postglacial emergence and distribution of late weichselian ice sheet loads in the northern barents and kara seas russia reconstructions of late weichselian glacier coverage on the continental shelves of the russian arctic range from a large ice sheet terminating in northern siberia to isolated ice caps restricted to arctic archipelagos this disparity in glacier reconstructions reflects the lack of chronological control on glacial and deglacial landforms we present new holocene relative sea level data from franz josef land and northern novaya zemlya russia that place the thickest glacier loads in the northern barents sea and not over novaya zemlya radiocarbon ages from shelf and terrestrial areas at the former ice sheet margin support deglaciation of the northern barents sea between 13 0 and 10 3 ka considerably later than inferred from isotopic records for the arctic ocean this analysis indicates that the barents sea ice sheet was a dominant sea level reservoir in northern eurasia and that glacier loading of novaya zemlya was comparatively limited during the last glaciation

impact of eastern arctic shelf waters on the nansen basin intermediate layers the eurasian shelves supply water to the nansen basin intermediate layers in two ways as buoyancy driven plumes of dense winter water and as permanent inflow of the barents sea branch of atlantic water while the plumes are local and seasonal phenomena the barents sea flow is part of the large scale circulation both interact with atlantic water which enters the arctic ocean through fram strait and moves as a subsurface boundary current eastward along the continental slope during the polarstern cruise ark ix 4 in summer 1993 the fram strait branch was observed as a narrow core within tens of kilometers of the barents sea shelf edge here several patches of cold low salinity water spread across the slope down to about 500 m depth their origin is assumed to be the northern barents sea they mix with the warm saline fram strait branch water fsbw so that the core properties of the latter become modified downstream in the eastern nansen basin the fram strait branch is displaced toward the inner basin by inflow of the barents sea branch of atlantic water bsbw this inflow appears as a broad 200 km wedge extending from 200 to 1300 m depth bsbw is colder and less saline than water of the fram strait branch and it is less dense and less stratified than the ambient water both branches appear to undergo vigorous mixing while spreading eastward so that any eastward continuation of the boundary flow transports about 50 bsbw and 50 fsbw above 600 m and about 80 bsbw and 20 fsbw below that level toward the canadian basin according to available observations the barents and kara seas are the only source areas for shelf waters ventilating the nansen basin below the halocline and these waters constitute a freshwater input rather than a salt input winter shelf water from the laptev sea cannot contribute to layers deeper than the upper halocline

the role of oceanic forcing in mid holocene northern hemisphere climatic change previous model investigations suggested that changes in orbital forcing and feedbacks associated with northward expansion of the boreal forest were both required to explain the full magnitude of enhanced high latitude northern hemisphere summer warming at 6 ka thus implying that biospheric feedbacks decreased planetary albedo associated with forest expansion may be large in the future foley et al 1994 tempo testing earth system models with paleo observations 1996 before the magnitude of past biospheric and other feedbacks can be estimated with confidence however the role of realistic high latitude oceanic forcing i e sea surface temperature sst increases and sea ice reductions should also be considered here we review existing paleoceanographic observations that suggest portions of the north atlantic were up to 4 c warmer than today at 6 ka we then combine our estimates of mid holocene north atlantic sst and sea ice conditions with new climate model simulations to suggest that a significant portion of high latitude summer warming at 6 ka in the northern hemisphere can be accounted for by altered orbital forcing ssts and sea ice relative to today our results underscore the importance of incorporating realistic boundary conditions when using paleoenvironmental data to evaluate the climate system s sensitivity to altered forcing and suggest that high latitude oceanic feedbacks were major contributors to enhanced high latitude summer warming in the northern hemisphere at 6 ka

central arctic surface ocean environment during the past 80 000 years stable oxygen and carbon isotope and sedimentological paleontological investigations supported by accelerator mass spectrometry 14 c datings were carried out on cores from north of 85 degrees n in the eastern central arctic ocean significant changes in accumulation rates provenance of ice rafted debris ird and planktic productivity over the past 80 000 years are documented during peak glacials i e oxygen isotope stages 4 and 2 the arctic ocean was covered by sea ice with decreased seasonal variation limiting planktic productivity and bulk sedimentation rates in early stage 3 and during termination i major deglaciations of the circum arctic regions caused lowered salinities and poor oxygenation of central arctic surface waters a meltwater spike and an associated ird peak dated to similar to 14 12 14 c ka can be traced over the southern eurasian basin of the arctic ocean this event was associated with the early and rapid deglaciation of the marine based barents sea ice sheet a separate termination ib meltwater event is most conspicuous in the central arctic and is associated with characteristic dolomitic carbonate ird this lithology suggests an origin of glacial ice from northern canada and northern greenland where lower paleozoic platform carbonates crop extensively out

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

holocene relative sea level history of franz josef land russia one of the largest uncertainties in ice volume changes during the late quaternary period is the extent of ice sheets over the barents and kara seas field research on central and eastern franz josef land russia provide new observations on postglacial emergence and deglaciation that further constrain the magnitude and timing of late weichselian glaciations radiocarbon dating of driftage from raised marine sequences place deglacial unloading prior to 9 4 ka at a number of localities within 1 to 2 km of the present glacier margin in situ shells from raised marine sediments yield 14c ages between 9 7 and 8 4 yr b p evidence that outlet glaciers were at or behind present margins by the early holocene period the altitude of the marine limit on franz josef land ranges from 49 to 20 m above sea level asl and is low compared to eastern svalbard 110 to 60 m asl the age of the marine limit ranges from 10 4 ka to ca 6 0 ka and exhibits greater diachrony where emergence is 35 m a low initial rate of emergence reflects glacio isostatic compensation offset by a eustatic rise in sea level and perhaps an additional component from renewed water loading of the barents sea after deglaciation the presence of raised beaches at 1 to 4 m asl that are 1 to 2 ka indicates that uplift is incomplete an exponential extrapolation of uplift data for franz josef land and eastern svalbard yields current maximum uplift estimates of 0 7 to 1 6 mm yr an inferred 5 5 m of uplift remaining these values are at least 50 to 80 lower than the inferred uplift residual for a modeled ice sheet in the barents and kara seas the discrepancy indicates that further refinement is needed for this ice sheet model the compilation of emergence data from franz josef land svalbard and novaya zemlya confine maximum glacio isostatic compensation to the barents sea comparatively minor ice sheet loads were over novaya zemlya and the southeastern barents sea emergence isobases since 5 and 9 ka descend northward across franz josef land indicating a diminishing glacio isostatic response into the arctic ocean

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

early preboreal cooling in the nordic seas region triggered by meltwater at the younger dryas preboreal transition a high resolution core from the northeastern norwegian sea reveals a two step warming of sea surface temperatures dated at respectively 10 200 10 000 and 9700 9500 14 c yr b p 11 450 11 350 and 11 150 11 000 cal yr b p warming was interrupted by a period having stable temperatures and a reduction in sea surface salinity and we suggest that this pause in warming was triggered by an increase in freshwater supply that may have hampered the north atlantic heat conveyor the freshwater influx correlates to an atmospheric cooling over both the greenland ice sheet and northwest europe and to cooling of surface temperatures in the nordic seas freshwater may have been supplied from the waning fennoscandian ice sheet

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

the impact of glaciation river discharge and sea level change on late quaternary environments in the southwestern kara sea sedimentary records from the southwestern kara sea were investigated to better understand the extent of the last glaciation on the eurasian arctic shelf sea level change and history of the ob and yenisey river discharge sediment core and seismic reflection data indicate that the quaternary depositional sequence in the southwestern kara sea consists of glacial glaciomarine and marine sedimentary units glaciogenic sediments in the deep novaya zemlya trough are presumably related to the last glacial maximum lgm whereas further east they may represent an earlier glaciation thus it is inferred that the southeastern margin of the lgm barents kara ice sheet was contained in the southwestern kara sea east of the novaya zemlya trough changes in mineralogical foraminiferal and stable isotopic composition of sediment cores indicate that riverine discharge strongly influenced sedimentary and biotic environments in the study area during the late weichselian and early holocene until ca 9 ka consistent with lowered sea levels subsequent proxy records reflect minor changes in the holocene hydrographic regime generally characterized by reduced riverine inputs

holocene glacial and climatic variations on spitsbergen svalbard holocene glacial and climatic variations have been inferred from investigations of sediment cores from the proglacial lake linnevatnet western spitsbergen a low content of glacially derived coal absence of regular laminations and a slow sedimentation rate in the lower part of the lacustrine sediments indicate that the former glaciers that existed within the catchment area during the last ice age melted quickly away as a result of the younger dryas holocene warming and during the next 6000 years there were no glaciers in the valley increasing coal content incipient laminations and rising sedimentation rates indicate that the glacier linnebreen started to form 4000 5000 years ago probably as a response to the late holocene cooling the holocene maximum extent of the glacier occurred during the little ice age starting with a pronounced ice advance in the thirteenth or fourteenth century a well dated core from billefjorden which is assumed to reflect glacial fluctuations in the inner part of the i

late quaternary paleochemistry of high latitude surface waters recent studies have stressed the role of high latitude nutrient levels and productivity in controlling the carbon isotopic composition of the deep sea and the co2 content of the atmosphere we undertook a study of the chemical composition of the polar planktonic foraminifer neogloboquadrina pachyderma s sinistral coiling from 30 late holocene samples and 49 down core records from the high latitude north and south atlantic oceans to evaluate the history of sea surface chemical change from glacial to interglacial time stable isotopic analysis of coretop samples from the atlantic pacific and southern oceans shows no significant correlation between the 13c of n pachyderma and either 13c or po4 in seawater conversely cd ca ratios in planktonic foraminifera are consistent with the po4 content of surface waters the level of maximum glaciation 18 000 yr b p identified by climap and 18o was chosen for mapping isopleths of 18o on n pachyderma s in the north atlantic reveal a pattern largely influenced by sea surface temperature s s t and generally support the s s t reconstruction of climap differences between the two suggest significantly lower salinity in north atlantic surface waters at high latitudes than in lower latitudes down core 13c records of n pachyderma confirm that low 13c values occurred in the northeast atlantic during the latest glacial maximum labeyrie and duplessy 1985 however a map of 13c for the 18 000 yr b p level for a much larger region in the north atlantic shows that minimum n pachyderma 13c occurred in temperate waters n pachyderma 13c decreased toward the southwest reaching a minimum of 1 at 37 n despite the variability seen in 13c records of n pachyderma none of our cores show significant temporal variability in cd ca from the combined cd ca and 13c data we can see no evidence for an upwelling gyre in the eastern north atlantic during the latest glacial maximum nor evidence that the southern and northern oceans had significantly different levels of preformed nutrients than today

oxygen isotope composition of living neogloboquadrina pachyderma sin in the arctic ocean data from the nansen basin of the arctic ocean are used to investigate the habitat and conditions under which the polar planktic foraminifer neogloboquadrina pachyderma sin calcifies the vertical distribution of 18o values of net sampled speciments together with their abundances and proportion of calcification are compared with 18o values from both water samples and foraminiferal tests from core top sediments within the nansen basin the average depth of habitat of n pachyderma sin changes from about 150 m in the southern part to about 80 m in the northern the average depth of calcification however in both regimes varies between 100 and 200 m water depth 18o data from net sampled n pachyderma sin are directly reflected in the core top sediment data but compared to equilibrium calcite 18o values derived from measurements of the ambient water a consistent offset of about 1 over all depth intervals is observed while in the southern part of the nansen basin advection through fram strait of planktic foraminifers from further south may play a role the data from the northern part of the nansen basin give clear evidence that the observed offset in 18o values is caused by a vital effect of n pachyderma sin

freshwater balance and the sources of deep and bottom waters in the arctic ocean inferred from the distribution of h218o data from sections across the eurasian basin of the arctic ocean occupied in 1987 and 1991 are used to derive information on the freshwater balance of the arctic ocean and on sources of the deep waters of the nansen amundsen and makarov basins using salinity h218o and mass balances we estimate the river runoff and the sea ice melt water fractions contained in the upper waters of the arctic ocean and infer pathways of the river runoff signal from the shelf seas across the central arctic ocean to fram strait the average mean residence time of the river runoff fraction contained in the arctic ocean halocline is determined to be about 11 to 14 years pacific water entering through bering strait is traced using silicate and its influence on the halocline waters of the canadian basin is estimated water column inventories of river runoff and sea ice melt water are calculated for a section just north of fram strait and implications of these inventories for sea ice export through fram strait are discussed comparison of the 18o 16o ratios of shelf water atlantic water and the deep waters of the arctic ocean indicate that the sources of the deep and bottom waters of the eurasian basin are located in the barents and kara seas

initialization of an ice sheet model for present day greenland we construct initial conditions for an ice flow model of the greenland ice sheet gris gris has been losing mass at an increasing rate over the past two decades and a significant proportion of this loss is due to dynamic thinning of narrow outlet glaciers we solve an inverse problem to estimate poorly known basal and englacial parameters given observed geometry and surface velocities a weighted cost function resolved to 4 km in the interior of the ice sheet and 1 km in regions of fast flowing ice at the margin is minimized to find two dimensional fields for a stiffness factor which is a coefficient of the effective viscosity and basal traction coefficient using these fields we run the model under present day climate to damp large amplitude short wavelength fluctuations in the flux divergence the time dependent model uses an adaptive mesh with resolution ranging from 8 km of the base grid to 500 m in areas of fast flowing ice to capture the behaviour of the main outlet glaciers the ice discharge calculated from the initial conditions for gris and individual glaciers compares well with values calculated from observations

the last deglaciation event in the eastern central arctic ocean oxygen isotope records of cores from the central arctic ocean yield evidence for a major influx of meltwater at the beginning of the last deglaciation 15 7 thousand years ago 16 650 calendar years b c the almost parallel trends of the isotope records from the arctic ocean the fram strait and the east greenland continental margin suggest contemporaneous variations of the eurasian arctic and greenland laurentide ice sheets or increased export of low saline waters from the arctic within the east greenland current during the last deglaciation on the basis of isotope and carbon data the modern surface and deep water characteristics and seasonally open ice conditions with increased surface water productivity were established in the central arctic at the end of termination lb about 7 2 thousand years ago or 6 000 calendar years b c

the influence of microhabitats on the carbon isotopic composition of deep sea benthic foraminifera we report 13c and 18o values for rose bengal stained benthic foraminifera from a set of box cores from continental margin environments in the atlantic and pacific oceans these isotopic results are compared with foraminiferal distribution data and pore water 13c profiles to evaluate the importance of environmental microhabitat effects on the carbon isotopic composition of benthic foraminifera the 13c values of infaunal taxa are consistently lower than those of epifaunal taxa suggesting that microhabitat effects on test composition do exist the 13c differences between foraminiferal carbonate and bottom water dissolved inorganic carbon are not correlated with the 18o differences between benthic foraminifera tests and equilibrium calcite but they do correlate with variations in the chemistry of sediment pore waters however interspecific 18o differences as well as 13c differences between species with similar vertical distributions in the sediments indicate that taxon specific vital effects also influence test composition

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

freshwater and atlantic water inflows to the deep northern barents and kara seas since ca 13 14 c ka foraminifera and stable isotopes foraminiferal stable isotopes and assemblages from franz victoria and st anna troughs provide a valuable record of freshwater and atlantic water flows to the northern barents and kara seas from deglaciation to present the d 18 o and d 13 c of planktonic neogloboquadrina pachyderma s and benthic elphidium excavatum were up to1 4 lower than present at ca 13 11 5 and 10 14 c ka global sea level corrected mostly reflecting substantial freshwater inputs coincident with glacial marine sediment deposition cassidulina teretis exceeded 40 of benthic foraminifera ca 13 and 10 14 c ka indicating subsurface penetrations of atlantic water the transition to postglacial marine conditions is marked by a 1 rise in foraminiferal d 18 o and a sharp fall in c teretis soon after 10 14 c ka these changes imply reduced inputs of freshwater and atlantic water subsequent isotopic and foraminiferal assemblage variations reflect changing atlantic water conditions upstream in the nordic seas and shifts between the warm fram strait and cold barents sea branches of atlantic water we hypothesize that glacial isostatically induced deepening by up to 150 m influenced atlantic water inflows to the northern barents sea during deglaciation and the holocene thus effects of isostatic recovery have to be factored into paleoceanographic reconstructions 2001 elsevier science ltd all rights reserved

glaciomarine sedimentation in epicontinental seas exemplified by the northern barents sea abstract sediments on high arctic shelves result from modern processes and the effect of former glaciations based on data from the northern barents sea an area with input from large and numerous surging glaciers we define two principal zones with different environmental regimes and corresponding sedimentary facies 1 a glacier proximal zone influenced by grounding line processes and the immediately adjacent areas affected by glacial sediment input and 2 a glacier distal sea ice and current controlled zone which also includes a wide sediment starved region dominated by biogenic carbonate accumulation characteristic of the glacier proximal zone are glacial surges which affect sedimentation rates and leave a diagnostic pattern of sea floor morphologies extensive ice gouging causes a homogeneous sediment texture in the glacier distal zone fine grained mud supplied from sea ice and infrequent coarser material deposited from icebergs is reworked by modern oceanographic processes on shallow banks in 30 50 m of water carbonates accumulate from a prolific bottom fauna formed in response to extensive reworking and nutrient supply

potential role of vegetation feedback in the climate sensitivity of high latitude regions a case study at 6000 years b p previous climate model simulations have shown that the configuration of the earth s orbit during the early to mid holocene approximately 10 5 kyr can account for the generally warmer than present conditions experienced by the high latitudes of the northern hemisphere new simulations for 6 kyr with two atmospheric mixed layer ocean models community climate model version 1 ccm1 and global environmental and ecological simulation of interactive systems version 2 genesis 2 are presented here and compared with results from two previous simulations with genesis 1 that were obtained with and without the albedo feedback due to climate induced poleward expansion of the boreal forest the climate model results are summarized in the form of potential vegetation maps obtained with the global biome model which facilitates visual comparisons both among models and with pollen and plant macrofossil data recording shifts of the forest tundra boundary a preliminary synthesis shows that the forest limit was shifted 100 200 km north in most sectors both ccmi and genesis 2 produced a shift of this magnitude genesis 1 however produced too small a shift except when the boreal forest albedo feedback was included the feedback in this case was estimated to have amplified forest expansion by approximately 50 the forest limit changes also show meridional patterns greatest expansion in central siberia and little or none in alaska and labrador which have yet to be reproduced by models further progress in understanding of the processes involved in the response of climate and vegetation to orbital forcing will require both the deployment of coupled atmosphere biosphere ocean models and the development of more comprehensive observational data sets

carbon isotope composition of tropical surface water during the past 22 000 years carbon isotope values of many species of planktonic foraminifera are size dependant values of 13c of individual size fractions are therefore an integration of low 13c values of calcite precipitated in the juvenile growth stage and high values precipitated in later stages in general the selection of a particular size fraction for downcore studies has been subjective analysis of different size fractions of planktonic foraminifera however yields different time series in downcore studies by measuring the 13c of many size fractions the 13c precipitated throughout the growth of the foraminifera can be calculated time series of the 13c of calcite precipitated in the late growth stages of planktonic foraminifera from two nearby cores from the caribbean sea result in a better correlation than time series of constant size fractions these 13c records indicate similar 13c values during the last glaciation and the late holocene and a broad deglacial minimum approximately synchronous with a minimum in the 13c records of benthic foraminifera from intermediate depth atlantic cores the deglacial minimum may be a reflection of the isotopic composition of the underlying intermediate water which may be affected by circulation changes or changes in preformed 13c values and or of the flux of water upwelled into the surface layer the small 0 2 to 0 0 glacial interglacial 13c difference in tropical surface water is also believed to be affected by the chemistry of the underlying source water

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

stable oxygen and carbon isotopes in planktic foraminifers from arctic ocean surface sediments reflection of the low salinity surface water layer planktic foraminifers neogloboquadrina pachyderma sin from 87 eastern and central arctic ocean surface sediment samples were analyzed for stable oxygen and carbon isotope composition additional results from 52 stations were taken from the literature the lateral distribution of 18o full size image 33 atlantic waters entering the arctic ocean through the fram strait 18o values decrease both to the barents shelf and to the north pole in accordance with the decreasing salinities of the halocline waters in the nansen basin a strong n s 18o gradient is in contrast with a relatively low salinity change and suggests contributions from different freshwater sources i e salinity reduction from sea ice meltwater in the south and from light isotope waters meteoric precipitation and river runoff in the northern part of the basin north of the gakkel ridge 18o and salinity gradients are in good accordance and suggest less influence of sea ice melting processes the 13c full size image 1 k values of n pachyderma sin from arctic ocean surface sediment samples are generally high 0 75 0 95 lower values in the southern eurasian basin appear to be related to the intrusion of atlantic waters the high 13c values are evidence for well ventilated surface waters because the perennial arctic sea ice cover largely prevents atmosphere ocean gas exchange ventilation on the seasonally open shelves must be of major importance lack of 13c gradients along the main routes of the ice drift from the siberian shelves to the fram strait suggests that primary production i e co2 consumption does probably not change the co2 budget of the arctic ocean significantly

recent calcium carbonate dissolution in the barents sea paleoceanographic applications abstract studies of benthic foraminifera in surface sediments of the arctic epicontinental barents sea show several indications of calcium carbonate dissolution low values of calcium carbonate correspond to low ratios of calcareous agglutinating foraminifera planktic benthic foraminifera high ratios of living dead foraminifera corroded calcareous foraminifera and high numbers of exposed organic linings of foraminifera dissolution increases eastwards and northwards in the study area we suggest that the dissolution is caused by the presence of dense cold saline and co 2 rich bottom water which is linked to sea ice production and the position of the oceanic polar front we also think calcium carbonate dissolution in this area indicates a sink for atmospheric co 2

the growth and decay of the late weichselian ice sheet in western svalbard and adjacent areas based on provenance studies of marine sediments the history of the late weichselian northwestern barents shelf including western svalbard has been investigated by provenance sedimentologist studies of five cores from the continental shelf and slope west of svalbard the chronostratigraphy of the cores is based on ams 14c dates and oxygen isotope analyses interpretations of the cores suggest that the ice sheets of western svalbard and northwestern barents sea experienced advances and retreats in two steps the first significant ice advance beyond the present coastline occurred ca 22 000 14c yr b p and was followed by an ice advance to the shelf edge ca 18 000 14c yr b p ice recession from the outer shelf and the southwestern barents sea began 14 800 14c yr b p and was followed by a second ice recession between 13 000 and 12 000 14 c yr b p during which ice withdrew from the inner shelf a minor readvance of the ice sheet on the shelf west of svalbard occurred close to 12 400 14c yr b p the first deglaciation event was associated with release of icebergs containing ice rafted detritus while the later episode also included significant amounts of meltwater and fine grained sediment

holocene relative sea level history of novaya zemlya russia and implications for late weichselian ice sheet loading abstract we present six new radiocarbon dated emergence curves that provide a detailed record of postglacial emergence of northern novaya zemlya and ages which constrain the emergence of vaygach island in the southern archipelago radiocarbon ages on hiatella sp from a lateral moraine in russkaya gavan and abundances of foraminifea in a marine core from nordenskiold bay 300 km south of our study area indicate that coastal deglaciation occurred prior to 10 000 cal yr b p however postglacial emergence commenced 7000 cal yr b p with stabilization of global sea level the total emergence is 13 11 m above sea level asl with apparent uplift rates of 1 2 mm yr for the past 2000 yr indicating modest glacier loads 11 000 cal yr b p deglaciation or both the isobase pattern showing no east west tilt across novaya zemlya and offshore moraines suggest a separate ice dispersal center over novaya zemlya for the later stages of the late weichselian glacial cycle and possibly earlier

late quaternary paleoceanography of the eurasian basin arctic ocean we reconstructed late quaternary deep 3000 4100 m and intermediate depth 1000 2500 m paleoceanographic history of the eurasian basin arctic ocean from ostracode assemblages in cores from the lomonosov ridge gakkel ridge yermak plateau morris jesup rise and amundsen and makarov basins obtained during the 1991 polarstern cruise modern assemblages on ridges and plateaus between 1000 and 1500 m are characterized by abundant relatively species rich benthic ostracode assemblages in part reflecting the influence of high organic productivity and inflowing atlantic water in contrast deep arctic eurasian basin assemblages have low abundance and low diversity and are dominated by krithe and cytheropteron reflecting faunal exchange with the greenland sea via the fram strait major faunal changes occurred in the arctic during the last glacial interglacial transition and the holocene low abundance low diversity assemblages from the lomonosov and gakkel ridges in the eurasian basin from the last glacial period have modern analogs in cold low salinity low nutrient greenland sea deep water glacial assemblages from the deep nansen and amundsen basins have modern analogs in the deep canada basin during termination 1 at intermediate depths diversity and abundance increased coincident with increased biogenic sediment reflecting increased organic productivity reduced sea ice and enhanced inflowing north atlantic water during deglaciation deep nansen basin assemblages were similar to those living today in the deep greenland sea perhaps reflecting deepwater exchange via the fram strait in the central arctic early holocene faunas indicate weaker north atlantic water inflow at middepths immediately following termination 1 about 8500 7000 year b p followed by a period of strong canada basin water overflow across the lomonosov ridge into the morris jesup rise area and central arctic ocean modern perennial sea ice cover evolved over the last 4000 5000 years late quaternary faunal changes reflect benthic habitat changes most likely caused by changes in the import of cold deepwater of greenland sea origin and warmer and middepth atlantic water to the eurasian basin through the fram strait and export of arctic ocean deepwater

deglacial meltwater discharge north atlantic deep circulation and abrupt climate change high resolution paleogeochemical data from the north atlantic ocean indicate that in the interval 15 000 to 10 000 14c years before present b p north atlantic deep water nadw production was decreased or eliminated four times at about 14 500 and probably older 13 500 12 000 and 10 500 years b p each of these changes occurred at the same time as abrupt events of meltwater discharge to the surface ocean inferred from oxygen isotope studies of planktonic foraminifera and from glacial geological studies on land in addition each of these times may be associated with brief episodes of cooler climate in the north atlantic region the best example of which is the younger dryas cooling of 10 500 years ago these results support models linking meltwater discharge decreased nadw production and decreased north atlantic heat flux

the distribution of living benthic foraminifera on the continental slope and rise off southwest norway abstract surface sediment samples taken by corer from 45 stations on the norwegian continental margin and in the norway basin have been investigated for their benthic foraminiferal content unlike previous studies the living benthic foraminiferal fauna was differentiated from empty tests comprising the foraminiferal death assemblage factor analysis of both the living and dead faunal data reveals six living species assemblages and five corresponding dead assemblages the additional living assemblage is characterized by the arenaceous speciescribrostomoides subglobosum that dominates between 1400 and 2000 m water depth but is rare in the dead faunal data trifarina angulosa and to a lesser extent cibicides lobatulus characterize the shallowest foraminiferal assemblage from 200 to 600 m water depth where it is associated with strong bottom currents and warm saline atlantic water of the north atlantic drift on the slope between 600 and 1200 m water depth themelonis zaandami species assemblage dominates particularly in areas characterized today by rapid sedimentation of terrigeneous material between 1000 and 1400 m depth where the slope is covered by fine grained organic rich terrigeneous mud the living foraminiferal assemblage is characterized bycassidulina teretis andpullenia bulloides below 1400 m three foraminiferal assemblages are found c subglobosum is found from 1400 to 2000 m cibicidoides wuellerstorfi andepistominella exigua predominantly live from 2000 to 3000 m water depth and below 3000 m oridorsalis umbonatus andtriloculina frigida dominate the fauna all of theelphidium excavatum tests found in this study and thecassidulina reniforme tests found above 500 m water depth were found to be reworked analysis of the sediment grain size distribution and the organic carbon content in surface samples from the deepest stations suggest that the abundance ofc wuellerstorfi ande exigua is positively correlated to relatively coarse caused by planktic foraminifera and organic rich sediments whereas high frequencies ofo umbonatus andt frigida coincide with low organic carbon content we suggest thatc wuellerstorfi is adapted to deep sea environments with relatively high food supply tolerating relatively low interstitial water oxygen content whereaso umbonatus may tolerate lower food supply prefering well oxygenated interstitial waters

the preboreal oscillation around the nordic seas terrestrial and lacustrine responses the occurrence of an early preboreal climatic cooling oscillation pbo in lacustrine and glacial records from northwest europe iceland and greenland is reviewed and documented the often subtle response of the proxy records to this oscillation in combination with its short duration make it difficult to detect owing to its chronostratigraphic position between the 10 000 9900 and 9600 9500 14 c plateaux c 11 300 11 150 calendar yr bp it is also difficult to 14 c date with precision we find that the vegetation response to the pbo varies between sites and regions in contrast to the pioneer vegetation in iceland and southern sweden the expanding birch pine forest in germany denmark was more susceptible to deteriorating growing conditions the combined lacustrine tree ring and glacial records imply that the pbo was characterised by cool and humid conditions throughout northwestern and central europe this is documented by vegetation changes decreased aquatic production increased soil erosion increased 2 h and 13 c content in tree rings readvances or stillstands of the ice sheet in norway and finland and ingression of brackish water into the baltic icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous preboreal period but not as extreme as during the younger dryas greenland records suggest that the early preboreal was characterised by ice readvances as an effect of cool climate and increased precipitation in relation to the younger dryas it was not until the end of the pbo that climate was warm enough to melt the land based ice sheet this preboreal oscillation found on both sides of the nordic seas is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the nordic seas which is implied by a simultaneous and distinct rise in the atmospheric 14 c 12 c ratio a slow down of the thermohaline circulation may tempor arily have pushed the polar front further south 1997 by john wiley sons ltd preboreal oscillation thermohaline circulation lacustrine records glacial records chronology

radiocarbon content of pre bomb marine mollusks and variations in the 14c reservoir age for coastal areas of the barents and kara seas russia fourteen mollusks collected alive between 1900 and 1945 from the russian barents and kara seas were analyzed by ams 14c dating to evaluate variations in the 14c marine reservoir for arctic coastal sites which is important for correcting ages in paleoenvironmental time series and advancing understanding of the exchange of carbon the 14c ages on the mollusks reveal a range of marine reservoir values r t from 159 14c yr to 764 14c yr the oldest r t values of 764 to 620 14c yr are for the bivalve portlandia arctica which often inhabit cold and low salinity waters and muddy substrates the depleted 14c content for this bivalve reflects possibly the incorporation of old carbon from freshwater inputs and or the consumption of old organic matter from the underlying sediments and pore waters other mollusks with sessile habitats and pelagic food sources gave significantly lower r t values between 159 and 344 14c yr the youngest r t values indicate enrichment in 14c and may partially reflect enhanced transfer of 14c enriched co2 from the atmosphere to the ocean surface with wind generated wave agitation this study underscores that a variety of processes can lead to variable 14c depletion and enrichment of surface waters yielding a ca 600 year age span for contemporaneous arctic mollusks there may be added uncertainty in the 14c reservoir correction for deposit feeder species such as portlandia sp and perhaps for certain benthic foraminifera e g nonion labradoricum because these taxa often incorporate old organic matter from the substrate a reservoir correction of 700 years may be more appropriate for infaunal deposit eater species particularly in glacier dominated environments mollusks and foraminifera with sessile habits and pelagic food sources should be selected preferentially for 14c dating because their shells may more closely reflect the 14c content of the global ocean mixed layer

modelling the influence of glacial isostasy on late weichselian ice sheet growth in the barents sea a fully integrated ice sheet and glacio isostatic numerical model was run in order to investigate the crustal response to ice loading during the late weichselian glaciation of the barents sea the model was used to examine the hypothesis that relative reductions in water depth caused by glacio isostatic uplift may have aided ice growth from scandinavia and high arctic island archipelagos into the barents sea during the last glacial two experiments were designed in which the bedrock response to ice loading was examined i complete and rapid glaciation of the barents sea when iceberg calving is curtailed except at the continental margin and ii staged growth of ice in which ice sheets are allowed to ground at different water depths model results predict that glacially generated isostatic uplift caused by an isostatic forebulge from loads on scandinavia svalbard and other island archipelagos affected the central barents sea during the early phase of glaciation isostatic uplift combined with global sea level fall is predicted to have reduced sea level in parts of the central barents sea by up to 200 m this reduction would have been sufficient to raise the sea floor of the central bank into a subaerial position such sea floor emergence is conducive to the initiation of grounded ice growth in the central barents sea the model indicates that prior to its glaciation the depth of the central deep would have been reduced from around 400 m to 200 m such uplift aided the migration of grounded ice from the central barents sea and scandinavia into the central deep we conclude that ice loading over scandinavia and arctic island archipelagos during the first stages of the late weichselian may have caused uplift within the central barents sea and aided the growth of ice across the entire barents shelf copyright 2000 john wiley sons ltd

late glacial and holocene paleoceanography and sedimentary environments in the st anna trough eurasian arctic ocean margin based on stratigraphical analysis of twelve sediment cores from the saint anna trough we reconstruct changes in paleoceanography and sedimentary environment during the last deglaciation and the holocene detailed analysis of benthic and planktic foraminiferal fauna stable oxygen and carbon isotope analysis lithostratigraphy and radiocarbon dates are used to reconstruct the following evolution after the deglaciation of the saint anna trough 13 300 yr b p until 9500 yr b p the environment was mainly characterised by low biogenic production carbonate dissolution and deposition of proximal to distal glaciomarine sediments intervals with high abundance of the benthic foraminifer cassidulina teretis may indicate influx of atlantic water at bottom the transition into the present interglacial started at 9500 yr b p reflected by increased production of foraminifera and bivalves after 8000 yr b p there was a marked drop in planktic 18o followed by a rise in planktic foraminifera and subsequently an increase of c teretis these paleoceanographic changes reflect increased heat transport into the area and are coupled to changes in nordic seas the early holocene warming of the saint anna trough were delayed by ca 2000 years relative to the northeast nordic seas early holocene sedimentation rates were relatively high 100 cm 1000 yr declining drastically after 8000 yr b p 50 cm 1000 yr this was presumably caused by reduction in winnowing and or riverine input

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

changes in the oceanic 13c 12c ratio during the last 140 000 years high latitude surface water records detailed records of the carbon and oxygen isotopic ratios of neogloboquadrina pachyderma are compared between nine high latitude sediment cores from the northern and southern hemispheres covering the last 140 000 yrs the strong analogies between the 13c records permit to define a 13c stratigraphic scale with three clear cut transitions simultaneous with the oxygen isotopic transitions 65 125 kyrs 54 65 kyrs and 21 13 kyrs the 13c records of n pachyderma in the high latitude cores which follow the changes in 13c of the surface water tco2 near areas of deep water formation present trends similar to the benthic foraminifera 13c records in cores v19 30 and m12 392 although amplitudes of the isotopic shifts are different this implies that a large part of the observed variations represents global changes in the carbon distribution between biosphere and ocean the 13c12c ratios of n pachyderma in the north atlantic cores display larger regional variations at 18 kyrs b p than at present to explain these differences we have plotted the 18 kyrs b p 13c values of n pachyderma from 17 cores distributed n of 40 n comparison with published surface water temperature distribution at 18 kyrs b p indicates that a strong divergent cyclonic cell centered approximatively 55 n and 15 w was active during most of the last ice age maximum this hydrology analogous to the present weddell sea explains the published evidences of bottom water formation if located on the northern flank of the gyre and the strong polar front on the southern flank probable location of intermediate water formation

environmental change in eastern greenland during the last 1300 years evidence from foraminifera and lithofacies in nansen fjord 68 n lithofacies and benthic foraminiferal analyses of two sediment cores bs1191 k13b and k14 from nansen fjord eastern greenland show evidence of changing oceanographic and sea ice conditions from

influence of insolation and glaciation on atmospheric circulation in the north atlantic sector implications of general circulation model experiments for the late quaternary climatology of europe abstract atmospheric general circulation models have been used to simulate the sensitivity of regional climates to late quaternary changes in insolation ice sheets and atmospheric co 2 model results for full glacial conditions 18 ka show the atlantic westerly jet strengthened and shifted south a corresponding southward shift of the icelandic low and a strengthening and northward shift of the subtropical anticyclone sta a glacial anticyclone developed over the european ice sheet and cold dry conditions prevailed over much of europe the full glacial climate anomaly for the north atlantic sector is explained by a combination of low atmospheric co 2 reducing global surface temperatures and circulation changes caused by the ice sheets by the early holocene 9 ka the ice sheets were much reduced while the orbital anomaly was near its maximum producing mid continental summer warming and winter cooling and a reduced latitudinal temperature gradient in the northern hemisphere in both seasons the jet and the icelandic low were displaced to north of their present position producing strong onshore flow and mild wet winters in northern europe while the sta was also shifted northwards producing offshore flow and dry summers in the same region during the late glacial transition the effects of insolation and glaciation were antagonistic for some features of the circulation and synergistic for others the model results suggest palaeoclimatic hypotheses that could be directly tested by comparison with palaeoclimatic data mapped at a synoptic scale

a multiproxy approach to reconstruct the environmental changes along the eurasian continental margin over the last 150 000 years abstract sediment cores located along the eurasian continental margin arctic ocean have been studied to reconstruct the environmental changes in terms of waxing and waning of the barents kara sea ice sheets atlantic water inflow and sea ice distribution over the last 150 kyr the stratigraphy of the cores is based on stable oxygen isotopes ams 14 c and paleomagnetic data we studied variations in marine and terrigenous input by a multiproxy approach involving direct comparison of sedimentological and organo geochemical data extensive episodes of northern barents sea ice sheet growth during marine isotope stages mis 6 and 2 have been supported by at least subsurface atlantic water inflow moisture bearing storms low summer insolation and minimal calving of ice ice advance during mis 4 was probably restricted to the shallow shelf between mis 4 and mis 2 large ice sheet fluctuations correspond to contemporary laurentide surging events and indicate short term climatic changes in the arctic ocean as has been recorded in lower latitudes in contrast in low precipitation areas in eastern eurasia glacial activity was rather limited only distinct ice rafted debris ird input during termination ii and early mis 3 reflects severe glaciations on the northern severnaya semlya margin during mis 6 and mis 4 we conclude that 1 oscillations of ice sheets are less frequent along the eastern eurasian margin than in areas with continuous moisture supply like the western eurasian margins and that 2 major fluctuations of the kara sea ice sheet during the last 150 kyr apparently followed the major interglacial glacial mis 5 4 and mis 7 6 transitions rather than the precession 23 kyr and the tilt 41 kyr cyclicity of the earth s orbit as observed for the scandinavian sis and the svalbard ice sheets respectively mangerud j jansen e landvik j y 1996 late cenozoic history of the scandinavian and barents sea ice sheets in solheim a riis f elverhoi a faleide j j jensen l n cloetingh s eds impact of glaciations on basin evolution data and models from the norwegian margins and adjacent basins global and planetary chance special issue 12 pp 11 26 surface and or subsurface atlantic water masses coupled with seasonally ice free conditions penetrated continuously to at least the franz victoria trough during the last 150 kyr however sustained periods of open water were largely restricted to substages 5 5 5 1 and the holocene as indicated by distinct carbonate dissolution and higher accumulation of marine organic matter mom signals of periodic open water conditions along the northern margin of severnaya semlya are of less importance higher production of foraminifera probably due to atlantic water inflow occurred between 38 and 12 14 c kyr and corresponds to periodic atlantic water advection penetrating into the arctic ocean however marine organic proxies indicate a continuous decrease of surface water productivity from the western to the eastern eurasian continental margin due to a more extensive sea ice cover over the last 150 kyr

calibration of stable isotopic data an enriched δ18o standard used for source gas mixing detection and correction we present empirically based calibrations of our measurements made on a finnigan mat252 equipped with a kiel device to vienna pee dee belemnite using an enriched 18o standard calibrations include corrections for biases caused by the differences in isotopic composition of carbonate standards measured on the two parallel extraction lines of the kiel device and for decreases in the isotopic difference between the reference and sample gas caused by mixing in the source after correcting for these biases the precision of 2200 nbs19 analyses 10 300 g is 0 07 for 18o and 0 03 for 13c we have shared our standard enriched in 18o with 18 laboratories engaged in paleoceanographic research producing the first large scale interlaboratory calibrations for this community using correction procedures reported here water mass reconstructions using data produced on multiple mass spectrometers may now be possible with a precision approaching the level necessary to reconstruct temperature salinity and density variability in the deep ocean

the late weichselian glaciation of the franz victoria trough northern barents sea ice sheet extent and timing high resolution seismic profiles parasound 4 khz and three sediment cores from the franz victoria trough and the adjacent continental slope were studied in order to constrain the timing and extent of the northern svalbard barents sea ice sheet during the late weichselian glaciation stacked debris flow lobes and layers of glacimarine diamicton on the lower continental slope indicate that large quantities of glacially derived sediments were deposited by the northern svalbard barents sea ice sheet directly onto the upper continental slope at approximately 23 14 c ka a grounding line advance to the shelf break is supported by the identification of diamicton interpreted as till in the seismic profile near the shelf break after several ice sheet instabilities marked by significant input of ice rafted detritus to the continental margin the disintegration of the northern svalbard barents sea ice sheet termination ia is indicated by a distinct pulse of ice rafted detritus at 15 4 14 c ka and the transition to an isotopically defined meltwater signal the drastic change in sedimentary pattern on the upper continental slope dated to about 13 4 14 c ka is interpreted as grounding line retreat from the shelf edge a further stepwise retreat of the northern svalbard barents sea ice sheet is indicated by pulses of ice rafted detritus which appear to be contemporaneous with the onset of distinct ice rafting events in adjacent areas and pulses of glacimarine sedimentation in the southwestern barents sea q 2000 elsevier science b v all rights reserved

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

late quaternary stratigraphy of western yamal peninsula russia new constraints on the configuration of the eurasian ice sheet ice sheet reconstructions for the last glacial maximum in northern eurasia range from nearly complete coverage by a contiguous marine based ice sheet to large unglaciated areas stratigraphic records from yamal peninsula russia provide new insight on the eastern limit of the eurasian ice sheet in the kara sea radiocarbon and infrared stimulated luminescence ages from coastal cliff sections date the emplacement of the kara diamicton as older than ca 40 ka reflecting regional glaciation ice wedge growth peat accumulation and eolian and fluvial deposition characterized the past 40 k y and do not support coverage of yamal peninsula by an ice sheet or proximity to a glacier margin thus the late weichselian eurasian ice sheet was largely confined to barents sea and its global sea level contribution is reduced to 7 m of sea level equivalent

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

living benthic foraminifers from the central arctic ocean faunal composition standing stock and diversity abstract fifty short sediment cores collected with a multiple corer and five box cores from the central arctic ocean were analysed to study the ecology and distribution of benthic foraminifers to work out living faunal associations standing stock and diversity separate analyses of living rose bengal stained and dead foraminifers were carried out for the sediment surface the size fractions between 63 and 125 m and 125 m were counted separately to allow comparison with former arctic studies and with studies from the adjacent norwegian greenland sea barents sea and the north atlantic ocean benthic foraminiferal associations are mainly controlled by the availability of food and competition for food while water mass characteristics bottom current activity substrate composition and water depth are of minor importance off spitsbergen in seasonally ice free areas high primary production rates are reflected by high standing stocks high diversities and foraminiferal associations 125 m that are similar to those of the norwegian greenland sea generally in seasonally ice free areas standing stock and diversity increase with increasing food supply in the central arctic ocean the oligotrophic permanently ice covered areas are dominated by epibenthic species the limited food availability is reflected by very low standing stocks and low diversities most of these foraminiferal associations do not correspond to those of the norwegian greenland sea the dominant associations include simple agglutinated species such as sorosphaerae placopsilinellae komokiacea and aschemonellae as well as small calcareous species such as stetsonia horvathi and epistominella arctica those of the foraminiferal species that usually thrive under seasonally ice free conditions in middle bathyal to lower bathyal water depth are found under permanently ice covered conditions in water depths about 1000 m shallower if present at all

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

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

in situ raman spectroscopic investigation of the hydrothermal speciation of tungsten implications for the ore forming process abstract knowledge on hydrothermal tungsten w species is vital towards a better understanding of tungsten transport and mineralization mechanisms in this study in situ raman spectra of a 0 005 0 1 mol kg m k2wo4 solution containing co2 hcl and nahco3 were collected at 50 400 c and 20 60 mpa the spectra for the symmetric stretching vibration mode of the w o bond v1 w o were analyzed to investigate the hydrothermal tungstate species results showed that carbonate bicarbonate do not associate with tungstate to form carbonic tungstate species nevertheless the presence of co2 can increase the fluid acidity which favors the formation of polymeric tungstate species at o modes of these species are centered at 930 cm 1 and 950 cm 1 based on the above observations we simulated the mineralization process in the context of fluid rock interactions using tungstate and alkali tungstate ion pairs as the only aqueous w species the thermodynamic simulations showed that a the timing of mineralization mainly depends on the w concentration in the initial mineralizing fluid and the availability of ca2 fe2 and mn2 with higher w concentrations generally favoring higher temperature mineralization b highly w enriched fluid is not essential for w mineralization while extremely low contents of fe mn and ca in the magma are useful to maintain the mobility of aqueous w until favorable host rocks are encountered and c a hydrogen reservoir effect was identified for dissolved co2 the presence of co2 can promote the extraction of fe ii from the pelitic host rocks thereby facilitating a high grade vein type w mineralization at o modes are centered at 965 995 cm 1 are important hydrothermal w species along with monomeric tungstates therefore polymeric tungstate species should be considered in future thermodynamic modeling of w transport and mineralization at

surface water changes in the norwegian sea during last deglacial and holocene times stable carbon and oxygen isotopes of the polar planktic foraminifera neogloboquadrina pachyderma sinistral from sediment cores of the norwegian sea reveal several anomalous 13c and 18o depletions in the surface water during the last glacial to interglacial transition and during the later holocene the depletions that are observed between the last glacial maximum lgm and the end of the main deglacial phase were caused by massive releases of freshwater from thawing icebergs which consequently resulted in a stratification of the uppermost surface water layer and a non equilibrium between the water below and the atmosphere at 8 5 ka 14c bp this strong iceberg melting activity ceased as defined by the cessation of the deposition of ice rafted detritus after this time the dominant polar and subpolar planktic foraminiferal species rapidly increased in numbers however this post deglacial evolution towards a modern type oceanographic environment was interupted by a hitherto undescribed isotopic event 7 8 ka which on a regional scale is only identified in eastern norwegian sea surface water this event may be associated with the final pulse of glacier meltwater release from fennoscandia which affected the onset of intensified coastal surface water circulation off norway during a time of regional sea level rise all these data indicate that surface water changes are an integral part of deglacial processes in general yet the youngest observed change noted around 3 ka gives evidence that such events with similar effects occur even during the later holocene when from a climatic point of view relativelystable conditions prevailed

quaternary paleoceanography of the deep arctic ocean based on quantitative analysis of ostracoda abstract ostracodes were studied from deep arctic ocean cores obtained during the arctic 91 expedition of the polarstern to the nansen amundsen and makarov basins the lomonosov ridge morris jesup rise and yermak plateau in order to investigate their distribution in arctic ocean deep water aodw and apply these data to paleoceanographic reconstruction of bottom water masses during the quaternary analyses of coretop assemblages from arctic 91 boxcores indicate the following ostracodes are common at all depths between 1000 and 4500 m and species distribution is strongly influenced by water mass characteristics and bathymetry quantitative analyses comparing eurasian and canada basin assemblages indicate that distinct assemblages inhabit regions east and west of the lomonosov ridge a barrier especially important to species living in lower aodw deep eurasian basin assemblages are more similar to those living in greenland sea deep water gsdw than those in canada basin deep water two upper aodw assemblages were recognized throughout the arctic ocean one living between 1000 and 1500 m and the other having high species diversity at 1500 3000 m downcore quantitative analyses of species abundances and the squared chord distance coefficient of similarity reveals a distinct series of abundance peaks in key indicator taxa interpreted to signify the following late quaternary deep water history of the eurasian basin during the last glacial maximum lgm a gsdw aodw assemblage characteristic of cold well oxygenated deep water 3000 m today inhabited the lomonosov ridge to depths as shallow as 1000 m perhaps indicating the influence of gsdw at mid depths in the central arctic ocean during termination 1 a period of high organic productivity associated with a strong inflowing warm north atlantic layer occurred during the mid holocene several key faunal events indicate a period of warming and or enhanced flow between the canada and eurasian basins a long term record of ostracode assemblages from kastenlot core ps2200 5 1073 m water depth from the morris jesup rise indicates a quasi cyclic pattern of water mass changes during the last 300 kyr interglacial ostracode assemblages corresponding to oxygen isotope stages 1 5 and 7 indicate rapid changes in dissolved oxygen and productivity during glacial interglacial transitions

stable isotopes in planktonic and benthic foraminifera from arctic ocean surface sediments oxygen and carbon isotopic analyses have been performed on the tests of planulina wuellerstorfi and three size fractions of sinistral neogloboquadrina pachyderma recovered from 33 arctic ocean surface sediment samples stable isotopic compositions of n pachyderma are found to be dependent on the test size larger specimens show considerable enrichment in both 18o and 18c the difference between the isotopic compositions of the 63 125 and 125 250 m size fractions in n pachyderma can be explained by biogenic fractionation effects during foraminiferal test growth larger 250 500 m n pachyderma displayed accretions of secondary calcite i e the outermost shell contained significant amounts of inorganically precipitated magnesium calcite thus larger foraminifera may not be suited for down core stable isotopic studies there is a difference of 2 between 18o values of surface samples from the eastern and western arctic ocean reflecting large differences between surface water salinity in these re

temperature accumulation and ice sheet elevation in central greenland through the last deglacial transition we present a combined heat and ice flow model constrained by measurements of temperature in the greenland ice sheet project 2 gisp2 borehole and by the gisp2 18o record and depth age scale which determines a history of temperature accumulation rate and ice sheet elevation for the past 50 000 years in central greenland important results are that the temperature increase from average glacial to holocene conditions was large approximately 15 c with a 20 c warming from late glacial to holocene that the average accumulation rate during the last glacial maximum between 15 and 30 kyr b p was 5 5 to 7 cm yr 1 approximately 25 of the modern accumulation rate that long term 500 1000 years averaged accumulation rate and temperature have been inversely correlated during the most recent 7 millennia of the holocene and that the greenland ice sheet probably thickened during the deglacial transition the inverse correlation of accumulation rate and temperature in the mid and late holocene suggests that the greenland ice sheet is more prone to volume reduction in a warmed climate than previously thought and demonstrates that accumulation rate is not a reliable proxy for temperature the elevation history of the ice sheet is poorly constrained by the model and independent evidence is needed we also present a simple estimate of the response time for thinning of the interior region of an ice sheet due to retreat of its margins this was approximately 1900 years for central greenland during deglaciation

holocene vegetational history and climatic change in west spitsbergen plant macrofossils from skardtjorna an arctic lake macrofossil analyses of a 335 cm long core from skardtjorna a small lake on the west coast of spitsbergen svalbard are presented the known processes of deposition of plant remains to arctic lake sediments are summarised and used in the interpretation of the vegetation history at skardtjorna the basal sediment is ams dated to 8110 110 bp the rest of the profile is dated by palaeomagnetic correlation the lowest sediments have the greatest macrofossil concentration and numbers of taxa per sample the occurrences of cassiope hypnoides and salix cf glauca before 4000 bp indicate a mean july temperature for the early holocene about 2 c higher than today comparable to the cassiope tetragona vegetation zone of the mid arctic region of the inner fjords increasing climatic severity resulted in the threshold from the cassiope to the dryas vegetation zone being passed at about 2500 bp the inferred climatic history at skardtjorna is compatible with other evidence from svalbard and elsewhere in the arctic

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