equilibrium line altitude variations with latitude today and during the late wisconsin abstract present day and late wisconsin glacier equilibrium line altitudes ela were compared on a transect from patagonia along the coastal cordillera to alaska and a transect from mexico along the sierra madre rocky mountains to alaska late wisconsin ela s were determined from cirques occupied during the late wisconsin and present day ela from observations of active cirque glaciers the mean change in ela from the late wisconsin to the present was 735 m with a standard deviation of 120 m this indicates that the change in snowline altitude from the present to the late wisconsin was approximately uniform and not latitudinally dependent

modeling mass balance changes during a glaciation cycle identification of present day climate setting and alpine glacier balance gradients indicates that the balance gradient of alpine glaciers is primarily determined by climatic conditions determination of balance gradients for specific climatic settings on present day ice sheets provides an analog for determining the mass balance on pal eo and future ice sheets

beringia impact on paleoclimates of northeast asia and north pacific during last pleistocene glaciation abstract the beringian land bridge that emerged repeatedly during ice ages was of great importance in the energy and matter redistribution within the continent ocean system and had a pronounced effect on air streams and surface marine currents in the north pacific region the paper considers an important and still unsettled paleogeographic problem of the arctic northeast of asia could beringia have been covered with an ice sheet at the last glacial maximum and what was the natural refrigerator impact on regional climate and paleo oceanography of the northern pacific based on studies of diatoms and pollen spectra recovered from deposits dated to the last glacial time western beringia was essentially ice free at that time this may be attributed to a deficiency of moisture supply from the pacific due to changes in vectors and intensity of the north pacific currents the thick snow cover needed for glacier formation could not accumulate western beringia was dominated by a unique landscape of cold and dry tundra steppe its topography being complicated with arcuate ridges end moraines of alpine and cirque glaciers the glaciation of the region developed according to the north yakutia scenario

detection of high altitude ionospheric irregularities with gps met 1 in this study radio occultation data from the gps met experiment are used for detection of high altitude ionospheric irregularities this is done by back propagation of the complex electromagnetic field observed in orbit while accounting for the direction of the earth s magnetic field the irregularities are detected mainly in the f region however for some occultations they are detected above the f2 peak at altitudes up to 1000 km and higher results of numerical simulations a description of the used algorithm and examples of the processed gps met data are presented

paleogeographic and paleoclimatic significance of diatoms from middle pleistocene marine and glaciomarine deposits on baldwin peninsula northwestern alaska abstract a newly revised diatom biostratigraphic scheme for the north pacific ocean based on studies of the diatom flora of the cape blossom and hotham inlet formations of baldwin peninsula northwestern alaska provides new information on the paleoceanography of kotzebue sound alaska during middle pleistocene time sediments exposed along coastal bluffs of baldwin peninsula contain subarctic north pacific zonal index species including extinct proboscia barboi pr curvirostris actinocyclus ochotensis var fossilis thalassiosira nidulus var nidulus th jouseae th gravida var fossilis and stephanopyxis dimorpha which are correlated with the middle part of the proboscia barboi zone 0 43 0 36 ma based on the distribution of the zonal diatom species and on changes in the paleoecological structure of the diatom assemblages e g warm vs cold water assemblages we conclude that the marine deposits of the cape blossom formation and lower baldwin silt member of the hotham inlet formation formed under relatively warm high sea level conditions associated with the marine oxygen isotope stage ois 11 transgression glaciomarine sedimentation middle and upper baldwin silt and selawik gravel members of the hotham inlet formation initiated during relatively warm conditions at the end of the stage 11 transgression and continued into stage 10 high latitude glacier growth during a global interglacial period was likely facilitated by warm surface waters on flooded continental shelves and limited regional sea ice cover the biostratigraphic record at baldwin peninsula provides further evidence that high latitude ice growth is favored by increased moisture supply during warm climatic intervals and inhibited by arid conditions during full glacial intervals

late pleistocene and holocene paleoenvironments of the north pacific coast abstract unlike the north atlantic the north pacific ocean probably remained free of sea ice during the last glacial maximum lgm 22 000 to 17 000 bp following a eustatic low in sea level of ca 120 m at 19 000 bp a marine transgression had flooded the bering and chukchi shelves by 10 000 bp post glacial sea level history varied widely in other parts of the north pacific coastline according to the magnitude and timing of local tectonism and glacio isostatic rebound glaciers covered much of the continental shelf between the alaska peninsula and british columbia during the lgm maximum glacier extent during the lgm was out of phase between southern alaska and southern british columbia with northern glaciers reaching their outer limits earlier between 23 000 and 16 000 bp compared to 15 000 14 000 bp in the south glacier retreat was also time transgressive with glaciers retreating from the continental shelf of southern alaska before 16 000 bp but not until 14 000 13 000 bp in southwestern british columbia major climatic transitions occurred in the north pacific at 24 000 22 000 15 000 13 000 and 11 000 9000 bp rapid climate changes occurred within these intervals including a possible younger dryas episode an interval of climate warmer and drier than today occurred in the early holocene cooler and wetter conditions accompanied widespread neoglaciation beginning in some mountain ranges as early as the middle holocene but reaching full development after 3000 bp

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

cenozoic ice volume history development of a composite oxygen isotope record to view cenozoic ice volume and ocean temperature history a composite 18 o time series was constructed for tropical shallow dwelling planktonic foraminifers and for deep water benthic foraminifers we conclude that cenozoic benthic 18 o primarily reflect considerable deep ocean temperature variation and that tropical planktonic 18 o afford the best record of cenozoic ice volume the planktonic composite indicates the presence of a significant ice budget for the past 40 m y the difference between the benthic and planktonic 18 o composites suggests that low latitude production of warm saline bottom water dominated tertiary thermohaline circulation

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

diatom evidence on wisconsin and holocene events in the bering sea abstract previous work on surface modern sediments has defined diatom species which appear to be good indicators of various oceanographic ecologic conditions in the north pacific ocean and marginal seas three long cores from the eastern and northern sides of the aleutian basin show changes in species assemblage which can be interpreted in terms of changes in the ocean environment during the last glaciation wisconsin and the holocene the early and late wisconsin maxima were times of prolonged annual sea ice cover and a short cool period of phytoplankton productivity during the ice free season the middle wisconsin interstade at least in the southern bering sea had greater seasonal contrast than today with some winter sea ice cover an intensified temperature minimum and high spring productivity variations in clastic and reworked fossil material imply varying degrees of transport to the basin by alaskan rivers the results of jouse from the central bering sea generally correspond with those presented here although there are problems with direct comparison

the paleogeography of arctic shelf and coastal zone of eurasia at the time of the last glaciation 18 000 yr b p abstract paleogeographic maps showing reconstructed environments of the eurasian arctic shelf and coastal zone during the last glacial maximum 18 000 yr b p were compiled within the project igcp 200 sea level correlations and applications the reconstruction shows conspicuous difference between eastern and western sectors of the arctic shelf of eurasia large glaciers existed in the west while the eastern arctic shelf was an emerged ice free lowland dominated by tundra landscapes and built of unconsolidated sediments with a variety of genesis

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

paleoglaciology s grand unsolved problem the paleoglaciological concept that during the pleistocene glacial hemi cycles a super large structurally complex ice sheet developed in the arctic and behaved as a single dynamic system as the antarctic ice sheet does today has not yet been subjected to concerted studies designed to test the predictions of this concept yet it may hold the keys to solutions of major problems of paleoglaciology to understanding climate and sea level changes the russian arctic is the least known region exposed to paleoglaciation by a hypothetical arctic ice sheet but now it is more open to testing the concept implementation of these tests is a chaillenging task as the region is extensive and the available data are controversial well planned and coordinated field projects are needed today as well as broad discussion of the known evidence existing interpretations and new field results here we present the known evidence for paleoglaciation of the russian arctic continental shelf and reconstruct possible marine ice sheets that could have produced that evidence

regional variations in provenance and abundance of ice rafted clasts in arctic ocean sediments implications for the configuration of late quaternary oceanic and atmospheric circulation in the arctic abstract the composition and distribution of ice rafted glacial erratics in late quaternary sediments define the major current systems of the arctic ocean and identify two distinct continental sources for the erratics in the southern amerasia basin up to 70 of the erratics are dolostones and limestones the amerasia suite that originated in the carbonate rich paleozoic terranes of the canadian arctic islands these clasts reached the arctic ocean in glaciers and were ice rafted to the core sites in the clockwise beaufort gyre the concentration of erratics decreases northward by 98 along the trend of the gyre from southeastern canada basin to makarov basin the concentration of erratics then triples across the makarov basin flank of lomonosov ridge and siltstone sandstone and siliceous clasts become dominant in cores from the ridge and the eurasia basin the eurasia suite the bedrock source for the siltstone and sandstone clasts is uncertain but bedrock distribution and the distribution of glaciation in northern eurasia suggest the taymyr peninsula kara sea regions the pattern of clast distribution in the arctic ocean sediments and the sharp northward decrease in concentration of clasts of canadian arctic island provenance in the amerasia basin support the conclusion that the modern circulation pattern of the arctic ocean with the beaufort gyre dominant in the amerasia basin and the transpolar drift dominant in the eurasia basin has controlled both sea ice and glacial iceberg drift in the arctic ocean during interglacial intervals since at least the late pleistocene the abruptness of the change in both clast composition and concentration on the makarov basin flank of lomonosov ridge also suggests that the boundary between the beaufort gyre and the transpolar drift has been relatively stable during interglacials since that time because the beaufort gyre is wind driven our data in conjunction with the westerly directed orientation of sand dunes that formed during the last glacial maximum on the north slope of alaska suggests that atmospheric circulation in the western arctic during late quaternary was similar to that of the present

evidence for restricted ice extent during the last glacial maximum in the koryak mountains of chukotka far eastern russia field evidence in the koryak mountains lake mainitz region of far eastern russia supports three pleistocene glacial advances the early wisconsinan and pre wisconsinan glaciations are represented by broad lobate moraines extending as much as 30 km north of the koryak mountains field evidence demonstrates that the terminal lateral and medial moraines as well as meltwater channels dead ice topography kettles and outwash plains mark the extent of ice during the last glacial maximum lgm during which glaciers reached no more than 20 km beyond their present limits those emanating from the southern koryak mountains may have reached the bering sea numerical and relative dating techniques support these results and test the theoretical models of the lgm in western beringia erratics on moraines and glaciofluvial terraces common to all valleys at 13 13 8 m above river level yield 36 cl exposure ages ranging from 10 08 to 25 78 ka the koryak mountains lake mainitz record of glaciation is spatially and temporally consistent with the glaciation pattern across central beringia found in other terrestrial and marine records glacier growth in the koryak mountains was sustained by possible increased summer sea surface temperatures and precipitation in the northwest pacific region evidence from the northern koryak mountains lat 64 n long 177 e indicates that the extent of ice in western beringia was limited to mountain and valley glaciers during the lgm this fieldbased research contradicts m g grosswald s theoretical beringian ice sheet hypothesis

response of western pacific marginal seas to glacial cycles paleoceanographic and sedimentological features abstract this paper reviews the recent progress in late quaternary studies in five northwestern pacific marginal seas especially the south china sea as an example a series of marginal seas separate asia from the pacific ocean and significantly modify the material and energy flux linkage between land and sea during glacial cycles the sea level induced environmental signal was amplified in the marginal seas giving rise to drastic changes in areas and configurations of these seas and to reorganization of sea water circulation in basins since most of the western pacific marginal seas are influenced by monsoon circulation and some of these are located within the western pacific warm pool the glacial geographic changes have produced a profound impact on regional and global climate for example the decrease of sea area and sea surface temperature sst in the marginal seas was one of the factors responsible for the enhanced aridity of inland china during the glaciation glacial intensification of the winter monsoon and increased seasonality of sst in marginal seas might explain at least partly the apparent discrepancy between the tropical paleotemperature estimations based on terrestrial and open ocean records in this region as the western pacific marginal seas trap terrigenous material supplied by east asia the deep water sedimentation rates there can be one to two orders of magnitude higher than in the open ocean down slope sediment transport is more active when the sea level changes particularly during the deglaciation at least four types of carbonate cycles have been recognized in the western pacific marginal seas and each of those contains environmental signals from the surface and deep sea water as well as from the drainage basin

the last interglaciation in alaska stratigraphy and paleoecology of potential sites at least 20 localities in alaska contain deposits that may provide information on the last interglaciation oxygen isotope substage 5e these widely dispersed localities include river bluffs coastal bluffs and terraces elevated marine shorelines lake basins and artificial excavations most of the inferred interglacial deposits contain macrofossils or pollen that are older than the range of radiocarbon dating and commonly indicate climate as warm as or warmer than the present at a few localities evidence for deep thaw of permafrost also indicates a warm paleoclimate at eight localities the old crow tephra occurs at or below organic deposits that may represent substage 5e the tephra occurs beneath conspicuous organic deposits at fairbanks the yukon palisades and holitna lowland and directly above a peat bed at hogatza mine at birch creek halfway house ky 11 and imuruk lake the tephra occurs within a paleosol or organic deposit but other organic horizons that more likely indicate interglacial conditions occur at higher stratigraphic levels the varied stratigraphic relations of the old crow tephra suggest that it may have been deposited close to the boundary between isotope substages 6 and 5 which is dated at about 130 ka in the marine record and between 132 and 140 ka on land these age relations suggests that the tephra may have been deposited about 135 5 ka validating the recent fission track age determination of 140 10 ka for this deposit six coastal localities contain deposits of probable interglacial age and these commonly are associated with evidence for eustatic sea levels higher than those of the present beach and sublittoral sediments of the pelukian transgression occur up to 12 m asl along the northwest coast of alaska and are correlative with barrier island and lagoonal sediments on the alaskan arctic coastal plain both sets of deposits commonly contain extralimital mollusks and microfauna that indicate marine water slightly warmer than present and suggest that seasonal sea ice did not extend south of bering strait during the last interglacial as it does today farther south elevated marine terrace deposits on amchitka island contain marine invertebrates that indicate a climate warmer than at present peat horizons in coastal exposure at goose bay and coastal terraces at lituya bay contain pollen spectra that suggest forests like those of the present day and spruce macrofossils exposed on baldwin peninsula indicate boreal forest more extensive than at present sediments from several lakes in northwestern alaska may contain continuous records of the last interglaciation a major warm interval possibly isotope substage 5e has been identified in a core from squirrel lake by a peak in picea pollen that indicates forest extension beyond present limits similar pollen records are potentially available from two maars which formed in the cape espenberg area more than 125 ka terrestrial organic deposits thought to record the last interglaciation occur interstratified with marine and glaciogenic sediments in the nushagak lowland of southwest alaska and on baldwin peninsula in kotzebue sound extensive exposures along the copper and nenana rivers may also contain organic deposits that record the last interglaciation

the antarctic ice sheet its history and response to sea level and climatic changes over the past 100 million years abstract the development surface form flow and erosive activity of the antarctic ice sheet over the past 100 million years is related to geological evidence that indicates long term trends of global climate the glaciological description of the evolution of the ice sheet covers its interactions with the atmosphere and with the ocean discussion focuses on changes of the equilibrium line altitude ela with time of the accumulation rate with global temperature and basal melting of ice shelves by ocean waters the tendency of global climate to change rapidly or to drift slowly between two near equilibrium states involves two types of changes the former that has been widely recognized is reversible a second type involving ice sheets or ice shelves appears to be almost irreversible since they remain in their changed state unless a much larger reversal of factors driving climate occurs we refer to any rapid but reversible changes as climatic jumps and to the latter as climate ice switches variability of climate in response to changing radiation with the earth s orbital parameters and other causes is included in our model extensive glaciation of east antarctica commenced after 40 m y b p with wide fluctuations until shortly after 20 m y b p a climate ice switch then prevented any major deglaciation a further climate ice switch associated with the ela falling below sea level occurred soon after 10 m y b p this led to rapid formation of ice shelves and the marine ice sheet of west antarctica which advanced as grounded ice to the edge of the continental shelf after 5 m y b p the grounded ice started to retreat extensive ice shelves remained and most glacial debris was then deposited beneath the inner regions of ice shelves response to northern hemisphere glaciation since 2 4 m y b p during glacial periods involved extension of the grounded ice area a large decrease of mass input and decreased melting of outer parts of large ice shelves while the melting rate beneath inner regions was probably similar to the present marine core evidence suggests that retreat caused by global cooling has been dominant since 5 m y b p and that changes in extent due to northern hemisphere glaciation since 2 4 m y b p have had different effects on the major and on smaller northerly ice shelves

middle pleistocene age of the nome river glaciation northwestern alaska abstract during the middle pleistocene nome river glaciation of northwestern alaska glaciers covered an area an order of magnitude more extensive than during any subsequent glacial intervals the age of the nome river glaciation is constrained by laser fusion 40 ar 39 ar analyses of basaltic lava that overlies nome river drift at minnie creek central seward peninsula that average 470 000 190 000 yr 1 milligram size subsamples of the lava were dated to identify and eliminate extraneous 40ar enrichments that rendered the mean of conventional k ar dates on larger bulk samples of the same flow too old 700 000 570 000 yr while the 40 ar 39 ar analyses provide a minimum limiting age for the nome river glaciation maximum ages are provided by a provisional k ar date on a basaltic lava flow that underlies the nome river drift at nearby lave creek by paleomagnetic determinations of the drift itself at and near the type locality and by amino acid epimerization analysis of molluscan fossils from nearshore sediments of the anvilian marine transgression that underlie nome river drift on the coastal plain at nome taken together the new age data indicate that the glaciation took place between 580 000 and 280 000 yr ago the altitude of the anvilian deposits suggests that eustatic sea level during the anvilian transgression rose at least as high as and probably higher than during the last interglacial transgression by correlation with the marine oxygen isotope record the transgression probably dates to stage 11 at 410 000 yr and the nome river glaciation is younger still analyses of floor altitudes of presumed nome river cirques indicate that the nome river regional snowline depression was at least twice that of the maximum late wisconsin the cause of the enhanced snowline lowering appears to be related to greater availability of moisture in northwestern alaska during the middle pleistocene

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

wisconsin holocene paleoenvironment of the bering sea evidence from diatoms pollen oxygen isotopes and clay minerals abstract a core from the southeastern bering sea contains a depositional record of the wisconsin glacial interval and the holocene four lithologic units show distinctive changes in diatom species palynomorphs oxygen isotopes in diatom silica and clay minerals unit 4 the oldest probably represents the glacial advance of the early wisconsin and records extensive sea ice cover and a soggy herbaceous tundra on the exposed continental shelf unit 3 represents the stades and interstades of the middle wisconsin including an early period of high seasonal variability and a later period with expansion of winter sea ice in the basin and of tundra onshore unit 2 represents the late wisconsin glacial maximum and subsequent deglaciation with a tundra covered shelf sea ice cover increased to a maximum during which the surface waters were probably covered by sea ice throughout the year subsequent to the sea ice maximum the isotope ratios record a major meltwater event unit 1 represents the holocene with expansion of shrub tundra or scrub forest in the coastal upland and waters of increased temperature and salinity in the bering sea

transgressions rethinking beringian glaciation abstract the purpose of this investigation is to encourage a fresh look at pleistocene beringia heretofore flooding of bering strait has been cited as the only barrier to migration with marine sea transgressions being a sea gate that closed off migration during glacial interstadials and interglaciations however the possibility exists that glacial advances were also barriers with marine ice transgressions being an ice gate that closed off migration during glacial stadials and glacial maxima this possibility proceeds from the marine ice transgression hypothesis mith which states that marine ice sheets form on the broad arctic continental shelf of northern hemisphere continents when sea ice thickens grounds and domes in shallow water and then transgresses landward as continental ice sheets and seaward as floating ice shelves hughes 1987 landward transgression is onto coastal lowlands during pleistocene glaciations a marine ice sheeet extending from spitsbergen to greenland may have transgressed the circumpolar continental landmass at its lowest and narrowest gap central beringia and calved into the pacific ocean four models of beringian glaciation are presented based on the distinction between marine glaciation and highland glaciation central beringia was glaciated only in highlands in the traditional model hopkins et al 1982 was also glaciated by a self sustaining ice shelf floating over the deep ocean basins of the bering sea in the model by grosswald and vozovik 1984 was glaciated by a marine ice sheet that covered highlands the continental shelf and supplied the ice shelf in a model for maximum pleistocene glaciation and was glaciated by a marine ice sheet in the chukchi sea that merged with highland glaciers transgressed the continental shelf of the western bering sea and calved into the southern bering sea along the edge of the continental shelf in a model for the last glaciation field tests are suggested to assess the viability of these four models the first model is already established for highland glaciation in alaska but less established in siberia the last model should be the easiest to evaluate for marine glaciation the last model limits human migration across the beringian land bridge to brief intervals between stadials and interstadials of the last glaciation cycle when both the ice gate and the sea gate were opened to human migration this model can influence the sea change now underway among quaternary scientists studying peopling of the americas based on the archaeological linguistic and ethnic diversity among native american populations

milankovitch theory of ice ages hypothesis of ice sheet linkage between regional insolation and global climate abstract j d hays j imbrie and n j shackleton 1976 science 194 1121 1132 showed that the astronomical theory explained many features of late quaternary ice age climates but they did not specify the physical mechanisms involved here it is proposed that interlocked variations of ice sheet heat sinks in both polar hemispheres amplified and transmitted milankovitch summer half year insolation changes a version of the astronomical theory between 45 and 75 n into the globally synchronous climate changes recorded in geologic records it is suggested that late quaternary ice sheets had terrestrial components grounded above sea level melting margins fluctuations controlled by climate and marine components grounded below sea level drained largely by ice streams limited melting margins fluctuations controlled primarily by sea level and secondarily by climate interior surface elevations coupled to downdraw through ice streams northern hemisphere ice sheets were largely marine with minor melting margins in the arctic and terrestrial with major melting margins in the midlatitudes west antarctic and peripheral east antarctic ice was marine based and lacked melting margins because of their geographic array these terrestrial and marine components formed an ice sheet system whose variations were coupled on a global scale milankovitch summer isolation changes near midlatitude northern hemisphere melting margins controlled most variations of this system because advance or retreat of melting margins initiated concurrent eustatic sea level change such sea level change afforded the critical interlocking mechanism between terrestrial and marine components because it forced simultaneous expansion or contraction of marine margins in both polar hemispheres this initiated an amplifying feedback loop among all marine components and influenced interior downdraw through ice streams arctic summer insolation change was less important because northern melting margins were relatively minor its greatest influence was on surface ablation of ice streams that controlled interior downdraw this affected eustatic sea level and activated global linkage of marine sectors by analogy with present day antarctica late quaternary ice sheets were enormous planetary heat sinks due to their reflective and radiative surface characteristics it is suggested that the effectiveness of these ice sheet heat sinks varied with their areal extent and interior surface elevation thus it is postulated that concurrent growth or decay of these interlocked ice sheet heat sinks in both polar hemispheres served as the global amplifier of regional milankovitch summer insolation

the western barents sea and the svalbard archipelago 18 000 years ago a finite difference computer model reconstruction a finite difference computer model was used to reconstruct a steady state ice sheet over the western barents sea and the svalbard archipelago at the last glacial maximum 18000 bp flowlines were reconstructed from the ice margin to the ice dome based on information about glacial geology bedrock topography basal thermal regime and the present precipitation pattern

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

last interglacial isotope stage 5 glacial and sea level history of coastal chukotka peninsula and st lawrence island western beringia abstract study of glacial and marine sequences along the outer coast of chukotka peninsula bering strait is the basis for major revisions of the regional stratigraphy the val katlen suite at its type section at the mouth of the enmelen river records the youngest high sea stand of the last interglaciation on chukotka peninsula marine deposits and glacial diamicton stratigraphically below the type section record respectfully the peak of the last interglacial marine oxygen isotope substage 5e and rapid glacierization of the coastal mountains probably during substage 5d or 5b correlative deposits recording a similar sequence of intra stage 5 events but once thought to be of early and middle pleistocene age include the upper and lower pinakul suite at cape pinakul and marine deposits near the nunyamo river on the gulf of anadyr based upon amino acid analyses biostratigraphy and supporting geochronology these deposits enclose warmer than present faunas and floras comparible to last interglacial pelukian marine deposits found along the coast of alaska the last major advance of glacial ice from chukotka peninsula across anadyr strait and onto st lawrence island was likely initiated during the later part of stage 5 based on our reinterpretaion of the stratigraphy at cape pinakul near the nunyamo river and on northwestern st lawrence island chukotkan ice probably reached st lawrence island sometime during oxygen isotope stage 4 ice extend across chukotka during the lgm was very imited

the origin and flux of icebergs released into the last glacial maximum northern hemisphere oceans the impact of ice sheet topography the precipitation fields of a palaeoatmospheric general circulation model are used to derive estimates of the geographical distribution and flux of icebergs from the laurentide fennoscandinavian and eastern siberian ice sheets at the last glacial maximum lgm the atmospheric model fields from lgm simulations using climap or peltier ice 4g ice orography were studied to test the sensitivity of the predicted flux the estimated northern hemispheric lgm iceberg flux is 3500 4000 km3 yr 1 of which about 60 issued directly into the north atlantic the iceberg flux from the st lawrence area is of similar significance to that issuing from hudson strait in all estimates both the north pacific and the arctic received substantial iceberg fluxes ca 700 km3 yr 1 with relatively minor differences occurring between the two ice sheet reconstructions apparent discrepancies between arctic deep sea core samples of ice rafted debris and our estimates of mean glacial iceberg flux may be ascribed to coastal trapping of bergs the existence of floating ice tongues or a rapid exit of icebergs from the arctic basin into the greenland sea through the fram strait copyright 2001 john wiley sons ltd

gps phase fluctuations in the equatorial region during the miseta 1994 campaign in this paper we present the first coordinated use of global positioning system gps multisite and multisatellite observations with ground based radar and optical diagnostics to investigate equatorial irregularity patterns thirty second samples of total electron content tec obtained from gps phase differences between 1 2 and 1 6 ghz signals are used to study phase fluctuations at several stations comparisons were made with various types of ground measurements during the multi instrument studies of the equatorial thermosphere aeronomy miseta period depletions of 6300a airglow emission from arequipa peru correlated with phase fluctuations recorded at the same site phase fluctuations at arequipa occurred at the times when the jicamarca radar backscatter returns from plumes were noted but were also seen on other nights when there were no radar returns from plumes levels of phase fluctuations noted at arequipa varied considerably on nights when only thin layers of irregularities were observed by the jicamarca radar differences of ionospheric conditions between the two sites separated by only 5 5 geographic longitude may account for the different behavior patterns of irregularities noted similar differences in the general behavior pattern of phase fluctuations were shown when data from arequipa and fortaleza brazil were compared these stations 33 apart but at the same dip latitude had different patterns for some days during a magnetic storm a very high altitude plume was observed by the radar and by phase fluctuations noted at santiago at 18 dip latitude this correlation of high plume altitude during some periods of magnetic activity was validated by additional examples of phase fluctuations from three other magnetic storms in the solar minimum years of 1994 and 1995

the eurasian ice sheet formation and collapse resulting from natural atmospheric co2 concentration variations finite element model simulations of ice sheet dynamics are conducted to investigate the role of natural atmospheric co2 variations obtained from ice core bubbles in creating climatic conditions necessary to glaciate the eurasian arctic effects of co2 variations are sufficient to support extensive marine ice sheet and ice shelf development at the last glacial maximum and to deglaciate the region during the holocene from approximately 14 ka to 9 ka the ice sheet coverage simulated for the last glacial maximum agrees with evidence for extensive ice sheet grounding over the shallow continental shelves of the barents kara laptev and east siberian seas an ice shelf also forms over the arctic ocean and greenland and norwegian seas

holocene emergence at cape herschel east central ellesmere island arctic canada implications for ice sheet configuration twenty five radiocarbon age determinations on marine molluscs basal organic pond sediments charred remains in archeological sites and a variety of other materials have allowed the construction of an emergence curve for cape herschel east central ellesmere island 78 35 n 74 40 w only a narrow fringe of land is present between the prince of wales icefield and smith sound yet emergence of the order of 135 m has taken place during the last 8500 8700 radiocarbon years the highest in situ shells were collected at an elevation of 107 5 m and ages of 8470 100 bp gsc 3314 and 8230 70 bp to 230 were obtained on this material the spectacular and fresh appearing glacial sculpture along both sides of smith sound coupled with the rapid emergence in holocene time and the fact that the oldest dates on marine shells at the fiord heads to the west are 3000 4000 years younger than those at cape herschel provides convincing evidence that an ice stream filled smith sound 500 m deep during the late wis

glaciation in alaska the geologic record edited by thomas d hamilton katherine m reed and robert m thorson alaska geological society anchorage 1986 265 pp us 18 95

the ice hill an example of retarded deglaciation in siberia abstract the geological structure of one of the southernmost sites of thick ice beds in the yenisei valley near the arctic circle is discussed the erosion contacts of the foliated and contorted ice abundance of glacial debris and the position between the basal till and ablation cover indicate a glacial origin for the ice layer the ice occurs in the cores of arcuate accretion ridges built of ablation materials the overlying sequence consists of a series of diamicton flows alternating with lacustrine and outwash sediments laterally the ice rock complex changes into thick lacustrine rhythmites underlain by basal tills the ice containing hummocky terrain is often lower than the adjacent lacustrine plain therefore inversion of ice controlled topography is suggested several stages of glaciokarst development are supposed to have occurred after an eastward moving ice lobe stagnated more than 50 ka bp the main depositional events are associated with the middle weichselian draining of ice dammed lake igarka and with early holocene topographic inversion the holocene warming apparently caused diapiric deformation of the buried ice probably because of the density and thickness differences between the ice and the overburden the long history of burial and preservation of the remnants of basal glacier ice was controlled by pleistocene permafrost landscape evolution in northern siberia is governed by such retarded deglaciation in contrast with atlantic environments the thick ablation sequence may be described in terms of a spitsbergen model but the siberian basal tills because of their position within the permafrost must be regarded as exfoliated layers of debris rich ice according to shantzer lavrushin s model the occurrence of buried glacier ice and the mode of distribution of the permafrost shows the relict nature of the latter in areas of modern and former retarded deglaciation intermittent diamicton flows are supposed to mark episodes of climatic amelioration like the pleistocene and holocene diamictons with driftwood at the ice hill such warm diamictons may account for some early holocene and similar puzzling interglacial ice advances

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

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

late pleistocene eolian sand sheets in alaska abstract nonglaciated lowlands in central and southwestern alaska contain extensive deposits of upper quaternary eolian sand derived largely from major outwash rivers although surface dunes are common deep exposures consistently reveal that subhorizontally stratified sand and silt deposits dominate over dune cross strata we hypothesize that 1 many of the subhorizontally stratified deposits represent full glacial eolian sand sheets formed when sand supply was limited by seasonally variable combinations of ice cementation snow cover high groundwater tables and vegetation and 2 many surface dunes reflect late glacial and postglacial reworking under conditions of increased short term availability of loose sand the morphology of some surface dunes may therefore reflect mainly the intensity of reworking since the last glacial maximum rather than full glacial paleowind vectors or the age of the bulk of the underlying deposits

new perspectives on paleoglaciology abstract paleoglaciology deals with glaciation cycles of the quaternary ice age it combines the dynamics of present day ice sheets deduced from glaciology with the history of former ice sheets deduced from glacial geology cosmogenic dating now makes a detailed chronology of a cycle possible radiocarbon dating has provided a detailed chronology for termination of the last cycle but cannot date how the cycle began here we identify the central challenge in applying paleoglaciology to quaternary glaciation cycles in general and initiation of these cycles in particular the challenge is the role of thickening sea ice in the arctic ocean possibly becoming thick ice shelves floating over deep arctic basins and high marine ice sheets grounded on shallow arctic continental shelves in that case an arctic ice sheet existed that was larger and less stable than the antarctic ice sheet is now or in the past two approaches to this problem are presented as part 1 and part 2 in part 1 the height of these former ice sheets is linked primarily to the strength of ice bed coupling which is deduced from glacial geology it provides snapshots of ice sheets that give ice elevations independent of the past history and largely independent of ice surface conditions temperatures and the mass balance in particular in part 2 heights of former ice sheets depend on both their past history particularly initial conditions and changing surface conditions during the glaciation cycle this provides a motion picture of ice sheets during the full cycle the challenge is to establish a mind meld of these two approaches they allow new perspectives on paleoglaciology

pleistocene glaciations in chukotka russia moraine mapping using satellite synthetic aperture radar sar imagery abstract using satellite synthetic aperture radar sar imagery we are able to identify many glacial features on the russian landscape that were previously unobservable by scientists outside russian institutes observations from sar imagery provide information on glacial extent moraine morphology and non sedimentary glacial features such as valley morphology and flow direction moraine sequences in several areas of chukotka record multiple pleistocene glacial events moraine position along with several morphologic characteristics such as relative degradation and surface slope can be determined from sar imagery and used to estimate relative age of glacial features by conducting comparative studies on moraines of known age in alaska we are able to estimate the ages of moraines in russia and develop a framework for the correlation of glacial history across bering strait our study of these images suggests that the last major glaciation late wisconsin was much less extensive than older pleistocene events whose marks remain on the landscape beyond the younger moraines

geomorphological correlation of late pleistocene glacial complexes of western and eastern beringia abstract many fundamental problems exist in comparing the chronology and correlation of late pleistocene glaciations between western and eastern beringia however geomorphological analysis complemented by palynological studies and radiocarbon age estimates of glacial complexes found in the ulakhan chistai bolshoi annachag and pekulney ranges northeastern russia and the kigluaik mountains and brooks range alaska allow for broad comparisons the data clearly confirm that in all regions the latest late pleistocene glaciation 24 0 10 5 ka was restricted in extent and characterized by well defined valley glaciers and coalescing valley glacier complexes emanating from local mountain centers differences in glacier size were due to local orographic and climatological characteristics

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

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

fully coupled discontinuous galerkin modeling of dam break flows over movable bed with sediment transport a one dimensional 1d discontinuous galerkin morphodynamic model has been devised with application to simulate of dam break flows over erodible beds with suspended sediment transport the morphodynamic equations adopt the shallow water equations swe considering the interaction of sediment transport and bed changes on the flow a local second order runge kutta discontinuous galerkin rkdg2 model has been reformulated to numerically solve the morphodynamic equations in a fully coupled manner and with a noncapacity sediment model the model s implementation is thoroughly detailed with focus on the discretization of the complex source terms the treatment of wetting and drying and other stabilizing issues pertaining to high solution gradients and the transient character of the topography the model has been favorably applied to replicate experimental dam break flow over erodible sediment beds

amino acid geochronology resolution and precision in carbonate fossils changes in indigenous proteins preserved in carbonate skeletons can be used to estimate the time elapsed since death of the organism racemization the most widely used reaction in amino acid geochronology refers to the inversion of l amino acids to their d configuration for the protein amino acid l isoleucine racemization occurs about only one of the two chiral carbon atoms this reaction epimerization proceeds from an initial dl ratio near zero to an equilibrium ratio of about 1 30 the reaction rate is controlled primarily by temperature and to a lesser degree by the nature of the proteins themselves a variable related to taxonomy and the extent of protein degradation analyzing monospecific samples minimizes the taxonomic variable the resolving power of dl ratios as relative age indices is a function of the reaction rate degree of natural variability and analytical uncertainty natural variability is defined as the spread in ratios in five well preserved shells of the same age from a single stratum and is primarily related to taxonomy it can range from 20 or more in taxa of low reliability to 1 in taxa of greatest integrity 5 to 10 is to be expected analytical uncertainty within a single laboratory is relatively insignificant amounting to no more than 2 but interlaboratory comparisons suggest caution in comparing ratios determined at different laboratories or by different techniques sampling appropriate portions of a shell is essential to minimize variability in dl ratios site temperature exerts the greatest control on reaction rate hence resolving power for tropical sites 25 c age differences 1 ka can be resolved within the holocene and ca 5 to 10 ka for older samples as the rate decreases equilibrium is attained after 150 to 300 ka the reaction rate is substantially lower at mid latitude sites ca 10 c where equilibrium requires about 2 ma and resolution within the last glacial cycle is no better than 10 to 20 ka arctic sites 10 c show almost no measurable racemization within the holocene and in extreme cases even within the last 100 ka equilibrium is not attained in 10 ma the extent of amino acid racemization epimerization in carbonate fossils provides chronological information for the critical time period beyond radiocarbon dating dl ratios can be used directly as relative age indices and with suitable calibration can provide reasonable estimates of absolute age and or effective diagenetic temperature improving the accuracy of racemization based age estimates requires a better understanding of racemization kinetics in carbonate systems

glacial geology of outer bjornoyrenna southwestern barents sea the upper cenozoic glacigenic succession in outer bjornoyrenna bear island trough southwestern barents sea is investigated utilizing data from six shallow boreholes 143 m below sea bed and seismic profiling overdeepened troughs in the lowermost part of a large plio pleistocene wedge at the shelf margin are interpreted as glacial erosion forms this suggests that the overlying succession which basinward attains a thickness of several km was deposited during a period with glaciations large scale possible sand ridges in the stratigraphic lower part of this succession are confined to two north south trending zones parallel to the present shelf break they probably formed in a continental shelf coastal environment with exceptionally high sediment supply and fluctuating relative sea level related to glaciations a core from a channel fill in the lower part of the succession consists of possibly glaciofluvial gravelly sand intercalated with till most of the other cores are dominated by middle and upper pleistocene muddy massive partly fissile diamictons interpreted to be mainly tills undrained shear strength of these cores ranges from about 20 kn m 2 to more than 300 kn m 2 and both underconsolidated intervals compared to the present burial depth are found an underconsolidated interval comprising eemian interglacial biourbated marine sediments overlain by laminated weichselian glaciomarine sediments on the outher shelf is covered by 50 100 m of muddy diamicton this diamicton is suggested to be mainly till deposited by a late weichselian ice sheet which was grounded to more than 500 m below present sea level earlier weichselian ice expansions did not reach the outer shelf based on the stratigraphy in the shallow cores and seismic interpretation we suggest that there have been five major expansions of grounded ice to the shelf break since ca 440 ka the present study suggests that glacial erosion was a major process in the late cenozoic denudation of the barents sea and in large areas perhaps as much as 200 250 m of preexisting strata could have been eroded by glaciers since about 440 ka

borehole evidence for a thick layer of basal ice in the central ronne ice shelf the ronne ice shelf floating between berkner island and the antarctic peninsula is the biggest ice shelf in antarctica it drains an estimated 1 2 106km2 of the antarctic ice sheet much of it resting on bedrock below sea level consequently the balance and dynamics of this ice shelf is of importance to antarctic glaciology especially with regard to the integration of this part of the cryo sphere into the global processes that control the climate of the earth extensive radio echo sounding res by robin and others revealed reflections in the central part of the ronne ice shelf at the relatively shallow depth of 100 200 m below surface1 the interpretation of these echoes which varied in strength was ambiguous and the possibility of internal reflecting horizons was thoroughly discussed but after surface elevation measurements by radar altimeter from drifting balloons appeared to fit the presence of thin ice it was decided to base a thickness map of the ronne ice shelf on these res echoes1 4 we now present direct observational evidence from boreholes that the total ice thickness is much greater than mapped and that the shallow res reflections therefore do come from internal horizons

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

gravity waves and ionospheric irregularities over tropical convection zones observed by gps met radio occultation gps met observations of the tropical atmo sphere of the southern hemisphere 5 st o 25 s during february 1997 are analysed when a high amount of con vective tropospheric water vapor is at these latitudes en hanced gravity wave activity of the lower stratosphere at h 22 28 km is associated to areas of increased tropospheric water vapor pressure at h 4 6 km regarded as a measure of tropical convection sporadic e and other ionospheric irregularities vertical scales less than 7 km of the meso sphere lower thermosphere are observed to be highly cor related to gravity wave activity in the lower stratosphere and to tropical convection zones we find 4 areas of en hanced ionospheric irregularities and stratospheric wave ac tivity over pacific around 140 w brazil 50 w africa 40 e and indonesia australia 110 e

late cenozoic environments in the barents sea we examine the paleoceanography and paleogeography of the barents sea during the late cenozoic glacial regime by seismostratigraphy and core analysis during the smaller glaciations which probably dominated the first period of the glaciogenic regime approximately 2 5 0 8 ma glaciomarine processes with sediment influx from the adjacent mainland prevailed the barents sea has been covered by grounded ice sheets several five to 10 times during the late cenozoic we speculate that these glaciations occurred during the last 0 8 ma during these larger glaciations the margin of the ice sheet expanded to the shelf edge and the continental shelf break and slope acted as a depocenter and prograded rapidly frequent sediment gravity flows accumulated on the lower continental slope during interglacials the barents sea was converted to a starved continental margin most of the barents sea was glaciated during the maximum of the last glaciation 19 16 ka a two stepped deglaciation 16 to 13 ka and 13 to 10 ka occurred incipient atlantic water reached the western areas about 13 ka and totally replaced the arctic water by 10 ka these paleoceanographic events were delayed in the eastern barents sea

pleistocene periglacial eolian deposits in southwestern alaska sedimentary facies and depositional processes abstract pleistocene periglacial eolian sediments are widespread in the nushagak holitna and upper kuskokwim lowlands of southwestern alaska these sediments comprise mainly sand sheet deposits and sand loess intergrades with subordinate sand dune deposits and loess sand sheet deposits range from 1 sharply defined parallel low angle laminae formed by migrating wind ripples to 2 irregular subhorizontal strata which reflect migration of poorly segregated wind ripples accumulation on a sparsely vegetated surface adhesion on a quasi planar bed and or niveo eolian deposition sand loess intergrades represent alternating bed load and suspension deposition related mainly to the stochastic and seasonal variability of former wind systems the dominance of sand sheet deposits over deposits of well formed dunes in the pleistocene eolian record of southwestern alaska reflects the limited availability of loose dry sand in this former periglacial environment immobilization of sand after deposition as low relief sheets resulted from a seasonally variable combination of ice cementation sparse vegetation high water tables and snow cover

new perspectives on beringian quaternary paleogeography stratigraphy and glacial history abstract aspects of the paleogeography stratigraphy and glacial history of beringia have been greatly revised over the past 15 20 yr access to north east russia in particular has provided the opportunity to evaluate the beringia landscape as a contiguous subcontinent during the quaternary for the first time new research has made clearer the connection between tectonic forces and the submergence of the bering strait during the middle pliocene revisions in the regional stratigraphy of glacial and interglacial deposits in northwest alaska and northeast russia provide a new foundation for assessing the causes for differences in glacial ice extent through time the consensus of all field workers verifies that glacial ice throughout most of beringia was of very limited extent during the last glacial maximum the onset of regional glaciation during the waning stages of the last interglaciation is clearly out of phase with glaciation at lower latitudes despite the lack of much glacial activity during the early holocene alaska contains a rich record of late holocene glacial response to neoglacial cooling changes in the holocene environment of beringia likely had a profound affect on early inhabitants the curiosity driven vision and spirit of both david hopkins and the late troy pewe have had a profound influence on arctic paleoenvironmental research

late quaternary pollen records from the kobuk and noatak river drainages northwestern alaska abstract pollen diagrams from joe and niliq lakes date to ca 28 000 and 14 000 yr b p respectively mesic shurb tundra grew near joe lake ca 28 000 to 26 000 yr b p with local populus populations prior to ca 27 000 yr b p shrub communities decreased as climate changed with the onset of itkillik ii glaciation 25 000 to 11 500 yr b p and graminoid dominated tundra characterized vegetation ca 18 500 to 13 500 yr b p herb tundra was replaced by shrub betula tundra near both sites ca 13 500 yr b p with local expansion of populus ca 11 000 to 10 000 yr b p and alnus ca 9000 yr b p mixed picea glauca p mariana woodland was established near joe lake ca 6000 yr b p these pollen records when combined with others from northern alaska and northwestern canada indicate 1 mesic tundra was more common in northwestern alaska than in northeastern alaska or northwestern canada during the duvanny yar glacial interval 25 000 to 14 000 yr b p 2 with deglaciation shrub betula expanded rapidly in northwestern alaska but slowly in areas farther east 3 an early postglacial thermal maximum occurred in northwestern alaska but had only limited effect on vegetation and 4 pollen patterns in northern alaska and northwestern canada suggest regional differences in late quaternary climates

paleoclimatic constraints on the maintenance of possible ice shelf cover in the norwegian and greenland seas we examine the controversial issue of whether or not an integrated ice shelf existed in the norwegian and greenland seas during glacial events of the pleistocene our method consists of testing for equilibrium ice shelf configurations with the use of a finite element model that predicts ice shelf evolution under a variety of atmospheric and oceanic forcing conditions ice flow at the margins of the simulated hypothetical ice shelf is determined from one of denton and hughes 1981 reconstructions of continental glaciation applicable to the last glacial maximum our results suggest that the existence of the ice shelf and possibly surrounding marine based ice sheets depends most sensitively on oceanic heat flux a heat flux of approximately 4 80 j m 2 s 1 corresponding to an area average basal melting rate of 0 50 m a 1 ice equivalent is near the upper limit allowing ice shelf equilibrium greater heat flux is found to cause an initial 450 m thick ice shelf to rapidly collapse the equilibrium ice shelf configurations examined provide effective buttressing support for the marine ice sheet grounded in the barents sea 18 kyr b p tests confirming the existence of ice shelf cover in the norwegian and greenland seas are possible through a comparison of the sedimentary record of ice rafted debris with ice shelf flow patterns deduced from our simulations

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

glaciation and the evolution of the canadian high arctic landscape the canadian arctic islands represent a tertiary fluvial landscape developed on a contiguous landmass subsequently fractured by block faulting nonetheless some theoretical models invoke pervasive high latitude ice sheets and continue to misattribute the faulted landscape to glacially scoured river valleys quaternary fieldwork on northern ellesmere island suggests that these models are inappropriate for high latitude ice sheets and should be abandoned if there was ever a regional ice sheet over arctic canada it likely occurred on a prefaulted contiguous landmass that had a more temperate climate than at present possibly during the late tertiary after block faulting the marine channels permanently prevented the ice from inundating the landscape it once crossed tectonics and not climate have led to a fundamental change in glacial style this block faulting also may have played a role in terminating the late tertiary boreal forest to 80 n by establishing cold marine channels that diminished the continentality of the once contiguous landmass for a thorough understanding of the canadian arctic landscape future research should determine the continuity between the tertiary and quaternary paleoenvironments the unknown ages of the fiords and interisland channels are of primary importance

chlorine 36 and 14c chronology support a limited last glacial maximum across central chukotka northeastern siberia and no beringian ice sheet abstract the pekulney mountains and adjacent tanyurer river valley are key regions for examining the nature of glaciation across much of northeast russia twelve new cosmogenic isotope ages and 14 new radiocarbon ages in concert with morphometric analyses and terrace stratigraphy constrain the timing of glaciation in this region of central chukotka the sartan glaciation last glacial maximum was limited in extent in the pekulney mountains and dates to 20 000 yr ago cosmogenic isotope ages 30 000 yr as well as non finite radiocarbon ages imply an estimated age no younger than the zyryan glaciation early wisconsinan for large sets of moraines found in the central tanyurer valley slope angles on these loess mantled ridges are less than a few degrees and crest widths are an order of magnitude greater than those found on the younger sartan moraines the most extensive moraines in the lower tanyurer valley are most subdued implying an even older probable middle pleistocene age this research provides direct field evidence against grosswald s beringian ice sheet hypothesis

abrupt climatic change related to unstable ice sheet dynamics toward a new paradigm ice streams are fast currents of ice that drain some 90 of present day ice sheets and probably drained a similar percent of ice from former ice sheets ice streams may have life cycles akin to but much longer than surge cycles of certain mountain glaciers the floating tongues of marine ice streams coalesce to form floating ice shelves that buttress marine ice sheets and the grounded lobes of terrestrial ice streams stabilize terrestrial ice sheets ice shelves and ice lobes form during the life cycles of ice streams and disintegrate rapidly to initiate new life cycles successive life cycles continue until the ice sheet collapses a new paradigm is postulated in which abrupt climatic change is driven by iceberg outbursts associated with life cycles of marine ice streams and dust storms associated with life cycles of terrestrial ice streams for pleistocene northern hemisphere ice sheets these mechanisms regulated north atlantic surface temperatures and salinity and perhaps planetary albedo and atmospheric co2 and thereby drove climatic change which tended to be abrupt because ice stream life cycles began and ended abruptly ice streams proliferated along the margins of northern hemisphere ice sheets after they advanced beyond the crystalline shields of north america and eurasia and spread over softer sedimentary rocks overlain by thick ice cemented sediments that progressively thawed especially along river valleys and marine troughs an increasing fraction of these ice sheets was then subjected to the unstable life cycles of ice streams as seen in the pronounced spikiness of the late glacial oxygen isotope stratigraphy in the greenland ice core at dye 3 life cycles of greenland ice streams during the holocene seem to be linked to episodes of regional climatic cooling most recently the little ice age when superimposed on the present milankovitch hemicycle of reduced insolation over the north atlantic this could abruptly initiate a new worldwide glaciation cycle in the aftermath of present day co2 greenhouse warming proliferation of antarctic ice stream life cycles during the period of greenhouse warming may also trigger global climatic change by forcing a reorganization of circumpolar thermohaline circulation in the southern ocean

late weichselian ice sheets in arctic and pacific siberia abstract interpretation of space images coupled with field data on glacial geomorphology and glacial geology of northern eurasia have provided compelling evidence for a continuous late weichselian ice sheet covering the entire arctic margin of the continent in addition to the scandinavian ice sheet three ice sheets of the same order the karan east siberian and beringian are identified within the major eurasian ice sheet also there is evidence and other considerations suggesting a former ice sheet in the sea of okhotsk ice spreading centers of the ice sheets were situated on the continental shelves off the siberian coasts thus we can term the ice sheets siberian so far the conventional stratigraphic approach to the problem of siberian glaciation has proven fruitless and yielded nothing but uncertainty while geomorphological studies have discovered a wealth of glacial landforms in arctic siberia it was these landforms and their spacing that made the existence of former siberian ice sheets evident the east siberian ice sheet rested on the shelves of the eastern laptev and east siberian seas and its flow was directed radially including up the yana and indigirka rivers the beringian ice sheet was grounded on the chukchi bering and beaufort sea shelves overriding the chukchi and seward peninsulas from the north and flowing through the bering strait it was continued by a thick floating ice shelf buttressed by the submarine aleutian commander ridge the okhotsk ice sheet was grounded on the okhotsk shelf specific gemorphic signatures of marine ice sheets the glacially cut corners have been identified on all promontories jutting out into the bering and okhotsk seas the beringian and okhotsk ice sheets are consistent with the results of deep sea drilling in the adjacent north pacific during leg 145 of d v joides resolution