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

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

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

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

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

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

the use of stable oxygen and carbon isotope stratigraphy as a dating tool abstract oxygen isotope stratigraphy in foraminifera from deep sea sediments provides a time series record of globally synchronous events with a resolution of a few thousand years for the quaternary despite deficiencies from problems of discerning local from global effects and from isotopic disequilibria and ecological effects oxygen isotope stratigraphy remains a highly powerful tool for dating and correlating deep sea sediments as well as for paleoclimatology in general oxygen isotope records per se do not provide absolute age control although carbon isotope records in some respects are more difficult to interpret than oxygen isotopes and are influenced by local factors such as biological productivity ocean ventilation rates and foraminiferal ecological factors carbon isotope records also reflect global phenomena they can therefore be utilized for correlation and dating purposes in a manner similar to oxygen isotope records and provide additional age control especially in areas where the oxygen isotope records may be influenced by temperature and low salinity overprints

memory enhanced plasticity modeling of sand behavior under undrained cyclic loading abstractthis work presents a critical state plasticity model for predicting the response of sands to cyclic loading the well known bounding surface sanisand framework by dafalias and manzari is en

late weichselian submarine debris flow deposits on the bear island trough mouth fan sedimentary processes on the bear island trough mouth fan during the last glacial were studied using high resolution reflection seismics and gravity cores the fan succession is dominated by large debris flow deposits of up to 24 km in width and 50 m thick debris lobes can be followed over 100 km downslope and the largest cover an area of 1880 km2 the large debris flows were generated when the barents sea ice sheet reached the shelf break glacigenic sediments transported to the grounding line were temporarily stored on the upper slope due to the high sedimentation rate the sediments were unstable and earthquakes oversteepening and or build up of excess pore pressure triggered sediment release generating large debris flows sediments were also eroded and incorporated during the downslope flow debris flows were the most important sediment distributing process due to the relatively high shear strength low flow mobility of the glacigenic diamicton and the low fan gradient the weichselian evolution of the fan was characterized by a relatively low sedimentation rate during the early and mid weichselian the barents sea ice sheet might have reached the shelf break twice during the late weichselian on average one large debris flow comprising 18 km3 of sediments was released between every 35 to 75 years during the last glacial maximum

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

modeling the effect of freshwater pulses on the early holocene climate the influence of high frequency climate variability freshwater 4 67 10 14 m 3 into the labrador sea at three different constant rates 1 5 sv 1 sv 1 10 6 m 3 s 1 i n 10 years 0 75 sv in 20 years and 0 3 sv in 50 years for each rate five ensemble experiments have been performed varying in initial conditions the freshwater pulses produce a weakening of the thermohaline circulation the perturbed state is in agreement with proxy evidence for the 8 2 ka event two types of recovery of the thermohaline circulation occurred differing in time scale 1 200 years and 2 200 years in the experiments with 10 year and 20 year pulses both types of recovery were observed this suggests that the model response is unpredictable in the range of parameters studied here it is hypothesized that the unpredictability is associated with annual to decadal climate variability our results demonstrate that several types of recovery may exist with the same kind of perturbation the interpretation of events observed in proxy data may be thus more complex than realized until now since the magnitude and duration of climatic events caused by freshwater pulses is likely to depend strongly on nonlinear dynamics inside the coupled atmosphere sea ice ocean system index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4255 oceanography general numerical modeling 4532 oceanography physical general circulation 4215 oceanography general climate and interannual variability 3309 9325 information related to geographic region atlantic ocean keywords holocene thermohaline circulation predictability meltwater coupled climate model

oceanic evidence for coherent fluctuations in fennoscandian and laurentide ice sheets on millennium timescales proxy temperature records from greenland ice cores1 2 and north atlantic sediment cores3 have provided evidence for a high degree of climate instability during the last glacial period much of this variability seems to be linked with the dynamics of the laurentide ice sheet that covered north america at this time3 which dis charged iceberg flotillas into the north atlantic that are now recorded in sediment cores as heinrich events4 how if at all this variability was manifested on the other side of the atlantic in the nordic seas and the ice sheets of northwest europe and scandinavia has been unclear here we present sediment micro fossil and oxygen isotope data from a sediment core in the norweg ian sea which reveal cooling events and iceberg discharges analogous to heinrich events we show that these climate fluctua tions in the norwegian sea were in phase or were phase locked with air temperatures over greenland suggesting that the rapid changes in heat fluxes in the north atlantic recorded in previous records3 were felt in this high latitude region the iceberg dis charges in our record seem to have come from the fennoscandian ice sheet implying that this and the laurentide ice sheets fluctu ated coherently on timescales shorter than those of milankovitch orbital cycles

water mass exchange between the north atlantic and the norwegian sea during the past 28 000 years the greenland iceland and norwegian gin seas are important regulators of heat transport in the northern hemisphere and of ocean atmosphere co2exchange1 5 rapid changes in the circulation of surface and deep waters in this region may induce nonlinear climatic effects and climate instabilities2 3 here we present carbon and oxygen isotope data that provide a record of circulation changes in the gin seas during and at the termination of the last glacial maximum lgm inflow of nutrient depleted waters from the gin seas to form intermediate waters of the north atlantic resulted in nutrient enrichment of north atlantic deep water and consequent enhanced drawdown of atmospheric co2 contributing to the lower atmospheric during the lgm the onset of deglaciation occurred at a time of low salinity in the gin seas and thus of reduced thermohaline circulation although strong thermohaline circulation was later reinitiated in the north atlantic as deglaciation proceeded it cannot therefore have caused the onset of warming similarly we find that rapid changes in thermohaline circulation cannot account for the transient return to a cooler climate during the younger dryas episode

stable isotope differences among morphotypes of neogloboquadrina pachyderma ehrenberg implications for high latitude palaeoceanographic studies summary the stable isotopic composition of planktonic foraminifera plays a paramount role in interpretations of past oceanographic and environmental conditions thus an accurate understanding of the factors which influence their isotopic composition is essential in order to increase the palaeoceanographic utility of the high latitude planktonic foraminifera neogloboquadrina pachyderma its shape and oxygen and carbon isotopic variability are quantitatively described in this study over 8200 specimens of n pachyderma from 36 gravity and piston core tops from surface sediments of the north atlantic and southern indian oceans were digitized and analysed via fourier series in closed form the morphological results are presented in detail elsewhere and are utilized in this study to select specimens for isotopic analyses significant isotopic differences exist between morphological variants of this important high latitude speaes specimens become depleted in both oxygen and carbon isotopes as the test shape becomes more pentagonal and less quadrate the isotopic differences cannot be attributed to test thickening nor to size or coiling direction this observation has important implications in the use of this speaes as a tracer in high latitude palaeoceanographic investigations in particular future isotopic investigations utilizing this species should analyse single forms to allow for clear interpretation of palaeoceanographic signals

reef drowning during the last deglaciation evidence for catastrophic sea level rise and ice sheet collapse elevations and ages of drowned acropora palmata reefs from the caribbean atlantic region document three catastrophic metre scale sea level rise events during the last deglaciation these catastrophic rises were synchronous with 1 collapse of the laurentide and antarctic ice sheets 2 dramatic reorganization of ocean atmosphere circulation and 3 releases of huge volumes of subglacial and proglacial meltwater this correlation suggests that release of stored meltwater periodically destabilized ice sheets causing them to collapse and send huge fleets of icebergs into the atlantic massive inputs of ice not only produced catastrophic sea level rise drowning reefs and destabilizing other ice sheets but also rapidly reduced the elevation of the laurentide ice sheet flipping atmospheric circulation patterns and forcing warm equatorial waters into the frigid north atlantic such dramatic evidence of catastrophic climate and sea level change during deglaciation has potentially disastrous implications for the future especially as the stability of remaining ice sheets such as in west antarctica is in question

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

quaternary tephrachronology on the iceland plateau north of iceland four major ash zones recorded in piston cores raised from the iceland plateau north of iceland are shown to be coincident with the last four interglacial isotopic stages their geochemical composition links the ashes to volcanic events on iceland the occurrence of these ash layers which record events orders of magnitude larger than the normal holocene volcanic eruptions can not be explained by changes in sea ice cover and atmospheric circulation alone it is suggested that these events are related to pressure releases in the magma chambers resulting from major deglaciations of the icelandic ice cap

patterns of ice rafted detritus in the glacial north atlantic 40 55 n the observation by heinrich 1988 that during the last glacial period much of the input of ice rafted detritus to the north atlantic sediments may have occurred as a succession of catastrophic events rekindled interest on the history of the northern ice sheets over the last glacial period in this paper we present a rapid method to study the distribution of these events both in space and time using whole core low field magnetic susceptibility we report on approximately 20 cores covering the last 150 to 250 kyr well defined patterns of ice rafted detritus appear during periods of large continental ice sheet extent although these are not always associated within their maxima most of the events may be traced across the north atlantic ocean for the six most recent heinrich layers hl two distinct patterns exist hl1 hl2 hl4 hl5 are distributed along the northern boundary of the glacial polar front over most of the north atlantic between 40 and 50 n hl3 is more restricted to the central and eastern part of the northern atlantic the nd sr isotopic composition of the material constituting different heinrich events indicates the different provenance of the two patterns hl3 has a typical scandinavia arctic icelandic young crust signature and the others have a large component of northern quebec and northern west greenland old crust material these isotopic results obtained on core su 9008 from the north american basin are in agreement with the study by jantschik and huon 1992 who used k ar dating of silt and clay size fractions of an eastern basin core me 68 89 these data confirm the large spatial scale of these events and the enormous amount of ice rafted detritus they represent

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

structure and timing of the last deglaciation oxygen isotope evidence foraminiferal oxygen isotope data from 24 tropical atlantic sediment cores constrained by 77 14c dates are stacked to form a composite record of isotopic termination 1 this record indicates that most of the isotopic transition at the end of the last ice age occurred between 14 ka bp and 6 ka bp minor isotopic expression of deglaciation is permitted as early as 16 ka bp but the most rapid rate of change occurred between 14 ka bp and 12 ka bp three steps of maximum change are present although they are close to the statistical limits of detection in the composite record the clear presence of the steps in individual records suggests that they are real we estimate their timing at 14 12 ka bp termination 1 a 10 9 ka bp termination 1 b and 8 6 ka bp termination 1 c centering of the termination near 11 ka bp is consistent with the milankovitch hypothesis that high summer insolation caused deglaciation in detail however maximum rates of change prior to the 11 ka bp insolation extreme and the inferred steps require additional mechanisms controlling the tempo of glacial interglacial climate change steps equivalent to those in 18o have not been detected in ice margin retreat data steps in the isotopic transition if real may record thinning of the ice sheets not accompanied by loss of area alternation between near equilibrium and near stagnant ice sheet profiles during deglaciation is hypothesized perhaps due to calving and unstable down draw of the ice sheets followed by partial re equilibration significant problems remain the effects of temperature on the isotope record are only partially constrained presently available data allow only semi quantitative intercalibration of ice volume sea level and isotopic estimates of glaciation

environmental variability off ne greenland western fram strait during the past 10 600 years to reconstruct the climatic and paleoceanographic variability offshore northeast greenland during the last 10 ka with multidecadal resolution sediment core ps93 025 from the outermost north east

stable oxygen and carbon isotopes in planktonic foraminifera neogloboquadrina pachyderma in the arctic ocean an overview of published and new surface sediment data abstract a summary study on oxygen and carbon stable isotopes in planktonic foraminifera from arctic ocean floor appeared in marine geology 20 years ago spielhagen and erlenkeuser 1994 we revisit this topic with a wealth of new data focused on the western amerasian arctic a spotlight in the current climatic and oceanic change neogloboquadrina pachyderma the most abundant polar planktonic foraminiferal species is an important tool for reconstructing surface subsurface water changes in the arctic our new data on n pachyderma 150 250 m from the surface sediments show 18 o and 13 c values of 18 o and 13 c are both influenced by complex water sources water column structure and foraminiferal depth habitat the observed distribution of n pachyderma stable isotopes confirms a shallow habitat of this species in the sea ice covered central arctic especially in the canada basin probably in relation to the shallow chlorophyll maximum the associated light n pachyderma 18 o reflects the long term storage of fresh water at the shelf break a deeper dwelling of n pachyderma with heavier 18 o is supported by a more extensive photic zone and nutrient availability air sea exchange plays an important role in 13 c distribution and is consistent with heavy n pachyderma 13 c in the perennially ice covered central arctic ocean light 13 c composition at the shelf break is additionally influenced by shelf bottom waters enriched in isotopically light remineralized terrestrial carbon distribution of foraminiferal 13 c on the chukchi shelf reflects primary production patterns in the area

sea surface conditions in the southern nordic seas during the holocene based on dinoflagellate cyst assemblages dinoflagellate cyst dinocyst records from the southern nordic seas were compiled in order to evaluate the evolution of upper ocean conditions on a millennial timescale and supported by a highly resolved record from the voring plateau after the transitional phase from the last deglaciation three main phases define the holocene the early holocene 7 5 ka bp features important numbers of cool temperate species dominated by nematosphaeropsis labyrinthus and impagidinium pallidum in the west the assemblage composition changes drastically at the transition from the early to the mid holocene from when on operculodinium centrocarpum dominates the changeover is dated between 6 1 and 7 5 ka bp perhaps earlier closer to the iceland scotland ridge and appears to be linked to the onset of a modern type of surface circulation warmest assemblages occur at the voring plateau shortly after the transition when atlantic waters also appear to have spread farthest westward the recurrence of colder elements can be linked to cooling from 2 4 ka bp at the voring plateau and presumably earlier in the west but is difficult to date there because of the low sedimentation rates this is a general issue in many areas of the nordic seas and appears to have an important effect on cyst concentrations and assemblage composition with the possible loss of oxygenation sensitive cysts in the older parts of the cores comparing dinocyst based quantitative reconstructions with those retrieved from other plankton reveals a significantly different trend between proxies linked to a differing autecological response to seasonal changes at their respective depth habitats

holocene north atlantic surface circulation and climatic variability evidence from diatom records diatom analyses have been performed on a 425cm long holocene marine sediment sequence from the north atlantic south of iceland and a 920cm sediment core spanning the last c 7500 years from skalafjord faeroe islands additional core data include stable isotopes and results from magnetic susceptibility measurements while chronostratigraphic control has been provided by ams 14c measurements the diatom records reveal distinct changes in north atlantic surface circulation and climate that have been correlated with published terrestrial and marine records initial holocene warming is dated at 9900 14c years bp and after a preboreal cold spell enhanced north atlantic current activity and warming prevailed from 9600 to 8800 14c years bp from 8800 to 8000 4c years bp the advection of warm atlantic water masses weakened presumably under atmospheric circulation conditions characterized by a dominating negative nao prior to the holocene climatic optimum 6000 5000 14c years bp distinct hydrographic gradient

late quaternary stage 2 and 3 meltwater and heinrich events northwest labrador sea two major meltwater events are documented in cores from the nw labrador sea one occurred ca 20 000 14c yr b p in association with deposition of a major detrital carbonate unit both prior to and after this event 18o values of near surface planktonic foraminifera were 4 5 indicating fully enriched glacial values a younger event ca 14 000 14 c yr b p is characterized by a dramatic change in 18o from 4 5 to 2 0 and coincided with the retreat of ice from the outer se baffin shelf possibly into hudson strait these meltwater events coincide with heinrich h layers 1 and 2 from north atlantic sediments the 14 000 14c yr b p meltwater event indicates that the eastern margin of the laurentide ice sheet also underwent rapid retreat at approximately the same time as other ice sheet margins around the ne north atlantic a third major detrital carbonate event at the base of hu87 033 009 possibly correlative with heinrich layer 3 occurred ca 33 960 675 14 c yr b p however this is older than the accepted date for h 3 of 27 000 14c yr b p and may be h 4

intermediate and deep water paleoceanography of the northern north atlantic over the past 21 000 years benthic foraminiferal stable isotope records from four high resolution sediment cores forming a depth transect between 1237 m and 2303 m on the south iceland rise have been used to reconstruct intermediate and deep water paleoceanographic changes in the northern north atlantic during the last 21 ka spanning termination i and the holocene typically a sampling resolution of 100 years is attained deglacial core chronologies are accurately tied to north greenland ice core project ngrip ice core records through the correlation of tephra layers and changes in the percent abundance of neogloboquadrina pachyderma sinistral with transitions in ngrip the evolution from the glacial mode of circulation to the present regime is punctuated by two periods with low benthic 13c and 18o values which do not lie on glacial or holocene water mass mixing lines these periods correlate with the late younger dryas early holocene 11 5 12 2 ka and heinrich stadial 1 14 7 16 8 ka during which time freshwater input and sea ice formation led to brine rejection both locally and as an overflow exported from the nordic seas into the northern north atlantic as earlier reported by meland et al 2008 the export of brine with low 13c values from the nordic seas complicates traditional interpretations of low 13c values during the deglaciation as incursions of southern sourced water although the spatial extent of this brine is uncertain the records also reveal that the onset of the younger dryas was accompanied by an abrupt and transient 200 300 year duration decrease in the ventilation of the northern north atlantic during the holocene iceland scotland overflow water only reached its modern flow strength and or depth over the south iceland rise by 7 8 ka in parallel with surface ocean reorganizations and a cessation in deglacial meltwater input to the north atlantic

last interglacial mis5e hydrographic shifts linked to meltwater discharges from the east greenland margin abstract proximal evidence of the surface ocean response to size reduction of the greenland ice sheet gis during the last interglacial mis5e and preceding glacial termination t2 remains largely elusive using a new sediment record from the western iceland sea the behavior of the northeastern gis and its relation to the subpolar north atlantic surface hydrography is examined extremely light oxygen isotopic 18o values are found off central east greenland during early mis5e and point to enhanced meltwater release potentially from the northeastern sector of the gis data from downstream the cold east greenland current egc and its eastward branches suggest a far reaching effect of this meltwater not only in the nordic seas but also in the se labrador sea in particular whereas an early mis5e warming at 128 5 126 5 ka in the two regions coincided with the relative reduction of meltwater input into the egc the subsequent cooling noted at 126 5 ka followed a renewed major freshwater event off central east greenland our data further indicate persistent freshwater influence from the east greenland margin over the entire mis5e interval and in addition also reveal a late mis5e meltwater event the latter event occurred just prior to the last glacial inception and emphasizes the importance of greenland meltwater as forcing factor on interglacial climates

significance of variability in turborotalita quinqueloba natland test size and abundance for paleoceanographic interpretations in the norwegian greenland sea biometric analyses on shells of turborotalita quinqueloba natland reflect the paleoceanographic conditions in the norwegian greenland sea ngs both median and mean size variations exhibit a steady increase after the last glacial maximum lgm after termination i the size eventually reaches a constant level with only minor fluctuation in contrast peak abundances of specimens occur somewhat later during the holocene climatic optimum and rapidly decrease again in the youngest sediments test sizes are larger at the voring plateau in the vicinity of incoming atlantic water than in water further to the west turborotalita quinqueloba first appeared in the southwestern part of the ngs with a preliminary major peak in abundance and size well below the younger dryas this species was present in sizes 125 m in this area during almost entire oxygen isotopic stage 2 this was not observed in the more easterly located cores it seems likely that size variations as a tool for ngs paleoceanographic interpretations are not only valuable for the time since the lgm but can also be applied to older isotopic stages where abundances of t quinqueloba are low or absent in the 125 m size fractions but are high in the 63 125 m fraction e g stages 7 9 and 11

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

a younger dryas ash bed in western norway and its possible correlations with tephra in cores from the norwegian sea and the north atlantic abstract a bed of volcanic ash up to 23 cm thick is found in lacustrine and marine sediments in western norway it is formally mamed the vedde ash bed and its age is approximately 10 600 yr b p i e mid younger dryas the bed consits of pure glass having a bimodal basaltic and rhyolitic somposition the geochemistry of the glass shards suggests an icelandic source by means of stratigraphic position and geochemistry the ash is correlated with ash zones found in cores from the continental shelf the norwegian sea and the north atlatic

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

response of the high latitude northern hemisphere to orbital climate forcing evidence from the nordic seas sediment cores from the nordic greenland iceland and norwegian seas provide evidence that this area acts as an initial responder to the forcing effect of orbitally driven changes in insolation on the climate system as postulated by j imbrie et al the 18 o record of the cores documents a widespread initial deglacial signal in the area between 15 and 13 ka 1000 yr before other deglacial signals from other parts of the northern hemisphere an even earlier meltwater event has been dated to 16 090 185 yr b p north of iceland at the initial rise of northern hemisphere insolation after the last glacial maximum during the period with lowered surface salinities the nordic seas were still cold reconstructions of the surface water conditions of the area show that as the summer insolation values of the northern hemisphere reached half of maximum values a sea ice free corridor opened along norway at 13 4 ka nearly contemporaneous fluctuations of the polar front and the sea surface temperatures with the insolation changes indicate that the nordic seas are very sensitive to insolation forcing especially in regions close to the sea ice margin a decrease in sea surface temperature and an increase in the areal extent of sea ice cover since 7 ka indicate that the area is currently on the way to glacial conditions supporting the predictions made earlier by j imbrie et al

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

can the greenland climatic jumps be identified in records from ocean and land sharp jumps in climate punctuate the records from borings in the greenland ice cap during the time interval 60 000 to about 20 000 yr ago rapid fluctuations are also seen in foraminifera records for cores from the northern atlantic and in a pollen record from a core from a bog in the vosges mountains in france in this paper we present a new radiocarbon chronology for northern atlantic deep sea core v23 81 which permits comparison with the radiocarbon dated vosges mountains pollen record because of the lack of a 14c chronology for the greenland ice record and of distortions peculiar to each of the three records it is not yet possible to say whether or not the events are genetically related

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

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