late quaternary paleoenvironments and growth of intrusive ice in eastern beringia eagle river valley northern yukon canada in this study the sediments exposed in a fluvial terrace and in the headwall of a thaw slump in the eagle river valley northern yukon provide new data about the timing of flooding of glacial lake old crow the formation of massive ground ice bodies and the vegetation and the fauna in eastern beringia during the late quaternary the stratigraphy and radiocarbon ages establish the following chronology of events 1 a gravel fluvial terrace was deposited by an overflow from glacial lake hughes into glacial lake old crow 2 a carbonate silty clay was deposited during the maximum level of glacial lake old crow at 15 120 14c year bp 3 permafrost and large intrusive ice bodies aggraded through the glaciolacustrine and underlying sediments following the drainage of glacial lake old crow from the site 4 at 11 290 14c year bp a shrub sedge tundra colonized an uneven surface deformed by the bodies of ground ice 5 a thaw lake drained at 6730 14c year bp after flooding the site 6 during the early h

permafrost tectonics and past and future regional climate change yukon and adjacent northwest territories late tertiary changes in the general circulation of the atmosphere regionally enhanced by uplift of the wrangell saint elias and coast mountains were sufficient to promote permafrost development in the western arctic permafrost developed in yukon territory and adjacent northwest territories during early pleistocene glacial periods after continued tectonic activity led to further modification of regional climate but degraded in the interglacials permafrost has been present in northern parts of the region since the illinoian glaciation but most ground ice in central yukon formed in the late wisconsinan the present interglacial is the only one with widespread evidence of permafrost which is maintained in the valleys of central and southern yukon by the saint elias mountains blocking continental penetration of maritime air from the gulf of alaska this reduces snow depth in winter while cold air drainage in the dissected terrain of the yukon plateaus enhances the near surface inversion leading t

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

an oxygen isotope paleothermometer from ice in siberian permafrost abstract there is a clear linear relationship between mean annual or seasonal air temperature at the earth s surface and the mean oxygen isotopic composition of precipitation in polar regions whereas this relationship is well preserved in polar ice caps it may not be in permafrost because freshly deposited snow in permafrost areas is subjected to great deflation and drifting by wind moreover melting and freezing within the snow cover and the active layer can lead to isotopic fractionation the 18 o of recent ground ice also depends on its geomorphic context and on the lithology content of organic matter of ice containing sediments nevertheless mean cold season air temperature near the ground surface and 18 o in recent ground ice are highly correlated therefore the 18 o of ground ice ice cement and segregated ice in permafrost areas can be used for paleoclimatic reconstructions

multiple water isotope proxy reconstruction of extremely low last glacial temperatures in eastern beringia western arctic abstract precipitation isotopes are commonly used for paleothermometry in high latitude regions here we present multiple water isotope proxies from the same sedimentary context perennially frozen loess deposits in the klondike goldfields in central yukon canada representing parts of marine isotope stages mis 4 3 and 2 allowing us to uniquely corroborate fractionations and temperature conversions during these late pleistocene cold stages we include new and existing proxy data from relict wedge ice a direct archive for snowmelt relict pore ice an archive for bulk soil water integrating year round precipitation and hydrated volcanic glass shards and fossil plant waxes which are also thought to integrate year round precipitation but are subject to large fractionations in some cases our temperature estimates based on existing proxy data are much cooler than previously estimated due to our use of source water corrections for the glacial ocean new transfer functions calibrated specifically for northern north america d precip 3 1 c 1 t 155 and 18 o precip 0 41 c 1 t 20 2 and novel insights on the apparent net fractionation correction for eastern beringian steppe tundra plant waxes e wax precip 59 10 the snowmelt origin of wedge ice ensures a relatively constrained winter spring seasonality of contributing precipitation as supported by the consistency between water isotope measurements from late holocene wedge ice and modern winter spring precipitation wedge ice dating to the transitional mis 3 2 is isotopically depleted relative to modern spring winter precipitation by an amount that indicates a temperature depression of 14 5 c below modern the soil water origin of pore ice and other proxies integrating year round precipitation from soil water allows for a more variable precipitation seasonality the isotopic composition of modern pore ice is consistent with mean annual precipitation however the isotopic composition of pore ice during mis 3 2 converges on wedge ice values signalling an increase in the ratio of cold to warm season precipitation integrated by pore ice during glacial times possibly due to drier summers as supported by the fossil record and climate model simulations in the study region water isotope proxies integrating year round precipitation may overestimate annual temperature differences between today and recent cold stages due to transient precipitation seasonality as detected here and thus are best interpreted as upper bound estimates based on these proxies we estimate that annual temperatures during mis 4 3 2 and 2 were depressed below the modern climate to a maximum of 18 c 16 c and 21 c 4 5 c respectively our study highlights the value of multiple water isotope proxies towards understanding changes in precipitation seasonality and developing robust reconstructions of past climate and may be particularly important for studies of the major climate transformations over glacial interglacial timescales

submarine active normal faults completely crossing the southwest ryukyu arc abstract several identified active faults located in the southwest ryukyu area may be an origin of m5 class earthquakes taking place frequently every year sometimes of m7 class earthquakes which cause a severe geohazard in this area the east ishigaki fault one of the officially identified active faults was studied precisely by multibeam echo sounding and the in situ rov observation the survey expedition figured the topographic feature of the fault clearly and more precisely than that mapped by the hydrographic department of japan the survey also identified the locations of northwestern and southeastern termini of the fault which revealed the total length to be 44 km corresponding to a m7 4 earthquake the new topographic map shows that the fault is composed of four or five segments with maximum vertical offset of 80 m in the southernmost segment not all of the segment can slip at once a reconnaissance survey of three of these segments by the rov hyper dolphin dives during the same expedition revealed that the headwall scarp is an outcrop made up of the ryukyu limestone of the middle pleistocene and that the lower scarp and the trough are covered with mostly talus apparently from the headwall at least two of these segments look fresher in fault activity rather than the others though all the observations show very recent activities along the fault based on these results the east ishigaki fault at least some of the segments might cause the 1771 tsunami and also future tsunamis with the similar magnitude

geomorphological and cryostratigraphical analyses of the zackenberg valley ne greenland and significance of holocene alluvial fans abstract in high arctic northern greenland future responses to climatic changes are poorly understood on a landscape scale here we present a study of the geomorphology and cryostratigraphy in the zackenberg valley in ne greenland 74 n containing a geomorphological map and a simplified geocryological map combined with analyses of 13 permafrost cores and two exposures cores from a solifluction sheet alluvial fans and an emerged delta were studied with regards to cryostructures ice and total carbon contents grain size distribution and pore water electrical conductivity and the samples were ams 14c dated the near surface permafrost on slopes and alluvial fans is ice rich as opposed to the ice poor epigenetic permafrost in the emerged delta ground ice and carbon distribution are closely linked to sediment transport processes which largely depend on lithology and topography holocene alluvial fans on the lowermost hillslopes covering 12 of the study area represent paleoenvironmental archives during the contrasting climates of the holocene the alluvial fans continued to aggrade through the warmer early holocene optimum the colder late holocene and the following climate warming and by 0 45 mm a 1 on average this is caused by three factors sedimentation ground ice aggradation and vegetation growth and is reflected by ams 14c dating and continuously alternating cryostructures highly variable sedimentation rates in space and time at the alluvial fans have been detected this is also reflected by alternating lenticular and microlenticular cryostructures indicating syngenetic permafrost aggradation during sedimentation with suspended and organic matrix cryostructures indicating quasi syngenetic permafrost aggradation in response to vegetation growth in periods with reduced or no sedimentation over time this causes organic matter to become buried indicating that alluvial fans represent effective carbon sinks that have previously been overlooked

cryostratigraphy of the klondike muck deposits west central yukon territory four late quaternary cryostratigraphic units are recognized in the unconsolidated valley bottom deposits of the klondike area yukon territory three of the units in ice rich loessal sediments of pre wisconsinan or wisconsinan age collectively compose the king solomon formation they are overlain by a holocene organic unit the units are distinguished by their cryostratigraphic characteristics and oxygen isotope ratios of included ground ice the basal unit is the last chance creek member a pre late wisconsinan deposit containing preserved ice wedges 18o 28 to 26 d 225 to 209 the overlying quartz creek member a late wisconsinan unit is dominated by organic rich loess massive ice is noticeably absent although the sediments are ice rich the isotopic composition of ice in this unit is characteristic of full glacial conditions 18o 32 to 29 d 234 to 257 an abrupt change to warmer and wetter conditions at the end of glaciation prior to the holocene is recorded by the i

late pleistocene precipitation δ18o interpolated across the global landmass global water cycles ecosystem assemblages and weathering rates were impacted by the 4 c of global warming that took place over the course of the last glacial termination fossil groundwaters can be useful indicators of late pleistocene precipitation isotope compositions which in turn can help to test hypotheses about the drivers and impacts of glacial interglacial climate changes here a global catalog of 126 fossil groundwater records is used to interpolate late pleistocene precipitation 18o across the global landmass the interpolated data show that extratropical late pleistocene terrestrial precipitation was near uniformly depleted in 18o relative to the late holocene by contrast tropical 18o responses to deglacial warming diverged late pleistocene 18o was higher than modern across india and south china but lower than modern throughout much of northern and southern africa groundwaters that recharged beneath large northern hemisphere ice sheets have different holocene pleistocene 18o relationships than paleowaters that recharged subaerially potentially aiding reconstructions of englacial transport in paleo ice sheets global terrestrial late pleistocene precipitation 18o maps may help to determine 3 d groundwater age distributions constrain pleistocene mammal movements and better understand glacial climate dynamics

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

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

cryostratigraphy of late pleistocene syngenetic permafrost yedoma in northern alaska itkillik river exposure abstract extremely ice rich syngenetic permafrost or yedoma developed extensively under the cold climate of the pleistocene in unglaciated regions of eurasia and north america in alaska yedoma occurs in the arctic foothills the northern part of the seward peninsula and in interior alaska a remarkable 33 m high exposure along the lower itkillik river in northern alaska opened an opportunity to study the unmodified yedoma including stratigraphy particle size distribution soil carbon contents morphology and quantity of segregated wedge and thermokarst cave ice the exposed permafrost sequence comprised seven cryostratigraphic units which formed over a period from 48 000 to 5 000 14c yr bp including 1 active layer 2 intermediate layer of the upper permafrost 3 4 two yedoma silt units with different thicknesses of syngenetic ice wedges 5 buried peat layer 6 buried intermediate layer beneath the peat and 7 silt layer with short ice wedges this exposure is comparable to the well known mus khaya and duvanny yar yedoma exposures in russia based on our field observations literature sources and interpretation of satellite images and aerial photography we have developed a preliminary map of yedoma distribution in alaska

holocene ice wedge polygon development in northern yukon permafrost peatlands canada ice wedge polygon iwp peatlands in the arctic and subarctic are extremely vulnerable to climatic and environmental change we present the results of a multidisciplinary paleoenvironmental study on iwps in the northern yukon canada high resolution laboratory analyses were carried out on a permafrost core and the overlying seasonally thawed active layer from an iwp located in a drained lake basin on herschel island in relation to 14 accelerator mass spectrometry ams radiocarbon dates spanning the last 5000 years we report sedimentary data including grain size distribution and biogeochemical parameters organic carbon nitrogen c n ratio d13c stable water isotopes d18o dd as well as fossil pollen plant macrofossil and diatom assemblages three sediment units sus correspond to the main stages of deposition 1 in a thermokarst lake su1 4950 to 3950 cal yrs bp 2 during transition from lacustrine to palustrine conditions after lake drainage su2 3950 to 3120 cal yrs bp and 3 in palustrine conditions of the iwp field that developed after drainage su3 3120 cal yrs bp to 2012 ce the lacustrine phase pre 3950 cal yrs bp is characterized by planktonic benthic and pioneer diatom species indicating circumneutral waters and very few plant macrofossils the pollen record has captured a regional signal of relatively stable vegetation composition and climate for the lacustrine stage of the record until 3950 cal yrs bp palustrine conditions with benthic and acidophilic diatom species characterize the peaty shallow water environments of the low centered iwp the transition from lacustrine to palustrine conditions was accompanied by acidification and rapid revegetation of the lake bottom within about 100 years since the palustrine phase we consider the pollen record as a local vegetation proxy dominated by the plant communities growing in the iwp ice wedge cracking in water saturated sediments started immediately after lake drainage at about 3950 cal yrs bp and led to the formation of an iwp mire permafrost aggradation through downward closed system freezing of the lake talik is indicated by the stable water isotope record the originally submerged iwp center underwent gradual drying during the past 2000 years this study highlights the sensitivity of permafrost landscapes to climate and environmental change throughout the holocene

the isotopic composition of the laurentide ice sheet and fossil groundwater stable isotopes have been used to study large scale changes in hydrology during the pleistocene epoch many of these efforts have required an estimate of the 18o value of runoff generated by melting ice sheets there is no consensus on representative values here we examine 18o values from fossil groundwater samples and isotope enabled general circulation models gcms to better understand the isotopic composition of the laurentide ice sheet lis groundwater 18o values ranged from 12 5 to 25 3 and tended to increase southward the 18o precipitation values predicted by gcms follow a similar trend but increase more steeply southward the difference in groundwater and gcm output can be explained by invoking movement of glacial ice and meltwater along with mixing within groundwater systems most groundwater 18o values are higher than an average lis 18o value of 25 4 2 5 calculated based on estimated ice sheet volumes and sea level data

massive ice of the tuktoyaktuk area western arctic coast canada the extensive coastal exposure of massive underground ice at peninsula point southwest of tuktoyaktuk northwest territories is believed to be intrasedimental ice the ice grew beneath a frozen d

cryostratigraphy paleogeography and climate change during the early holocene warm interval western arctic coast canada botanical and cryostratigraphic records from northwest canada indicate that the climate of the early holocene was considerably warmer than today tree line was over 100 km farther north and a thaw unconformity dating from 8000 14c years bp formed at the base of an active layer 2 5 times thicker than at present numerous thermokarst lake basins formed in the preceding millennia both the botanical and cryostratigraphic indices described are products of summer conditions previous reconstructions of early holocene climate have not assessed the significance of paleocoastal location on the seasonality and extent of apparent climate warming at present there is a steep gradient in growing season conditions between cooler sites on the beaufort sea coast and warmer inland locations winter conditions are more uniform because both sea and land are snow covered coastal retreat in the region has been rapid due to sea level rising over a gently sloping shelf containing readily erodible sediments the coastlin

stratigraphic isotopic and mineralogical evidence for an early holocene thaw unconformity at mayo yukon territory ice rich glaciolacustrine sediments near mayo yukon territory reveal a thaw unconformity in the form of truncated ice wedges and abrupt changes in cryotexture the unconformity has been radiocarbon dated at 8870 200 years bp which is within the holocene period of optimal climatic conditions in northern yukon and the mackenzie delta area reported by other workers analysis of the mineralogy of the sediments indicates that the material above the unconformity is enriched in minerals that are the products of a more intense weathering environment than those deeper in the profile oxygen isotope ratios of ground ice in the sediments suggest the presence of two genetically distinct ice units above and below the unconformity an average rate of upward permafrost growth in this area of 0 1 0 2 mm year 1 is calculated for the period since the climatic optimum

age of sheep creek tephra pleistocene in central alaska from thermoluminescence dating of bracketing loess the age of the sheep creek tephra sct a widespread marker ash bed in eastern alaska and western yukon territory has been ambiguous and controversial we have obtained three reliable thermoluminescence age estimates from bracketing loess near fairbanks that imply a deposition age of about 190 000 20 000 yr for sct three of six loess samples near and closely bracketing the sct beds near fairbanks yielded younger age estimates 117 000 and 135 000 yr most likely based on field aspects because of reworking and contamination by translocated grains the new reliable age assignment of 190 000 yr confirms independent stratigraphic evidence of a pre last interglaciation age and stratigraphic evidence from one site upper eva creek that sct is older than the more widespread 140 000 yr old old crow tephra the sct age also has implications for regional correlations of glacial and nonglacial deposits in particular it supports the stratigraphic and geomorphic interpretation that the delta glaciation in the east central alaska range and the reid glaciation in western yukon territory are older than the last interglaciation isotope substage 5e

ice wedges on hillslopes and landform evolution in the late quaternary western arctic coast canada in rolling to hilly areas of the western arctic coast of canada anti syngenetic wedges which by definition are those that grow on denudational slopes are the most abundant type of ice wedge through prolonged slope denudation hilltop epigenetic wedges can evolve into hillslope anti syngenetic wedges and some bottom slope anti syngenetic wedges by means of deposition from upslope can evolve into bottom slope syngenetic wedges the axis of a hillslope wedge is oriented perpendicular to the slope so the wedge foliation varies according to the trend of the wedge with respect to the slope because the tops of hillslope wedges are truncated by slope recession the mean chronological age of anti syngenetic wedge ice decreases with time so the growth record for an old wedge is incomplete summer and winter measurements show that a thermally induced net movement of the active layer of hillslope polygons tends to transport material from their centres towards their troughs independent of the trends of the t

patterns and rates of riverbank erosion involving ice rich permafrost yedoma in northern alaska abstract yedoma a suite of syngenetically frozen silty ice and organic rich deposits with large ice wedges that accumulated during the late pleistocene is vulnerable to thermal degradation and erosion because of the extremely high ice contents this degradation can result in significant surface subsidence and retreat of coastal bluffs and riverbanks with large consequences to landscape evolution infrastructure damage and water quality we used remote sensing and field observations to assess patterns and rates of riverbank erosion at a 35 m high active yedoma bluff along the itkillik river in northern alaska the total volumetric ground ice content including wedge segregated and pore ice was estimated to be 86 the process of riverbank erosion and stabilization include three main stages typical of the areas with ice rich permafrost 1 thermal erosion combined with thermal denudation 2 thermal denudation and 3 slope stabilization active riverbank erosion at the main study site started in july 1995 when the itkillik river changed its channel the total retreat of the riverbank during 1995 2010 within different segments of the bluff varied from 180 to 280 m the average retreat rate for the most actively eroded part of the riverbank was almost 19 m y from august 2007 to august 2011 the total retreat varied from 10 to almost 100 m the average retreat rate for the whole 680 m long bluff was 11 m y for the most actively eroded central part of the bluff 150 m long it was 20 m y ranging from 16 to 24 m y more than 180 000 m3 of ground ice and organic rich frozen soil or almost 70 000 metric tons t of soil solids including 880 t of organic carbon were transported to the river from the retreating bank annually this study reports the highest long term rates of riverbank erosion ever observed in permafrost regions of eurasia and north america

intensity of the earth s magnetic field since precambrian from thellier type palaeointensity data and inferences on the thermal history of the core summary we present a compilation of palaeointensity data obtained by the thellier method from magmatic rocks up to 3 5 gyr old no apparent very long term variation occurs from present to early precambrian the overall data are compatible with a gravitationally powered dynamo model in which the inner core is some 4 0 gyr old however palaeointensity data are still too incomplete to dismiss the possibility of a more complex field history with a geodynamo first thermally driven then gravitationally powered despite the limited number of data currently available large differences in the dipole field moment are clearly documented with a time scale of the order of 50 100myr the changes in intensity can be due to repetitive instabilities of the thermal boundary layer at the base of the mantle

synchronized terrestrial atmospheric deglacial records around the north atlantic on the basis of synchronization of three carbon 14 c 14 dated lacustrine sequences from sweden with tree ring and ice core records the absolute age of the younger dryas preboreal climatic shift was determined to be 11 450 to 11 390 80 years before the present a 150 year long cooling in the early preboreal associated with rising delta 14 c values is evident in all records and indicates an ocean ventilation change this cooling is similar to earlier deglacial coolings and box model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the north atlantic heat conveyor although the younger dryas may have begun as an anomalous meltwater event

air temperature snow cover creep of frozen ground and the time of ice wedge cracking western arctic coast the time of ice wedge cracking is examined for several sites with young and old ice wedges along the western arctic coast the correlation between sharp air temperature drops and ice wedge cracking is highest where the snow cover is thin and least where the snow cover is thick the favoured duration and rate of a temperature drop that results in cracking is about 4 days at a rate of about 1 8 c d such temperature drops have a minimal effect in cooling the top of permafrost wherever there is an appreciable snow cover since short duration temperature drops often result in ice wedge cracking the thermal stresses that trigger cracking probably originate more within the frozen active layer than at greater depth in permafrost although most ice wedges tend to crack during periods of decreasing air temperatures about one third of those monitored have cracked during periods of increasing air temperatures long term measurements show that the active layer and top of permafrost move differentially all year in

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

paleoecology of beringian packrat middens from central yukon territory canada rodent middens from ice rich loess deposits are important new paleoenvironmental archives for eastern beringia plant macrofossils recovered from three middens associated with dawson tephra ca 24 000 14 c yr b p at two sites in yukon territory include diverse graminoids forbs and mosses these data suggest substantial local scale floristic and habitat diversity in valley settings including steppetundra on well drained soils moist streamside meadows and hydric habitats fossil arctic ground squirrel burrows and nesting sites indicate that permafrost active layers were thicker during pleistocene glacial periods than at present on north facing slopes d 2004 university of washington all rights reserved

on the nature and origin of muck deposits in the klondike area yukon territory organic rich muck deposits which blanket auriferous gravels in the klondike area yukon territory comprise two principal stratigraphic units i a silty late pleistocene deposit and ii holocene organics lying unconformably on the silt the deposits are found predominantly in valley bottoms and if undisturbed are normally perennially frozen field and laboratory investigations of particle size mineralogy and morphology as well as organic matter and sedimentary structures indicate that the silt is both primary massive and redeposited bedded loess by weight 87 medium and coarse silt and fine sand radiocarbon dates indicate that the loess was deposited during late wisconsinan mcconnell glaciation beginning after 27 000 14c years bp the loess was likely derived from the floodplain of the yukon river during periods of low flow turf in growth position and organic matter in the silt similar to that of loessal grasslands near kluane lake suggest a grassland environment for the area during

age and significance of the late pleistocene dawson tephra in eastern beringia abstract dawson tephra recently recognized in the klondike area of yukon territory records one of the largest quaternary volcanic eruptions in beringia its composition is similar to that of old crow tephra indicating a source in the aleutian arc alaska peninsula region of southwestern alaska its primary thickness in central yukon is nearly twice that of old crow tephra which has an estimated eruption volume of 50 km 3 the distribution of dawson tephra is still poorly known but based on its source area and occurrence in central yukon it should be widespread across southern alaska yukon and the gulf of alaska new radiocarbon ages indicate the eruption occurred at about 24 000 14 c yr bp ca 27 000 cal yr bp the dawson tephra is a valuable marker bed for correlating late pleistocene records across large areas of eastern beringia and adjacent marine records

seasonality of the late pleistocene dawson tephra and exceptional preservation of a buried riparian surface in central yukon territory canada abstract the late pleistocene dawson tephra was deposited by one of the largest quaternary eruptions in northwestern north america its distribution is known sparsely from sites near the source area in southwestern alaska and central yukon territory where more than 20 occurrences are documented in the klondike region dawson tephra erupted about 25 300 14 c yr bp near the onset of the last glaciation and provides a stratigraphic marker across eastern beringia we report radiocarbon ages paleobotanical data and cryostratigraphic observations from a new dawson tephra locale at goldbottom creek in the klondike region of yukon territory which collectively indicate that the eruption occurred in the late winter or early spring multiple fining upward tephra rich ice beds are interpreted as remnants of surface icings which presently are common in the region during spring a buried in situ riparian meadow preserved below the icing and tephra consists of abundant tufted hair grass deschampsia caespitosa with interspersed horsetails equisetum cf palustre and mosses detrital plant remains and preserved in situ grass inflorescences entombed in the icing had expelled their fruits consistent with a late season surface when the icing was active the extraordinary thickness of dawson tephra in central yukon likely reflects reworking of a winter deposited tephra by snow melt in the spring following the eruption indicating that the primary thickness may be overestimated at valley bottom sites winter deposition of the tephra may have in part minimized the terrestrial ecological impacts of the eruption on zonal steppe tundra vegetation through the retransportation of tephra from hillslopes to the riparian areas where the tephra became incorporated into local fluvial systems

the frequency of ice wedge cracking 1967 1987 at garry island western arctic coast canada the frequency of ice wedge cracking has been studied at garry island northwest territories for the 1967 1987 period sites have included low centre polygons intermediate centre polygons and polygons that do not fit any classification system analyses of crack frequency have included trough characteristics polygon characteristics and ice wedge types the results show that crack frequencies are highly variable within one site and also between two adjacent sites the correlation between crack frequency and a low air temperature is poor crack frequencies for a site with 59 wedges ranged from 8 to 42 between 1967 and 1979 and for a nearby site with 32 wedges from 22 to 75 between 1967 and 1987 in view of the wide range in crack frequencies at a given site the use of mean ice wedge growth rates for estimating ages of ice wedges and their casts in environmental reconstruction may be hazardous the data show that the common twofold classification into active and inactive wedges is difficult to apply be

dune stabilization in central and southern yukon in relation to early holocene environmental change northwestern north america abstract eolian deposits of central and southern yukon northwestern canada consist of loess mantles small areas of active dunes and larger stabilized dune fields dune fields in valley settings within the region are situated both within and beyond the limit of the last glaciation infrared stimulation luminescence irsl dating in central and southern yukon reveals that these dune fields stabilized as late as 9 8 5 ka well after the retreat of cordilleran glaciers these findings are comparable to other valley setting dune fields and loess from central alaska which record activity during the period from the lateglacial to the holocene thermal maximum htm and reduced or altered activity after 9 8 ka post glacial dune activity was most likely related to warm dry conditions during the htm under predominantly shrub tundra vegetation early holocene stabilization of these dunes probably occurred in response to cooler moister conditions and replacement of predominantly tundra by boreal forest cover dominated by spruce stabilization of dune fields in southern yukon and alaska most likely represented an extension of the time transgressive stabilization of dune fields that occurred across northwestern north america with the post glacial expansion of the boreal forest

cryostructures in permafrost tuktoyaktuk coastlands western arctic canada the shape and distribution of ice and sediment within frozen ground constitute its cryostructure observations on perennially frozen sediments in the tuktoyaktuk coastlands enable six cryostructures to be identified 1 structureless 2 lenticular 3 layered 4 reticulate 5 crustal and 6 suspended these cryostructures can be transitional or composite five cryofacies types can also be identified according to volumetric ice content and grain size they can be grouped into cryofacies assemblages the utility of the descriptive classification of ice rich sediments is illustrated from a palaeothaw layer at crumbling point

large arctic temperature change at the wisconsin holocene glacial transition analysis of borehole temperature and greenland ice sheet project ii ice core isotopic composition reveals that the warming from average glacial conditions to the holocene in central greenland was large approximately 15 c this is at least three times the coincident temperature change in the tropics and mid latitudes the coldest periods of the last glacial were probably 21 c colder than at present over the greenland ice sheet

calibration of radiocarbon ages and the interpretation of paleoenvironmental records abstract calibration of the radiocarbon timescale of paleoecological records is essential if they are to be explained correctly in terms of their governing ecological or climatological controls the differences between calendar ages and radiocarbon ages that arise from variations in 14c production through time can distort the chronologies of individual records and the interpretations based on them misleading impressions of synchrony or diachrony of events among multiple records can result and estimates of the apparent duration of episodes and rates of sedimentation and local population changes can be biased displays of the temporal patterns of migration or extinction may also be affected spurious correlations may arise between records with radiocarbon controlled chronologies and time series of potential controls that are expressed on a calendar time scale support for particular explanations of features in a paleoecological record may vary depending on whether radiocarbon ages are calibrated or not this situation is illustrated using the eastern beringian populus subzone as an example when the radiocarbon ages that control the timing of the populus subzone are calibrated the contemporaneous decrease in ice volume and increase in summer insolation are implicated as the ultimate controls of the occurrence of the subzone

early wisconsinan mis 4 arctic ground squirrel middens and a squirrel eye view of the mammoth steppe abstract fossil arctic ground squirrel spermophilus parryii middens were recovered from ice rich loess sediments in association with sheep creek klondike and dominion creek tephras ca 80 ka exposed in west central yukon these middens provide plant and insect macrofossil evidence for a steppe tundra ecosystem during the early wisconsinan mis 4 glacial interval midden plant and insect macrofossil data are compared with those previously published for late wisconsinan middens dating to 25 2914c ka bp mis 3 2 from the region although multivariate statistical comparisons suggest differences between the relative abundances of plant macrofossils the co occurrence of steppe tundra plants and insects e g elymus trachycaulus kobresia myosuroides artemisia frigida phlox hoodii connatichela artemisiae provides evidence for successive reestablishment of the zonal steppe tundra habitats during cold stages of the late pleistocene arctic ground squirrels were well adapted to the cold arid climates steppe tundra vegetation and well drained loessal soils that characterize cold stages of late pleistocene beringia these glacial conditions enabled arctic ground squirrel populations to expand their range to the interior regions of alaska and yukon including the klondike where they are absent today arctic ground squirrels have endured numerous quaternary climate oscillations by retracting populations to disjunct interglacial refugia during warm interglacial periods e g south facing steppe slopes well drained arctic and alpine tundra areas and expanding their distribution across the mammoth steppe biome during cold arid glacial intervals

ground ice investigations klondike district yukon territory massive bodies of ground ice 2 0 4 0 m thick are regularly exposed in small placer mining operations in the klondike district yukon at mayes claim hunker creek the ice is underlain by 2 0 3 0 m of creek gravels and overlain by 10 0 15 0 m of organic rich and ice rich muck deposits the crystallographic and petrographic characteristics of the ice and its stratigraphic occurrence suggest that the ice body either had a segregation origin or was a residual snowbank subsequently buried by muck deposits and recrystallized

cryostratigraphic record of permafrost degradation and recovery following historic 1898 1992 surface disturbances in the klondike region central yukon territory we present a detailed cryostratigraphic reconstruction of the degradation and recovery of near surface permafrost in the southern klondike goldfields central yukon territory two ice rich layers a

late quaternary glaciation in the northern ogilvie mountains revised correlations and implications for the stratigraphic record new geomorphic paleolimnological and radiocarbon data suggest that a terminal moraine complex in the northern ogilvie mountains yukon territory canada may represent the mcconnell glaciation late wisconsinan rather than the reid glaciation marine isotope stage 8 illinoian as previously thought relict fluvial channels on the surface of the moraine and analysis of a suite of lake sediment cores from chapman lake a closed basin kettle on the surface of the moraine suggest that flow from the blackstone river passed over the moraine and through the lake until ca 12 500 bp at which time the blackstone river was captured by the east blackstone river diverting flow from the lake subsequent incision by the blackstone river has left its base level more than 10 m below the level of chapman lake perched former outlets from chapman lake indicate that this incision must postdate stream capture because the chapman lake moraine is a topographic barrier across the blackstone river valley incision must