mis 3 to mis 1 temporal and lgm spatial variability in arctic ocean sea ice cover reconstruction from biomarkers using the sea ice proxy ip25 and phytoplankton derived biomarkers brassicasterol and dinosterol arctic sea ice conditions were reconstructed for marine isotope stage mis 3 to 1 with special emphasis on the last glacial maximum lgm in sediment cores from the northern barents sea continental margin across the central arctic ocean to the southern mendeleev ridge our results suggest more extensive sea ice cover than present day during latter part of mis 3 increasing sea ice growth during mis 2 and decreased sea ice cover during the last deglacial the summer ice edge remained north of the barents sea even during extremely cold i e last glacial maximum lgm as well as warm periods i e bolling allerod during the lgm the western svalbard margin and the northern barents sea margin areas were characterized by high concentrations of both ip25 and phytoplankton biomarkers interpreted as a productive ice edge situation caused by the inflow of warm atlantic water in contrast the lgm central arctic ocean north of 84 n was covered by thick permanent sea ice throughout the year with rare break up indicated by zero or near zero biomarker concentrations the spring summer sea ice margin significantly extended southwards to the laptev sea shelf southern lomonosov ridge and southern mendeleev ridge during the lgm our proxy reconstructions are very consistent with published model results based on the north atlantic arctic ocean sea ice model naosim

deglaciation of the northern hemisphere at the onset of the eemian and holocene high resolution tims u series dating of sea level events obtained from coral reef complexes suggests that global deglaciation from the saale penultimate glacial to the eem interglacial marine 18o stages 6 5 may have occurred earlier in relation to milankovitch insolation forcing than that from the wisconsinan glacial to the holocene interglacial marine 18o stages 2 1 however the interpretation of these data has been problematic because of the possibility of isotope exchange in order to investigate whether these different lead lag relations between milankovitch forcing and ice volume are feasible from the point of view of large scale ice sheet dynamics and thermodynamics the three dimensional polythermal ice sheet model sicopolis simulation code for polythermal ice sheets is applied to the entire northern hemisphere which gives the major contribution to global ice volume changes due to the relative stability of the antarctic ice sheet and simulations through the last two climatic cycles are conducted the simulations cover the interval from 250 kyr bp until today and are driven by surface temperature reconstructions of deep ice cores grip vostok and simple parameterizations for the change of precipitation with time discussion of the results is focused on the saale eem and the wisconsinan holocene transitions the amount and rate of deglaciation are in good agreement with the specmap record for both cases and the evidence of the data for an early start of the eem interglacial is supported

the sensitivity of northern hemisphere ice sheets to atmospheric forcing during the last glacial cycle using pmip3 models the evolution of northern hemisphere ice sheets through the last glacial cycle is simulated with the glacial index method by using the climate forcing from one general circulation model cosmos by comparing the simulated results to geological reconstructions we first show that the modelled climate is capable of capturing the main features of the ice sheet evolution however large deviations exist likely due to the absence of nonlinear interactions between ice sheet and other climate components the model uncertainties of the climate forcing are examined using the output from nine climate models from the paleoclimate modelling intercomparison project phase iii the results show a large variability in simulated ice sheets between the different models we find that the ice sheet extent pattern resembles summer surface air temperature pattern at the last glacial maximum confirming the dominant role of surface ablation process for high latitude northern hemisphere ice sheets this study shows the importance of the upper boundary condition for ice sheet modelling and implies that careful constraints on climate output is essential for simulating realistic glacial northern hemisphere ice sheets

constraints on the pleistocene chronology of sediments from the lomonosov ridge 1 despite its importance in the global climate system age calibrated marine geologic records reflecting the evolution of glacial cycles through the pleistocene are largely absent from the central arctic ocean this is especially true for sediments older than 200 ka three sites cored during the integrated ocean drilling program s expedition 302 the arctic coring expedition acex provide a 27 m continuous sedimentary section from the lomonosov ridge in the central arctic ocean two key biostratigraphic datums and constraints from the magnetic inclination data are used to anchor the chronology of these sediments back to the base of the cobb mountain subchron 1215 ka beyond 1215 ka two best fitting geomagnetic models are used to investigate the nature of cyclostratigraphic change within this chronology we show that bulk and mineral magnetic properties of the sediments vary on predicted milankovitch frequencies these cyclic variations record glacial and interglacial modes of sediment deposition on the lomonosov ridge as evident in studies of ice rafted debris and stable isotopic and faunal assemblages for the last two glacial cycles and were used to tune the age model potential errors which largely arise from uncertainties in the nature of downhole paleomagnetic variability and the choice of a tuning target are handled by defining an error envelope that is based on the best fitting cyclostratigraphic and geomagnetic solutions

variable history of quaternary ice sheet advance across the beaufort sea margin arctic ocean the seismic stratigraphy and architecture of the beaufort sea shelf and slope are investigated using a comprehensive grid of high resolution two dimensional seismic reflection data three cross shelf troughs representing locations of former ice streams draining a 1000 km long section of the laurentide ice sheet lis are examined the mackenzie amundsen gulf and m clure strait systems dynamics of these paleo ice streams influenced ice sheet configuration and may have forced abrupt climatic change through delivery of ice and freshwater to the arctic ocean a comprehensive understanding of their geometry and dynamics is crucial for constraining numerical models of the lis evidence for two quaternary ice advances to the shelf break is interpreted from the mackenzie trough by contrast seismic stratigraphy of the amundsen gulf trough 400 km east of the mackenzie trough records at least nine quaternary ice advances here the outer shelf consists of stacked till sheets extending to the shelf break and forming a trough mouth fan the contrasting glacial histories of these neighboring ice streams are explained by their positions within the lis the mackenzie trough ice stream was situated at the extreme northwest ice sheet margin whereas the amundsen gulf ice stream had a more central location and larger drainage basin supplying significant quantities of ice and sediment to the arctic ocean through much of the quaternary the m clure strait trough probably possesses a similar architecture to the amundsen gulf trough and an even larger trough mouth fan

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

methane oxidation following submarine permafrost degradation measurements from a central laptev sea shelf borehole submarine permafrost degradation has been invoked as a cause for recent observations of methane emissions from the seabed to the water column and atmosphere of the east siberian shelf sediment drilled 52 m down from the sea ice in buor khaya bay central laptev sea revealed unfrozen sediment overlying ice bonded permafrost methane concentrations in the overlying unfrozen sediment were low mean 20 m but higher in the underlying ice bonded submarine permafrost mean 380 m in contrast sulfate concentrations were substantially higher in the unfrozen sediment mean 2 5 mm than in the underlying submarine permafrost mean 0 1 mm using deduced permafrost degradation rates we calculate potential mean methane efflux from degrading permafrost of 120 mg m 2 yr 1 at this site however a drop of methane concentrations from 190 m to 19 m and a concomitant increase of methane 13c from 63 to 35 directly above the ice bonded permafrost suggest that methane is effectively oxidized within the overlying unfrozen sediment before it reaches the water column high rates of methane ebullition into the water column observed elsewhere are thus unlikely to have ice bonded permafrost as their source

revision of the nw laurentide ice sheet implications for paleoclimate the northeast extremity of beringia and arctic ocean sedimentation abstract for the past half century reconstructions of north american ice cover during the last glacial maximum have shown ice free land distal to the laurentide ice sheet primarily on melville and banks islands in the western canadian arctic archipelago both islands reputedly preserve at the surface multiple laurentide till sheets together with associated marine and lacustrine deposits recording as many as three pre late wisconsinan glaciations the northwest corner of banks island was purportedly never glaciated and is trimmed by the oldest and most extensive glaciation banks glaciation considered to be of matuyama age 780 ka bp inside the limit of banks glaciation younger till sheets are ascribed to the thomsen glaciation pre sangamonian and the amundsen glaciation early wisconsinan stade the view that the western canadian arctic archipelago remained largely ice free during the late wisconsinan is reinforced by a recent report of two woolly mammoth fragments collected on banks and melville islands both dated to 22 ka bp these dates imply that these islands constitute the northeast extremity of beringia a fundamental revision of this model is now warranted based on widespread fieldwork across the adjacent coastlines of banks and melville islands including new dating of glacial and marine landforms and sediments on dundas peninsula southern melville island ams 14 c dates on ice transported marine molluscs within the most extensive laurentide till yield ages of 25 49 ka bp these dates require that late wisconsinan ice advanced northwestward from visount melville sound excavating fauna spanning marine isotope stage 3 laurentide ice that crossed dundas peninsula 300 m asl coalesced with melville island ice occupying liddon gulf coalescent laurentide and melville ice continued to advance westward through m clure strait depositing granite erratics at 235 m asl that require grounded ice in m clure strait as do streamlined bedforms on the channel floor deglaciation is recorded by widespread meltwater channels that show both the initial separation of laurentide and melvile ice and the successive retreat of laurentide ice southward across dundas peninsula into viscount melville sound sedimentation from these channels deposited deltas marking deglacial marine limit forty dates on shells collected from associated glaciomarine rhythmites record near synchronous ice retreat from m clure strait and dundas peninsula to north central victoria island 11 5 ka bp along the adjacent coast of banks island deglacial shorelines also record the retreat of laurentide ice both eastward through m clure strait and southward into the island s interior the elevation and age 11 5 ka bp of deglacial marine limit there is fully compatible with the record of ice retreat on melville island the last retreat of ice from mercy bay northern banks island previously assigned to northward retreat into m clure strait during the early wisconsinan is contradicted by geomorphic evidence for southward retreat into the island s interior during the late wisconsinan this revision of the pattern and age of ice retreat across northern banks island results in a significant simplification of the previous quaternary model our observations support the amalgamation of multiple till sheets previously assigned to at least three pre late wisconsinan glaciations into the late wisconsinan this revision also removes their formally named marine transgressions and proglacial lakes for which evidence is lacking erratics were also widely observed armouring meltwater channels originating on the previously proposed never glaciated landscape an extensive late wisconsinan laurentide ice sheet across the western canadian arctic is compatible with similar evidence for extensive laurentide ice entering the richardson mountains yukon farther south and with the innuitian ice sheet to the north widespread late wisconsinan ice in a region previously thought to be too arid to sustain it has important implications for paleoclimate ice sheet modelling arctic ocean ice and sediment delivery and clarifying the northeast limit of beringia

the russian component of an arctic ice sheet during the last glacial maximum abstract the extent of late weichselian glaciation in arctic russia remains a problem our model of 1995 1998 suggests a continuous and long lived ice sheet centered on the kara sea other reconstructions suggest a smaller and diachronous glaciation the vast majority of dates support the model of restricted glaciation we show that these dates are inconsistent with the geologic record of ice flow across the kara barents divide with second order glacial geology of kola peninsula and with evidence for glacial surges they are also inconsistent with late weichselian climate of the arctic with eurasian continental paleohydrology including meltwater drainage systems cataclysmic megafloods major transgressions of the caspian sea and with the entire paleogeographic context of northern eurasia we believe that due to impeded ventilation of the pleistocene arctic ocean these dates are often too old and that recycling and contamination of the samples would also contribute to the dating errors destructive impacts of late glacial ice sheet surges and megafloods upon the arctic glacial sequences would also aggravate the situation by ignoring the dates until these problems are addressed we find that the field evidence supports continuous glaciation of arctic russia at the lgm and that the resulting ice sheet was part of an arctic ice sheet that included an ice shelf in the arctic ocean and ice sheets in greenland and north america we present 3 d reconstructions of the arctic ice sheet and with an enlarged antarctic ice sheet we show that the ice volume is equivalent to an lgm sea level that was 130 135 m lower than at present the reconstructions depict the arctic ice sheet before and after massive thawing of the bed that allows partial gravitational collapse of the overlying ice with a minimal change in ice volume

an arctic ocean ice shelf during mis 6 constrained by new geophysical and geological data the hypothesis of floating ice shelves covering the arctic ocean during glacial periods was developed in the 1970s in its most extreme form this theory involved a 1000 m thick continuous ice shelf covering the arctic ocean during quaternary glacial maxima including the last glacial maximum lgm while recent observations clearly demonstrate deep ice grounding events in the central arctic ocean the ice shelf hypothesis has been difficult to evaluate due to a lack of information from key areas with severe sea ice conditions here we present new data from previously inaccessible unmapped areas that constrain the spatial extent and timing of marine ice sheets during past glacials these data include multibeam swath bathymetry and subbottom profiles portraying glaciogenic features on the chukchi borderland southern lomonosov ridge north of greenland morris jesup rise and yermak plateau sediment cores from the mapped areas provide age constraints on the glaciogenic features combining these new geophysical and geological data with earlier results suggests that an especially extensive marine ice sheet complex including an ice shelf existed in the amerasian arctic ocean during marine isotope stage mis 6 from a conceptual oceanographic model we speculate that the cold halocline of the polar surface water may have extended to deeper water depths during mis 6 inhibiting the warm atlantic water from reaching the amerasian arctic ocean and thus creating favorable conditions for ice shelf development the hypothesis of a continuous 1000 m thick ice shelf is rejected because our mapping results show that several areas in the central arctic ocean substantially shallower than 1000 m water depth are free from glacial influence on the seafloor

glacial geomorphology of the central arctic ocean the chukchi borderland and the lomonosov ridge the last decade of geophysical seafloor mapping in the arctic ocean from nuclear submarines and icebreakers reveals a wide variety of glaciogenic geomorphic features at water depths reaching 1000 in these findings provide new and intriguing insights into the quaternary glacial history of the northern hemisphere here we integrate multi and single beam bathymetric data chirp sonar profiles and sidescan images from the chukchi borderland and lomonosov ridge to perform a comparative morphological seafloor study this investigation aims to elucidate the nature and provenance of ice masses that impacted the arctic ocean sea floor during the quaternary mapped glaciogenic bedforms include iceberg keel scours most abundant at water depths shallower than similar to 350 400 m flutes and megascale glacial lineations extending as deep as similar to 1000 m below the present sea level small drumlin like features and morainic ridges and grounding zone wedges the combination of these features indicates that very large glacial ice masses extended into the central arctic ocean from surrounding north american and eurasian ice sheets several times during the quaternary ice shelves occupied large parts of the arctic ocean during glacial maxima and ice rises were formed over the chukchi borderland and portions of the lomonosov ridge more geophysical and sediment core data combined with modeling experiments are needed to reconstruct the timing and patterns of these events

holocene variability in sea ice cover primary production and pacific water inflow and climate change in the chukchi and east siberian seas arctic ocean in this study we present new detailed biomarker based sea ice records from two sediment cores recovered in the chukchi sea and the east siberian sea these new biomarker data may provide new insights on processes controlling recent and past sea ice changes the biomarker proxy records show i minimum sea ice extent during the early holocene ii a prominent mid holocene short term high amplitude variability in sea ice primary production and pacific water inflow and iii significantly increased sea ice extent during the last ca 4 5k cal a bp this late holocene trend in sea ice change in the chukchi and east siberian seas seems to be contemporaneous with similar changes in sea ice extent recorded from other arctic marginal seas the main factors controlling the millennial variability in sea ice and surface water productivity are probably changes in surface water and heat flow from the pacific into the arctic ocean as well as the long term decrease in summer insolation the short term centennial variability observed in the high resolution middle holocene record is probably related to solar forcing our new data on holocene sea ice variability may contribute to synoptic reconstructions of regional to global holocene climate change based on terrestrial and marine archives

quaternary dinoflagellate cysts in the arctic ocean potential and limitations for stratigraphy and paleoenvironmental reconstructions abstract the arctic ocean is a siliciclastic depositional environment which lacks any rock forming biogenic calcareous and siliceous components during large parts of its quaternary history these hemipelagic sediments are nevertheless suitable for the study of organic walled microfossils of which the fossil remains of dinoflagellates dinoflagellate cysts are the most important group dinoflagellate cysts have become an important tool in paleoceanography of the high northern latitudes but their potential for quaternary biostratigraphy has remained largely unexplored dinoflagellate cysts are the dominant marine palynomorph group which is more continuously present in the marginal seas e g barents sea bering sea than in the arctic ocean itself throughout the quaternary most species have long stratigraphic ranges are temporary absent and show abundance variations on glacial interglacial timescales of the more than 30 taxa recorded only habibacysta tectata and filisphaera filifera became extinct in the pleistocene the highest persistent occurrence of h tectata at ca 2 0 ma and the top of f filifera acme at ca 1 8 ma can be used for supra regional stratigraphic correlation between the arctic ocean and adjacent basins these events corroborate a slow sedimentation rate model for the quaternary section on the central lomonosov ridge but a combination of different methods will have to be applied to provide a detailed chronostratigraphy the occurrence of cysts of phototrophic dinoflagellates in certain stratigraphic intervals on lomonosov ridge supports published evidence of episodic opening of the multiyear arctic sea ice cover during the quaternary probably related to a stronger inflow of atlantic water this contradicts the hypothesis of a permanently ice covered central arctic ocean in the quaternary

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

seabed erosion on the lomonosov ridge central arctic ocean a tale of deep draft icebergs in the eurasia basin and the influence of atlantic water inflow on iceberg motion 1 the submarine lomonosov ridge which bisects the arctic ocean is covered by 450 m of hemipelagic sediments high resolution chirp sonar and side scan data have documented erosion of a section of the ridge here we present multichannel seismic and chirp sonar data which show removal of unconsolidated sediments along the eurasia basin side of the lomonosov ridge where the central ridge is shallower than 1000 m the incomplete erosion of the hemipelagic drape and probable topographic control of ice motion suggest that the deepest draft glacier ice which reached the central arctic ocean from the eurasia basin was in the form of armadas of large icebergs embedded in sea ice rather than a single continuous floating ice shelf massive rapid discharge of glacier ice was probably required to produce the deepest draft 800 m icebergs eastward and northward drift trajectories from a likely iceberg source area on the kara barents sea margin would reflect the relative strength of atlantic inflow through the fram strait however only icebergs with drafts exceeding bathymetric thresholds on the lomonosov ridge would leave an erosive imprint on the seabed advection of atlantic water may have been relatively strong at times of discharge from the saalian ice sheet icebergs exiting the arctic ocean caused massive erosion and redeposition of the hemipelagic sediments on top of yermak plateau

influence of bering strait flow and north atlantic circulation on glacial sea level changes sea level fluctuations of about 20 30m occurred throughout the last glacial period these fluctuations seem to have been derived primarily from changes in the volume of northern hemisphere ice sheets 1 3 and cannot be attributed solely to ice melt caused by varying solar radiation 4 here we use a fully coupled climate model to show that the transport of relatively fresh pacific water into the north atlantic ocean was limited when lower sea level restricted or closed the bering strait resulting in saltier north atlantic surface waters this invigorated deep convection in the north atlantic ocean strengthening meridional overturning circulation and northward heat transport in our model which consequently promoted melting of ice sheets in north america and europe our simulations show that the associated sea level rise led to a reopening of the bering strait the flux of relatively fresh water into the north atlantic ocean muted meridional overturning circulation and led to cooling and ice sheet advance in the northern hemisphere we conclude that the repetition of this cycle could produce the sea level changes that have been observed throughout the last glacial cycle

the micromorphology of paraglacial and periglacial slope deposits a case study from morfa bychan west wales uk micromorphological analysis of the crudely stratified diamictons exposed in coastal sections at morfa bychan west wales is presented and discussed three major units yellow head blue head and brown head have been recognised and their crudely stratified nature plus clast orientations indicate that they were all subject to mass movement down the flanks of the adjacent coastal hills earlier workers have suggested a periglacial environment for this mass movement but recently it has been proposed that the blue head at least may have accumulated in a paraglacial environment through gravitational redistribution of recently deposited unstable till it is shown here that the yellow head contains occasional dense silt rich coatings on the upper surfaces of sand and gravel grains although other cryogenic micromorphological phenomena were not observed the blue head however contains no clear cryogenic micromorphological features although there is abundant evidence for sediment shearing and grain rotation within the matrix the brown head contains diffuse grain coatings and lenticular aggregates very similar to those observed elsewhere in periglacial solifluction deposits thus it is concluded that accumulation of the blue head was rapid and took place in a paraglacial environment as a result of mudflow the yellow head may represent periglacial solifluction immediately prior to glaciation whereas the brown head accumulated above the blue head as a result of periglacial weathering of the adjacent exposed hill tops and subsequent downslope solifluction of the weathering product 1998 john wiley sons ltd

repeated pleistocene glaciation of the east siberian continental margin during glacial periods ice sheets covered continental margins through much of arctic north america greenland and western eurasia marine structures suggest that an ice sheet up to a kilometre in depth periodically covered the east siberian continental shelf as well

submarine glacial landforms and rates of ice stream collapse the rate of deglacial ice sheet retreat across polar continental shelves and possible ice stream collapse and sea level rise has been much debated high resolution imagery of seafloor morphology is available for many polar shelves and fjords the rapidity of ice retreat is inferred from diagnostic assemblages of submarine landforms produced at ice stream sedimentary beds these landforms exposed by ice retreat across high latitude shelves demonstrate that deglaciation occurs in three main ways rapidly by flotation and breakup episodically by still stands and or grounding events punctuating rapid retreat or by slower retreat of grounded ice submarine landform assemblages imply through the presence of grounding zone wedges overprinting mega scale glacial lineations on many polar shelves that ice stream retreat is more often episodic than catastrophic these observations provide a robust test of the ability of numerical models to predict the varied response of ice sheet basins to environmental changes

palaeoclimate a fresh look at arctic ice sheets during the last glacial maximum ice sheets in eurasia terminated at the edge of the laptev sea seismic data now suggest that a separate ice sheet was repeatedly centred further east in the east siberian sea during previous glacial periods

marginal formation of de geer moraines and their implications to the dynamics of grounding line recession de geer moraine ridges occur in abundance in the coastal zone of northern sweden preferentially in areas with proglacial water depths in excess of 150 m at deglaciation from detailed sedimentological and structural investigations in machine dug trenches across de geer ridges it is concluded that the moraines formed due to subglacial sediment advection to the ice margin during temporary halts in grounding line retreat forming gradually thickening sediment wedges the proximal part of the moraines were built up in submarginal position as stacked sequences of deforming bed diamictons intercalated with glaciofluvial canal infill sediments whereas the distal parts were built up from the grounding line by prograding sediment gravity flow deposits distally interfingering with glaciolacustrine sediments the rapid grounding line retreat ca 400 m yr 1 was driven by rapid calving in turn enhanced by fast iceflow and marginal thinning of ice due to deforming bed conditions the spatial distribution of the moraine ridges indicates stepwise retreat of the grounding line it is suggested that this is due to slab and flake calving of the ice cliff above the waterline forming a gradually widening subaqueous ice ledge which eventually breaks off to a new grounding line followed by regained sediment delivery and ridge build up less

basal mechanics of ice stream b west antarctica 1 till mechanics data from laboratory geotechnical tests on till recovered from beneath ice stream b west antarctica at the upstream b camp hereinafter the upb till show that failure strength of this till is strongly dependent on effective stress but is practically independent of strain and strain rate these data support use of a coulomb plastic rheology in modeling of ice stream behavior and subglacial till deformation our testing program combined triaxial ring shear and confined uniaxial tests to investigate till strength and compressibility results show that the upb till follows closely coulomb s equation in which shear strength is a linear function of normal effective stress apparent cohesion near zero and internal friction angle equal to 24 till compressibility is best described by a logarithmic function that relates void ratio to normal effective stress in general the behavior of the upb till is consistent with other experimental evidence regarding mechanical behavior of granular materials based on our laboratory results we formulate the compressible coulomb plastic till model in which there are three interrelated primary state variables shear strength void ratio and normal effective stress this model is used in the second part of our study to simulate response of subglacial till to realistic effective stress forcings these simulations demonstrate that the model is capable of reproducing fundamental aspects of subglacial till kinematics 1 occurrence of tilt rate oscillations and negative tilt rates in tiltmeter records and 2 distributed till deformation to depths of 0 1 1 0 m beneath the ice base our laboratory and modeling results substantiate application of the compressible coulomb plastic model in simulations of the motion of ice stream b over its weak till bed

calcareous microfossil based orbital cyclostratigraphy in the arctic ocean abstract microfaunal and geochemical proxies from marine sediment records from central arctic ocean cao submarine ridges suggest a close relationship over the last 550 thousand years kyr between orbital scale climatic oscillations sea ice cover marine biological productivity and other parameters multiple paleoclimate proxies record glacial to interglacial cycles to understand the climate cryosphere productivity relationship we examined the cyclostratigraphy of calcareous microfossils and constructed a composite arctic paleoclimate index api stack from benthic foraminiferal and ostracode density from 14 sediment cores following the hypothesis that api is driven mainly by changes in sea ice related productivity the api stack shows the arctic experienced a series of highly productive interglacials and interstadials every 20 kyr these periods signify minimal ice shelf and sea ice cover and maximum marine productivity rapid transitions in productivity are seen during shifts from interglacial to glacial climate states discrepancies between the arctic api curves and various global climatic sea level and ice volume curves suggest abrupt growth and decay of arctic ice shelves related to climatic and sea level oscillations

climate science a great arctic ice shelf newly mapped features on the floor of the arctic ocean suggest that the arctic basin was once covered by a one kilometre thick flowing ice shelf derived from large ice sheets in eastern siberia arctic canada and the barents sea

differences between the last two glacial maxima and implications for ice sheet δ18o and sea level reconstructions studies of past glacial cycles yield critical information about climate and sea level ice volume variability including the sensitivity of climate to radiative change and impacts of crustal rebound on sea level reconstructions for past interglacials here we identify significant differences between the last and penultimate glacial maxima lgm and pgm in terms of global volume and distribution of land ice despite similar temperatures and radiative forcing our analysis challenges conventional views of relationships between global ice volume sea level seawater oxygen isotope values and deep sea temperature and supports the potential presence of large floating arctic ice shelves during the pgm the existence of different glacial modes calls for focussed research on the complex processes behind ice age development we present a glacioisostatic assessment to demonstrate how a different pgm ice sheet configuration might affect sea level estimates for the last interglacial results suggest that this may alter existing last interglacial sea level estimates which often use an lgm like ice configuration by several metres likely upward

paleogeography and geochronology in the russian eastern arctic during the second half of the quaternary abstract during the conclusion of the middle pleistocene continental glaciation was initiated in the western part of northern eurasia while alpine glaciers developed in the mountain ranges in the east small ice caps developed on wrangel and delong islands and most of the chukchi peninsula was glaciated the continental shelves of the laptev and east siberian seas remained ice free and subaerially exposed as indicated by cryogenic and aeolian sediments xerophytic herbaceous palynological assemblages and remains of mammuthus primigenius the initiation of the late pleistocene was marked by a major marine transgression over the eastern part of the arctic ocean shelf correlative with the pelukian transgression of alaska and the sangamonian interglacial isotope stage 5e of north america sea levels exceeded present values by approximately 10 15 m a subsequent regression marked the onset of sartanian glaciation ca 25 000 bp climate warming began ca 14 000 bp reaching an optimum ca 8000 bp and was accompanied by renewed marine transgression climate fluctuations persisted throughout the holocene as indicated by alternating tundra shrub tundra and taiga palynomorph assemblages

an east siberian ice shelf during the late pleistocene glaciations numerical reconstructions abstract a recent data campaign in the east siberian sea has revealed evidence of grounded and floating ice dynamics in regions of up to 1000 m water depth and which are attributed to glaciations older than the last glacial maximum 21 kyrs bp the main hypothesis based on this evidence is that a small ice cap developed over beringia and expanded over the east siberian continental margin during some of the late pleistocene glaciations other similar evidence of ice dynamics that have been previously collected on the shallow continental shelves of the arctic ocean have been attributed to the penultimate glaciation i e marine isotopes stage 6 140 kyrs bp we use an ice sheet model forced by two previously simulated mis 6 glacial maximum climates to carry out a series of sensitivity experiments testing the impact of dynamics and mass balance related parameters on the geometry of the east siberian ice cap and ice shelf results show that the ice cap developing over beringia connects to the eurasian ice sheet in all simulations and that its volume ranges between 6 and 14 m sle depending on the climate forcing this ice cap generates an ice shelf of dimensions comparable with or larger than the present day ross ice shelf in west antarctica although the ice shelf extent strongly depends on the ice flux through the grounding line it is particularly sensitive to the choice of the calving and basal melting parameters finally inhibiting a merging of the beringia ice cap with the eurasian ice sheet affects the expansion of the ice shelf only in the simulations where the ice cap fluxes are not large enough to compensate for the fluxes coming from the eurasian ice sheet

identification and preservation of landforms diagnostic of past ice sheet activity on continental shelves from three dimensional seismic evidence ice ages have occurred a number of times in earth9s history and are important in understanding changes in long term climate however it is difficult to demonstrate the presence of ice sheets in the ancient record because their sedimentary products can resemble those from nonglacial processes e g debris flows diagnostic large scale glacial landforms produced beneath ice sheets and preserved on continental shelves after deglaciation can establish a glacial origin three dimensional seismic evidence from the 2 7 ma naust formation norwegian margin illustrates several glacial landforms that are also commonly occurring features on modern high latitude shelves 1 streamlined mega scale lineations produced by fast flowing ice streams 2 ploughmarks formed by iceberg keels and 3 regularly spaced transverse ridges or push moraines formed during ice retreat we have found for example buried ice keel ploughmarks on a paleoshelf dating to ca 2 ma norwegian margin seismic stratigraphy data show that ice advanced and retreated many times and some paleoshelf surfaces were preserved such paleosurfaces must survive ocean basin destruction for glacial landforms to be useful in identification of ancient depositional environments

ice complex formation on bol shoy lyakhovsky island new siberian archipelago east siberian arctic since about 200 ka late quaternary landscapes of unglaciated beringia were largely shaped by ice wedge polygon tundra ice complex ic strata preserve such ancient polygon formations here we report on the yukagir ic from bol shoy lyakhovsky island in northeastern siberia and suggest that new radioisotope disequilibria 230th u dates of the yukagir ic peat confirm its formation during the mis 7a c interglacial the preservation of the ice rich yukagir ic proves its resilience to last interglacial and lateglacial holocene warming this study compares the yukagir ic to ic strata of mis 5 mis 3 and mis 2 ages exposed on bol shoy lyakhovsky island besides high intrasedimental ice content and syngenetic ice wedges intersecting silts sandy silts the yukagir ic is characterized by high organic matter om accumulation and low om decomposition of a distinctive drepanocladus moss peat the yukagir ic pollen data reveals grassshrub moss tundra indicating rather wet summer conditions similar to modern ones the stable isotope composition of yukagir ic wedge ice is similar to those of the mis 5 and mis 3 ics pointing to similar atmospheric moisture generation and transport patterns in winter ice complex data from glacial and interglacial periods provide insights into permafrost and climate dynamics since about 200 ka

relative sea level variations in the chukchi region arctic ocean since the late eocene 1 relative sea level rsl variations are a result of tectonic activity changing of the water volume in ocean basins e g due to increasing decreasing of ice volume evaporation and variations in regional to global climate which influence erosional processes and material transport we present multi channel seismic data combined with dated sediment horizons from the chukchi shelf arctic ocean based on a series of prograding sequences in the upper 4 km of sediments and the method of seismic sequence stratigraphy we introduce the first rsl curve for the chukchi region beginning in the late eocene 40 ma the comparison of the chukchi rsl curve with the global rsl curve shows that rsl lowering events in the chukchi region do not correlate with global events for the eocene oligocene early miocene between the eocene oligocene and the late oligocene the chukchi rsl variations were small 100 m since the late oligocene the chukchi rsl increased until the opening of the fram strait in the early miocene we show that the chukchi rsl variations are representative for the arctic ocean and conclude that the arctic ocean was an isolated basin for the eocene oligocene early miocene

pleistocene iceberg dynamics on the west svalbard margin evidence from bathymetric and sub bottom profiler data large icebergs leave evidence of their drift via ploughing of the seabed thereby providing a geological record of episodes of calving from thick ice sheets we interpret large scale curvilinear depressions on the western svalbard margin as ploughmarks produced by the keels of icebergs that grounded on the seafloor as they drifted through this area iceberg ploughmarks were identified at modern water depths between 300 m and 1000 m and in two distinct stratigraphic units combining data from sediment cores with seismic stratigraphy from sub bottom profiler data suggests that the ploughmarks developed in two phases 1 during marine isotope stage mis 6 and 2 during mis 2 indicating the presence of large drifting icebergs on the western svalbard margin during both the late saalian and late weichselian glaciations sediment core data along the western svalbard margin indicate a sharp increase in mass transported sediments dated at 23 7 0 2 ka consistent with the mis 2 age of the younger iceberg ploughed surface the ploughmarks are oriented in two main directions sw ne and s n s n oriented ploughmarks which shallow to the north indicate iceberg drift from the south with a sw ne component marking the zone of splitting of the west spitsbergen current wsc into the yermak slope current ysc and north spitsbergen current nsc large mis 6 and mis 2 icebergs most likely had an arctic ocean source we suggest that these icebergs probably left the arctic ocean southward through fram strait and circulated within the norwegian greenland sea before being transported northwards along the svalbard margin by the wsc an additional likely source of icebergs to the western svalbard margin during mis 2 was the ice sheet terminating in the western barents sea from which icebergs drifted northward

seismostratigraphy of the siberian sector of the arctic ocean and adjacent laptev sea shelf a new seismostratigraphic model has been established within the arctic ocean adjacent to the east siberian shelf on the basis of multichannel seismic reflection data acquired along a transect at 81 n ages for the sedimentary units were estimated via links to seismic lines and drill site data of the us chukchi shelf the lomonosov ridge and the adjacent laptev shelf two distinct seismic units were mapped throughout the area and are the constraints for dating the remaining strata the lower marker unit a pronounced high amplitude reflector sequence hars is the most striking stratigraphic feature over large parts of the arctic ocean it indicates a strong and widespread change in deposition conditions probably it developed during oligocene times when a reorientation of arctic plates took place accompanied by the gradual opening of the fram strait and a widespread regression of sea level the top of the hars likely marks the end of oligocene early miocene 23ma an age estimate for the base of the sequence is less clear but likely corresponds to base of eocene 56ma the second marked unit detected on the seismic lines parallels the seafloor with a thickness of about 200ms two way travel time 160 m its base is marked by a change from a partly transparent sequence with weak amplitude reflections below to a set of continuous high amplitude reflectors above this interface likely marks the transition to large scale glaciation of the northern hemisphere and therefore is ascribed to the top miocene 5 3 ma

antarctic temperature and global sea level closely coupled over the past five glacial cycles sea level has varied by over one hundred metres across glacial interglacial cycles over the past 520 000 years an extended sea level reconstruction shows a strong coupling between these sea level changes and antarctic surface temperatures over the past five glacial cycles

late quaternary glaciations in northeastern russia a summary of the extent and chronology of quaternary glaciations in ne russia is presented in this paper the complex timing and style of glaciations include asynchronous development of alpine glaciers in the western and eastern part of the area while in the eastern part of ne russia well preserved moraines have been dated to the global last glacial maximum 18 24 ka in the westernmost part of the area no glacial advance took place at this time in general glacial advances were more extensive earlier rather than later in the last glacial cycle although only a handful of studies with reliable absolute ages in the vast area of ne russia exist it is clear that the number of advances throughout the region varies variable glacial response to global climate patterns is attributable to contrasting sources of precipitation an atlantic moisture source dominates in the western part of ne russia while a pacific source influences the eastern part of the region the glacial advances in the interior of ne russia are largely unexplored and further research is needed in order to understand quaternary climate change in the region copyright 2008 john wiley sons ltd

a new holocene relative sea level curve for western brittany france insights on isostatic dynamics along the atlantic coasts of north western europe abstract this study presents new relative sea level rsl data that were obtained in the finistere region western tip of brittany france and the implications those data have for the understanding of the isostatic dynamics across north western europe and more specifically along the atlantic and channel coasts new stratigraphic sequences were obtained and analyzed to derive 24 new sea level index points in which 6 are basal these new data considerably increase the knowledge we have of the rsl evolution along the coasts of western brittany since the last 8 kyr b p from this new dataset rsl was estimated to rise continuously over the last 8 kyr with a major inflection at ca 6 kyr cal bp our results show large vertical discrepancies between the rsl records of brittany and south western uk with the latter plotting several meters below the new data from this comparison we suggest that the two regions underwent a very different pattern and or amplitude of subsidence during the last 8 kyr which has implications for the spatial and temporal pattern of the peripheral bulge of the european ice sheets we compared our data against predictions from glacio isostatic adjustment models gia models there are large misfits between rsl observations and the predictions of the global ice 5g vm2a peltier 2004 glac1 b tarasov and peltier 2002 tarasov et al 2012 briggs et al 2014 and regional uk models biis bradley et al 2009 bradley et al 2011 kuchar kuchar et al 2012 which can t be resolved through significant changes to the deglaciation history and size of the british irish ice sheet paleo tidal modelling corrections indicate regional changes in the tidal ranges played a negligible role in the data model misfits hence we propose that the misfits are due to some combination of i unaccounted mass loss of far field ice sheets antarctic ice sheet or laurentide ice sheet ii unresolved differences in the deglaciation history and size of the fennoscandian ice sheet or more likely iii significant lateral variations in the earth s structure across the english channel

neolithic and aeneolithic environments in the central primor ye region the bol shaya ussurka valley the russian far east abstract holocene climates and environmental changes in the russian primor ye are still insufficiently documented in comparison with the more southerly far east asian areas systematic field investigations performed during the last years in the central primor ye region adjacent to manchuria have produced a new and most fascinating picture on the local cultural development between 9th and 3rd mill bp multi proxy palaeoecology records from the key stratified archaeological sites in the bol shaya ussurka iman river basin display marked environmental shifts witnessed by the contextual geological and pollen evidence from the occupations loci believed to reflect the early prehistoric formation in these woodland territories during the early and mid holocene the reconstructed vegetation history shows a good correlation of the neolithic appearance in the iman basin with the mapped trend of a regional climate amelioration characterized by increased temperature and humidity rates culminating in the holocene climatic optimum 9 6 ka bp and the subsequent cultural diversification and progress during the late neolithic and aeneolithic palaeo metal periods changes in the regional vegetation cover extrapolated from pollen sequences 14 c dated to ca 4500 3500 cal bp are likely linked to anthropogenic pressure to the pristine environment with the site vicinity taiga clearance for new pastures by people of the almazinka culture marking the climax of the local neolithic development a uniform adaptation to local natural settings with mixed basic hunting gathering and extensive pastoral economies persisted throughout millennia until historical times most of the cultural horizons are sealed in abiotically distorted palaeosols indicating climate instability and marked environmental shifts in the north central primor ye area during the holocene

arctic ocean glacial history while there are numerous hypotheses concerning glacial interglacial environmental and climatic regime shifts in the arctic ocean a holistic view on the northern hemisphere s late quaternary ice sh

widespread multi source glacial erosion on the chukchi margin arctic ocean abstract multibeam bathymetry and sub bottom profiler data acquired in 2011 from r v marcus langseth in a broad grid over the chukchi sea margin reveal multiple glacigenic features on the top and slopes of the outer chukchi shelf rise and adjacent borderland glacial lineations record a complex pattern of erosion likely formed by both local glaciation and far traveled ice shelves streams sourced from the laurentide and possibly east siberian ice sheets multiple till units and stacked debris flows indicate recurrent glacial grounding events composite till wedges of several hundred meters thick extend the shelf edge by 10 20 km in places distribution of ice marginal features on the chukchi rise suggests stepwise deglacial retreat towards the shelf backing up the broad bathymetric trough at the eastern side of the rise glacigenic features other than extensive iceberg scouring cannot be identified above 350 m depth and no glacigenic bedforms are present on the current swept shallow shelf despite the resulting uncertainty with the southern extent of the glaciation the data suggest a widespread grounded ice presence on the northern chukchi shelf which makes it an important previously underestimated component of the arctic paleo glacial system

the extent and chronology of cenozoic global glaciation abstract the quaternary is synonymous with extensive glaciation of earth s mid and high latitudes although there were local precursors significant glaciation began in the latest eocene ca 35 ma in eastern antarctica it was followed by glaciation in mountain areas through the miocene in alaska greenland iceland and patagonia later in the pliocene e g in the bolivian andes and possibly in tasmania and in the earliest pleistocene e g in the alps new zealand iceland and greenland today evidence from both the land and the ocean floors demonstrates that the major continental glaciations outside the polar regions rather than occurring throughout the 2 6 ma of the quaternary were markedly restricted to the last 1 ma 800 ka or less marine isotope stage mis 22 ca 870 880 ka included the first of the major worldwide events with substantial ice volumes that typify the later pleistocene glaciations i e mis 16 12 10 6 4 2

constraint on the penultimate glacial maximum northern hemisphere ice topography 140 kyrs bp abstract the penultimate glacial maximum pgm 140 kyrs bp is known to be the most extensive glaciation on record that occurred during the last 400 kyrs over eurasia we used a coupled atmosphere ocean sea ice land model to simulate the climate of the pgm accounting for a reconstruction of the large pgm eurasian ice sheet due to uncertainties in the pgm laurentide ice sheet topography two simulations with different ice sheet topographies over north america large as for the last glacial maximum lgm and small as for 13 kyrs bp are performed results show that the simulated pgm glacial maximum climates are of comparable magnitude with previous simulations of the lgm in both cases assuming a small laurentide ice sheet instead of the lgm one in our pgm simulations results in a shift in the planetary waves this causes an increase in storm track activity over the north atlantic as well as higher temperatures and precipitation rates over north america north atlantic and over the eurasian ice sheet in addition it induces a negative temperature anomaly over east siberia yielding a thick snow cover which seems to be in agreement with data from recent arctic campaigns suggesting that an ice cap developed over beringia during the pgm all together the changes in large scale circulation and regional climate simulated using a small laurentide ice sheet match the proxies well based on our findings we suggest that the laurentide ice sheet might have been smaller during the pgm than during the lgm in turn also implying a larger eurasian ice sheet than during the lgm which is supported by various geological evidence of the pgm

hydrodynamic pressures on arch dam during earthquakes a complete three dimensional finite difference scheme has been developed and used to analyze the nonlinear hydrodynamic pressures on arch dam during earthquakes both free surface waves and nonlinear convective acceleration are included in the analysis various dam shapes and reservoir banks were studied and the characteristic of nonlinear contribution due to curved geometry and free surface waves are discussed numerical experiments have been made to determine the desirable mesh size arrangements and time increments the effects of surface wave and convective acceleration on hydrodynamic pressure could augment the hydrodynamic pressure to 10 larger than that of a linear analysis for an earthquake with large ground displacement a large rise of the water surface could probably happen and be a severe threat to human safety in recreational areas and even cause overflow to affect the safe operation of the arch dam an empirical formula is given to predict approximate hydrodynamic force