methodology of the last climatic cycle reconstruction in france from pollen data abstract a numerical method has been devised to reconstruct the climate of the last climatic cycle from pollen data reliable annual reconstructions have been published recently for the two french long sequences of la grande pile and les echets covering the last 140 millennia this paper gives more details on the method used it proposes new reconstructions based on an extended modern pollen data base these reconstructions are consistent with the previous ones especially detailed information is obtained on the seasonal characteristics of climate computations of gcm on the climate variations from 125 kyr to 115 kyr b p are confirmed for western europe the insolation variations have induced at that time a decrease of seasonality accompanied by an increased cyclonic activity in winter this has been the beginning of the first ice growth after the last interglacial other glacier growth phases are detected at the end of substage 5c and particularly at the end of substage 5a

organic walled microfossils and geochemical tracers sedimentary indicators of productivity changes in the north water and northern baffin bay during the last centuries analyses performed on 26 surface sediment samples collected with a box corer at 17 stations throughout the north water and northern baffin bay 75 791n 68 801w revealed abundantorganic walled microfossils most ly dinoflagellate cysts 10 3 10 4 cysts g 1 and organic linings of benthic foraminifers 10 2 10 3 ol g 1 as well as high organic carbon concentrations 0 87 2 81 dry weight these data indicate high productivity in both the pelagic and benthic environments of the north water and slightly lower productivity in northern baffin bay the data also showed calcium carbonate and biogenic silica dissolution throughout the study area the dinocyst assemblages were relatively uniform in the north water and dominated by heterotrophic taxa algidasphaeridium minutum and brigantedinium spp whereas northern baffin bay assemblages were dominated by autotrophic taxa notably operculodinium centrocarpum and spiniferites elongatus the difference between these two assemblages may be related to higher diatomaceous primary production in the north water than in northern baffin bay since diatoms constitute the principal food source of heterotrophic dinoflagellates the biogeographical boundary between the north water and northern baffin bay has been maintained for at least the last few centuries as shown by analyses of microfossils and geochemical tracers in two sediment cores one taken in the southeastern part of the north water 76117 0 n 72102 0 w and the other in northeastern baffin bay 75135 0 n 70148 0 w the analyses of the north water core revealed relatively uniform microfossil assemblages and organic carbon fluxes ranging from 1 1 to 1 5 mg corg cm 2 yr 1 for the last few centuries which corresponded to 4 6 of the present annual primary production in the euphotic zone these data suggest high productivity and relatively stable conditions in the polynya on a decadal time scale in the northeastern baffin bay core the analyses indicated generally lower organic carbon fluxes ranging from 0 3 to 0 6 mg corg cm 2 yr 1 and from the microfossil data significant variations in sea surface conditions at this lower latitude over the last centuries r 2002 elsevier science ltd all rights reserved

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

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

warm atlantic surface water inflow to the nordic seas 34 10 calibrated ka b p a number of short lasting warm periods interstadials interrupted the otherwise cold climate of the last glacial period these events are supposedly linked to the inflow of the warm atlantic surface water to the nordic seas however previous investigations of planktonic foraminifera from the nordic seas have not been able to resolve any significant difference between the interstadials and intervening cold stadials as the faunas are continuously dominated by the polar species neogloboquadrina pachyderma s here we examine the planktonic foraminifera assemblages from a high resolution core link17 taken at 1500 m water depth off northern scotland below the warmest part of the inflowing atlantic water the core comprises the time period 34 10 calibrated ka b p the coldest period of the last glaciation and the deglaciation the results reveal a hitherto unknown faunistic variability indicating significant fluctuations in both surface water inflow and in summer sea surface temperatures during the interstadials relatively warm atlantic surface water 4 7 c flowed north into the eastern norwegian sea during the stadials and heinrich events the surface inflow stopped and the temperatures in the study area dropped to 2 c the last glacial maximum was nearly as warm as the interstadials but the inflow was much more unstable the data reveal two previously unrecognized warming events each lasting more than 1600 years and preceding heinrich events he3 and he2 respectively by destabilizing the ice sheets on the shelves the warmings may have played a crucial role for the development of heinrich events he2 and he3

initiation of fennoscandian ice sheet retreat during the last deglaciation although the retreat history of the southern margin of the laurentide ice sheet during the last deglaciation has been well known for several decades1 3 and recently supported by evidence from accelerator mass spectrometer ams radiocarbon dating of meltwater in the gulf of mexico4 and the north atlantic subtropical gyre5 the retreat history of the fennoscandian ice sheet before 13kyr ago is still poorly documented from ams 14c dating and isotopic analysis of a rapidly deposited series of supra till sediments in the norwegian channel north sea we find that the southern margin of the fennoscandian ice sheet was in retreat by 15 kyr bp before present approximately 2 000 yr earlier than previously supposed oxygen isotope analyses in the channel sediments confirm earlier evidence from deep norwegian sea sediment cores for low salinity due to ice sheet discharge beginning 15 14 5 kyr bp ref 6 recent recalibration of the 14c timescale indicates that the onset of deglaciation within the norwegian sea occurred during an interval of rapidly increasing summer insolation beginning 18 000 calendar yr bp ref 7 suggesting that ice sheet retreat may have been caused by increasing insolation acting on a particularly climate sensitive ice sheet configuration fresh water and icebergs discharged into the norwegian sea at this time reached the north atlantic and may have contributed to a brief interval of extreme oceanic cooling8 and reduced production of north atlantic deep water9 10 these factors may also have helped to briefly reverse the deglaciation trend erie interstade already underway in north america

termination 1 timing in radiocarbon dated regional benthic δ18o stacks benthic 18o changes are often assumed to be globally synchronous but studies comparing 2 9 radiocarbon dated records over the most recent deglaciation termination 1 have proposed differences in the timing of benthic 18o change between the atlantic and pacific intermediate and deep and north and south atlantic because of the relatively small number of records used in these previous studies it has remained unclear whether these differences are local or regional in scale here we present seven regional benthic 18o stacks for 0 40 kyr b p that include 252 records with independent regional age models constrained by 852 planktonic foraminiferal 14c dates from 61 of these cores we find a 4000 year difference between the earliest termination onset in the intermediate south atlantic at 18 5 95 confidence interval 17 9 19 0 kyr b p and the latest in the deep indian at 14 5 14 1 15 0 kyr b p the termination onset occurs at 17 5 kyr b p in the intermediate and deep north atlantic deep south atlantic and deep pacific however throughout the termination deep north atlantic benthic 18o leads the deep pacific by an average of 1000 year and a maximum of 1700 year additionally the intermediate pacific termination onset at 16 5 16 1 16 9 kyr b p demonstrates that intermediate depth benthic 18o change was not globally synchronous these regional stacks provide better age models than a global stack across termination 1 and potentially important constraints on deglacial ocean circulation changes

a new late weichselian and holocene marine chronology for the western svalbard slope 30 000 0 cal years bp abstract data have been compiled from eleven sediment cores from 76 to 80 n on the western svalbard slope the cores are from water depths between 630 and 1880 m and show clear similarities in lithology and magnetic susceptibility all cores penetrated into mass transported sediments from glacigenic debris flow events and turbidity flow events the mass transport probably occurred when the ice reached the shelf edge the deposits date between 24 080 150 and 23 550 185 calibrated cal years bp the records also include laminated fine grained sediments interpreted as deposits from sediment laden meltwater plumes dated between 14 780 220 and 14 300 260 cal years bp in holocene sediments a diatom rich fine grained layer dates 10 100 150 to 9840 200 cal years bp the eleven cores have been stacked into one record with absolute age control from 35 ams14c dates together with oxygen isotope stratigraphy and contents of ice rafted detritus the stacked record provides a useful chronology tool for cores on the western svalbard slope our study improves the age control of earlier well documented glacial events and shows that the maximum glacial state and the onset of the deglaciation both occurred 2500 3000 years earlier than previously reconstructed for the western svalbard margin the results indicate that during the last 30 000 years advance and retreat of the svalbard barents sea ice sheet was closely linked to the flow of atlantic water and polar water over the margin

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

a late glacial early holocene multiproxy record from the eastern fram strait polar north atlantic the paleoceanographic development of the eastern fram strait during the transition from the cold late glacial and into the warm early holocene was elucidated via a multiproxy study of a marine sediment record retrieved at the western svalbard slope the multiproxy study includes analyses of planktic foraminiferal fauna bulk sediment grain size and caco3 content in addition to mg ca ratios and stable isotopes delta c 13 and delta o 18 measured on the planktic foraminifer neogloboquadrina pachyderma furthermore paleosubsurface water temperatures were reconstructed via mg ca ratios ssst mg ca and transfer functions ssst transfer enabling comparison between the two proxies within a single record the age model was constrained by four accelerator mass spectrometry ams c 14 dates from 14 000 to 10 300 cal yr b p n pachyderma dominated the planktic fauna and cold polar sea surface conditions existed the period was characterized by extensive sea ice cover iceberg transport and low subsea surface temperatures ssst transfer similar to 2 1 degrees c ssst mg ca similar to 3 5 degrees c resulting in restricted primary production atlantic water inflow was reduced compared to the present day and likely existed as a subsurface current at ca 10 300 cal yr b p atlantic water inflow increased and the arctic front retreated north westward resulting in increased primary productivity higher foraminiferal fluxes and a reduction in sea ice cover and iceberg transport the fauna rapidly became dominated by the subpolar planktic foraminifer turborotalita quinqueloba and summer ssst transfer increased by similar to 3 5 degrees c concurrently the ssst mg ca recorded by n pachyderma rose only similar to 0 5 degrees c from ca 10 300 to 8600 cal yr b f the average ssst mg ca and ssst transfer were similar to 4 0 degrees c and similar to 55 degrees c respectively the relatively modest change in ssst mg ca compared to ssst transfer can probably be tied to a change of the main habitat depth and or shift in the calcification season for n pachyderma during this period

process length variation of the cyst of the dinoflagellate protoceratium reticulatum in the north pacific and baltic skagerrak region calibration as an annual density proxy and first evidence of pseudo cryptic speciation process length variation of cysts of the dinoflagellate protoceratium reticulatum claparede et lachmann butschli in surface sediments from the north pacific was investigated the average process

variability of sea surface temperature and sea ice cover in the fram strait over the last two millennia abstract a sediment core located on the west spitzbergen margin in the fram strait 78 54 931 n 6 46 005 e water depth 1497 m was analyzed for its dinocyst content in order to reconstruct hydroclimatic variations of the last 2500 years the relative abundance of dinocyst taxa and principal component analysis show a major transition at about 300 cal years bp it is characterized by the disappearance of thermophilic taxa spiniferites mirabilis hyperacanthus and impagidinium sphaericum and the increase of polar subpolar taxa impagidinium pallidum and pentapharsodinium dalei sea surface temperature sst estimates suggest warmer conditions than present anomaly 2 c averaging at 7 c in summer until 300 cal years bp although cooling pulses are recorded around 1700 1500 1200 and 800 cal years bp the last 300 years were marked by a cooling from 7 6 to 3 5 c and sea ice cover increasing up to 7 months yr the results demonstrate that the fram strait area is sensitive to hydroclimatic variations notably with respect to sea ice and ssts which are linked to the relative strength of northward flow of north atlantic waters to the east and southward outflow of cold and fresh waters from the arctic ocean based on our data the warmest part of our record around 1320 cal years bp is the only interval of the last 2500 years that provides a possible analogue for the modern post ad 2000 interval which is characterized by sea ice free conditions

late weichselian and holocene sedimentary environments and ice rafting in isfjorden spitsbergen abstract multi proxy analyses of two sediment cores from central isfjorden were used to reconstruct the glacial history in central spitsbergen during the late weichselian and the holocene and to relate iceberg rafting and sea ice rafting to climatic and oceanographic changes in the north atlantic region a basal till was deposited beneath an ice stream prior to 12 700 cal years bp calendar years before the present several tidewater glaciers influenced the sedimentary environment during the younger dryas and probably already during the allerod the younger dryas cooling might be reflected by enhanced sea ice formation and suspension settling as well as reduced iceberg rafting the final deglaciation was dominated by intense iceberg rafting it terminated around 11 200 cal years bp optimum holocene climatic and oceanographic conditions with significantly reduced ice rafting occurred between c 11 200 and 9000 cal years bp ice rafting occurred almost exclusively from icebergs after 10 200 cal years bp the icebergs most probably originated from tidewater glaciers on east spitsbergen indicating the presence of a strong east west temperature gradient at this time an increase of iceberg rafting around 9000 cal years bp followed by enhanced sea ice rafting reflects the onset of a general cooling in the western barents sea svalbard region comparatively intense rafting from icebergs and sea ice between 9000 and 4000 cal years bp is related to this cooling a general reduction in ice rafting after 4000 cal years bp is most probably the result of the enhanced formation of shore fast and or more permanent sea ice cover reducing the drift of icebergs and sea ice in the fjord the results indicate that the palaeoenvironmental conditions on central spitsbergen to a large degree depended on the oceanographic conditions in the western barents sea and west off spitsbergen however climatic trends affecting greenland and the entire north atlantic region can also be identified

dinocyst based reconstructions of sea ice cover concentration during the holocene in the arctic ocean the northern north atlantic ocean and its adjacent seas abstract sea ice cover extent expressed in terms of mean annual concentration was reconstructed from the application of the modern analogue technique to dinocyst assemblages the use of an updated database which includes 1492 sites and 66 taxa yields sea ice concentration estimates with an accuracy of 1 1 10 holocene reconstructions of sea ice cover were made from dinocyst counts in 35 cores of the northern north atlantic and arctic seas in the canadian arctic the results show high sea ice concentration 7 10 with little variations throughout the interval in contrast in arctic areas such as the chukchi sea and the barents sea the reconstructions show large amplitude variations of sea ice cover suggesting millennial type oscillations with a pacing almost opposite in western vs eastern arctic other records show tenuous changes with some regionalism either in trends or sea ice cover variability during the mid holocene and notably at 6 0 5 ka minimum sea ice concentration is recorded in the eastern fram strait northern baffin bay and labrador sea however this minimum cannot be extrapolated at the scale of the arctic and circum arctic the comparison of recent observations and reconstructions suggests larger variations in the arctic sea ice cover during the last decades than throughout the holocene

time slice reconstructions of ocean circulation changes on the continental shelf in the nordic and barents seas during the last 16 000 cal yr b p abstract ocean circulation changes along the continental shelf of the nordic and barents seas have been investigated in order to reconstruct regional changes in the inflow of atlantic water aw through the last 16 000 calibrated cal years yr b p we have selected five time slices representing the late glacial 16 000 15 000 cal yr b p the bolling allerod warm interstadials 14 500 13 500 cal yr b p the younger dryas cold stadial 12 500 11 500 cal yr b p the early holocene 9500 7500 cal yr b p and the late holocene 4000 2000 cal yr b p twelve previously published records of the distribution of benthic foraminifera faunas and ice rafted debris have been compiled the earliest sign of atlantic water inflow was recorded at the northern iceland shelf at 16 000 15 000 cal yr b p the inflow of warm aw to the nordic seas shelf has been persistent since but with variable strength and geographic pattern an apparent zonal seesaw pattern in the strength of the norwegian atlantic current nwac and the irminger current ic during the late glacial bolling allerod and younger dryas periods was found during the holocene no zonal differences in the inflows of nwac and ic were found a strong meridional gradient with warmer conditions at lower latitudes and relatively cold conditions at high northern latitudes existed

multiproxy approach for the reconstruction of the glacial ocean surface margo michal kucera antoni rosell mele ralph schneider claire waelbroeck mara weinelt department of geology royal holloway university of london egham tw20 0ex uk icrea and institute of environmental science and technology universitat autonoma de barcelona 08193 bellaterra catalonia spain departement de geologie et oceanographie umr5805 epoc cnrs universite de bordeaux1 33405 talence cedex france laboratoire des sciences du climat et de l environnement laboratoire mixte cnrs cea f 91198 gif sur yvette france institute for geosciences university of kiel olshausen strasse 40 d 24098 kiel germany

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

the younger dryas cold interval as viewed from central greenland abstract greenland ice core records provide an exceptionally clear picture of many aspects of abrupt climate changes and particularly of those associated with the younger dryas event as reviewed here well preserved annual layers can be counted confidently with only 1 errors for the age of the end of the younger dryas 11 500 years before present ice flow corrections allow reconstruction of snow accumulation rates over tens of thousands of years with little additional uncertainty glaciochemical and particulate data record atmospheric loading changes with little uncertainty introduced by changes in snow accumulation confident paleothermometry is provided by site specific calibrations using ice isotopic ratios borehole temperatures and gas isotopic ratios near simultaneous changes in ice core paleoclimatic indicators of local regional and more widespread climate conditions demonstrate that much of the earth experienced abrupt climate changes synchronous with greenland within thirty years or less post younger dryas changes have not duplicated the size extent and rapidity of these paleoclimatic changes

the arctic circumpolar boundary current abstract the main water transformations in the arctic mediterranean take place in the boundary current of atlantic water which crosses the greenland scotland ridge from the north atlantic into the eastern norwegian sea it enters and flows around the arctic ocean before it exits the arctic mediterranean as the east greenland current primarily through denmark strait on route it experiences numerous branchings and mergings by examining how the properties of this circumpolar boundary current evolve it is possible to identify and describe the processes causing the water mass transformations in the arctic mediterranean it is also possible to follow the arctic ocean deep waters as they spread into the nordic seas and eventually provide 40 of the overflow water supplying the north atlantic deep water

oceanographic regimes in the northwest labrador sea since marine isotope stage 3 based on dinocyst and stable isotope proxy records abstract sea surface temperature sst salinity and density gradients in the upper water column of the northwest labrador sea have been reconstructed based on high resolution analysis of a core hu2008 029 004pc spanning the last 36 ka raised off hudson strait the modern analogue technique was applied to dinocyst assemblages and combined with stable isotope data from neogloboquadrina pachyderma left coiled npl for this purpose three oceanographic regimes were identified broadly corresponding to the glacial deglacial and postglacial intervals the site remained under the direct influence of the laurentide ice sheet lis margin until the postglacial and did not record the bolling allerod warming and weakly recorded the younger dryas event the glacial regime lasted until 12 2 cal ka bp it was characterized by generally low concentrations of dinocysts within an assemblage indicative of quasi perennial sea ice the deglacial regime ca 12 2 8 3 cal ka bp was marked by increased biogenic fluxes and more diversified dinocyst assemblages and possibly an enhanced subsurface inflow of north east atlantic deep water warm summer 11 c but low winter 0 c sea surface temperatures sea ice cover during about 3 months per year and low summer salinity 28 suggest strong stratification in the upper water layer in relation to meltwater supply from the lis following the final drainage of glacial lake agassiz through hudson strait which is dated here at 8 3 cal ka bp and the subsequent lis collapse increased summer salinity up to 35 was accompanied by a reduced seasonal gradient of sea surface temperature from winter 3 8 c to summer 8 6 c suggesting enhanced penetration of north atlantic water weakened stratification of the surface water layer then allowed for winter convection and labrador sea water formation which is consistent with increased npl 13c values in response to higher ventilation of the subsurface water layer

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

meltwater routing and the younger dryas the younger dryas the last major cold episode on earth is generally considered to have been triggered by a meltwater flood into the north atlantic the prevailing hypothesis proposed by broecker et al 1989 nature 341 318 321 more than two decades ago suggests that an abrupt rerouting of lake agassiz overflow through the great lakes and st lawrence valley inhibited deep water formation in the subpolar north atlantic and weakened the strength of the atlantic meridional overturning circulation amoc more recently tarasov and peltier 2005 nature 435 662 665 showed that meltwater could have discharged into the arctic ocean via the mackenzie valley 4 000 km northwest of the st lawrence outlet here we use a sophisticated high resolution ocean sea ice model to study the delivery of meltwater from the two drainage outlets to the deep water formation regions in the north atlantic unlike the hypothesis of broecker et al freshwater from the st lawrence valley advects into the subtropical gyre 3 000 km south of the north atlantic deep water formation regions and weakens the amoc by 30 we conclude that meltwater discharge from the arctic rather than the st lawrence valley was more likely to have triggered the younger dryas cooling

a highly unstable holocene climate in the subpolar north atlantic evidence from diatoms a composite record lo09 14 of three sediment cores from the subpolar north atlantic reykjanes ridge was investigated in order to assess surface ocean variability during the last 11 kyr the core site is today partly under the influence of the irminger current ic a branch of the north atlantic drift continuing northwestward around iceland however it is also proximal to the sub arctic front saf that may cause extra dynamic hydrographic conditions we used statistical methods applied to the fossil assemblages of diatoms to reconstruct quantitative sea surface temperatures ssts our investigations give evidence for different regional signatures of holocene surface oceanographic changes in the north atlantic core lo09 14 reveal relatively low and highly variable ssts during the early holocene indicating a weak ic and increased advection of subpolar water over the site a mid holocene thermal optimum with a strong ic occurs from 7 5 to 5 kyr and is followed by cooler and more stable late holocene surface conditions several intervals throughout the holocene are dominated by the diatom species rhizosolenia borealis which we suggest indicates proximity to a strongly defined convergence front most likely the saf several coolings reflecting southeastward advection of cold and ice bearing waters occur at 10 4 9 8 8 3 7 9 6 4 4 7 4 3 and 2 8 kyr the cooling events recorded in the lo09 14 ssts correlate well with both other surface records from the area and the nadw reductions observed at odp site 980 indicating a surface deepwater linkage through the holocene

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

branching of atlantic water within the greenland spitsbergen passage an estimate of recirculation atlantic water aw supplies the largest source of heat mass and salt to the arctic ocean via fram strait greenland spitsbergen passage yet it represents only a fraction of the atlantic water that resides in the greenland iceland norwegian and barents seas this is a result of both the branching of the central core of aw along its northward flow and the modification of its t s signature through air sea ice interactions and internal mixing this paper addresses the quantitative analysis of the three dominant atlantic water cores within fram strait and north of 76 n using an 11 year 1977 to 1987 hydrographic database spatial variations of heat volume and salt along its flow path of some 600 km showed that the major core of atlantic water that directly enters the arctic ocean svalbard branch did not extend past 20 e of the 9719 km3 of atlantic water existing within the region one third resided within the svalbard branch the remainder 22 and 45 were held within the return atlantic current and the yermak branches respectively restricting the analysis to a southern limit of 79 n effectively removed the return atlantic current and showed a nearly equal split between the two remaining branches work completed by bourke et al 1988 indicated that the yermak branch is largely recirculated to the south if true this analysis supports rudels 1987 model estimate of a 50 recirculation of aw within this region

late quaternary sedimentation and glacial history of the western svalbard continental margin abstract glacigenic sediments recovered in shallow cores from the western svalbard continental slope are subdivided into five facies associations based on grain size sedimentary structure mineralogy petrography and geochemistry two diamicton facies are recognised one of which is interpreted as hemipelagic mud with variable amounts of ice rafted debris ird and the other as a product of mass movement the diamictons are associated with melting of icebergs during glacial melt events and debris flow deposition on the submarine fans during peak glaciation respectively laminated to layered mud and turbidites seem to be closely related to eustatic fall in sea level and erosion of banks located on the continental shelf resulting in accumulation of fine grained organic rich deposits and thin silt and sand layers on the continental slope middle weichselian was characterised by several phases of extensive iceberg production and input of ird the first phase 60 55 ka is correlated with a glacier advance on svalbard but the following phases 54 44 ka can not be correlated with glacier advances on land this demonstrates that there may have been more glaciations than recorded on svalbard and that ice sheets at high northern latitudes fluctuated more frequently than previously assumed the composition of the ird deposited after 54 ka suggests that the ice sheets during these advances were located in the eastern svalbard barents sea area the late weichselian growth of the svalbard barents sea ice sheet occurred probably in two steps nucleation of a continental based ice sheet between 27 and 22 5 ka followed by a rapid advance to the shelf edge when the ice margin reached the soft clay rich sediments on the continental shelf eustatic lowering of the sea level during the initial phase led to bank exposure and erosion bringing large quantities of fine grained organic rich sediments to the deep sea during peak glaciation glaciers provided a localised supply of sediments to the shelf troughs and the upper slope which were redistributed by debris flows the marine based svalbard barents sea ice sheet started to retreat around 14 5 ka through massive iceberg discharge the retreat was interrupted by a short lived advance accompanied by erosion of the shelf banks and redistribution of organic rich sediments to the continental slope the final ice recession started around 12 ka and ended close to 9 ka when the fjords of svalbard were essentially ice free large amounts of meltwater released during the removal of the svalbard barents sea ice sheet cooled down the surface waters of the norwegian greenland sea and formed a widespread sea ice cover between 12 and 8 ka input of terrigenous material was greatly reduced during the early part of holocene the present interglacial is characterised by erosion of the shelf and upper slope by bottom currents leaving a prominent lag deposit

past extent of sea ice in the northern north atlantic inferred from foraminiferal paleotemperature estimates 1 using 150 core top samples we developed a conservative but fairly robust new measure to reconstruct past changes in maximum seasonal sea ice distribution in the northern north atlantic hitherto a major unknown the proxy is based on similarity maximum modern analog technique simmax estimates of threshold temperatures near the sea surface sst today almost 100 of all sites with sst 2 5 c during summer 0 4 for winters 1978 1987 and 0 75 c for little ice age winters lie seaward of the sea ice margin when applied to 60 sediment records of the last glacial maximum this proxy shows that peak glacial sea ice was far more restricted than in the classic climap project members 1981 reconstruction during glacial summer sea ice only covered the arctic ocean and western fram strait the northern north atlantic and nordic seas were largely ice free and thus formed a high latitude moisture source for the continued buildup of continental ice sheets in contrast sea ice spread far south across the iceland faeroe ridge during glacial winter with an inferred patch of sea ice also in the central east atlantic near the center of the azores high a broad ice free channel extended from 50 to 60 n forming an ideal site for large scale convection of glacial upper north atlantic deep water the extreme seasonality in glacial sea ice formation and melt in the nordic seas implies a major consumption of the regional energy income

accelerated drawdown of meridional overturning in the late glacial atlantic triggered by transient pre h event freshwater perturbation 1 abrupt decreases of the atlantic meridional overturning circulation moc during the late pleistocene have been directly linked to catastrophic discharges of glacimarine freshwater triggering disruption of northward marine heat transport and causing global climate changes here we provide measurements of excess sedimentary 231 pa 230 th from a high accumulation sediment drift deposit in the ne atlantic that record a sequence of sudden variations in the rate of moc associated deep ocean ventilation and surface ocean climatology the data series reveal a sequential decrease in the moc rate at 18 0 ka bp ago that coincides with only transient and localized freshwater inputs this change represents a substantial though not total cessation in moc that predates the major heinrich h1 meltwater event by at least 1 200 years these results highlight the potential of targeted freshwater perturbations in promoting substantial moc changes without a direct linking with catastrophic freshwater surges citation hall i r s b moran r zahn p c knutz c c shen and r l edwards 2006 accelerated drawdown of meridional overturning in the late glacial atlantic triggered by transient pre h event freshwater perturbation geophys res lett 33 l16616 doi 10 1029 2006gl026239

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

apparent long term cooling of the sea surface in the northeast atlantic and mediterranean during the holocene reconstructions of upper ocean temperature t during the holocene 10 0 ka b p were established using the alkenone method from seven high accumulation sediment cores raised from the northeast atlantic and the mediterranean sea 361n 751n all these paleo t records document an apparent long term cooling during the last 10 kyr in records with indication of a constant trend the apparent cooling ranges from 0 27 to 0 151c kyr 1 records with indication of time variable trend show peak to peak amplitudes in apparent temperatures of 1 2 2 91c a principal component analysis shows that there is one factor which accounts for a very large fraction 67 of the total variance in the biomarker paleo t records and which dominates these records over other potential secondary influences two possible contributions are 1 a widespread surface cooling which may be associated with the transition fromthe hypsithermal interval b9 5 7 ka b p to the neoglaciation b5 7 0 ka b p and 2 a change in the seasonal timing and or duration of the growth period of alkenone producers prymnesiophyte algae the first contribution is consistent with many climate proxy records from the northeast atlantic area and with climate model simulations including milankovitch forcing the second contribution is consistent with the divergence between biomarker and summer faunal paleo t fromearly to late holocene observed in two cores further work is necessary and in particular the apparent discordance between biomarker and faunal t records for the relative stable holocene period must be understood to better constrain the climatic and ecological contributions to the apparent cooling observed in the former records r 2002 elsevier science ltd all rights reserved

glacial history and paleoceanography of the southern yermak plateau since 132 ka bp abstract the southern yermak plateau yp is situated at the entrance to the arctic ocean in the narrow marginal ice zone miz between the polar and arctic fronts north west of svalbard a gravity core jm10 02gc has been analysed in order to reconstruct paleoceanographic conditions and the movement of the sea ice margin as well as the glacier ice conditions of the svalbard barents sea ice sheet sbis during the last interglacial glacial cycle the distribution of planktic and benthic foraminifera planktic and benthic oxygen and carbon isotopes and variations in ice rafted debris ird has been investigated the sediment core covers the time interval from the marine isotope stage mis 6 5e transition termination ii c 132 ka bp to the early holocene during termination ii tii the sbis retreated and the sea ice margin was in distal position whereas during mis 5 to mis 4 the sea ice margin was close to the core site several core intervals interpreted as representing mis 5e mis 5c mis 5a mis 3 and mis 1 were barren of calcareous microfossils whereas the intervals representing mis 4 and mis 2 were characterised by high productivity hp of planktic and benthic foraminifera these glacial hp zones were associated with the open water conditions resulting from the advection of atlantic water aw and retreat of the sea ice margin the barren zones during mis 5 mis 3 and mis 1 resulted from the proximity of the sea ice margin whereas during mis 2 the likely cause was an advance of the sbis

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

holocene sea subsurface and surface water masses in the fram strait comparisons of temperature and sea ice reconstructions highlights holocene sea subsurface temperatures after husum hald 2012 estimated from planktic foraminifer fauna in e fram strait biomarkers and ip25 derived indices including dip25 indicate surface water variability delayed onset of early holocene conditions in subsurface 10 6 ka compared to surface 11 7 ka water conditions warm atlantic layer likely occupied uppermost 200 m in eastern fram strait between 10 and 9 ka diverging late holocene trends in surface and subsurface conditions linked to presence of strong pycnocline stratification abstract two high resolution sediment cores from eastern fram strait have been investigated for sea subsurface and surface temperature variability during the holocene the past ca 12 000 years the transfer function developed by husum and hald 2012 has been applied to sediment cores in order to reconstruct fluctuations of sea subsurface temperatures throughout the period additional biomarker and foraminiferal proxy data are used to elucidate variability between surface and subsurface water mass conditions and to conclude on the holocene climate and oceanographic variability on the west spitsbergen continental margin results consistently reveal warm sea surface to subsurface temperatures of up to 6 c until ca 5 cal ka bp with maximum seawater temperatures around 10 cal ka bp likely related to maximum july insolation occurring at that time maximum atlantic water aw advection occurred at surface and subsurface between 10 6 and 8 5 cal ka bp based on both foraminiferal and dinocyst temperature reconstructions probably a less stratified ice free nutrient rich surface ocean with strong aw advection prevailed in the eastern fram strait between 10 and 9 cal ka bp weakened aw contribution is found after ca 5 cal ka bp when subsurface temperatures strongly decrease with minimum values between ca 4 and 3 cal ka bp cold late holocene conditions are furthermore supported by high planktic foraminifer shell fragmentation and high 18o values of the subpolar planktic foraminifer species turborotalita quinqueloba while ip25 associated indices as well as dinocyst data suggest a sustained cooling due to a decrease in early summer insolation and consequently sea ice increase since about 7 cal ka bp in surface waters planktic foraminiferal data including stable isotopes indicate a slight return of stronger subsurface aw influx since ca 3 cal ka bp the observed decoupling of surface and subsurface waters during the later holocene is most likely attributed to a strong pycnocline layer separating cold sea ice fed surface waters from enhanced subsurface aw advection this may be related to changes in north atlantic subpolar versus subtropical gyre activity

brine formation in relation to climate changes and ice retreat during the last 15 000 years in storfjorden svalbard 76 78 n storfjorden svalbard is an area of intense brine formation the brine is cold dense rich in oxygen and co2 and has reduced ph storfjorden is unique because it contains well preserved agglutinated foraminifera dating back to the beginning of the last deglaciation we have investigated the distribution of calcareous and agglutinated benthic foraminifera benthic oxygen and carbon isotopes calcium carbonate total organic carbon and ice rafted debris in five cores from storfjorden comprising the holocene and the deglaciation the purpose of the study is to reconstruct brine formation in the past under different climate scenarios the data indicate that in storfjorden the ratio of agglutinated to calcareous benthic foraminifera can be taken as a measure of the strength of brine formation the foraminiferal data which are supported by stable isotopes degree of fragmentation and geochemical parameters signify that brine formation intensified during cold periods and weakened during warm periods during the deglaciation increased brine flow coincides with the older dryas the intra allerod cold period and the younger dryas brine formation increased from circa 8200 years b p reaching periodic maxima during the last 4000 years b p in response to the unstable climate maximum brine production correlates with the dark ages cold period circa 1500 1100 years b p and the little ice age circa 600 100 years b p lower production correlates with the roman warm period circa 2500 2000 years b p and the medieval warm period circa 1000 700 years b p

atlantic water advection to the eastern fram strait multiproxy evidence for late holocene variability a multiproxy data set of an ams radiocarbon dated 46 cm long sediment core from the continental margin off western svalbard reveals multidecadal climatic variability during the past two millennia investigation of planktic and benthic stable isotopes planktic foraminiferal fauna and lithogenic parameters aims to unveil the atlantic water advection to the eastern fram strait by intensity temperatures and salinities atlantic water has been continuously present at the site over the last 2 000 years superimposed on the increase in sea ice icebergs a strengthened intensity of atlantic water inflow and seasonal ice free conditions were detected at 1000 to 1200 ad during the well known medieval climate anomaly mca however temperatures of the mca never exceeded those of the 20th century since 1400 ad significantly higher portions of ice rafted debris and high planktic foraminifer fluxes suggest that the site was located in the region of a seasonal highly fluctuating sea ice margin a sharp reduction in planktic foraminifer fluxes around 800 ad and after 1730 ad indicates cool summer conditions with major influence of sea ice icebergs high amounts of the subpolar planktic foraminifer species turborotalia quinqueloba in size fraction 150 250 m indicate strengthened atlantic water inflow to the eastern fram strait already after 1860 ad nevertheless surface conditions stayed cold well into the 20th century indicated by low planktic foraminiferal fluxes most likely at the beginning of the 20th century cold conditions of the terminating little ice age period persisted at the surface whereas warm and saline atlantic water already strengthened hereby subsiding below the cold upper mixed layer surface sediments with high abundances of subpolar planktic foraminifers indicate a strong inflow of atlantic water providing seasonal ice free conditions in the eastern fram strait during the last few decades

a new concept for the paleoceanographic evolution of heinrich event 1 in the north atlantic new records of planktonic foraminiferal 18o and lithic and foraminiferal counts from eirik drift are combined with published data from the nordic seas and the ice rafted debris ird belt to portray a sequence of events through heinrich event 1 h1 these events progressed from an onset of meltwater release at not vert similar19 ka bp through the conventional h1 ird deposition phase in the ird belt starting from not vert similar17 5 ka bp to a final phase between 16 5 and not vert similar15 ka bp that was characterised by a pooling of freshwater in the nordic seas which we suggest was hyperpycnally injected into that basin after not vert similar15 ka bp this freshwater was purged from the nordic seas into the north atlantic which preconditioned the nordic seas for convective deep water formation this allowed an abrupt re start of north atlantic deep water nadw formation in the nordic seas at the bolling warming 14 6 ka bp in contrast to previous estimates for the duration of h1 i e 1000 years to only a century or two the total combined composite h1 signal presented here had a duration of over 4000 yrs not vert similar19 14 6 ka bp which spanned the entire period of nadw collapse it appears that deep water formation and climate are not simply controlled by the magnitude or rate of meltwater addition instead the location of meltwater injections may be more important with nadw formation being particularly sensitive to surface freshening in the arctic nordic seas

holocene sea surface conditions in the north atlantic contrasted trends and regimes in the western and eastern sectors labrador sea vs iceland basin abstract two sediment cores from the labrador sea and one from the iceland basin were analysed in order to compare holocene sea surface conditions across the northern north atlantic 18o measurements on meso and epi planktonic foraminifera neogloboquadrina pachyderma left coiling and globigerina bulloides along with sea surface condition reconstructions using transfer functions based on dinoflagellate cyst assemblages were used to document thermohaline properties of the upper water column at the labrador sea sites a decreasing trend in sea surface temperature following an early holocene maximum is observed at the iceland basin site a hiatus between 13 and 8 ka bp prevents us from documenting the entire holocene but a stable to slightly decreasing trend is observed from 8 ka bp onwards sea surface salinity and potential density show little variation at the orphan knoll site in the labrador sea since 7 ka bp whereas they depict a decreasing trend at the two other sites since ca 8 ka bp this shift in values suggests a progressive enhancement of labrador sea water formation and a relative decrease in the nordic seas components of the north atlantic deep water i e denmark strait overflow water and norwegian sea overflow water discrepancies are also observed with regard to millennial frequency oscillations in sea surface conditions at the easternmost site they likely match previously documented cold water pulses in the north eastern atlantic whereas they do not show any clear pattern at the westernmost sites hence the western and eastern areas show different behaviours with respect to both long term and high frequency fluctuations

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

variability of north atlantic heat transfer during mis 2 1 short term changes in sea surface conditions controlling the thermohaline circulation in the northern north atlantic are expected to be especially efficient in perturbing global climate stability here we assess past variability of sea surface temperature sst in the northeast atlantic and norwegian sea during marine isotope stage mis 2 and in particular during the last glacial maximum lgm five high resolution sst records were established on a meridional transect 53 n 72 n to trace centennial scale oscillations in sst and sea ice cover we used three independent computational techniques simmax modern analogue technique artificial neural networks ann and revised analog method ram to reconstruct sst from planktonic foraminifer census counts simmax and ann reproduced short term sst oscillations of similar magnitude and absolute levels while ram owing to a restrictive analog selection appears less suitable for reconstructing cold end sst the simmax and ann sst reconstructions support the existence of a weak paleo norwegian current during dansgaard oeschger do interstadials number 4 3 2 and 1 during the lgm two warm incursions of 7 c water to occurred in the northern north atlantic but ended north of the iceland faroe ridge a rough numerical estimate shows that the near surface poleward heat transfer from 53 across the iceland faroe ridge up to to 72 n dropped to less than 60 of the modern value during do interstadials and to almost zero during do stadials summer sea ice was generally confined to the area north of 70 n and only rarely expanded southward along the margins of continental ice sheets internal lgm variability of north atlantic 40 n sst in the glamap 2000 compilation sarnthein et al 2003b pflaumann et al 2003 indicates maximum instability in the glacial subpolar gyre and at the iberian margin while in the nordic seas sst was continuously low

the last glacial maximum of svalbard and the barents sea area ice sheet extent and configuration abstract the timing extent and configuration of the late weichselian barents ice sheet has been debated for several decades this debate has arisen largely because of the limited or conflicting field evidence on which most models have been based in particular reconstruction of the marine parts of the former barents ice sheet has been controversial this paper aims to review the geological observations and interpretations regarding the size and timing of the late weichselian ice sheet combined with numerical modelling of its formation in order to produce a reconstruction of ice sheet extent and behaviour sub glacial till with overlying glacimarine deposits dated to the late weichselian is found over most of the barents sea floor and the continental shelf west of svalbard glacially induced debris flow deposits on the large bjonoya and isfjorden trough mouth fans strongly support the idea of ice sheet extension to the shelf edge during maximum glaciation isobase maps show a centre of post glacial uplift in the north central barents sea and glaciological and isostatic modelling suggest that the ice sheet was 2000 3000 m thick in this area the ice sheet was confluent with ice over the kara sea but the interaction between the barents and kara ice sheets is not yet fully understood the deglaciation of the barents ice sheet started ca 15 ka probably by calving within the deeper troughs by 12 ka most of the central barents sea was ice free and ice remained over the svalbard franz josef land and novaja zemlya archipelagos and adjacent shallow shelf areas the coasts and fjords of these islands were ice free by 10 ka

quantitative assessment of carbonate dissolution in marine sediments from foraminifer linings vs shell ratios davis strait northwest north atlantic a new method to evaluate quantitatively the degree of calcium carbonate preservation and dissolution in high latitude marine sediments is proposed on the basis of relative abundance of caco 3 shells and organic linings of benthic foraminifers this method was applied to a late quaternary sequence from davis strait in the northwest north atlantic and shows that caco 3 dissolution in sediments has increased since the last glacial maximum ca 18 000 b p and peaked when subpolar interglacial conditions were established in surface waters the dissolution in davis strait sediments appears to be closely related to organic biogenic production in surface waters with a regional pattern of bottom water formation and circulation

formal subdivision of the holocene series epoch a discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommission on quaternary stratigraphy international commission on stratigraphy this discussion paper by a working group of intimate integration of ice core marine and terrestrial records and the subcommision on quaternary stratigraphy sqs of the international commission on stratigraphy ics considers the prospects for a formal subdivision of the holocene series epoch although previous attempts to subdivide the holocene have proved inconclusive recent developments in quaternary stratigraphy notably the definition of the pleistocene holocene boundary and the emergence of formal subdivisions of the pleistocene series epoch mean that it may be timely to revisit this matter the quaternary literature reveals a widespread but variable informal usage of a tripartite division of the holocene early middle or mid and late and we argue that this de facto subdivision should now be formalized to ensure consistency in stratigraphic terminology we propose an early middle holocene boundary at 8200 a bp and a middle late holocene boundary at 4200 a bp each of which is linked to a global stratotype section and point gssp should the proposal find a broad measure of support from the quaternary community a submission will be made to the international union of geological sciences iugs via the sqs and the ics for formal ratification of this subdivision of the holocene series epoch copyright 2012 john wiley sons ltd

early holocene temperature variability in the nordic seas the role of oceanic heat advection versus changes in orbital forcing received 7 january 2011 revised 15 july 2011 accepted 21 july 2011 published 22 october 2011 1 the separate roles of oceanic heat advection and orbital forcing on influencing early holocene temperature variability in the eastern nordic seas is investigated the effect of changing orbital forcing on the ocean temperatures is tested using the 1dice model and the 1dice results are compared with new and previously published temperature reconstructions from a transect of five cores located underneath the pathway of atlantic water from the faroe shetland channel in the south to the barents sea in the north the stronger early holocene summer insolation at high northern latitudes increased the summer mixed layer temperatures however ocean temperatures underneath the summer mixed layer did not increase significantly the absolute maximum in summer mixed layer temperatures occurred between 9 and 6 ka bp representing the holocene thermal maximum in the eastern nordic seas in contrast maximum in northward oceanic heat transport through the norwegian atlantic current occurred approximately 10 ka bp the maximum in oceanic heat transport at 10 ka bp occurred due to a major reorganization of the atlantic ocean circulation entailing strong and deep rejuvenation of the atlantic meridional overturning circulation combined with changes in the north atlantic gyre dynamic causing enhanced transport of heat and salt into the nordic seas

atlantic water advection versus sea ice advances in the eastern fram strait during the last 9 ka multiproxy evidence for a two phase holocene a sediment core from the west spitsbergen continental margin was studied to reconstruct climate and paleoceanographic variability during the last 9 ka in the eastern fram strait our multiproxy evidence suggests that the establishment of the modern oceanographic configuration in the eastern fram strait occurred stepwise in response to the postglacial sea level rise and the related onset of modern sea ice production on the shallow siberian shelves the late early and mid holocene interval 9 to 5 ka was generally characterized by relatively unstable conditions high abundance of the subpolar planktic foraminifer species turborotalita quinqueloba implies strong intensity of atlantic water aw inflow with high productivity and or high aw temperatures resulting in a strong heat flux to the arctic a series of short lived cooling events 8 2 6 9 and 6 1 ka occurred superimposed on the warm late early and mid holocene conditions our proxy data imply that simultaneous to the complete postglacial flooding of arctic shallow shelves and the initiation of modern sea ice production strong advance of polar waters initiated modern oceanographic conditions in the eastern fram strait at 5 2 ka the late holocene was marked by the dominance of the polar planktic foraminifer species neogloboquadrina pachyderma a significant expansion of sea ice icebergs and strong stratification of the water column although planktic foraminiferal assemblages as well as sea surface and subsurface temperatures suggest a return of slightly strengthened advection of subsurface atlantic water after 3 ka a relatively stable cold water layer prevailed at the sea surface and the study site was probably located within the seasonally fluctuating marginal ice zone during the neoglacial period

holocene variations of sea surface conditions in the southeastern barents sea reconstructed from dinoflagellate cyst assemblages palynomorphs were analysed in two sediment cores from the southeastern barents sea representing the past 8 3 and 4 4 kyr high dinocyst contents and species diversity enabled the application of the best analogue method to quantitatively reconstruct sea surface salinities temperatures and ice cover using 677 modern reference sites from the north atlantic and arctic seas including new data from the barents sea reported here at the southern core site where waters are affected by the atlantic inflow sea surface conditions were relatively warm and stable between ca 8000 and 5000 calendar yr bp in contrast the past 5 kyr had periods with cooler temperatures and extended ice cover fluctuating mostly at 1 1 5 kyr frequencies at both sites most pronounced coolings occurred around 8 1 5 3 5 3 2 and 2 5 ka the northern site additionally shows younger cooling events tentatively dated to 1 4 0 3 and 0 1 ka identified variations in sea surface conditions indicate changes in atlantic water inputs to the barents sea our results generally correlate to palaeoclimatic reconstructions from northwestern eurasia exemplified by palynological records from karelia this correlation suggests that sea surface variations in the barents sea reflect large scale changes in atmospheric and oceanic interactions between the north atlantic and the arctic copyright 2001 john wiley sons ltd

changes in the flow of atlantic water into the arctic ocean since the last deglaciation evidence from the northern svalbard continental margin 80 n 1 the svalbard archipelago is located in the high arctic 76 80 n within the northernmost reach of the west spitsbergen current which is the continuation of the north atlantic current in this specific setting close to the polar front even small variations in the current system are expected to give large and distinct signals in paleoceanographic parameters thus the svalbard area is ideal for monitoring the past history of the inflow of atlantic water to the arctic ocean we have studied sediment core np94 51 taken outside the mouth of the hinlopen strait on the northern svalbard shelf the paleoceanographic development of the last deglaciation and the holocene has been reconstructed using benthic and planktonic foraminifera oxygen isotopes and ice rafted detritus the results show that the first strong subsurface inflow of atlantic water to the arctic ocean after the last glacial maximum commenced at 12 6 14c kyr b p circa 15 000 calendar cal years b p during the bolling allerod interstadial during the younger dryas polar conditions prevailed at the surface with extensive sea ice cover and the inflow of atlantic derived water was generally diminished the inflow of more saline but still cold atlantic water was relatively strong during the early holocene and caused intensified seasonal biological productivity the atlantic water inflow declined gradually during the mid holocene between 4500 and 1100 cal years b p the inflow was very weak and the bottom waters over the northern svalbard margin were cold and of lower salinity during the last 1000 years climatic conditions improved such that the subsurface inflow of atlantic derived water increased however the surface waters were still cold

arctic warming through the fram strait oceanic heat transport from 3 years of measurements we present estimates of volume and heat transport through fram strait for the period 1997 to 2000 from data of moored instruments full depth volume transports at 78 55 n were in the order of 10 sv both northwards and southwards with an annual mean net transport between 2 and 4 sv to the south the temperature of the northward flow of atlantic water had a strong seasonality with a minimum in winter nevertheless the northward heat transport was highest in winter caused by the winter maximum of northward volume transport during the three years of observation the heat transport in the west spitsbergen current increased from 28 to 46 tw as a result of both increased speed and temperature in contrast to the west spitsbergen current the volume and heat transport of east greenland current remained fairly constant an integration over a subsection of the east greenland current showed similar values of volume transport to that obtained by measurements in the 1980s foldvik et al 1988 the southward heat transport through modified atlantic water weakened slightly between 1997 and 1999 despite increased temperatures

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

intermediate water ventilation in the nordic seas during mis 2 1 a high resolution marine record from the northern norwegian continental margin off lofoten is used to reconstruct changes in the oceanography of the nordic seas during marine isotope stage mis 2 including the last glacial maximum and early deglaciation circa 25 to 16 ka the period was characterized by generally warm subsurface water temperatures 2 c and inflow of atlantic surface water several events were characterized by decrease in ventilation of the intermediate water and low subsurface temperature and salinity they correlate with colder atmospheric temperatures as seen in ice cores the events terminated with gradual strengthening of the intermediate water ventilation and increase in subsurface temperature the generation of intermediate water was unstable and experienced climate and ventilation changes on millennial and centennial timescales the changes appear consistent with modeling experiments that predict short lasting circulation stops during mis 2 due to release of meltwater in the nordic seas

variations in temperature and extent of atlantic water in the northern north atlantic during the holocene we compare six high resolution holocene sediment cores along a s n transect on the norwegian svalbard continental margin from ca 601n to 77 41n northern north atlantic planktonic foraminifera in the cores were investigated to show the changes in upper surface and subsurface water mass distribution and properties including summer sea surface temperatures sst the cores are located below the axis of the norwegian current and the west spitsbergen current which today transport warm atlantic water to the arctic sediment accumulation rates are generally high at all the core sites allowing for a temporal resolution of 10 10 2 years sst is reconstructed using different types of transfer functions resulting in very similar sst trends with deviations of no more than 71 0 1 51c a transfer function based on the maximum likelihood statistical approach is found to be most relevant the reconstruction documents an abrupt change in planktonic foraminiferal faunal composition and an associated warming at the younger dryas preboreal transition the earliest part of the holocene was characterized by large temperature variability including the preboreal oscillations and the 8 2 k event in general the early holocene was characterized by ssts similar to those of today in the south and warmer than today in the north and a smaller s n temperature gradient 0 231c 1n compared to the present temperature gradient 0 461c 1n the southern proxy records 60 691n were more strongly influenced by slightly cooler subsurface water probably due to the seasonality of the orbital forcing and increased stratification due to freshening the northern records 72 77 41n display a millennial scale change associated with reduced insolation and a gradual weakening of the north atlantic thermohaline circulation thc the observed northwards amplification of the early holocene warming is comparable to the pattern of recent global warming and future climate modelling which predicts greater warming at higher latitudes the overall trend during mid and late holocene was a cooling in the north stable or weak warming in the south and a maximum s n sst gradient of ca 0 71c 1n at 5000 cal years bp superimposed on this trend were several abrupt temperature shifts four of these shifts dated to 9000 8000 5500 3000 and 1000 and 400 cal years bp appear to be global as they correlate with periods of global climate change in general there is a good correlation between the northern north atlantic temperature records and climate records from norway and svalbard r 2007 elsevier ltd all rights reserved

sub sea surface temperatures in the polar north atlantic during the holocene planktic foraminiferal mg ca temperature reconstructions holocene sea surface temperatures in the eastern fram strait are reconstructed based on mg ca ratios measured on the planktic foraminifer neogloboquadrina pachyderma sin the reconstructed sub sea surface temperatures ssstmg ca fluctuate markedly during the earliest holocene at 11 7 and 10 5 kyr bp this is probably in response to the varying presence of sea ice and deglacial meltwater between 10 5 7 9 kyr bp the ssstmg ca values are relatively high 4 c and more stable reflecting high insolation and intensified poleward advection of atlantic water after 7 9 kyr bp the ssstmg ca values decline to an average of 3 c throughout the mid holocene these changes can be attributed to a combined effect of reduced poleward oceanic heat advection and a decline in insolation as well as a gradually increased influence of eastward migrating arctic water the ssstmg ca values increase and vary between 2 1 c and 5 8 c from 2 7 kyr bp to the present this warming is in contrast to declining late holocene in

surface water conditions and calcium carbonate preservation in the fram strait during marine isotope stage 2 28 8 15 4 kyr 1 we present a high resolution record of calcium carbonate preservation alongside the distribution pattern of planktic foraminifera from the fram strait the record covers the marine isotope stage mis 2 28 8 to 15 4 kyr including the last glacial maximum lgm and the early deglaciation in multidecadal temporal resolution the investigation is based on the distribution patterns of planktic foraminifera stable isotopes mean shell weight of neogloboquadrina pachyderma the degree of fragmentation of planktic shells caco3 content and geochemical and sedimentological data the dissolution proxies indicate long lasting periods of markedly reduced preservation of calcium carbonate at 28 8 27 2 24 1 23 2 and 16 6 15 4 kyr in addition to a number of short lasting periods 300 year during the lgm these periods are accompanied by a simultaneous and significant reduction in specimens of subpolar planktic foraminifera indicating a southward expansion of arctic surface water masses prolonged periods with high abundances of subpolar foraminiferal species and good preservation of calcium carbonate are attributed to increased influence of atlantic water masses which appears to persist throughout most of the mis 2 comparison to holocene mis 1 shell weight records shows that the preservation during mis 2 was overall better even during the events of dissolution this was probably a reflection of the low concentration of atmospheric co2 at the time

some remarks on the stability of sphene in diagenetic environments abstract equilibrium diagrams showing the chemical stability of sphene and the assemblage rutile quartz calcite in the range 25 300 c and 1 2000 bar were constructed from mineral reactions that likely occur in diagenetic environments the results reveal that stability of sphene depends on activities of hco 3 ca 2 sio 2 aq and h given appropriate conditions sphene is predicted to be stable even in surficial environments

a multiproxy reconstruction of the evolution of deep and surface waters in the subarctic nordic seas over the last 30 000yr on the basis of various lithological mircopaleontological and isotopic proxy records covering the last 30 000 calendar years cal kyr the paleoenvironmental evolution of the deep and surface water circulation in the subarctic nordic seas was reconstructed for a climate interval characterized by intensive ice sheet growth and subsequent decay on the surrounding land masses the data reveal considerable temporal changes in the type of thermohaline circulation open water convection prevailed in the early record providing moisture for the fennoscandian barents ice sheets to grow until they reached the shelf break at 26 cal kyr and started to deliver high amounts of ice rafted debris ird into the ocean via melting icebergs low epibenthic 18o values and small sized subpolar foraminifera observed after 26 cal kyr may implicate that advection of atlantic water into the nordic seas occurred at the subsurface until 15 cal kyr although modern like surface and deep water conditions first developed at 13 5 cal kyr thermohaline circulation remained unstable switching between a subsurface and surface advection of atlantic water until 10 cal kyr when ird deposition and major input of meltwater ceased during this time two depletions in epibenthic 13c are recognized just before and after the younger dryas indicating a notable reduction in convectional processes despite an intermittent cooling at 8 cal kyr warmest surface conditions existed in the central nordic seas between 10 and 6 cal kyr however already after 7 cal kyr the present day situation gradually evolved verified by a strong water mass exchange with the arctic ocean and an intensifying deep convection as well as surface temperature decrease in the central nordic seas this process led to the development of the modern distribution of water masses and associated oceanographic fronts after 5 cal kyr and eventually to today s steep east west surface temperature gradient the time discrepancy between intensive vertical convection after 5 cal kyr but warmest surface temperatures already between 10 and 6 cal kyr strongly implicates that widespread postglacial surface warming in the nordic seas was not directly linked to the rates in deep water formation

advection of atlantic water to the western and northern svalbard shelf since 17 500 cal yr bp abstract the changes in flow and character of the warm atlantic water through the last 17 500 cal yr are reconstructed from the distribution of benthic foraminifera species planktonic and benthic foraminifera abundances stable oxygen isotopes and lithology in two cores from the western and northern shelf of svalbard the results show almost continuous presence of atlantic water at the shelf areas since 14 500 cal yr bp the bolling and allerod intervals stand out as periods of highest bottom waters temperatures the strong inflow of saline but chilled atlantic water during the early holocene was followed by cooling and freshening of the bottom waters during the mid and late holocene the two records reveal synchronous oceanographic changes that are closely tied to changes in the flow of atlantic water recorded further south in the nordic seas the early holocene warming was not just an effect of higher solar insolation but was also due to increased heat flux from the stronger atlantic water inflow driven by wind force and or thermohaline circulation

10be surface exposure ages on the late pleistocene and holocene history of linnebreen on svalbard abstract arctic glaciers were sensitive to past changes in high latitude winter precipitation and summer temperature here we develop a late pleistocene to holocene history for linnebreen linne glacier in western svalbard using 10 be surface exposure ages on isolated erratic and moraine boulders we show that linnebreen had separated from the larger ice sheet over svalbard and was retreating up valley around the start of the younger dryas cold period we attribute this retreat during a cold period on svalbard to moisture starvation of linnebreen from advanced sea ice and or elevated shortwave boreal summer insolation that overwhelmed any reduction in sensible heat after an ice free period during the early to middle holocene linnebreen reformed sometime after 4 6 0 2 ka and was at a position roughly equivalent to its little ice age lia maximum extent before it began to retreat at 1 6 0 2 ka comparison with calibrated 14 c dates from three other glaciers could suggest that this period of ice retreat at 1 6 ka could be regional in extent linnebreen occupied the pre lia moraine when there was an increased ratio of cold arctic sourced relative to warm atlantic sourced waters around svalbard and advanced sea ice the retreat of linnebreen at 1 6 ka was concurrent with the increased presence of warm atlantic waters around svalbard and attendant sea ice retreat these coincident changes in ocean temperatures sea ice extent and linnebreen moraine age could imply a climatic forcing of the pre lia advance and retreat of linnebreen summer temperatures rather than changes in precipitation would then be dominant in driving ice retreat although the possibility of stochastic glacier margin variability cannot be excluded our data therefore suggest that linnebreen may have responded differently to past changes in sea ice extent that could depend on the background climate state deglacial climate vs late holocene climate which highlights the complexity in climatic controls on arctic glaciers

reconstruction of inflow of atlantic water to isfjorden svalbard during the holocene correlation to climate and seasonality abstract the distribution patterns of benthic foraminifera faunas stable isotopes and ice rafted debris ird have been studied in piston core jm98 845 pc from isfjorden western svalbard to reconstruct changes in the flow of atlantic water during the holocene interglacial the paleoenvironmental conditions in isfjorden and the inflow of the atlantic water followed closely the changes in insolation with strong seasonality in the early holocene and weaker seasonality in the middle to late holocene a summer temperature maximum of the bottom water occurred in the early holocene 10 500 c 8200 years bp cooling began at 9000 years bp with stepwise coolings at c 8200 7400 and 4000 years bp the cooling correlated with an increase in ice rafting and increased influence of polar water and seasonal sea ice cover between 4000 and 2000 years bp bottom water temperatures reached a minimum after 2000 years bp episodic inflow of warmer atlantic water at the bottom of the fjord occurred and conditions became more unstable the data indicate close interaction of the flow of atlantic water with the development of the terrestrial climate and the amount of polar meltwater and sea ice

foraminiferal biofacies across mangrove mudflat environments at cocoa creek north queensland australia contemporary and relict subsurface intertidal foraminiferal dead assemblages were collected from a site near to cocoa creek north queensland australia and analysed for the purpose of understanding fossil assemblage development and preservation a marked dichotomy was identified between dead foraminiferal assemblages within mangrove sediments and those within adjacent mudflat sediments mangrove assemblages were almost exclusively represented by agglutinated species mainly arenoparrella mexicana haplophragmoides wilberti milliammina fusca m obliqua trochammina inflata while calcareous species dominated the mudflat mainly ammonia aoteana pararotalia venusta parrellina hispidula surface and subsurface test abundances were also an order of magnitude greater within mudflat sediments 1000 3000 tests per cm3 than in the sediments beneath the mangroves 100 300 tests per cm3 statistically significant differences in the abundance of calcareous and agglutinated tests between wet and dry seasons within the mangrove suggest that tests are systematically lost from this part of the system on an annual basis a model of assemblage formation under shoreface progradation is presented which makes a direct link between surface assemblages post depositional processes and the composition and environmental resolution of the fossil assemblages entering the stratigraphic record assemblages within the mangrove undergo rapid taphonomic loss and are then overprinted during burial by the deep infaunal communities associated with the prograding higher elevation environments as such much of the eventual mangrove sequence is represented entirely by assemblages produced relatively recently within an upper mangrove environment and therefore cannot be differentiated according to elevation at the time of deposition in addition organic enrichment of upper mudflat deposits by mangrove roots which occurs during progradation results in the dissolution of calcareous tests from an 40 cm thick stratigraphic interval it is argued that in order to reliably recognise the changes to foraminiferal assemblages which occur during burial assemblages must be compared with respect to stratigraphy rather than reflexively downcore

paleoceanographic evolution of the sw svalbard margin 76 n since 20 000 14c yr bp abstract two cores from the southwestern shelf and slope of storfjorden svalbard taken at 389 m and 1485 m water depth have been analyzed for benthic and planktic foraminifera oxygen isotopes and ice rafted debris the results show that over the last 20 000 yr atlantic water has been continuously present on the southwestern svalbard shelf however from 15 000 to 10 000 14c yr bp comprising the heinrich event h1 interval the bolling allerod interstades and the younger dryas stade it flowed as a subsurface water mass below a layer of polar surface water in the benthic environment the shift to interglacial conditions occurred at 10 000 14c yr bp due to the presence of a thin upper layer of polar water surface conditions remained cold until ca 9000 14c yr bp when the warm atlantic water finally appeared at the surface neither extensive sea ice cover nor large inputs of meltwater stopped the inflow of atlantic water its warm core was merely submerged below the cold polar surface water

abrupt climatic change during the last interglacial glacial cycle in the polar north atlantic abstract we have investigated five sediment cores from the margin and abyssal plain off western svalbard barents sea in the polar north atlantic we discuss the palaeoceanography and its relationship to glacial history during the last interglacial glacial cycle based on detailed stratigraphic analyses of planktic and benthic foraminiferal fauna oxygen and carbon isotopes on foraminifera ice rafted debris grains 500 m and radiocarbon dates the sediment cores combined cover the last interglacial glacial cycle including marine isotope stage mis 5 1 sedimentation rates are generally high ranging from 3 to 100 cm 1000 years atlantic water repeatedly reached the polar north atlantic during the last interglacial glacial cycle and was present for at least 50 of the total time interval periods having atlantic water advection termed hp zones hp high productivity are characterised by high planktic foraminiferal production a small increase of benthic and subpolar planktic foraminifera benthic foraminiferal and stable isotope data indicate active deep water formation during the hp zones in substage 5e there are indications of sea surface temperatures similar to those of today the major glaciations on svalbard during the last interglacial glacial cycle are related to hp zones some hp zones correspond to an early build up phase of the ice sheets peak glacials all correspond to one hp zone that subsequently is terminated by a meltwater event however periods with advection of atlantic water during mid mis 3 do not correlate to a glacial phase on svalbard but rather to the western fennoscandian ice sheet the records in the present study are correlated to the northeast atlantic the arctic ocean and to the greenland ice core record and show parallel millennial scale variability

paleoceanographic changes and calcium carbonate dissolution in the central fram strait during the last 20 ka article i nfo article history received 31 october 2011 available online xxxx a deep sea sediment core covering thelast20 ka and located between thepolar and thearctic fronts in themar ginal ice zone miz of the central fram strait has been investigated for changes in paleoceanography and calcium carbonatepreservation the reconstructionisbased on the distribution patternsofplankticforaminifera mean shell weight and the degree of fragmentation of their shells stable isotopes and other geochemical and sedimentological data the results show that the planktic foraminifera shells are poorly preserved throughout most of the record only the intervals comprising the early holocene from 10 8 to 8 cal ka bp and the last 800 yr show improved preservation of caco3 the dissolution correlated with the extent of arctic water and the associated marginal ice zone miz and high organic productivity dissolution of planktic foraminifera is generally high during the late deglaciation mid and late holocene prior to 800 cal yr bp the abundance of small subpolar species increases in the surface sediments dating from the last century which could be interpreted as a large and significant surface water warming however this apparent high magnitude warming seems to be overestimated due to preservation changes in the youngest sediments

arctic ocean during the last glacial maximum atlantic and polar domains of surface water mass distribution and ice cover on the basis of 52 sediment cores analyzed and dated at high resolution the paleoceanography and climate of the last glacial maximum lgm were reconstructed in detail for the fram strait and the eastern and central arctic ocean sediment composition and stable isotope data suggest three distinct paleoenvironments 1 a productive region in the eastern to central fram strait and along the northern barents sea continental margin characterized by atlantic water advection frequent open water conditions and occasional local meltwater supply and iceberg calving from the barents sea ice sheet 2 an intermediate region in the southwestern eurasian basin up to 84 85 n and the western fram strait characterized by subsurface atlantic water advection and recirculation a moderately high planktic productivity and a perennial ice cover that breaks up only occasionally and 3 a central arctic region north of 85 n in the eurasian basin characterized by a low salinity surface water layer and a thick ice cover that strongly reduces bioproduction and bulk sedimentation rates although the total inflow of atlantic water into the arctic ocean may have been reduced during the lgm its impact on ice coverage and halocline structure in the fram strait and southwestern eurasian basin was strong

distribution patterns of dinoflagellate cysts and other organic walled microfossils in recent norwegian greenland sea sediments dinoflagellate cysts and other organic walled microfossils have been studied in recent surface sediments from the entire norwegian greenland sea more than 30 taxa have been recognized of which only few show a distinct distribution pattern and allow description of four assemblages the occurrence of most taxa is related to the relatively warmer waters of the norwegian sea algidaspaeridium minutum s 1 brigantedinium simplex and impagidinium pallidum are the only species showing a preference for colder water masses two species i pallidum and nematosphaeropsis labyrinthus are mainly restricted to the oceanic environment whereas the other species have also been reported from neritic environments in previous studies due to the limited knowledge of the ecological and sedimentological factors influencing the occurrence of dinoflagellate cysts in oceanic environments their distribution in recent sediments can be only related to surface water masses in a broad sense although the distribution of assemblages correlates with specific surface water masses comparison with assemblages recovered from sediment traps deployed basinwide in the norwegian greenland sea dale and dale 1992 revealed some major discrepancies in species composition and percentage abundances the differences cannot be explained with certainty at the moment although there is some evidence that transport of dinoflagellate cysts and other fossilizable microplankton in water masses by currents in sea ice and sediments may modify the assemblages found in recent oceanic surface sediments from the norwegian greenland sea

paleoceanography of northeastern fram strait since the last glacial maximum palynological evidence of large amplitude changes abstract sea surface conditions in northeastern fram strait since the last glacial maximum lgm were reconstructed from cores msm5 5 712 2 and ps2863 1 2 based on palynological assemblages ecological preferences of dinocysts and application of the modern analog technique dinocyst in lgm sediments are sparse but their assemblages reflect mild summer conditions given the regional context and evidence from other tracers the dinocyst assemblages of the lgm could relate to regional fluxes of dinocysts during exceptional mild summers from 19 to 14 7 ka dinocyst data suggest very cold conditions with extensive sea ice cover while abundant reworked palynomorphs indicate intense glacial erosion an abrupt transition at 14 7 14 5 ka was marked by a peak in summer temperatures coinciding with a rapidly deposited sediment layer related to a regional meltwater plume event in western svalbard from 14 7 to 12 6 ka large seasonal temperature contrasts with mild summers and cold winters together with low salinity indicate continuous melting of the svalbard barents sea ice sheet fostered by warm climate at 12 6 ka the regional onset of the younger dryas was marked by cooling and increased salinity on a regional scale the 12 6 12 ka interval corresponds to an important transition involving enhanced circulation of arctic waters around svalbard and establishment of coastal fronts along its northern and western margins modern like oceanic conditions with relatively high salinity and low seasonal temperature contrast developed at about 7 6 ka since then a slight cooling is observed especially in winter this study offers a comprehensive picture of the deglacial phases in eastern fram strait with unique data on the sea surface salinity which controls surface water stratification and plays an important role in ocean circulation

evidence from fram strait 78 n for early deglaciation recent syntheses of the history of the last northern hemisphere glaciation and deglaciation illustrate that understanding of the mechanisms and timing of deglaciation before approximately 12 000 years bp1 5 is limited after 12 000 yr bp however there is sufficient evidence from radiocarbon dated moraines raised beaches varved lake sediments and pollen records to provide a reasonable temporal and geographic picture of the decay of the ice sheets here we report on the first oxygen isotope record from the norwegian greenland sea that is radiocarbon dated directly by accelerator mass spectrometry a significant light oxygen isotope event is recorded at approximately 15 000 years bp which suggests that the marine based barents shelf ice sheet disintegrated rapidly at this time recent studies6 7 have estimated that the decay of this ice sheet could have contributed as much as 15 metres to eustatic sea level rise the decay of the barents shelf ice sheet is the earliest major deglacial event yet dated and may have triggered subsequent deglacial events through eustatic sea level effects

variations in surface water mass conditions in the norwegian sea evidence from holocene coccolith and dinoflagellate cyst assemblages coccolith and dinoflagellate cyst assemblages have been investigated in five sediment cores from the norwegian sea and fram strait both fossil groups are characterized by similar patterns of composition the assemblages contain high proportions of single species the coccolith flora is of low diversity and consists almost entirely of coccolithus pelagicus and emiliania huxleyi the dinoflagellate cysts are generally dominated by operculodinium centrocarpum and nematosphaeropsis labyrinthus other species especially bitectatodinium tepikiense peridinium faeroense and impagidinium pallidum sometimes contribute considerably to the assemblages based on the abundance of the assemblages and the ratio change between the dominating species it has been possible to establish three intervals of distinct major changes in surface water mass conditions sparse occurrences of coccoliths and dinoflagellate cysts have been observed before 10 000 yrs b p indicating harsh environmental conditions with a distinct influence of meltwater and temporarily very slight inflow of atlantic water the modern surface water circulation pattern was reinitiated during termination ib the assemblages suggest slightly cooler and probably less saline surface water conditions than are present today until 7500 yrs b p solar insolation may have caused a first temperature peak which is responsible for the early holocene productivity maximum a considerable change in the composition of dinocyst and coccolith assemblages occurs corresponding approximately to the onset of the holocene climatic optimum this change was most probably linked to an almost synchronous reorganization of the hydrographic properties in the entire north atlantic realm after the ice sheets had vanished since 6000 yrs b p the norwegian current with its modern oceanographic and ecological properties has been fully established