late quaternary glacial interglacial changes in sediment composition at the east greenland continental margin and their paleoceanographic implications stable isotope records and sedimentological and organic geochemical investigations of marine sediments from the east greenland sea at 70 n provide important information about glacial interglacial variations of paleoenvironments through the last 225 kyr the oxygen isotope records established on the planktonic foraminifer n pachyderma sin show some excursions from the global climate pattern probably due to local regional overprint by meltwater supply the cold low saline east greenland current and fluctuations in sea ice covering were a crucial element controlling the carbonate production in the subsurface surface water column in the east greenland sea over the last 225 kyr the beginning of termination ia is ams 14c dated at about 15 8 kyr b p and interpreted as a greenland ice sheet meltwater signal the stage 2 3 boundary is dated at about 25 kyr b p the timing of the onset of the last deglacial meltwater event is about 800 years earlier than that of the barents shelf ice sheet meltwater signal recorded in the fram strait several major pulses of increased supply of coarse grained terrigenous material by glacio marine processes occurred during the last 225 kyr the supply of coarse grained ice rafted debris at the east greenland continental slope reached maximum values during the last glacial maximum stage 2 weichselian 15 19 kyr b p the drastic climatic change and the gradual retreat of continental ice masses glaciers during the last deglaciation termination i are clearly documented in the marine sedimentary sequences from shelf and upper slope environments this process resulted in distinctly decreased supply and deposition of ice rafted debris in the open shelf upper slope environments during termination i the sea ice cover also decreased causing an increase in surface water productivity indicated by increased organic carbon and biogenic opal deposition

origin of the northern atlantic s heinrich events as first noted by heinrich 1988 glacial age sediments in the eastern part of the northern atlantic contain layers with unusually high ratios of ice rafted lithic fragments to foraminifera shells he estimated that these layers are spaced at intervals of roughly 10 000 years in this paper we present detailed information documenting the existence of the upper five of these layers in odp core 609 from 50 n and 24 w their ages are respectively 15 000 radiocarbon years 20 000 radiocarbon years 27 000 radiocarbon years about 40 000 years and about 50 000 years we also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers although we are not of one mind regarding the origin of these layers we lean toward an explanation that the heinrich layers are debris released during the melting of massive influxes of icebergs into the northern atlantic these sudden inputs may be the result of surges along the eastern margin of the laurentide ice sheet

the central paratethys during oligocene as an ancient counterpart of the present day black sea unique records from the coccolith limestones abstract four isochronous oligocene coccolith limestone horizons from the carpathians were examined in order to reconstruct paleoceanographic conditions in the central paratethys the dominance of small and size uniform pyrite framboids the occurrence of low diversity dinoflagellate cysts and coccolithophorids and the presence of biomarker molecule 28 30 dinorhopane indicate that the water column was stratified with the upper water column being relatively well oxygenated but the bottom water being anoxic the latter is confirmed by the fine and consistent horizontal laminations in various parts of the basin scarcity of benthic organisms and their trace fossils the limestones exhibit typical marine 13c values but are significantly depleted in 18o and enriched in 87sr relative to contemporaneous ocean water these isotopic compositions result from a decreased salinity of the surface waters caused by an increased riverine input this is confirmed by the lack or impoverishment of planktonic foraminifers presence to abundance of goniodomid dinoflagellate cysts and massive occurrence of low diversity nannoplankton assemblages which indicates decreased salinities as low as 17 and high productivity in the upper water column these observations indicate that the limestones were formed during periods when connection of the central paratethys with the global ocean was limited which impeded water exchange causing the development of low salinity conditions of surface water and bottom water anoxia during the deposition of the oldest tylawa horizon primary productivity was enhanced and chemocline was positioned exceptionally high in the water column moreover decreased 13c values in both carbonates and organic matter of this horizon suggest that widespread methane venting took place in the basin during np23 all these data show that during the oligocene the central paratethys experienced similar conditions to those of the current black sea which can be used as a modern analogue especially for the tylawa horizon therefore the tylawa horizon can be perceived as a potential effect of future post depositional processes of coccolith marls analogous to those having been deposited in the black sea for 2 7 kyr

the quaternary geology of the labrador shelf the regional distribution of glacial and postglacial sediments on the labrador shelf was mapped by medium and high resolution seismics and shows a succession of tills that extend to the continental shelf edge at approximately 600 m the uppermost of these tills is less laterally extensive and does not occur on the labrador shelf bank tops in water depths less than 160 m we infer that the last glacial episode was less extensive than the preceding ones glaciomarine stratified silts and postglacial muds are found overlying the upper till in the deep basins that separate the banks the upper till glaciomarine silts and postglacial muds are interpreted to constitute one complete deglacial cycle radiocarbon age determination suggests this deglacial sequence began at approximately 20 000 years bp on the northernmost labrador shelf and hudson strait seismic evidence indicates a late glacial readvance locally deposited a till that overlies the glaciomarine sediments associated with the last glacial advance

composition and origin of sediments on the mid oceanic kolbeinsey ridge north of iceland in order to characterize the sediments of the south kolbeinsey ridge and to determine the influence of morpho and hydrodynamic conditions in this area a comprehensive sedimentological investigation was combined with detailed geochemical analyses lithological composition and grain size are mainly controlled by the input from two different sources the submarine active mid ocean ridge and iceland coarse grained volcanic material dominates in the ridge area whereas fine grained detritus from iceland characterizes the adjacent basin further the distribution of these sediments is largely influenced by hydrodynamic conditions and redeposition processes strong bottom water currents indicated by the benthic foraminifer species cibicides lobatulus prevent extensive deposition of fine grained material on the top of the ridge the ridge slope is characterized by redeposited sediments of various grain sizes bulk sediment chemical analyses show element distribution patterns that are strongly correlated with the ratio of volcanic vs detritic particle composition this ratio reflects particle input and distribution processes two element associations are notable elements coupled with 1 ridge derived volcanic particles and 2 the detrital 2 m fraction which reflects weathered material from iceland

ice sheet and ocean interactions margin of the east greenland ice sheet 14 ka to present diatom evidence seven marine sediment cores were collected from the kangerdlugssuaq trough off the southeast coast of greenland the trough cuts across the continental shelf from the fjord mouth to the upper slope in denmark strait and provides a sedimentary environment sheltered from the east greenland current flowing along the shelf the cores have been 14c dated accelerator mass spectroscopy dates and analyzed for diatom accumulation rates and changes in floral composition it was found that the shelf probably was not glaciated by grounded ice but occupied by an ice shelf and or permanent sea ice between 14 000 years b p and the present average retreat rates of glacial permanent sea ice were circa 60 m yr between circa 13 500 and 11 000 years b p the retreat rates increased to about 150 m yr between 11 000 to 10 000 years b p the increase is unexpected because this correlates with fairbanks 1989 projected low glacial meltwater discharge for the same time which is coeval with the younger dryas several events of sea surface warming cooling took place on the outer shelf from 12 000 to 9000 years b p followed by cooling to the present with a possible warming between 3000 4000 years bp on the inner shelf pulses of warm cool surface water occurred from 9000 to 6000 years b p which was succeeded by surface water cooling until present

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

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

cryosphere ocean interactions at the margin of the laurentide ice sheet during the younger dryas chron se baffin shelf northwest territories cores hu82 034 057 and hu84 035 008 resolution basin se baffin shelf contain 200 and 450 cm respectively of sediment that spans the younger dryas chron in both cores the interval is bracketed by 14c dates on foraminifera or molluscs these sites were close to the margin of the late wisconsin foxe ice sheet as it flowed toward the labrador sea prior to 11 ka both cores record moderate to high accumulations of foraminifera relatively high del 18o values in planktonic foraminifera and low values of detrital carbonate the diatom and percent opal records imply occasional seasonally open water conditions during part of the younger dryas chron both the diatom and opal analyses imply a shutoff of biogenic silica production suggesting surface water conditions affected by increased sea ice and or reduced nutrients in addition the younger dryas interval is marked by an increase in coarse sand and detrital carbonate a decrease in total organic carbon and foraminifera and high rates of sediment accumulation the inferred environment during the younger dryas is ice proximal in hu82 034 057 the foraminifera and other data suggest a change in conditions during the middle part of the younger dryas chron

10 be data from meltwater channels suggest that jameson land east greenland was ice covered during the last glacial maximum along the northeast greenland continental margin bedrock on interfjord plateaus is highly weathered whereas rock surfaces in fjord troughs are characterized by glacial scour based on the intense bedrock weathering and lack of glacial deposits from the last glaciation interfjord plateaus have long been thought to be ice free throughout the last glacial maximum lgm in recent years there is growing evidence from shelf and fjord settings that the northeast greenland continental margin was more extensively glaciated during the lgm than previously thought however little is still known from interfjord settings we present cosmogenic 10be data from meltwater channels and weathered sandstone outcrops on jameson land an interfjord highland north of scoresby sund the mean exposure age of samples from channel beds n 3 constrains on the onset of deglaciation on interior jameson land to 18 5 1 3 21 4 1 9 ka for erosion conditions of 0 10 mm ka respectively this finding adds to growing evidence that the northeast greenland continental margin was more heavily glaciated during the lgm than previously thought

variations in felsic versus mafic sources in the western nordic seas during mis 1 to mis 4 abstract the goal of this paper is to employ quantitative methods to first describe the spatial variations in the quantitative non clay and clay mineral composition of seafloor surface sediments secondly use those data to describe the temporal variations in mineral compositions of nine cores that extend variously between the present day and 85 ka bp and thirdly describe regional variations in the transport of felsic versus mafic rich glacial marine sediments at four sites close to denmark strait k mean clusters of recent seafloor samples n 156 distinguished four mineral facies which characterize a range of mafic to felsic compositions these samples serve as a training set to identify the down core mineral facies in eight cores n 1053 the degree of provenance mixing is measured by fuzzy clustering on an unsupervised cluster analysis classification decision trees validate the mineral facies only 6 misclassified and indicate that variations in the weight of pyroxene are of primary importance in defining cluster membership mineral compositions identify two end member core sites jm07 174gc greenland sea and lo9 18 reykjanes ridge while the cores north and south of the greenland faroes ridge cores ps2644 md99 2274 2280 and 2323 are a mixture of mafic rich and felsic rich mineral facies variations in magnetic susceptibility and quartz wt exhibit coherent runs of values above or below their medians in three of the cores occurred indicating that these cannot be ascribed to random variations p

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 east greenland continental margin 65 n since the last deglaciation changes in seafloor properties and ocean circulation nine gravity cores collected on the east greenland continental margin off kangerdlugssuaq fjord reveal a drastic decrease in average sedimentation rates from the cross shelf through the continental slope from 43 2 cm kyrs to 2 2 cm kyrs respectively since the last deglaciation beginning at 2g cm2kyrs at 4000 yrs b p both caco3 and non caco3 accumulation rates became high g cm2kyrs since 3000 yrs b p these rates distinctly decreased melting of glaciers and current activity which drastically changed in space and time controlled the terrigenous sediment input and thus the grain size distribution and the physical properties of sediments across the shelf these observations suggest that current winnowing on sediments is one of the dominant processes at present this is seen in the acoustic reflectivity and in the acoustically hard seafloor particularly at the upper continental slope in addition icebergs transported southward along the continental margin have scoured the sediment surface in water depths 350m

the glacier influenced scoresby sund fan east greenland continental margin evidence from gloria and 3 5 khz records a major submarine fan gradient about 2 offshore of the scoresby sund fjord system is indicated by the crescentic shape of the shelf break gloria long range side scan sonar imagery was obtained over about 20 000 km2 of the fan along with 1000 km of 3 5 khz records three acoustic facies were defined from gloria backscatter signatures and sea floor morphology and sediment acoustic character on 3 5 khz records facies 1 includes a series of acoustically transparent features 0 5 2 km in width elongate downslope with irregular surface topography which are interpreted as debris flows this makes up the bulk of relatively recent sedimentation on the upper fan diamictic sediments in a core support a debris flow origin facies 2 is featureless on gloria images 3 5 khz profiles reveal irregular former sea floor morphology above which is a draping unit 15 m thick this northern region of the fan is a less active area where hemipelagic sediments and limited ice rafted debris overlie older material formed by past debris flow activity the more distal area of the adjacent ocean basin has a flat floor with parallel sub bottom reflectors of facies 3 this facies is probably an area of low energy hemipelagic sedimentation punctuated by occasional ice rafting and turbidity current activity the debris flows interpreted from gloria and 3 5 khz data are basic building blocks in the long term development of the scoresby sund fan glacier influenced fan volume is about 15 000 5000 km3 based on seismic reflection studies during full glacials in east greenland the inland ice sheet advances to fill the scoresby sund fjord system and extends across the shelf to reach the shelf break in some glacial cycles debris flows form in areas of most rapid sediment flux the scoresby sund fan is relatively similar to the storfjorden fan on the eastern polar north atlantic margin but differs from the larger bear island fan in having a steeper fan gradient much smaller debris flows and no large scale slides

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

ocean circulation in the norwegian sea during the last deglaciation isotopic evidence abstract three cores from different depths in the southeastern norwegian sea have been investigated for benthic and planktonic foraminiferal stable isotope records the cores confirm that the last deglaciation occurred in two distinct steps the first step termination ia may have occurred at about 13 000 yr b p while the second step took place shortly after 10 000 yr b p the benthic oxygen isotopes reveal strong influence of deglacial intermediate waters possibly flowing in from the north atlantic with a maximum influence at about 12 000 yr b p both carbon and oxygen isotopic records show that bottom water formation in the norwegian sea was reinitiated after 12 000 yr b p during the first part of the deglaciation the deep water circulation pattern may have been opposite to that of the present the oxygen content in the norwegian sea deep water was low during the last glacial maximum and remained low during the first part of the deglaciation due to low vertical circulation rates the large variations in deep water circulation in the norwegian sea during the last deglaciation may have had important consequences for the interchange of co 2 between ocean and atmosphere

surface sediment diatom distribution and holocene paleotemperature variations in the greenland iceland and norwegian sea one hundred and four surface sediment samples and two piston cores from the greenland iceland and the norwegian gin sea hopkins 1988 were analyzed diatoms were common to abundant in most surface sediment samples and throughout the holocene q mode factor analysis allowed the definition of six significantly different floral assemblages which explained 91 7 of the total variance mapping of the six factors showed their close affinity to hydrographic regimes these are the norwegian atlantic current assemblage thalassionema nitzschioides paralia sulcata proboscia alata arctic water assemblage thalassiosira gravidaspores sea ice assemblage nitzschia grunowii nitzschia cylindra thalassiosira hyalina arctic norwegian waters mixing assemblage rhizosolenia hebetata f semispina rhizosolenia borealis atlantic assemblage thalassiosira oestrupii and norwegian arctic waters mixing assemblage thalassiosira gravida vegetative cells transfer functions gint2 relating factor distributions to winter february and summer august surface water temperatures were generated the transfer functions have a standard error of estimate of 1 5 c august and 1 0 c february downcore studies of core 52 43 from the norwegian basin and core 57 5 from the iceland plateau revealed diatom abundance and sea surface paleotemperature trends in the area during the holocene the first appearance of diatoms in cores 52 43 and 57 5 occurs within the vedde ash layer 10 600 years b p and the saksunarvatn ash layer 9100 years b p respectively diatom abundances increase steadily throughout the pre boreal atlantic time to 25 and 35 million valves per gram dry sediment in the norwegian basin and iceland plateau cores respectively application of the temperature transfer functions gint2 to the two holocene records revealed higher than present sea surface temperatures during the boreal atlantic chronozones for the iceland plateau and during the middle younger dryas sub boreal chronozones for the norwegian basin core temperatures decreased steadily since then with a slight increase to the present values both the iceland and the norwegian seas experienced a strong influx of temperate atlantic surface waters in the beginning of the holocene sea surface temperatures dropped steadily in the latter part of the holocene as the influx of the atlantic surface waters diminished

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

detrital carbonate rich sediments northwestern labrador sea implications for ice sheet dynamics and iceberg rafting heinrich events in the north atlantic much of the bed of the central and eastern sectors of the laurentide ice sheet was underlain by paleozoic carbonates we propose that pulses of detrital carbonate rich sediments in two cores from the northwestern labrador sea reflect episodes when an ice stream from the hudson strait extended to the shelf break and delivered sediment onto the slope and deep sea plain atomic mass spectroscopy 14 c dating of planktonic foraminifera in cores hu75 009 iv 55 2 4 km water depth and hu87 033 009 1 4 km water depth and 150 km north northwest indicates that the youngest event occurred between ca 14 and 15 ka and another occurred between 19 and 21 ka the two carbonate intervals in northwestern labrador sea cores are coeval with heinrich events 1 and 2 in the eastern north atlantic lat 45 50 n long 20 w where they are associated with an increase in lithic fragments and a drastic reduction in the numbers of foraminifera these changes have been linked with the massive production of icebergs associated with ice sheet surges our evidence indicates that heinrich events 1 and 2 are associated with the dynamics of the hudson strait ice stream and denote considerable glaciological instability

water partitioning in the earth s mantle abstract we have conducted h2o partitioning experiments between wadsleyite and ringwoodite and between ringwoodite and perovskite at 1673 k and 1873 k respectively these experiments were performed in order to constrain the relative distribution of h2o in the upper mantle the mantle transition zone and the lower mantle we successfully synthesized coexisting mineral assemblages of wadsleyite ringwoodite and ringwoodite perovskite that were large enough to measure the h2o contents by secondary ion mass spectrometry sims combining our previous h2o partitioning data chen et al 2002 with the present results the determined water partitioning between olivine wadsleyite ringwoodite and perovskite under h2o rich fluid saturated conditions are 6 30 15 1 respectively because the maximum h2o storage capacity in wadsleyite is 3 3 wt e g inoue et al 1995 the possible maximum h2o storage capacity in the olivine high pressure polymorphs are as follows 0 7 wt in olivine upper mantle just above 410 km depth 3 3 wt in wadsleyite 410 520 km depth 1 7 wt in ringwoodite 520 660 km depth and 0 1 wt in perovskite lower mantle if we assume 0 2 wt of the h2o content in wadsleyite in the mantle transition zone estimated by recent electrical conductivity measurements e g dai and karato 2009 the estimated h2o contents throughout the mantle are as follows 0 04 wt in olivine upper mantle just above 410 km depth 0 2 wt in wadsleyite 410 520 km depth 0 1 wt in ringwoodite 520 660 km depth and 0 007 wt in perovskite lower mantle thus the mantle transition zone should contain a large water reservoir in the earth s mantle compared to the upper mantle and the lower mantle

late quaternary calcium carbonate sedimentation and terrigenous input along the east greenland continental margin nine large box cores collected in the western greenland iceland norwegian gin sea were analyzed for calcium carbonate content and coarse fraction components stratigraphic control is based on oxygen isotope records performed on four of the cores all cores were correlated using oxygen and carbon isotope data fluctuations in calcium carbonate content coarse terrigenous particle content and volcanic ash beds glacial and interglacial cycles are documented by a number of terrigenous particle events and differentiated calcium carbonate production which can be correlated to major paleoceanographic and paleoclimatic shifts in the older core sections extensive deposition of ice rafted detritus ird persisted until about oxygen isotope stage 9 and document a relatively stable environment in this area strongly influenced by cold surface water masses the following interval was characterized by variations in the general surface water circulation pattern although high amounts of ird are still present in iceland sea sediments pronounced shifts in terrigenous input and pelagic carbonate records were identified close to the oxygen isotope stage full size image 1 k and full size image 1 k boundaries indicating massive melting of icebergs in the western gin sea these enormous inputs of debris were followed by an increase in calcium carbonate production caused by maximum intrusion of warm atlantic surface waters relatively high calcium carbonate contents also show that only little dilution by fine grained material and a minimum of ice melting occurred during these warm phases during oxygen isotope stage 5 conditions were more uniform indicating a less pronounced westward penetration of atlantic waters as compared to the holocene the last glacial stages 4 2 is characterized by the occurrence of heinrich like events although high ird contents were present throughout this interval a distinct contrast between the northernmost cores and the cores in the south is indicative of a rather strong westward penetration of atlantic water in the north and of an area dominated by cold water east of the kolbeinsey ridge during the holocene however conditions west of jan mayen seem to have remained constantly dominated by cold surface waters throughout the whole time investigated

the origin of massive diamicton facies by iceberg rafting and scouring scoresby sund east greenland almost 90 of 39 m of core material recovered from scoresby sund and the adjacent east greenland shelf is massive diamicton interpreted to be formed predominantly by the release of iceberg rafted debris and reworking by iceberg scouring there is also likely to be a contribution from suspension settling of fines derived from glaciofluvial sources model calculations suggest that the 14c derived holocene sedimentation rate of 0 1 0 3 m 1000 yr 1 in scoresby sund can be accounted for mainly by iceberg rafting of debris a further 4 of core material is of gravel or coarse sand lenses interpreted to reflect iceberg dumping of debris intensive iceberg scouring which reworks sea floor sediments is observed on acoustic records from over 30 000 km2 of the scoresby sund fiord system and the adjacent east greenland shelf 69 72 n and 75 n the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg rafting and scouring may be important over a significant proportion of the 500 000 km2 area above the shelf break the relatively extensive modern occurrence of massive diamicton formed by iceberg rafting and scouring together with suspension settling of fines suggests that it may also be a significant facies in the glacier influenced geological record the recognition in the geological record of the massive diamicton facies described above may also indicate the former presence of fast flowing ice sheet outlet glaciers

paleoclimatic inferences from glacial fluctuations on svalbard during the last 20 000 years the climate history of western spitsbergen svalbard is deduced from variations of glaciers during the last 20 000 years a major depression of the regional equilibrium line altitude ela occurred during the late weichselian glacial maximum 18000 13000y ago when low summer temperatures may have caused year round snow accumulation on the ground this rapid expansion of the glaciers also indicates nearby moisture sources suggesting partly open conditions in the norwegian sea during the summers a rapid glacial retreat around 13 000 12 500 y bp was caused by a sudden warming during the younger dryas the ela along the extreme western coast of spitsbergen was not significantly lower than at present in contrast to fennoscandia the british isles and the alps there is no evidence for readvance of local glaciers during younger dryas on western spitsbergen this difference is attributed to a much dryer climate on spitsbergen and probably only slight changes in sea surface temperatures in addition summer melting in this high arctic area is more sensitive to orbitally increased insolation around 10 000 y bp another rapid warming occurred and during early and mid holocene the summer temperatures were significantly higher than at present a temperature decline during the late holocene caused regrowth of the glaciers which reached their maximum holocene position during the last century

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

the sizes frequencies and freeboards of east greenland icebergs observed using ship radar and sextant the scoresby sund fjord system east greenland contains the most productive fast flowing outlet glaciers draining east from the greenland ice sheet calving 18 km3 a 1 of icebergs the sizes frequencies and freeboards of 1900 icebergs were measured from f s polarstern using ship x band radar and sextant radar beam spreading exaggerates iceberg width by 60 m per nautical mile of range beyond the first mile data sets on iceberg size e g that collated for antarctic icebergs collected using ship radars which do not take this effect into account will overestimate iceberg dimensions significantly the location and concentration of icebergs within the fjord complex can be explained by 1 the locations of the principal source glaciers and 2 fjord topography and bathymetry iceberg concentration maximum 0 6 icebergs km 2 declines with distance from the major iceberg sources we found that 69 of icebergs within the fjord system are 1 km in length the largest is 2 7 km long icebergs become spread more evenly over the range of size classes in the outer fjord and shelf modal iceberg keel depth calculated from freeboard measurements is 4 500 m in the inner fjords shifting to lower values in the outer fjords reflecting shallower bathymetry radar measurements of iceberg width cannot be used to infer keel depths accurately because width and keel depth are only weakly correlated comparison between freeboards and keel depths for icebergs from east greenland and the barents sea indicates that the iceberg source i e floating or grounded exerts a fundamental control on iceberg dimensions the drift pattern of icebergs is from the head to the mouth of the fjord system although fjord bifurcations bathymetry and currents provide additional complications the trends in observed iceberg size and frequency and in inferred keel depth in the scoresby sund region are likely to be applicable to other fjords and shelves around greenland

iceberg scouring in scoresby sund and on the east greenland continental shelf modern and relict scours produced by iceberg keels have been reported from a number of high latitude continental shelves in the northern hemisphere and antarctica but observations are largely absent from the east greenland shelf about 18 km3 yr 1 of icebergs are calved into the scoresby sund fjord system east greenland these icebergs have submarine keels with drafts up to 550 m modern iceberg contacts with the sea floor are inferred from calculated keel depths and stationary icebergs identified on sequential landsat imagery acoustic profiles parasound 3 5 khz of the sea floor show that scouring is a significant process in water depths 550 m iceberg scouring intensity varies inversely with water depth the most intense scouring occurs at depths of 300 400 m iceberg scours were observed on over 25 000 km2 of the east greenland shelf at 69 72 n and 75 n scours are being actively produced on the modern shelf but relict scours probably dating back to the late weichselian are also present the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg scouring is important over a significant proportion of the 500 000 km2 area above the shelf break around greenland

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

holocene glacimarine sedimentation inner scoresby sund east greenland the influence of fast flowing ice sheet outlet glaciers abstract holocene glacimarine sedimentation associated with fast flowing outlet glaciers draining the greenland ice sheet is investigated using sedimentary and acoustic data from inner scoresby sund east greenland sedimentation in inner scoresby sund is dominated by three processes which are influenced by differences in proximity to fast flowing outlet glaciers extent of glacier ice cover and fjord bathymetry 1 sediment gravity flow principally in the form of turbidity currents and debris flows 2 suspension sedimentation from turbid meltwater plumes and 3 iceberg rafting these processes result in texturally and sedimentologically heterogeneous lithofacies proportionally fine grained muds laminated stratified and massive facies dominate cores recovered from inner scoresby sund accounting for 80 of the total whereas diamict facies account for only 15 abundant fine grained muds demonstrate that meltwater flux and sedimentation is significant in this high arctic glacimarine environment in settings proximal to fast flowing outlet glaciers with increasing distance from these glacier termini muds are replaced progressively by iceberg rafted coarse grained sediment the dominance of this iceberg rafted sediment in outer scoresby sund reflects both its more distal location from fast flowing glacier termini and the high calving flux associated with these ice masses laminated muds deposited by turbidity currents and suspension settling from overflow plumes in inner scoresby sund are similar to lithofacies produced in temperate and subpolar glacimarine systems this implies a similarity in sedimentation processes and resulting facies across a wide spectrum of climatically glaciologically fast flowing and non fast flowing ice masses and oceanographically variable glacimarine settings recognition of laminated fine grained facies in the geological record therefore does not necessarily indicate a temperate palaeo glacial setting however the predominance of iceberg rafted diamict facies in ice distal sedimentary records suggests the former presence of relatively cold environmental conditions in which iceberg sedimentation played a dominant role

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

calibrating a glaciological model of the greenland ice sheet from the last glacial maximum to present day using field observations of relative sea level and ice extent we constrain a three dimensional thermomechanical model of greenland ice sheet gris evolution from the last glacial maximum lgm 21 ka bp to the present day using primarily observations of relative sea level rsl as well as field data on past ice extent our new model huy2 fits a majority of the observations and is characterised by a number of key features i the ice sheet had an excess volume relative to present of 4 1 m ice equivalent sea level at the lgm which increased to reach a maximum value of 4 6 m at 16 5 ka bp ii retreat from the continental shelf was not continuous around the entire margin as there was a younger dryas readvance in some areas the final episode of marine retreat was rapid and relatively late c 12 ka bp leaving the ice sheet land based by 10 ka bp iii in response to the holocene thermal maximum htm the ice margin retreated behind its present day position by up to 80 km in the southwest 20 km in the south and 80 km in a small area of the northeast as a result of this retreat the modelled ice sheet reaches a minimum extent between 5 and 4 ka bp which corresponds to a deficit volume relative to present of 0 17 m ice equivalent sea level our results suggest that remaining discrepancies between the model and the observations are likely associated with non greenland ice load differences between modelled and observed present day ice elevation around the margin lateral variations in earth structure and or the pattern of ice margin retreat

late pleistocene paleo oceanography of the norwegian greenland sea benthic foraminiferal evidence fluctuations in benthic foraminiferal faunas over the last 130 000 yr in four piston cores from the norwegian sea are correlated with the standard worldwide oxygen isotope stratigraphy one species cibicides wuellerstorfi dominates in the holocene section of each core but alternates downcore with oridorsalis tener a species dominant today only in the deepest part of the basin o tener is the most abundant species throughout the entire basin during periods of particularly cold climate when the norwegian sea presumably was ice covered year round and surface productivity lowered portions of isotope stages 6 3 and 2 are barren of benthic foraminifera this is probably due to lowered benthic productivity perhaps combined with dilution by ice rafted sediment there is no evidence that the norwegian sea became azoic the holocene and substage 5e the last interglacial are similar faunally this similarity combined with other evidence supports the presumption that the norwegian sea was a source of dense overflows into the north atlantic during substage 5e as it is today oxygen isotope analyses of benthic foraminifera indicate that norwegian sea bottom waters warmer than they are today from substage 5d to stage 2 with the possible exception of substage 5a these data show that the glacial norwegian sea was not a sink for dense surface water as it is now and thus it was not a source of deep water overflows the benthic foraminiferal populations of the deep norwegian sea seem at least as responsive to near surface conditions such as sea ice cover as they are to fluctuations in the hydrography of the deep water benthic foraminiferal evidence from the norwegian sea is insufficient in itself to establish whether or not the basin was a source of overflows into the north atlantic at any time between the substage 5e 5d boundary at 115 000 yr b p and the holocene

sedimentary facies of glacial interglacial cycles in the norwegian sea during the last 350 ka sediment fluxes were highest in the norwegian sea during late glacial early deglacial periods i e at oxygen isotope transition 43 below transition 65 at various levels within stage 6 and below stage 9 dark diamictons deposited at these times reflect intense iceberg rafting in surface waters fed by surges along the front of the marine based parts of the continental ice sheets in the southeastern sector of the norwegian sea the high organic carbon content 0 5 1 3 in these layers reflects input from erosion of terrigenious matter rich sediments outcropping on the shelves partial oxidation of organic matter and decreased deep water renewal may explain the strong carbonate dissolution observed during these periods interglacial environments were strongly variable throughout the last 350 ka circulation patterns of stage 5e best resemble modern conditions while stage 7 and 9 sediments record a much weaker norwegian current

evidence for the asynchronous retreat of large outlet glaciers in southeast greenland at the end of the last glaciation recent rapid changes in the marine terminating sectors of the greenland ice sheet gris have prompted concerns about the future stability of the ice sheet long term records of ice sheet behaviour provide valuable context to assess the magnitude of current change and may help resolve the mechanisms driving deglaciation we report 23 new 10be exposure ages which constrain the deglacial history of two large fjord systems in southeast se greenland we compare our chronologies with existing data from the centre of the sector to examine the timing and style of deglaciation at a regional scale glacial erratic 10be exposure ages demonstrate that kangerdlugssuaq fjord deglaciated at 11 8 ka at the end of the younger dryas yd 12 8 11 6 ka retreat at kangerdlugssuaq fjord coincided with known incursion of the warm irminger current ic onto the continental shelf this is inferred to have initiated retreat comparison with recently published results from sermilik fjord and new 10be ages from bernstorffs fjord indicates deglaciation occurred 1 ka later in the south of the se region sermilik fjord 10 9 ka and bernstorffs fjord 10 4 ka deglaciated later retreat likely occurred in response to dramatic climatic amelioration at the termination of the yd stadial we suggest that the disparate timing of deglaciation across the se region may be primarily explained by the varying influence of the warm ic glaciers in southern se greenland were isolated from warm atlantic waters during the yd by complex shelf bathymetry in all fjord settings ice retreat was rapid and persistent consistent with the absence of geomorphological evidence for stillstand or readvance events ice retreat was accompanied by rapid thinning and likely continued to well within present day ice sheet margins glacial erratic 10be age determinations and geomorphological observations show no evidence for holocene readvance events prior to the little ice age lia

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

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr