oxygen and carbon isotope record of east pacific core v19 30 implications for the formation of deep water in the late pleistocene north atlantic abstract a detailed oxygen and carbon isotope record has been obtained from benthic foraminifera in core v19 30 from the carnegie ridge on the south side of the panama basin expressing these records and the oxygen and carbon isotope records previously published for atlantic core m 12392 on a common timescale it is apparent that the oxygen isotope records are very similar but that the carbon isotope records are quite different by obtaining the carbon isotope gradient between the two sites as a function of time we show that the production of north atlantic deep water has varied over a wide range during the late pleistocene and that the pattern of variation is not simply related to the well known oxygen isotope record although the two oxygen isotope records are very similar changes in the interoceanic gradient are detectable and support the hypothesis that in the glacial mode the north atlantic was colder and less oxygenated than it is today shackleton s 1 1977 interpretation whereby the carbon isotope record from the atlantic core reflects changes in the terrestrial biomass is an over simplification however the record from the pacific core v19 30 probably can be explained in these terms since it probably approximates the carbon isotope record of global mean oceanic dissolved co 2

quaternary sediments and environments on the continental shelf off northern norway abstract based on lithologic palaeontologic and chronostratigraphic investigations of close to 200 gravity cores from troughs deep banks and shallow banks the following late quaternary environment can be outlined in the weichselian deposition of basal tills was followed by deposition of laminated clay in a sea ice environment later a pebbly pelite was deposited in the troughs at the same time as the banks were iceberg ploughed then 13 000 yrs b p a period with incipient winnowing occurred on the deep banks and deposition of sandy pelite took place in the troughs the holocene commenced with a marked environmental change due to intrusion of atlantic water the fauna changed from arctic to boreal high energy winnowing forming a lag deposit took place on the banks and high accumulation rates in the troughs occurred due to the winnowing and sediment influx from the downwasting continental icesheet during the later part of the holocene the winnowing diminished on the deeper banks on the shallow banks and on the shelf break it still prevails and in the troughs calcareous sandy mud is being deposited the surface sediments comprise three main facies bouldery and pebbly sand sand and sandy mud whose distribution mainly depends on the prevailing bottom current regime the composition of the older quaternary sediments is demonstrated by some selected seismic profiles

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

late glacial and deglacial palaeoceanographic changes at vestnesa ridge fram strait methane seep versus non seep environments abstract two cores from 1200 m water depth from vestnesa ridge on the western svalbard margin have been investigated for the distribution of benthic and planktic foraminiferal assemblages oxygen and carbon isotopes geochemical and sedimentological parameters including magnetic susceptibility total organic carbon toc and caco 3 content of the sediment vestnesa ridge is known for the presence of numerous pockmarks where methane gas is bubbling out from the seafloor one core was taken from a pockmark with active seepage of methane while the second core was taken just outside the seepage area for comparison the purpose of the study is to reconstruct the palaeoceanography and compare to published palaeoceanographic records from the area and evaluate if seepage of methane have had any impact on the distribution patterns of benthic foraminiferal species and the sedimentary environments through time the results indicate almost continuous presence of atlantic water throughout the last 43 000 years during the heinrich h1 interval ca 18 000 15 300 years atlantic water flowed subsurface along the bottom and the period stands out with the highest bottom water temperatures of the last 43 000 years settlement of a community of chemo synthesizing bivalves indicates increase in the release of methane beginning during h1 however in both records of seep versus non seep environments the distribution patterns of benthic foraminiferal species diversity and productivity of the specimens were the same indicating that seepage of methane had no influence on the foraminiferal faunas our results show that the palaeoceanographic development at vestnesa ridge was similar to the development over the western svalbard margin and the fram strait confirming previously published results we conclude that the benthic foraminifera at the methane seep site were mainly controlled by palaeoceanographic changes and associated changes in the sedimentary environment and palaeoproductivity overprinting any eventual influence of seepage of methane

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

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

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

fluctuations of the svalbard barents sea ice sheet during the last 150 000 years abstract on spitsbergen western svalbard three major glacial advances have been identified during the weichselian all three reached the continental shelf west of the svalbard archipelago radiocarbon luminescence and amino acid dating of interbedded interstadial and interglacial sediments indicate that these glacial advances have early isotope stage 5d middle stage 4 and late weichselian ages stage 2 an additional more local advance has been dated to isotope stage 5b the late weichselian ice sheet expanded across the entire barents sea however in the south western barents sea the late weichselian till is the only till above eemian sediments indicating that the early and middle weichselian ice advances were restricted to the svalbard archipelago and the northern barents sea a major problem with the onshore sites is the dating of events beyond the range of the radiocarbon method to overcome this the onshore record has been correlated with marine cores from the continental slope and the deep sea west of svalbard where a chronology has been established by oxygen isotope stratigraphy ice rafted detritus ird was used as the main monitor of glaciation the ird record closely mirrors the glaciation history as interpreted from the onshore sections during the late weichselian the largest ird peak occurred during deglaciation a pattern also postulated for the earlier events given this the results from the marine cores indicate that the ages for the first glacial advances during the weichselian were a few thousand years older than interpreted from the onshore stratigraphy

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

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

late 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

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

the role of the north atlantic drift in the millennial timescale glacial climate fluctuations abstract the greenland ice core records show that the overall cold climate of the last glacial period was repeatedly interrupted by short rapid warmings the events known as dansgaard oeschger d o events are strongly imprinted in the north atlantic marine records suggesting that they were linked to north atlantic circulation changes however the causes of the d o events are poorly understood and they represent one of the most intriguing puzzles of the last glacial period in order to investigate a possible mechanism we have studied variations in the distribution of benthic and planktonic foraminifera oxygen isotopes and ice rafted debris during the last glacial period in eight cores from the north atlantic and the nordic seas taken at mid depth from 853 to 1760 m the parameters indicate in agreement with previous studies that the circulation system during the interstadials resembled the present system atlantic surface water flowed north into the nordic seas where most of it sank through convection and as cold deep water flowed back into the north atlantic during the stadials a halocline was established in the nordic seas and in the northernmost part of the north atlantic and the outflow from the nordic seas stopped however below the cold light surface layer the relatively warm water of the north atlantic drift continued to flow across the north atlantic and into the nordic seas here warming up the deep water masses we suggest that the warm water gradually made the water column unstable the pivotal abrupt climate warmings were caused by sudden upwelling of the deep warm water masses causing overturning of the entire water column and onset of convection

the last interglacial glacial period on spitsbergen svalbard the glaciation history of svalbard 78 n and the nw barents sea is reconstructed for the last 130 ka based on studies of sediments exposed in coastal cliffs at the head of isfjorden four different till beds separated by marine sediments are recognized the lowest marine formation containing mytilus edulis reflects warmer conditions than at present and is correlated with the last interglacial the eemian of europe and oxygen isotope substage 5e in the deep sea the post eemian tills are inferred to represent major glaciations around 110 ka bp 75 50 ka bp and 25 10 ka bp during the intervening intervals the glaciers on svalbard were not significantly larger than at present and the nw barents sea was probably ice free the ice free periods named phantomodden and kapp ekholm interstadials lasted from about 110 to 75 and from 50 to 25 ka bp respectively the marine fauna from both these interstadials indicate seasonally ice free conditions the ages of the recorded glaciations coincide with or are slightly younger than periods with insolation minima which at this latitude is determined by a low tilt of the earth s axis thus we postulate that the quaternary glaciations of svalbard were driven by orbital variations with the 41 ka tilt period in contrast to the lower latitude glaciations of scandinavia that were partly driven by the precession cycle with a periodicity of around 23 ka

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

the gin sea a synthesis of its physical oceanography and literature review 1972 1985 abstract a synthesis and review of the physical oceanography of the gin sea greenland iceland and norwegian seas is presented an accompanying bibliography is included from 1972 through 1985 some 1986 works are also noted emphasis is placed on describing the gin sea as a major semi enclosed basin that plays a role unique among the world s oceans by providing a strong two way advective exchange between the ice covered polar sea and the north atlantic ocean and at the same time acting as the primary site for northern hemisphere bottom water formation the water masses for the gin sea are defined in a manner as consistent as possible with the literature the large scale oceanographic and meteorological factors influencing the water mass formation and circulation are described a sample calculation of the various horizontal and vertical thermohaline driven exchanges is given

benthic and planktic community changes at the north siberian margin in response to atlantic water mass variability since last deglacial times the eastward penetration of atlantic derived water adw into the eurasian basin of the arctic ocean was investigated at the western laptev sea continental margin for the time since c 17 6 ka using a high resolution investigation of the lithology geochemistry planktic and benthic foraminifers and ostracods on a sediment core from 270 m water depth major steps in the environmental evolution of the region are recognized in general adw was continuously present in the study area between 17 6 and 15 4 ka adw manifested itself through open water polynyas and associated upwelling events comparison between the laptev sea and northern svalbard shelf using cassidulina neoteretis allows assuming an unmodified subsurface inflow of adw within its northern branch between 15 4 and 13 2 which was strongest after 14 7 ka and in line with the overall climate amelioration a local freshwater event at 13 ka followed by shelf flooding and the establishment of a freshened shelf water mass resulted in an off shelf displacement of adw from the studied site as suggested by the disappearance of c neoteretis between 12 and 7 ka as evidenced by an abundance peak in nonion labradoricum the sea ice marginal zone was located at the site around 12 11 ka but then shifted northward during the early holocene warming enhanced adw inflow since 7 ka correlated with climate cooling and southward retreat of the seasonal drift ice margin the inflow of adw during mid late holocene differed from deglacial times because of the combined influence of northern and eastern adw branches

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

marine calcium carbonate preservation vs climate change over the last two millennia in the fram strait implications for planktic foraminiferal paleostudies abstract we present a high resolution study of planktic foraminiferal distribution patterns in a deep sea core from the eastern fram strait position 78 55 n 06 46 e water depth 1497 m the sediment core is located below atlantic water masses flowing into the arctic ocean and spans the last 2400 years the investigation is based on planktic foraminiferal species distribution stable isotopes and sedimentological data the mean shell weight of neogloboquadrina pachyderma fragmentation organic and inorganic carbon content and the presence of benthic organic linings were also investigated as an indication of preservation changes the results indicate that the planktic foraminifera are affected by dissolution and point to five periods of especially poor preservation at 200 bce 300 650 ce 700 850 ce 1400 1500 ce and from 1800 ce to present in the last century small and fragile subpolar species turborotalita quinqueloba and globigerinita uvula are preserved the increased percentage of these subpolar species together with increases in the caco 3 toc and total foraminiferal flux would point to surface water warming however our data suggest that these fragile species may not have been preserved in sediments older than 1900 ce due to selective dissolution consequently the magnitude of the previously recorded recent surface water warming in the fram strait may be overestimated

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

asynchronous deposition of ice rafted layers in the nordic seas and north atlantic ocean instabilities in ice stream flow within the north american laurentide ice sheet leading to the periodic release of armadas of icebergs into the north atlantic ocean over the past 60 000 years have produced extensive layers of coarse grained iceberg rafted debris heinrich layers in north atlantic sediments1 2 correlation of these layers with iceberg discharge events from the ice sheets on greenland iceland and scandinavia suggested in previous studies for some heinrich layers and in some areas3 4 5 would imply that ice sheet instability had been synchronous across the north atlantic presumably in response to a common environmental cause here we show a lack of widespread systematic correlations both between ice rafted debris layers in different sediment cores from the nordic seas and between the nordic layers and the north atlantic heinrich layers this suggests that the full glacial nordic ice sheets did not exhibit unstable behaviour coincident with iceberg discharge from the vast hudson bay drainage basin of the laurentide ice sheet6 7 off the hudson strait significant ice sheet discharge of melt water is indicated by size sorted sandy and muddy turbidite sediments different from the poorly sorted debris flows which dominate sedimentation on the margins of the nordic seas8 9 10 together these results suggest that the dynamics of quaternary ice sheets surrounding the nordic seas were different from the outlet glacier draining the hudson bay basin and they provide evidence against a common circum north atlantic mechanism driving the discharge of icebergs

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

variability in surface and deep water conditions in the nordic seas during the last interglacial period abstract stable isotope foraminifera and ice rafted detritus ird records covering the last interglacial the eemian from 7 sediment cores in a transect from the norwegian to the greenland sea are presented the percentages of neogloboquadrina pachyderma s and globigerina quinqueloba foraminiferal content and to some extent planktonic stable isotope records demonstrate marked regional changes in surface water conditions importantly the variability in the abundances of subpolar foraminifera and foraminiferal content are not coherent implying that these two types of proxies fluctuated independently of each other and most likely reflect changes in sea surface temperature and surface water carbonate productivity respectively paleoceanographic reconstructions demonstrate significant movements of the oceanographic fronts at the warmest periods the arctic front was located far west of the present day location at least within the iceland sea region at 126 125 ka this was most probably due to a stronger or more westerly located norwegian current within the later warm intervals higher heat flux to the western part of the basin reflects a combination of a stronger irminger current and or a weaker east greenland current during the main cold spell at 124 ka a diffuse arctic front had a more southeasterly location than today and intrusion of atlantic surface waters was probably limited to a narrow corridor in the eastern norwegian sea a general correspondence between minima in sea surface temperatures and light benthic 18o may indicate enhanced influx of freshwater to the basin within the cold events at least in the norwegian sea we find some evidence that the changes in surface water conditions are associated with changes in deep water ventilation the majority of the fluctuations may be related to occasional breakdown or reduction of the thermohaline circulation within the nordic seas in the earliest eemian this could result from meltwater forcing during the remaining part of the last interglacial the fine balance between temperature and salinity which the deep water formation is depending on may have been disturbed by periodic increases in fresh water supply or variable influx of warm atlantic surface waters

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

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

floodplain persistence and dynamic equilibrium conditions in a canyon environment abstract canyon river systems are laterally constrained by steep walls strath terraces and bedrock intrusions however semialluvial reaches are nested within these environments as discontinuous floodplains along the river margins these semialluvial floodplains provide an example of dynamic equilibrium set within high energy fluvial systems marking areas where the river is free to alter its boundary conditions most research has focused on hydraulic conditions necessary for floodplain formation and persistence in unconfined systems whereas little is known about canyon streams this paper focuses on 1 characterizing dynamic equilibrium 2 describing the controls on floodplain formation and distribution and 3 evaluating the performance of extremal hypotheses to identify dynamic equilibrium and floodplain persistence in high energy semiconfined canyon environments these objectives were addressed with field and numerical data derived from a one dimensional hydraulic model for bankfull and 100 year return interval flood events supported by closely spaced cross sections for the lower 38 km canyon reach of the deadwood river idaho under bankfull conditions critical energy thresholds for equilibrium floodplain persistence at this study site present the upper limits of slope 0 018 shear stress 175 n m 2 and specific stream power 400 w m 2 channel and floodplains near equilibrium quantified with a near zero sediment transport divergence exner equation were successfully identified by the minimum unit stream power extremal hypothesis and to a lesser degree by the other extremal hypotheses that minimize energy expenditure minimum specific stream power minimum total stream power and minimum froude number provided backwater environments and major tributaries could be identified extremal results were compared to hydraulic geometry relations to evaluate how closely equilibrium floodplains approached values for unconfined alluvial river systems

reflection of scandinavian ice sheet fluctuations in norwegian sea sediments during the past 150 000 years the record of glacier fluctuations in western scandinavia as reconstructed from continental data has been correlated with records of ice rafted detritus ird from well dated sediment cores from the norwegian sea covering the past 150 000 yr b p the input of ird into the ocean is used as a proxy for ice sheet advances onto the shelf and thus for the calibration of a glaciation curve the marine results generally support land based reconstructions of glacier fluctuations and improve the time control on glacial advances the saalian ice sheet decayed very rapidly approximately 125 000 yr b p in the early weichselian a minor but significant ird maximum indicates the presence of icebergs in isotope substage 5b especially between 95 000 and 83 000 yr b p reduced amounts of calcareous nannofossils indicate that surface waters were influenced by meltwater discharges during isotope substages 5d and 5b an extensive build up of inland ice began again during isotope stage 4 but maximum glaciation was reached only in early stage 3 58 000 53 000 yr b p marine sediments have minimum carbonate content indicating strong dilution by lithogenic ice rafted material generally the ird accumulation rate was considerably higher in stages 4 2 than in stage 5 a marked peak in ird accumulation rates from 47 000 to 43 000 yr b p correlates well with a second middle weichselian ice sheet advance dated by the laschamp olby paleomagnetic event minimum ice extent during the alesund interstade 38 500 32 500 yr b p and several glacial oscillations during the late weichselian are also seen in the ird record of several late weichselian glacial oscillations on the shelf at least four correspond to the north atlantic heinrich events ice sheet behavior was either coupled or linked by external forcing during these events whereas internal ice sheet mechanisms may account for the noncoherent fluctuations

northeast atlantic sea surface circulation during the past 30 10 14c kyr b p a study was made of three cores from the faeroe shetland gateway based on planktonic foraminifera oxygen isotopes accelerator mass spectrometry 14c dates magnetic susceptibility and counts of ice rafted debris ird the data covering the period 30 10 ka show that during the last glacial maximum the arctic front occupied a position close to the faeroes allowing a persisting inflow of atlantic surface water into the faeroe shetland channel the oceanographic environment during deposition of two ird layers is influenced by atlantic surface water masses during the lower ird layer with transport of icebergs from n nw polar surface water conditions prevailed only during deposition of the upper ird layer there is no indication of surface meltwater influence in the region during the deglaciation but there is a persistent influence of atlantic surface water masses in the region thus we conclude that during almost the entire period 30 10 ka the faeroe shetland channel was a gateway for transport of atlantic surface water toward the norwegian sea

history of a stable ice margin east greenland during the middle and upper pleistocene abstract the east greenland record of glaciation and environmental change is based on a combination of onshore and offshore studies glaciological work on contemporary outlet glaciers provides background for interpreting the glaciation styles of the past the scoresby sund fjord system the single largest outlet of the inland ice in east greenland and the adjacent continental shelf and slope were the main working areas the regionality of these results was tested with onshore and offshore work on sites further to the north in the east greenland fjord zone the record spans the period since isotope stage 7 ca 240 ka the most extensive glaciation phases were the lollandselv and scoresby sund glaciations isotope stages 7 and 6 the langelandselv interglaciation isotope substage 5e comprises shallow marine sediments at more than 20 sites onshore and cibicides wuellerstorfii carrying sediments on the continental slope summer temperatures were 2 3 warmer than the holocene optimum and there was vigorous advection of warm atlantic water into the fjords the warm period seems to be accompanied by a eustatic sea level rise of ca 20 m during the weichselian there were three major glacier advances the aucellaelv jyllandselv and flakkerhuk stades isotope substages 5d 5b and stages 3 2 all three advances mark a shift from one topographically determined stable position to another in each phase the glaciers occupied almost the same space in the fjord basins and had their fronts on the inner shelf but the glacial regime and duration was different the aucellaelv stade lasted ca 10 ka and the regime resembled that of present day outlet glaciers 600 km further to the north the flakkerhuk stade lasted for ca 50 ka but left only thin and sporadic till as well as glaciolacustrine sediments in ice dammed river valleys the regime was polar similar to present day glaciers in antarctica its culmination the last glacial maximum in the period between 22 and 14 ka is shown by a maximum in ird deposition on the continental slope after 12 ka and before 10 ka the outer fjord basins in the southern fjord zone had been abandoned by the glaciers and at ca 9 5 ka the last resurgence the milne land stade had ended

late weichselian deglacial history of the svyataya saint anna trough northern kara sea arctic russia abstract marine sediment core and seismic records from the svyataya saint anna trough provide new insight into the distribution of late weichselian glacial coverage ice retreat pattern and post glacial environments in the northern barents and kara seas these records indicate that the saint anna trough was filled with grounded glacier ice which likely reached the shelf edge during the late weichselian maximum several radiocarbon dates suggest early deglaciation of the deep axial part of the trough prior to 13 3 ka two sandy beds in the deglacial section of the cores imply distinct pulses of iceberg calving and or melting which were probably associated with stepwise retreat of the ice margin morainic ridges and glacial sole markings in the western part of the saint anna trough indicate that the northern central barents sea was a site of a large ice mass during deglaciation a smaller ice cap is inferred for the northern kara plateau at later stages ice retreat on the western flank of the trough was directed towards franz josef land and was presumably facilitated by a separation of the barents sea and novaya zemlya ice domes deglaciation of the saint anna trough was completed by ca 10 ka high post glacial sediment fluxes between 10 and 8 ka were probably related to sea floor coastal erosion and or siberian river discharge during the rising sea level

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

rapid changes in the mechanism of ocean convection during the last glacial period high amplitude rapid climate fluctuations are common features of glacial times the prominent changes in air temperature recorded in the greenland ice cores1 2 are coherent with shifts in the magnitude of the northward heat flux carried by the north atlantic surface ocean3 4 changes in the ocean s thermohaline circulation are a key component in many explanations of this climate flickering5 here we use stable isotope and other sedimentological data to reveal specific oceanic reorganizations during these rapid climate change events deep water was generated more or less continuously in the nordic seas during the latter part of the last glacial period 60 to 10 thousand years ago but by two different mechanisms the deep water formation occurred by convection in the open ocean during warmer periods interstadials but during colder phases stadials a freshening of the surface ocean reduced or stopped open ocean convection and deep water formation was instead driven by brine release during sea ice freezing these shifting magnitudes and modes nested within the overall continuity of deep water formation were probably important for the structuring and rapidity of the prevailing climate changes

new aspects of organic carbon deposition and its paleoceanographic implications along the northern barents sea margin during the last 30 000 years we studied variations in terrigenous tom and marine organic matter mom input in a sediment core on the northern barents sea margin over the last 30 ka using a multiproxy approach we reconstructed processes controlling organic carbon deposition and investigated their paleoceanographic significance in the north atlantic arctic gateways variations in paleo surface water productivity are not documented in amount and composition of organic carbon the highest level of mom was deposited during 25 23 ka as a result of scavenging on fine grained reworked and tom rich material released by the retreating svalbard barents sea ice sheet during the late weichselian a second peak of mom is preserved because of sorptive protection by detrital and terrigenous organic matter higher surface water productivity due to permanent intrusion of atlantic water and high suspension load release by melting sea ice during 15 9 11 2 ka

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

millennial scale iceberg discharges in the irminger basin during the last glacial period relationship with the heinrich events and environmental settings high resolution records of coarse lithic content and oxygen isotope have been obtained in a piston core from the irminger basin the last glacial period is characterized by numerous periods of increased iceberg discharges originating partly from iceland and corresponding to millennial scale instabilities of the coastal ice sheets and ice shelves in the nordic area a comparison with midlatitude sediment cores shows that ice rafted material corresponding to the heinrich events was deposited synchronously from 40 to 60 n there are thus two oscillating systems every 5 10 kyr massive iceberg armadas are released from large continental ice caps whereas more frequent instabilities of the coastal ice sheets in the high latitude regions occur every 1 2 3 8 kyr at the time of the heinrich events the synchroneity of the response from all the northern hemisphere ice sheets attests the existence of strong interactions between the two systems

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

stable isotope stratigraphy of the arctic ocean fram strait to central arctic abstract a comparison of stable isotope and textural records of sediment cores from the fram strait and central arctic ocean to isotopic records from low latitude oceans indicates that the arctic mediterranean responded dynamically to climatic change during the pleistocene core mg 123 from the fram strait shows at least four significant low 18 o intervals 5 high 13 c intervals and five intervals with a low amount of coarse sediment the association of high 18 o values with coarse sediment intervals indicates increased glacial ice in the fram strait during glacial phases of the climate cycle peaks within the low 18 o intervals increase in magnitude from oldest to youngest suggesting that glacial interglacial transitions are pulsed the magnitude of the different low 18 o intervals increases from oldest to youngest this is interpreted to indicate that there has been a progressive intensification of the oceanographic response to glacial interglacial transitions in the fram strait during the past 524 ky time series spectral analysis suggests an age of approximately 524 ky for the oldest sediment in core mg 123 yielding an average sedimentation rate of approximately 1 66 cm 1000 yr stable isotope records from the central arctic ocean indicate that sedimentation rates are on the order of 1 3 mm 1000 yr the isotope records support the established central arctic ocean lithostratigraphy coarse sediment deposition in the central arctic is not as clearly related to glacial conditions as it is in the fram strait the oxygen isotope range of central arctic ocean records is accentuated relative to the global ice volume signal recorded from lower latitude cores this may be caused by variations in salinity temperature and thickness of the arctic ocean s low salinity surface layer oceanographic responses to climatic change recorded in the fram strait are also recorded in the central arctic ocean but with decreased resolution due to the magnitude of difference in the sedimentation rates between the two areas

climatic instability ice sheets and ocean dynamics at high northern latitudes during the last glacial period 58 10 ka bp abstract oxygen isotope magnetic susceptibility and foraminiferal distribution data are presented for a high resolution core enam93 21 located at the northeast faeroe margin this core recorded a rapid succession of faunistic sedimentologic and isotopic variations which paralleled the greenland ice core isotopic records with their typical succession of abrupt temperature rises and gradual coolings the dansgaard oeschger cycles the most notable feature was the contemporaneous changes in surface and bottom water conditions and circulation that appeared tightly coupled with the rapid climate fluctuations warm episodes interstadials were appeared with higher sea surface temperatures and thermohaline convection in the norwegian greenland sea the polar front was located north of the enam93 21 site cold episodes stadials were associated with an increase in the input of melting fennoscandian icebergs low sea surface temperature and salinity and no thermohaline convection in the norwegian greenland sea intermediate waters changed to an estuarine mode at the faeroe margin with a reversed flow pattern through the faeroe shetland channel the polar front was located south of the enam93 21 site

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

the δ13c in benthic foraminiferal tests of fontbotia wuellerstorfi schwager relative to the δ13c of dissolved inorganic carbon in southern ocean deep water implications for glacial ocean circulation models on a transect between 20 and 70 s in the eastern atlantic ocean and weddell sea water samples from 19 hydrographic stations and bottom water from 55 surface sediment samples taken with a multiple corer were investigated for the stable carbon isotopic composition of the total dissolved inorganic carbon 13c co2 these measurements were compared to 13c values determined on live specimens of the benthic foraminifer fontbotia wuellerstorfi and closely related genera from the same stations in addition at 16 stations the stable carbon isotope composition of sedimentary organic carbon was measured general deepwater and bottom water mass circulation patterns as inferred from the 13c co2 are in close agreement with those known from other nonconservative tracers very low 13c values of upper circumpolar deep water 0 3 pee dee belemnite pdb in the polar front region and the eastern limb of the weddell gyre coincide with nutrient maxima however a significant decoupling of the dissolved phosphate signal from the 13c co2 signal is indicated in the abyssal weddell sea we attribute this to temperature dependent fractionation processes during gas exchange of surface waters with the atmosphere at sites of bottom water formation multiple corer water from the sediment water interface is slightly 13c depleted relative to deepwater and bottom water 13 co2 the surface sediment organic carbon 13c is 3 to 4 lower south of the polar front than north of it and the 13corg in freshly accumulated phytodetritus is 3 to 4 lower than surface sediment organic carbon 13c comparison of live f wuellerstorfi 13c and related genera with bottom water 13c co2 exhibits at most stations between the subtropical front 41 s and the southern boundary of the antarctic circumpolar current 55 s a significant lowering of foraminiferal 13c values compilation of a mean last glacial interglacial 13c amplitude 13c from six published southern ocean cores results in a shift of 0 99 0 13 pdb this shift is greater than that in all other regions however all of these cores are from positions close to recent oceanic fronts thus for these peripheral areas of the southern ocean we suggest about half of the glacial interglacial shift can be explained by varying frontal zone positions and widths accompanied by a change in mode and height of export production

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

ice rafting history from the spitsbergen ice cap over the last 200 kyr abstract three piston cores taken from the mid to upper continental slope of the spitsbergen margin have been used to elucidate the calving history of the spitsbergen ice mass for the last 200 kyr the abundance of clasts larger than 2 mm was used as a measure of ice rafted detritus ird in the cores these clasts were counted from x ray photographs the fraction coarser than 63 m was also measured and compared to the clast counts to assess the validity of this parameter as a measure of ird content the correlation between clast counts and the fraction 63 m was poor and it was concluded that the fraction 63 m was a poor measure of ird in the spitsbergen cores in cores close to a major continental landmass or from an area of steep submarine relief the fraction 63 m is likely to be affected by factors other than ice rafting alone the ird peaks identified in this study were thought to be produced by the following advance of the spitsbergen ice cap during periods of increased moisture supply during interstadial periods mid stage 5 and stage 3 disintegration of a large ice mass on the continental shelf during deglaciations stages 6 5e 5b 5a and 2 1 boundaries summer melting of a large ice mass during glacial periods stage 6 a good correlation was found between interpreted ice advances from ird input to the spitsbergen margin and postulated ice advances from terrestrial evidence the ird peaks found from the spitsbergen margin appear to be produced by a different mechanism from that proposed for the production of the heinrich layers of the north atlantic these are thought to be produced by the collapse of the laurentide ice sheet once it reaches a threshold size correlation of heinrich layers produced from a mid latitude ice sheet with the ird events of the norwegian greenland sea is not possible due to their different mechanism of formation in fact there is possibly an antiphase relationship as heinrich layers are formed mainly during glacial periods whereas ird peaks in the greenland sea are produced during periods of rapid ice advance when moisture supply is high when relatively warm atlantic waters enter the norwegian greenland sea during interstadial periods as well as during melting events

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

changes in east atlantic deepwater circulation over the last 30 000 years eight time slice reconstructions using 95 epibenthic 13c records eight time slices were reconstructed to trace the distribution of east atlantic deepwater and intermediate water masses over the last 30 000 years our results show that there have been three distinct modes of deepwater circulation near the stage 3 2 boundary the origin of north atlantic deep water nadw was similar to today mode 1 however after late stage 3 the source region of the nadw end member shifted from the norwegian greenland sea to areas south of iceland mode 2 a reduced nadw flow persisted during the last glacial maximum with constant preformed 13c values the nutrient content of nadw increased markedly near the azores fracture zone from north to south probably because of the mixing of upwelled antarctic bottom water aabw from below which then advected with much higher flux rates into the northeast atlantic later the spread of glacial meltwater over the north atlantic led to a marked short term ventilation minimum below 1800 m about 13 500 14c years ago mode 3 the formation of nadw recommenced abruptly north of iceland 12 800 12 500 years ago and reached a volume approaching that of the holocene in the younger dryas 10 800 10 350 years b p another short term shutdown of deepwater formation followed between 10 200 and 9 600 years b p linked to a further major meltwater pulse into the atlantic each renewal of deepwater formation led to a marked release of fossil co2 from the ocean the likely cause of the contemporaneous 14c plateaus over the last 9000 years deepwater circulation varied little from today apart from a slight increase in aabw about 7000 14c years ago it is also shown that the oxygenated mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30 000 years

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

transition zone reflections and permafrost analysis the usual study of seismic reflections is limited to those from sharply defined contrasts in acoustic impedance for reflections resulting from transition zones in which acoustic impedance is continuously variable such as the zones encountered in permafrost the frequency selective nature of attenuation and phase distortion leads to a number of characteristics which may be used in the sense of pattern recognition to identify such reflections an rms velocity analysis procedure can be used to estimate depths and velocity gradients associated with transition zones some simple approximations allow us to avoid solving a system of nonlinear equations in many cases of interest and the result is a practical technique which can be applied to many transition zone reflections at reasonable computational cost

high resolution stratigraphy of the faeroe shetland channel and its relation to north atlantic paleoceanography the last 87 kyr abstract two piston cores from the faeroe shetland channel have been investigated for stratigraphic and paleoceanographic correlation with atlantic ocean and norwegian sea records the high resolution cores have been analyzed for the downcore distribution of planktic and benthic foraminifera and oxygen isotopes ams 14 c dates and the position of ash layers i and ii form the basis for the correlation core na81 10 covers the period from isotope stage 3 to recent stage 1 while core na81 04 covers isotope stages 5a to 1 the holocene is well represented in core na81 10 by 2 m of sediment whereas it is only 50 cm in core na81 04 which is situated directly under the main core of the norwegian sea deep water outflow the transition of isotope stage 2 to stage 1 is affected by dissolution and thus is less clearly represented ams 14 c dates show that termination ia begins at 16 ka and ends at about the 13 ka level the last glacial maximum lgm defined at 19 16 ka is characterized by an ird peak faunal planktic foraminifera maxima dated at 17 3 and 18 25 ka and a high percentage of globigerina quinqueloba apparently open water conditions and circulation within the norwegian sea prevailed at least from 22 5 to 14 8 ka during the greatest part of stage 2 including the lgm and well onto termination ia a preservation maximum is observed throughout stage 2 isotope stage 3 with a nearly complete record of isotope substages is well represented in both cores oxygen isotope depletion peaks correlate with fauna minima and in time to north atlantic heinrich events h5 h1 faunal data indicate that deep water is generated within the norwegian greenland sea repeatedly since 26 ka with stops prior to 26 ka 22 5 20 8 20 5 ka and between 14 9 and 13 ka h3 h2 and h1 all isotope depletion peaks since ca 50 ka are anticorrelated with fauna and are mainly controlled by surface salinity changes isotope stages and substages are directly correlated to fauna peaks and temperature between 87 and ca 50 ka the faeroe shetland channel record shows that repeated presences of atlantic surface water and deep convection alternating with convection shutdowns have occurred within the norwegian sea greenland sea from the beginning of stages 5a to 1

arctic ocean record of last two glacial interglacial cycles off north greenland ellesmere island implications for glacial history a sediment record from the practically unknown southernmost part of the lomonosov ridge off north greenland ellesmere island has been studied greenice core 10 encompasses marine isotope stages mis 7 1 and reveals changing paleoceanographic conditions and land ocean connections during the last two glacial interglacial cycles the isotope record of planktic foraminifera neogloboquadrina pachyderma s show large similarities to other arctic ocean key records supporting that the pattern reflect over regional changes of the halocline structure the relatively low 18 o values of subpolar foraminifera turborotalita quinqueloba in the last interglacial unit support that the specimens represent local production related to warm interglacial conditions and a reduced sea ice cover in the interior arctic ocean enhanced deposition of coarse ice rafted debris took place during the mis 8 7 transition periods of mis 6 mis 6 5 transition mis 5d mis 4 and late mis 3 30 40 14 c kyr bp in mis 2 ird flux was low in the area the ird contains detrital carbonate similar to other amerasia basin records the occurrence of finegrained calcite rich detrital carbonate layers at glacial interglacial transitions seems unique to this area we suggest that detrital carbonate was transported and deposited from nepheloid flows during deglaciations of ellesmere island when the atlantic water boundary current along the continental margin was gaining strength 2007 elsevier b v all rights reserved

benthic foraminiferal δ13c and accumulation rates of organic carbon uvigerina peregrina group and cibicidoides wuellerstorfi the glacial to interglacial 13c records of the benthic foraminifera cibicidoides wuellerstorfi and the uvigerina peregrina group from deep sea cores cannot be adjusted by a generally valid constant the 13c values of the u peregrina group largely correlate with the accumulation rates of organic carbon suggesting a local habitat effect those of c wuellerstorfi vary independently with respect to the carbon flux and record fluctuations in the 13c of the ambient bottom water isotopic composition

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