past glacial and interglacial conditions in the arctic ocean and marginal seas a review past changes in the arctic ocean and its marginal seas have been profound even during the last 10 000 years understanding these changes such as those occurring during the transition from glacial to interglacial climates are important for research on modern processes because this knowledge provides a framework and unique perspective in which to view the modern physical and biological processes this paper discusses our current understanding of past environmental change and processes relative to those currently in progress special emphasis is placed on the most recent transition from a glacial state to the modern interglacial conditions

numerical reconstructions of lgm climate across the eurasian arctic abstract although limits of the eurasian ice sheet at the last glacial maximum lgm are known relatively well from geological evidence the palaeoclimate coexistent with this ice sheet has yet to be identified confidently a simple ice sheet model has been used to determine lgm climate conditions by finding the ice sheet mass balance configuration that permits model results to match with geological data relating to the extent of lgm ice cover these conditions are compared with atmospheric general circulation model agcm calculations of the climate at the lgm which reveal the meteorological conditions associated with the ice sheet mass balance the western margin of scandinavia is characterised by a maritime climate influenced by the nearby warm seasonally sea ice free ocean conditions however further east the warming effect of the north atlantic diminishes and an extreme polar desert climate dominates across the kara sea similar to east antarctica today the lgm climate that we establish is in contrast to many previous reconstructions involving snow laden warm westerly winds originating from the north atlantic affecting the entire eurasian arctic severely cold conditions across the eurasian arctic are compatible with a stable circulation cell over the kara sea that isolates the region climatically and or cold dry westerly winds from the fennoscandian ice sheet that flow across the rest of the eurasian arctic

new evidence from the western canadian arctic archipelago for the resubmergence of bering strait widespread molluscan samples were collected from raised marine sediments to date the last retreat of the nw laurentide ice sheet from the western canadian arctic archipelago at the head of mercy bay northern banks island deglacial mud at the modern coast contains hiatella arctica and portlandia arctica bivalves as well as cyrtodaria kurriana previously unreported for this area multiple h arctica and c kurriana valves from this site yield a mean age of 11 5 14c ka bp with 740 yr marine reservoir correction the occurrence of c kurriana a low arctic taxon raises questions concerning its origin because evidence is currently lacking for a molluscan refugium in the arctic ocean during the last glacial maximum elsewhere the oldest late glacial age available on c kurriana comes from the laptev sea where it is 10 3 14c ka bp and attributed to a north atlantic source this is 2000 cal yr younger than the mercy bay samples reported here making the laptev sea 3000 km to the west an unlikely source an alternate route from the north atlantic into the canadian arctic archipelago was precluded by coalescent laurentide innuitian and greenland ice east of banks island until 10 14c ka bp we conclude that the presence of c kurriana on northern banks island records migration from the north pacific this requires the resubmergence of bering strait by 11 5 14c ka bp extending previous age determinations on the reconnection of the pacific and arctic oceans by up to 1000 yr this renewed ingress of pacific water likely played an important role in re establishing arctic ocean surface currents including the evacuation of thick multi year sea ice into the north atlantic prior to the younger dryas geochron

rapid climatic shifts during isotope stages 2 4 in the polar north atlantic sediment cores from the polar north atlantic provide evidence of six periods of sea ice breakup during isotope stages 4 3 and 2 probably caused by inflow of north atlantic surface water into the polar north atlantic these periods are characterized by having a high number of foraminifera g they last from 2000 to 10000 yr and constitute 50 of the total time span these periods of sea ice breakup correlate temporarily to the heinrich events and the early temperature maximum in the bond cycles of the north atlantic and greenland ice record our hypothesis is that massive iceberg discharges that flooded the north atlantic during each heinrich event probably triggered an oceanographic regime that gave a much more vigorous surface circulation pattern in the polar north atlantic which contributed to the breakup of the sea ice cover open water conditions in the polar north atlantic are inversely related to terrestrial interstadials of coastal norway suggesting ice sheet starvation during the cold periods and ice sheet growth when an open water surface circulation existed in the polar north atlantic our data document synchronous variations on a october 1900 yr time scale between arctic oceanic climate northern hemisphere ice sheet dynamics and ocean atmosphere temperature changes

flux of ice rafted detritus from sea ice in the fram strait abstract a three year particle flux record from the eastern fram strait between greenland and svalbard revealed a rather untypical seasonal flux pattern compared to other particle flux studies from the nordic seas in the eastern fram strait this pattern is characterised by a sudden four to six fold increase of the particle flux in january when no daylight is available to support any biological productivity comparison with sea ice distribution maps led to the conclusion that the sudden increase in the flux is due to ice rafted detritus released from sea ice which originated from the svalbard archipelago and from the northern barents sea detailed grain size analyses of the silt fraction indicated the 10 m fraction of the lithogenic matter to be clearly enriched due to ird input even more important is the observation that lithogenic material 40 m occurs exclusively during the ice rafting event and therefore appears to be a suitable indicator for ird transported on sea ice thus in addition to coarse ird e g 500 m which is mainly derived from icebergs the analysis of fine ird 40 m in deep sea sediments can be used to reconstruct paleo sea ice extensions

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

advection and removal of 210pb and stable pb isotopes in the oceans a general circulation model study abstract natural pb isotope variability in the oceans encodes information about the sources of continental material to the oceans about ocean circulation and about pb removal in order to use this information we must understand the natural cycle of pb in the oceans which is overprinted by large anthropogenic input in this study we use 210 pb which has not been significantly anthropogenically perturbed to investigate oceanic pb geosecs 226 ra and model derived atmospheric fluxes of 210 pb are used to input 210 pb into an ocean general circulation model irreversible scavenging of this 210 pb onto settling biogenic particles and at the seafloor are tuned so that the model replicates the observed pattern of 210 pb in the oceans the best fit model run provides a map of the variability of residence time for pb the global average residence time of pb in this model is 48 yr but there is over an order of magnitude variation between areas of high and low productivity this is expected to enhance provinciality of pb isotope ratios in the oceans because stable pb isotopes are expected to behave in seawater in a similar fashion to 210 pb the pattern of removal of 210 pb derived by the model can be used to investigate the behavior of stable pb isotopes we use a simplified input of pb consisting of five point sources representing major rivers and a disseminated dust input although this simplified input scheme does not allow precise reconstruction of pb concentration and isotopes in the oceans it allows us to answer some first order questions about the behavior of pb as an ocean tracer with a total pb input of 6 3 10 7 mol yr chow t j and patterson c c the occurrence and significance of pb isotopes in pelagic sediments geochim cosmochim acta 26 263 308 1962 the model predicts natural seawater pb concentrations averaging 2 2 pmol kg even in the absence of anthropogenic input the model ocean exhibits a near surface maximum in pb concentration and the model suggests natural pb concentrations in the northern hemisphere an order of magnitude higher than in the southern hemisphere a point source of pb is suggested to dominate the seawater pb inventory close to the source but is reduced to typically less than 10 of the inventory by the time that pb is advected out of the originating ocean this length scale of advection for pb isotope signals confirms their potential as tracers of ocean circulation assuming an 8 dissolution of dust their input to the open ocean are seen to be a significant portion of pb inventory throughout the oceans and make up 50 of the pb inventory in the model s southern ocean finally a preliminary investigation of the response of pb isotope distributions to changes in boundary conditions between glacial and interglacial times illustrates that significant variation in the pb isotopes are expected in some regions even for reasonably small changes in climate conditions

a palaeoclimatic and palaeoceanographic record of the last 11 000 14c years from the skagerrak kattegat northeastern atlantic margin marine sediments of about 116 m drilled onshore at skagen near the northernmost tip of jutland denmark provides a continuous and detailed palaeoceanographic and palaeoenvironmental record of the last 11 000 14c years in the skagerrak kattegat the whole younger dryas was characterized by an arctic subarctic environment where the north jutland current flows today instead of being succeeded by a minor climate warming at about 10 600 bp as recorded in the southern kattegat and in the areas strongly influenced by the baltic current and currents along the swedish west coast the changes in components of diatom assemblages combined with previously published benthic foraminiferal data from the present core reflect a two step climatic warming and consequently environmental change during the transition from the younger dryas to the preboreal an abrupt warming of the sea surface waters took place at about 10 100 bp which resulted from the inflow of warm atlantic surface water summer sea surface temperature

late quaternary glaciation history of northernmost greenland evidence of shelf based ice abstract we present the mapping of glacial landforms and sediments from northernmost greenland bordering 100 km of the arctic ocean coast one of the most important discoveries is that glacial landforms sediments including till fabric measurements striae and stoss lee boulders suggest eastward ice flow along the coastal plain volcanic erratic boulders document ice transport from 80 to 100 km west of the study area we argue that these findings are best explained by local outlet glaciers from the greenland ice sheet and local ice caps that merged to form a shelf based ice in the arctic ocean and possibly confirming an extensive ice shelf in the lincoln sea between greenland and ellesmere island it is speculated that the shelf based ice was largely affected by the presence of thick multiyear sea ice in the arctic ocean that prevented it from breaking up and forced the outlet glaciers to flow eastwards during the initial retreat the coastal area was dammed by the shelf based ice and kame and glaciolacustrine sediments were deposited up to 50 m above the marine limit before the final deglaciation and marine transgression the timing of the shelf based ice is constrained on land by dating glaciolacustrine sediments with osl and marine molluscs with radiocarbon and by re evaluating ird events in cores from the fram strait results show that the shelf based ice started to build up as early as 30 cal ka bp and reached a maximum during the last glacial maximum lgm the shelf based ice began to retreat ca 16 ka to 10 3 cal ka bp before the final break up which took place ca 10 1 cal ka bp probably as a combined result of increased inflow of warm atlantic water through the fram strait a shallower halocline and higher summer temperatures corresponding to orbital maximum solar insolation at this time the existence of extensive shelf based ice north of greenland provides an important contribution to the understanding of the lgm glaciation history of the arctic ocean

alternative routing of lake agassiz overflow during the younger dryas new dates paleotopography and a re evaluation abstract overflow from glacial lake agassiz has been implicated in affecting late glacial ocean circulation and climate the timing of the diversion of lake agassiz overflow away from its southern routing to the gulf of mexico correlates closely with the younger dryas ca 11 10 14 c ka new models of paleotopography in the eastern outlet region of lake agassiz adjusted for differential isostatic rebound show that overflow to the superior basin would have occurred when the lake formed its herman norcross and tintah beaches just after 10 9 14 c ka if the laurentide ice sheet lis had retreated from the thunder bay ontario region by that time however the absence of coarse flood deposits normally associated with large overflows plus the morphology of possible overflow channels in the thunder bay region suggest that agassiz overflow may not have been routed into the great lakes during the younger dryas as previously believed in addition non carbonate radiocarbon dates in the thunder bay area are all younger than 10 14 c ka suggesting that this area may not have been deglaciated until after the younger dryas thus preventing lake agassiz overflow through this area an alternative route of overflow from lake agassiz during the younger dryas could have been through the northwestern clearwater outlet to the arctic ocean although all research to date shows that this region was covered by ice until 10 14 c ka on the other hand it is possible that older and coarser overflow sediment may now lie buried beneath finer deposits associated with the 10 14 c ka marquette readvance of the lis which ponded waters in valleys between lake agassiz and lake superior or that eastward overflow in this area was not catastrophic

weathering versus circulation controlled changes in radiogenic isotope tracer composition of the labrador sea and north atlantic deep water geological reconstructions and general circulation models suggest that the onset of both northern hemisphere glaciation 2 7 myr ago and convection of labrador sea water lsw were caused by the closure of the panama gateway 4 5 myr ago time series data that have been obtained from studies of ferromanganese crusts from the northwestern atlantic suggest that radiogenic isotopes of intermediate ocean residence time pb and nd can serve as suitable tracers to reconstruct these events however it has been unclear until now as to whether the changes that have been observed in isotope composition at this time are the result of increased thermohaline circulation or due to the effects of increased glacial weathering in this paper we adopt a box model approach to demonstrate that the shifts in radiogenic isotope compositions are unlikely to be due to changes in convection in lsw but can be explained in terms of increases of erosion levels due to the glaciation of greenland and canada furthermore we provide experimental evidence for the incongruent release of a labile fraction of strongly radiogenic pb and nonradiogenic nd from continental detritus eroding into the labrador sea this can be attributed to the glacial weathering of old continents and accounts for the paradox that one of the areas of the world most deficient in radiogenic pb should provide such a rich supply of radiogenic pb to the oceans an important general conclusion is that the compositions of radiogenic isotopes in seawater are not always a reflection of their continental sources perhaps more importantly the transition from chemical weathering to mechanical erosion is likely to result in significant variations in radiogenic tracers in seawater

a new approach to the nd residence time in the ocean the role of atmospheric inputs concentrations of rare earth elements ree and nd isotopic ratios were analyzed for seawater filtered suspension and sediment trap samples collected in the tropical atlantic ocean eumeli program eutrophic mesotrophic and oligotrophic sites 20 n 18 21 w this is the first ree nd dataset on solution and different sized particles collected at the same site we present direct evidence of the nd isotopic exchange between particulate lithogenic fraction and seawater without significant mass transfer this exchange is probably one of the main factors that simultaneously constrains the nd concentration and isotopic ratio budget we propose a new approach to estimate the residence time of nd in the ocean nd based on isotopic exchange 200 yr nd 1000 yr the exchange requires a partial dissolution of lithogenic nd we estimate that the fraction of soluble nd proportion in atmospheric dust is of the order of 20 based on the isotopic ratios we suggest that the partial dissolution of atmospheric fallout is probably one of the main ree sources of the ocean

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

stratigraphic constraints on late pleistocene glacial erosion and deglaciation of the chukchi margin arctic ocean at least two episodes of glacial erosion of the chukchi margin at water depths to 450 m and 750 m have been indicated by geophysical seafloor data we examine sediment stratigraphy in these areas to verify the inferred erosion and to understand its nature and timing our data within the eroded areas show the presence of glaciogenic diamictons composed mostly of reworked local bedrock the diamictons are estimated to form during the last glacial maximum lgm and an earlier glacial event possibly between ois 4 to 5d both erosional events were presumably caused by the grounding of ice shelves originating from the laurentide ice sheet broader glaciological settings differed between these events as indicated by different orientations of flutes on eroded seafloor postglacial sedimentation evolved from iceberg dominated environments to those controlled by sea ice rafting and marine processes in the holocene a prominent minimum in planktonic foraminiferal 18 o is identified in deglacial sediments at an estimated age near 13 000 cal yr bp this 18 o minimum also reported elsewhere in the amerasia basin is probably related to a major laurentide meltwater pulse at the younger dryas onset the bering strait opening is also marked in the composition of late deglacial chukchi sediments

north american origin of pink white layers at the mendeleev ridge arctic ocean new insights from lead and neodymium isotope composition of detrital sediment component abstract dolomite rich layers of distinct pinkish colour are used as lithostratigraphic markers in the amerasian basin of the arctic ocean however origin of dolomite in these sediment units has not been studied in detail in this study lead pb and neodymium nd isotope composition of detrital clay size fraction from different lithofacies were investigated in core ps72 340 5 recovered at the eastern flank of the mendeleev ridge prior to the geochemical analyses grain size distribution was analyzed in order to minimize the grain size effect on the provenance signature for provenance discrimination results of isotope measurements were compared with marine surface sediment data and values for the circum arctic subaerial provinces late quaternary sediment supply variability was analyzed using the mixing model constrained by two tracers 207pb 206pb and end variations of sediment isotopic composition are inferred to result from mixing of volcanic and plutonic components usage of pb isotopic ratios alone does not allow distinction between these two types of sources results confirm that over the last estimated ca 200 ka dolomite rich pink layers at the mendeleev ridge were deposited during events probably associated with intensified iceberg transport from north america in general however sedimentation was mostly controlled by terrigenous input from the chukchi and east siberian seas whereas sediment supply from the laptev sea area remained less important and relatively constant at the studied location

arctic ice export events and their potential impact on global climate during the late pleistocene 1 ice sheets in the north american arctic and to a lesser extent those in northern eurasia calved large quantities of icebergs that drifted through fram strait into the greenland sea several times during the late pleistocene these icebergs deposited fe oxide grains 45 250 m and coarse lithic clasts 250 m matched to specific circum arctic sources four massive arctic iceberg export events are identified from the laurentide and the innuitian ice sheets between 14 and 34 ka calendar years in a sediment core from fram strait these relatively short duration 1 4 kyr events contain 3 5 times the background levels of fe oxide grains they began suddenly as indicated by a steep rise in the number of grains matched to an ice sheet source suggesting rapid purges of ice through fram strait due perhaps to collapse of ice sheets the larger events from the northwestern laurentide ice sheet are preceded by events from the innuitian ice sheet despite the chronological uncertainties the arctic export events appear to occur prior to heinrich events

arctic vs north atlantic water mass exchanges in fram strait from pb isotopes in sediments surface sediment samples n 10 collected between spitzbergen and greenland and two cores raised east c04 and west c16 from fram strait were analyzed for their chemical and isotopic pb compositions to trace the source of sediments and water masses exchanging between the arctic and the north atlantic oceans in surface sediments variable major and trace element concentrations suggest variations in both the mineralogy carbonate and quartz dilution of other silicate minerals and source regions of detrital supplies based on th zr and to a lesser extent on th u ratios each core site shows specific but nearly constant th zr ratios indicating homogeneous source supplies at both core sites pb concentrations and isotopic compositions display similar patterns homogeneous low pb and radiogenic crustal signals below 5 10 cm contrasting with high pb and less radiogenic anthropogenic inputs at core tops however the differing pre anthropogenic pb isotopic ratios in c04 and c16 confirm the involve

remobilisation of the continental lithosphere by a mantle plume major trace element and sr nd and pb isotope evidence from picritic and tholeiitic lavas of the noril sk district siberian trap russia the late permian to early triassic siberian traps have been sampled by drill core core sg 9 and from surface exposure section 1f in the noril sk region of the siberian platform russia combined major trace element and nd sr and pb isotope data on selected samples through the siberia trap offer new chemostratigraphic criteria for the identification and characterisation of two fundamentally different magma types and 9 of the 11 formations of lava developed near noril sk a lower sequence of sub alkalic basalts tholeiites and picritic basalts upwards these are the ivakinsky syverminsky and gudchichinsky formations are overlain by an upper sequence of picritic basalts and tholeiites interbedded with tuffs upwards these are the khakanchansky tuklonsky nadezhdinsky morongovsky mokulaevsky and kharayelakhsky formations the gudchichinsky and tuklonsky formations contain both picritic and tholeiitic lavas the tuklonsky formation tholeiites and picrites have moderate gd yb 1 6 1 8 low tio2 0 45 0 95 wt a significant negative ta and nb anomaly nb la 0 42 0 57 and unradiogenic nd nd chur to 4 6 in contrast both the gudchichinsky formation tholeiites and picrites have high gd yb 2 3 3 1 and tio2 1 2 2 3 wt no significant nb or ta anomaly nb la 0 8 1 1 and radiogenic nd nd chur to 7 3 the low ti and nb la high la sm and unradiogenic nd isotope signatures of the picritic tuklonsky formation lavas and the tholeiitic lavas of the upper sequence are characteristic of magmas strongly influenced by material from the continental lithosphere whereas the high ti and nb la low la sm and radiogenic nd isotope signatures of the lower sequence are more comparable to deeper asthenospheric mantle plume generated lavas similar to oceanic island basalts the lavas overlying the tuklonsky formation have mg numbers of 0 63 to 0 68 and are more evolved than the tuklonsky mg number 0 62 and have more radiogenic nd chur tuklonsky 0 03 to 4 66 mokulaevsky 0 60 to 1 61 but have many of the incompatible trace element features of the tuklonsky sky type magma these lavas show a progressive upwards decline in sio2 55 49 wt la sm 4 6 2 0 and ur sr 67 to 13 which has previously been attributed to a decrease in the proportion of crustal material contributed to the magma this paper explores and alternative model where a component of the crustal contribution might be derived from within an ancient region of the mantle lithosphere as recycled sediment rather than from the overlying continental crust

the periglacial climate and environment in northern eurasia during the last glaciation this paper summarizes the results of studies of the late weichselian periglacial environments carried out in key areas of northern eurasia by several queen teams european science foundation esf programme quaternary environment of the eurasian north the palaeoglaciological boundary conditions are defined by geological data on timing and extent of the last glaciation obtained in the course of the eu funded project eurasian ice sheets these data prove beyond any doubt that with the exception of the northwestern fringe of the taymyr peninsula the rest of the eurasian mainland and severnaya zemlya were not affected by the barents kara sea ice sheet during the last glacial maximum lgm inversed modelling based on these results shows that a progressive cooling which started around 30 ka bp caused ice growth in scandinavia and the northwestern areas of the barents kara sea shelf due to a maritime climate with relatively high precipitation along the western flank of the developing ice sheets in the rest of the eurasian arctic extremely low precipitation rates less than 50 mm yr 1 did not allow ice sheet growth in spite of the very cold temperatures palaeoclimatic and palaeoenvironmental conditions for the time prior to during and after the lgm have been reconstructed for the non glaciated areas around the lgm ice sheet with the use of faunal and vegetation records permafrost eolian sediments alluvial deposits and other evidences the changing environment from interstadial conditions around 30 ka bp to a much colder and drier environment at the culmination of the lgm at 20 15 ka bp and the beginning of warming around 15 ka bp have been elaborated from the field data which fits well with the modelling results

early to middle holocene valley glaciations on northernmost greenland abstract this paper presents the glacial stratigraphy and palaeoenvironmental evolution around constable bugt johannes v jensen land located on the north coast of greenland this is a land of extreme climate polar desert conditions and a coast bound by a permanent sea ice cover our data covers the period from the last glacial maximum lgm 18 22 cal ka bp into the holocene it records the history of a shelf based glaciation with ice flowing eastward along the coast as well as two local valley glacier advances from the south during the holocene with ice on the coastal plain during the lgm glaciolacustrine basins formed in marginal positions and in ice dammed valleys to the south into the mountainous area of peary land with the break up of shelf based ice there was a gradual marine inundation at which the marine limit formed at 45 m a s l this initial early holocene ice advance from the south formed prominent valley mouth moraines especially in sifs valley here both glaciolacustrine and marine sediments were remoulded and or dislocated as thrust blocks into a moraine ridge spanning more than 1 km in width and 60 m in height radiocarbon ages of sediments incorporated in this moraine as well as from on lapping sediments suggest that the moraine formed between 9 6 and 6 3 cal ka bp based on 14 c dating results the youngest ice advance phase can be narrowed down to 14 c ages between 5 5 5 0 cal ka bp the recorded ice advances took place during the holocene thermal maximum htm for north greenland the last one close to the beginning of the neoglacial cooling during the htm we have recorded a period of 2500 years during which the north coast of greenland as opposed to today experienced an absence to very restricted occurrence of land fast or multi year sea ice this observation can be explained by the altitudinal and temporal distribution of beach ridge complexes that must have formed by wave action and thus requiring at least partial open water conditions with a moisture source at hand we propose that this lead to enhanced precipitation in the near coastal areas which coupled to documented htm cold reversals caused a lowered glaciation limit and led to a positive mass balance and subsequent ice advance

atlantic water flow pathways revealed by lead contamination in arctic basin sediments contaminant lead in sediments underlying boundary currents in the arctic ocean provides an image of current organization and stability during the past 50 years the sediment distributions of lead stable lead isotope ratios and lead 210 in the major arctic ocean basins reveal close coupling of the eurasian basin with the north atlantic during the 20th century they indicate that the atlantic water boundary current in the eurasian basin has been a prominent pathway that contaminant lead from the laptev sea supplies surface water in the transpolar drift and that the canadian and eurasian basins have been historically decoupled

sources of labrador sea sediments since the last glacial maximum inferred from nd pb isotopes pb isotopes have been measured in the clay size fraction of late glacial and holocene deep sea sediments recovered from two labrador sea piston cores that have been previously analyzed for nd isotopes the newly acquired pb isotopic data allow us to better constrain the different source areas that supplied clay size material during the last deglaciation until 8 6 kyr calendar ages nd pb data can be modeled mainly as a mixture between a precambrian crust and lower paleozoic material originating from the denudation of the pan african orogen the old material originates mainly from the archean lower proterozoic or both terranes of greenland and also probably corresponding terranes of labrador although minor input of other precambrian material is recorded in some detrital carbonate rich deglacial samples from orphan knoll the phanerozoic crustal end member consists of sediment material mainly originating from northwestern europe this source area is found to be the only significant source of young crustal material in early holocene sediments from the greenland rise no significant input from the mid atlantic volcanism is apparent this study puts further constraints on the deep circulation pattern during the last deglaciation it is concluded that at that time european phanerozoic material was carried from the norwegian sea through the wyville thompson ridge into the iceland basin by the north east atlantic deep water no evidence for an overflow is found either south of the iceland iceland scotland ridge or through the denmark strait

quaternary arctic ocean sea ice variations and radiocarbon reservoir age corrections a short sediment core from a local depression forming an intra basin on the lomonosov ridge was retrieved during the healy oden trans arctic expedition 2005 hotrax it contains a record of the marine isotope stages mis 1 3 showing exceptionally high abundances of calcareous microfossils during parts of mis 3 based on radiocarbon dating linear sedimentation rates of 7 9 cm ka persist during the last deglaciation the last glacial maximum lgm is partly characterized by a hiatus planktic foraminiferal abundance variations of neogloboquadrina pachyderma sinistral and calcareous nannofossils reflect changes in arctic ocean summer sea ice coverage and probably inflow of subpolar north atlantic water calibration of the radiocarbon ages using modeled reservoir corrections from previous studies and the microfossil abundance record of the studied core results in marine reservoir ages of 1400 years or more at least during the last deglaciation paired benthic planktic radiocarbon dated foraminiferal samples indicate a slow decrease in age difference between surface and bottom waters from the lateglacial to the holocene suggesting circulation and ventilation changes c 2010 elsevier ltd all rights reserved

late weichselian glaciation of the russian high arctic a numerical ice sheet model was used to reconstruct the late weichselian glaciation of the eurasian high arctic between franz josef land and severnaya zemlya an ice sheet was developed over the entire eurasian high arctic so that ice flow from the central barents and kara seas toward the northern russian arctic could be accounted for an inverse approach to modeling was utilized where ice sheet results were forced to be compatible with geological information indicating ice free conditions over the taymyr peninsula during the late weichselian the model indicates complete glaciation of the barents and kara seas and predicts a maximum sized ice sheet for the late weichselian russian high arctic in this scenario full glacial conditions are characterized by a 1500 m thick ice mass over the barents sea from which ice flowed to the north and west within several bathymetric troughs as large ice streams in contrast to this reconstruction a minimum model of glaciation involves restricted glaciation in the kara sea where the ice thickness is only 300 m in the south and which is free of ice in the north across severnaya zemlya our maximum reconstruction is compatible with geological information that indicates complete glaciation of the barents sea however geological data from severnaya zemlya suggest our minimum model is more relevant further east this in turn implies a strong paleoclimatic gradient to colder and drier conditions eastward across the eurasian arctic during the late weichselian

oceanic and atmospheric variations during the last deglaciation in the fram strait arctic ocean a coupled high resolution organic geochemical and sedimentological study abstract from a high sedimentation rate core obtained from the yermak slope arctic ocean we deduced short term climatic fluctuations of the last deglaciation lasting from 17 000 to 9000 years bp by using a coupled organic geochemical and sedimentological approach we reconstructed near bottom current conditions and assessed their significance in relation with comparable global thermohaline circulation patterns and surface water conditions highest concentrations and fluctuations of specific marine phytoplankton biomarkers were obtained in the bolling allerod when the major deglaciation of the svalbard barents sea ice sheet sbis occurred the marine biomarker record and the sedimentological record are consistent with climate reconstructions obtained from greenland ice cores and thermohaline circulation variations however beginning with the younger dryas yd episode bottom currents decreased during this time period but surface waters remained very productive the atmospheric conditions of the western fram strait reconstructed from biomarker data and thermohaline circulation signals reconstructed from sedimentological data were decoupled in the yd maximum insolation values of solar radiation and fohn like winds enabled open water conditions and increased productivity values in the northern fram strait at least in summer

sea ice transport a highly variable link between arctic and north atlantic the variability of the ice volume flux into the northeast atlantic is investigated with an optimized dynamic thermodynamic sea ice model using 40 years 1958 1997 of atmospheric forcing fields derived from the ncep ncar reanalysis project the simulated sea ice export from the arctic exhibits considerable interannual to decadal variability and is primarily a linear response to sea level pressure anomalies over greenland and over the barents and kara seas our model results suggest that ice export anomalies such as in 1968 which supposedly caused the so called great salinity anomaly in the northern north atlantic are not unique but rather frequent events as part of the variability of the arctic climate system

an improved method for extracting marine sediment fractions and its application to sr and nd isotopic analysis the radiogenic isotopic composition of both detrital and fe mn fractions in marine sediments can be used in paleoceanography to infer changes of bottom water circulation we have examined various chemical techniques for the analysis of sr and nd isotope ratios in these fractions and present a robust method that can be used to separate both the fe mn oxides and the detrital fraction from a marine sediment sample for isotopic analysis our sequential leaching procedure involves the use of 10 acetic acid followed by 1 m hydroxylamine hydrochloride in 25 acetic acid to remove the carbonate component and the fe mn oxide fraction respectively the applicability of our chemical procedure is illustrated with examples from a marine sediment core raised from the northern cape basin southeast atlantic ocean

variability of sea ice conditions in the fram strait over the past 30 000 years sea ice is a critical component of the climate and oceanographic system in the north atlantic ocean a biomarker record reveals millennial scale and glacial interglacial fluctuations in sea ice coverage in the northernmost atlantic ocean over the past 30 000 years

constraining the timing of the most recent cataclysmic flood event from ice dammed lakes in the russian altai mountains siberia using cosmogenic in situ 10be ice dammed lakes were repeatedly formed in intermontane basins in the russian altai mountains throughout the pleistocene these cataclysmic outburst floods caused by ice dam failures were documented as earth9s largest flood waves by other geoscientists using in situ 10 be we successfully dated surfaces of flood associated boulders located in a former lake basin and downvalley from a former ice dam our precise surface exposure ages suggest that all boulders were associated with the most recent out of a number of cataclysmic floods that occurred at 15 8 1 8 ka the field location of the boulders implies that they were deposited by the largest late pleistocene flood that drained the chuya katun lake completely following initial dam failure a published reconstruction of the late glacial paleoenvironment in the vicinity of the former ice dam indicates that dam failure was likely a result of climatically induced downwasting of glaciers the failure of the ice dam provides more evidence for the timing of widespread warming during the late glacial in southern russia this flooding event in the headwaters of the ob river coincides with a freshwater peak as recorded in isotopic records of the kara sea and the arctic ocean

strontium neodymium and lead isotope variations of authigenic and silicate sediment components from the late cenozoic arctic ocean implications for sediment provenance and the source of trace metals in seawater proven ance changes of silicate sediment deposited during the late cenozoic 5 0 ma on the alpha ridge central arctic ocean are determined from variations in strontium lead and neodymium isotope compositions whereas strontium and lead isotope compositions are relatively invariant from 5 to 1 7 ma end values start to increase at 3 ma subsequently s7sr 86sr and 2 6pb z 4pb ratios progressively increase and end values progressively decrease from 1 7 ma to the present day from these isotope variations three different endmember compositions for sediment source regions are defined the two endmember compositions defined by sediment that was deposited by sea ice from 5 to 1 7 ma are consistent with a significant component being derived from the east siberian shelf the progressive change in isotope compositions from 1 7 to 0 ma correlates with an increase in coarse detritus deposited by icebergs over this time period the isotope data are consistent with a progressive increase in the proportion of sediment that was deposited in the central arctic ocean since 1 7 ma having been derived from the northern canada or queen elizabeth island region changes in the strontium neodymium and lead isotope compositions of arctic seawater are determined by analyzing the oxide fractions of fe mn micronodules strontium isotope compositions of the microno dule oxide fractions are similar to published late cenozoic seawater data and indicate that 97 of the sr is seawater derived but minute contributions of sr from silicate detritus prohibit using the hydrogenous fractions for chronostratigraphic purposes neodymium and lead isotope compositions of the micronodule oxide fractions which reflect those of arctic seawater follow the isotope variations of the silicate components throughout the late cenozoic these relations indicate that river water can not be the primary source of rare earth elements and pb to the dissolved reservoir in arctic seawater and that ice rafted detritus by dissolution or exchange processes is an important source of trace elements to seawater in ice covered oceans copyright 1997 elsevier science ltd

arctic ocean deep sea record of northern eurasian ice sheet history the sediment composition of deep sea cores from the central arctic ocean the fram strait and the yermak plateau was analyzed for several parameters to reconstruct the history of marine paleoenvironment and terrestrial glaciation in the last 200 000 years layers with high amounts of coarse terrigenous ice rafted debris ird and often high contents of smectite were deposited during extensive glaciations in northern eurasia when ice sheets reached the northern continental margins of the barents and kara seas and discharged icebergs into the arctic ocean intercalated layers with relatively low ird and smectite contents but abundant planktic foraminifers in the coarse fraction were deposited during periods of atlantic water inflow to the arctic ocean and seasonally open waters leads in a sea ice cover with only few icebergs in the arctic ocean high ird contents in the sediments reflect the presence of ice sheets on the kara and barents seas shelves and the hinterland during the entire oxygen isotope stage 6 ca 190 130 ka in substage 5b ca 90 80 ka at the stage boundary 5 4 around 75 ka and in late stage 4 early stage 3 ca 65 50 ka these results are in excellent correlation with those from recent field work in northern scandinavia european russia siberia and on the shelves relatively low amounts of ird in central arctic ocean sediments from the late weichselian glacial maximum ca 24 18 ka correlate well with the recent reconstruction of a very limited eastern ice sheet extension during this time oxygen and carbon isotope records of planktic foraminifers from the analyzed sediment cores show a number of prominent excursions which can be interpreted as evidence for freshwater events in the arctic ocean the synchroneity of freshwater events and ird input suggests a common source strongest events were associated with deglaciations of the barents and kara seas after the ice sheets had blocked the outflow of large rivers for several millennia the outflow of freshwater from large ice dammed lakes occurred at ca 130 80 75 and 52 ka freshwater events in the central arctic ocean during the last deglaciation ca 18 ka were relatively small compared to the previous events this indicates that during most of the late weichselian glacial maximum a river outflow from northern siberia to the arctic ocean was possible atlantic water inflow to the arctic ocean and seasonally open waters in the ice leads occurred during the interglacials ofoxygen isotope stage 1 and substage 5e during several interstadials stage 3 substages 5a and 5c and to a lesser degree within stadials and glacials stages 2 4 and 6 with the exception ofthe interglacials these periods were times ofstrong ice growth on the continents as revealed by terrestrial data the coincidence suggests that open waters in the arctic ocean and the nordic seas were an important moisture source in addition to more southerly sources which fostered the growth of ice sheets on northern eurasia

neodymium isotopic composition and rare earth element concentrations in the deep and intermediate nordic seas constraints on the iceland scotland overflow water signature neodymium isotopic composition and rare earth element concentrations were measured in seawater samples from eleven stations in the nordic seas these data allow us to study how the iceland scotland overflow water isow acquires its neodymium signature in the modern ocean the waters overflowing the faroe shetland channel are characterized by nd 8 2 0 6 in good agreement with the only other data point published 19 years ago in the greenland and iceland seas the water masses leading to the formation of the isow display lower neodymium isotopic composition with nd around 11 and 9 respectively since no water masses in the nordic seas are characterized by nd 8 the radiogenic signature of the isow likely reflects inputs from the highly radiogenic norwegian basin basaltic margins jan mayen iceland faroe with nd 7 in addition to the neodymium isotopic composition the rare earth element patterns suggest that these inputs occur via the remobilization which includes resuspension and dissolution of sediments deposited on the margins whereas the neodymium isotopic composition behaves conservatively in the oceans in the absence of lithogenic inputs and can be used as a water mass tracer these results emphasize the role of interactions between sediments deposited on margins and seawater in the acquisition of the neodymium isotopic composition of water masses these results should allow a better use of this parameter to trace the present and the past circulation in the north atlantic

retreat of the laurentide ice sheet tracked by the isotopic composition of pb in western north atlantic seawater during termination 1 during the last glacial maximum much of north america was covered by the laurentide ice sheet its melting during termination 1 led to systematic changes in proglacial lake formation continental runoff and possibly north atlantic meridional overturning circulation the accompanying change in chemical weathering rates in the interior of north america throughout the deglaciation resulted in a pronounced change in seawater pb isotope composition in the western north atlantic ocean here we present the first high resolution records of seawater pb isotope variations of north atlantic deep water extracted from authigenic fe mn oxyhydroxides in three sediment cores 51ggc 1790 m depth 31ggc 3410 m depth 12jpc 4250 m depth from the blake ridge off florida these data reveal a striking excursion from relatively unradiogenic 206pb 204pb as low as 18 93 towards highly radiogenic pb isotope compositions that was initiated during the bolling allerod interstadial and was most pronounced in both intermediate and deep waters during and after the younger dryas 206pb 204pb as high as 19 38 at 8 8 ka in 4250 m this pattern is interpreted to be a direct function of increased inflow of continent derived radiogenic pb into the western north atlantic supplied through chemical weathering of north american rocks that had been eroded and freshly exposed during the preceding glacial cycle these sediment derived data are complemented by new laser ablation pb isotope data from a ferromanganese crust from the blake plateau at 850 m water depth which show only small glacial interglacial pb isotope variations of the florida current 206pb 204pb between 19 07 and 19 16 the lack of change in the blake plateau record at the same time as the radiogenic excursion in the deeper sediments supports a northern origin of the pulse of radiogenic pb after the younger dryas the deep western north atlantic has experienced a persistent highly radiogenic pb supply that was most pronounced during the first half of the holocene and still lasts until today

lead isotopic systematics of major river sediments a new estimate of the pb isotopic composition of the upper continental crust abstract the lead isotopic composition of river sediments is reported in the present work for the earth s major river basins from old cratonic to young orogenic areas and from subarctic to tropical climates sediment samples from these large river basins provide a useful tool to calculate the average upper crustal composition because they are large scale integrated samples of the weathering products of the present day upper continental crust ucc two different and complementary calculations were done to estimate the average lead isotopic composition of the ucc the first based on the flux weighted average of particulate lead delivered by the rivers gave values of 19 07 15 74 and 39 35 for 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios respectively to avoid over estimating the contribution of orogenic areas which produces a bias because the flux of particulate lead depends strongly on the physical erosion rate a second calculation was done by averaging with drainage areas of each river basin this gave values of 18 93 15 71 and 39 03 for 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios respectively these direct calculations of the lead isotopic composition of the ucc are similar and are in agreement with previous estimates made using an indirect approach

tephra in deglacial ocean sediments south of iceland stratigraphy geochemistry and oceanic reservoir ages icelandic tephra layers within deglacial ocean sediment cores from south of iceland have been detected and their timing with respect to the climate shifts of the last deglaciation constrained geochemical analysis of the tephra allowed the likely source volcanic systems to be identified the previously known saksunarvatn ash and vedde ash are recognised and described several other major tephra layers are examined basaltic eruption s of katla at 8 4 ka a basaltic eruption of katla at 12 6 ka a rhyolitic eruption of katla at 13 6 ka producing tephra similar in appearance and composition to the vedde ash a basaltic eruption of katla at 14 0 ka and two basaltic eruptions of grimsvotn at 14 6 ka and 15 0 ka abundant rhyolitic ash with a similar appearance and chemistry to the vedde ash is found throughout the deglacial interval predating the vedde ash by up to 3000 years supporting previous suggestions that there were pre vedde ash eruptions of rhyolite that may have contributed to north atlantic ash zone 1 this study expands the tephro stratigraphic framework of the north atlantic and provides a marine archive in which the timing of tephra layers useful as isochrons can be directly compared to major ocean and climate events of the last deglaciation furthermore by correlating tephra layers and abundance changes in the polar foraminifera neogloboquadrina pachyderma sinistral to equivalent tephra events and inferred abrupt cooling warming in greenland ice cores contemporaneous 14c dated planktonic foraminifera have been used to estimate changes in the surface radiocarbon reservoir age south of iceland consistent with previous studies larger surface reservoir ages are calculated during late heinrich stadial 1 and the younger dryas 2000 years and 800 1900 years respectively

the effect of orthophosphate on carbonate mineral dissolution rates in seawater the dissolution kinetics of a variety of synthetic and biogenic carbonates low mg calcite mg calcite and aragonite were investigated in gulf stream seawater salinity s 35 spiked with orthophosphate to a concentration of 50 m phosphate is known to inhibit calcite dissolution and has been reported to catalyze the dissolution of aragonite the main goal of the study was to assess whether the degree of inhibition depends on the mineralogy of the dissolving carbonate phase dissolution experiments were conducted at 25 c and a pco2 of 10 2 5 atm using the ph stat technique dissolution rates were measured at saturation states ranging from 0 1 to 0 8 times saturation with respect to the dissolving carbonate mineral and were compared to rates measured in low phosphate seawater the degree of inhibition caused by phosphate addition increased as saturation state with respect to the dissolving carbonate mineral increased at a saturation state of 0 2 addition of phosphate reduced dissolution rates by about a factor of 2 closer to equilibrium at a saturation state of 0 8 dissolution rates were reduced by about a factor of 4 more importantly all carbonate samples whether of synthetic or biogenic origin were inhibited to similar degrees at equivalent saturation states the catalysis reported by previous workers for synthetic aragonite appears to be an artifact of its anomalous non linear dissolution rate over time because phosphate inhibits the dissolution of different carbonate minerals to similar degrees selective dissolution of aragonite from metastable carbonate sediments cannot be promoted by the presence of orthophosphate

pb isotopes and geochemical monitoring of arctic sedimentary supplies and water mass export through fram strait since the last glacial maximum 1 elemental and pb isotope measurements were performed on leachates and residues from surface sediments and two 50 cm cores mc04 and mc16 collected along a ne sw transect through fram strait geochemical and isotopic properties of residues from surface sediments define three distinct spatial domains within the strait 1 the easternmost edge of the strait 2 the eastern part of the strait off the svalbard margins and 3 the western part of the strait influenced by supplies from svalbard the nordic seas with possible contributions from northwestern siberian margins and sea ice and water outflow from the arctic respectively core mc16 in the third domain beneath the outflowing arctic waters spans the last glacial maximum present interval sediments from this core were leached to obtain detrital residues and exchangeable leachates fractions detrital supplies to core mc16 are believed to originate mainly from melting of the overlying sea ice and thus can be used to document changes in arctic sedimentary sources detrital 206pb 204pb and 208pb 206pb ratios illustrate two mixing trends trends a and b corresponding to the pre and post younger dryas yd intervals respectively these trends represent binary mixtures with a common end member canadian margins and either a siberian trend a or greenland trend b margin end member the yd is marked by an isotopic excursion toward the canadian end member suggesting a very active beaufort gyre possibly triggered by massive drainage of the laurentide ice sheet pb isotope compositions of leachates thought to represent the signature of the overlying water masses define a unique linear trend coincident with trend a this suggests that water masses acquired their signature through exchange with particulate fluxes along the canadian and siberian continental margins

authigenic pb isotopes from the laurentian fan changes in chemical weathering and patterns of north american freshwater runoff during the last deglaciation climate dependent chemical weathering trends have a strong impact on the dissolved pb isotopic composition of continental runoff during glacial terminations so that this tracer can be used to reconstruct the impact of the north american deglaciation on aspects of freshwater runoff and ocean chemistry here we present authigenic fe mn oxyhydroxide derived pb isotope records from lower laurentian fan sediments that trace the local deglacial continental runoff signal through the gulf of st lawrence we use these records to investigate changes in the pb isotopic composition of the north american runoff and their relationship to deglacial processes the new pb isotope records are very similar to those from the subtropical deep nw atlantic locations though the new data are at higher resolution and exhibit much greater amplitudes of change due to their laurentide ice sheet proximal setting unradiogenic compositions 206pb 204pb as low as 18 8 at 18 5 ka during the latest glacial change towards highly radiogenic compositions during the early holocene 206pb 204pb 20 1 at 11 2 ka late holocene 206pb 204pb values return to intermediate values around 206pb 204pb 19 6 these new data support previous inferences that the pb isotopic composition of the deep atlantic is controlled during deglaciation by changes in the pattern and intensity of continental chemical weathering in more detail the most significant change in the entire pb isotope record starts at 12 5 ka and lasts until about 11 ka this observation of strong pb isotopic changes across a climatically cold period in the north atlantic region suggests that at this location pb isotopic compositions recorded in deep marine authigenic fe mn oxyhydroxides not only trace deglacial changes in chemical weathering intensity but also highly depend on major freshwater runoff routes in interior north america our data suggest a gradual opening of the eastward freshwater runoff route in the course of the younger dryas

atlantic meridional overturning and climate response to arctic ocean freshening 1 the global deglaciation event that followed last glacial maximum was punctuated by a sequence of rapid climate changes this began with the laurentide ice sheet derived calving event called heinrich event 1 continued with the bolling allerod warming that occurred synchronously with meltwater pulse 1a and was in turn followed by the younger dryas abrupt return to cold conditions although it has long been believed that these events are consequences of the response of atlantic meridional overturning circulation to freshwater inputs it has always been assumed that these inputs were applied directly to the atlantic ocean itself we address the question of how the atlantic meridional overturning circulation would have responded to the recently hypothesized addition of freshwater into the arctic ocean at the time of onset of the younger dryas and thereby demonstrate that this response is essentially identical to the response to north atlantic freshening

nd and pb isotope signatures of the clay size fraction of labrador sea sediments during the holocene implications for the inception of the modern deep circulation pattern holocene on the basis of sediment supply variations for the last 12 kyr three sources have contributed to the sediment mixture the north american shield the pan african and variscan crusts and the mid atlantic ridge clay isotope signatures indicate two mixtures of sediment sources the first mixture 12 2 6 5 ka is composed of material derived from the north american shield and from a young crustal source from 6 5 ka onward the mixture is characterized by a young crustal component and by a volcanic component characteristic of the midatlantic ridge since the significant decrease in proximal deglacial supplies the evolution of the relative contributions of the sediment sources suggests major changes in the relative contributions of the deep water masses carried by the western boundary undercurrent over the past 8 4 kyr the progressive intensification of the western boundary undercurrent was initially associated mainly with the transport of the northeast atlantic deep water mass until 6 5 ka and with the denmark strait overflow water thereafter the establishment of the modern circulation at 3 ka suggests a reduced influence of the denmark strait overflow water synchronous with the full appearance of the labrador seawater mass our isotopic data set emphasizes several changes in the relative contribution of the two major components of north atlantic deep water throughout the holocene index terms 4267 oceanography general paleoceanography 4558 oceanography physical sediment transport 1040 geochemistry isotopic composition chemistry 9325 information related to geographic region atlantic ocean 9604 information related to geologic time cenozoic keywords clay size fraction sedimentary mixings deep circulation nd and pb isotopes north atlantic labrador sea

glacial and oceanic history of the polar north atlantic margins an overview abstract the five year ponam polar north atlantic margin late cenozoic evolution programme was launched by the european science foundation in 1989 its aim was to study the major climate driven environmental variations in the norwegian greenland also nordic sea and its continental margins over the last 5 milliion years the programme has provided substantial new insights into the contrasting behaviour of the ice sheets covering the svalbard barents sea and east greenland over the last glacial interglacial cycle in particular the highly dynamic svalbard barents sea ice sheet after reaching the shelf edge during each stadial almost vanished during subsequent interstadials by contrast the east greenland ice sheet showed only minor advances confined to fjord basins or ending on the inner shelf although there is a striking correspondence in the timing and duration of the first post eemian ice advance in east greenland and on svalbard their chronology and dynamics have been very different since about 65 ka the svalbard barents sea ice sheet showed well defined middle and late weichselian ice advances whereas the east greenland ice sheet was characterised by a 55 kyr long period with a relatively stable ice margin located in fjords or the inner shelf the contrasting behaviour of the two ice sheets is probably linked to the palaeoceanographic circulation pattern in the polar north atlantic east greenland is under the influence of the cold east greenland current whereas the development and behaviour of ice in the barents sea is influenced by the continuous but highly variable north atlantic meridional current system that has resulted in a northward inflow of relatively warm waters of atlantic origin on the eastern side of the polar north atlantic of particular interest are the so called nordway events in glacial stages 6 and 4 to 2 these represented periods of pronounced inflow of temperate waters from the south and an associated increase in seasonally open waters providing moisture for ice sheet growth the largest of these events ended in major glaciations which were reflected in terrestrial glacial sequences and in deep sea records of ice rafted debris differences in ice extent and dynamics around the polar north atlantic are expressed in the evolution and architecture of its east and west continental margins the svalbard barents sea ice sheet developed much later than the east greenland ice sheet in the late pliocene as compared with the middle late miocene the svalbard barents sea margin is characterised by major prograding fans built mainly of stacked debris flows these fans are interpreted as products of rapid sediment delivery from fast flowing ice streams reaching the shelf break during full glacial conditions such major submarine fans are not found north of the scoresby sund fan off east greenland where ice seldom reached the shelf break sedimentation rates were relatively low and sediment transport appears to have been localised in several major deep sea submarine channel systems few debris flows are present and more uniform acoustically stratified sediments predominate in general the greenland ice sheet has been more stable than those on the european north atlantic margin which reflect greater variability in heat and moisture transfer at timescale varying from 100 000 year glacial cycles to millennial scale fluctuations

weathering fluxes and sediment provenance on the sw scottish shelf during the last deglaciation the reconstruction of past ice sheet dynamics can shed a light on long term ice stream activity and in turn provide constraints on the response of modern ice sheets to climate change the hebrides ice stream his flowed across part of the western scottish shelf to the shelf break during the last glacial cycle and drained a large portion of the northern sector of the british irish ice sheet to investigate the deglacial dynamics of the his following the last glacial maximum lead pb isotope records were extracted from the femn oxyhydroxide and detrital fractions of recovered laminated glacimarine mud sequences to monitor the changing activity of his during its retreat these provide timing and some source information of glacially weathered inputs to the marine environment the femn oxyhydroxide fraction in the samples is dominated by allochthonous particles pre formed and shows a marked decrease from radiogenic 20 05 206pb 204pb at 21 cal ka bp to less radiogenic pb isotope compositions 19 48 towards the windermere interstadial 15 4 13 ka this decrease represents a reduction in the flux of subglacially derived radiogenic pb to the continental shelf is interpreted as being associated with the break up of the ice stream in western scotland around that time the pb sr and nd isotopic signatures of the detrital fraction indicate a preponderance of moine sourced fine sediments originated from the nw highlands in the core locations from 21 to 15 cal ka bp dimlington stadial windermere interstadial most likely dictated by the orientation of ice flow tidal and oceanic current directions and sediment delivery in contrast ice rafted debris in a 21 cal ka bp old basal diamicton contains volcanic derived material suggesting different provenance for different grain sizes the femn oxyhydroxide 208pb 204pb ratio shows an unusual inversion relative to the other pb isotope ratios and is attributed to the introduction of secondary weathering phases from a source with contrasting 208pb 204pb but similar 206pb 204pb and 207pb 204pb in the detrital fraction the inversions are constrained to periodic spikes which may indicate an increased contribution from a high th u source potentially the neighbouring archaean amphibolitic lewisian basement in the outer hebrides this study demonstrates how geochemical investigation on continental shelves can be used to constrain the timing activity and flow sources of palaeo ice streams