variability of the north atlantic thermohaline circulation during the last interglacial period studies of natural climate variability are essential for evaluating its future evolution greenland ice cores suggest that the modern warm period the holocene has been relatively stable for the past 9 000 years much less is known about other warm interglacial periods which comprise less than 10 of the climate record during the past 2 5 million years here we present high resolution ocean sediment records of surface and deep water variables from the bermuda rise spanning the last interglacial period about 118 000 127 000 years ago in general deep water chemical changes are coincident with transitions in surface climate at this site the records do not show any substantial fluctuations relative to the much higher variability observed during the preceding and subsequent cool climates the relatively stable interglacial period begins and ends with abrupt changes in deep water flow we estimate using 230 th measurements to constrain the chronology that transitions occur in less than 400 years

holocene coastal glaciation of alaska holocene uctuations of the three cirque glaciers on the seward peninsula and ve groups of tidewater and land terminating glaciers along the northernmost gulf of alaska provide a proxy record of late holocene climatic change furthermore the movements of the coastal glaciers were relevant to late holocene native american migration the earliest expansion was recorded about 6850 yr bp by hubbard glacier at the head of yakutat bay in the gulf of alaska however its down fjord advance to the bay mouth was delayed until 2700 bp similarly expansions of the icy bay bering and mccarty glaciers occurred near their present termini by 3600 3000 bp compatible with marked cooling and precipitation increases suggested by the alaskan pollen record decrease in glacier activity 2000 bp was succeeded by advances of gulf coastal glaciers between 1500 and 1300 bp correlative with early medieval expansions across the northern hemisphere a medieval optimum encompassing at least a few centuries prior to ad 1200 is recognized by general retreat of land terminating glaciers but not of all tidewater glaciers little ice age advances of land based glaciers many dated with the precision of tree ring cross dating were centered on the middle 13th or early 15th centuries the middle 17th and the last half of the 19th century a d strong synchrony of these events across coastal alaska is evident 2000 elsevier science ltd all rights reserved

pedogenic carbonate formation recrystallization versus migration process rates and periods assessed by 14c labeling 1 under arid to semihumid climatic conditions dissolution of primary carbonate and recrystallization with carbon c from soil co2 leads to accumulation of significant amounts of pedogenic secondary carbonate most soils of arid and semiarid regions contain a carbonate accumulation horizon the depth of which is related to climatic conditions and properties of parent material it remains unclear whether this carbonate migrates from the upper horizons before or after recrystallization with soil co2 the aim of this study was to determine recrystallization rates during initial pedogenesis and to estimate the accumulation depth of secondary carbonate based on c isotopic exchange during secondary carbonate formation in an experiment with alternating moisture conditions maize grown on 1 m high loess filled columns was pulse labeled in14co2 atmosphere every 3 weeks after 6 months portions of secondary recrystallized caco3 were determined in 5 cm segments based on 14c respired in the rhizosphere and subsequently incorporated into newly formed secondary carbonate more than 80 of recrystallized carbonate ca14co3 was leached from the uppermost 15 cm of the loess column and more than 70 of total secondary carbonate were accumulated in a depth between 15 and 50 cm based on the recrystallization rate calculated for the uppermost 15 cm of the loess column 1 77 0 26 10 5 day 1 between 300 and more than 1 700 years are necessary for complete decalcification of the upper 15 cm our modeled data are consistent with formation of calcic horizons under relatively humid conditions

climate impacts of an ice sheet in east siberia during the last glacial maximum abstract recent evaluations of geomorphological evidence in east siberia strongly suggest that no ice sheet existed on the east siberian arctic shelf during the last glacial maximum lgm contrary to the hypothesis of some authors because most general circulation model gcm simulations of the lgm have included such an ice sheet the impact of an east siberian ice sheet is crucial for understanding previous model simulations of the lgm the experiments in this study use the global environmental and ecological simulation of interactive systems genesis 2 0 gcm and the equilibrium vegetation ecology eve vegetation model to simulate the lgm climate with previously published simulation and without new simulation an east siberian ice sheet most lgm simulations have shown increased southerly advection into beringia resulting from the dynamics of the continental ice sheets which acts to alleviate the hemispheric glacial cooling in beringia the east siberian ice sheet provides a secondary source of warm air advection into beringia in the simulation with an east siberian ice sheet a glacial anticyclone develops over the ice sheet during winter resulting in subsidence of air flowing off the ice sheet increased southerly advection along the western margin of the ice sheet and warming to the south of the ice sheet during summer the ice sheet blocks northerly flow from the arctic also resulting in warming south of the ice sheet the primary vegetation difference is in the ratio of tundra to polar desert the more mild climate with the ice sheet present produces more tundra and less polar desert

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

origin and causes of the mammoth steppe a story of cloud cover woolly mammal tooth pits buckles and inside out beringia to account for the vastness of the northern arid steppes during glacial episodes i propose the proximate key variable was simply frequent clear skies this hitherto under emphasized point is the hub which best explains many questions low maritime cloud cover best accounts for today s tundra and in a related way the cloudy polar front accounts for the whole of the taiga even during glacial maxima the proximity of the sea to the bering isthmus created intermittent maritime cloud cover this regional cloud cover produced an ecological interruption or buckle of the arid steppe belt while this beringian mesic buckle did not serve as an intercontinental ecological barrier to most steppe adapted species it does seem to have limited the distributions of woolly rhinos camels american kiangs short faced bears badgers and some others at the beginning of the holocene this narrow refugium seems to have been a source of some mesic adapted species which colonized westward into the now tundra vegetation of northern asia and eastward into northern north america this holocene expansion from a limited and regional pleistocene refugium created our present misconceptions about beringia the mid strait mesic ecological conditions were the exception to the more extensive arid adapted communities of the mammoth steppe 2000 published by elsevier science ltd all rights reserved

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

evidence from lake baikal for siberian glaciation during oxygen isotope substage 5d abstract the paleoclimatic record from bottom sediments of lake baikal eastern siberia reveals new evidence for an abrupt and intense glaciation during the initial part of the last interglacial period isotope substage 5d this glaciation lasted about 12 000 yr from 117 000 to 105 000 yr b p according to correlation with the specmap isotope chronology lithological and biogeochemical evidence of glaciation from lake baikal agrees with evidence for the advance of ice sheet in northwestern siberia during this time period and also with cryogenic features within the strata of kazantzevo soils in southern siberia the severe 5d glaciation in siberia was caused by dramatic cooling due to the decrease in solar insolation as predicted by the model of insolation changes for northern asia according to milankovich theory coupled with western atmospheric transport of moisture from the open areas of northern atlantic and arctic seas which became ice free due to the intense warming during preceeding isotope substage 5e other marine and continental records show evidence for cooling during 5d but not for intense glaciation late pleistocene glaciations in the northern hemisphere may have begun in northwestern siberia

late wisconsin environments of the bering land bridge abstract late wisconsin paleobotanical and fossil insect data from the central and northern sectors of the bering land bridge indicate widespread mesic shrub tundra environments even during the last glacial maximum vegetation before the last glacial maximum was a birch heath graminoid tundra with few or no steppe elements shrubs were not an important element of the vegetation but were present in small numbers during the interval 20 000 14 000 yr bp land bridge vegetation was dominated by birch graminoid tundra with small ponds containing aquatic plants heaths were relatively unimportant insects from this interval were indicative of arctic climate with drier tundra than during the late glacial during the late glacial interval 14 000 11 000 yr bp land bridge vegetation was dominated by birch heath graminoid tundra with small ponds choked with aquatic plants the insect record indicates open ground habitats dominated by mesic tundra by 11 000 yr bp insect data suggest that summer temperatures on the emergent bering shelf were warmer than present day upland regions in western alaska summer temperatures on the chukchi shelf were warmer than the present day north slope of alaska contrary to previous hypotheses we found no evidence of steppe tundra on the land bridge new accelerator mass spectrometer ams 14c dates show that much of the land bridge was above sea level and thus available for human and animal migration until as late as 11 000 yr bp

a 15 000 year paleoenvironmental record from meiji seamount far northwestern pacific late glacial and holocene hemipelagic sediments from meiji seamount in the far northwest pacific contain common to abundant planktonic and benthic foraminifera for ams 14c dating for stable isotope analysis and for interpreting paleoclimate change we present here chronostratigraphic faunal and geochemical results from a piston core which indicate that during glacial times as young as 14 000 yrs bp the northwest pacific sea surface salinity was at least as low as today effectively inhibiting convective overturn between 12 000 and 13 000 yrs ago after a major flux of ice rafting there is faunal and 18o evidence of an abrupt decrease in surface ocean salinity coincident with this event was an increase in biological productivity shown by higher fluxes of calcium carbonate organic carbon opal and greater abundances and lower 13o of the benthic foraminifera uvigerina oxygen isotope ratios in uvigerina and cibicidoides show step like decreases at about 13 000 14 000 11 000 10 000 and 6000 8000 yrs bp these events may be analogous to steps in the north atlantic 18o record during meltwater events if this interpretation is correct then the temperature and salinity history of the deep pacific lags that of the north atlantic by about 1000 yrs consistent with the transport time of deep water from the north atlantic to the north pacific

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

vegetation and paleoclimate of the last interglacial period central alaska the last interglacial period is thought to be the last time global climate was signi cantly warmer than present new stratigraphic studies at eva creek near fairbanks alaska indicate a complex last interglacial record wherein periods of loess deposition alternated with periods of soil formation the eva forest bed appears to have formed about the time of or after deposition of the old crow tephra dated to 160 to 120 ka and is therefore correlated with the last interglacial period pollen macrofossils and soils from the eva forest bed indicate that boreal forest was the dominant vegetation and precipitation may have been greater than present around fairbanks during the peak of the last interglacial period a new compilation of last interglacial localities indicates that boreal forest was extensive over interior alaska and yukon territory boreal forest also extended beyond its present range onto the seward and baldwin peninsulas and probably migrated to higher elevations now occupied by tundra in the interior comparison of last interglacial pollen and macrofossil data with atmospheric general circulation model results shows both agreement and disagreement model results of warmer than present summers are in agreement with fossil data however numerous localities with boreal forest records are in con ict with model reconstructions of an extensive cool steppe in interior alaska and much of yukon territory during the last interglacial 2000 elsevier science ltd all rights reserved

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

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

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

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

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

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

late quaternary sea level change in southern beringia postglacial emergence of the western alaska peninsula abstract postglacial sea level trends have varied dramatically across the bering platform because of differences in coastal and shelf geologic settings emergent shorelines and basal peats along the western alaska peninsula indicate that relative sea level has fallen since regional deglaciation occurred ca 13 000 cal yr bp age elevation determinations on four shorelines 25 m 10 ka 16 m 9 6 6 ka 6 m 2 1 ka and 2 3 m 1 8 0 6 ka in the vicinity of cold and morzhovoi bays provide an estimate of the pace and timing of of sea level change since the last glacial maximum lgm 22 17 ka isostatic recovery and shoreline regression following the disintegration of continental and alpine ice has been interrupted by transgressive conditions at least twice since deglaciation changes in the balance between eustatic sea level rise and isostatic uplift resulted in the reactivation of marine scarps during the early to middle holocene but terrace cutting and a gap in the archaeological record about 2 1 ka suggest that sudden tectonic displacements also influence the record reconstructions of coastal paleogeography constrain the timing and distribution of regional archaeological settlement periods of shoreline erosion during stillstands or transgressions and the episodic reorganization of intertidal environments that accompanies tectonic displacements have conditioned site preservation potential and long term adaptive strategies

the early holocene milankovitch thermal maximum and humans adverse conditions for the denali complex of eastern beringia abstract calibration of 14c ages has forced the revision of paleoecological relationships with the milankovitch thermal maximum 10 000 9000 cal bp edwards and barker palaeogr palaeoclimatol palaeoecol 109 1994 127 in eastern beringia paleo geographic factors had dramatic consequences for humans many represented by the late pleistocene early holocene 13 000 7000 cal bp denali complex calibration of 71 radiocarbon ages associated with denali occupations indicates that the earliest precede both the milankovitch maximum and the spread of spruce in interior alaska by 2000 yr some denali occupations co occur with weakly developed forest soil horizons that reflect stabilized surfaces later capped by loess denali occupations peaked during the worldwide temperature decline between 8500 and 8000 cal bp the mesoglacial beget geology 11 1983 389 or the younger younger dryas fewer sites date to the milankovitch maximum and suggest an inverse relationship between warmer climate and human population

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

aminostratigraphic correlations and paleotemperature implications pliocene pleistocene high sea level deposits northwestern alaska abstract multiple periods of late pliocene and pleistocene high sea level are recorded by surficial deposits along the coastal plains of northwestern alaska analyses of the extent of amino acid epimerization in fossil molluscan shells from the nome coastal plain of the northern bering sea coast and from the alaskan arctic coastal plain of the chukchi and beaufort sea coasts allow recognition of at least five intervals of higher than present relative sea level three late pliocene transgressions are represented at nome by the complex and protracted beringian transgression and on the arctic coastal plain by the colvillian bigbendian and fishcreekian transgressions these were followed by a lengthy period of non marine deposition during the early pleistocene when sea level did not reach above its present position a middle pleistocene high sea level event is represented at nome by the anvilian transgression and on the arctic coastal plain by the wainwrightian transgression anvilian deposits at the type locality are considerably younger than previously thought perhaps as young as oxygen isotope stage 11 410 000 bp finally the last interglacial pelukian transgression is represented discontinuously along the shores of northwestern alaska amino acid epimerization data together with previous paleomagnetic measurements radiometric age determinations and paleontologic evidence provide geochronological constraints on the sequence of marine deposits they form the basis of regional correlations and offer a means of evaluating the post depositional thermal history of the high sea level deposits provisional correlations between marine units at nome and the artic coastal plain indicate that the temperature difference that separates the two sites today had existed by about 3 0 ma since that time the effective diagenetic temperature was lowered by about 3 4 c at both sites and the mean annual temperature was lowered considerably more this temperature decrease was largely accomplished by the close of the fishcreekian beringian iii transgression ca 2 5 2 1 ma since then intervals of warm temperature must have been extremely brief these data suggest that the steep latitudinal temperature gradient and the frigid temperatures that characterize the high latitudes of alaska today are ancient features of arctic climate

compositional variation and provenance of late cenozoic distal tephra beds fairbanks area alaska abstract thin fine grained discontinuous tephra beds from interior alaska can be divided into two compositional groups by their mineralogy and major and trace element glass geochemistry the source vents of these beds are unknown but are believed to be in the aleutian arc alaskan peninsula and wrangell volcanic field type i tephra has evolved trace element profiles while type ii is primitive type ii contains abundant hydrous minerals that are absent or rare in type i trace elements were used to compare the fairbanks tephra beds to volcanic rocks in the potential source areas there are very few published glass trace element analyses from these regions this necessitates comparing whole rock with glass analyses for this reason incompatible elements particularly rare earth elements are most useful whole rock analyses and petrography of lavas throughout the aleutian arc alaskan peninsula and the wrangell volcanic field are similar to type i tephra lavas and intrusive rocks similar to type ii tephra are rare and occur at one volcano in the alaskan peninsula and at three volcanoes in the wrangell volcanic field

paleoclimate simulations for north america over the past 21 000 years features of the simulated climate and comparisons with paleoenvironmental data maps of upper level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21 000 years for north america we review a the large scale features of circulation temperature and precipitation that appear in the simulations from the ncar community climate model version 1 ccm 1 b the implications of the simulated climate for the past continental scale distributions of three plant taxa picea spp pseudotsuga menziesii and artemisia tridentata which are broadly representative of the vegetation across the continent and c the potential explanations in terms of atmospheric circulation or surface energy and water balance processes for mismatches between the simulations and observations most of the broad scale features of previous paleoclimatic simulations with the ncar ccm 0 for north america are present in the current simulations many of the elements of a conceptual model based on previous climate simulations that describes the controls of paleoclimatic variations across north america during the past 21 000 years are found in simulations reviewed here these include 1 displacement of the jet stream by the laurentide ice sheet to the south of its present position in both winter and summer 2 generation of a glacial anticyclone over the ice sheet at the lgm and the consequent induction of large scale sinking motions induced over eastern north america 3 changes in the strength of surface atmospheric circulation features through time including weakening of the aleutian low in winter and strengthening of the eastern pacific and bermuda high pressure systems in summer as the ice sheet decreased in size 4 development of a heat low at the surface and a strengthened ridge in the upper atmosphere over the continent at the time of the maximum summer insolation anomaly 5 increases in summer temperature earlier in regions remote from the ice sheet these increases appear earlier in the present ccm 1 simulations than in the previous ccm 0 ones however and 6 continuation of negative winter temperature anomalies into the middle holocene in general simulated surface conditions that are discordant with paleoenvironmental observations can be attributed to the simulation of particular atmospheric circulation patterns e g those that suppress precipitation or advect warm air into a region with these mismatches amplified in beringia and the southeastern united states by surface energy and water balance processes

pleistocene glacial history of the southern ahklun mountains southwestern alaska soil development morphometric and radiocarbon constraints abstract four new ams 14 c ages glacial mapping and measurements of soil development loess thickness and moraine morphology constrain the age and extent of at least three quaternary advances by outlet lobes of an ice cap over the ahklun mountains of southwestern alaska the relative age data are from 107 sites correlated to 25 ice marginal positions in the kanektok goodnews togiak and kulukak river valleys and along the southeastern flank of the range radiocarbon ages provide minimum ages for six and a maximum age for one of the former ice margins soil and morphometric parameters subdivide the ice limits into three relative age groups one to three pre wisconsin advances probably middle pleistocene in age are represented by drift with relatively thick b horizons 60 5 cm with bt horizons thick loess caps 80 12 cm and broad moraines 135 134 m with gentle side slopes 7 5 an extensive early wisconsin sensu lato s l advance 39 9 ka and three associated stillstands or readvances are characterized by intermediate soil and morphometric parameters bw and weak bt horizons with thicknesses of 40 11 cm loess thicknesses of 69 46 cm crest widths of 38 13 m and slope angles of 14 4 the maximum late wisconsin advance 16 9 ka and two readvances or stillstands are associated with thin 20 5 cm weakly to moderately developed bw horizons thin loess caps 28 8 cm narrow crest widths 28 9 m and steep slope angles 18 3 the data confirm that early wisconsin glaciers in southeast beringia were much more extensive than late wisconsin glaciers which were apparently limited by availability of moisture

quaternary glacial lacustrine and fluvial interactions in the western noatak basin northwest alaska abstract the 130 km long noatak basin is surrounded by mountains of the western brooks range middle and late pleistocene glaciers flowing southeast into the basin dammed a succession of proglacial lakes defined by shorelines outlet channels and upper limits of wave erosion more than 60 bluffs along the noatak river and its principal tributaries expose glacial and glaciolacustrine sediments that exhibit cut and fill relationships with interglacial and interstadial river channel and floodplain deposits this report focuses on the western noatak basin where high bluffs created by deep postglacial erosion record four major glacial advances during the cutler advance a floating ice tongue terminated in a large proglacial lake that filled the noatak basin the retreating glacier abandoned a trough along the valley center that subsequently filled with about 40 m of sediment during several younger glaciations and probably two major interglacial episodes alluvium that formed near the beginning of the younger interglaciation contains the 140 000 yr old old crow tephra the subsequent closely spaced okak and makpik advances are clearly younger than the maximum of the last interglaciation but they preceded a middle wisconsin 36 30 ka nonglacial interval in the noatak basin the okak advance terminated in an extensive lake whereas glaciers of the makpik and the subsequent anisak advances flowed into much narrower lakes that filled only the basin center the anisak advance bracketed by radiocarbon ages of about 35 and 13 6 ka represents the last glacial maximum lgm in the western noatak basin correlations with the oldest and youngest glacial deposits of the central brooks range are clear but relationships to events of intermediate age are more tenuous early pleistocene and older glacial advances from the central brooks range must have filled the noatak basin and overflowed northward through howard pass a younger glacial advance of inferred middle pleistocene sagavanirktok river age extended down the noatak valley into the basin center but its deposits are deeply buried beneath the basin floor and must be older than the cutler moraine the cutler advance may have been synchronous with the older of two advances of itkillik i age in the atongarak creek area but other evidence indicates that the okak makpik moraine succession more likely was synchronous with the two atongarak creek moraines radiocarbon ages surface morphology soil and weathering profiles and lake level history all support correlation of the last anisak major glacial advance in the western basin with the douglas creek moraine farther east and with itkillik ii late wisconsin glaciation of the central brooks range

stratigraphy and paleoceanography of pliocene deposits of karaginsky island eastern kamchatka u s s r abstract the lithology and paleontology of pliocene deposits from karaginsky island off eastern kamchatka peninsula u s s r are described in order to provide a paleoceanographic reconstruction of this region of the eastern north pacific ocean the stratigraphic sequence is divided into three suites the limimtevayamian the ust limimtevayamian and the tusatuvayamian which correspond to three standard pacific diatom zones the thalassiosira oestrupii neodenticula koizumi n kamtschatica and n koizumi the entire sequence is further subdivided into six members and 18 distinct beds on the basis of molluscan assemblages and three members and seven beds on the basis of benthic foraminiferal assemblages marine ostracodes are described from the limimtevayamian suite the marine invertebrate assemblages from karaginsky island provide evidence that 1 ocean water temperatures were warmer than today about 4 ma and again about 3 5 3 0 ma 2 several arctic atlantic species of molluscs and ostracodes migrated to the eastern north pacific between 4 2 3 0 ma presumably through the proto bering strait 3 many species found in the karaginsky island pliocene represent pacific taxa which migrated through the arctic into the north atlantic during the late pliocene

late pleistocene glaciation of the southwestern ahklun mountains alaska glacial deposits in the southwestern ahklun mountains southwestern alaska record two major glacier advances during the late pleistocene the arolik lake and klak creek glaciations took place during the early and late wisconsin respectively during the arolik lake glaciation outlet glaciers emanated from an ice cap centered over the central portion of the ahklun mountains and expanded beyond the present coast during the klak creek glaciation ice cap outlet glaciers terminated 60 km upvalley from arolik lake moraines the area also supported numerous alpine glaciers that expanded from small massifs during both episodes of glaciation these alpine glaciers apparently reached their maximum positions sometime after the retreat of the ice cap outlet glaciers equilibrium line altitudes for reconstructed alpine glaciers of the klak creek glaciation average 390 6 100 m elevation in the western ahklun mountains which is at most 500 m and possibly only 200 m below the estimated modern equilibrium line altitude the maximum late pleistocene advance in the southwestern ahklun mountains occurred during the early wisconsin similar to advances elsewhere in western alaska but in contrast to the isotopic signal in the deep sea record of global ice volume the restricted extent of klak creek glaciers might reflect the increased distance to the bering sea resulting from eustatic sea level regression and decreased evaporation resulting from lower s ea surface t emperatures a nd i ncreased s ea ice extent 2000 university of washington

late pleistocene environments of the western noatak basin northwestern alaska glacial lake noatak formed repeatedly during middle and late pleistocene time as expanding glaciers from the delong mountains blocked the noatak river valley downcutting by the noatak river has exposed thick sediment successions in bluffs up to 86 m high two river bluffs nk 26 and nk 29a contain correlative organic rich flood plain deposits that were formed during and after deposition of the old crow tephra at about the transition between oxygen isotope stage 6 and oxygen isotope stage 5 at the beginning of the last interglaciation both bluffs also contain older interglacial or interstadial flood plain deposits of uncertain age pollen and beetle remains were recovered from the older and younger flood plain deposits at each bluff pollen from the younger flood plain deposits suggests tundra vegetation with local dominance of sedge juniperus abundances were locally high especially around the time of old crow tephra deposition mutual climatic range mcr estimates from the insect fossil assemblages suggest that mean summer temperatures tmax near the time of old crow tephra deposition were about 2 c colder than modern mean winter temperatures were very similar to those of today a younger sample from the same interglacial deposit yielded a tmax estimate of 2 c warmer than modern signaling interglacial warming pollen from the older interglacial deposit at nk 29a suggests mesic tundra with boreal forest more distant than it is today mcr analysis of a possibly correlative older interglacial deposit at nk 26 suggests a tmax about 2 c below present

evidence of quaternary climatic variations in a sequence of loess and related deposits at birch creek alaska implications for the stage 5 climatic chronology abstract a 45 m outcrop of quaternary sediments on birch creek near circle alaska reveals a record of fluctuating environmental conditions that probably spans several glacial interglacial cycles from base to top the deposits are forested floodplain warm colluvium with ice wedges cold forest soil warm loess cold paleosol containing old crow tephra oct cool to warm loess cold lacustrine very warm loess cold and modern forest soil warm resolution of the paleoclimatic history associated with the oct event is critical to understanding the nature of stage 5 in the western north american arctic application of recent age estimates for the oct tephra ca 140 000 yr bp to the birch creek section would indicate that either i the tephra paleosol dates from the 6 5 5 transition a strongly developed glacial interval occurred within stage 5 and the overlying very warm interval occurred in 5 3 or 5 1 or ii the tephra was deposited during a non milankovitch warming event late in stage 6 a paleoclimate chronology provides an alternative interpretation iii in which the tephra paleosol corresponds to stage 6 or even stage 7 the overlying loess to stage 6 and the lake sediments to all or part of stage 5 but the oct is older than 140 000 yr bp chronologies ii and iii imply a very warm beginning to stage 5 consistent with paleoclimate model simulations and data from other regions

the last interglaciation in northeast siberia abstract alluvial fluvial and organic deposits of the last interglaciation are exposed along numerous river terraces in northeast siberia although chronological control is often poor the paleobotanical data suggest range extensions of up to 1000 km for the primary tree species these data also indicate that boreal communities of the last interglaciation were similar to modern ones in composition but their distributions were displaced significantly to the north northwest inferences about climate of this period suggest that mean july temperatures were warmer by 4 to 8 c and seasonal precipitation was slightly greater mean january temperatures may have been severely cooler than today up to 12 c along the arctic coast but similar or slightly warmer than present in other areas the direction and magnitude of change in july temperatures agree with atmospheric general circulation models but the 126 000 year b p model results also suggest trends opposite to the paleobotanical data with simulated cooler winter temperatures and drier conditions than present during the climatic optimum

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

emergent marine record and paleoclimate of the last interglaciation along the northwest alaskan coast the last interglacial high sea level stand the pelukian transgression of isotope substage 5e is recorded along the western and northern coasts of alaska by discontinuous but clearly traceable marine terraces and coastal landforms up to about 10 m altitude the stratigraphy indicates that sea level reached this altitude only once during the last interglacial cycle from the type area at nome to st lawrence island in the bering sea to the eastern limit of the beaufort sea pelukian deposits contain extralimital faunas indicating that coastal waters were warmer than present amino acid ratios in molluscs from these deposits decrease to the north toward barrow consistent with the modern regional temperature gradient fossil assemblages at nome and st lawrence island suggest that the winter sea ice limit was north of bering strait at least 800 km north of its present position and the bering sea was perennially ice free microfauna in pelukian sediments recovered from boreholes indicate that atlantic water may have been present on the shallow beaufort shelf suggesting that the arctic ocean was not stratified and the arctic sea ice cover was not perennial for some period in coastal regions of western alaska spruce woodlands extended westward beyond their modern range and in northern alaska on the arctic coastal plain spruce groves may have entered the upper colville river basin the flaxman member of the gubik formation on the alaskan arctic coastal plain was deposited during marine isotope substage 5a and records the breakup of an intra stage 5 ice sheet over northwestern keewatin

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

stable isotope profiles of last interglacial pelukian transgression mollusks and paleoclimate implications in the bering strait region abstract the marine paleoclimate during the last interglaciation in the bering strait region is inferred from the stable oxygen and carbon isotope profiles of fossil bivalve mollusks specimens were collected from the marine highstand deposits of the pelukian transgression from the arctic alaskan coastal plain the nome coastal plain st lawrence island and the val katlen suite on the chukotka peninsula as a calibration modern mollusks were obtained from the major water masses in the bering chukchi seas system and from coastal environments near the fossil localities the 18 o composition of the modern mollusks accurately reflects the seawater 18 o differences among the water masses and the ambient temperature range at each site seasonal paleotemperature ranges are estimated from the 18 o profiles of the fossils by comparison with those of the modern specimens a simple model is developed to correct the paleotemperature ranges for the influence of differences in seawater 18 o between water masses and seasonal variations caused by freshwater discharge paleotemperatures calculated for the skull cliff site alaskan arctic coastal plain are close to but slightly cooler than those of modern specimens from peard bay and icy cape the isotopic composition of a pelukian specimen collected near wainwright shows the obvious influence of locally reduced salinities with a correction for lower seawater 18 o this profile yields a summer temperature of 13 c which is 3 c warmer than that from the modern icy cape specimen the isotope records of two specimens from the nome coastal plain suggest salinities that were 3 5 psu lower than the modern eastern bering shelf the paleotemperature range of 0 15 c is consistent with modern conditions in norton sound the character of the isotope profiles of the pelukian specimens from st lawrence island is very different than that of modern specimens near the island but matches the 18 o values of shells from deeper sites in anadyr water this suggests that the fossil mollusks were living in anadyr strait and were transported by a glacial advance from the chukotka peninsula the last interglacial specimens from the val katlen suite have isotope profiles with large seasonal 18 o ranges and the clear influence of a reduced salinity coastal water mass calculated paleotemperatures from the val katlen specimens range from 0 to 13 c differences in the 13 c of shell carbonate between sites appears to reflect the regional distribution of the 13 c of sedimentary organic matter som which is a mixture between terrestrial organic matter mean 13 c of 24 and marine phytoplankton 21 partitioning of 13 c between shallow and deep waters by phytoplankton productivity and remineralization may also affect the regional distribution differences in shell 13 c between taxa may relate to feeding mode and the type and isotopic composition of ingested particles the filter feeders mya and astarte typically have 13 c values 1 2 more positive than the deposit feeders macoma and serripes this effect is attributed to a 13 c difference between marine phytoplankton and som with a component of terrestrial organic carbon

central andean crustal structure from receiver function analysis abstract the central andean plateau 15 27 s is a high plateau in excess of 3 km elevation associated with thickened crust along the western edge of the south america plate in the convergent margin between the subducting nazca plate and the brazilian craton we have calculated receiver functions using seismic data from a recent portable deployment of broadband seismometers in the bolivian orocline 12 21 s region and combined them with waveforms from 38 other stations in the region to investigate crustal thickness and crust and mantle structures results from the receiver functions provide a more detailed map of crustal thickness than previously existed and highlight mid crustal features that match well with prior studies the active volcanic arc and altiplano have thick crust with moho depths increasing from the central altiplano 65 km to the northern altiplano 75 km the eastern cordillera shows large along strike variations in crustal thickness along a densely sampled sw ne profile through the bolivian orocline there is a small region of thin crust beneath the high peaks of the cordillera real where the average elevations are near 4 km and the moho depth varies from 55 to 60 km implying the crust is undercompensated by 5 km in comparison a broader region of high elevations in the eastern cordillera to the southeast near 20 s has a deeper moho at 65 70 km and appears close to isostatic equilibrium at the moho assuming the modern day pattern of high precipitation on the flanks of the andean plateau has existed since the late miocene we suggest that climate induced exhumation can explain some of the variations in present day crustal structure across the bolivian orocline we also suggest that south of the orocline at 20 s the thicker and isostatically compensated crust is due to the absence of erosional exhumation and the occurrence of lithospheric delamination

evidence for an early opening of the bering strait the first opening of the bering strait was an important palaeogeographical and biogeographical event for marine and terrestrial biotas in asia and north america1 2 3 and an oceanographic event of global importance4 5 6 this event however has never been precisely dated so it has not been accurately incorporated into models of global biogeography and oceanography a recent find of the bivalve mollusc astarte in southern alaska is a clear signal that the strait had opened by at least the late miocene or earliest pliocene epochs because this genus otherwise dwelled only in the arctic and north atlantic oceans at that time1 2 here we show that marine diatoms with astarte are correlative with subzone b of the neodenticula kamtschatica zone of the north pacific diatom biochronology yielding an age range of 4 8 5 5 myr refs 7 8 stratigraphic information suggests that this may be a minimum age range for the strait s first opening which evidently occurred between 4 8 and 7 3 7 4 myr ago our results contrast with past studies9 10 11 12 13 that suggested an age of 3 1 4 1 myr for the initial opening of the bering strait

new evidence for the age of bering strait abstract the earliest known opening of bering strait in signaled by the presence in southern alaskan neogene strata of the marine bivalve mollusk astarte which had dwelled throughout the cenozoic in the arctic and north atlantic oceans astarte occurs with age diagnostic marine diatoms in the middle and upper miocene bear lake formation of the alaska peninsula southwestern alaska the diverse diatom flora of more than 100 taxa contains species characteristic of subzone b of the neodenticula kamtchatica zone of the north pacific diatom biochronology which has an age range of 4 8 5 5 ma this inferred age for an early opening of bering strait predates the generally cited ages of 3 1 4 1 ma stratigraphic data suggest that the first opening of the strait may have occurred even earlier

a 3 m y record of pliocene pleistocene loess in interior alaska many distal tephra beds exist in the thick fossiliferous loess deposits near fairbanks interior alaska isothermal plateau fission track ages determined on glass shards from tephra beds in conjunction with tephrostratigraphic and magnetostratigraphic techniques indicate that loess deposition began in the late pliocene an antiquity previously unsuspected hence there is the opportunity now to reconstruct a detailed well dated record of environmental changes in interior alaska during the past 3 m y

seismicity of the bering strait region evidence for a bering block newly compiled russian and u s seismological data support an independent bering block in motion relative to the north american plate this motion is likely to be driven by the westward extrusion of southwestern alaska resulting from compression in southern alaska due to subduction of the pacific plate and terrane accretion seismicity extends from central alaska through the bering strait and into chukotka in eastern chukotka several southwest trends are evident some of which continue through the koryak highlands to kamchatka the seismicity outlines the bering block which includes most of the bering sea chukchi peninsula seward peninsula and parts of western alaska focal mechanisms young basaltic volcanism and normal faults in western alaska and chukotka indicate that the bering strait is under northeast southwest extension this in conjunction with thrust faulting in the koryak highlands indicates that the bering block is rotating clockwise relative to the north american plate

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

age of pre late wisconsin glacial estuarine sedimentation bristol bay alaska pleistocene glacial estuarine sediment deposited in an intertidal environment of northeastern bristol bay southwestern alaska was dated using a variety of approaches including infrared stimulated and thermoluminescence irsl and tl techniques analysis of modern and14c dated holocene tide flat mud demonstrates that the bulk of sediment in this environment is reset by solar radiation thereby lending confidence to ages obtained from similar pleistocene deposits by luminescence techniques irsl seems to be especially well suited for dating with resolution on time scales of 10 000 yr the ages of tide flat mud of the nushagak formation derived from the ahklun mountains to the northwest of bristol bay and of halfmoon bay drift derived from the alaska peninsula to the southeast suggest contemporaneous glacial estuarine deposition related to independent glacial source areas about 75 000 80 000 yr ago this age is consistent with other geochronological data that indicate a pre late wisconsin and post substage 5e age including nonfinite14c ages a lack of interglacial indicators and old crow tephra 140 000 yr atop the drift normal paleomagnetic inclinations and amino acid isoleucine epimerization ratios aile ile aile ile ratios inportlandia arctica 0 052 0 003 from a marine lag horizon at south naknek beach which separates halfmoon bay drift above from older glacial estuarine drift below are only slightly higher than inmya truncata 0 041 0 007 from last interglacial pelukian deposits at nome as laboratory heating experiments show that the two genera epimerize at similar rates these data imply correlation of the marine lag at south naknek beach with pelukian deposits hence glaciers on the alaska peninsula experienced major pre late wisconsin advances both before and after the last interglaciation shells reworked into halfmoon bay drift yield aile ile ratios of 0 028 0 005 forportlandiaat second point and 0 027 0 001 forhiatella arcticaat etolin point together with assumptions about the postdepositional temperature history these ratios indicate that the shells are at least 55 000 yr and probably closer to 90 000 yr although the uncertainty in this age estimate is broad the amino acid and luminescence data converge on an age between about 75 000 and 90 000 yr late during oxygen isotope stage 5 for a major ice advance far beyond late wisconsin limits

epiguruk a late quaternary environmental record from northwestern alaska epiguruk a prominent bluff along the kobuk river in northwestern alaska exposes a rich depositional record of quaternary eolian and fluvial sand with associated loess paleosols and periglacial features three major complexes of alluvial and eolian deposits are separated by two conspicuous organic rich paleosols which formed during cool moist interstadial intervals sediments between the two paleosols include eolian channel and flood plain deposits that formed during alluviation of the kobuk river to a height of about 12 m above the present level the youngest depositional complex which overlies the upper paleosol is divisible into late wisconsinan and holocene components and into fluvial channel flood plain eolian dune sand sheet loess and pond facies eolian sand from the active kobuk sand sea overloaded the river during late wisconsinan time causing it to alluviate to about 13 m above its modern level the holocene record reflects erosion and deposition by a small southern tributary to the kobuk river downcutting by the kobuk river toward its modern level and subsequent erosion across a meander belt nearly 8 km wide sixty six radiocarbon ages many from rooted shrubs provide a firm chronology for the past 35 k y at epiguruk the kobuk river incised to near its present level by about 35 ka and the upper paleosol began forming near that level about 33 ka coincident with the fox termal event of central alaska although higher standing sandy facies of this paleosol began forming earlier thick peat beds did not accumulate until about 33 ka at those sites late wisconsinan loess influx and alluviation began about 24 ka synchronous with the itkillik ii glaciation of the brooks range the river overlapped progressively higher surfaces of the upper paleosol attaining its maximum height of about 13 m above modern river level between 20 and 19 ka it downcut about 18 5 ka and subsequently migrated northward deposits at the north end of the bluff show that the river had begun building its modern flood plain by 8 6 ka and it has varied little in elevation since that time

pre late wisconsin glacial history coastal ahklun mountains southwestern alaska new amino acid thermoluminescence and 40ar 39ar results abstract new stratigraphic and geochronologic data from the togiak bay area of southwestern alaska indicate that glaciers advanced from the southern ahklun mountains at least three and as many as six times prior to the late wisconsin the oldest glaciations are represented by glacial marine sediment in coastal exposures on hagemeister island the extent of amino acid isoleucine epimerization in fossil molluscs indicates that at least one and possibly four older middle pleistocene glacial intervals are represented with age estimates spanning 500 280 ka and averaging 400 100 ka the youngest glacial marine drift on hagemeister island may correlate with the eruption of the togiak tuya a new 40 ar 39 ar age on basalt that overlies pillow lava indicates that the volcano erupted through glacial ice at least 300 m thick 263 22 ka the youngest drift in the region overlies the old crow tephra 140 10 ka and a 70 10 ka basaltic lava flow dated by thermoluminescence analysis of underlying baked sediment the drift delimits flat piedmont lobes that spread out onto the continental shelf and terminated 100 km from their source areas during the early wisconsin sensu lato the glacial geologic evidence suggests that major expansions of glaciers were out of phase with global ice volume

aminostratigraphy of pliocene pleistocene high sea level deposits nome coastal plain and adjacent nearshore area alaska amino acid epimerization ratios aile ile measured in 295 fossil molluscan shells of 3 genera provide a basis to evaluate the number and relative timing of high sea level events represented by deposits blanketing the nome coastal plain and adjacent nearshore area northwestern alaska frequency distribution analysis along with a new approach that relies on the ranked data distribution was used to identify clusters aminozones in the aile ile data each of which presumably represents a discrete period of marine inundation of the study area six periods of high relative sea level were distinguished some are recognized only by redeposited shells rather than in situ bio or lithostratigraphic units the oldest period is represented by shells recovered from the deepest sections of two offshore boreholes aile ile ratios in these shells 1 0 are much higher than in any found onshore and probably date to the late miocene early pliocene the oldest aminozone lies below nonfossiliferous sediments which in turn are overlain by glacigenic and marine deposits containing largely fragmented shells with aile ile ratios ranging from 0 35 to 0 65 this range coincides with aile ile ratios from various onshore deposits previously ascribed to the middle pliocene 3 m y beringian transgression ratios in this range can be subdivided into three evenly spaced aminozones each of which may represent multiple short duration 10 4 yr high sea stands separated by a longer period 10 5 yr sea level oscillation on the basis of a new empirical model of parabolic epimerization kinetics and an assumed age of 3 2 m y for the oldest beringian aminozone the approximate age of the initial submergence of bering strait the estimated length of time represented by the three beringian aminozones is between 0 5 and 1 7 m y the youngest beringian highstand was followed in the late pliocene or early pleistocene by a lengthy period of nonmarine deposition during which local valley glaciers advanced onto the coastal plain at least once relative sea level apparently did not again surpass that of today until the middle pleistocene anvilian transgression the oldest higher than present stand of the pleistocene yet considerably younger than previously thought glaciers overran the nome coastal plain at least once following the anvilian transgression incorporating abundant shells into their drift the drift is notched by a shoreline formed during the pelukian transgression of the last interglaciation although well represented onshore no pelukian deposits have been found offshore

continuous late quaternary proxy climate records from loess in beringia abstract loess deposits in eastern beringia contain continuous proxy records of the effects of past climatic change on terrestrial landscapes at high latitudes variations of environmental magnetism and sedimentology of high latitude loess deposits indicate that the timing and pattern of responses to local variations in wind intensity storminess and pedogenesis in eastern beringia closely resemble the pattern of global climate change during the late quaternary deduced from studies of marine and ice core records the age of paleoclimatic fluctuations permafrost features volcanic ash horizons buried forest layers and paleosols and other features of the eastern beringian loess record can be determined using a variety of quaternary dating methods tephrochronologic correlations between the loess record and the glacial history of eastern beringia indicate the delta glaciation occurred during marine isotope stage 6 several other middle and late quaternary glaciations across eastern beringia can be tephrochronologically tied to the loess record and appear to have been in phase with episodes of global cooling recorded in deep sea records

late quaternary lacustrine pollen records from southwestern beringia sediment cores from three lakes in the upper kolyma region northeast russia provide the first well dated continuous record of late quaternary vegetation change from far southwestern beringia the oldest pollen zone tentatively assigned to the karginsk mid wisconsinan interstade indicates an artemisia shrub tundra with pinus pumila betula and alnus at mid to low elevations with the onset of the sartan late wisconsinan stade pinus disappeared probably indicating severely cold dry winters and cool summers as conditions deteriorated further an artemisia gramineae tundra developed selaginella rupestris and minor herb taxa indicate the presence of poor soils and disturbed ground this herb tundra was replaced by a short lived 1000 yr betula alnus shrub tundra followed by the rapid establishment of a larix dahurica forest with a betula exilis ericales lichen understory populus suaveolens and chosenia may have formed limited hardwood gallery forests at this time modern vegetation associations probably developed during the early holocene with the arrival of pinus pumila ca 9000 yr b p this shrub became important in the forest understory and with b exilis formed a belt of shrub tundra beyond altitudinal treeline comparison of the upper kolyma and alaskan pollen records indicates that important differences in vegetation types and timing of vegetation change occurred across beringia during the late quaternary

last interglacial age of the eva forest bed central alaska from thermoluminescence dating of bracketing loess abstract the eva forest bed in the yukon tanana upland of east central alaska represents a frozen buried boreal forest this bed consists of well preserved peat lenses sticks roots logs as well as rooted and unrooted stumps of trees where preserved the eva forest bed is overlain by the goldstream formation and underlain by gold hill loess almost all exposures have a prominent unconformity at the top of the gold hill loess even where the forest bed is not preserved attempts have been made over the last 50 yr to determine the age of this bed numerically we report here details of thermoluminescence tl dating of 14 samples of loess from above and below this unconformity in the fairbanks area together with knowledge about the climatic indicators from the eva forest bed these tl age estimates 1 indicate that the most probable age of the eva forest bed is 125 ka the time of the warmest part of oxygen isotope stage 5 and 2 confirm stratigraphic inferences from tephra beds in the upper gold hill loess that erosion has removed variable thicknesses of the original loess complex just prior to the development of the eva forest bed

sea level surface salinity of the japan sea and the younger dryas event in the northwestern pacific ocean abstract the japan sea was profoundly different during glacial times than today available 18 o evidence indicates that sea surface salinity was lower by several per mil this probably increased the stability of the water column and caused anoxic sedimentary conditions in the deep sea as shown by the absence of benthic microfossils and the presence of laminated sediment these changes are likely related to the effects of late quaternary sea level change on the shallow sills ca 130 m across which the japan sea exchanges with the open ocean the hwang he yellow river has previously been implicated as the source of fresh water to the japan sea during glaciation but the possible roles of the amur river and excess precipitation over evaporation must also be considered ambiguous radiocarbon chronologies for the latest quaternary of japan sea cores do not adequately constrain the timing of salinity lowering previous studies have suggested that lowest sea surface salinity was achieved 27 000 to 20 000 14 c yr b p however if global sea level fall restricted exchange with the open ocean circulation then lowest salinity in the japan sea may have occurred as recently as 15 000 to 20 000 yr ago when sea level was lowest if this alternative is correct then as sea level abruptly rose about 12 000 yr ago relatively fresh water must have been discharged to the open pacific this might have affected the dynamics of outflow local faunal and floral expression of the polar front and stable isotope ratios in foraminifera these environmental changes could be misinterpreted as evidence for the cooling of younger dryas age which has not been identified in nearby terrestrial records

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