar to 1000 years older than co occurring foraminifera in the chilean margin sediments in contrast alkenones and foraminifera were of similar age within 2 sigma error or better in the nw african and south china sea sediments total organic matter and alkenone ages were similar off namibia age difference toc alkenones 200 700 years chile 100 450 years and nw africa 360 770 years suggesting minor contributions of preaged terrigenous material in the south china sea total organic carbon is significantly 2000 3000 years older owing to greater inputs of preaged terrigenous material age offsets between alkenones and planktic foraminifera are attributed to lateral advection of organic matter physical characteristics of the depositional setting such as seafloor morphology shelf width and sediment composition may control the age of co occurring sediment components in particular offsets between alkenones and foraminifera appear to be greatest in deposition centers in morphologic depressions aging of organic matter is promoted by transport age offsets are correlated with organic richness suggesting that formation of organic aggregates is a key process

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr