osmotic generation of anomalous fluid pressures in geological environments osmotic pressures are generated by differences in chemical potential of a solution across a membrane but whether osmosis can have a significant effect on the pressure of fluids in geological environments has been controversial because the membrane properties of geological media are poorly understood anomalous pressures large departures from hydrostatic pressure that are not explicable in terms of topographic or fluid density effects are widely found in geological settings and are commonly considered to result from processes that alter the pore or fluid volume which in turn implies crustal changes happening at a rate too slow to observe directly yet if osmosis can explain some anomalies there is no need to invoke such dynamic geological processes in those cases here i report results of a nine year in situ measurement of fluid pressures and solute concentrations in shale that are consistent with the generation of large up to 20 mpa osmotic pressure anomalies which could persist for tens of millions of years osmotic pressures of this magnitude and duration can explain many of the pressure anomalies observed in geological settings they require however small shale porosity and large contrasts in the amount of dissolved solids in the pore waters criteria that may help to distinguish between osmotic and crustal dynamic origins of anomalous pressures

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

late quaternary glacial history of the karlik range easternmost tian shan derived from 10be surface exposure and optically stimulated luminescence datings abstract the karlik range located in the easternmost part of the tian shan is a key area in reconstructing paleoclimate in central asia but few studies have been conducted to constrain the timing and extent of quaternary glaciations in its highlands we investigated the late quaternary glacial history in the turgan valley on the northern slopes of the karlik range using cosmogenic 10be surface exposure and optically stimulated luminescence osl dating techniques four major glacial events were dated to 0 79 0 59 ka little ice age lia 15 8 1 6 ka lateglacial 37 4 4 0 44 2 4 3 ka marine oxygen isotope stage mis 3 and 60 2 3 3 79 3 5 2 ka mis 4 or older with a pattern of continuously restricted glaciations after mis 4 this glacial chronology is consistent with the studies from other parts of the tian shan the overall pattern of glaciations across the tian shan suggests that change in precipitation brought by the westerlies was the primary factor influencing the timing and extent of glacial advances during the last glaciation however lower temperature of the karlik range affected by the siberian high may counteract the effect of lower precipitation to drive a relatively extensive glacial advance in the easternmost tian shan

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

pleistocene glaciations of central asia results from 10be surface exposure ages of erratic boulders from the pamir tajikistan and the alay turkestan range kyrgyzstan abstract we have determined the timing of glaciations in the pamir tajikistan and the alay turkestan range kyrgyzstan using 10be surface exposure dating glacial advances in the area have occurred 93 136 60 80 40 55 27 25 22 20 19 17 16 15 15 13 and 11 9 cal ka bp all late pleistocene glaciers in the pamir and the alay turkestan ranges have been valley glaciers except for the most extended glaciers on the pamir plateau which have formed local piedmont glaciations in the eastern pamir these are characterized by ela depressions of 370 380 m thar 0 5 in the turkestan range and alay range ela depressions at the same time were 750 and 600 m respectively late pleistocene glacier advances all over western high asia were contemporaneous with climatic cold phases rather than monsoonal maxima their maximum extent and that of the western hemisphere ice sheets were asynchronous due to increasing aridity in the region over the course of the last glacial late pleistocene climate in central asia seems to have been influenced by the interplay of the westerly circulation and the siberian anticyclone some indirect monsoonal influence in the eastern pamir may be responsible for the existence of some of the lateglacial moraine stages in this area high altitude glaciers seem to have reached their maximum extent earlier mis 5 4 than low altitude glaciers first half of mis 3 possibly due to prolonged glacial aridity imparting with moisture advection onto high altitude sites inducing glacial retreat but prolonged cold during the same time imparting with glacier ablation at lower altitude sites inducing glacial advance

timing of terminal pleistocene deglaciation at high elevations in southern and central british columbia constrained by 10be exposure dating abstract the cordilleran ice sheet cis covered most of british columbia and southern yukon territory at the local last glacial maximum llgm during marine oxygen isotope stage 2 however its subsequent demise is not well understood particularly at high elevations east of its ocean terminating margin we present 10be exposure ages from two high elevation sites in southern and central british columbia that help constrain the time of initial deglaciation at these sites we sampled granodiorite erratics at elevations of 2126 2230 m a s l in the marble range and 1608 1785 m a s l in the telkwa range at the western margin of the interior plateau the erratics at both sites are near ice marginal meltwater channels that delineate the local ice surface slope and thus the configuration of the ice sheet during deglaciation the locations of the erratics and their relations to meltwater channels ensure that the resulting 10be ages date cis deglaciation and not the retreat of local montane glaciers our sample sites emerged above the surface of the cis as its divide migrated westward from the interior plateau to the axis of the coast mountains two of the four samples from the summit area of the marble range yielded apparent exposure ages of 14 0 0 7 and 15 2 0 8 ka these ages are 1 8 3 0 ka younger than the well established llgm age of ca 17 ka for the puget lobe of the cis in washington state they are 1 7 ka younger than the llgm age for the puget lobe if a snow shielding correction to their uncertainty weighted mean age is applied the other two samples yielded much older apparent exposure ages 20 6 1 4 and 33 0 1 5 ka indicating the presence of inherited isotopes four samples collected from the summit area of the telkwa range in the hazelton mountains yielded well clustered apparent exposure ages of 10 1 0 6 10 2 0 7 10 4 0 5 and 11 5 1 1 ka significant present day snow cover introduces a large uncertainty in the apparent exposure ages from this site a snow shielding correction based on present day snow cover data increases the uncertainty weighted mean exposure age of the telkwa range erratics to 12 4 0 7 ka consistent with deglacial 14c ages from areas near sea level to the west our exposure ages show a thinning of the southern portion of the cis shortly after the llgm and persistence of a remnant mountain ice cap in the central coast mountains into the younger dryas chronozone our data also show that the summit area of the marble range was ice covered during the llgm the presence of an ice body of considerable dimension in north central british columbia until or possibly even after the younger dryas highlights the need for geomorphological and geochronological studies of the ice dispersal centre over the skeena mountains in northwest british columbia and the need for better understanding of the response of the cis to lateglacial climate fluctuations

in situ cosmogenic 10be production rate at lago argentino patagonia implications for late glacial climate chronology abstract when calculated with the commonly accepted average northern hemisphere production rate 10 be dates of surface boulders on moraines in the lago argentino area of patagonia are younger than minimum limiting 14 c ages for the same landforms this disagreement could result from the lack of a regional 10 be production rate calibration site to assess this possibility we here present high precision measurements of 10 be in samples collected from surface boulders on the herminita and puerto bandera moraine complexes deposited alongside lago argentino on the eastern flank of the andes at 50 s in patagonia together with maximum and minimum limiting 14 c ages for the two moraine systems these measurements confine the local 10 be production rate to between 3 60 and 3 82 atoms g yr midpoint 3 71 0 11 atoms g yr when using a time dependent scaling method that incorporates a high resolution geomagnetic model this range includes upper and lower error bounds of acceptable production rates derived from both the herminita and the puerto bandera sites the upper limit of this range is more than 12 below the average northern hemisphere production rate as calculated using the same scaling method given in balco et al quat geochron 3 2008 174 195 other scaling models yield production rates with similarly large offsets from the balco et al 2008 rate on the other hand the range of acceptable production rate values determined from patagonia overlaps at 1 with and encompasses the production rate recently derived in macaulay valley in the southern alps of new zealand a putnam et al quat geochron 5 2010a 392 409 within uncertainties i e overlap at 1 sigma this patagonian production rate range also agrees with a recently determined production rate from low elevation sites in northeastern north america and northern norway when the macaulay production rate is used to calculate patagonian exposure dates 14 c and 10 be chronologies are mutually compatible for late glacial moraine systems both chronologies then indicate that outlet glaciers of the southern patagonian icefield achieved a late glacial maximum in the western reaches of lago argentino at 13 000 cal yr bp at the end of the antarctic cold reversal 14 500 12 900 cal yr bp outlet glaciers subsequently receded to near present day ice margins during the younger dryas stadial 12 900 11 700 cal yr bp this general retreat was interrupted about 12 200 cal yr bp when upsala glacier constructed an interlobate complex of moraine ridges on herminita peninsula mountain glaciers in patagonia and new zealand on both sides of the south pacific ocean exhibited a coherent pattern of late glacial ice margin fluctuations

tephrochronology and paleoclimatology of the last interglacial glacial cycle recorded in alaskan loess deposits abstract alaskan loess deposits contain long paleoclimatic records analogous to those found in marine and lacustrine sediments and in ice sheets the sedimentology and geophysical properties of alaskan loess were influenced by climatically forced changes in wind intensity storminess temperature and precipitation loess deposits also contain evidence of episodic permafrost and paleosol formation explosive volcanic eruptions paleoecologic changes in high latitude regions quaternary fossils and early human sites and artifacts the old crow tephra ca 140 000 10 000 bp dates the transition between full glacial conditions and the last interglaciation in central alaska climatic amelioration in alaska apparently began prior to astronomically forced increases in insolation a finding consistent with the well dated devil s hole record however time series analysis of loess proxy climate data also demonstrates the effects of orbital precession and obliquity on alaskan climate change numerous short term climate events are recorded in alaskan loess deposits including a climate reversal corresponding to the younger dryas

early wisconsinan mis 4 glaciation on haida gwaii british columbia and implications for biological refugia sea cliffs at cape ball on graham island british columbia expose a thick sequence of pleistocene sediments deposited during at least two glaciations in sequence from the base of the section the units are 1 stony mud 2 till 3 silt sand and peat 4 stony mud 5 laminated sand and silt 6 cross bedded sand and 7 till of special interest is unit 4 a massive to weakly stratified mud containing scattered stones that was deposited during the penultimate pleistocene glaciation marine isotope stage mis 4 this unit contains wood and marine shell fragments that have yielded non finite radiocarbon ages sand and silt with thin stringers of peat unit 3 directly underlie this stony mud and returned an optical age of 57 3 5 7 ka the stony mud is unconformably overlain by ponded sediments unit 5 and advance outwash unit 6 and till unit 7 deposited during the fraser glaciation mis 2 the optically dated unit and a correlative peat and silty sand unit at a nearby exposure have p

late quaternary tephrostratigraphy ahklun mountains sw alaska radiocarbon dated sediment cores from six lakes in the ahklun mountains south western alaska were used to interpolate the ages of late quaternary tephra beds ranging in age from 25 4 to 0 4 ka the lakes are located downwind of the aleutian arc and alaska peninsula volcanoes in the northern bristol bay area between 159 and 161 w at around 60 n sedimentation rate age models for each lake were based on a published spline fit procedure that uses monte carlo simulation to determine age model uncertainty in all 62 14c ages were used to construct the six age models including 23 ages presented here for the first time the age model from lone spruce pond is based on 18 ages and is currently the best resolved holocene age model available from the region with an average 2 age uncertainty of about 109 years over the past 14 5 ka the sedimentary sequence from lone spruce pond contains seven tephra beds more than previously found in any other lake in the area of the 26 radiocarbon dated tephra beds at the six lakes and from a soil pit seven are correlated between two or more sites based on their ages the major element geochemistry of glass shards from most of these tephra beds supports the age based correlations the remaining tephra beds appear to be present at only one site based on their unique geochemistry or age the 5 8 ka tephra is similar to the widespread aniakchak tephra 3 7 0 2 1 ka but can be distinguished conclusively based on its trace element geochemistry the 3 1 and 0 4 ka tephras have glass major and trace element geochemical compositions indistinguishable from prominent aniakchak tephra and might represent redeposited beds only two tephra beds are found in all lakes the aniakchak tephra 3 7 0 2 ka and tephra b 6 1 0 3 ka the tephra beds can be used as chronostratigraphic markers for other sedimentary sequences in the region including cores from cascade and sunday lakes which were previously undated and were analyzed in this study to correlate with the new regional tephrostratigraphy copyright 2012 john wiley sons ltd

a late quaternary loess paleosol record at kurtak southern siberia a high resolution paleoclimatic record for the last two glacial interglacial cycles has been documented at kurtak in southern siberia a unique 34 m high late quaternary loess section section 29 with a series of 32 variably developed paleosol horizons provides evidence of a strongly fluctuating but patterned climatic change mineralogical composition and grain morphology of the undifferentiated aeolian and colluviated loess indicate a local provenance and a short transport of the silt derived by glacial erosion of the granitic and metamorphic bedrock in the kuznetskiy alatau and eastern sayan mountains and subsequently subaerially redeposited from the alluvial plain in the yenisey river valley the succession of chernozemic brunisolic and gleyed regosolic soils alternating with nonweathered or weakly weathered loess events matched by parallel changes in magnetic susceptibility can be correlated with marine isotope stages 1 7 the magnetic susceptibility pattern is completely opposite to

accuracy of cosmogenic ages for moraines analyses of all published cosmogenic exposure ages for moraine boulders show an average age range of 38 between the oldest and youngest boulders from each moraine this range conflicts with the common assumption that ages of surface boulders are the same as the age of the landform the wide spread in boulder ages is caused by erosion of the moraine surface and consequent exhumation of fresh boulders a diffusion model of surface degradation explains the age range and shows that a randomly sampled small set of boulders n 3 7 will always yield a lower age limit for the moraine the model indicates that for identical dating accuracy six to seven boulders are needed from old and tall moraines 40 000 100 000 yr 50 100 m initial height but only one to four boulders from small moraines 20 000 100 000 yr 10 20 m by following these guidelines the oldest obtained boulder age will be 90 of the moraine age 95 probability this result is only weakly sensitive to a broad range of soil erosion rates our analysis of published boulder ages indicates that 3 of all moraine boulders have prior exposure and 85 of these boulders predate the dated moraine

climatic and topographic controls on the style and timing of late quaternary glaciation throughout tibet and the himalaya defined by 10be cosmogenic radionuclide surface exposure dating abstract temporal and spatial changes in glacier cover throughout the late quaternary in tibet and the bordering mountains are poorly defined because of the inaccessibility and vastness of the region and the lack of numerical dating to help reconstruct the timing and extent of glaciation throughout tibet and the bordering mountains we use geomorphic mapping and 10 be cosmogenic radionuclide crn surface dating in study areas in southeastern gonga shan southern karola pass and central western nyainqentanggulha shan and tanggula shan tibet and we compare these with recently determined numerical chronologies in other parts of the plateau and its borderlands each of the study regions receives its precipitation mainly during the south asian summer monsoon when it falls as snow at high altitudes gonga shan receives the most precipitation 2000 mm a 1 while near the margins of monsoon influence the karola pass receives moderate amounts of precipitation 500 600 mm a 1 and in the interior of the plateau little precipitation falls on the western nyainqentanggulha shan 300 mm a 1 and the tanggula shan 400 700 mm a 1 the higher precipitation values for the tanggula shan are due to strong orographic effects in each region at least three sets of moraines and associated landforms are preserved providing evidence for multiple glaciations the 10 be crn surface exposure dating shows that the formation of moraines in gonga shan occurred during the early mid holocene neoglacial and little ice age on the karola pass during the lateglacial early holocene and neoglacial in the nyainqentanggulha shan date during the early part of the last glacial cycle global last glacial maximum and lateglacial and on the tanggula shan during the penultimate glacial cycle and the early part of the last glacial cycle the oldest moraine succession in each of these regions varies from the early holocene gonga shan lateglacial karola pass early last glacial western nyainqentanggulha shan and penultimate glacial cycle tanggula shan we believe that the regional patterns and timing of glaciation reflect temporal and spatial variability in the south asian monsoon and in particular in regional precipitation gradients in zones of greater aridity the extent of glaciation has become increasingly restricted throughout the late quaternary leading to the preservation of old 100 ka glacial landforms in contrast in regions that are very strongly influenced by the monsoon 1600 mm a 1 the preservation potential of pre lateglacial moraine successions is generally extremely poor this is possibly because lateglacial and holocene glacial advances may have been more extensive than early glaciations and hence may have destroyed any landform or sedimentary evidence of earlier glaciations furthermore the intense denudation mainly by fluvial and mass movement processes which characterize these wetter environments results in rapid erosion and re sedimentation of glacial and associated landforms which also contributes to their poor preservation potential

late pleistocene cosmogenic 36cl glacial chronology of the southwestern ahklun mountains alaska thirty two cosmogenic 36cl surface exposure ages constrain the timing of two late pleistocene glacial advances in the western ahklun mountains southwestern alaska boulders were sampled from one early wisconsin sensu lato and six late wisconsin moraines deposited by ice cap outlet glaciers and local alpine glaciers four moraine boulders deposited during an extensive early wisconsin ice cap outlet glacier advance have a mean surface exposure age of 60 300 3200 yr a moraine deposited by an ice cap outlet glacier during the restricted late wisconsin advance has a mean surface exposure age of 19 600 1400 yr five moraines deposited by late wisconsin alpine glaciers have mean ages that range between 30 000 and 17 000 yr the 36cl ages are consistent with limiting 14c and thermoluminescence ages from related deposits and indicate that ahklun mountains glaciers reached their most extensive position of the last glaciation early during the late pleistocene in contrast to the deep sea isotopic record of global ice volume 1

evidence for a 55 50 ka early wisconsin glaciation of the cordilleran ice sheet yukon territory canada abstract cosmogenic 10be ages on boulders of 54 51 ka n 4 on a penultimate cordilleran ice sheet cis drift confirm that marine oxygen isotope stage mis 4 early wisconsin glaciation was extensive in parts of yukon territory the first confirmed evidence in the canadian cordillera we name the glaciation inferred from the mapped and dated drift the gladstone these results are in apparent contrast to the mis 6 illinoian age of the penultimate reid glaciation to the east in central yukon but are equivalent to exposure ages on mis 4 drift in alaska contrasting penultimate ice extents in yukon requires that different source areas of the northern cis in yukon responded differently to climatic forcing during glaciations the variation in glacier extent for different source areas likely relates to variation in precipitation during glaciation as the northern cis was a precipitation limited system causes for a variation in precipitation remain unclear but likely involve the style of precipitation delivery over the st elias mountains possibly related to variations in the aleutian low

last glacial maximum and holocene climate in ccsm3 abstract the climate sensitivity of the community climate system model version 3 ccsm3 is studied for two past climate forcings the last glacial maximum lgm and the mid holocene the lgm approximately 21 000 yr ago is a glacial period with large changes in the greenhouse gases sea level and ice sheets the mid holocene approximately 6000 yr ago occurred during the current interglacial with primary changes in the seasonal solar irradiance the lgm ccsm3 simulation has a global cooling of 4 5 c compared to preindustrial pi conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at lgm tropical sea surface temperature sst cools by 1 7 c and tropical land temperature cools by 2 6 c on average simulations with the ccsm3 slab ocean model suggest that about half of the global cooling is explained by the reduced lgm concentration of atmospheric co2 50 of present day concentrations there is an increase in the antarctic circumpolar current an

a multi proxy reconstruction of environmental change spanning the last 37 000 years from burial lake arctic alaska abstract sediment cores from burial lake located in the western brooks range in arctic alaska record paleoenvironmental changes that span the last 37 000 calendar years before present cal yr bp we identified four distinct lithologic subunits based on physical properties dry bulk density magnetic susceptibility sediment composition and geochemical proxies organic matter biogenic silica c n organic matter 13c and 15n and elemental data from scanning x ray fluorescence the multi proxy approach and relatively high temporal resolution at multi decadal to centennial time scales of our proxy analysis compared with previous studies of intermediate water depth cores from burial lake provide new insights into the paleoenvironmental history of the region spanning the period prior to the last glacial maximum relatively high lake levels and gradually decreasing in lake and terrestrial productivity occur during the mid wisconsin interstadial from 37 200 to 29 600 cal yr bp the subsequent period is defined by falling and lower lake levels with decreasing effective moisture windier conditions and sustained low aquatic productivity throughout the lgm between 29 600 and 19 600 cal yr bp the last deglaciation that commenced by 19 600 cal yr bp is characterized by gradual changes in several sediment physical and geochemical proxies including increasing c n ratios and terrestrial productivity decreasing magnetic susceptibility and clastic sediment flux along with rising and relatively higher lake levels a decrease in aeolian activity after 16 500 cal yr bp is inferred from the appearance of fine very fine sandy silt sediment compared to coarse sediments through the lgm and last deglaciation the highest levels of terrestrial inputs along with increasing and variable aquatic productivity occur during the lateglacial to early holocene interval between 16 500 and 8800 cal yr bp the absence of multi proxy evidence for a strong climatic reversal during the younger dryas from burial lake sediments contrasts with some paleorecords showing cooler temperatures and or dry conditions in northern alaska at this time peak levels of sediment organic content and terrestrial productivity at burial lake between 10 500 and 9900 cal yr bp coincide with the early holocene summer insolation maxima which likely represents summertime warming and an enhanced flux of watershed derived organic matter from permafrost degradation the remainder of the holocene since 8800 cal yr bp at burial lake is characterized by relatively high and stable lake levels landscape stabilization and relatively high and variable levels of aquatic productivity

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

cenozoic potassium rich mafic volcanism in the western u s a its relationship to deep subduction cenozoic potassium rich volcanism characterized by k 2 o na 2 o and sio 2 60 wt follows a northeast to southwest younging trend in the western u s a correlation of this trend with the outer limits of arc related magmatism based on variable dip subduction models suggests that potassium rich volcanism may be related to deep subduction rather than intraplate tectonics

near synchronous interhemispheric termination of the last glacial maximum in mid latitudes isotopic records from polar ice cores imply globally asynchronous warming at the end of the last glaciation however 10be exposure dates show that large scale retreat of mid latitude last glacial maximum glaciers commenced at about the same time in both hemispheres the timing of retreat is consistent with the onset of temperature and atmospheric co2 increases in antarctic ice cores we suggest that a global trend of rising summer temperatures at the end of the last glacial maximum was obscured in north atlantic regions by hypercold winters associated with unusually extensive winter sea ice

cosmogenic exposure dating of late pleistocene moraine stabilization in alaska seventy three new 1 0 be 2 6 al ages from 57 moraine boulders and 2 tors together with 43 previously published cosmogenic exposure ages from 41 moraine boulders allow us to critique the use of cosmogenic exposure ce dating of moraine boulders in alaska boulder exhumation during moraine degradation likely gives rise to the largest uncertainty in constraining the timing of initial moraine stabilization following ice retreat isotopic inheritance appears to be most important for moraines deposited close to their cirque headwalls boulder surface bedrock erosion rate can be roughly constrained and leads to a range in moraine stabilization ages snow cover history is difficult to constrain but its effect is thought to be minor for the tall boulders sampled despite these complications the ce ages provide important new information regarding the timing of the last and penultimate glaciations in alaska three penultimate moraines yielded ce ages that overlap with marine isotope stage mis 4 early mis 3 45 65 ka rather than mis 6 ca 140 ka based on a combination of our new ce chronologies and existing 1 4 c ages from six study areas glaciers retreated from their local late wisconsin maxima ca 24 27 ka kokrines hills west interior alaska ca 24 26 ka northeastern brooks range ne alaska ca 21 23 ka yukon tanana upland east interior alaska ca 22 ka ahklun mountains sw alaska ca 20 ka western alaska range central alaska ca 16 18 ka chuilnuk mountains sw alaska overall glacier retreat was concurrent with the peak of the last global glacial maximum probably in response to limited moisture availability

constraints on the late quaternary glacial history of the inylchek and sary dzaz valleys from in situ cosmogenic 10be and 26al eastern kyrgyz tian shan abstract paleoclimatic constraints from regions at the confluence of major climate systems are particularly important in understanding past climate change using geomorphic mapping based on remote sensing and field investigations combined with in situ cosmogenic 10be and 26al dating of boulders associated with glacial landforms we investigate the chronology of past glaciation in the inylchek and sary dzaz valleys in the eastern kyrgyz tian shan a tectonically active area with some of the highest peaks in the world outside of the himalayas cosmogenic 10be and 26al exposure ages of boulders on moraines record up to five glacial advances including lateglacial age lateral moraine remnants and meltwater channels in the upper inylchek valley last glacial maximum lgm marine oxygen isotope stage mis 2 moraines in the sary dzaz valley and in a terminal moraine complex at the west end of the inylchek valley overriding older moraines an mis 4 or 5 moraine remnant above the inylchek terminal moraine complex and an older high moraine remnant down valley from the confluence of the inylchek and sary dzaz valleys the evidence for glacial extent in this study is consistent with a limited ice expansion hypothesis for tian shan glaciation published results from the western and central kyrgyz tian shan do not show evidence for significant lgm glacier expansion which in combination with the results presented here indicate a spatial variation in glacier records along the tian shan this may reflect either paleoclimatic gradients or the impact of local physiographic conditions on responses to regional climate change or both

the greenland ice sheet project 2 depth age scale methods and results the greenland ice sheet project 2 gisp2 depth age scale is presented based on a multiparameter continuous count approach to a depth of 2800 m using a systematic combination of parameters that have never been used to this extent before the ice at 2800 m is dated at 110 000 years b p with an estimated error ranging from 1 to 10 in the top 2500 m of the core and averaging 20 between 2500 and 2800 m parameters used to date the core include visual stratigraphy oxygen isotopic ratios of the ice electrical conductivity measurements laser light scattering from dust volcanic signals and major ion chemistry gisp2 ages for major climatic events agree with independent ages based on varve chronologies calibrated radiocarbon dates and other techniques within the combined uncertainties good agreement also is obtained with greenland ice core project ice core dates and with the specmap marine timescale after correlation through the 18 o of o 2 although the core is deformed below 2800 m and the continuity of the record is unclear we attempted to date this section of the core on the basis of the laser light scattering of dust in the ice

the mckinley sequence of granitic rocks a key element in the accretionary history of southern alaska the mckinley sequence of granitic rocks consists of several discrete plutons in the central alaska range most of these plutons crop out south of the denali fault system dfs in the talkeetna quadrangle plutons of the mckinley sequence largely intrude deformed upper meszoic flysch between the dfs and the northern edges of wrangellia and the peninsular terrane which jointly make up the talkeetna superterrane the average k ar age of biotite from nine granites of the mckinley sequence is 57 3 ma rb sr data for whole rock samples indicate that the mckinley sequence cannot be older than 60 ma a selected suite of 20 samples of granite and granodiorite range in sio2 from 65 9 to 77 6 all 20 samples are corundum normative and 18 are moderately peraluminous initial 87sr 86sr ratios range from 0 7054 to 0 7085 the 18o values range from 11 2 to 14 6 these high and variable sr isotopic ratios peraluminous nature rare earth element patterns and high 18o values suggest that granitic rocks of the mckinley sequence crystallized from hybrid magmas produced by assimilation of sedimentary rocks by a mantle derived melt mesozoic flysch is the likely source of the crustal component of the hybrid magmas geologic evidence suggests that the talkeetna superterrane collided with stable alaska after early cretaceous time the flysch basin lying south of stable alaska was closed by northward movement of the talkeetna superterrane maximum age for basin closure and terrane accretion is middle cretaceous cenomanian paleomagnetic evidence indicates that all terranes north of the dfs have been part of stable alaska since the paleocene and that northward movement of wrangellia was completed by 50 ma granitic rocks of the mckinley sequence may be products of terrane accretion the granitic rocks crystallized from hybrid magmas produced during terrane collision and deformation of the flysch basin isotopic ages of the mckinley sequence establish the time of final accretion of the talkeetna superterrane as paleocene

beryllium 10 chronology of early and late wisconsinan moraines in the revelation mountains alaska insights into the forcing of wisconsinan glaciation in beringia abstract we present 32 new cosmogenic 10be exposure ages from a moraine sequence deposited during the wisconsinan glaciation in the swift river valley revelation mountains western alaska range 10be ages from an early wisconsinan marine isotope stage 4 moraine average 59 7 3 6 ka n 9 excluding one outlier and 10be ages from a late wisconsinan marine isotope stage 2 terminal moraine inboard moraines and two recessional end moraines average 21 3 0 8 ka n 3 excluding two outliers 20 2 1 0 ka n 7 excluding three young outliers 19 6 1 0 ka n 2 excluding one outlier and 17 7 0 8 ka n 4 excluding two outliers respectively the early wisconsinan moraine age coincides with the close of mis 4 consistent with previous chronologies from beringia whereas southern hemisphere glaciers retreated prior to the onset of heinrich stadial 6 64 60 ka the mis 4 glacier advance in the swift river valley terminated at the close of heinrich stadial 6 possibly in response to abrupt north atlantic warming our late wisconsinan ages indicate significant initial glacier retreat between ca 21 3 17 7 ka prior to any significant increase in co2 likely in response to amplified warming from rising insolation preservation of mis 4 moraines in beringia has traditionally been ascribed to limited mis 2 glacier advance modulated by low regional moisture availability stemming from the exposed bering land bridge however we hypothesize that atmospheric re organization forced by the laurentide ice sheet resulted in relatively higher temperatures and drier conditions in beringia during mis 2 than mis 4 allowing for the preservation of early wisconsinan moraines

the southern glacial maximum 65 000 years ago and its unfinished termination abstract glacial maxima and their terminations provide key insights into inter hemispheric climate dynamics and the coupling of atmosphere surface and deep ocean hydrology and cryosphere which is fundamental for evaluating the robustness of earth s climate in view of ongoing climate change the last glacial maximum lgm 26 19 ka ago is widely seen as the global cold peak during the last glacial cycle and its transition to the holocene interglacial dubbed termination 1 t1 as the most dramatic climate reorganization during this interval climate records show that over the last 800 ka ice ages peaked and terminated on average every 100 ka 100 ka world however the mechanisms pacing glacial interglacial transitions remain controversial and in particular the hemispheric manifestations and underlying orbital to regional driving forces of glacial maxima and subsequent terminations remain poorly understood here we show evidence for a full glacial maximum in the southern hemisphere 65 1 2 7 ka ago and its unfinished termination our 10 be chronology combined with a model simulation demonstrates that new zealand s glaciers reached their maximum position of the last glacial cycle during marine isotope stage 4 mis 4 southern ocean and greenhouse gas records indicate coeval peak glacial conditions making the case for the southern glacial maximum about halfway through the last glacial cycle and only 15 ka after the last warm period mis 5a we present the hypothesis that subsequently driven by boreal summer insolation forcing a termination began but remained unfinished possibly because the northern ice sheets were only moderately large and could not supply enough meltwater to the north atlantic through heinrich stadial 6 to drive a full termination yet the unfinished termination left behind substantial ice on the northern continents about 50 of the full lgm ice volume and after another 45 ka of cooling and ice sheet growth the earth was at inter hemispheric last glacial maximum configuration when similar orbital forcing hit maximum size northern ice sheets and ushered in t1 and thus the ongoing interglacial this argument highlights the critical role of full glacial conditions in both hemispheres for terminations and implies that the southern hemisphere climate could transition from interglacial to full glacial conditions in about 15 000 years while the northern hemisphere and its continental ice sheets required half a glacial cycle

a 31 000 year record of paleoenvironmental and lake level change from harding lake alaska usa physical and geochemical proxy analyses of sediment cores from harding lake in central alaska are used to reconstruct paleoenvironmental change and millennial scale fluctuations in lake level for the last similar to 31 000 years we analyzed a composite 422 cm core from the lake depocenter 42 1 m water depth and identified 4 distinct lithologic units based on variability in dry bulk density organic matter biogenic silica carbon to nitrogen mass ratios c n organic matter carbon isotopes delta c 13 pollen and elemental abundances via scanning x ray fluorescence with age control provided by 16 accelerator mass spectrometry radiocarbon dates and pb 210 dating in addition we analyzed a transect of cores from 7 1 m 10 75 m 15 91 m and 38 05 m water depths to identify lake level fluctuations and to characterize sediment compositional changes as a function of water depth organic matter content and magnetic susceptibility values in surface sediments from all transect cores show a strong correlation with water depth interpretation of four lithologic units with well dated contacts produced a record of water depth variations that is consistent with independent climate records from eastern beringia basal coarse grained sediments quartz pebble diamicton were deposited prior to 30 700 calendar years before present yr bp possibly from fluvial reworking or deflation during a period of severe aridity unit 1 sediments were deposited between 30 700 and 15 700 yr bp and are characterized by a low organic matter content a high magnetic susceptibility and low biogenic silica concentrations resulting from very low lake levels low terrestrial and in lake productivity and a high flux of clastic sediment an abrupt increase in organic matter and biogenic silica concentration marks the transition into unit 2 sediments which were deposited between 15 700 and 9 400 yr bp when lake levels were higher and variable relative to unit 1 the transition to full interglacial conditions at 9 400 yr bp marks the beginning of unit 3 here an abrupt increase in the sedimentation rate organic matter and biogenic silica concentration occurs along with a corresponding decrease to low magnetic susceptibility these high values persist until 8 700 yr bp signifying a rapid rise to higher lake levels in comparison to units 1 and 2 unit 4 sediments were deposited between 8 700 yr bp to 2010 ad and generally contain high concentrations of organic matter and biogenic silica with low magnetic susceptibility suggesting that lake levels were relatively high and stable during the middle to late holocene c 2014 elsevier ltd all rights reserved

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

a 37 000 year environmental magnetic record of aeolian dust deposition from burial lake arctic alaska abstract environmental magnetism and radiocarbon dating of burial lake sediments constrain the timing and magnitude of regional aeolian deposition for the noatak region of western arctic alaska for the last 37 000 years burial lake 68 43 n 159 17 w 21 5 m water depth is optimally located to monitor regional dust deposition because it is perched above local drainage and isolated from glacial processes cores collected in the summer of 2010 were studied through the application of magnetizations and progressive alternating field af demagnetization of u channel samples with additional data provided by computed tomography ct derived density hysteresis measurements isothermal remanent magnetization irm acquisition experiments organic carbon content biogenic silica physical grain size radiocarbon dating of wood seeds and plant macrofossils point source magnetic susceptibility and x ray fluorescence xrf with similar magnetic properties to regional alaskan loess deposits low coercivity highly magnetic material deposited during the late pleistocene contrasts with a high coercivity weakly magnetic component found throughout the record consistent with locally derived detritus the relative proportion of low coercivity to high coercivity magnetic material defined by the s ratios is used to reconstruct the regional input of dust to the basin over time a four fold decrease in the low coercivity component through the deglacial transition is interpreted to reflect diminished dust input to the region comparisons with potential sources of dust show that the timing of deposition in burial lake is largely consistent with general aridity lack of vegetative cover and increased windiness rather than glacial advances or retreats the influence from subaerial exposure of continental shelves cannot be ruled out as a significant far field source of dust to interior alaska during the last glacial maximum lgm but is unlikely to have been the sole source or to have contributed to increased dust in both the early and late holocene

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

a 40 000 yr record of environmental change from burial lake in northwest alaska abstract burial lake in northwest alaska records changes in water level and regional vegetation since 39 000 cal yr bp based on terrestrial macrofossil ams radiocarbon dates a sedimentary unconformity is dated between 34 800 and 23 200 cal yr bp during all or some of this period there was a hiatus in deposition indicating a major drop in lake level and deflation of lacustrine sediments mis 3 vegetation was herb shrub tundra more xeric graminoid herb tundra developed after 23 200 cal yr bp the tundra gradually became more mesic after 17 000 cal yr bp expansions of salix then betula at 15 000 and 14 000 cal yr bp respectively are coincident with a major rise in lake level marked by increasing fine grained sediment and higher organic matter content several sites in the region display disrupted sedimentation and probable hiatuses during the last glacial maximum lgm together regional data indicate an arid interval prior to and during the lgm and continued low moisture levels until 15 000 cal yr bp ams 14c dates from burial lake are approximately synchronous with ams 14c dates reported for the betula expansion at nearby sites and sites across northern alaska but 1000 2000 yr younger than bulk sediment dates

old crow tephra 140 10 ka constrains penultimate reid glaciation in central yukon territory abstract old crow tephra 140 10 ka is closely associated with deposits from the penultimate reid glaciation along the pelly river in central yukon territory the elevation of the tephra above present base level and association with deglacial sediments suggests a close minimum age estimate confirming a mis 6 age for the reid glaciation this is in contrast to a mis 4 age for the penultimate gladstone glaciation in southwest yukon this study demonstrates that the assumed synchrony of the penultimate advance of the cordilleran ice sheet has little support and regional controls on the mass balance of source regions of the ice sheet are more important than previously considered

late quaternary glaciation in the kyrgyz tien shan the tien shan of kyrgyzstan contains multiple moraines and drift from late quaternary glaciations the spatial temporal distribution of the glaciers inferred from the moraines suggests that the main factor controlling glacier advance here was the availability of moisture the dominant modern climatic signatures in northern central asia include orographic thunderstorms in summer cold and dry siberian high pressure cells in winter and westerly cyclonic storms from the north atlantic and eastern mediterranean in spring and fall changes in any of these systems during the late quaternary would have varied precipitation delivery to and glacier growth in the kyrgyz tien shan geomorphic mapping and reconnaissance level 10be cosmic ray exposure dating of moraine sequences in six drainages indicate that there were multiple maximum advances of similar extents and equilibrium line depressions across the range glaciers in the north and east of the kyrgyz tien shan last advanced to their maximum positions during marine oxygen isotope stage mis 5 and again during mis 4 while in the south and west of the range advance occurred during mis 3 in contrast to maritime europe and north america there is no evidence of a major glacial advance during mis 2 glacier advances during mis 2 and since were restricted to the vicinity of modern glaciers allowing the older glacial record to be preserved well