ground ice and slope sediments archiving late quaternary paleoenvironment and paleoclimate signals at the margins of el gygytgyn impact crater ne siberia an accumulation terrace close to the el gygytgyn impact crater in northeastern siberia contains stratigraphic and periglacial evidence of the paleoenvironmental and paleoclimatic history and permafrost dynamics during late quaternary time a succession of paleo active layer deposits that mirror environmental changes records periods favorable for the establishment and growth of ice wedge polygonal networks and sediment variations these two elements of the periglacial landscape serve as complementary paleoenvironmental archives that can be traced back to 14 000 cal yr bp the slope sediments and the ground ice contained therein have prominent relative maxima and minima in properties grain size total organic content oxygen isotopes they document a regional early holocene thermal maximum at about 9000 cal yr bp followed by a transition to slightly cooler conditions and a subsequent transition to slightly warmer conditions after about 4000 cal yr bp results from sedimentary analysis resemble morphological and geochemical oxygen and hydrogen isotopes results from ice wedge studies in which successive generations of ice wedge polygonal networks record warmer winters in late holocene time moreover peaks of light soluble cation contents and quartz grain surface textures reveal distinct traces of cryogenic weathering we propose a conclusive sedimentation model illustrating terrace formation in a permafrost terrain

a new crocodylian eusuchia from the uppermost cretaceous of alberta canada1 albertosuchus knudsenii gen et sp nov is described on the basis of an incomplete skeleton from the lower part uppermost cretaceous of the scollard formation southern alberta canada it is probably a crocodyloid the only canadian representative of the group and also the sole crocodylian known during the latest cretaceous in canada within the crocodyloidea a knudsenii is one of the most basal forms and shares a sister group relationship with the european genus arenysuchus however it needs to be emphasized that because of its incompleteness phylogenetic relationships proposed here for a knudsenii may change when better preserved specimens are found albertosuchus knudsenii differs from other crocodyloids in having no premaxilla maxillary notch a very short mandibular symphysis with the involvement of the splenial and an extremely deep hypapophysis on the last cervical and anterior dorsal vertebrae the discovery of a knudsenii may expand the geographical range of the crocodyloidea into cana

weathering control over geomorphology of supermature proterozoic delhi quartzites of india quartz and quartzite are thought to be resistant as a mineral and a rock respectively however we have shown that the presence of small amounts of pyrite in the quartzites makes them vulnerable to weathering we observe that weathering of proterozoic quartzite in the semi arid conditions around delhi proceeded from fractures towards the inside and produced weathering rinds the chemical index of alteration cia which is actually a measure of weathering of aluminosilicate minerals increases from the core outwards through the rinds although aluminosilicate minerals occur only as minor phases 2 per cent their weathering indicates a movement of the weathering front from the periphery towards the core we have suggested a coupled mechanism in which the dissolution of pyrites by moving water produced a sulphate bearing acidic solution and ferrous iron which reacted with aluminosilicate minerals and quartz respectively this initially makes the delhi quartzite porous and subsequently friable the total disintegration of grain to grain contacts imparted friability to this quartzite to produce silica sand subsequent physical erosion of loose sand produced during rind development in the outermost zones has given rise to features like tors spheroids gullies cavities and small scale caves on these quartzites thus the terrain has acquired ruggedness in semi arid conditions copyright 2003 john wiley sons ltd

preliminary paleoenvironmental analysis of permafrost deposits at batagaika megaslump yana uplands northeast siberia a megaslump at batagaika in northern yakutia exposes a remarkable stratigraphic sequence of permafrost deposits 50 80 m thick to determine their potential for answering key questions about quaternary environmental and climatic change in northeast siberia we carried out a reconnaissance study of their cryostratigraphy and paleoecology supported by four rangefinder 14c ages the sequence includes two ice complexes separated by a unit of fine sand containing narrow syngenetic ice wedges and multiple palaeosols overall the sequence developed as permafrost grew syngenetically through an eolian sand sheet aggrading on a hillslope wood remains occur in two forest beds each associated with a reddened weathering horizon the lower bed contains high amounts of larix pollen 20 plus small amounts of picea and pinus pumila and is attributed to interglacial conditions pollen from the overlying sequence is dominated by herbaceous taxa 70 80 attributed to an open tundra landscape during interstadial climatic conditions of three hypothetical age schemes considered we tentatively attribute much of the batagaika sequence to marine isotope stage mis 3 the upper and lower forest beds may represent a mid mis 3 optimum and mis 5 respectively although we cannot discount alternative attributions to mis 5 and 7

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

explosive origin of silicic lava textural and δd h2o evidence for pyroclastic degassing during rhyolite effusion a long standing challenge in volcanology is to explain why explosive eruptions of silicic magma give way to lava a widely cited idea is that the explosive to effusive transition manifests a two stage degassing history whereby lava is the product of non explosive open system gas release following initial explosive closed system degassing direct observations of rhyolite eruptions indicate that effusive rhyolites are in fact highly explosive as they erupt simultaneously with violent volcanic blasts and pyroclastic fountains for months from a common vent this explosive and effusive overlap suggests that pyroclastic processes play a key role in rendering silicic magma sufficiently degassed to generate lava here we use precise h isotope and magmatic h2o measurements and textural evidence to demonstrate that effusion results from explosion s lavas are the direct product of brittle deformation that fosters batched degassing into transient pyroclastic channels tuffisites that repetitively and explosively vent from effusing lava our measurements show specifically that d h ratios and h2o contents of a broad suite of explosive and effusive samples from chaiten volcano hydrous bombs plinian pyroclasts tuffisite veins and lava define a single and continuous degassing trend that links wet explosive pyroclasts 1 6 wt h2o d 76 4 to dry obsidian lavas 0 13 wt h2o d 145 7 this geochemical pattern is best fit with batched degassing model that comprises small repeated closed system degassing steps followed by pulses of vapour extraction this degassing mechanism is made possible by the action of tuffisite veins which by tapping already vesicular or brecciated magma allow batches of exsolved gas to rapidly and explosively escape from relatively isolated closed system domains and large tracts of conduit magma by giving them long range connectivity even though tuffisite veins render magma degassed and capable of effusing they are nonetheless the avenues of violent gas and particle transport and thus have the potential to drive explosions when they become blocked or welded shut thus the effusion of silicic lava traditionally thought to be relatively benign process presents a particularly hazardous form of explosive volcanism

influence of changing atmospheric circulation on precipitation δ18o temperature relations in canada during the holocene postglacial precipitation 18o history has been reconstructed for two regions of canada long term shifts in the oxygen isotope composition of annual precipitation 18op in southern ontario appear to have occurred with a consistent isotope temperature relation throughout the past 11 50014c yr the modern isotope temperature relation in central canada near present boreal treeline evidently became established between 5000 and 4000 years ago although the relation during the last glacial maximum and deglaciation may also have been similar to present in the early holocene however unusually high 18opapparently persisted in spite of low temperature locally probably associated with high zonal index a rudimentary sensitivity analysis suggests that a small reduction in distillation of moisture in pacific air masses traversing the western cordillera perhaps accompanied by a higher summer winter precipitation ratio could have been responsible for the observed effect equivalent isotope temperature anomalies apparently occurred elsewhere in western north america in response to changing early holocene atmospheric circulation patterns suggesting that a time slice map of 18opfor north america during this period might provide a useful target for testing and validation of atmospheric general circulation model simulations using isotopic water tracers

geochemistry of the loessic sediments on delhi ridge eastern thar desert rajasthan implications for exogenic processes abstract quartzite ridges in the delhi region include in their local depressions thick piles of unconsolidated unstratified yellowish brown homogenous loamy sediments these delhi ridge sediments drs have textural mineralogical and geochemical characteristics similar to those of loess sediments geochemically drs just as other loess sediments are similar to average exposed upper continental crust of taylor and mclennan taylor s r mclennan s m 1985 the continental crust its composition and evolution blackwell london 311 pp the calculated chemical index of alteration nesbitt h w young g m 1984 prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations geochim cosmochim acta 54 1523 1534 nesbitt h w young g m 1989 formation and diagenesis of weathering profiles j geol 97 129 147 and other chemical parameters suggest a provenance of chemically less weathered rocks during the process of wind transport and deposition not only the dilution effect of silica on the ree abundance was counterbalanced but also the ree pattern was kept similar to the ucc and paas by the appropriate concentration and mixing of the ree bearing phases the immediate source to these sediments is likely to be mechanically ground sediments of glacial origin the last phase of the upliftment of the himalayas accompanied by pleistocene glaciation could have provided a vast glacio fluvial outwash plain the aeolian processes associated with prevailing w to sw winds in the hot arid condition seem to have been selectively transporting fertile silt materials leaving behind infertile desert sands

pollen based continental climate reconstructions at 6 and 21 ka a global synthesis subfossil pollen and plant macrofossil data derived from 14c dated sediment profiles can provide quantitative information on glacial and interglacial climates the data allow climate variables related to growing season warmth winter cold and plant available moisture to be reconstructed continental scale reconstructions have been made for the mid holocene mh around 6 ka and last glacial maximum lgm around 21 ka allowing comparison with palaeoclimate simulations currently being carried out as part of the fifth assessment report ar5 of the intergovernmental panel on climate change the synthesis of the available mh and lgm climate reconstructions and their uncertainties obtained using modern analogue regression and model inversion techniques is presented for four temperature variables and two moisture variables reconstructions of the same variables based on surface pollen assemblages are shown to be accurate and unbiased reconstructed lgm and mh climate anomaly patterns are coherent consistent between variables and robust with respect to the choice of technique they support a conceptual model of the controls of late quaternary climate change whereby the first order effects of orbital variations and greenhouse forcing on the seasonal cycle of temperature are predictably modified by responses of the atmospheric circulation and surface energy balance

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

early cenozoic uplift of the puna plateau central andes based on stable isotope paleoaltimetry of hydrated volcanic glass uplift of the central andes is largely thought to have occurred during the past 10 m y based on paleoaltimetry studies from the altiplano of bolivia however the spatio temporal uplift history may not be uniform across the central andes we present new stable isotopic results from the salar de antofalla salina del fraile and arizaro basin on the puna plateau 24 26 s of northwestern argentina samples of volcanic glass give d paleowater values and modeled paleoelevations that indicate an elevated 4 km puna plateau since ca 36 ma with limited

hydrologic cycling over antarctica during the middle miocene warming global warmth 20 15 million years ago allowed vegetation to grow on formerly ice covered areas of antarctica leaf wax and pollen data show that this growth was supported by increased hydrologic activity over the antarctic coast derived from a local moisture source

a catalogue of late cenozoic tephra beds in the klondike goldfields and adjacent areas yukon territory preece s j westgate j a froese d g pearce n j g perkins w t 2011 a catlogue of late cenozioc tephra beds in the klondike goldfields and adjacent areas yukon canadian journal of earth sciences 48 10 1386 1418

reconstructing the interacting effects of base level climate and tectonic uplift in the lower mino river terrace record a gradient modelling evaluation the origin of the lower mino river terraces in the nw iberian peninsula has been a topic of debate since the 1940s various hypotheses about their main controlling factors have been put forward but general consensus is still lacking field studies of terrace distribution and the weathering of quartzite pebbles in the terrace deposits demonstrated that terrace longitudinal correlation is not parallel to the current river bed in addition the longitudinal profile model fluver2 was used to simulate the profile evolution of the mino river over the past 450 ka a reconstructed longitudinal profile and an offshore climate record were used as inputs several scenarios with variable uplift rates were investigated and evaluated against properties of four selected reaches along the river for a match with the number of terraces their relative altitude timing and sediment thickness an uplift scenario with a net constant vertical uplift rate of 0 08 m ka 1 yielded the best results the best fit scenarios indicate that base level changes from glacioeustatic changes in combination with tectonic uplift are the main driving forces of the observed terrace formation and valley incision contrary to most nw european fluvial systems the timing of upstream controlled sediment supply has a less dominant effect on terrace formation this can be explained by the close proximity to the narrow passive atlantic margin

a global review of solutional weathering forms on quartz sandstones abstract solutional landforms in limestone have been described for over a hundred years but landforms of similar morphology on highly siliceous sandstones and quartzites have also been identified in a wide variety of environments and generally termed pseudokarst these include large bedrock pinnacles and towers caves corridors grikes solution basins and runnels and even silica speleothems quartzites and quartz sandstones have been held to be amongst the most chemically resistant of rocks but the similarity both in morphology and genetic process of many landforms developed from them to features of known solutional origin on limestone has prompted some authors to refer to these quartzose landforms as true karst the most detailed studies of quartzose karst landforms have been in present day tropical regions or areas believed to have been tropical in the geologically recent past this concentration of research in hot wet areas allied with the long held assertion of the insolubility of silica especially quartz has led to a belief that tropical climatic conditions are necessary for karstic solution of these rocks however the existence of quartzose karst landforms in temperate and even sub polar latitudes especially where there is no evidence of prior tropical conditions suggests that the requirement of tropical weathering is no longer tenable the reports of these quartzose solutional landforms are widely scattered through the geomorphological and geological literature but a comprehensive world wide review of the range of solutional landforms on quartzose rocks has not previously been published because of the increasing awareness in this karst type such a summary is sorely overdue

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

comparison of soil derived tetraether membrane lipid distributions and plant wax δd compositions for reconstruction of canadian arctic temperatures abstract polar amplification of climate warming has received much attention as these rapidly rising temperatures have the potential to alter ecosystem function and biogeochemical cycles in particular carbon preserved in arctic tundra soil and permafrost may be especially vulnerable resulting in carbon cycle perturbations providing an additional positive feedback to climate change reliable methods for reconstructing past temperature changes in polar regions have been established from ice cores and marine sediments however techniques for the continental terrestrial environments are lacking but are imperative to examine polar amplification of climate warming here we compare two molecular methods for reconstructing continental annual mean air temperature mat for the canadian arctic based on the distribution of soil bacterial derived glycerol dialkyl glycerol tetraether gdgt membrane lipids mbt cbt proxy and the hydrogen isotopic composition d of plant wax derived n alkanes these two proxies were applied to both modern soil and paleosols collected from the yukon territory canada to evaluate both the accuracy of the reconstructed absolute temperatures as well as the relative change in temperature between the last glacial and the holocene branched gdgt based estimates using the recently revised mbt cbt calibration are overall higher by ca 6 c compared to the original calibration mat estimates for modern soils based on the original mbt cbt calibration are comparable with those based on the d of extracted c29 n alkanes and instrumental data however produced a 6 c higher temperature signal for the glacial paleosols therefore branched gdgt based temperature reconstructions for glacial soils in the high arctic may represent the higher temperatures at the time of soil formation when bacterial activity was optimal whereas d of c29 n alkane plant lipids appear to integrate an average annual signal when used in tandem these geochemical proxies may provide a more comprehensive method for reconstructing arctic paleoclimate

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

middle cenozoic uplift and concomitant drying in the central rocky mountains and adjacent great plains when and how the central rocky mountains rockies of western north america gained modern topography remain controversial questions we reconstruct the middle and late cenozoic topography along a transect that extends from the great plains of western nebraska across the central rockies in wyoming based on reconstructed surface water d values from volcanic glass d values our data show gradual increases of surface water d values in both the central rockies and adjacent great plains during middle and late cenozoic time and the establishment of a similar to present surface water d gradient between the central rockies and western great plains before earliest oligocene time these observations suggest that the region underwent differential uplift to form relief similar to that of today before earliest oligocene time this uplift has caused regional drying and the gradual increase of surface water d values over the past 35 m y when placed in the context of other paleoaltimetry studies our work suggests that along our transect the central rockies and adjacent great plains underwent uplift during the late eocene and have not undergone any large magnitude 500 m uplift since that time

an abrupt decrease in southern hemisphere terrestrial temperature during the eocene oligocene transition abstract earth s climate transitioned from the greenhouse conditions of the eocene to the icehouse of the oligocene 34 million years ago global cooling was triggered by a decrease in atmospheric pco2 and is associated with the first appearance of large permanent ice sheets on antarctica the eocene oligocene transition eot is marked by a large two step increase in the 18 o of benthic foraminifera reflecting a combination of cooler global temperatures and continental ice growth we measured the hydrogen isotope composition of hydrated volcanic glasses deposited in patagonia during the eot to reconstruct stable isotope hydrology and associated changes in temperature during this critical climate transition these data show changes in stable hydrogen isotope ratios that are consistent with patagonian terrestrial mean annual temperature decreasing by 5 c during the eot before returning to 2 c below pre eot values by the early oligocene this is approximately synchronous with northern hemisphere cooling during the eot and indicates close coupling of temperature and atmospheric pco2

arctic ground squirrels of the mammoth steppe paleoecology of late pleistocene middens 24000 29450 14c yr bp yukon territory canada abstract this paper presents paleoecological analyses of 48 fossil arctic ground squirrel spermophilus parryii middens nests and caches recovered from ice rich loess sediments in the klondike region of west central yukon territory ams radiocarbon dates and stratigraphic association of middens with dawson tephra 25 300 14 c yr bp indicate these paleoecological data reflect the onset of glacial conditions of early marine isotope stage mis 2 and terminal mis 3 24 000 29 450 14 c yr bp plant macrofossils include at least 60 plant taxa including diverse graminoids poa elymus trachycaulus kobresia myosuroides steppe forbs penstemon gormanii anemone patens var multifida plantago cf canescens tundra forbs draba spp bistorta vivipara dwarf shrubs salix cf arctica s cf polaris sage artemisia frigida and rare trees picea mariana many of these taxa identified in the middens represent the first recorded fossils for these plants in eastern beringia and add to our knowledge of the floristic composition of pleistocene vegetation and biogeography in this region fossil beetles include typical members of the eastern beringian steppe tundra fauna lepidophorus lineaticollis and connatichela artemisiae and others suggesting predominantly dry open habitats cache forage selection is suggested by some plant taxa which were particularly frequent and abundant in the middens bistorta vivipara kobresia myosuroides ranunculus spp potentilla erysimum cf cheiranthoides poa carex and draba factors such as proximity of vegetation to burrows and abundance of fruits and seeds per plant were probably important in cache selection glacial conditions enabled arctic ground squirrels to form widespread and dense populations in regions such as the klondike in which they are rare or absent at present this fossil midden record supports previous hypotheses that suggest arctic ground squirrels evolved in and are well adapted to the open steppe tundra vegetation loessal soils and glacial climates of the mammoth steppe biome

the grip deuterium excess record abstract ice cores from greenland and antarctica are ideal archives for retrieving long time series of deuterium excess d d 8 18 o a parameter influenced by conditions prevailing in the oceanic regions which provide moisture for polar snow the central greenland grip deuterium excess record has recently been interpreted in terms of oceanic source temperatures both for the holocene and for the last glacial period this approach being less straightforward for the latter period because of changes in the precipitation seasonality between glacial and interglacial periods this article examines why a conventional or sea surface temperature interpretation of the grip excess record seems inconsistent with inferred site and source temperature changes in addition the grip excess record is extended back into the penultimate glacial period and we assess its geographic significance through a comparison with existing dye 3 and north grip data we examine why low d 18o slopes observed during glacial times are associated with low deuterium excess values similarities between the greenland grip and antarctic vostok excess records are discussed in terms of potential links with insolation and insolation gradient changes finally the isotope records in specific do events are examined in light of intruiging differences between the isotope ratios d or 18o and the excess records that may result from a feedback mechanism linked with freshwater oceanic input

vegetation buried under dawson tephra 25 300 14c years bp and locally diverse late pleistocene paleoenvironments of goldbottom creek yukon canada paleoecological research at goldbottom creek in the klondike region of yukon territory nw canada documents an in situ riparian grassy meadow that was buried during the winter or early spring by dawson tephra near the onset of marine isotope stage mis 2 ca 25 300 14 c years bp analyses of vascular plant macrofossils bryophytes pollen insects and paleosols from the riparian meadow contrast with evidence for well drained upland steppe tundra habitats obtained from fossil arctic ground squirrel middens within the same valley the mesic valley bottom vegetation consisted of grasses deschampsia caespitosa alopecurus sedges carex horsetail equisetum cf palustre diverse bryophytes and few forbs upland habitats with dry loessal soils along the valley slopes contained graminoids elymus festuca kobresia myosuroides sage artemisia frigida and diverse steppe and tundra forbs phlox hoodii plantago cf canescens anemone patens var multifida bistorta vivipara draba these paleoecological data highlight the effect of topographic position and moisture on substrates and their control on local scale habitat variability this study represents the first recorded in situ riparian surface from the unglaciated pleistocene refugium of beringia and provides well documented evidence for local habitat heterogeneity and ecosystem structure within the mammoth steppe biome other radiocarbon dated paleoecological data from our study sites indicate that full glacial steppe tundra habitats in west central yukon territory were established during the later stages of the mis 3 interstadial by 29 000 14 c years bp the diverse data obtained through integration of multiple paleoecological methods

permafrost evidence for severe winter cooling during the younger dryas in northern alaska 1 the younger dryas cold event a rapid reversion to glacial climate conditions at the pleistocene holocene transition has generally been attributed to the release of meltwater from the laurentide ice sheet to the north atlantic or arctic oceans the reaction of the north pacific region to this shutdown of the thermohaline circulation in the north atlantic during younger dryas is little understood in this paper we present the first radiocarbon dated centennial scale stable water isotope record from permafrost in northern alaska this late glacial winter climate reconstruction from barrow ice wedges demonstrates the existence of a younger dryas cold event formerly believed to be reduced or absent in this area our stable isotope data display a gradual change of the atmospheric moisture source conditions during the younger dryas likely associated with the successive opening of the bering strait

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

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

environmental controls on the 2h 1h values of terrestrial leaf waxes in the eastern canadian arctic the hydrogen isotope composition of plant waxes preserved in lacustrine sediments is a potentially valuable tool for reconstructing paleoenvironmental changes in the arctic however in contrast to

northern hemisphere controls on tropical southeast african climate during the past 60 000 years the processes that control climate in the tropics are poorly understood we applied compound specific hydrogen isotopes d and the tex86 tetraether index of 86 carbon atoms temperature proxy to sediment cores from lake tanganyika to independently reconstruct precipitation and temperature variations during the past 60 000 years tanganyika temperatures follow northern hemisphere insolation and indicate that warming in tropical southeast africa during the last glacial termination began to increase 3000 years before atmospheric carbon dioxide concentrations d data show that this region experienced abrupt changes in hydrology coeval with orbital and millennial scale events recorded in northern hemisphere monsoonal climate records this implies that precipitation in tropical southeast africa is more strongly controlled by changes in indian ocean sea surface temperatures and the winter indian monsoon than by migration of the intertropical convergence zone

the oxygen isotopic composition of seawater during the last glacial maximum high resolution oxygen and hydrogen isotope measurements were made on pore fluids from deep sea sediments from sites in the north and south atlantic the data provide direct measurements of changes in the isotopic composition of bottom waters during the last glacial maximum lgm results from ocean drilling program odp site 981 in the north atlantic currently bathed in north atlantic deep water nadw reproduces previous results from the ceara and bermuda rises constraining the glacial interglacial change in 18 o of the deep atlantic to be 0 7 0 8 results from site 984 which is located north of site 981 and at a shallower water depth yield a similar value 0 8 providing insight into the properties of glacial north atlantic intermediate water gnaiw sites from odp leg 177 in the south atlantic span the modern boundary between northern and southern sources of deep water data from the northern site 1088 yield a similar result to sites in the tropical and north atlantic 0 7 at the southern site 1093 located south of the polar front the change is substantially larger 1 1 representing the change in 18 o of southern source waters since the lgm these results confirm previous estimates that the global average change in 18 o of seawater is 1 0 0 1 hydrogen isotopes measured on pore fluids from three sites are consistent with the oxygen isotopes from these locations giving further support to these results at all sites studied the temperature of the deep ocean during the lgm calculated by combining the pore fluid results with oxygen isotope data from benthic foraminifera was within 1 c of the freezing point of seawater

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

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

sea level and deep sea temperature variability over the past 5 3 million years ice volume and hence sea level and deep sea temperature are key measures of global climate change sea level has been documented using several independent methods over the past 0 5 million years myr older periods however lack such independent validation all existing records are related to deep sea oxygen isotope 18o data that are influenced by processes unrelated to sea level for deep sea temperature only one continuous high resolution mg ca based record exists with related sea level estimates spanning the past 1 5 myr here we present a novel sea level reconstruction with associated estimates of deep sea temperature which independently validates the previous 0 1 5 myr reconstruction and extends it back to 5 3 myr ago we find that deep sea temperature and sea level generally decreased through time but distinctly out of synchrony which is remarkable given the importance of ice albedo feedbacks on the radiative forcing of climate in particular we observe a large temporal offset during the onset of plio pleistocene ice ages between a marked cooling step at 2 73 myr ago and the first major glaciation at 2 15 myr ago last we tentatively infer that ice sheets may have grown largest during glacials with more modest reductions in deep sea temperature a novel approach to the estimation of sea level and deep sea temperature has been used to determine these quantities over the past 5 3 million years this approach based on oxygen isotope records from the eastern mediterranean shows that temperature and sea level histories are broadly correlated but also show intriguing temporal offsets most records of past sea level variation and associated changes in ocean temperature rely on variations in oxygen isotopes recorded in deep sea marine microorganisms these signals unfortunately are confounded by other influences making it difficult to extract a clear climate related signal eelco rohling and colleagues now present a novel approach to estimating sea level and deep sea temperature variations for the past 5 3 million years the record based on oxygen isotope variations from the eastern mediterranean avoids the issues of the deep sea approach and generally corresponds to an independent record of the past 1 6 million years as expected temperature and sea level are broadly correlated but also show intriguing temporal discontinuities as at the initiation of plio pleistocene ice ages when a major sea level drop lagged a sharp temperature decline by several hundred thousand years

eastern beringia and beyond late wisconsinan and holocene landscape dynamics along the yukon coastal plain canada terrestrial permafrost archives along the yukon coastal plain northwest canada have recorded landscape development and environmental change since the late wisconsinan at the interface of unglaciated beringia i e komakuk beach and the northwestern limit of the laurentide ice sheet i e herschel island the objective of this paper is to compare the late glacial and holocene landscape development on both sides of the former ice margin based on permafrost sequences and ground ice analyses at these sites involved a multi proxy approach including sedimentology cryostratigraphy palaeoecology of ostracods stable water isotopes in ground ice hydrochemistry and ams radiocarbon and infrared stimulated luminescence irsl dating ams and irsl age determinations yielded full glacial ages at komakuk beach that is the northeastern limit of ice free beringia herschel island to the east marks the late wisconsinan limit of the northwest laurentide ice sheet and is composed of ice thrust sediments containing plant detritus as young as 16 2 cal ka bp that might provide a maximum age on ice arrival late wisconsinan ice wedges with sediment rich fillings on herschel island are depleted in heavy oxygen isotopes mean delta o 18 of 29 1 parts per thousand this together with low d excess values indicates colder than modern winter temperatures and probably reduced snow depths grain size distribution and fossil ostracod assemblages indicate that deglaciation of the herschel island ice thrust moraine was accompanied by alluvial proluvial and eolian sedimentation on the adjacent unglaciated yukon coastal plain until similar to 11 cal ka bp during a period of low glacio eustatic sea level the late glacial holocene transition was marked by higher than modern summer temperatures leading to permafrost degradation that began no later than 11 2 cal ka bp and caused a regional thaw unconformity cryostructures and ice wedges were truncated while organic matter was incorporated and soluble ions were leached in the thaw zone thermokarst activity led to the formation of ice wedge casts and deposition of thermokarst lake sediments these were subsequently covered by rapidly accumulating peat during the early holocene thermal maximum a rising permafrost table reduced peat accumulation and extensive ice wedge growth resulted from climate cooling starting in the middle holocene until the late 20th century the reconstruction of palaeolandscape dynamics on the yukon coastal plain and the eastern beringian edge contributes to unraveling the linkages between ice sheet ocean and permafrost that have existed since the late wisconsinan

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

borehole versus isotope temperatures on greenland seasonality does matter new simulation results obtained with the hamburg atmosphere general circulation model echam 4 under maximum glacial boundary lgm conditions confirm the paleotemperatures on greenland determined by borehole thermometry the disagreement between 18o isotope based temperatures and the borehole temperatures of the lgm is not only reproduced by the model but the simulation results provide a plausible explanation paleotemperatures inferred from 18o measurements in ice cores are biased by a substantially increased seasonality of precipitation over greenland during the lgm during the glacial winter a much more zonal circulation prevents the effective transport of moisture to the greenland ice sheet and therefore reduces the contribution of isotopically strongly depleted winter snow to the annual mean isotope signal

the oxygen isotopic composition and temperature of southern ocean bottom waters during the last glacial maximum we provide two new determinations of the oxygen isotopic composition of seawater during the last glacial maximum lgm high resolution oxygen isotopic measurements were made on interstitial waters from ocean drilling program odp sites 1168 and 1170 in the southeast indian ocean sector of the southern ocean we use a diffusion advection numerical model to calculate the glacial interglacial change in bottom water 18osw from the pore water 18o profiles the first such determinations from this part of the oceans statistical analyses of the model runs indicate that circumpolar deep water cdw 18osw changed by 1 0 1 1 0 15 since the last glacial maximum lgm our results are consistent with a previous calculation from a south atlantic southern ocean location odp site 1093 also situated within cdw the new values determined in this study together with previous estimates are converging on a global average 18osw of 1 0 1 1 using the calculated bottom water 18osw we have extracted the temperature component from the benthic foraminiferal 18o record at sites 1168 and 1170 since the lgm bottom waters at these two sites warmed by 2 6 and 1 9 c respectively the absolute temperature estimates for the lgm 0 5 c 0 6 c at site 1168 and 0 2 c 0 4 c at site 1170 are slightly warmer than those reported from previous studies using the same technique but are consistent with more homogenous deep ocean temperatures during the lgm relative to the modern

last glacial maximum records in permafrost of the east siberian arctic palaeontological proxy data and cryolithological information from siberian arctic permafrost preserves records of late quaternary climate and environmental conditions in west beringia and their variability which results from interglacial glacial and interstadial stadial dynamics to date the last glacial maximum lgm period has been rather poorly represented in east siberian permafrost records here we present pollen sediment and ground ice stable water isotope data obtained from coastal exposures on bol shoy lyakhovsky island new siberian archipelago arctic ocean that mirror the coldest conditions during the sartan period between about 26 and 22 ka bp using pollen and sediment data for summer conditions and stable water isotope data for winter conditions the pollen record revealed a cold tundra steppe vegetation with characteristic predominance of grass pollen over sedge pollen while the stable isotope ice wedges data indicate extremely cold winter temperatures with mean values of d 18 oo f about 37 dd of about 290 combined with available regional lgm permafrost records that extend from the taymyr peninsula in the west to the yana river lowland in the east the new data set from bol shoy lyakhovsky island indicate that the regional appearance of lgm conditions depended on atmospheric circulation patterns that were influenced by the extent of the northern hemisphere glaciation

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

the principles of cryostratigraphy abstract cryostratigraphy adopts concepts from both russian geocryology and modern sedimentology structures formed by the amount and distribution of ice within sediment and rock are termed cryostructures typically layered cryostructures are indicative of syngenetic permafrost while reticulate and irregular cryostructures are indicative of epigenetic permafrost cryofacies can be defined according to patterns of sediment characterized by distinct ice lenses and layers volumetric ice content and ice crystal size cryofacies can be subdivided according to cryostructure where a number of cryofacies form a distinctive cryostratigraphic unit these are termed a cryofacies assemblage the recognition if present of i thaw unconformities ii other ice bodies such as vein ice ice wedges aggradational ice and thermokarst cave pool ice and iii ice sand and gravelly pseudomorphs is also important in determining the nature of the freezing process the conditions under which frozen sediment accumulates and the history of permafrost

ice complex formation in arctic east siberia during the mis3 interstadial abstract a continuous 15 m long sequence of ice complex permafrost yedoma exposed in a thermo cirque at the southern coast of bol shoy lyakhovsky island new siberian archipelago dmitry laptev strait was studied to reconstruct past landscape and environmental dynamics the sequence accumulated during the marine isotope stage 3 mis3 interstadial between 49 and 29 ka bp in an ice wedge polygon the frozen deposits were cryolithologically described and sampled on a vertical bluff between two ice wedges according to sedimentological and geochronological data the section is subdivided into three units which correlate with environmental conditions of the early middle and late mis3 period palynological data support this stratification the stable isotope signature of texture ice in the polygon structure reflects fractionation due to local freeze thaw processes while the signature of an approximately 5 m wide and more than 17 m high ice wedge fits very well into the regional stable water isotope record regional climate dynamics during the mis3 interstadial and local landscape conditions of the polygonal patterned ground controlled the ice complex formation the sequence presented here completes previously published mis3 permafrost records in northeast siberia late quaternary stadial interstadial climate variability in arctic west beringia is preserved at millennial resolution in the ice complex a mis3 climate optimum was revealed between 48 and 38 ka bp from the ice complex on bol shoy lyakhovsky island

magnitude of isotope temperature scaling for interpretation of central antarctic ice cores 1 the conventional interpretation of ice core deuterium and oxygen 18 isotope profiles based on the use of present day observations spatial slope underestimates glacialinterglacial surface temperature changes in central greenland by up to a factor of two this likely results from changes in the seasonality of the precipitation due to the particular location of the greenland ice sheet next to the highly variable northern polar front in this regard the situation is much simpler for central antarctica and this should be reflected in the temperature interpretation of ice core isotopic records with this in mind we closely examine all relevant information focusing on the east antarctic plateau where both model and empirical isotope temperature estimates are available we point to the fact that correctly accounting for the influence of ocean isotopic change is important when interpreting deuterium profiles from ice cores in this region the evidence presently available indicates that unlike for greenland the present day spatial slope can probably be taken as a surrogate of the temporal slope to interpret glacial interglacial isotopic changes at sites such as vostok and epica dome c corresponding temperature changes are within 10 to 30 of those obtained from the conventional interpretation based on the use of the spatial slope index terms 1040 geochemistry isotopic composition chemistry 1827 hydrology glaciology 1863 3344 meteorology and atmospheric dynamics paleoclimatology 9310 information related to geographic region antarctica keywords water isotopes temperature estimate antarctica deuterium oxygen 18

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

low and high frequency climate variability in eastern beringia during the past 25 000 yearsthis article is one of a series of papers published in this special issue on the theme polar climate stability network we present new temperature and precipitation reconstructions for the past 25 000 cal years bp from across eastern beringia based on a network of pollen diagrams an updated modern pollen calibration database and an improved methodology using the modern analogue technique mat time series show july temperatures were around 4 c lower during full glacial and january temperatures were about 2 c lower than present annual temperatures rose beginning around 16 000 cal years bp reaching a maximum around 12 000 cal year bp the warming was more rapid in southern beringia annual precipitation varied by 250 mm during the past 25 000 cal years bp maps of reconstructed precipitation patterns show increasingly drier conditions since 12 000 cal years bp that vary regionally suggesting holocene atmospheric circulation changes at multiple time and space scales orbitally forced seasonality changes during the late glacial and early holocene resulted in reversed seasonal temperature reconstructions due to me

nature and origin of a pleistocene age massive ground ice body exposed in the chapman lake moraine complex central yukon territory canada abstract a massive ground ice body was found exposed in the headwall of a thaw flow developed within the chapman lake terminal moraine complex on the blackstone plateau ogilvie mountains central yukon territory which is contemporaneous to the reid glaciation based on visible cryostructures in the 4 m high headwall two units were identified massive ground ice overlain sharply by 2 m of icy diamicton the nature and origin of the chapman lake massive ground ice was determined using cryostratigraphy petrography stable o h isotopes and the molar concentration of occluded gases co2 o2 n2 and ar entrapped in the ice a new technique in the field of periglacial geomorphology that allows to distinguish between glacial and non glacial intrasedimental ice collectively the results indicate that the chapman lake massive ground ice formed by firn densification with limited melting refreezing and underwent deformation near its margin given that the massive ground ice body consists of relict glacier ice it suggests that permafrost persisted at least locally on plateau areas in the central yukon territory since the middle pleistocene in addition the d value of chapman lake relict glacier ice suggests that the ice covering the area during the reid glaciation originated from a local alpine glaciation in the ogilvie mountains

hydrogen isotope fractionation in leaf waxes in the alaskan arctic tundra abstract leaf wax hydrogen isotopes dwax are increasingly utilized in terrestrial paleoclimate research applications of this proxy must be grounded by studies of the modern controls on dwax including the ecophysiological controls on isotope fractionation at both the plant and landscape scales several calibration studies suggest a considerably smaller apparent fractionation between source water and waxes eapp at high latitudes relative to temperate or tropical locations with major implications for paleoclimatic interpretations of sedimentary dwax here we investigate apparent fractionation in the arctic by tracing the isotopic composition of leaf waxes from production in modern plants to deposition in lake sediments using isotopic observations of precipitation soil and plant waters living leaf waxes and waxes in sediment traps in the brooks range foothills of northern alaska we also analyze a lake surface sediment transect to compare present day vegetation assemblages to eapp at the watershed scale source water and eapp were determined for live specimens of eriophorum vaginatum cottongrass and betula nana dwarf birch two dominant tundra plants in the brooks range foothills the d of these plants xylem water closely tracks that of surface soil water and reflects a summer biased precipitation source leaf water is enriched by 23 15 relative to xylem water for e vaginatum and by 41 19 for b nana evapotranspiration modeling indicates that this leaf water enrichment is consistent with the evaporative enrichment expected under the climate conditions of northern alaska and that 24 h photosynthesis does not cause excessive leaf water isotope enrichment the eapp determined for our study species average 89 14 and 106 16 for b nana n alkanes and n acids respectively and 182 10 and 154 26 for e vaginatum n alkanes and n acids which are similar to the eapp of related species in temperate and tropical regions indicating that apparent fractionation is similar in arctic relative to other regions and there is no reduced fractionation in the arctic sediment trap data suggest that waxes are primarily transported into lakes from local watershed scale sources by overland flow during the spring freshet and so dwax within lakes depends on watershed scale differences in water isotope compositions and in plant ecophysiology as such the large difference between our study species suggests that the relative abundance of graminoids and shrubs is potentially an important control on dwax in lake sediments these inferences are supported by dwax data from surface sediments of 24 lakes where eapp relative to dxylem averages 128 13 and 130 8 for n acids and n alkanes respectively and co varies with vegetation type across watersheds these new determinations of plant source water seasonality and eapp for the arctic will improve the dwax paleoclimate proxy at high latitudes

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

downward water movement into frozen ground western arctic coast canada field studies carried out mainly since 1975 in permafrost areas of alaska canada china and the soviet union have been combined with the results of laboratory investigations to show that in summer water can move from the thawing active layer into the subjacent frozen active layer and under certain conditions even into the top of permafrost direct field evidence discussed includes data from drilling and neutron probe logging which show a summer increase in the ice content of already frozen ground summer heave of heavemeters with heave occurring in the frozen active layer and increase in the ice content of the subjacent frozen ground in both permafrost and non permafrost areas caused by snowmelt infiltration indirect field and laboratory evidence is also added to support the direct lines of evidence the conditions that favor the downward migration of water from thawed to frozen ground are examined in terms of thermally induced hydraulic gradients hydraulic conductivity content of unfrozen pore