the bering land bridge a moisture barrier to the dispersal of steppe tundra biota the bering land bridge blb connected the two principal arctic biological refugia western and eastern beringia during intervals of lowered sea level in the pleistocene fossil evidence from lowland blb organic deposits dating to the last glaciation indicates that this broad region was dominated by shrub tundra vegetation and had a mesic climate the dominant ecosystem in western beringia and the interior regions of eastern beringia was steppe tundra with herbaceous plant communities and arid climate although western and eastern beringia shared many species in common during the late pleistocene there were a number of species that were restricted to only one side of the blb among the vertebrate fauna the woolly rhinoceros was found only to the west of the blb north american camels bonnet horned musk oxen and some horse species were found only to the east of the land bridge these were all steppe tundra inhabitants adapted to grazing the same phenomenon can be seen in the insect faunas of the western and eastern beringia the steppe tundra beetle fauna of western beringia was dominated by weevils of the genus stephanocleonus a group that was virtually absent from eastern beringia the dry adapted weevils lepidophorus lineaticollis and vitavitus thulius were important members of steppe tundra communities in eastern beringia but were either absent or rare in western beringia the leaf beetles chrysolina arctica c brunnicornis bermani and galeruca interrupta circumdata were typical members of the pleistocene steppe tundra communities of western beringia but absent from eastern beringia on the other hand some steppe tundra adapted leaf beetles managed to occupy both sides of the blb such as phaedon armoraciae much of the blb remains unstudied but on biogeographic grounds it appears that there was some kind of biological filter that blocked the movements of some steppe tundra plants and animals across the blb

historical ecology in beringia the south land bridge coast at st paul island a 14 m core of lake sediments from st paul island yields a long environmental history of the south coast of the bering land bridge tritium assay demonstrates that sands in the bottom 8 m of deposit are injected with modern water suggesting that a radiocarbon anomaly is the result of modern carbon introduced in groundwater the remaining radiocarbon chronology coupled with a time stratigraphic pollen zone boundary suggests that the record penetrates to the mid wisconsin interstadial pollen percentage data picea pollen influx and pollen species lists allow reconstruction of the land bridge vegetation which was tundra without shrubs or trees with bare ground and comparable to bering land bridge tundras found further north there was no coastal mild or wet strip plant associations comparable to those of the modern aleutians or pribilofs probably did not exist along the land bridge coast and the region was probably not suitable for breeding by fur seals and other marine mammals a cold dry continental air mass system reached to the coast itself the south land bridge coast did not offer an environment to aboriginal human populations that was significantly milder than that of the land bridge plains to the north at about 11 000 yr b p the wisconsin dry climate was replaced by a regimen comparable to that at the modern tree line of the interior and this climate in turn was replaced with the modern system at about 9500 yr b p climatic change was independent of fluctuating sea level

analytical expressions for transient specific yield and shallow water table drainage 1 new closed form expressions are introduced to capture the dependence of specific yield on time and depth to water table the expressions allow the user to convert observations of water table fluctuations to volumes of water released from storage in a shallow water table aquifer whereas a linear relationship between water table fluctuations and released volumes holds for a deep water table aquifer this relationship is nonlinear for shallow water table aquifers the dependence of specific yield on time stems from the slow drainage of soil water from pores above the water table the new expressions allow determination of transient specific yield and time to drain the soil water profile for a given water table fluctuation if the time step in a numerical groundwater model is longer than the time for limiting specific yield then a constant time independent specific yield can be justifiably adopted the new expressions are easy to use and require knowledge of soil hydraulic properties which are readily available from soil water retention data and surveys

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 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

formation of alunite jarosite and hydrous iron oxides in a hypersaline system lake tyrrell victoria australia abstract alunite kal 3 so 4 2 oh 6 and jarosite kfe 3 so 4 2 oh 6 are common weathering products of aluminosilicates and pyrite long range transport of the constituents forming these minerals and the subsequent deposition of alunite and jarosite in an evaporite setting have not been previously documented such conditions for the occurrence of alunite and jarosite were investigated in a hypersaline system where acid groundwater enriched in k al fe iii and so 4 enter a saltplaya lake sediment cores were studied by thin section xrd and sem eds groundwater and pore water chemistries were also analyzed the results show that alunite and jarosite occur together or as individual layers and cements within the top 20 cm of the sediments where the groundwater is most concentrated due to evaporation hydrous fe oxides also occur as cements or vein fillings with the alunite and jarosite but are distributed throughout the 70 cm sediment column studied the results are consistent with a model in which alunite and jarosite precipitate as a result of the evaporation of water thermodynamic modeling indicates that the pore water in the playa sediments maybe in equilibrium with alunite jarosite and hydrous fe oxides

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

late quaternary vegetation of chukotka northeast russia implications for glacial and holocene environments of beringia abstract two lake records from the kankaren region of southern chukotka when combined with other palynological and macrofossil data document spatial and temporal variations in the regional vegetation history since 21 000 14c 25 400 cal yr bp full glacial environments were severely cold and arid in central and northern chukotka whereas southern sites experienced conditions that were relatively moist although still drier than present southern chukotka may represent a western extension of environments of the land bridge proper including a possible moisture barrier to intercontinental migration shrub betula tundra established earliest in southern chukotka 15 800 14 000 14c 19 000 16 700 cal yr bp 13 000 14c 15 300 cal yr bp central and north pinus pumila earliest in the north 9600 14c 11 100 cal yr bp 7600 14c 8400 cal yr bp south and shrub alnus earliest in both the south and north 12 000 11 000 14c 13 800 12 900 cal yr bp these patterns support the presence of cryptic refugia for betula and alnus in chukotka during the full glaciation in contrast p pumila probably migrated into chukotka from populations located in the northern coastal lowlands and from mountainous regions of southwestern beringia evidence for a thermal optimum 11 000 8000 14c 12 900 9000 cal yr bp is strong in northern chukotka but is absent in central and southern areas

late quaternary vegetation and climate history of the central bering land bridge from st michael island western alaska pollen analysis of a sediment core from zagoskin lake on st michael island northeast bering sea provides a history of vegetation and climate for the central bering land bridge and adjacent western alaska for the past 30 000 14 c yr b p during the late middle wisconsin interstadial 30 000 26 000 14 c yr b p vegetation was dominated by graminoid herb tundra with willows salix and minor dwarf birch betula nana and ericales during the late wisconsin glacial interval 26 000 15 000 14 c yr b p vegetation was graminoid herb tundra with willows but with fewer dwarf birch and ericales and more herb types associated with dry habitats and disturbed soils grasses poaceae dominated during the peak of this glacial interval graminoid herb tundra suggests that central beringia had a cold arid climate from 30 000 to 15 000 14 c yr b p between 15 000 and 13 000 14 c yr b p birch shrub ericales sedge moss tundra began to spread rapidly across the land bridge and alaska this major vegetation change suggests moister warmer summer climates and deeper winter snows a brief invasion of populus poplar aspen occurred ca 11 000 9500 14 c yr b p overlapping with the younger dryas interval of dry cooler climate during the latest wisconsin to middle holocene the bering land bridge was flooded by rising seas alder shrubs alnus crispa colonized the st michael island area ca 8000 14 c yr b p boreal forests dominated by spruce picea spread from interior

the history of the origin evolution and dispersal of the late pleistocene mammuthus coelodonta faunal complex in eurasia large mammals

the periglacial climate and environment in northern eurasia during the last glaciation this paper summarizes the results of studies of the late weichselian periglacial environments carried out in key areas of northern eurasia by several queen teams european science foundation esf programme quaternary environment of the eurasian north the palaeoglaciological boundary conditions are defined by geological data on timing and extent of the last glaciation obtained in the course of the eu funded project eurasian ice sheets these data prove beyond any doubt that with the exception of the northwestern fringe of the taymyr peninsula the rest of the eurasian mainland and severnaya zemlya were not affected by the barents kara sea ice sheet during the last glacial maximum lgm inversed modelling based on these results shows that a progressive cooling which started around 30 ka bp caused ice growth in scandinavia and the northwestern areas of the barents kara sea shelf due to a maritime climate with relatively high precipitation along the western flank of the developing ice sheets in the rest of the eurasian arctic extremely low precipitation rates less than 50 mm yr 1 did not allow ice sheet growth in spite of the very cold temperatures palaeoclimatic and palaeoenvironmental conditions for the time prior to during and after the lgm have been reconstructed for the non glaciated areas around the lgm ice sheet with the use of faunal and vegetation records permafrost eolian sediments alluvial deposits and other evidences the changing environment from interstadial conditions around 30 ka bp to a much colder and drier environment at the culmination of the lgm at 20 15 ka bp and the beginning of warming around 15 ka bp have been elaborated from the field data which fits well with the modelling results

the late pleistocene environment of the eastern west beringia based on the principal section at the main river chukotka chukotka is a key region for understanding both quaternary environmental history and transcontinental migrations of flora and fauna during the pleistocene as it lies at the far eastern edge of asia bordering the bering sea the now submerged land bridge is the least understood region of beringia yet the most critical to understanding migrations between the old and new worlds the insect fauna of the main river ledovy obryv ice bluff section which is late pleistocene in age mis 3 2 is markedly different from coeval faunas of areas further to the west as it is characterized by very few thermophilous steppe elements from the fauna we reconstruct a steppe tundra environment and relatively cold conditions the reconstructed environment was moister than that of typical steppe tundra described from further west the data from this locality if typical of the chukotka peninsula as a whole may indicate that a barrier associated with the environments of the land bridge restricted trans beringian migrations particularly the more thermophilous and xeric adapted elements of the beringian biota supporting the hypothesis of a cool but moist land bridge filter inferred from evidence from several other studies

on the connexion of vegetation dynamics with climatic changes in high asia abstract within the scope of research on environmental changes in high asia indications of desiccation and thermal oscillations are described they refer to different periods and are caused by different climatic factors distribution patterns of forest constituents with disjunctions in the central and eastern himalayas are explained with changes in monsoonal rainfall presumably during the holocene in southern tibet the plant relicts of one of the younger holocene phases of higher humidity kobresia pygmaea age have been widely destroyed by the himalaya fohn giving way to semiarid alpine steppe on stone pavements field observations of a recent intensification of gelifluction processes in the southeastern part of the tibetan plateau is in accordance with a cooling period between the late 1950s and the late 1970s the obviously decreased vigour and lacking regeneration of the climax vegetation in the alpine belt becomes conceivable under the presumption that the respective cover of alpine turf is a relict of the climatic optimum which slowly but increasingly deteriorated since then a decrease of plant vigour at climatically sensitive vegetation borders upper treeline drought limit of forests transition zone between alpine cyperaceae mats and the free gelifluction belt transition zone between humid alpine mats and alpine steppe gives evidence of diminishing winter precipitation during the last 30 to 40 years in the karakorum

beringian climate during the late pleistocene and holocene abstract the difference between the climates of the bering land bridge and asiatic western beringia 18 20 ka ago is discussed the climatic reconstructions of the bering land bridge and western beringia are based upon two methods first we discuss the ecological and thermal requirements of the thermophilic weevils coleoptera curculionidae in the genus stephanocleonus second we discuss the effect of climatic continentality on soil temperatures we suggest that for western beringia the climate was suitable for the warm steppe environment mean july air temperatures were at least 10 11 c and an annual sum of daily temperatures above 0 c sdd at the soil surface was up to 2500 c in contrast to these conditions the climate of the bering land bridge was very similar to that found in the modern arctic tundra zone

dated wood from alaska and the yukon implications for forest refugia in beringia abstract postulations on the existence of forest refugia in parts of beringia during the last glacial have been in large part based on ambiguous evidence existing data on radiocarbon dated and identified fossil wood and macrofossils from alaska and northwest canada are synthesized here and are augmented by results of palynological studies in an effort to show the persistence of some and total extinction of other tree and large shrub species possible dispersal routes taken by species that reinvaded beringia in postglacial times are also reconstructed from the fossil record macrofossil and pollen evidence when combined with climatic factors makes cottonwood a good candidate for survival during the last glacial larch and aspen are also candidates though the evidence for them is less positive pollen and macrofossils of alder are very scarce in deposits of the last glacial age and if it survived at all it was probably in very isolated vegetatively reproducing clones shrub birch may have been present in beringia but tree birch probably was reintroduced during the holocene spruce also appears to have been absent in alaska from about 30 000 to 11 500 yr ago and probably reinvaded beringia from a refugium south of the laurentide ice sheet

full glacial upland tundra vegetation preserved under tephra in the beringia national park seward peninsula alaska the nature of the full glacial vegetation of beringia has been the subject of a great deal of investigation and debate here we present a reconstruction of an intact example of the full glacial upland vegetation of part of the northern seward peninsula at one point in time the area was blanketed by more than 1 m of tephra ca 18 000 14c bp ca 21 500 cal bp and the former land surface was preserved in the permafrost the discovery of the land surface provides a unique opportunity to study a fossil ecosystem preserved in situ macrofossils were used to reconstruct the vegetation growing at several sites on the buried land surface the macrofossil assemblages indicate a vegetation characterized by graminoids and forbs with the occasional occurrence of salix arctica the vegetation was dominated by kobresia myosuroides other sedges carex and grasses with a ne scale mosaic related to snow accumulation and moisture availability overall the vegetation was a closed dry herb rich tundra grassland with a continuous moss layer growing on calcareous soil that was continuously supplied with loess nutrient renewal by loess deposition was probably responsible for the relatively fertile vegetation and the occurrence of a continuous mat of acrocarpous mosses good physiognomic analogues can be suggested but no exact modern vegetational analogues have been found probably because the full glacial environment and climate with loess deposition do not occur today 2000 elsevier science ltd all rights reserved

mutual climatic range reconstructions of seasonal temperatures based on late pleistocene fossil beetle assemblages in eastern beringia abstract the mutual climatic range mcr method of paleoclimate reconstruction has been employed by paleoentomologists for the last decade a quantitative calibrated method mcr has many advantages over qualitative methods the method has now been developed for arctic faunas climate envelopes for beetle species found in eastern beringia have been compiled using a 25 km gridded north american climate database that pairs climate parameters with modern collection sites linear regressions of predicted on observed values yielded equations used to calibrate the mcr estimates this study presents the initial results from the mcr analysis of 46 fossil beetle assemblages from alaska and the yukon territory the assemblages range in age from about 150 000 9200 yr bp isotope stage six assemblages yielded estimates of mean july temperature tmax 4 5 c colder than at present assemblages associated with the old crow tephra oct dated approximately 140 000 yr bp likewise indicated tmax values well below modern levels isotope stage 5e faunas showed tmax values as much as 3 5 c warmer than modern early wisconsinan assemblages showed climatic cooling with tmax levels dropping as low as 6 c colder than at present a mid wisconsinan interstadial period is marked by warming of mean summer temperatures to near modern levels at some sites last glacial maximum assemblages reflect cooling of tmax to a level about 6 4 c colder than at present although most assemblages from this period yielded mean january temperatures above modern levels warming of summer temperatures began at least by 12 500 yr bp and warmer than modern tmax values were recorded from all assemblages between then and 9200 yr bp

stratigraphy of the colorado creek mammoth locality alaska abstract the colorado creek mammoth locality in west central alaska contains the remains of two mammoths that were scavenged by carnivores sedimentologic interpretations of the reworked eolian deposits surrounding the bones supplemented by 10 radiocarbon dates indicate that the lower and upper mammoths died and were buried within separate but superimposed thaw gullies about 23 000 and 16 000 yr ago respectively from our results we propose a polycyclic taphonomic model for thaw gullies governed largely by slope aspect rather than regional climate and in which mixing between faunal horizons is more likely than not variations in the rate of silt influx and the position of the permafrost table provide a paleoclimatic proxy record that can be correlated to other records in eastern beringia

paleoenvironmental reconstruction of the last glacial maximum inferred from insect fossils from a tephra buried soil at tempest lake seward peninsula alaska abstract sediments and vegetation dated 21 570 cal yr bp were buried under tephra on the northern seward peninsula this buried surface has yielded plant macrofossils in growth position as well as numerous insect fossils excellently preserved in permafrost it appears that many of the insects were buried alive by the volcanic ash the species composition and ecological affinities of this fossil fauna are typical of alaskan late pleistocene steppe tundra environments the assemblages are dominated by the weevil lepidophorus lineaticollis one of the most common species in eastern beringian pleistocene fossil assemblages many other members of the ancient steppe tundra insect community are preserved in these assemblages including the pill beetle morychus sp and weevils of the genus coniocleonus in alaska most of these species but not all of them survived the pleistocene holocene environmental transition but are restricted today to relict patches of steppe like vegetation faunal diversity is low in spite of the recovery of more than 1000 individual insects and mites including more than 600 beetles this reflects the small number of species adapted to the cold dry environments of the lgm in eastern beringia they represent an ecosystem which no longer exists

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 paleoenvironments and modern pollen data from wrangel island northern chukotka abstract new lacustrine records from central and southern wrangel island are analyzed for their pollen content in an attempt to clarify possible linkages between paleoenvironmental shifts and the dwarfing and or extinction of the island s mammoth population a younger dryas aged peat is also examined to provide better understanding of the regional climatic history samples of surficial lake sediments from wrangel island and chukotka aid in interpreting the lacustrine records the modern spectra differentiate the herb dominated tundra of wrangel island from the shrub tundras of the mainland and are unique when compared to other arctic assemblages analysis of the fossil data indicates that a herb dominated tundra has been present on southern and central wrangel island since at least 11 ka bp comparison to modern palynological data implies little change in vegetation during the holocene the lacustrine interpretations contrast to those based on paleobotanical study of peats and alluvium which suggest modern vegetation was not present until ca 4 3 ka bp pre holocene assemblages have high percentages of cyperaceae pollen perhaps indicating more moderate conditions summer climate is inferred to be warmer and moister than present during the latest pleistocene and early holocene the pattern of postglacial warming on wrangel island is more like that from eastern beringia than from other areas of western beringia modern synoptic anomaly maps indicate that such a climatic pattern is reasonable and related to the presence of negative anomalies over western beringia and a region of weaker positive 500 mb pressure centered over the beaufort sea

late quaternary vegetational change in the kotzebue sound area northwestern alaska abstract two sediment cores from kaiyak and squirrel lakes in northwestern alaska yielded pollen records that date to ca 39 000 and 27 000 yr b p respectively between 39 000 and 14 000 yr b p the vegetation around these lakes was dominated by gramineae and cyperaceae with some salix and possibly betula nana glandulosa forming a local shrub component of the vegetation betula pollen percentages increased about 14 000 yr b p indicating the presence of a birchdominated shrub tundra alnus pollen appeared at both sites between 9000 and 8000yr b p and picea pollen mostly p mariana arrived at squirrel lake about 5000 yr b p the current foresttundra mosaic around squirrel lake was established at this time whereas shrub tundra existed near kaiyak lake throughout the holocene when compared to other pollen records from north western north america these cores 1 represent a meadow component of lowland beringian tundra between 39 000 and 14 000 yr b p 2 demonstrate an early holocene arrival of alnus in northwestern alaska that predates most other alnus horizons in northern alaska or northwestern canada and 3 show an east to west migration of picea across northern alaska from 9000 to 5000 yr b p

ice age refugia and quaternary extinctions an issue of quaternary evolutionary palaeoecology abstract quaternary palaeoecology as a discipline involves the analysis of a large range of fossil organisms from the last ca 2 million years this paper considers the role that these quaternary records can take in better understanding the evolution of those organisms we also discuss the surprisingly low uptake of evolutionary biology in quaternary palaeoecological studies this leads us to encourage an advance on both these fronts with a greater degree of collaboration with phylogeographic and ancient dna researchers these discussions accompany a summary of a special issue of quaternary science reviews representing the proceedings of the xvii inqua held in cairns australia in 2007 this special issue includes papers on a wide variety of quaternary evolutionary palaeoecological and population dynamic subjects including extinct pacific island palm trees beringian beetles scandinavian trees and the effects on human and animal populations of an extraterrestrial impact event in the late glacial of north america

high resolution pollen analysis of tundra polygons from the north slope of alaska modern and fossil pollen analyses have established the local vegetation succession and landscape evolution along the meade river near atqasuk alaska three data sets were analyzed 1 a 142 cm long peat deposit on the exposed river bluff face 2 a short 13 cm peat monolith from the near surface sediment and 3 a modern data set of surface samples collected along a transect representative of a geomorphic gradient of low center transitional and high center polygons pollen microfossil assemblages changed significantly along this gradient detailed analysis of the short pollen profile shows successional vegetation changes over the last 250 years the long profile a 9400 year record of past vegetation indicates that initially the site was covered by shallow lakes eolian activity had a substantial effect on sediment deposition but a period of rapid peat growth from 8500 to 5000 14c year b p is coincident with increased vegetation cover of mixed grass shrub tundra following this period peat growth slowed and shrub vegetation was replaced by tussock forming sedge vegetation

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