cenozoic ice rafting history of the central arctic ocean terrigenous sands on the lomonosov ridge the cenozoic ice rafted debris ird history of the central arctic is reconstructed utilizing the terrigenous coarse sand fraction in iodp 302 cores from 0 to 273 meters composite depth this holocene middle eocene quantitative record of terrigenous sand accumulation on the lomonosov ridge along with qualitative information on grain texture and composition confirms the interpretation that ice initiation sea ice and glacial ice occurred 46 ma in the arctic and provides a long term pattern of arctic ice expansion and decay since the middle eocene ird mass accumulation rates range from 0 to 0 13 g cm2 ka in the middle eocene and from 0 to 0 36 g cm2 ka in the neogene ird mass accumulation rate mar maxima in the miocene and pliocene cooccur with either glacial initiation or intensification in the sub arctic the 46 25 ma ird onset in the central arctic slightly precedes the earliest evidence of ice in the antarctic and compares in timing with a 1000 ppm decrease in atmospheric concentrations of co2 the decline of pco2 in the middle eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface arctic ocean especially during times of low insolation

eco environmental effects of the qinghai tibet plateau uplift during the quaternary in china the qinghai tibet plateau uplifted 3000 m in the quaternary period the average rate of uplift was 1 1 1 mm year the uplifting has remolded the geomorphology of china the landform in china was changed from west low and east high to west high and east low in three steps the qinghai tibet plateau uplift is an important factor that affected the climate and the environment of china in the quaternary period it controls atmospheric circulation and climatic change in asia and even the northern hemisphere by dividing the westerlies into two branches south and north the plateau gradually became a heat source in summer and a cold source in winter the uplift had a decisive effect on the formation of the east asia monsoon which increased the climatic differences between the glacial period and the interglacial period the climate and environment of china are characterized by the influences of the plateau uplift the east of china became the south east monsoon area whereas the south west became the south west monsoon area and the north west turned into an arid inland region the gobi and large scale deserts that formed in the inland basins are ceaselessly extending the climate of northern china became more arid as the qinghai tibet plateau continued to uplift the plateau uplift affected glacial evolvement and loess formation and propelled the migration of cold and warm blooded animals which differed from other regions of the world at the same latitude

implications of quartz grain microtextures for onset eocene oligocene glaciation in prydz bay odp site 1166 antarctica abstract this paper presents the results of the scanning electron microscopic sem analysis of quartz grains from a selection of samples at site 1166 ocean drilling program leg 188 drilled site 1166 on the prydz bay continental shelf antarctica to document onset and fluctuations of east antarctic glaciation this site recovered upper pliocene holocene glacial sediments directly above cretaceous through lower oligocene sediments recording the transition from preglacial to early glacial conditions sem analysis of quartz grains at site 1166 was used to characterize the glacial and preglacial sediments by their diagnostic textures angular edges edge abrasion as well as arcuate to straight steps are the most frequent features in glacial deposits the highest frequency of grains with round edges is present in middle late eocene fluvio deltaic sands however angular outlines fractured plates with subparallel linear fractures and edge abrasion indicating glacier influence are also present preglacial carbonaceous mudstone and laminated gray claystone show distinctive high relief quartz grains and some chemical weathering on grain surfaces the results of the microtextural analysis of quartz grains are used to verify some critical periods of ice sheet evolution such as the transition from the east antarctic preglacial to glacial conditions on the continental shelf from middle late eocene to late eocene early oligocene time

is the central arctic ocean a sediment starved basin abstract numerous short sediment cores have been retrieved from the central arctic ocean many of which have been assigned sedimentation rates on the order of mm ka implying that the arctic basin was starved of sediments during plio pleistocene times a review of both shorter term sedimentation rates through analysis of available sediment core data and longer term sedimentation rates through estimates of total sediment thickness and bedrock age suggests that cm ka scale rates are pervasive in the central arctic ocean this is not surprising considering the physiographic setting of the arctic ocean being a small land locked basin since its initial opening during early cretaceous times we thus conclude that the central arctic ocean has not been a sediment starved basin either during plio pleistocene times or during pre pliocene times rigorous chronstratigraphic analysis permits correlation of sediment cores over a distance of 2600 km from the northwestern amerasia basin to the northwestern eurasia basin via the lomonosov ridge using paleomagnetic biostratigraphic and cyclostratigraphic data

direct observation of basal sliding and deformation of basal drift at sub freezing temperatures in a tunnel at the base of sub polar urumqi glacier no 1 china three new mechanisms of glacier flow at sub freezing temperatures have been observed taken individually or in combination these modes of flow can account for nearly all 60 80 of the overall glacier motion and yet they act only within the lowermost 1 2 of the effective glacier thickness these mechanisms are 1 enhanced deformation of the frozen and ice laden subglacial drift 2 motion across discrete shear planes or shear bands within the frozen drift or at the ice drift interface and 3 basal sliding at an ice rock interface at a temperature of nearly 5 c the ice laden drift has an effective viscosity of more than one hundred times less than that measured in the overlying ice thus allowing very rapid shear deformation the observed rate or basal sliding at the ice rock interface agrees favorably with that predicted by the recent work of shreve 1984 if proper account is taken of the measured surface roughness and reduced ice viscosity

early paleozoic amalgamation of the songnen zhangguangcai range and jiamusi massifs in the eastern segment of the central asian orogenic belt geochronological and geochemical evidence from granitoids and rhyolites abstract to constrain the early paleozoic tectonic evolution of the songnen zhangguangcai range and jiamusi massifs we undertook zircon u pb dating and geochemical analyses major and trace elements and hf isotopic compositions of early paleozoic igneous rocks in the lesser xing an zhangguangcai range of eastern heilongjiang province ne china the zircons from one diorite two rhyolites and four granitoids are euhedral subhedral and display fine scale oscillatory growth zoning indicating a magmatic origin la icp ms zircon u pb age data indicate the occurrence of magmatic events in the late ordovician 443 451 ma and middle silurian 424 430 ma the late ordovician igneous rocks are composed mainly of diorite tonalite and rhyolite whereas the middle silurian igneous rocks consist mainly of monzogranites the early paleozoic igneous rocks have sio2 59 65 76 11 wt mgo 0 13 1 23 wt and na2o k2o 4 68 7 77 wt and are chemically a calc alkaline series they are characterized by enrichment in light rare earth elements and large ion lithophile elements and depletion in heavy rare earth elements and high field strength elements such as nb ta and ti consistent with the chemistry of igneous rocks from an active continental margin setting in situ hf analyses of zircons show that ehf t values of zircons that formed in the early ordovician captured and inherited zircons in late ordovician igneous rocks range from 0 1 to 7 1 those of zircons that formed in the late ordovician including captured and inherited zircons in middle silurian monzogranite vary from 2 6 to 5 6 and those of zircons that formed in the middle silurian vary from 3 0 to 3 2 the progressive decrease in zircon ehf t values from the early ordovician to the middle silurian suggests an increasing involvement of ancient crust in the magma sources corresponding to the transition from subduction to collision take together these data suggest that the formation of late ordovician diorite tonalite and rhyolite in the zhangguangcai range adjacent to the mudanjiang fault may have been related to the westward subduction of an oceanic plate between the songnen zhangguangcai range and jiamusi massifs in contrast coeval rhyolites from the lesser xing an range located far from the mudanjiang fault may have formed in the supra subduction zone the occurrence of a middle silurian monzogranite association combined with geochronological data for detrital zircons from early devonian sedimentary rocks in eastern heilongjiang province suggests that the amalgamation between the songnen zhangguangcai range and jiamusi massifs occurred in the middle silurian

the plio pleistocene glaciation of the barents sea svalbard region a new model based on revised chronostratigraphy based on a revised chronostratigraphy and compilation of borehole data from the barents sea continental margin a coherent glaciation model is proposed for the barents sea ice sheet over the past 3 5 million years ma three phases of ice growth are suggested 1 the initial build up phase covering mountainous regions and reaching the coastline shelf edge in the northern barents sea during short term glacial intensification is concomitant with the onset of the northern hemisphere glaciation 3 6 2 4 ma 2 a transitional growth phase 2 4 1 0 ma during which the ice sheet expanded towards the southern barents sea and reached the northwestern kara sea this is inferred from step wise decrease of siberian river supplied smectite rich sediments likely caused by ice sheet blockade and possibly reduced sea ice formation in the kara sea as well as glacigenic wedge growth along the northwestern barents sea margin hampering entrainment and transport of sea ice sediments to the arctic atlantic gateway 3 finally large scale glaciation in the barents sea occurred after 1 ma with repeated advances to the shelf edge the timing is inferred from ice grounding on the yermak plateau at about 0 95 ma and higher frequencies of gravity driven mass movements along the western barents sea margin associated with expansive glacial growth

ice sheet action versus reaction distinguishing between heinrich events and dansgaard oeschger cycles in the north atlantic 1 glaciers and ice sheets play an active role in the climate system and the global hydrological cycle the stability of continental ice sheets must be better understood for assessments of future sea level rise and to uncover the causes of millennial scale climate variability that characterized the last glacial period ice rafted debris ird in the midlatitude oceans and subpolar seas tells of widespread calving of icebergs from the northern hemisphere ice sheets during the last glacial period but the climatic implications of this ird are unclear does the sediment record indicate repeated dynamical collapse of the ice sheets with ice sheets actively forcing the climate system alternatively were ice sheet margins simply advancing and retreating in response to climate vacillations on the basis of simulations of iceberg delivery to the ocean during the last glacial cycle we argue that the marine record exemplifies both of these phenomena heinrich events were clearly episodes of internal dynamical instability of the laurentide ice sheet while millennial scale ird is more simply interpreted as a response of the circum atlantic ice sheets to dansgaard oeschger climate cycles ice sheets in different coastal regions respond differently to climate fluctuations but overall iceberg fluxes increase in cold periods peaking within a few centuries of climatic cooling regions with relatively warm wet climates scandinavia western north america and svalbard are the most sensitive to millennial climate variability with rapid response times and large millennial variability in iceberg fluxes

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

ice dammed lakes and rerouting of the drainage of northern eurasia during the last glaciation during the quaternary period ice sheets centred over the barents and kara seas expanded several times onto mainland russia and blocked northflowing rivers such as the yenissei ob pechora and mezen large ice dammed lakes with reversed outlets e g toward the caspian sea formed south of these ice sheets some lakes are reconstructed from shorelines and lacustrine sediments others mainly from ice sheet configuration ice dammed lakes considerably larger than any lake on earth today are reconstructed for the periods 90 80 and 60 50 ka the ages are based on numerous optically stimulated luminescence osl dates during the global last glacial maximum lgm about 20 ka the barents kara ice sheet was too small to block these eastern rivers although in contrast to the 90 80 and 60 50 ka maxima the scandinavian ice sheet grew large enough to divert rivers and meltwater across the drainage divide from the baltic basin to the river volga and that way to the caspian sea climate modelling shows that the lakes caused lower summer temperatures on the continent and on the lower parts of the ice sheet the final drainage of the best mapped lake is modelled and it is concluded that it probably emptied within few months we predict that this catastrophic outburst had considerable impact on sea ice formation in the arctic ocean and on the climate of a much larger area c 2003 elsevier ltd all rights reserved less

sources of sediment found in sea ice from the western arctic ocean new insights into processes of entrainment and drift patterns 1 the geochemical fingerprint of entrained fe oxide mineral grains in arctic ocean sea ice is used to determine precise sources of this sediment this approach substantiates the importance of the laptev sea as a source of sea ice and even the presence of russian ice in the beaufort sea off alaska fe oxide grains from the laptev sea were found in floes in the beaufort sea chukchi borderland and central arctic ocean demonstrating the importance of sea ice in distributing itself throughout the arctic ocean and the potential of transporting sediment from russian rivers to north american shelves banks island shelf is the most important source of sediment sampled from ice floes in the beaufort sea northern chukchi sea and chukchi borderland area although most of the entrained sediment fits the criteria for suspension freezing in shallow water the presence of winter polynyas with offshore winds and not the size of shallow areas appears to be the critical factor for sea ice entrainment seven of the 18 ice floes sampled contained fe oxide grains from more than one source area the two most common sources that are found in the same ice floes are banks island and the laptev sea multiple sources in ice floes suggest that either mingling of fragmented ice floes occurs or that a source area containing grains from both these sources has yet to be located the addition of fine sand sized windblown sediment is not thought to be significant

mid to late pleistocene ice drift in the western arctic ocean evidence for a different circulation in the past the provenance of ice rafted debris ird in four arctic sediment cores implies that icebergs from the northwestern laurentide ice sheets drifted across the western arctic ocean along the 180 0 meridian toward fram strait during mid to late pleistocene deglaciations within the last 700 000 years this iceberg drift was different from the present day beaufort gyre circulation and resembled a dislocated transpolar drift tpd sea ice mainly followed the iceberg trajectories but also frequently drifted from the russian shelves eastward into the amerasian basin

frost weathering versus glacial grinding in the micromorphology of quartz sand grains processes and geological implications abstract micromorphology of quartz sand grains is used to reconstruct processes occurring in the glacial environment and to distinguish the latter from other environments two processes dominate in the glacial environment i e crushing and abrasion or a combination thereof their effect is a wide range of microstructures on the surface of quartz grains e g chattermarks conchoidal fractures and multiple grooves however the periglacial environment also effectively modifies the surface of quartz grains the active layer of permafrost is considered to have a significantly higher contribution to the formation of crushed grains and the number of microstructures resulting from mechanical destruction e g breakage blocks or conchoidal fractures as compared to deposits which are not affected by freeze thaw cycles however only a few microstructures are found in both environments at the same time there are several processes in subglacial environments related to freeze thaw cycles e g regelation congelation basal adfreezing and glaciohydraulic supercooling most likely therefore the role of the glacial environment in the destruction of quartz grains has been misinterpreted and consequently the conclusions regarding environmental processes drawn on the basis of the number of crushed grains and edge to edge contacts are erroneous

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

arctic ice export events and their potential impact on global climate during the late pleistocene 1 ice sheets in the north american arctic and to a lesser extent those in northern eurasia calved large quantities of icebergs that drifted through fram strait into the greenland sea several times during the late pleistocene these icebergs deposited fe oxide grains 45 250 m and coarse lithic clasts 250 m matched to specific circum arctic sources four massive arctic iceberg export events are identified from the laurentide and the innuitian ice sheets between 14 and 34 ka calendar years in a sediment core from fram strait these relatively short duration 1 4 kyr events contain 3 5 times the background levels of fe oxide grains they began suddenly as indicated by a steep rise in the number of grains matched to an ice sheet source suggesting rapid purges of ice through fram strait due perhaps to collapse of ice sheets the larger events from the northwestern laurentide ice sheet are preceded by events from the innuitian ice sheet despite the chronological uncertainties the arctic export events appear to occur prior to heinrich events

optically stimulated luminescence dating supports central arctic ocean cm scale sedimentation rates 1 this paper presents new results from optically stimulated luminescence osl dating on a sediment core raised from the crest of the lomonosov ridge in the central arctic ocean there has been much debate about dating sediment cores from the central arctic ocean and by using an independent absolute dating technique we aim to test whether or not relatively fast cm scale ka sedimentation rates were typical of arctic s pleistocene depositional mode on the basis of mainly paleomagnetic reversal stratigraphy many previous studies suggest mm scale ka sedimentation rates a common feature in these studies is that the first down core paleomagnetic negative inclination is consistently interpreted as the brunhes matuyama boundary at about 780 ka our osl dating results indicate that this assumption is not generally valid and that the first encountered negative inclination represents younger age excursions within the brunhes chron implying reinterpretation of many published core studies where paleoenvironmental reconstructions have been made for the central arctic ocean our dating results furthermore corroborates a correlation of the uppermost 2 3 m of the lomonosov ridge cores to a well dated core located off the barents kara sea margin that in turn is correlated to cores in the fram strait valuable information on the paleoceanographical evolution in the arctic ocean from mis 6 to the holocene is given through this correlation of records from the central arctic ocean to records off the eurasian continental margin

an investigation of subglacial processes at the microscale from briksdalsbreen norway the subglacial processes at briksdalsbreen norway are examined by a combination of sedimentology thin section and scanning electron microscope sem analysis of till samples from an exposed subglacial surface and from beneath the glacier studies of a fluted surface indicate that subglacial deformation is occurring on a field scale with flutes forming behind most clasts 0 6 m high at the thin section scale 0 014 2 0 mm it is seen that deformation is by rotation and attenuation and is dependent on till texture at the sem scale 0 1 0 4 mm it is seen that erosion is controlled by abrasion and percussion which produces distinct grain styles as part of an erosional continuum overall it is shown that rotation and attenuation is a dominant process at all scales and that the clast interactions associated with different scale perturbations within the shear zone control erosion and deposition as well as landform and fabric production

cold glaciers erode and deposit evidence from allan hills antarctica here we report previously undescribed features of erosion and deposition by a cold polar glacier a recent study challenged the assumption that cold glaciers neither slide nor abrade their beds but no geological evidence was offered the features we describe include abrasion marks subglacial deposits glaciotectonically deformed substrate isolated blocks ice cored debris mounds and boulder trains all products of a recent cold ice advance and retreat mapping these features elsewhere in antarctica will document recent shifts in the east antarctic ice sheet margin providing new insight on regional mass balance changes

surface textural analysis of quartz sand grains from odp site 918 off the southeast coast of greenland suggests glaciation of southern greenland at 11 ma shipboard analysis of the 1 183 m sedimentary section recovered at site 918 in the irminger basin during ocean drilling program leg 152 revealed material of glacial origin diamictons ice rafted debris ird and dropstones as deep as 543 m below sea floor bsf the sediment containing the deepest dropstone was biostratigraphically dated shipboard as approximately 7 ma pushing back the date for the onset of glaciation on southern greenland by 5 ma thin layers of fine sand were found as much as 60 m deeper in the core raising the possibility of an even earlier date for glaciation to determine the sedimentary history of these deeper sand layers the surface textures on quartz grains from eleven cores bracketing the interval of interest were analyzed by scanning electron microscope the results suggest that the grains in the 60 m interval below the deepest dropstone have a glacial history at that level an 11 ma sr isotope date was obtained from planktonic foraminifers this late miocene timing is supported biostratigraphically by both nanofossil and foraminifer assemblages indicating a new minimum age for the onset of glaciation on southern greenland and in the north atlantic

a comparative sem study on the micromorphology of glacial and nonglacial clasts with varying age and lithology preliminary research on striated clasts from a variety of depositional environments suggests that scanning electron microscopy sem of striated clasts of varying lithology in diamictons may prove useful in interpreting a glacial origin evaluating whether sem analysis of clasts from diamictons is an applicable technique to define a glacial origin requires a better understanding of the microfeatures occurring on glacial and nonglacial clasts we describe microtextures and surface characteristics for samples of quartzite granite limestone basalt chert pillow basalt and quartz pebbles collected from a variety of depositional environments our study suggests that it is possible to differentiate between glacial and nonglacial deposits based on frequency and morphology of diagnostic surface microfeatures observed on entrained clasts these microfeatures are best preserved and identified on competent and monomineralic samples e g quartzite chert limestone and poorly preserved on less resistant and p

microtextures on quartz grains in tills from antarctica quartz grains of the sand 63 2000 m fractions from tills of oligocene to quaternary age in antarctica were analyzed by scanning electron microscope sem to test the hypothesis that relative ice thickness and distance of transport influence the type and range of microtextures observed on individual grains in this study replicated subsamples were analyzed from tills emplaced by thick glaciers with both short and long transport distances till samples with grains transported over long distances up to several hundred km under thick ice 1000 m were compared with quartz grains from relatively thinner e g 500 m thick outlet glaciers with shorter transport distances 100 km a range of microtextures including subparallel linear fractures conchoidal fractures arc shaped steps grain relief edge sharpness grain angularity and roundness straight and curved grooves crescentic gouges dissolution features precipitation features and presence of adhering particles was used to determine the environmental history of these grains microtextures on sand size clasts including microfractures abrasion etching and coatings can provide important information on paleoenvironmental history including glacier activity and severity of weathering inferred from etching and dissolution features

plio pleistocene trends in ice rafted debris on the lomonosov ridge although more than 700 sediment cores exist from the arctic ocean the plio pleistocene evolution of the basin and its marginal seas remains virtually unknown this is largely due the shallow penetration of most of these records and difficulties associated with deriving chronologies for the recovered material the integrated ocean drilling program s iodp expedition 302 arctic coring expedition acex recovered 197 m of neogene quaternary sediment from the circumpolar regions of the lomonosov ridge as detailed analyses of this material emerge research is beginning to formulate a long term picture of paleoceanographic changes in the central arctic ocean this paper reviews the acex plio pleistocene age model identifies uncertainties and addresses ways in which these may be eliminated within the established stratigraphic framework a notable reduction in the abundance of ice rafted debris ird occurs in the early part of the pleistocene and persists until marine isotope stage 6 mis 6 therefore while global oceanographic proxies indicate the gradual growth of terrestrial ice sheets during this time ird delivery to the central arctic ocean remained comparatively low and stable within the resolution of existing data the pleistocene reduction in ird is synchronous with predicted changes in both the inflow of north atlantic and pacific waters which in modern times are known to exert a strong influence on sea ice stability

late weichselian glaciation of the russian high arctic a numerical ice sheet model was used to reconstruct the late weichselian glaciation of the eurasian high arctic between franz josef land and severnaya zemlya an ice sheet was developed over the entire eurasian high arctic so that ice flow from the central barents and kara seas toward the northern russian arctic could be accounted for an inverse approach to modeling was utilized where ice sheet results were forced to be compatible with geological information indicating ice free conditions over the taymyr peninsula during the late weichselian the model indicates complete glaciation of the barents and kara seas and predicts a maximum sized ice sheet for the late weichselian russian high arctic in this scenario full glacial conditions are characterized by a 1500 m thick ice mass over the barents sea from which ice flowed to the north and west within several bathymetric troughs as large ice streams in contrast to this reconstruction a minimum model of glaciation involves restricted glaciation in the kara sea where the ice thickness is only 300 m in the south and which is free of ice in the north across severnaya zemlya our maximum reconstruction is compatible with geological information that indicates complete glaciation of the barents sea however geological data from severnaya zemlya suggest our minimum model is more relevant further east this in turn implies a strong paleoclimatic gradient to colder and drier conditions eastward across the eurasian arctic during the late weichselian

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

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

arctic ocean evidence for late quaternary initiation of northern eurasian ice sheets a high resolution multiparameter stratigraphy allows the identification of late quaternary glacial and interglacial cycles in a central arctic ocean sediment core distinct sandy layers in the upper part of the otherwise fine grained sediment core from the lomonosov ridge lat 87 5 n correlate to four major glacials since ca 0 7 ma the composition of these ice rafted terrigenous sediments points to a glaciated northern siberia as the main source in contrast lithic carbonates derived from north america are also present in older sediments and indicate a northern north american glaciation since at least 2 8 ma we conclude that large scale northern siberian glaciation began much later than other northern hemisphere ice sheets

microfeatures of modern sea ice rafted sediment and implications for paleo sea ice reconstructions distinguishing sea ice rafted debris sird from iceberg rafted debris is crucial to an interpretation of ice rafting history however there are few paleo sea ice proxies this study characterizes quartz grain microfeatures of modern sird from the arctic ocean and compares these results with microfeatures from representative glacial deposits to potentially differentiate sird from ice rafted sediments which have been recently subjected to glacial processes this allows us to evaluate the use of grain microfeatures as a paleo sea ice proxy sird grains were largely subrounded with medium relief pervasive silica dissolution and a high abundance of breakage blocks and microlayering the glacial grains were more angular with lower relief and higher abundances of fractures and striations gouges discriminate analysis shows a distinct difference between sird and glacial grains with 7 of the sird grains containing typical glacial microtextures suggesting this method is a useful means of inferring paleo sea ice presence in the marine record we propose that differences in microfeatures of sird and glacial ice rafted debris reflect differences in sediment transport and weathering histories sediment transported to a coastal setting and later rafted by sea ice would be subject to increased chemical weathering whereas glaciers that calve icebergs would bypass the coastal marine environment thus preserving their glacial signature

manganese and color cycles in arctic ocean sediments constrain pleistocene chronology sequential variations in manganese mn content and color of deepsea sediments retrieved from the lomonosov ridge 87 n in the central arctic ocean apparently mimic low latitude 18 o glacial interglacial cyclicity thereby providing stratigraphic information that together with biostratigraphic data permit the construction of a detailed chronological model correlation of this mn and color chronology to established apparent brunhes age estimates of geomagnetic excursions reveals a remarkable fit between these two independently derived time scales the mn and color cycles probably provide paleoenvironmental information about material fluxes in the arctic ocean over the past 1 m y we suggest that the primary source for the observed manganese variations in our sediment core is northern siberia which has extensive peat bogs and boreal forests these siberian source areas could operate in an off and on mode tuned to pleistocene glacial and interglacial periods contrasts in ventilation of arctic ocean waters during interglacial glacial cycles probably could also enhance the observed mn and color variability

new insights on arctic quaternary climate variability from palaeo records and numerical modelling terrestrial and marine geological archives in the arctic contain information on environmental change through quaternary interglacial glacial cycles the arctic palaeoclimate and its extremes apex scientific network aims to better understand the magnitude and frequency of past arctic climate variability with focus on the extreme versus the normal conditions of the climate system one important motivation for studying the amplitude of past natural environmental changes in the arctic is to better understand the role of this region in a global perspective and provide base line conditions against which to explore potential future changes in arctic climate under scenarios of global warming in this review we identify several areas that are distinct to the present programme and highlight some recent advances presented in this special issue concerning arctic palaeo records and natural variability including spatial and temporal variability of the greenland ice sheet arctic ocean sediment stratigraphy past ice shelves and marginal marine ice sheets and the cenozoic history of arctic ocean sea ice in general and holocene oscillations in sea ice concentrations in particular the combined sea ice data suggest that the seasonal arctic sea ice cover was strongly reduced during most of the early holocene and there appear to have been periods of ice free summers in the central arctic ocean this has important consequences for our understanding of the recent trend of declining sea ice and calls for further research on causal links between arctic climate and sea ice

dynamics of the barents kara ice sheet as revealed by quartz sand grain microtextures of the late pleistocene arctic ocean sediments abstract during the entire quaternary ice sheets advanced and retreated across the circum arctic margins in a series of climate related glacial interglacial cycles it is critical to obtain evaluation of the nature of initiated glaciers at the arctic margins after the pronounced interglacial periods in this study this will be done by inferring from glacially generated quartz sand grain surface microtextures and related sedimentology extracted from the central arctic ocean sediments these microtextures can be correlated with the generation and fluctuations in the extent of the late pleistocene eurasian ice sheet i e barents kara ice sheet the central arctic ocean sediments in the lomonosov ridge having been deposited after the late pleistocene interglaciations and having had no internal hiatuses provide an excellent time window for usage of quartz sand grain surface textures for evaluating possible evolving glaciers and continental ice sheets this is based on the fact that iceberg and sea ice transported quartz sand grains and their mechanically formed surface textures created under high cryostatic stress are diagnostic for glacier thickness and dynamics having been existed in sediment source areas sand sized quartz grains in deep marine sediments favour iceberg or sea ice transportation with characteristic content of microtextures formed prior this transportation the sand grain surface microtextures and their frequencies of the selected submarine lomonosov ridge sediments during marine isotope stage mis 5 to mis 3 are analysed using a scanning electron microscope sem coring during the arctic ocean 96 expedition core 96 12 1pc provided alternating clay to silty clay sediments which are characterised by prominent silt to sand size containing intervals the specific glacial crushing and high cryostatic stress generated features such as high angularity conchoidal fractures steps and sub parallel linear fractures were observed from quartz sand grain surfaces continental ice generation and extent are evident soon after the eemian interglaciation and the following mis 4 stage shows the highest frequencies of glacigenic microtextures the microtexture generation under high cryostatic pressure underneath ice more than 1 km thick can be taken as concurrent signal of the temporal expansion of the northernmost continental ice sheets which could easily have reached the shelf break of the barents kara and western laptev seas during that time

a simple method to classify diamicts by scanning electron microscope from surface microtextures interpretation of quartz sand grain surface microtextures with scanning electron microscopy has been riddled with inconsistencies invalid assumptions and much subjectivity therefore a novel classification for analysing grain surface microtextures is presented based on the origin of complete grain surfaces this novel method has solved most of the earlier problems of interpretation of surface microtextures and it is easy to use and to quickly find evident genetic interpretations of diamicts the data are plotted graphically in 2 history diagrams or 3 history diagrams for quick visual inspection and statistical evaluation source rocks and quaternary glacial deposits from scandinavia and southern ontario representing different ice substrate dynamics are analysed to define surface microtextures from typical glacigenic grains bedrock and fluvially transported grains typical glacially crushed grains display large scale fractures and abrasion shield bedrock grains display large or small scale fractures and solution precipitation microtextures fluvially transported grains exhibit abrasion and solution precipitation microtextures

first high resolution chirp sonar profiles from the central arctic ocean reveal erosion of lomonosov ridge sediments the swedish arctic ocean 96 expedition to the central arctic ocean with the icebreaker oden carried out a geological geophysical program focused mainly on lomonosov ridge sediments approximately 195 km of high resolution seismic data from the ridge crest and slope were collected with a chirp sonar system providing new insights into the sediment stratigraphy and the accompanying depositional history these data reveal evidence of substantial erosion that acted in laterally limited areas on shallow parts of the investigated ridge segment more than 50 m of sediment stratigraphy is missing in the most eroded parts moreover the chirp sonar records indicate that below the erosional surface the ridge crest and slope is characterized by a low energy sedimentary environment the termination of the erosional phase is indicated by a prominent reflector the subsequent depositional phase resulted in an approximately 3 m thick stratigraphic unit the cause of the erosion is attributed to either ice grounding or current erosion furthermore oden echo sounding data has been used together with data from the us navy scicex program in order to update existing bathymetric charts in the arctic ocean 96 working area the update shows a narrower ridge crest with a different outline than in previously published charts with a minimum depth of 607 m which is the shallowest depth of the lomonosov ridge recorded in the public domain in the central arctic ocean 1999 elsevier science b v all rights reserved