paleoclimatic significance of the stratigraphic occurrence of photosynthetic biomarker pigments in the nordic seas sedimentary chlorins and porphyrins are diagenetic products of chlorophyll molecules and are considered to be chemical fossils or biomarkers of phototrophic organisms the stratigraphic occurrence of such components was investigated in four cores from the nordic seas that span the last deglacial period the presence of chlorins in all the samples deposited during the younger dryas and at the end of the last glacial period indicated that photosynthetic activity occurred during these cold episodes and hence that ice free conditions existed at least seasonally in the nordic seas vanadyl porphyrins were found in sediments deposited during termination ia in only two of the cores close to the barents shelf we argue that they derive from erosion and advection of organic rich deposits as ice rafted debris during melting of the barents ice sheet thus we suggest that the sedimentary occurrence of vanadyl porphyrins in nordic sea cores can be used as a marker of ice rafted debris from the barents ice sheet the absence of such components during termination ib indicates that the complete destruction of the barents ice sheet took place during the first stage of the deglaciation

pore fluid constraints on deep ocean temperature and salinity during the last glacial maximum pore water records of 18 o and cl from odp site 1063a on the bermuda rise constrain the change in seawater 18 o and salinity from the last glacial maximum lgm to the holocene to be 0 75 0 05 and 2 5 0 1 respectively coupled with a measured benthic foraminiferal 18 o change this result means that bottom waters were 4 6 0 8 c cooler than the holocene at the lgm and therefore at or near the seawater freezing point coupled 18 o and chlorinity results give an extrapolated mean ocean lgm to holocene change in 18 o of 0 95 0 09 these data also constrain the past southern source deep water salinity to be 35 76 0 04 psu which is within error of the mean deep ocean value for this time

strong middepth warming and weak radiocarbon imprints in the equatorial atlantic during heinrich 1 and younger dryas we present a benthic foraminiferal multiproxy record of eastern equatorial atlantic eea middepth water 1295m covering the last deglacial we show that eea middepth water temperatures were elevated by 3 90 5 degrees c and 5 21 2 degrees c during heinrich event 1 h1 and younger dryas yd respectively the radiocarbon content of the eea middepth during h1 and yd is relatively low and comparable to the values of the pre h1 episode and bolling allerod respectively a transient earth system model simulation which mimics the observed deglacial atlantic meridional overturning circulation amoc history qualitatively reproduces the major features of the eea proxy records the simulation results suggest that fresh water induced weakening of the amoc leads to a vertical shift of the horizon of southern ocean sourced water and a stronger influence of eea sea surface temperatures via mixing our findings reaffirm the lack of a distinctive signature of radiocarbon depletion and therefore do not support the notion of interhemispheric exchanges of strongly radiocarbon depleted middepth water across the tropical atlantic during h1 and yd our temperature reconstruction presents a critical zonal and water depth extension of existing tropical atlantic data and documents a large scale and basin wide warming across the thermocline and middepth of the tropical atlantic during h1 and yd significant difference in the timing and pace of h1 middepth warming between tropical atlantic and north atlantic likely points to a limited role of the tropical atlantic middepth warming in the rapid heat buildup in the north atlantic middepth

variability of the arctic front during the last climatic cycle application of a novel molecular proxy in the nordic seas the arctic front af marks the boundary between the waters of the north atlantic drift norwegian current and those of the arctic domain long or short term shifts in the position of the af may affect climate conditions in the northern hemisphere arctic water masses are also the loci of modern open ocean convection hence defining these areas in the past is important for reconstructing and modelling ocean circulation and its variability c37 alkenones are biomarkers for some algae of the class prymnesiophyceae e g coccolitho phorids such as emiliania huxleyi these alga occur in most parts of the oceans in ice free conditions and are found nowadays throughout the nordic seas we have related the sedimentary abundance of the tetraunsaturated c37 alkenone c37 4 to two types of water masses in the nordic seas in locations affected by atlantic water masses percentages of c37 4 are less than 5 whereas in arctic type water masses these increase to more than 5 we propose that this observation can be used as a modern analogue to reconstruct the position of the af in north atlantic quaternary sediments using this novel molecular proxy we can infer that the southward migration of the af in the ne atlantic reached 50 n during the last glacial maximum lgm but perhaps only 60 n during the younger dryas and that ocean conditions free of sea ice prevailed throughout the northern north atlantic in summer

stable sr isotope sr ca mg ca li ca and mg li ratios in the scleractinian cold water coral lophelia pertusa the aragonitic skeletons of scleractinian cold water corals can serve as valuable archives in paleoceanographic studies the potential of 88 86sr sr ca mg ca li ca and mg li ratios of the cold water coral lophelia pertusa to record intermediate water mass properties has been investigated here we used samples from several locations along the european continental margin spanning a large temperature range from 6 to 14 c stable strontium isotope measurements were carried out with the recently developed double spike tims technique and our results differ from those obtained with less precise methods in contrast to the strong positive relationship with temperature of previous studies our results suggest that 88 86sr measured in scleractinian cold water corals is not controlled by seawater temperature but reflects the sr isotopic composition of seawater with an offset of 88 86sr 0 196 as found in previous studies the elemental ratios sr ca li ca and mg li measured in corals are significantly related to water temperature and do not correlate with salinity moreover sr ca ratios in l pertusa display the expected inverse correlation with temperature however the variance in the sr ca data severely limits the accuracy of paleotemperature estimates the li ca and mg ca ratios reveal other influences besides temperature such as ph and or growth or calcification rate however corresponding mg li ratios in l pertusa are more tightly related to temperature as they remove these secondary effects in particular the mg li ratio in l pertusa may serve as a new promising paleotemperature proxy for intermediate water masses our dataset represents the most extensive geochemical examination of l pertusa to date revealing a temperature sensitivity of 0 015 mol mmol c for mg li however using this temperature dependence and the precision of 5 3 2sd only temperature variations larger than 1 5 c can be resolved with 95 confidence

climate and oceanographic variability in the sw barents sea during the holocene the holocene section of the marine sediment core psh 5159n located in the sw barents sea has been studied at high resolution with a multiproxy approach a well stratified water column occurred at the site 11 9 8 ka bp the stratification was probably a result of a winter sea ice cover and or fresh warm surface waters during summer stratification and resultant reduction in air sea interaction allowed for warmer bottom water temperatures the general situation 11 9 8 ka bp could have been associated with an anomalous high pressure system over the nordic seas and the arctic ocean during the 11 10 5 ka bp interval the polar front was located close to the barents sea margin the polar front moved towards the site from 10 5 ka bp and from 9 8 to 7 5 ka bp it was probably located close to the site at 7 5 ka bp the polar front retreated eastwards as the present day oceanographic pattern established the mid holocene was in general characterized by rather stable conditions in contrast highly variable cond

the effect of a large freshwater perturbation on the glacial north atlantic ocean using a coupled general circulation model abstract the commonly held view of the conditions in the north atlantic at the last glacial maximum based on the interpretation of proxy records is of large scale cooling compared to today limited deep convection and extensive sea ice all associated with a southward displaced and weakened overturning thermohaline circulation thc in the north atlantic not all studies support that view in particular the strength of the overturning circulation is contentious and is a quantity that is difficult to determine even for the present day quasi equilibrium simulations with coupled climate models forced by glacial boundary conditions have produced differing results as have inferences made from proxy records most studies suggest the weaker circulation some suggest little or no change and a few suggest a stronger circulation here results are presented from a three dimensional climate model the hadley centre coupled model version 3 hadcm3 of the coupled atmosphere ocean sea ice system suggesting i

constraints on the magnitude and patterns of ocean cooling at the last glacial maximum observation based reconstructions of sea surface temperature from relatively stable periods in the past such as the last glacial maximum represent an important means of constraining climate sensitivity and evaluating model simulations1 the first quantitative global reconstruction of sea surface temperatures during the last glacial maximum was developed by the climate long range investigation mapping and prediction climap project in the 1970s and 1980s refs 2 3 since that time several shortcomings of that earlier effort have become apparent4 here we present an updated synthesis of sea surface temperatures during the last glacial maximum rigorously defined as the period between 23 and 19 thousand years before present from the multiproxy approach for the reconstruction of the glacial ocean surface margo project5 we integrate microfossil and geochemical reconstructions of surface temperatures and include assessments of the reliability of individual records our reconstruction reveals the presence of large longitudinal gradients in sea surface temperature in all of the ocean basins in contrast to the simulations of the last glacial maximum climate available at present6 7

mg ca temperature proxy in benthic foraminifera new calibrations from the florida straits and a hypothesis regarding mg li 1 over the past decade the ratio of mg to ca in foraminiferal tests has emerged as a valuable paleotemperature proxy however large uncertainties remain in the relationships between benthic foraminiferal mg ca and temperature mg ca was measured in benthic foraminifera from 31 high quality multicore tops collected in the florida straits spanning a temperature range of 5 8 to 18 6 c new calibrations are presented for uvigerina peregrina planulina ariminensis planulina foveolata and hoeglundina elegans the mg ca values and temperature sensitivities vary among species but all species exhibit a positive correlation that decreases in slope at higher temperatures the decrease in the sensitivity of mg ca to temperature may potentially be explained by mg ca suppression at high carbonate ion concentrations it is suggested that a carbonate ion influence on mg ca may be adjusted for by dividing mg ca by li ca the mg li ratio displays stronger correlations to temperature with up to 90 of variance explained than mg ca alone these new calibrations are tested on several last glacial maximum lgm samples from the florida straits lgm temperatures reconstructed from mg ca and mg li are generally more scattered than core top measurements and may be contaminated by high mg overgrowths the potential for mg ca and mg li as temperature proxies warrants further testing

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

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

high latitude forcing of the south american summer monsoon during the last glacial the climate of the last glacial period 10 000 to 110 000 years ago was characterized by rapid millennial scale climate fluctuations termed dansgaard oeschger d o and heinrich events we present results from a speleothem derived proxy of the south american summer monsoon sasm from 16 000 to 50 000 years ago that demonstrate the occurrence of d o cycles and heinrich events this tropical southern hemisphere monsoon reconstruction illustrates an antiphase relationship to northern hemisphere monsoon intensity at the millennial scale our results also show an influence of antarctic millennial scale climate fluctuations on the sasm this high resolution precisely dated tropical precipitation record can be used to establish the timing of climate events in the high latitudes of the northern and southern hemispheres

environmental and biological controls on mg and li in deep sea scleractinian corals abstract deep sea scleractinian corals precipitate aragonite skeletons that provide valuable archives of past ocean conditions during calcification biological mediation causes variability in trace metal incorporation and isotopic ratios of the aragonite such that signals caused by environmental controls can be overwhelmed this complicates the interpretation of geochemical proxies used for paleo reconstructions in this study we examine the environmental controls on the mg li ratio of 34 individuals from seven genera of deep sea scleractinian corals desmophyllum balanophyllia caryophyllia enallopsammia flabellum trochocyanthus and lophelia in addition we examine the microscale distributions of mg and li in desmophyllum and balanophyllia using laser ablation inductively coupled plasma mass spectrometry la icp ms both mg ca and li ca ratios increased by more than a factor of two in the center of calcification regions compared to the outer fibrous regions of the coral skeleton as a result replicate 10 mg subsamples of coral show less variability in the mg li ratio than mg ca microscale mg and li results are consistent with rayleigh type incorporation of trace metals with additional processes dominating the composition within centers of calcification comparison of mg li to seawater properties near the site of collection shows that the ratio is not controlled by either carbonate ion or salinity it appears that temperature is the major control on the mg li ratio for all 34 samples the temperature correlation r2 0 62 is significantly better than for mg ca r2 0 06 for corals of the family caryophyllidae the r2 value increases to 0 82 with the exclusion of one sample that was observed to have an altered chalky texture despite this excellent correlation the scatter in the data suggests that the mg li ratio of deep sea corals cannot be used to reconstruct temperature to better than approximately 1 6 c without better temperature control and additional calibration points on modern coral samples

moisture supply for northern ice sheet growth during the last glacial maximum during the last ice age the barents sea ice sheet began to grow 22 kyr ago1 only 8 kyr before it began to disintegrate2 this implies that the ice must have grown very rapidly from the coast to the edge of the continental shelf such rapid growth of a large ice sheet requires significant amounts of moisture3 but the origin of this moisture has been unclear particularly as the climap climate reconstruction suggests4 5 that the greenland iceland norwegian gin seas were perennially ice covered during this period here we present data from deep sea sediment cores from the fram strait which suggest that relatively warm water from the north atlantic ocean was advected into the gin seas in two short term events 27 22 5 and 19 5 14 5 kyr ago we suggest that the resulting seasonally ice free waters were an important regional moisture source for the barents sea ice sheet and that the gin seas played a much more active role in climate during the last glaciation than has previously been supposed

radiocarbon and 230th data reveal rapid redistribution and temporal changes in sediment focussing at a north atlantic drift abstract in locations of rapid sediment accumulation receiving substantial amounts of laterally transported material the timescales of transport and accurate quantification of the transported material are at the focus of intense research here we present radiocarbon data obtained on co occurring planktic foraminifera marine haptophyte biomarkers alkenones and total organic carbon toc coupled with excess thorium 230 230thxs measurements on four sediment cores retrieved in 1649 2879 m water depth from two such high accumulation drift deposits in the northeast atlantic bjorn and gardar drifts while 230thxs inventories imply strong sediment focussing no age offsets are observed between planktic foraminifera and alkenones suggesting that redistribution of sediments is rapid and occurs soon after formation of marine organic matter or that transported material contains negligible amounts of alkenones an isotopic mass balance calculation based on radiocarbon concentrations of co occurring sediment components leads us to estimate that transported sediment components contain up to 12 of fossil organic matter that is free of or very poor in alkenones but nevertheless appears to consist of a mixture of fresh and eroded fossil material considering all available constraints to characterize transported material our results show that although focussing factors calculated from bulk sediment 230thxs inventories may allow useful approximations of bulk redeposition they do not provide a unique estimate of the amount of each laterally transported sediment component furthermore our findings provide evidence that the occurrence of lateral sediment redistribution alone does not always hinder the use of multiple proxies but that individual sediment fractions are affected to variable extents by sediment focussing

climatic dependence of the organic matter contributions in the north eastern norwegian sea over the last 15 000 years abstract lipids are used for the evaluation of the different organic matter contributions in the north eastern norwegian sea m23258 site 75 n 14 e over the last 15 000 years development of a mass balance model based on the down core quantification of the c 37 alkenones the odd carbon numbered n alkanes a odd and the unresolved complex mixture of hydrocarbons ucm has allowed three main organic matter inputs involving marine continental and ancient reworked organic matter to be recognized the model shows good agreement between measured and reconstructed toc values similarly a strong parallelism is observed between predicted components such as marine toc and carbonate content which was determined independently representation of the model results within a time scale based on 15 ams 14 c measurements shows that the main changes in organic matter constituents are coincident with the major climatic events of the last 15 000 years thus the predominance of reworked organic matter is characteristic of termination ia up to 70 continental organic matter was dominant during the bolling allerod b a and younger dryas yd periods about 85 and a strong increase of marine organic matter occurred in the holocene between 50 and 75 this agreement reflects the main hydrographic changes that determined the deposition of sedimentary materials between 0 and 15 cal ka ice rafted detritus from the barents continental platform ice melting waters from the arctic fluvial system discharging into the barents sea and dominance of north atlantic currents respectively in this respect the high resolution down core record resulting from the mass balance and lipid measurements allows for the identification of millennial scale events such as the increase of reworked organic matter at the final retreat of the barents ice sheet at the end of the deglaciation period termination ib

a simple biomineralization model to explain li mg and sr incorporation into aragonitic foraminifera and corals abstract in contrast to li ca and mg ca li mg is strongly anticorrelated with temperature in aragonites precipitated by the benthic foraminifer hoeglundina elegans and a wide range of scleractinian coral taxa we propose a simple conceptual model of biomineralization that explains this pattern and is consistent with available abiotic aragonite partition coefficients under this model the organism actively modifies seawater within its calcification pool by raising its ca2 using a pump that strongly discriminates against both li and mg2 rayleigh fractionation during calcification effectively reverses this process removing ca2 while leaving most li and mg2 behind in the calcifying fluid the net effect of these two processes is that li mg in the calcifying fluid remains very close to the seawater value and temperature dependent abiotic partition coefficients are expressed in the biogenic aragonite li mg ratio we further show that coral sr ca is consistent with this model if the ca2 pump barely discriminates against sr2 in h elegans the covariation of sr ca and mg ca requires either that the pump more strongly discriminates against sr2 or that cation incorporation is affected by aragonite precipitation rate via the mechanism of surface entrapment in either case li mg is minimally affected by such vital effects which plague other elemental ratio paleotemperature proxies

muted change in atlantic overturning circulation over some glacial aged heinrich events several periods of massive iceberg discharge into the north atlantic and widespread cooling marked the last glacial period reconstructions of northward flow along the florida margin suggest that not all cold events were associated with a change in the strength of the atlantic meridional overturning circulation

mg ca in the benthic foraminifera cibicidoides wuellerstorfi and cibicidoides mundulus temperature versus carbonate ion saturation magnesium calcium mg ca ratios in two widely used benthic foraminiferal species cibicidoides wuellerstorfi and cibicidoides mundulus cibicidoides kullenbergi picked from global ocean core tops and from six cores in the north atlantic ocean have been measured to investigate mg ca variability cleaning effect and influences from bottom water temperature bwt and deep water carbonate ion saturation co32 replicate measurements of the two species reveal mg ca variability of 0 07 0 07 mmol mol compared with mg ca in samples cleaned by oxidative cleaning mg ca ratios are significantly lowered by 0 10 0 09 mmol mol in samples cleaned by reductive cleaning likely due to preferential leaching during the reductive cleaning step the cleaning influence is large relative to glacial interglacial mg ca changes 0 05 0 31 mmol mol by this study regression of core top data from a wide range of locations show that c wuellerstorfi mg ca is strongly affected by deep water co32 with a sensitivity of 0 009 mmol mol per mol kg when bwt is included in regressions the correlation is slightly more significant with a weak bwt sensitivity on mg ca of between 0 03 0 01 and 0 07 0 02 mmol mol per c because co32 and bwt co vary for most core top samples an alternate method of separating the two effects was made by comparing glacial to interglacial changes in mg ca from a depth transect of north atlantic cores where the bwt and carbonate ion histories since the last glacial period have been well constrained results from this transect suggest that the bwt effect is 0 03 mmol mol per c weaker than inferred from the core top study therefore core top and down core data suggest that c wuellerstorfi mg ca is insensitive to bwt changes the weak bwt effect when compared with natural variability complicates the use of mg ca in this species to reconstruct past bwt taking all measured samples from various environments into account c mundulus mg ca ratios show no correlation with bwt or deep water co32

millennial scale tropical atmospheric and atlantic ocean circulation change from the last glacial maximum and marine isotope stage 3 abstract abrupt millennial scale climate oscillations known as dansgaard oeschger d o cycles characterized the climate system of the last glacial period although proxy evidence shows that d o cycles resulted in large scale changes in atmospheric circulation patterns around the planet an understanding of how atlantic meridional overturning circulation amoc varied across these events remains unclear here we take advantage of the fact that both tropical atmospheric circulation changes corresponding to north south shifts in the intertropical convergence zone itcz and large scale changes in ocean circulation associated with amoc variability can be reconstructed in the same sediment core from the florida straits to examine the relationship between atmospheric and ocean circulation changes across d o events to reconstruct surface water conditions mg ca paleothermometry and stable isotope measurements were combined on the planktonic foraminifera globigerinoides ruber white variety from sediment core knr166 2 jpc26 24 19 61 n 83 15 14 w 546 m depth to reconstruct a high resolution record of sea surface temperature and o seawater 18 a proxy for upper mixed layer salinity during marine isotope stages mis 2 and 3 from 20 35 ka bp as an additional proxy for upper water column salinity change we also generate a faunal abundance record of the salinity sensitive planktonic foraminifera neogloboquadrina dutertrei our results suggest that rapid reductions in sea surface salinity occurred at the onset of d o interstadials while stadials are characterized by increased surface salinities the most likely cause of these salinity changes was variation in the strength and position of the itcz across d o events finally we examine the relationship between millennial scale atmospheric circulation changes recorded in the planktonic records and ocean circulation changes inferred from the benthic o 18 record from our core our results provide some of the first evidence that amoc strength did vary across at least one of the millennial scale d o cycles of mis 3

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

postdepositional oxic degradation of alkenones implications for the measurement of palaeo sea surface temperatures free and bound long chain alkenones c37 2 and c37 3 in oxidized and unoxidized sections of four organic matter rich pliocene and miocene madeira abyssal plain turbidites one from ocean drilling program site 951b and three from site 952a were analyzed to determine the effect of severe post depositional oxidation on the value of u37k the profiles of both alkenones across the redox boundary show a preferential degradation of the c37 3 compared to the c37 2 compound because of the high initial u37k values and the way of calculating the u37k this degradation hardly influences the u37k profiles however for lower u37k values measured selective degradation would increase u37k up to 0 17 units equivalent to 5 c for most of the u37k band width much smaller degradation already increases u37k beyond the analytical error 0 017 units consequently for interpreting the u37k record in terms of past sea surface temperatures selective degradation needs serious consideration

alkenones in cretaceous black shales blake bahama basin western north atlantic abstract we here report the discovery of unusual distributions of long chain alkenones c37 c42 in two cretaceous black shales from the blake bahama basin western north atlantic these sediments are cenomanian c 95 ma and mid albian c 105 ma in age thus significantly extending the geological range of these compounds the precise source of these lipids is as yet unknown although they may derive from an ancient ancestor of emiliania huxleyi

a salinity related occurrence of a novel alkenone and alkenoate in late pleistocene sediments from the japan sea abstract the novel alkenoate ethyl tetratriacontadienoate c34 2ee has been found in late quaternary sediments of the japan sea by using gas chromatography mass spectrometry gc ms it accompanied hexatriacontadien 3 one c36 2ek previously found in black sea sediments a linear relationship between c36 2ek and c34 2ee concentrations points to both compounds being derived from the same source most likely a specific haptophyte the relative abundance of c34 2ee in total alkenones and alkenoates was significantly higher during the last glacial maximum when the 18o in planktonic foraminifera was anomalously light strongly suggesting that c34 2ee is associated with low salinity environments as samples with abundant c34 2ee also possessed anomalously high u 37 k values low salinity may have an ecological or physiological influence on both the unsaturation and carbon chain length of alkenones and alkenoates

alkenones and coccoliths in ice rafted debris during the last glacial maximum in the north atlantic implications for the use of uk37 as a sea surface temperature proxy the uk37 index has proven to be a robust proxy to estimate past sea surface temperatures ssts over a range of time scales but like any other proxy it has uncertainties for instance in reconstructions of the last glacial maximum lgm in the northern north atlantic uk37 indicates higher temperatures than those derived from foraminiferal proxies here we evaluate whether such warm glacial estimates are caused by the advection of reworked alkenones in ice rafted debris ird to deep sea sediments we have quantified both coccolith assemblages and alkenones in sediments from glaciogenic debris flows in the continental margins of the northern north atlantic and from a deep sea core from the reykjanes ridge certain debris flow deposits in the north atlantic were generated by the presence of massive ice sheets in the past and their associated ice streams such deposits are composed of the same materials that were present in the ird at the time they were generated we conclude that ice rafting from some locations was a transport pathway to the deep sea floor of reworked alkenones and pre quaternary coccolith species during glacial stages but that not all of the ird contained alkenones even when reworked coccoliths were present we speculate that the ratio of reworked coccoliths to alkenone concentration might be useful to infer whether significant reworked alkenone inputs from ird did occur at a particular site in the glacial north atlantic we also observe that alkenones in some of the debris flows contain a colder signal than estimated for lgm sediments in the northern north atlantic this is also clear in the deep sea core studied where the warmest intervals do not correspond to the intervals with large inputs of reworked coccoliths or ird we conclude that any possible bias to uk37 estimates associated with reworked alkenones is not necessarily towards higher values and that the high sst anomalies for the lgm are unlikely to be the result of a bias caused by ird inputs

comparison of alkenone estimates with other paleotemperature proxies 1 to a certain degree all sea surface temperature sst proxies suffer from uncertainty due to signal preservation problems and to perturbations by other environmental variables however a multiproxy reconstruction is justified because most biases should in principle cancel out as they are specific to the biological groups and or to the analyzed chemical species such a multiproxy strategy has proven crucial for calibrating these proxies and is also useful in assessing downcore profiles until now there have been only a dozen deep sea cores where it is possible to compare directly alkenone based ssts with other paleotemperature records from this still limited data set the broad picture is of general agreement for the amplitude of changes at low and middle latitudes the few observed discrepancies suggest that alkenone based temperatures are more comparable to those based on mg ca ratios than those obtained through statistical analysis of the foraminiferal distribution more systematic differences are noted at higher latitudes where alkenones indicate warmer temperatures during the glacial period than transfer functions based on foraminifera or diatoms several reasons have been invoked to resolve the mismatch but more ground truthing work is needed before deciding which temperature changes are the most accurate

modifications of the c37 alkenone and alkenoate composition in the water column and sediment possible implications for sea surface temperature estimates in paleoceanography 1 the literature pertaining to c37 alkenone and c37 and c38 alkenoate production and diagenesis has been reviewed and evaluated for issues that might jeopardize their usefulness in paleotemperature estimation we also examined the use of the c37 alkenones as paleoproductivity indicators the stability of their 13c isotopic compositions and their incorporation into the nonsolvent extractable organic matter fraction biological transformation of organic matter by bacteria and zooplankton does not appear to cause significant changes to the ratio of c37 2 and c37 3 alkenones but there are major alterations in the relative composition of alkenoates studies of water column processes and postdepositional sedimentary changes indicate overall stability in the c37 2 c37 2 c37 3 ratio leading to effective preservation of the paleotemperature signal this is not the case for alkenoates and there also appear to be some doubts about the dependence between sea surface temperature and the sedimentary abundance of the c37 4 alkenone c37 alkenones may provide useful qualitative estimates of marine paleoproductivity although these compounds are apparently only derived from haptophycea changes in their quantitative composition might reflect changes in nutrient availability that on sedimentary timescales should also be generally significant of other algal species one caveat is that in highly productive upwelling systems productivity may be expressed mostly in diatom growth and thus not measurable by the c37 alkenones no changes in 13c c37 alkenone composition are observed upon zooplankton ingestion although this is expected from a theoretical perspective further studies are encouraged in order to fully assess the stability of the isotopic signal during c37 alkenone diagenesis finally alkenones bound in the nonextractable fraction of sedimentary organics have not been adequately studied and further work is required to clarify any possible correspondence with a temperature signal

intermediate water circulation changes in the florida straits from a 35 ka record of mg li derived temperature and cd ca derived seawater cadmium abstract we generated a high resolution ocean record of bottom water temperature and seawater cd from 546 m in the florida straits the record extends to 35 000 yr before present including all of marine isotope stages mis 2 and part of mis 3 previously seawater cadmium cdw has been used as a proxy for the strength of the atlantic meridional overturning circulation amoc during the last deglaciation we now consider the temperature and oxygen isotopic composition of seawater reconstructed from the same core in order to provide a fuller picture of water mass properties and circulation at this location during the last glacial maximum lgm cdw levels were generally low and a novel mg li derived temperature record reveals persistently cold temperatures 3 6 c two to three degrees colder than during the holocene or marine isotope stage 3 during the younger dryas and early heinrich stadial 1 cdw was low and temperatures were elevated compared with periods of inferred stronger amoc by contrast there is no indication of amoc variability over heinrich stadials 2 and 3 consistent with previous studies that conclude the amoc is less sensitive to freshwater forcing during glaciations than during the last deglaciation while there is some inconsistency between proxies cdw increases over some mis3 dansgaard oeschger interstadials providing qualified support for a strengthening in amoc this is similar to our previous finding that cdw tracks amoc variability during the deglaciation this study highlights the distinct nature of water masses and circulation during the lgm relative to the stadial weak amoc periods of the deglaciation and late mis 3

evidence for a warm last glacial maximum in the nordic seas or an example of shortcomings in uk 37 and uk 37 to estimate low sea surface temperature the occurrence of ice free conditions in the nordic seas during the last glacial maximum has been demonstrated using microfossil and biomarker approaches an accurate picture of the prevailing oceanographic conditions may be more difficult to ascertain thus uncertainties for most proxies increase at the cold extreme of temperature calibrations and glacial sediments contain small amounts of microfossils and biomarkers here we discuss sea surface temperature estimates derived from alkenone indices for the last glacial maximum in the nordic seas that provide a surprising scenario where surface temperatures were warmer than at present we conclude that the uk37 and uk37 estimates may not be interpreted in terms of sea surface temperature as several factors may have conspired to bias the molecular signal however using an alternative index based on the abundance of the c37 4 alkenone we estimate a maximum temperature of 6 c

oxygen isotope compositions of sinistral neogloboquadrina pachyderma tests in surface sediments north atlantic ocean abstract neogloboquadrina pachyderma left coiled is a planktonic foraminifer indicator species for polar waters it is present in both the glacial and interglacial sediments of the high latitude oceans and therefore is frequently used as a signal carrier for constructing late pleistocene holocene planktonic 18 o records in this study the 18 o compositions of n pachyderma l tests from deep sea surface sediments are compared with surface water 18 o values and summer sea surface temperatures sst in the north atlantic ocean the norwegian greenland sea and the labrador sea we document that for a temperature range of 2 8 c the planktonic 18 o values follow paleotemperature equations with an offset of less than 0 4 and that above 8 c the planktonic 18 o compositions become almost independent of sst and remain nearly constant this pattern suggests that n pachyderma l precipitates its shell nearly at isotopic equilibrium with surface waters colder than 8 c and that in warmer surface waters n pachyderma l changes its habitat depth or its growth season to secrete its shell at an ambient temperature around 7 9 c

high resolution alkenone sea surface temperature variability on the north icelandic shelf implications for nordic seas palaeoclimatic development during the holocene the palaeoceanography of the northern icelandic shelf for the holocene period was reconstructed from alkenone indices measured in core jr51 gc35 this contains a continuous record of holocene sedimentation spanning 0 10 2 cal kyr bp with a resolution of 20 yr cm we have identified a general holocene cooling trend that has superimposed millennial scale oscillations of 28c their timing is in close agreement with the timing of glacier advances in northern iceland for the later half of the holocene the alkenone sea surface temperature sst record from jr51 gc35 correlates with proxy data for the strength of nadw formation recorded in cores south of iceland this is interpreted as evidence of a close connection existing between north icelandic sea surface temperatures and the north atlantic meridonal overturning circulation the timing of the millennial scale sst variability in our core off north iceland is found to be out of phase or anti phased with the sst variability of a record in the eastern nordic seas md952011 this suggests that the evolution of holocene climate in the nordic seas was more complex than previously proposed and it is likely to be caused by differential responses of the irminger and norwegian currents and modulated by changes in atmospheric circulation analogous to the north atlantic oscillation

sensitivity of last glacial maximum climate to sea ice conditions in the nordic seas published reconstructions of last glacial maximum lgm sea surface temperatures and sea ice extent differ significantly we here test the sensitivity of simulated north atlantic climates to two different reconstructions by using these reconstructions as boundary conditions for model experiments an atmospheric general circulation model has been used to perform two simulations of the lgm and a modern day control simulation standard climap reconstructions of sea ice and sea surface temperatures have been used for the first simulation and a set of new reconstructions in the nordic seas northern atlantic have been used for the second experiment the new reconstruction is based on 158 core samples and represents ice free conditions during summer in the nordic seas with accordingly warmer sea surface temperatures and less extensive sea ice during winter as well the simulated glacial climate is globally 5 7 k colder than modern day with the largest changes at mid and high latitudes due to more intense hadley circulation the precipitation at lower latitudes has increased in the simulations of the lgm relative to the simulation with the standard climap reconstructions reduction of the sea ice in the north atlantic gives positive local responses in temperature precipitation and reduction of the sea level pressure only very weak signatures of the wintertime icelandic low occur when the standard climap sea surface temperature reconstruction is used as the lower boundary condition in lgm with reduced sea ice conditions in the nordic seas the icelandic low becomes more intense and closer to its present structure this indicates that thermal forcing is an important factor in determining the strength and position of the icelandic low the arctic oscillation is the most dominant large scale variability feature on the northern hemisphere in modern day winter climate in the simulation of the lgm with extensive sea ice this pattern is significantly changed and represents no systematic large scale variability over the north atlantic reduction of the north atlantic sea ice extent leads to stronger variability in monthly mean sea level pressure in winter the synoptic variability appears at a lower level in the simulation when standard reconstructions of the sea surface in the lgm are used a closer inspection of storm tracks in this model experiment shows that that the synoptic lows follow a narrow band along the ice edge during winter the trajectories of synoptic lows are not constrained to the sea ice edge to the same degree when the sea ice extent is reduced seasonally open waters in the nordic seas in the new reconstruction apparently act as a moisture source consistent with the current understanding of the rapid growth of the fennoscandian and barents ice sheets during the lgm the signal from the intensified thermal forcing in the north atlantic in boreal winter is carried zonally by upper tropospheric waves and thus generates non local responses to the changed sea ice cover

distributions of long chain alkenones and alkyl alkenoates in marine surface sediments from the north east atlantic abstract the abundances of long chain alkenones and alkyl alkenoates are reported for a suite of surface sediments from the ne atlantic 0 75 n despite the differing conditions of their biologies and differing extents of water column degradation and of early diagenesis in the sediments the degree of unsaturation of the alkenones e g the u 37 k parameter and the relative proportion of alkyl alkenoates to alkenones display linear correlations with average temperature for surface waters warmer than 5 c there is evidence that the chain length distribution of the alkenones and of the ratio between the ethyl and methyl c 38 alkenones are species dependent which would enable their use as chemotaxonomic tools

evidence from the florida straits for younger dryas ocean circulation changes 1 the waters passing through the florida straits today reflect both the western portion of the wind driven subtropical gyre and the northward flow of the upper waters which cross the equator compensating north atlantic deep water export as part of the large scale atlantic meridional overturning circulation it has been postulated from various lines of evidence that the overturning circulation was weaker during the younger dryas cold event of the last deglaciation we show here that the contrast in the oxygen isotopic composition of benthic foraminiferal tests across the florida current is reduced during the younger dryas this most likely reflects a decrease in the density gradient across the channel and a decrease in the vertical shear of the florida current this reduced shear is consistent with the postulated reduction in the atlantic meridional overturning circulation we find that the onset of this change in density structure and flow at the start of the younger dryas is very abrupt occurring in less than 70 years

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

constraints on sst estimates for the northern north atlantic nordic seas during the lgm abstract a map of estimated calcification temperatures of the planktic foraminifer neogloboquadrina pachyderma sinistral tnps for the nordic seas and the northern north atlantic for the last glacial maximum was produced from oxygen isotopes with support of mg ca ratios to arrive at the reconstruction several constraints concerning the plausible salinity and 18 o fields were employed the reconstruction indicates inflow of temperate waters in a wedge along the eastern border of the nordic seas and at least seasonally ice free waters the reconstruction from oxygen isotopes shows similarities with mg ca based paleotemperatures in the southern and southeastern sector while unrealistically high mg ca values in the central nordic seas prevent the application of the method in this area the oxygen isotope based reconstruction shows some agreement with temperature reconstructions based on the modern analogue technique but with somewhat lower temperatures and a stronger internal gradient inside the nordic seas all told our results suggest a much more ice free and dynamic high latitude ocean than the climap reconstruction

microbial degradation of the marine prymnesiophyte emiliania huxleyi under oxic and anoxic conditions as a model for early diagenesis long chain alkadienes alkenones and alkyl alkenoates to investigate the effect of bacterial diagenesis on the distributions of algal lipids the marine haptophyte emiliania huxleyi was incubated with estuarine sediment slurries under defined conditions oxic sulfate reducing and methanogenic rapid initial degradation of lipids corresponded to increased bacterial populations both of which subsequently declined under oxic conditions the algal c31 dienes were rapidly and completely degraded within 178 days extensive degradation of the characteristic c37 methyl alkenones occurred under all conditions up to 85 under oxic conditions however the u37k index remained essentially constant except for a slight increase at the longest oxic incubation time under anoxic conditions the alkyl alkenoates were preferentially degraded relative to the alkenones and changes in the aa36 index occurred these results demonstrate that lipids are part of the labile organic matter however they were generally degraded at multiple rates which slowed during incubation resulting in their partial preservation hence laboratory experiments conducted over only short periods cannot predict the preservation potential of lipid components furthermore preservation differed between sulfate reducing and methanogenic conditions so the roles of anaerobic processes need to be considered individually with regard to oxic vs anoxic preservation

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

deep water mass geometry in the glacial atlantic ocean a review of constraints from the paleonutrient proxy cd ca 1 paleonutrient proxies currently provide the strongest constraints on the past spatial distribution of deep water masses we review the state of knowledge derived from the trace metal proxy cd ca for the atlantic ocean during the last glacial maximum lgm we compile published benthic foraminiferal cd ca data supplemented with new data to reconstruct meridional cd sections through the holocene and lgm atlantic holocene cd ca reflects the modern water masses north atlantic deep water nadw antarctic bottom water aabw and antarctic intermediate water aaiw reasonably well except for anomalously high values in the intermediate to mid depth far north atlantic lgm cd ca clearly shows that nadw was replaced by the shallower glacial north atlantic intermediate water gnaiw with significant northward expansion of aabw the boundary level between gnaiw and aabw was very abrupt occurring between 2200 and 2500 m modern water depth combined cd ca and cibicidoides d 13 c data allow us to also calculate the air sea signature of d 13 c d 13 cas the lgm atlantic can be explained entirely by mixing between high d 13 cas gnaiwand low d 13 cas aabw negative d 13 cas values in glacial aabw were likely caused by poor ventilation during formation probably associated with extensive sea ice coverage overall our knowledge base would benefit from improved data coverage in the south atlantic and southern ocean and a better understanding of ancillary effects on the cd ca proxy itself

high resolution record of late glacial and deglacial sea ice changes in fram strait corroborates ice ocean interactions during abrupt climate shifts the transition from last glacial to deglacial and subsequently to modern interglacial climate conditions was accompanied by abrupt shifts in the palaeoceanographic setting in the subpolar north atlantic knowledge about the role that sea ice coverage played during these rapid climate reversals is limited since most marine sediment cores from the higher latitudes provide only a coarse temporal resolution and often poorly preserved microfossils here we present a highly resolved reconstruction of sea ice conditions that characterised the eastern fram strait a key area for water mass exchange between the arctic ocean and the north atlantic for the past 30 ka bp this reconstruction is based on the distribution of the sea ice biomarker ip25 and phytoplankton derived biomarkers in a sediment core from the continental slope of western svalbard during the late glacial 30 ka to 19 ka bp recurrent advances and retreats of sea ice characterised the study area and point to a hitherto less considered oceanic and or atmospheric variability a long lasting perennial sea ice coverage in eastern fram strait persisted only at the very end of the last glacial maximum i e from 19 2 to 17 6 ka bp and was abruptly reduced at the onset of heinrich event 1 coincident with or possibly even inducing the collapse of the atlantic meridional overturning circulation amoc further maximum sea ice conditions prevailed during the younger dryas cooling event and support the assumption of an amoc reduction due to increased formation and export of arctic sea ice through fram strait a significant retreat of sea ice and sea surface warming are observed for the early holocene

impact of abrupt deglacial climate change on tropical atlantic subsurface temperatures both instrumental data analyses and coupled ocean atmosphere models indicate that atlantic meridional overturning circulation amoc variability is tightly linked to abrupt tropical north atlantic tna climate change through both atmospheric and oceanic processes although a slowdown of amoc results in an atmospheric induced surface cooling in the entire tna the subsurface experiences an even larger warming because of rapid reorganizations of ocean circulation patterns at intermediate water depths here we reconstruct high resolution temperature records using oxygen isotope values and mg ca ratios in both surface and subthermocline dwelling planktonic foraminifera from a sediment core located in the tna over the last 22 ky our results show significant changes in the vertical thermal gradient of the upper water column with the warmest subsurface temperatures of the last deglacial transition corresponding to the onset of the younger dryas furthermore we present new analyses of a climate model simulation forced with freshwater discharge into the north atlantic under last glacial maximum forcings and boundary conditions that reveal a maximum subsurface warming in the vicinity of the core site and a vertical thermal gradient change at the onset of amoc weakening consistent with the reconstructed record together our proxy reconstructions and modeling results provide convincing evidence for a subsurface oceanic teleconnection linking high latitude north atlantic climate to the tropical atlantic during periods of reduced amoc across the last deglacial transition

organo and lithofacies of glacial interglacial deposits in the norwegian greenland sea responses to paleoceanographic and paleoclimatic changes abstract based on a multiparameter approach a combined litho and organofacies concept was developed for glacial and interglacial sediment sections along an e w transect through the central part of the norwegian greenland sea ngs modern and past surface water regimes are clearly displayed by specific litho and organofacies patterns interglacial conditions reveal specific atlantic water associated lithofacies a and b3 in the eastern and central sector of the norwegian greenland sea ngs corresponding interglacial organofacies in general are not well correlated to lithofacies due to strong diagenetic degradation of labile e g autochthonous organic matter om while in near surface sediments a marine dominated organofacies i 1 is preserved under atlantic water masses this correlation is not evident for lower holocene and isotope stage 5 deposits however during isotopic event 5 5 1 increased proportions of marine om are recorded in a high accumulating core on the voring plateau glaciomarine background lithofacies b and c indicate minor input of ice rafted debris ird and seasonal variable sea ice cover corresponding organofacies ii 1 non oxidized and ii 2 oxidized are dominated by allochthonous om most spectacular are glacial diamictons lithofacies e and f evidencing short term sediment pulses due to a sudden disintegration of far advanced tide water ice margins on the outer shelves these diamictons bear specific organofacies iii 1 and iii 2 with a clear predominance of terrigenous and reworked om some of the diamictons seem to occur contemporaneous with the so called heinrich layers h1 and h2 suggesting a common trigger mechanism for the almost simultaneous disintegration of huge continental ice masses along the shelves of north america and the eastern margin of the ngs application of a combined organo and lithofacies concept provides essential information on spatial and temporal variations of water mass characteristics the oceanic effects of ice sheet dynamics and circulation models

atlantic core top calibration of the u37k index as a sea surface palaeotemperature indicator abstract a field calibration of the uk index with sea surface temperature is discussed through analysis of an extensive suite of surface sediments n 109 from the northeastern atlantic 2 s 75 n values of u 37 k are compared with sea surface temperatures for overlying waters measured at different depths and seasons to obtain a correlation suitable for palaeotemperature reconstructions the best fit is obtained using surface 0 m temperatures corresponding to caloric winter and autumn months however the annual average spring and summer surface temperature equations also have high correlation coefficients and are also appropriate for climatic studies the results further validate the general applicability of the u 37 k as a climatic proxy because the calibration equations are valid over a wide range of surface water temperatures 0 28 c for different algal populations and are representative of the average contribution of alkenones to sediments as found in sediment cores

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

precise multielemental ratios in small foraminiferal samples determined by sector field icp ms inductively coupled plasma mass spectrometry icp ms holds two main advantages over other techniques for the measurement of foraminiferal elemental ratios 1 numerous trace metals may be precisely and simultaneously measured and 2 smaller samples may theoretically be used methods are presented for the precise determination of mg ca sr ca cd ca zn ca li ca u ca mn ca and fe ca by sector field icp ms analytical precision is largely independent of sample size over the range of 5 to 125 g caco3 eliminating the need for narrow target dilutions long term 1 precisions are as follows mg ca 0 54 sr ca 0 57 cd ca 1 8 zn ca 3 2 li ca 0 88 u ca 1 9 mn ca 0 97 and fe ca 1 4 for mg ca actual foraminiferal samples appear to give reliable results below 10 g caco3 postcleaning mass

timing of deglacial amoc variability from a high resolution seawater cadmium reconstruction a new high resolution record of benthic seawater cd cdw was generated from a florida straits sediment core at 546 m water depth the record provides additional evidence for cdw below modern values in this channel during the younger dryas and heinrich stadial 1 climatological periods associated with ice sheet melt lower cdw values are interpreted as a weakening of the atlantic meridional overturning circulation amoc reflecting a decreased northward transport of southern sourced higher nutrient intermediate waters by the surface return flow of amoc comparison of this new cdw record with previously published neodymium isotope and 18o records from the same core shows synchronous transitions further illustrating the connection between cdw levels and amoc strength in the florida straits an increase in cdw near 16 ka bolsters existing evidence for a resumption of upper branch amoc strength approximately midway through heinrich stadial 1

environmental processes of the ice age land oceans glaciers epilog knowledge of the state of the earth at the last glacial maximum lgm an interval around 21 000 years ago is an important benchmark for understanding the sensitivity of global environmental systems to change much progress in understanding climates of the lgm has occurred in the 20 years since the end of the climap project of the 1970s climate long range investigation mapping and prediction here we review this progress based on presentations and discussion at a rst open science meeting of the epilog project environmental processes of the ice age land oceans glaciers held in delmenhorst germany may 1999 we outline key controversies and document protocols for epilog contributions so that a new synthesis of the lgm earth can emerge as an open project of the world s community of scientists 2001 elsevier science ltd all rights reserved

intermediate depth warming in the tropical atlantic related to weakened thermohaline circulation combining paleoclimate data and modeling results for the last deglaciation 1 benthic foraminiferal oxygen isotope ratios from two sediment cores recovered at 426 and 1299 m water depth in the eastern and western tropical atlantic show that a slowdown of the thermohaline circulation thc during heinrich event h1 and the younger dryas was accompanied by rapid and intense warming of intermediate depth waters millennial scale covariations of low paleosalinities in the subpolar north atlantic with decreased benthic oxygen isotope ratios in the eastern tropical atlantic throughout the past 10 000 years suggest that thc weakening might be related to middepth warming during the holocene period as well climate model experiments simulating a strong reduction of the thc in the atlantic ocean under present day and glacial conditions reveal that the increase of temperature in the middepth tropical and south atlantic is a common feature for both climatic states caused by a reduced ventilation of cold intermediate and deep waters in conjunction with downward mixing of heat from the thermocline from the similarity of the paleoclimatic records with the model simulations we infer that the characteristic pattern of temperature change in the atlantic ocean related to weakened thermohaline circulation can serve as an indicator of present day and future thc slowdown

coccolithophore fluxes in the norwegian greenland sea seasonality and assemblage alterations abstract coccolithophore fluxes were investigated by sediment trap studies at two well separated oceanographic sites in the norwegian and greenland seas from 1990 to 1992 each trap mooring comprised traps at 500 and 1000 m water depth and 300 m above the seafloor both sites were characterized by a strong seasonality in coccolithophore fluxes in the norwegian sea fluxes were about 10 to 20 times higher than in the greenland sea maximum fluxes 13 106 ind m 2d 1 for the norwegian sea and 2 4 106 ind m 2d 1 for the greenland sea were reached during high sedimentation phases in late summer and autumn the settling assemblages represented already highly altered remnants of the former living communities dominant species were emiliania huxleyi in the norwegian sea and coccolithus pelagicus in the greenland sea despite severe alterations the coccolithophore assemblages of each site were characterized by a distinct signature reflecting the local oceanography the settling assemblages underwent only minor alterations during sinking from 500 to 1000 m water depth by contrast resuspension and lateral advection within an extensive bottom nepheloid layer strongly influenced the assemblages of the deep sediment traps 300 m above the seafloor wiping out the distinct seasonality in coccolithophore fluxes and diminishing the differences in assemblage compositions between the two sites

the influence of salinity on mg ca in planktic foraminifers evidence from cultures core top sediments and complementary δ18o the mg ca ratio in foraminiferal calcite is one of the principal proxies used for paleoceanographic temperature reconstructions but recent core top sediment observations suggest that salinity may exert a significant secondary control on planktic foraminifers this study compiles new and published laboratory culture experiment data from the planktic foraminifers orbulina universa globigerinoides sacculifer and globigerinoides ruber in which salinity was varied but temperature ph and light were held constant combining new data with results from previous culture studies yields a mg ca sensitivity to salinity of 4 4 2 3 4 7 1 2 and 3 3 1 7 per salinity unit 95 confidence respectively for the three foraminifer species studied here comparison of these sensitivities with core top data suggests that the much larger sensitivity 27 4 per salinity unit derived from atlantic core top sediments in previous studies is not a direct effect of salinity rather we suggest that the dissolution correction often applied to mg ca data can lead to significant overestimation of temperatures we are able to reconcile culture calibrations with core top observations by combining evidence for seasonal occurrence and latitude specific habitat depth preferences with corresponding variations in physico chemical environmental parameters although both mg ca and 18o yield temperature estimates that fall within the bounds of hydrographic observations discrepancies between the two proxies highlight unresolved challenges with the use of paired mg ca and 18o analyses to reconstruct paleo salinity patterns across ocean basins the first step towards resolving these challenges requires a better spatially and seasonally resolved 18osw archive than is currently available nonetheless site specific reconstructions of salinity change through time may be valid

mg ca temperature calibration for the benthic foraminifer cibicidoides pachyderma 1 the recent development of foraminiferal mg ca as a paleotemperature proxy has enabled the extraction of global ice volume and local salinity from the more traditional paleotemperature proxy 18o the benthic foraminiferal genus cibicidoides is widely used in paleoceanographic reconstructions because of its epifaunal habitat and cosmopolitan distribution and it has received early attention in mg ca work however existing temperature calibrations for cibicidoides rely heavily on c pachyderma core top data from one location little bahamas bank where authigenic processes and or reworking may result in elevated warm water mg ca values here we present new c pachyderma mg ca data from a series of 29 high quality multicore tops collected in the florida straits spanning a temperature range of 5 8 18 6 c in contrast to previous calibrations we find no evidence for a strongly exponential response to temperature the data are best explained by a linear relationship with a sensitivity of 0 12 mmol mol 1 per c

alkenone distributions in the north atlantic and nordic sea surface waters 1 the c37 c39 alkenones were quantified in suspended particulate matter obtained from the surface waters of the north atlantic including the nordic seas over a temperature range of 4 20 c u37k values were linearly correlated to temperature over the entire range covered by our data set i e 4 20 c u37k 0 027t 0 036 r2 0 97 the compilation of water column data from the atlantic pacific and southern ocean and mediterranean sea suggests that the linear model may not be the best function for fitting u37k and in situ temperature values it also shows that suspended matter data from warm waters t 20 c are still needed to constrain the equation of the global curve high abundances of c37 4 were found in the coldest polar waters around 4 c c37 4 represented up to 35 a value that dropped to zero at temperatures above 10 c values of c37 4 were linearly correlated to temperature c37 4 3 7t 43 7 r2 0 50 and salinity c37 4 48 1s 1691 r2 0 78 further investigations from other oceanic basins are necessary to confirm these findings

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

the oxygen isotopic composition of seawater during the last glacial maximum high resolution oxygen and hydrogen isotope measurements were made on pore fluids from deep sea sediments from sites in the north and south atlantic the data provide direct measurements of changes in the isotopic composition of bottom waters during the last glacial maximum lgm results from ocean drilling program odp site 981 in the north atlantic currently bathed in north atlantic deep water nadw reproduces previous results from the ceara and bermuda rises constraining the glacial interglacial change in 18 o of the deep atlantic to be 0 7 0 8 results from site 984 which is located north of site 981 and at a shallower water depth yield a similar value 0 8 providing insight into the properties of glacial north atlantic intermediate water gnaiw sites from odp leg 177 in the south atlantic span the modern boundary between northern and southern sources of deep water data from the northern site 1088 yield a similar result to sites in the tropical and north atlantic 0 7 at the southern site 1093 located south of the polar front the change is substantially larger 1 1 representing the change in 18 o of southern source waters since the lgm these results confirm previous estimates that the global average change in 18 o of seawater is 1 0 0 1 hydrogen isotopes measured on pore fluids from three sites are consistent with the oxygen isotopes from these locations giving further support to these results at all sites studied the temperature of the deep ocean during the lgm calculated by combining the pore fluid results with oxygen isotope data from benthic foraminifera was within 1 c of the freezing point of seawater

tropical north atlantic subsurface warming events as a fingerprint for amoc variability during marine isotope stage 3 the role of atlantic meridional overturning circulation amoc as the driver of dansgaard oeschger do variability that characterized marine isotope stage 3 mis 3 has long been hypothesized although there is ample proxy evidence suggesting that do events were robust features of glacial climate there is little data supporting a link with amoc recently modeling studies and subsurface temperature reconstructions have suggested that subsurface warming across the tropical north atlantic can be used to fingerprint a weakened amoc during the deglacial because a reduction in the strength of the western boundary current allows warm salinity maximum water of the subtropical gyre to enter the deep tropics to determine if amoc variability played a role during the do cycles of mis 3 we present new high resolution mg ca and 18o records spanning 24 52 kyr from the near surface dwelling planktonic foraminifera globigerinoides ruber and the lower thermocline dwelling planktonic foraminifera globorotalia truncatulinoides in southern caribbean core vm12 107 11 33 n 66 63 w 1079 m depth our subsurface mg ca record reveals abrupt increases in mg ca ratios the largest equal to a 4 c warming during the interstadial stadial transition of most do events during this period this change is consistent with reconstructions of subsurface warming events associated with cold events across the deglacial using the same core additionally our data support the conclusion reached by a recently published study from the florida straits that amoc did not undergo significant reductions during heinrich events 2 and 3 this record presents some of the first high resolution marine sediment derived evidence for variable amoc during mis 3

radiometrically determined sedimentary fluxes in the sub polar north atlantic during the last 140 000 years abstract we have examined the record of sediment input during the last 140 000 years in a deep sea core from 49 27 n 22 16 w in the eastern north atlantic using uranium series disequilibria to constrain time we have calculated mass fluxes of total sediment as well as mass and particle fluxes of major sedimentary components sediment accumulation rates were generally lower and relatively constant during broadly defined interglacial intervals driven primarily by the burial of biogenic material accumulation rates were higher and more variable during glacial intervals and were influenced primarily by terrigenous material peaks in bulk mass fluxes were associated with particular episodes heinrich events within the last glacial and during each of the last two deglaciations the flux of ice rafted debris as uniquely identified by coarse detrital fragments was higher during layers representing each of the glacial heinrich events with modest increases during events h3 and h6 and dramatic increases during the others confirming the widespread interpretation of these layers as episodes of enhanced iceberg delivery the burial flux of foraminifera was markedly lower during each of the glacial heinrich events also confirming the original identification of these layers as barren intervals ice rafting events within marine isotope stage 5 left neither a large detrital nor biogenic flux imprint at our study site variations in the burial rates of non carbonate sediments were largely responsible for overall changes in sediment accumulation throughout the last climate cycle ice rafting was apparently an important delivery mechanism for this terrigenous material the instantaneous chronometer established here for the last 140 000 years in the subpolar north atlantic allows the transformation of existing and subsequent data from relative values to absolute burial fluxes

comparing proxies for the reconstruction of lgm sea surface conditions in the northern north atlantic abstract within the frame of the multiproxy approach for the reconstruction of the glacial ocean margo project sea surface conditions of the last glacial maximum lgm 23 19 ka were reconstructed using different proxies which were calibrated to a standardized modern hydrography in the north atlantic the revised lgm margo data set provides a comprehensive coverage including the nordic seas the data set includes reconstruction based on planktonic foraminifer assemblages dinocyst assemblages alkenone coccolithophorid biomarkers and mg ca ratios in planktonic foraminifers several hydrological features of the lgm north atlantic can be identified that are supported by all four proxies they include an extensive perennial sea ice cover along the eastern canadian and greenland margins seasonally ice free central north atlantic and norwegian sea and the winter sea ice limit being located at about 55 n all proxies also suggest significantly colder than modern sea surface conditions in the southeastern part of the north atlantic and a more zonal temperature pattern than at present with a steep sst gradient of the order of 10 c between 40 n and 45 n however in the nordic seas large discrepancies remain well above the level of uncertainty of the sst reconstructions these discrepancies might be related to stratification of the upper water mass linked to large annual amplitude of temperature with contrasting winter and summer conditions high interannual interdecadal variability or taphonomic processes affecting some of the proxies the average lgm sst in the nordic seas cannot at present be assessed with confidence however the existing evidence suggests that highly variable sea surface conditions and at least occasional advection of north atlantic waters may have characterised the glacial nordic seas

alkenones and alkenes in surface waters and sediments of the southern ocean implications for paleotemperature estimation in polar regions abstract the concentration of c37 c39 long chain alkenones and alkenes were determined in surface water and surface sediment samples from the subpolar waters of the southern ocean distributions of these compounds were similar in both sample sets indicating little differential degradation between or within compound classes the relative amounts of the tri to tetra unsaturated c37 alkenones increased with increasing temperature for temperatures below 6 c similar to the di and tri unsaturated c37 alkenones the c37 di tri and tetra unsaturated methyl alkenones are used in paleotemperature calculations via the u37k and the u37k ratios in these datasets the relative abundances of the c37 2 and the c37 3 alkenones as a proportion of the total c37 alkenones were opposite and strongly related to temperature the latter with more scatter but the abundance of the c37 4 alkenone showed no relationship with temperature the original definition of u37k includes the abundance of 37 4 in both the numerator and denominator and thus it is perhaps not surprising that there is considerable scatter in the values obtained for u37k at low temperatures of the two we suggest that u37k is the better parameter for use in paleotemperature estimations even in cold locations u37k values in the sediments fall on virtually the same regression line obtained for the water column samples of sikes and volkman 1993 indicating that their calibration is suitable for use in southern ocean sediments the comparison of water column data with sedimentary temperature estimates suggests that the alkenone distributions are dominated by contributions from the summer when the biomass of emiliania huxleyi and presumably flux to the sediment is expected to be high

reworked nannofossils in the north atlantic ocean and subpolar basins implications for heinrich events and ocean circulation the age and geographic distribution of reworked nannofossils in surface sediments from the north atlantic ocean suggest that their major source is northwest europe the concentration of reworked nannofossils in down core sediments indicates discharge of icebergs from the british and fennoscandian ice sheets throughout the last glacial interval during heinrich intervals 1 and 2 an increased number of icebergs from these sources reached the northeastern labrador sea these results suggest that the origin of heinrich intervals 1 and 2 involved both north american and european ice sheets

combined coccolith foraminiferal and biomarker reconstruction of paleoceanographic conditions over the past 120 kyr in the northern north atlantic 59 n 23 w we present data for north atlantic core biogeochemical ocean flux study bofs 16k 59 n 23 w water depth 2370 m including coccolith flora 18o planktonic foraminiferal sea surface temperatures ssts by fa20 and simmax methods and alkenone based u37k and u37k ssts a good correlation exists between the abundances of cold water coccolith species and foraminifera and a broad correlation exists between coccolith and alkenone abundances except in the holocene reworked cretaceous coccoliths at the last glacial maximum are coincident with warm deviations of the u37k signal assessment of various calibrations of u37k and u37k with paleotemperature shows the inappropriateness of a global correlation we have produced a north atlantic u37k calibration on the basis of north atlantic data alone u37k 0 026t 0 186 which produces sst data for summer season at 0 m water depth comparable to the warm season foraminiferal ssts except during the intervals 26 36 58 65 and 100 120 ka when the alkenones indicate somewhat cooler surface waters

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

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

the greenland ice core chronology 2005 15 42 ka part 1 constructing the time scale the greenland ice core chronology 2005 gicc05 is extended back to 42 ka b2k before 2000 ad i e to the end of greenland stadial 11 the chronology is based on independent multi parameter counting of annual layers using comprehensive high resolution measurements available from the north greenland ice core project ngrip these are measurements of visual stratigraphy conductivity of the solid ice electrolytical melt water conductivity and the concentration of na c a 2 s o 4 n o 3 n h 4 a n uncertainty estimate of the time scale is obtained from identification of uncertain annual layers which are counted as 0 570 5 years the sum of the uncertain annual layers the so called maximum counting error of the presented chronology ranges from 4 in the warm interstadial periods to 7 in the cold stadials the annual accumulation rates of the stadials and interstadials are on average one third and half of the present day values respectively and the onset of the greenland interstadials 2 3 and 8 based on 20 year averaged d 18 o

changes in east atlantic deepwater circulation over the last 30 000 years eight time slice reconstructions using 95 epibenthic 13c records eight time slices were reconstructed to trace the distribution of east atlantic deepwater and intermediate water masses over the last 30 000 years our results show that there have been three distinct modes of deepwater circulation near the stage 3 2 boundary the origin of north atlantic deep water nadw was similar to today mode 1 however after late stage 3 the source region of the nadw end member shifted from the norwegian greenland sea to areas south of iceland mode 2 a reduced nadw flow persisted during the last glacial maximum with constant preformed 13c values the nutrient content of nadw increased markedly near the azores fracture zone from north to south probably because of the mixing of upwelled antarctic bottom water aabw from below which then advected with much higher flux rates into the northeast atlantic later the spread of glacial meltwater over the north atlantic led to a marked short term ventilation minimum below 1800 m about 13 500 14c years ago mode 3 the formation of nadw recommenced abruptly north of iceland 12 800 12 500 years ago and reached a volume approaching that of the holocene in the younger dryas 10 800 10 350 years b p another short term shutdown of deepwater formation followed between 10 200 and 9 600 years b p linked to a further major meltwater pulse into the atlantic each renewal of deepwater formation led to a marked release of fossil co2 from the ocean the likely cause of the contemporaneous 14c plateaus over the last 9000 years deepwater circulation varied little from today apart from a slight increase in aabw about 7000 14c years ago it is also shown that the oxygenated mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30 000 years

decreased influence of antarctic intermediate water in the tropical atlantic during north atlantic cold events abstract antarctic intermediate water aaiw is a key player in the global ocean circulation contributing to the upper limb of the atlantic meridional overturning circulation amoc and influencing interhemispheric heat exchange and the distribution of salinity nutrients and carbon however the deglacial history of aaiw flow into the north atlantic is controversial here we present a multicore top neodymium isotope calibration which confirms the ability of unclean foraminifera to faithfully record bottom water neodymium isotopic composition e nd values in their authigenic coatings we then present the first foraminifera based reconstruction of e nd from three sediment cores retrieved from within modern aaiw in the western tropical north atlantic our records reveal similar glacial and interglacial contributions of aaiw and a pronounced decrease in the aaiw fraction during north atlantic deglacial cold episodes heinrich stadial 1 hs1 and younger dryas yd our results suggest two separate phases of reduced fraction of aaiw in the tropical atlantic during hs1 with a greater reduction during early hs1 if a reduction in aaiw fraction also reflects reduced amoc strength this finding may explain why in many regions there are two phases of hydrologic change within hs1 and why atmospheric co2 rose more rapidly during early than late hs1 our result suggesting less flow of aaiw into the atlantic during north atlantic cold events contrasts with evidence from the pacific where intermediate depth e nd records may indicate increased flow of aaiw into the pacific during the these same events antiphased e nd behavior between intermediate depths of the north atlantic and pacific implies that the flow of aaiw into atlantic and pacific seesawed during the last deglaciation

structure of the upper water column in the northwest north atlantic modern versus last glacial maximum conditions 1 during the last glacial maximum the northwestern north atlantic constituted a major conduit for labrador and greenland ice sheet meltwaters vertical density gradients in its upper water masses have been reconstructed by combining information from transfer functions based on dinocysts and from oxygen isotope measurements 18o in planktonic foraminifera transfer functions yield temperature and salinity and thus potential density for the warmest august and coldest february months in the photic zone the 18o values in different size fractions of epipelagic globigerina bulloides and mesopelagic neogloboquadrina pachyderma left coiled npl foraminifera allow us to assess gradients through the pycnocline between surface and intermediate waters based on the calibration of a versus 18o relationship from transfer function reconstructions the size and density of npl shells provide further constraints on these gradients the results show the development of a very strong pycnocline during the lgm with a difference of about 3 summer to 1 5 winter units between surface and underlying waters they indicate conditions unfavorable for vertical convection and support the hypothesis of the spreading of a shallow low salinity buoyant layer over the northern north atlantic this layer depicted a strong e w gradient with maximum seasonal contrast and minimum absolute values westward

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

migration of trace elements from basalt substrate to co located vegetation lichens and mosses at the wudalianchi volcanos northeast china abstract vegetation e g lichens and mosses living on the basalt substrate have potential to accumulate trace elements in their tissues here we analyze the trace elements in basalt collected from major volcanic center to jet plate places representing four different eruption phases and adjacent lichens and mosses to assess their elemental source receptor relation the results indicate that as sr mo cd and ba are enriched in basalt and depleted in lichens and mosses however zn hg and pb are enriched in lichens and mosses and depleted in basalt moreover with the increase of basalt age cr mn fe ni and cu are gradually enriched in lichen and moss but gradually depleted in basalt compared with transition metals large ion lithophiles the platinum group and rare earth elements cr co cu zn and os are more easily absorbed by no 1 lichen specifically s is highly assimilated in vegetation with a highest value of 166 followed by i c pb zn and hg in addition the hydrogen and oxygen isotopic compositions of water samples suggest that the surface water in the wenbo area came from meteoric waters in summer with a high humidity while the underground water in the beiyaoquan area came from meteoric waters in winter with a low humidity

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

plankton in the norwegian greenland sea from living communities to sediment assemblages an actualistic approach a synoptic study is carried out to reconstruct the development of the plankton community in the late quaternary in the norwegian greenland sea it comprises quantitative analyses of coccolithophores dinoflagellate cysts diatoms and radiolarians an actualistic approach is applied to evaluate the different fossil records of these plankton groups the preliminary results of the current investigation are reported here

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes

interhemispheric appraisal of the value of alkenone indices as temperature and salinity proxies in high latitude locations alkenone sediment data from the nordic seas and north atlantic are compared to those from sikes et al 1997 for the southern ocean to evaluate further uk37 and uk37 as proxies to estimate cold temperatures 10 c and the effect of salinity and temperature in the relative abundance of 37 4 to the total abundance of c37 alkenones 37 4 uk37 and uk37 are found to be equally viable as proxies but there are significant regional differences in their cold temperature dependence the measurement of 37 4 in cores from the north atlantic region can be used to identify situations when uk37 is not a reliable paleothermometer variations in salinity are probably responsible for changes in the sedimentary record of 37 4 and a preliminary calibration has been obtained for 37 4 f salinity this new relationship should be further confirmed through field or laboratory experiments but it paves the way to derive a molecular proxy to reconstruct paleosalinity in surface waters

particle transport processes at slope environments event driven flux across the barents sea continental margin abstract recent studies of the vertical flux of organic matter into the deep ocean have prompted the search for key organic compounds biomarkers as tracers for its production flux and burial into the sediment particulate matter was collected with sediment traps moored at the barents sea continental margin 75 11 78 n 12 29 21 e water depth 2050 m at 610 1840 and 1950 m depth the compositions of the organic material in the two bottoms near traps differ significantly this difference cannot be the result of a change of the vertical sedimentation alone a combination of biomarker analyses quantitative microscopy and bulk parameter determinations on water and sediment trap samples is used in this study to demonstrate that a turbidity plume event at the shelf edge is a vehicle to transport organic and lithogenic particles at high velocities to the benthos of the lower continental margin it is suggested that fine particles were advected into the trap at 1850 m whereas the coarser fraction of higher settling velocities passing several resuspension loops entered the lower trap