response to comment on mixed layer deepening during heinrich events a multi planktonic foraminiferal δ18o approach hillaire marcel and de vernal question our hypothesis of the homogenization of the upper water masses of the north atlantic during heinrich events 0 1 and 4 here we respond to their specific points and synthesize data from the southern labrador sea cores the basic tenet of hillaire marcel and de vernal s arguments

inversion of aeromagnetic data using digital terrain models although draped magnetic surveys contain more information about the magnetization of the rocks near the surface of the earth than surveys at constant elevation allowance for the effects of the terrain is critical for their correct interpretation a new method for calculating the magnetic effect of the topography from a digital terrain model by integrating analytically in the vertical direction and then numerically in the horizontal plane is presented this method lends itself to the calculation of anomalies when the magnetization of the rocks varies with position and thus is well suited to the inversion of draped aeromagnetic surveys to obtain the apparent magnetization of the surficial rocks this inversion is achieved by repeated use of an approximate inverse function in the form of a two dimensional 2 d filter that is applied to gridded data an example using draped magnetic data collected over white island an active volcanic island of high relief shows that although the anomaly pattern is domina

identification et distribution des grandes masses d eau dans les mers du labrador et d irminger the main deep water masses present at the time of the css hudson cruises in labrador and irminger seas in june 1990 and october november 1991 have been identified using characteristic temperatures t and salinities s the purpose of this study was to establish the transfer functions between micropaleontological assemblages of top sediments and thermohaline characteristics of water masses the water mass at the top of the labrador sea labrador sea water lsw is formed after intense movements of winter convection in the first 900 m depth of the water column below that depth the lsw parameters reach a double minimum s 34 80 and t 2 9 c only the sediments located on the continental slopes of greenland and labrador between depths of 500 and 1500 m are in contact with the lsw below the lsw the superior fraction of the north east atlantic deep water neadw1 is characterized by a temperature maximum 3 3 c and as such is distinguishable from the inferior fraction neadw2 the latter is ch

isotope stratigraphy sedimentation rates deep circulation and carbonate events in the labrador sea during the last 200 ka high resolution stable isotope and accelerator mass spectrometry 14c measurements in 25 box and piston cores from the labrador sea allow the reconstruction of major paleoceanographical changes during the last 200 ka in this basin and also document the links between the interior of the laurentide ice sheet and the north atlantic ocean during this interval two deep circulation regimes are indicated by contrasting sedimentation rates on the slopes i the modern situation is characterized by a gyre of the north atlantic deep water nadw components into the basin which is responsible for the high energy western boundary undercurrent this regime also prevailed during the former true interglacials and possibly during shorter warm intervals e g bolling allerod ii a more frequent nadw free situation during glacial and interstadial intervals is marked by the presence of a vertically homogeneous water mass in the basin sedimentological records also indicate that carbonate events i e pulses of

surface water temperature salinity and density changes in the northeast atlantic during the last 45 000 years heinrich events deep water formation and climatic rebounds we developed a new method to calculate sea surface salinities sss and densities ssd from planktonic foraminiferal 18o and sea surface temperatures sst as determined from planktonic foraminiferal species abundances sst sss and ssd records were calculated for the last 45 000 years for biogeochemical oceanic flux study bofs cores 5k and 8k recovered from the northeast atlantic the strongest feature is the dramatic drop in all three parameters during the heinrich ice rafting events we modelled the possibility of deepwater formation in die northeast atlantic from the ssd records by assuming that the surface waters at our sites cooled as they flowed further north comparison with modelled north atlantic deepwater densities indicates that there could have been periods of deepwater formation between 45 000 and 30 000 14c years b p interrupted by iceberg meltwater input of heinrich event 3 and 4 at 27 000 and 38 000 14c years b p and during the holocene no amount of cooling in the northeast atlantic between 30 000 and 13 000 years could cause deep water to form because of the low salinities resulting from the high meltwater inputs from icebergs our records indicate that after each heinrich event there were periods of climatic rebound with milder conditions persisting for up to 2000 years as indicated by the presence of warmer and more saline water masses after these warm periods conditions returned to average glacial levels these short term cold and warm episodes in the northeast atlantic are superimposed on the general trend towards colder conditions of the last glacial maximum lgm heinrich event 1 appears to be unique as it occurs as insolation rose and was coeval with the initial melting of the fennoscandian ice sheet we propose that meltwater input of heinrich event 1 significantly reduced north atlantic deep water formation reducing the heat exchange between the low and high latitudes thus delaying deglaciation by about 1500 radiocarbon years 2000 calendar years

evidence for changes in the north atlantic deep water linked to meltwater surges during the heinrich events abstract deep sea sediment records from north atlantic cores 40 n 55 n provide evidence of several massive iceberg discharges known as heinrich events during the last glacial period high resolution benthic 18 o and 13 c records from north atlantic sediment cores were used to monitor the impact of heinrich events on thermohaline circulation and to estimate the sensitivity of deep oceanic circulation to changes in freshwater input to the north atlantic surface waters our data indicate that major rearrangements of deep water masses were directly associated with these massive iceberg discharges to trace in detail the deep water conditions in the north atlantic benthic 13 c values in several cores were used to generate time slices before during and after heinrich event 4 dated at 35 ka bp although north atlantic deep water continued to form during the oxygen isotope stage 3 at 37 ka bp deep circulation was characterized by an increased incursion of deep waters of southern origin which reduced the 13 c composition of north atlantic deep waters particularly in the eastern atlantic basin north atlantic deep water production was reduced during heinrich layer 4 hl4 at 35 ka bp synchronously with the changes in the surface water hydrology deep convection processes may have occurred in areas not affected by the salinity decrease soon after hl4 33 ka bp the 13 c distribution was similar to that before the event similarly a rapid return to initial 13 c values was observed at the end of the most clearly defined heinrich events hl5 hl4 and hl1 comparison between deep circulation patterns corresponding to hl4 the last glacial maximum and heinrich event 1 indicates that each of these periods was characterized by a different circulation state associated with changes in convection sites

evidence from the northeastern atlantic basin for variability in the rate of the meridional overturning circulation through the last deglaciation a first study from the subtropical western atlantic using 231pa 230th ratios as a kinematic proxy for deep water circulation provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation moc over the last deglaciation however these results warrant confirmation from additional locations and water depths because the interpretation of the sedimentary 231pa 230th ratio in terms of circulation vigor can be biased by variations in particle flux and composition we have measured 231pa 230th in a core from the iberian margin in the northeastern atlantic basin and have compared these new results to the data from the western atlantic basin we find that the reduction in the circulation during h1 and yd and the subsequent increases first recognized in the sediment deposited on bermuda rise are also evident in the eastern basin in a totally different sedimentary regime confirming that sedimentary 231pa 230th ratios record basin wide changes in deep water circulation however some differences between the eastern and western records are also recognized providing preliminary evidence to differentiate between renewal rates in the two north atlantic basins and between shallower and deeper overturning our results suggest the possible existence of two sources of glacial north atlantic intermediate deep water gnaiw one in the south labrador sea and another west of rockall plateau both sources contributed to the meridional overturning but the two had different sensitivity to meltwater from the laurentide and the fennoscandian ice sheets during the deglaciation these results indicate that additional information on the geometry and strength of the ventilation of the deep atlantic can be obtained by contrasting the evolution of sediment 231pa 230th in different sections of the atlantic ocean

global water balance and atmospheric water vapour transport at last glacial maximum climate simulations with the canadian climate centre for modelling and analysis atmospheric general circulation model a series of new simulations of the climate state at last glacial maximum has been performed using the canadian second generation atmospheric general circulation model and are described herein the

improving past sea surface temperature estimates based on planktonic fossil faunas a new method of past sea surface temperature sst reconstruction based on the modern analog technique prell 1985 and on the indirect approach bartlein et al 1986 has been developed the revised analog method ram applied to planktonic foraminifera this technique leads to significant improvements in modern sst reconstruction with respect to former methods our estimates are characterized by much lower residuals and a better coverage of the observed sst range moreover the error of ram estimates of past ssts is lower than that associated with former reconstructions particularly at middle and high latitudes in low latitudes cold season ssts reconstructed by ram during glacials are 1 3 c lower than previously estimated our results tend thus to reconcile paleoestimates of glacial temperatures based on planktonic microfossils and on continental data in the tropics

18 o modelling of freshwater inputs in baffin bay and canadian arctic coastal waters 18o salinity modelling of marine environments has been proposed for various areas including some arctic seas the present report concerns arctic coastal waters collected along the west coast of greenland northern baffin bay the arctic archipelago and the north shore of alaska measurements of 18o versus salinity allow the identification of three main components marine standard water continental freshwater and sea ice meltwater continental waters may be represented by either glacial meltwater western greenland land drainage mackenzie areas or both quantitative determinations of the respective parts involved in mixed coastal waters imply a precise knowledge of the isotopic characteristics of the local continental waters these determinations may be achieved either numerically or graphically

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

bias in foraminiferal multispecies reconstructions of paleohydrographic conditions caused by foraminiferal abundance variations and bioturbational mixing a model approach abstract a simple box model was applied to study the combined effect of bioturbation and foraminiferal abundance variations using synthetic isotope records constructed from the greenland oxygen isotope record gisp2 apart from the well known general smoothing of the signal the attenuation of peak heights and the up or downwards shift of the proxy records at intervals of changing abundance the modeling results draw attention to two effects of special importance to climatic reconstructions based on the comparison of proxy signals from two or more planktonic foraminifer species first the bioturbational mixing of tests out of abundance maxima and into over and underlying sediment can lead to the introduction of stratigraphic shifts between different species when species with opposing abundance patterns are used this shifting of the signals can easily result in apparent increases or decreases in the isotopic gradients between different species especially at intervals of rapidly changing climate conditions second in intervals with rapidly changing environmental conditions such as dansgaard oeschger cycles where species with different preferences often show opposing abundance patterns the mixing of foraminifer tests out of their respective abundance maxima can result in a general but artificial offset between the two species this offset then may disappear during intervals of slower variability these artifacts have the potential of seriously biasing any paleoceanographic and paleoclimatic reconstructions based on multispecies analysis where the studied species show opposing abundance patterns it is therefore highly recommended that species with as low abundance variations as possible or at least with similar abundance variations are used whenever multispecies reconstructions are attempted

sea ice cover sea surface salinity and halo thermocline structure of the northwest north atlantic modern versus full glacial conditions abstract seasonal sea ice develops along the eastern continental margins in the northern north atlantic where freshwater and or meltwater outflow are responsible for relatively low salinity in surface waters and very pronounced water mass stratification sea ice constitutes a major parameter in the marine ecosystem since the duration and extent of its seasonal spreading constrain the plankton distribution and the related microfossil assemblages on the sea floor organic walled dinoflagellate cysts that are highly resistant to dissolution were recovered from surface sediments of the northern north atlantic and used to develop transfer functions best analogue method for the reconstruction of the seasonal spreading and duration of sea ice cover in addition to salinity and temperature of the warmest month of the year application of the best analogue approach to cores from the labrador sea reveals large variations in sea ice cover and sea surface conditions throughout the last glacial stage and during the early holocene isotopic analyses in epipelagic and mesopelagic planktonic foraminifers also suggest important changes in salinity and temperature gradients between the surface and sub surface water masses specific study of the last glacial maximum lgm time slice 16 20 ka on a 14 c time scale in the northwestern north atlantic shows much more extensive sea ice than at present with perennial sea ice lying along the continental margins of eastern canada seasonal spreading of the cover of sea ice offshore was accompanied by large seasonal contrasts in temperature with very cold winters but relatively warm summers a pattern linked to strong stratification between a buoyant low saline surface layer having a low thermal inertia and the underlying intermediate oceanic waters

paleo sea surface temperature calculations in the equatorial east atlantic from mg ca ratios in planktic foraminifera a comparison to sea surface temperature estimates from u37k oxygen isotopes and foraminiferal transfer function we present two 270 kyr paleo sea surface temperature sst records from the equatorial divergence and the south equatorial current derived from mg ca ratios in the planktic foraminifer globigerinoides sacculifer the present study suggests that the magnesium signature of g sacculifer provides a seasonal sst estimate from the upper 50 m of the water column generated during upwelling in austral low latitude fall winter common to both down core records is a glacial interglacial amplitude of 3 3 5 c for the last climatic changes and lower holocene and glacial oxygen isotope stage 2 temperatures compared with interglacial stage 5 5 and glacial stage 6 temperatures respectively the comparison to published sst estimates from alkenones oxygen isotopes and foraminiferal transfer function from the same core material pinpoints discrepancies and conformities between methods

reconstruction of sea surface conditions at middle to high latitudes of the northern hemisphere during the last glacial maximum lgm based on dinoflagellate cyst assemblages abstract a new calibration database of census counts of organic walled dinoflagellate cyst dinocyst assemblages has been developed from the analyses of surface sediment samples collected at middle to high latitudes of the northern hemisphere after standardisation of taxonomy and laboratory procedures the database comprises 940 reference data points from the north atlantic arctic and north pacific oceans and their adjacent seas including the mediterranean sea as well as epicontinental environments such as the estuary and gulf of st lawrence the bering sea and the hudson bay the relative abundance of taxa was analysed to describe the distribution of assemblages the best analogue technique was used for the reconstruction of last glacial maximum lgm sea surface temperature and salinity during summer and winter in addition to sea ice cover extent at sites from the north atlantic n 63 mediterranean sea n 1 and eastern north pacific n 1 three of the north atlantic cores from the continental margin of eastern canada revealed a barren lgm interval probably because of quasi permanent sea ice six other cores from the greenland and norwegian seas were excluded from the compilation because of too sparse assemblages and poor analogue situation at the remaining sites n 54 relatively close modern analogues were found for most lgm samples which allowed reconstructions the new lgm results are consistent with previous reconstructions based on dinocyst data which show much cooler conditions than at present along the continental margins of canada and europe but sharp gradients of increasing temperature offshore the results also suggest low salinity and larger than present contrasts in seasonal temperatures with colder winters and more extensive sea ice cover whereas relatively warm conditions may have prevailed offshore in summer from these data we hypothesise low thermal inertia in a shallow and low density surface water layer

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

stable isotope clue to episodic sea ice formation in the glacial north atlantic sea ice is a determinant parameter of the climate system which acts as amplifier through positive ice albedo feedbacks and induces deep water formation through brine production it is also one of the most elusive parameters in the paleoclimate record most proxies of sea ice provide information on its presence and extent of e g diatoms or dinocysts but do not permit assessment on its rate of formation however seemingly off equilibrium low 18o values in mesopelagic planktic foraminifer species as observed today in the arctic ocean are thought to relate to the production of isotopically light brines during sea ice formation and might thus provide a clue on the rate of sea ice growth with reference to the isotopic properties of modern planktic foraminifers in the arctic ocean and using multi proxy data sets from the last glacial stage in the northwest north atlantic we re examined some of the current interpretations of planktic isotope records in the glacial nw north atlantic the large amplitude light isotopic excursions recorded in neogloboquadrina pachyderma left coiling during heinrich events 1 for example correspond to extensive sea ice cover as reconstructed from dinocysts and do not seem unequivocally linked to low salinity pulses such light isotopic excursion more likely responded to enhanced rates of sea ice formation resulting in the production and sinking of isotopically light brines on the contrary the isotopically heavy planktic foraminifers of the last glacial maximum lgm interval stricto sensu would rather suggest relatively low rates of brine production thus low sea ice growth rates in the area this would imply that the lgm distribution of sea ice in the north atlantic was primarily linked to spreading and drifting from marginal and nordic source areas and not from enhanced in situ production at the scale of glacial interglacial cycles isotopic distillation processes relating to sea ice production at high latitudes could be one of the factors controlling the 18o salinity relationship in deep ocean water masses that might deserve closer examination as it would be independent of continental ice volume changes

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

reconstruction of sea surface temperature salinity and sea ice cover in the northern north atlantic during the last glacial maximum based on dinocyst assemblages past sea surface conditions over the northern north atlantic during the last glacial maximum were examined from the study of 61 deep sea cores the last glacial maximum time slice studied here corresponds to an interval between heinrich layers h2 and h1 and spanningabout 20 16 ka on a 14c time scale transfer functions based on dinocyst assemblages were used to reconstruct sea surface temperature salinity and sea ice cover the results illustrate extensive sea ice cover along the eastern canadian margins and sea ice spreading only during winter over most of the northern north atlantic on the whole much colder winter prevailed despite relatively mild conditions in august 10 15 c at most offshore sites thus suggesting a larger seasonal contrast of temperatures than today lower salinity than at present is reconstructed especially along the eastern canadian and scandinavian margins likely because of meltwater supply from the surrounding ice sheets these reconstructions contrast with those established by climap on the basis of planktonic foraminifera these differences are discussed with reference to the stratigraphical frame of the last glacial maximum which was not the coldest phase of the last glacial stage the respective significance of dinocyst and foraminifer records is also examined in terms of the thermohaline characteristics of surface waters and the vertical structure of upper water masses which was apparently much more stratified than at present in the northern north atlantic thus preventing deep water formation

climate science asymmetric response the surface layer of the southern ocean connects the atmosphere with the deep subtropical ocean ocean observations reveal that the thickness of this layer important for biological productivity is controlled by the strength and position of the southern circumpolar winds

last glacial maximum lgm primary productivity in the northern north atlantic oceanthis article is one of a series of papers published in this special issue on the theme polar climate stability network to reconstruct oceanic primary productivity in the northern north atlantic ocean during the last glacial maximum lgm we have applied the modern analogue technique to dinocyst assemblages using a northern hemisphere database that includes 1171 reference sites the reconstructions were made in lgm sediments 21 2 ka of a set of 62 cores collected from 36 n to 75 n here we present the compilation of reconstructed seasonal and annual productivity during the lgm results show lower mean annual productivity during the lgm than at present in the northern north atlantic at most high latitude locations lgm productivity has been estimated at 200 gc m 2 a 1 with extremely low values 100 gc m 2 a 1 in the labrador sea baffin bay and along the margins of greenland such low values might be the result of reduced atlantic meridional overturning circulation and stratified water that characterized the glacial episode of the north atlantic ocean

last glacial maximum temperatures over the north atlantic europe and western siberia a comparison between pmip models margo sea surface temperatures and pollen based reconstructions abstract evaluating the ability of models to simulate climates different from the modern one is important for climate prediction here we present a first comparison between results from simulations of the last glacial maximum climate and continental and surface ocean reconstructions for the north atlantic europe and western siberia the simulations include prescribed sea surface temperature sst and slab ocean atmospheric general circulation model runs performed within the pmip1 project and atmosphere ocean fully coupled runs performed after pmip1 and within the pmip2 project the surface ocean reconstructions are from the margo project continental reconstructions are based on pollen data over the north atlantic most models simulate the strengthening of the sst meridional gradient suggested by the reconstructions but most do not reproduce the lgm control sst anomaly at the right location nor with the right amplitude over western siberia the model results are much improved when a new ice sheet reconstruction ice 5g is used to force the models the main discrepancy remains for western europe winter temperatures for which lgm control anomalies are significantly underestimated by all models all models indicate that this region during the lgm experienced significantly higher interannual variability in coldest month temperatures compared to the control runs this increased variability could have conspired to bias the apparently extremely cold pollen based temperature reconstructions

the formation of labrador sea water part i large scale processes abstract data obtained in the western labrador sea during march 1976 by hudson are analysed to show that new labrador sea water was being formed at this time on the basis of hydrographic and moored current meter data it is hypothesized that a 200 km scale cyclonic gyre forms in winter in the western labrador sea and that this gyre retains the developing deep mixed layers in this general area long enough for the transformation to labrador sea water to take place using a model it is demonstrated that water columns found along the western boundary of the labrador sea can be modified by cooling evaporation and mixing to form deep mixed layers with the properties of labrador sea water approximately 105 km3 of new labrador sea water was formed in 1976 an estimate that is consistent with earlier estimates of mean annual production rates this water 2 9 c 34 84 is some 0 6 c cooler and 0 06 fresher than that defined by lazier 1973 from his data collected in 1966 the variation of labrador sea water

a 200 ka geomagnetic chronostratigraphy for the labrador sea indirect correlation of the sediment record to specmap abstract a chronostratigraphic framework for the last 200 ka based on relative variations of geomagnetic paleointensity has been derived for the labrador sea where 18o stratigraphies are compromised by lack of benthic foraminifera and environmental perturbations of the planktic record relative paleointensity records derived from three labrador sea piston cores are correlated to a recently developed 200 ka paleointensity composite sint 200 y guyodo j p valet earth planet sci lett 143 1996 23 36 the chronology for sint 200 was derived by correlating oxygen isotope stratigraphies from individual paleointensity records to the specmap chronostratigraphy the correlation of sint 200 to labrador sea paleointensity records allows the specmap chronology to be imported into the labrador sea although comparisons of the chronostratigraphy based on paleointensity correlations with those derived from ams 14c dates and 18o data indicate significant discrepancies support for the new chronostratigraphic framework is provided by 1 consistent correlation of labrador sea detrital layers to north atlantic heinrich layers 2 general consistency between planktic 18o values and the specmap reference curve and 3 feasible prediction for the age of ash layer 2 as the new chronostratigraphy is tied to specmap labrador sea sediment cores can now be directly compared with any specmap dated record

the magnetic signature of rapidly deposited detrital layers from the deep labrador sea relationship to north atlantic heinrich layers rock magnetic parameters from deep labrador sea piston core p 094 are useful for recognizing rapidly deposited detrital layers some of which correlate with north atlantic heinrich layers variations in magnetic properties and lithology distinguish two classes of rapidly deposited detrital layers during the last ice age 1 seven detrital carbonate dc layers have high carbonate content and mean magnetite grain diameters about 4 times greater than the background sediments 2 six low detrital carbonate ldc layers have very similar magnetic properties to dc layers but low carbonate content similar to the background sediments the magnetite associated with dc and ldc layers is well sorted and relatively uniform within and between layers ice rafted detritus ird recognized by increased percentage of the 125 micron grain size fraction and by high magnetic susceptibility is associated with most dc and ldc layers but is not the dominant detrital constituent the correspondence of dc and ldc layers with increased grain size of well sorted magnetite but not with coarse fraction content precludes ice rafting as the primary depositional mechanism dc and ldc layers may have been deposited from suspended sediment derived from turbidite activity in the nearby northwest atlantic mid ocean channel namoc this interpretation is supported by a piston core p 013 from a greenland rise site largely but not completely outside the influence of the namoc the association of dc layers with ird and the apparent age correlation of dc layers to north atlantic heinrich layers suggest that the ice advances which produced the ird in p 094 and in correlative north atlantic heinrich layers also triggered turbiditic flows down the namoc several dc and ldc layers however do not correlate with recognized heinrich layers but appear to be coeval with recently discovered high frequency ird rich layers in the north atlantic

surface ocean density gradients during the last glacial maximum we have compiled published planktonic foraminiferal oxygen isotope values from the tropical to subtropical atlantic and pacific for the late holocene and last glacial maximum lgm we interpret the spatial distribution of 18o values in terms of meridional density gradients in the lgm surface ocean and discuss implications on tropical ocean thermocline structure in both oceans glacial 18o values display a pattern of interhemispheric asymmetry evidenced by increasingly higher glacial 18o values toward northern latitudes the 18o derived density estimates suggest that the northern subtropical surface ocean density was higher during the lgm than today which has significant implications on lgm thermocline ventilation in the atlantic steeper density gradients in the northern subtropics during the lgm are consistent with a more compressed subtropical gyre and thermocline water formation farther south than today in the pacific the steeper density gradients suggest a significant reduction in freshwater fluxes to the northern tropical and subtropical regions which raises the possibility of a more significant component of northern hemisphere source waters to the tropical pacific thermocline these predictions could be tested with numerical ocean models that assess the structure of the tropical thermocline in the glacial ocean

distribution of planktic foraminifera at the ice margin in the arctic fram strait planktic foraminifera were collected in net tows 63 m along two east west transects at 78 and 80 n in the fram strait northern nordic seas at five concurrent depth intervals in the upper 200 m of the water column in the ice free zone absolute abundances in the upper 200 m of the water column up to 500 individuals m3 were obtained along the ice margin the absolute abundances reached up to 1250 ind m3 while in the ice covered areas not more than 50 ind m3 have been found surprisingly these strong variations in abundance are not accompanied by significant changes in faunal assemblages between the ice free and the ice covered regions neogloboquadrina pachyderma is the dominant species in most samples making up to 60 of the total faunal assemblage globigerina quinqueloba contributes 38 and all other species combined make up only 2 of the total fauna both absolute and relative abundances of the collected foraminifera are strongly dependent on the mesh size used using smaller mesh sizes provides a wider species spectrum which is of special interest for paleoceanographic reconstructions in the nordic seas where fossil assemblages 150 m often consist of only one species the specific hydrographic conditions in the fram strait with warm atlantic waters underlying cold polar surface waters result in a rather atypical depth distribution of the planktic foraminifera all species seem to prefer the temperate atlantic waters between 50 m and 200 m thus the species composition as well as geochemical tracers do not reflect the surface ocean conditions which again has potentially interesting implications for paleoceanographic reconstructions

accelerator mass spectrometry radiocarbon stratigraphies in deep labrador sea cores paleoceanographic implications foraminiferal accelerator mass spectrometry ams 14c ages and benthic planktonic age differences in surface layer sediments of labrador sea are influenced by bioturbation and by changes in the relative abundance of foraminiferal species carrying the 14c signal using benthic mixing models we demonstrate that inverse benthic planktonic age differences can be generated when the effect of benthic mixing and abundance change exceeds apparent age differences between surface water and deep water ams 14c ages obtained put constraints on the timing of major paleoceanographic changes in the basin notably on the history of the western boundary undercurrent which was clearly reinitiated during the mid deglaciation and intensified during the last 2 3 ka

size dependent isotopic composition of planktic foraminifers from chukchi sea vs nw atlantic sediments implications for the holocene paleoceanography of the western arctic abstract in arctic and sub arctic seas shell growth and or secondary calcite overgrowth of neogloboquadrina pachyderma left coiled npl occur along the pycnocline and their 13c and 18o values are size and weight dependent however whereas the npl 18o data from the nw atlantic indicate near equilibrium conditions with ambient waters and a positive relationship between shell weight and 18o content assemblages from box cored sediments of the chukchi sea western arctic are depleted by 2 with respect to equilibrium values with modern conditions and depict a negative relationship between shell weight and its 18o value 0 15 0 03 g on vpdb scale a similar feature is also depicted by the dextral form of n pachyderma npd we associate the reverse shell size or weight vs 18o relationship to the reverse temperature gradient observed along the thermocline between the surface cold and dilute water layer and the underlying near 3 c warmer saline north atlantic water mass the analysis of two late to post glacial sedimentary sequences from the chukchi sea indicates that such a water mass stratification with a reverse thermocline persisted throughout the holocene thus reflecting an early onset of the modern like linkage between the arctic ocean and the north atlantic moreover lower 18o values in both npl and npd together with larger 18o gradients between the different shell sizes at ca 9 7 ka bp suggest 3 c higher temperatures in the upper north atlantic water mass in comparison with the present approximately 1 c at the study site thus likely a higher inflow rate of this water mass during the early holocene

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

geomagnetic paleointensity and environmental record from labrador sea core md95 2024 global marine sediment and ice core chronostratigraphy for the last 110 kyr piston core md95 2024 from the labrador rise provides a continuous record of rapidly deposited detrital layers denoting laurentide ice sheet lis instability the core also provides a high resolution record of geomagnetic paleointensity that is consistent with but at higher temporal resolution than previous labrador sea records correlation to the greenland summit ice cores grip gisp2 is achieved by assuming that labrador sea detrital layers correspond to cold stadials in the ice cores this allows a gisp2 official chronology to be placed on md95 2024 which is consistent with the inverse correlation between paleointensity and the flux of cosmogenic isotopes 10 be and 36 cl in greenland ice cores synchronous millennial scale variability observed from the md95 2024 paleointensity

higher laurentide and greenland ice sheets strengthen the north atlantic ocean circulation during the last glacial interglacial cycle changes in the large scale north atlantic ocean circulation occurred and at the same time topography of the laurentide and greenland ice sheets also varied in this study we focus on detecting the changes of the north atlantic gyres western boundary current and the atlantic meridional overturning circulation amoc corresponding to different laurentide and greenland ice sheet topographies using an earth system model we conducted simulations for five climate states with different ice sheet topographies pre industrial mid holocene last glacial maximum 32 kilo years before present and eemian interglacial our simulation results indicate that higher topographies of the laurentide and greenland ice sheets strengthen surface wind stress curl over the north atlantic ocean intensifying the subtropical and subpolar gyres and the western boundary currents the corresponding decrease in sea surface height from subtropical to subpolar favors a stronger amoc an offshore shift of the gulf stream is also identified during the glacial periods relative to that during the pre industrial due to lower sea levels explaining a weaker glacial gulf stream detected in proxy data meanwhile the north atlantic gyres and amoc demonstrate a positively correlated relation under each of the climate conditions with higher ice sheets

rapid changes in the mechanism of ocean convection during the last glacial period high amplitude rapid climate fluctuations are common features of glacial times the prominent changes in air temperature recorded in the greenland ice cores1 2 are coherent with shifts in the magnitude of the northward heat flux carried by the north atlantic surface ocean3 4 changes in the ocean s thermohaline circulation are a key component in many explanations of this climate flickering5 here we use stable isotope and other sedimentological data to reveal specific oceanic reorganizations during these rapid climate change events deep water was generated more or less continuously in the nordic seas during the latter part of the last glacial period 60 to 10 thousand years ago but by two different mechanisms the deep water formation occurred by convection in the open ocean during warmer periods interstadials but during colder phases stadials a freshening of the surface ocean reduced or stopped open ocean convection and deep water formation was instead driven by brine release during sea ice freezing these shifting magnitudes and modes nested within the overall continuity of deep water formation were probably important for the structuring and rapidity of the prevailing climate changes

refining the eustatic sea level curve since the last glacial maximum using far and intermediate field sites the eustatic component of relative sea level change provides a measure of the amount of ice transferred between the continents and oceans during glacial cycles this has been quantified for the period since the last glacial maximum by correcting observed sea level change for the glacio hydro isostatic contributions using realistic ice distribution and earth models during the last glacial maximum lgm the eustatic sea level was 125 5 m lower than the present day equivalent to a land based ice volume of 4 6 4 9 107 km3 evidence for a non uniform rise in eustatic sea level from the lgm to the end of the deglaciation is examined the initial rate of rise from ca 21 to 17 ka was relatively slow with an average rate of ca 6 m ka 1 followed by an average rate of ca 10 m ka 1 for the next 10 ka significant departures from these average rates may have occurred at the time of the younger dryas and possibly also around 14 ka most of the decay of the large ice sheets was completed by 7 ka but 3 5 m of water has been added to the oceans since that time

neogloboquadrina pachyderma sinistral coiling as paleoceanographic tracers in polar oceans evidence from northeast water polynya plankton tows sediment traps and surface sediments the abundance and chemistry of the planktonic foraminifera neogloboquadrina pachyderma sinistral coiling have long been used as tools for monitoring polar surface ocean changes and for correlating these changes to atmospheric and thermohaline circulation fluctuations however due to its remote habitat very little is known about how modern n pachyderma s respond to changing environmental conditions in the polar seas modern samples of n pachyderma s from the northeast water polynya provide a means for studying how environmental conditions affect the vertical distribution and chemistry of this species highest abundances of n pachyderma s were associated with the chlorophyll maximum in the surface 20 80 m where they are exploiting their primary food source evidence suggests that the addition of a calcite crust modifies the calcite tests of some n pachyderma s between 50 and 200 m increasing shell density and modifying shell chemistry the shell mass of encrusted forms is 3 4 times greater than the nonencrusted forms between 50 and 200 m the oxygen isotope composition of n pachyderma s shells increase by 1 5 in response to local water column gradients the 13c values of n pachyderma s are basically invariant with depth in this region are consistently 1 0 depleted in comparison with the 13c for equilibrium calcite and remain basically constant during the shell thickening process mass balance calculations suggest that encrustation occurs at all depths but abundance counts suggest that the process occurs mostly at the depth of the main pycnocline sediment fluxes of n pachyderma s occur during a 2 week bloom event and decrease to almost zero below complete ice cover the decoupling of the processes controlling abundances and shell chemistry explain the discrepancies between transfer function and isotopically derived paleotemperature estimates of surface conditions in some oceanic settings the ability of 18o to record surface ocean conditions will depend on vertical water column gradients as evidenced by the differences in core top calibrations between the north and south atlantic

oxygen 18 16 variability in greenland snow and ice with 10 3 to 105 year time resolution the 3 km long greenland ice sheet project 2 gisp2 ice core presents a 100 000 year detailed oxygen isotope profile covering almost a full glacial interglacial cycle measuranents of isotopic fluctuations in snow frost and atmospheric water vapor samples collected during summer field seasons up to 20 0 are compatible with the large and abrupt 80 160 changes observed in accumulated tim snow pit 15 80 profiles from the gisp2 summit area however show rapid smoothing of the 180 160 signal near the surface beyond about 2 m depth the smoothedi5180 signal is fairly well preserved and can be interpreted in terms of average local weather conditions and climate the longer climate fluctuations also have regional and often global significance in the older part of the record corresponding to marine isotope stages mis 5a to 5d the effect of orbital climate forcing via the 19 and 23 kyr precession cycles and the 41 kyr obliquity cycle is obvious from the end ofmis 5a at about 75 000 years b p till the end of the glacial at the younger dryas preboreal transition at 11 650 years b p the o180 160 record shows frequent rapid switches between intermediate interstadial and low stadial values fourier spectra of the oscillations that are superimposed on the orbitally induced changes contain a strong periodicity at 1 5 kyr a broad peak at 4 0 kyr and additional shorter periods detailed comparison of the gisp2 180 160 record with the vostok antarctica 15d record pacific ocean foraminiferal 180 160 grande pile france tree pollen and insolation indicates that a counterpart to many of the rapid 180 160 fluctuations of gisp2 can be found in the other records and that the gisp2 isotopic changes clearly are the local expression of climate changes of worldwide extent correlation of events on the independent gisp2 and specmap time scales for the interval 10 000 50 000 years b p shows excellent chronometric agreement except possibly for the event labeled 3 1 the glacial to interglacial transition evidently started simultaneously in the arctic and the antarctic but its development and its expression in greenland isotopes was later suppressed by the influence of meltwater especially from the barents sea ice sheet on deep water formation and ocean circulation meltwaters from different ice sheets bordering the north atlantic also influenced ocean circulation during the bolling allerod interstadial complex and the younger dryas and led to a distinct development of european climate and greenland 180 160 values the holocene interval with long term stable mean isotopic values contains several fluauations with periods from years to millennia dominant is a 6 3 year oscillation with amplitude up to 3 to 4 0 periodicities of 11 and 210 years also found in the solar modulated records of the cosmogenic isotopes 1obe and 14c suggest solar processes as the cause of these cycles depression of180 160 values cooling by volcanic eruptions is observed in stacked gisp215 80 records but the effect is small and not likely to trigger major climate changes

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

millennial scale iceberg discharges in the irminger basin during the last glacial period relationship with the heinrich events and environmental settings high resolution records of coarse lithic content and oxygen isotope have been obtained in a piston core from the irminger basin the last glacial period is characterized by numerous periods of increased iceberg discharges originating partly from iceland and corresponding to millennial scale instabilities of the coastal ice sheets and ice shelves in the nordic area a comparison with midlatitude sediment cores shows that ice rafted material corresponding to the heinrich events was deposited synchronously from 40 to 60 n there are thus two oscillating systems every 5 10 kyr massive iceberg armadas are released from large continental ice caps whereas more frequent instabilities of the coastal ice sheets in the high latitude regions occur every 1 2 3 8 kyr at the time of the heinrich events the synchroneity of the response from all the northern hemisphere ice sheets attests the existence of strong interactions between the two systems

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

the role of the deep ocean in north atlantic climate change between 70 and 130 kyr ago the suggestion1 that changes in north atlantic deep water nadw production are linked through surface heat flux to the atmospheric temperature over greenland is supported by earlier indications2 3 that nadw production decreased during glacial times and by the subsequent finding4 6 that it declined during the younger dryas cool period at the end of the last glaciation changes in north atlantic surface temperatures have been found7 to mirror high frequency temperature changes recorded in greenland ice cores over the past 80 kyr but the connection to abyssal circulation has yet to be established except for one or two isolated oscillations8 9 here we present carbon and oxygen isotope analyses of benthic foraminifera in a high resolution north atlantic deep sea sediment core for the period 70 130 kyr ago these data allow us to reconstruct the history of nadw production which shows a close correlation with greenland climate variability for much of this time interval suggesting that the climate influence of nadw variability was widespread we see no evidence however for changes in nadw production during substage 5e the eemian interglacial period in contrast with recent ice core data10 which suggest severe climate instability in greenland during this time period our results may support suggestions based on data from a second ice core that this apparent instability is an artefact caused by ice flow11 alternatively the eemian climate instability may have had a different origin from the subsequent climate events

foraminifer isotope study of the pleistocene labrador sea northwest north atlantic iodp sites 1302 03 and 1305 with emphasis on paleoceanographical differences between its inner and outer basins article i nfo coresraisedduringiodpexpedition303offsoutherngreenland eirikridgesite1305 andoffthelabradorcoast orphanknollsite1302 1303 wereanalyzedtoestablishanisotopestratigraphy respectivelyforthe inner and outer basins of the labrador sea ls these isotopic data also provide information on the atlantic meridional overturning circulation amoc notably with regard to the intensity of the western boundary under current wbuc which is tightly controlled by the production of denmark strait overflow water dsow and the production of labrador sea water lsw in the inner basin through winter cooling and convection the upper 184 m of sediment at eirik ridge spans marine isotope stages mis 32 to 1 at this site two distinct regimes are observed prior to mis 20 the isotopic record resembles that of the open north atlantic records of the interval

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

sensitivity of the european lgm climate to north atlantic sea surface temperature recent reconstructions of sea surface temperatures ssts for the last glacial maximum lgm 21kyr bp based on foraminifera and dinoflagellate proxies suggest that the north atlantic may have been warmer than estimated by climap 1981 to better understand the impact of such a warm north atlantic on the global lgm climate we used two different agcms to perform sensitivity studies with the new warmer ssts both models simulate a hydrological cycle and temperatures very different from those obtained with the climap boundary conditions the most noticeable differences occur in winter over north america and siberia whereas southern europe is only weakly affected at all seasons whichever the conditions prescribed over the north atlantic both models underestimate the large cooling recorded by continental proxy data over the mediterranean basin

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

simulated influence of carbon dioxide orbital forcing and ice sheets on the climate of the last glacial maximum a coupled atmosphere ocean sea ice model is used to investigate the climate of the last glacial maximum 21 000 years ago and the relative climate forcing effects of atmosphere co2 the earth s orbital parameters and ice sheet albedo tropical temperatures are found to be 2 2 c less than today s slightly colder than indicated by the climap palaeoclimate reconstruction this result is consistent with a low to medium climate sensitivity to radiative perturbations temperatures are colder still in the northern north atlantic region owing to a weakening and shallowing of the thermohaline circulation a sensitivity analysis suggests that changes in ocean circulation since the last glacial maximum have not contributed directly to the global mean temperature change since that time

instabilities in the labrador sea water mass structure during the last climatic cycle in the modern labrador sea the north atlantic deep water components are found below the 2 km deep intermediate labrador sea water lsw mass which is renewed locally through winter convective mixing this water mass structure remained relatively stable since 9 5 14 c ka bp as indicated by isotopic studies of foraminifer assem blages from deep sea cores almost constant differences in 18 o values are observed between major species these av erage 0 5 between the epipelagic species globigerina bulloides and the mesopelagic species neogloboquadrina pachyderma left coiled and 1 between neogloboquadrina pachydermaand the benthic species cibicides wuellerstorfi after correction for cibicides wuellerstorfi specific fractionation these isotopic compositions represent thermohaline conditions in surface waters in the pycnocline with the lsw and in the deep component of the north atlantic deep water respectively a drastically different structure characterized the glacial labrador sea differences in 18 o values of 2 to 2 5 are then observed between globigerina bulloides and benthic species indicative of a strong halocline between the corresponding water masses thus for reduced production of intermediate waters during the same interval neogloboquadrina pachydermashows 13 c and 18 o fluctuations of 1 to 1 5 amplitude in phase with heinrich bond events and higher frequency climate oscillations the 18 o values in neogloboquadrina pachyderma vary between those of globigerina bulloides and of benthic foraminifers suggesting large amplitude bathymetric fluctuations of the halo thermocline above and below the bathymetric range occupied by neogloboquadrina pachyderma minimum 18 o values in neogloboquadrina pachydermamatch intervals of maximum ice rafting deposition such as the late heinrich events thus intervals with a deeper more dilute buoyant surface water layer

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