flux and provenance of ice rafted debris in the earliest pleistocene sub polar north atlantic ocean comparable to the last glacial maximum relatively little is known in detail about the locations of the early pleistocene ice sheets responsible for ice rafted debris ird inputs to the sub polar north atlantic ocean during intensification of northern hemisphere glaciation inhg to shed new light on this problem we present the first combined in depth analysis of ird flux and geochemical provenance of individual sand sized ird deposited in the sub polar north atlantic ocean during the earliest large amplitude pleistocene glacial marine isotope stage mis 100 2 52 ma arguably the key glacial during inhg ird provenance is assessed using laser ablation lead pb isotope analyses of single feldspar grains we find that the pb isotope composition 206pb 204pb 207pb 204pb and 208pb 204pb of individual ice rafted 150 m feldspars deposited at dsdp site 611a odp site 981 and iodp site u1308 during mis 100 records a shift from predominantly archaean aged circum north atlantic ocean continental sources during early glacial ice rafting events to dominantly palaeozoic and proterozoic aged sources during full glacial conditions the distribution of feldspars in pb pb space for full glacial mis 100 more closely resembles that documented for feldspars deposited at the centre of the last glacial ird belt at iodp dsdp site u1308 609 during ambient non heinrich event ice rafting episodes of mis 2 23 8 ka than that documented for mis 5d 106 ka comparison of our early pleistocene and last glacial cycle datasets suggests that mis 100 was characterised by abundant iceberg calving from large ice sheets on multiple continents in the high northern latitudes not just on greenland

the sensitivity of the late saalian 140 ka and lgm 21 ka eurasian ice sheets to sea surface conditions this work focuses on the late saalian 140 ka eurasian ice sheets surface mass balance smb sensitivity to changes in sea surface temperatures sst an atmospheric general circulation model agcm forced with two preexisting last glacial maximum lgm 21 ka sst reconstructions is used to compute climate at 140 and 21 ka reference glaciation contrary to the lgm the ablation almost stopped at 140 ka due to the climatic cooling effect from the large ice sheet topography late saalian sst are simulated using an agcm coupled with a mixed layer ocean compared to the lgm these 140 ka sst show an inter hemispheric asymmetry caused by the larger ice albedo feedback cooling climate the resulting late saalian ice sheet smb is smaller due to the extensive simulated sea ice reducing the precipitation in conclusion sst are important for the stability and growth of the late saalian eurasian ice sheet

numerical reconstructions of lgm climate across the eurasian arctic abstract although limits of the eurasian ice sheet at the last glacial maximum lgm are known relatively well from geological evidence the palaeoclimate coexistent with this ice sheet has yet to be identified confidently a simple ice sheet model has been used to determine lgm climate conditions by finding the ice sheet mass balance configuration that permits model results to match with geological data relating to the extent of lgm ice cover these conditions are compared with atmospheric general circulation model agcm calculations of the climate at the lgm which reveal the meteorological conditions associated with the ice sheet mass balance the western margin of scandinavia is characterised by a maritime climate influenced by the nearby warm seasonally sea ice free ocean conditions however further east the warming effect of the north atlantic diminishes and an extreme polar desert climate dominates across the kara sea similar to east antarctica today the lgm climate that we establish is in contrast to many previous reconstructions involving snow laden warm westerly winds originating from the north atlantic affecting the entire eurasian arctic severely cold conditions across the eurasian arctic are compatible with a stable circulation cell over the kara sea that isolates the region climatically and or cold dry westerly winds from the fennoscandian ice sheet that flow across the rest of the eurasian arctic

topography relief and trmm derived rainfall variations along the himalaya 1 along the southern himalayan topographic front the indian summer monsoon modulates erosive processes and rates to investigate the influence of topography and relief on rainfall generation and resultant erosion we processed satellite rainfall amounts for the last 8 years 1998 2005 from the tropical rainfall measurement mission trmm based upon a spatial resolution of 5 5 km for the himalaya we identify 1 the spatial distribution of rainfall and 2 the large scale relationships between topography relief and rainfall locations our results show two distinct rainfall maxima along strike in the himalaya the first outer rainfall peak occurs along the southern margin of the lesser himalaya within a narrow band of mean elevation 0 9 0 4 km and mean relief 1 2 0 2 km the second discontinuous inner band typically occurs along the southern flank of the greater himalaya elevation and relief both 2 1 0 3 km

controls of tor formation cairngorm mountains scotland tors occur in many granitic landscapes and provide opportunities to better understand differential weathering we assess tor formation in the cairngorm mountains scotland by examining correlation

modeling the tor dotted crests bedrock edges and parabolic profiles of high alpine surfaces of the wind river range wyoming abstract broad low curvature surfaces common to many alpine landscapes and particularly well expressed in the laramide ranges of the western usa appear to be roughly in steady state with respect to the current surface processes uniform thin order 1 m regolith covers the crystalline bedrock with the exception of occasional tors at ridgecrests the surfaces are commonly edged by bedrock lips at the tops of cliffs that bound the intervening glacial troughs regolith production is low order 10 m year on bare bedrock and reaches a maximum under tens of centimeters of regolith all of these characteristics may be accounted for with a numerical model that is faithful to the periglacial surface processes presently operating on these surfaces hillslope transport is modeled assuming the dominant process is frost creep transport efficiency depends linearly upon local slope and appropriately vanishes in the absence of regolith frost frequency scales the rate of motion while the ratio of frost penetration depth to regolith thickness dictates the degree to which the process is curtailed by available regolith initial conditions include initial mean slope and bedrock roughness and a uniform regolith cover boundary conditions are imposed by dictating that the edges of the calculation space be lowered at a rate appropriate for glacial incision broad convex surfaces emerge over time scales of order 1 million years all surfaces rapidly decouple from the bounding glacial troughs as the high negative curvature at the edges disallows accumulation of regolith these bedrock edges lower at a few microns per year while the troughs lower at many times this rate as the bedrock edges therefore serve as the effective boundary condition for the remaining surface the surfaces operate independently of both lowering and widening of the glacial troughs for a reasonable set of transport and weathering rates the final steady state landscape is sensitive to the initial condition in particular the steeper the initial landscape the more likely tors are to develop as the high curvature disallows accumulation of regolith these tors in turn limit the lowering rate of the crest and the landscape retains significant local relief low relief initial conditions more likely lead to parabolic surfaces that lack tors that tors are more likely on the crests reflects the high initial curvature at the crest tors on the side slopes are eliminated the present high surfaces in the laramide ranges of the western usa imply operation of periglacial surface processes over millions of years the occasional tors imply a steeper rather than flatter initial landscape the strong decoupling of surfaces from glacial troughs justifies their use as local geomorphic markers that allow calculation of relief production since glacial incision was initiated on the other hand their present low curvature does not require a landscape history in which these surfaces were once joined as an initially widespread erosion surface

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

drainage basin sensitivity to tectonic and climatic forcing implications of a stochastic model for the role of entrainment and erosion thresholds long term average rates of channel erosion and sediment transport depend on the frequency magnitude characteristics of ood ows that exceed an erosion threshold using a poisson model for rainfall and runoff analytical solutions are developed for average rates of stream incision and sediment transport in the presence of such a threshold solutions are derived and numerically tested for three erosion transport formulas the howard kerby shear stress incision model the bridge dominic sediment transport model and a generic shear stress sediment transport model results imply that non linearity resulting from threshold effects can have a rst order impact on topography and patterns of dynamic response to tectonic and climate forcing this non linearity becomes signi cant when fewer than about half of ood events are capable of detaching rock or sediment predicted morphology and uplift gradient scaling is more closely consistent with observations and laboratory experiments than conventional slope linear or shear linear erosion laws these results imply that particle detachment thresholds are not details that can be conveniently ignored in long term landscape evolution models copyright 2004 john wiley sons ltd

n2o record spanning the penultimate deglaciation from the vostok ice core nitrous oxide n2o is an important atmospheric trace gas whose concentration is determined by numerous sources and sinks over the past 200 years n2o has increased by 17 3 due primarily to increased anthropogenic emissions over the last glacial interglacial transition data from ice cores show that n2o increased by 35 this increase may be related to increased terrestrial n2o emissions resulting from a global climate amelioration here i describe a new dry extraction technique for measuring the elemental and isotopic composition of n2o in ice core samples results from a shallow gisp ii ice core spanning the last 200 years provide an estimate for the preanthropogenic n2o concentration of 266 4 ppb in addition 11 ice samples from the last interglacial period show fairly uniform n2o values 269 9 ppb during the penultimate glacial period 131 160 ka n2o concentrations of air trapped in the glacier fluctuated between 190 ppb and 320 ppb while co2 and ch4 concentrations were relatively low and stable two local n2o maxima were observed during the penultimate glacial period that actually exceeded normal interglacial n2o values 265 ppb the maxima were located in portions of the core which exhibit both elevated dust concentrations and elevated bacterial counts the 15n and 18o of n2o in this portion of the vostok core were 15 higher and 12 lower than during the warm eemian period respectively the isotopic data and coincidence between the elevated n2o concentrations and the high bacterial counts may be related to in situ n2o production by bacteria the lower 18o values are consistent with the isotopic composition of n2o produced by in situ nitrification

ice age terrestrial carbon changes revisited n shackleton 1977 first proposed that changes in the marine 13 c record 13 c could be used to infer ice age changes in carbon storage on land the previously published best estimate from the marine record is equivalent to about 490 gt 0 32 13 c however adams et al 1990 utilized a pollen database to estimate a 1350 gt change in carbon storage which would cause a 13 c of about 0 90 the nearly trillion ton difference in estimates amounts to almost half of the total carbon stored on land to address the nature of this discrepancy i have reexamined the terrestrial carbon record based on a new pollen database compiled by r webb and the cooperative holocene mapping project cohmap group i estimate about 750 1050 gt glacial interglacial change in terrestrial carbon storage with the range reflecting uncertainties in carbon storage values for different biomes additional uncertainties apply to rainforest and wetland extent and presence of c4 plants which have a significantly different isotopic signature than c3 plants although some scenarios overlap a new estimate of carbon storage based on the oceanic 13 c record revised to 0 40 and 610 gt most estimates seem to fall outside the envelope of uncertainty in the marine record several possible explanations for this gap involve 1 a missing sink may be involved in land sea carbon exchange e g continental slopes 2 the geochemistry of the exchange process is not understood 3 carbon storage by biome may have changed under ice age boundary conditions or 4 the standard interpretation of whole ocean changes in the marine 13 c record requires reevaluation this latter conclusion receives some support from comparison of the 13 c records for 18 o stages 2 and 6 for the stage 6 glacial the 13 c changes are 50 60 larger than for the stage 2 glacial yet implications of increased aridity are not supported by longterm trends in atmospheric dust loading to summarize the above analysis implies that despite the uncertainties remaining in estimates of terrestrial carbon storage changes a case can be made that our understanding of the transfer process is incomplete and that the eventual explanation may require clarification of factors affecting the marine 13 c record

timescales for dust variability in the greenland ice core project grip ice core in the last 100 000 years the calcium representing dust concentration record of the last 100 000 years from the greenland ice core project grip ice core shows a huge dynamic range factor 100 the relationship between dust concentrations and temperature represented by the oxygen isotope ratio is not a simple one as has often been assumed a rapid alternation factor of 5 10 between low concentrations during the dansgaard oeschger interstadial periods and high levels in colder periods is superimposed on a long term trend encompassing a further factor of 5 10 within climate periods there is only a very weak relationship between ca concentration and temperature previous authors biscaye et al 1997 have suggested that the most likely source for the increased dust is eastern asia for the first time we consider each possible cause of both rapid and slow increases from source to deposition we suggest that to account for the size and rapidity of the fast changes significantly higher wind speed in the source area is required although changes in atmospheric residence time could also play a role for the slower long term variability changes in transport speed or possibly route are probably also involved changes in the size of the source area could give some change on longer time periods the probable importance of changes in source area wind speed almost simultaneous with greenland temperature changes confirms that climatic parameters in high and low latitudes were strongly coupled through the atmosphere during glacial climatic changes this adds to evidence that the atmospheric circulation system underwent almost instantaneous large scale changes during the last glacial period

basins and bedrock spatial variation in 10be erosion rates and increasing relief in the southern rocky mountains usa we used measurements of cosmogenic 10 be in alluvium to estimate erosion rates on a 10 3 10 4 yr time scale for small 0 01 47 km 2 unglaciated basins in northern colorado southern wyoming and adjacent western nebraska western united states basins formed in proterozoic cores of laramide ranges are eroding more slowly 23 7 mm k y 1 n 19 than adjacent basins draining weakly lithified cenozoic sedimentary rocks 75 36 mm k y 1 n 20 erosion rates show a relationship to rock resistance and for granitic rocks to basin slope but not to mean annual precipitation we estimated longer term 10 5 yr time scale erosion rates for the granitic core of the front range by measuring the concentration of 10 be and 26 al produced mainly by muon interactions at depths 1 7 10 m below the surface concentrations imply erosion rates of 9 31 mm k y 1 similar to shorter term erosion rates inferred from alluvial sediment the spatial distribution of erosion rates and stratigraphic evidence imply that relief in the southern rocky mountains increased in the late cenozoic modern relief probably dates from post middle miocene time

mudball surface dust and snowball earth deglaciation 1 recent modeling results have raised doubts about the ability to deglaciate from a global glaciation at atmospheric carbon dioxide levels that are realistic for a neoproterozoic snowball earth here we argue that over the lifetime of a snowball event ice dynamics should lead to the development of a layer of continental and volcanic dust at the ice surface in the tropics that would significantly lower the tropical surface albedo and encourage deglaciation this idea leads to the prediction that clay drapes found on top of neoproterozoic glaciations should be thicker in tropical than extratropical regions we test this idea by running the foam general circulation model gcm with an added tropical dust layer of different sizes and albedos and find that the tropical dust layer causes snowball deglaciation at pco2 0 01 0 1 bar in a reasonable regime of these parameters we find similar though more nuanced results from a limited number of test cases using national center for atmospheric research s cam gcm

rainfall variability in the himalayan orogen and its relevance to erosion processes rainfall is an important driver of erosion processes the mean rainfall rate is often used to account for the erosive impact of a particular climate however for some erosion processes erosion rate is a nonlinear function of rainfall e g due to a threshold for erosion when this is the case it is important to take into account the full distribution of rainfall instead of just the mean in light of this we have characterized the variability of daily rainfall over the himalayan orogen using high spatial and temporal resolution rainfall data sets we find significant variations in rainfall variability over the himalayan orogen with increasing rainfall variability to the west and north of the orogen by taking into account variability of rainfall in addition to mean rainfall rate we find a pattern of rainfall that from a geomorphological perspective is significantly different from mean rainfall rate alone using these findings we argue that short term rainfall variability may help explain observed short and long term erosion rates in the himalayan orogen

simulating arctic climate warmth and icefield retreat in the last interglaciation in the future arctic warming and the melting of polar glaciers will be considerable but the magnitude of both is uncertain we used a global climate model a dynamic ice sheet model and paleoclimatic data to evaluate northern hemisphere high latitude warming and its impact on arctic icefields during the last interglaciation our simulated climate matches paleoclimatic observations of past warming and the combination of physically based climate and ice sheet modeling with ice core constraints indicate that the greenland ice sheet and other circum arctic ice fields likely contributed 2 2 to 3 4 meters of sea level rise during the last interglaciation

influence of oceanic boundary conditions in simulations of antarctic climate and surface mass balance change during the coming century abstract this article reports on high resolution 60 km atmospheric general circulation model simulations of the antarctic climate for the periods 1981 2000 and 2081 2100 the analysis focuses on the surface mass balance change one of the components of the total ice sheet mass balance and its impact on global eustatic sea level contrary to previous simulations in which the authors directly used sea surface boundary conditions produced by a coupled ocean atmosphere model for the last decades of both centuries an anomaly method was applied here in which the present day simulations use observed sea surface conditions while the simulations for the end of the twenty first century use the change in sea surface conditions taken from the coupled simulations superimposed on the present day observations it is shown that the use of observed oceanic boundary conditions clearly improves the simulation of the present day antarctic climate compared to model runs using boundary conditions from a coupled climate

biomarkers in lake van sediments reveal dry conditions in eastern anatolia during 110 000 10 000 years b p lipid biomarkers were analyzed in lake van sediments covering the last 600 ka with a focus on the period between 110 and 10 ka when a broad maximum in pore water salinity as a relict from the past suggests dry conditions the occurrence and distribution of biomarkers indicative for terrestrial plants long chain n alkane c29 haptophyte algae methyl alkenones c37 and halophilic archaea archaeol all point toward a dry climate in lake van region during this time interval the hydrogen isotopic composition of c29 n alkanes dc29 and c37 alkenones dc37 is enriched between mis 4 and mis 2 which is interpreted as a decrease in the regional ratio of precipitation to evaporation similarly the low abundance of the acyclic glycerol dialkyl glycerol tetraether gdgt 0 relative to archaeol quantified by the archaeol and caldarchaeol ecometric ace is assumed to reflect the presence of halophilic euryarchaeota adapted to high salinity water the climate around lake van appears in phase with the yammouneh basin 800 km southwest and lake urmia 250 km southeast of lake van over the last two glacial periods the results highlight the potential of combining ace dc29 and dc37 for reconstructing salinity changes and regional precipitation to evaporation ratio from lake sediments

characterizing potentially induced earthquake rate changes in the brawley seismic zone southern california the brawley seismic zone bsz in the salton trough of southern california has a history of earthquake swarms and geothermal energy exploitation some earthquake rate changes may have been induced by fluid extraction and injection activity at local geothermal fields particularly at the north brawley geothermal field nbgf and at the salton sea geothermal field ssgf we explore this issue by examining earthquake rate changes and interevent distance distributions in these fields in oklahoma and arkansas where considerable wastewater injection occurs increases in background seismicity rate and aftershock productivity and decreases in interevent distance were indicative of fluid injection induced seismicity here we test if similar changes occur that may be associated with fluid injection and extraction in geothermal areas we use stochastic epidemic type aftershock sequence models to detect changes in the underlying seismogenic processes shown by statistically significant changes in the model parameters the most robust model changes in the ssgf roughly occur when large changes in net fluid production occur but a similar correlation is not seen in the nbgf also although both background seismicity rate and aftershock productivity increased for fluid injection induced earthquake rate changes in oklahoma and arkansas the background rate increases significantly in the bsz only roughly corresponding with net fluid production rate increases moreover in both fields the interevent spacing does not change significantly during active energy projects this suggests that although geothermal field activities in a tectonically active region may not significantly change the physics of earthquake interactions earthquake rates may still be driven by fluid injection or extraction rates particularly in the ssgf

far flung moraines exploring the feedback of glacial erosion on the evolution of glacier length abstract over many glacial cycles the glacial erosion of alpine valleys can be sufficient to reduce the length of glaciers in the most recent cycles we document field cases illustrative of this erosional feedback and model the long term evolution of glacier lengths analytically and numerically the general feature we target is a moraine deposited well beyond the last glacial maximum lgm limit which we refer to as a far flung moraine firstly we assemble published observations to illustrate that far flung moraines are documented around the world the observations suggest that the downvalley distance to such far flung moraines can exceed the distance to lgm moraines by up to twofold secondly we address the problem analytically making several simplifying assumptions to demonstrate that glacier length scales linearly with erosion depth finally we employ a numerical model to test the analytical solution this 1d depth integrated flowline model includes i a depth averaged longitudinal coupling stress approximation ii prescribed winter and summer surface mass balance profiles iii evolving ice temperature calculated via the conventional heat equation and iv glacier sliding velocity parameterized as a function of basal ice temperature and spatially and temporally variable prescribed flotation fraction the simulated alpine landscape is modified through the competing processes of glacier erosion which is dependent on glacier sliding velocity and prescribed bedrock erodibility and prescribed uplift rate the climate controlling surface mass balance is prescribed by time series of air temperature and snowfall approximated by the sum of two sinusoidal cycles the recurrence statistics of these prescribed climate drivers closely match those of the marine isotopic record hence the prescribed climate drivers faithfully mimic observed long term climate drivers consistent with earlier landscape evolution studies we find that the primary effect of repeated glaciations is to flatten a valley floor and steepen its headwall effectively cutting a longitudinal notch in a fluvial valley profile analytical and numerical model results also demonstrate that far flung moraines are an inevitable consequence of repeated glaciations glaciers in tectonically inactive regions can sufficiently erode their valleys so that the earliest glaciations leave moraines many kilometers down valley from moraines left by the latest glaciations despite similar climates this suggests that a different landscape rather than a different climate is capable of explaining the early glacier extents as a corollary the long term drift toward reduced glacier length favors the survival of early moraines in the face of later glacial advances finally rock uplift can defeat this erosional feedback while rock subsidence enhances the feedback

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

paleohydrologic bounds and extreme flood frequency of the upper arkansas river colorado usa article i nfo article history the upper arkansas river basin has experienced notable large floods including the event of 2 6 june 1921 that devastated the city of pueblo colorado we investigated flood and paleoflood hydrology at strategic sites to determine the frequency and geographic extent of extreme floods within the basin for a dam safety application streamgage historical and paleoflood data were utilized to develop frequency curves at sites near salida cotopaxi parkdale and pueblo soil stratigraphic descriptions radiocarbon dating and hydraulic modeling were used to estimate paleoflood nonexceedance bounds at the four sites which ranged from 400 to 2200 ybp for late holocene surfaces to late pleistocene surfaces near cotopaxi peak flow data are from lower magnitude snowmelt runoff in may and june in the upper basin and from high magnitude rainfall runoff from june to august in the lower basin flood frequency curves reflect this transition near parkdale from snowmelt to extreme rainfall runoff for similar return periods paleoflood peak discharges increase from about 480 m 3 s upstream at loma linda to about 4250 m 3 s downstream near pueblo this increase is attributed to the larger rainfall component derived from lower elevations between loma linda and pueblo return periods for design floods at pueblo dam exceeded 10 000 years based on paleoflood frequency curve extrapolations

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

evaluating the timing of former glacier expansions in the tian shan a key step towards robust spatial correlations the timing of past glaciation across the tian shan provides a proxy for past climate change in this critical area correlating glacial stages across the region is difficult but cosmogenic exposure

paleohydrologic techniques used to define the spatial occurrence of floods abstract defining the cause and spatial characteristics of floods may be difficult because of limited streamflow and precipitation data new paleohydrologic techniques that incorporate information from geomorphic sedimentologic and botanic studies provide important supplemental information to define homogeneous hydrologic regions these techniques also help to define the spatial structure of rainstorms and floods and improve regional flood frequency estimates the occurrence and the non occurrence of paleohydrologic evidence of floods such as flood bars alluvial fans and tree scars provide valuable hydrologic information the paleohydrologic research to define the spatial characteristics of floods improves the understanding of flood hydrometeorology this research was used to define the areal extent and contributing drainage area of flash floods in colorado also paleohydrologic evidence was used to define the spatial boundaries for the colorado foothills region in terms of the meteorologic cause of flooding and elevation in general above 2300 m peak flows are caused by snowmelt below 2300 m peak flows primarily are caused by rainfall the foothills region has an upper elevation limit of about 2300 m and a lower elevation limit of about 1500 m regional flood frequency estimates that incorporate the paleohydrologic information indicate that the big thompson river flash flood of 1976 had a recurrence interval of approximately 10 000 years this contrasts markedly with 100 to 300 years determined by using conventional hydrologic analyses flood discharge estimates based on rainfall runoff methods in the foothills of colorado result in larger values than those estimated with regional flood frequency relations which are based on long term streamflow data preliminary hydrologic and paleohydrologic research indicates that intense rainfall does not occur at higher elevations in other rocky mountain states and that the highest elevations for rainfall producing floods vary by latitude the study results have implications for floodplain management and design of hydraulic structures in the mountains of colorado and other rocky mountain states

hillslope response to tectonic forcing in threshold landscapes hillslopes are thought to poorly record tectonic signals in threshold landscapes numerous previous studies of steep landscapes suggest that large changes in long term erosion rate lead to little change in mean hillslope angle measured at coarse resolution new lidar derived topography data enables a finer examination of threshold hillslopes here we quantify hillslope response to tectonic forcing in a threshold landscape to do so we use an extensive cosmogenic beryllium 10 10 be based dataset of catchment averaged erosion rates combined with a 500 km 2 lidar derived 1 m digital elevation model to exploit a gradient of tectonic forcing and topographic relief in the san gabriel mountains california we also calibrate a new method of quantifying rock exposure from lidar derived slope measurements using high resolution panoramic photographs two distinct trends in hillslope behavior emerge below catchment mean slopes of 30 modal slopes increase with mean slopes slope distribution skewness decreases with increasing mean slope and bedrock exposure is limited above mean slopes of 30 our rock exposure index increases strongly with mean slope and the prevalence of angle of repose debris wedges keeps modal slopes near 37 resulting in a positive relationship between slope distribution skewness and mean slope we find that both mean slopes and rock exposure increase with erosion rate up to 1 mm a in contrast to previous work based on coarser topographic data we also find that as erosion rates increase the extent of the fluvial network decreases while colluvial channels extend downstream keeping the total drainage density similar across the range our results reveal important textural details lost in 10 or 30 m resolution digital elevation models of steep landscapes and highlight the need for process based studies of threshold hillslopes and colluvial channels

sensitivity of the late saalian 140 kyrs bp and lgm 21 kyrs bp eurasian ice sheet surface mass balance to vegetation feedbacks this work uses an atmospheric general circulation model agcm asynchronously coupled to an equilibrium vegetation model to investigate whether vegetation feedbacks could be one of the reasons why

a direct link between the china loess and marine δ 18 o records aeolian flux to the north pacific most studies of quaternary climates conducted during the past 150 years have focused on glacial sequences and for the past 25 years marine sediments have provided significant further understanding of glacial and interglacial palaeoclimates an important goal of palaeoclimatology however to link the well known detailed continental records to marine records of similar resolution has yet to be realized the classic loess sequences of china provide an apparently continuous record of continental climate over the past 2 4 million years1 2 the oxygen isotope 18o timescale developed from the marine record3 gives us a global chrono stratigraphy of late pleistocene climates previously it has been suggested in studies of the aeolian component in pelagic sediments that it may be possible to link these two records directly by finding a suitable core from the north west pacific downwind from china4 5 here we report the results of such an effort for core v21 146 fig 1 and tie the last 500 000 years of the chinese loess soil sequence directly to the 18o timescale and in so doing refine the dating of regional loess and soil horizons

hillslope and channel evolution in a marine terraced landscape santa cruz california a flight of marine terraces along the central california coastline provides a unique setting for the study of topographic evolution wavecut platforms mantled by 2 6 m of marine terrace cover deposits are separated by 10 50 m tall decaying sea cliffs paleocliff edges become more rounded with age yet the details of the profiles and frequent bedrock exposure on the upper slopes imply weathering limited transport five bedrock stream channels etched through the marine terrace sequence display one to three distinct convexities in their longitudinal profiles detailed hand level surveys of the hillslopes and of the stream channel longitudinal profiles constrain hillslope evolution and channel incision components of a numerical model of landscape evolution we account for regolith production as a function of regolith depth in accord with the field observation that hillslope processes are presently dominated by the activities of burrowing rodents the transport process is taken to be diffusive stream incision is assumed to be controlled by stream power for which we use the surrogate of local drainage area slope product best fits of the numerical model to field data imply hillslope diffusivity is 10 m2 kyr 1 regolith production rate on bare bedrock is 0 3 m kyr 1 and falls off rapidly with regolith cover and the constant controlling the efficiency of stream incision is 5 to 7 10 7m 1 kyr1

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

possible role of atmosphere biosphere interactions in triggering the last glaciation we coupled a global biome model iteratively with an atmospheric general circulation model to study the possible role of vegetation in the climate system at the time of glacial inception 115 000 years ago orbital forcing alone was not sufficient to initiate glaciation when other components of the climate system were kept as present atmospheric composition oceans biosphere and cryosphere summers were however cold enough to induce major vegetation shifts in high northern latitudes southward migration of the boreal forest tundra limit helped to create favourable conditions for continental ice sheet growth with increasing snow depth and duration in labrador arctic canada and northern western fennoscandia these results support a role for biogeophysical feedback in initiating glaciations

quaternary glaciations in the verkhoyansk mountains northeast siberia geomorphological mapping revealed five terminal moraines in the central verkhoyansk mountains the youngest terminal moraine i was formed at least 50 ka ago according to new irsl infrared optically stimulated luminescence dates older terminal moraines in the western foreland of the mountains are much more extensive in size although the smallest of these older moraines moraine ii has not been dated moraine iii is 80 to 90 ka moraine iv is 100 to 120 ka and the outermost moraine v was deposited around 135 ka this glaciation history is comparable to that of the barents and kara ice sheet and partly to that of the polar ural mountains regarding the timing of the glaciations however no glaciation occurred during the global last glacial maximum mis 2 based on cirque orientation and different glacier extent on the eastern and western flanks of the verkhoyansk mountains local glaciations are mainly controlled by moisture transport from the west across the eurasian continent thus glaciations in the verkhoyansk mountains not only express local climate changes but also are strongly influenced by the extent of the eurasian ice sheets

influence of precipitation phase on the form of mountain ranges observations of precipitation fall speeds and precipitation patterns suggest that precipitation phase rain versus snow is a significant control on the relationship between precipitation patterns and topography due to the potential for increased downwind advection of snow relative to rain a coupled model of orographic precipitation and surface erosion shows that for a range of climate variables steady state precipitation patterns vary from nearly uniform and maximizing over the highest topography to highly spatially variable closely coupled to topography and reaching a maximum on low slopes precipitation patterns are a first order control on modeled range scale and ridge valley scale relief channel concavity and the position of the drainage divide an association between cool climates spatially uniform precipitation and efficient erosion of high topography is indicated the importance of precipitation phase to the evolution of precipitation patterns and topography further demonstrates the fundamental importance of the coupled climate erosion and tectonic system in the evolution of mountain topography

diagenetic variation in the oregon coast range implications for rock strength soil production hillslope form and landscape evolution the mechanisms by which lithology modulates geomorphic processes are poorly known in the oregon coast range ocr rhythmically bedded sandstones of the eocene tyee formation underlie steep soil mantled hillslopes with relatively uniform ridge valley spacing these characteristic landforms are perturbed where diagenetic variations manifest as resistant cliffs here we use petrology rock mechanics and lidar to characterize grain scale variations in rock properties and their influence on rock strength hillslope processes and landscape morphology in two adjacent watersheds petrographic analyses suggest that a suite of diagenetic products in the resistant bedrock account for a 2 5 times increase in tensile strength relative to typical tyee bedrock our reference catchment exhibits negligible resistant outcrops and consistent hillslope gradients and longitudinal valley profiles by contrast the adjacent catchment teems with resistant 1 to 10 m thick noncontiguous sandstone beds that form hanging valleys with gentle upstream hillslopes and anomalously narrow valleys mechanical and topographic analyses suggest that the low fracture density characteristic of these resistant beds may render them relatively impervious to comminution by tree root activity the dominant ocr soil production mechanism based on both hillslope gradient and hilltop curvature erosion models we estimate that hillslopes perched above resistant beds erode at approximately half the pace of hillslopes unencumbered by downstream knickpoints the diagenetic variations likely influence relief at the watershed scale depositional position and diagenetic processes appear to control the occurrence of resistant beds providing a framework to quantify how seemingly subtle variations in rock properties can impose first order controls on landscape form and evolution

modeling the water masses of the atlantic ocean at the last glacial maximum 1 we produced gridded monthly sea surface boundary conditions for the atlantic ocean at the last glacial maximum lgm based on the sea surface temperature reconstruction of the glamap project we used an ocean general circulation model ogcm subject to these sea surface boundary conditions and a corresponding wind stress field from an atmospheric general circulation model to study the differences in the distribution of the main water masses between the lgm and the present our global ogcm is characterized by high vertical resolution low vertical diffusion and isopycnal mixing and hence allows for a realistic representation of the hydrology and circulation of the modern atlantic ocean according to a series of lgm experiments with an increasing sea surface salinity anomaly in the weddell sea the ventilated thermocline was colder than today by 2 3 c in the north atlantic ocean and in the experiment with the largest anomaly 1 0 beyond the global anomaly by 4 5 c in the south atlantic ocean its depth was reduced by 50 m on average most notably in the tropics in the north atlantic ocean the outcrop locations of the thermocline isopycnal surfaces migrated southward by 5 10 and the ventilation increased in the south atlantic ocean the mixed layer and thermocline water masses were dominated by cold water originating from drake passage and the import of warm water from the indian ocean was reduced to about 4 sv or 40 of its modern value antarctic intermediate water was colder by 3 4 c and could be traced as far as 10 n the meridional overturning rates of north atlantic deep water nadw and antarctic bottom water aabw in the atlantic ocean were similar to those of the present day experiment 9 10 sv and 4 sv respectively however nadw cooled by 2 5 c and aabw by 1 c aabw was near the freezing point of seawater at the surface and the saltiest water mass in the atlantic ocean even saltier than nadw we show that the differences between the lgm and the present day experiments can be traced back to the changes in the subpolar and interhemispheric sea surface density gradients

arctic ocean deep sea record of northern eurasian ice sheet history the sediment composition of deep sea cores from the central arctic ocean the fram strait and the yermak plateau was analyzed for several parameters to reconstruct the history of marine paleoenvironment and terrestrial glaciation in the last 200 000 years layers with high amounts of coarse terrigenous ice rafted debris ird and often high contents of smectite were deposited during extensive glaciations in northern eurasia when ice sheets reached the northern continental margins of the barents and kara seas and discharged icebergs into the arctic ocean intercalated layers with relatively low ird and smectite contents but abundant planktic foraminifers in the coarse fraction were deposited during periods of atlantic water inflow to the arctic ocean and seasonally open waters leads in a sea ice cover with only few icebergs in the arctic ocean high ird contents in the sediments reflect the presence of ice sheets on the kara and barents seas shelves and the hinterland during the entire oxygen isotope stage 6 ca 190 130 ka in substage 5b ca 90 80 ka at the stage boundary 5 4 around 75 ka and in late stage 4 early stage 3 ca 65 50 ka these results are in excellent correlation with those from recent field work in northern scandinavia european russia siberia and on the shelves relatively low amounts of ird in central arctic ocean sediments from the late weichselian glacial maximum ca 24 18 ka correlate well with the recent reconstruction of a very limited eastern ice sheet extension during this time oxygen and carbon isotope records of planktic foraminifers from the analyzed sediment cores show a number of prominent excursions which can be interpreted as evidence for freshwater events in the arctic ocean the synchroneity of freshwater events and ird input suggests a common source strongest events were associated with deglaciations of the barents and kara seas after the ice sheets had blocked the outflow of large rivers for several millennia the outflow of freshwater from large ice dammed lakes occurred at ca 130 80 75 and 52 ka freshwater events in the central arctic ocean during the last deglaciation ca 18 ka were relatively small compared to the previous events this indicates that during most of the late weichselian glacial maximum a river outflow from northern siberia to the arctic ocean was possible atlantic water inflow to the arctic ocean and seasonally open waters in the ice leads occurred during the interglacials ofoxygen isotope stage 1 and substage 5e during several interstadials stage 3 substages 5a and 5c and to a lesser degree within stadials and glacials stages 2 4 and 6 with the exception ofthe interglacials these periods were times ofstrong ice growth on the continents as revealed by terrestrial data the coincidence suggests that open waters in the arctic ocean and the nordic seas were an important moisture source in addition to more southerly sources which fostered the growth of ice sheets on northern eurasia

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

enhanced ice sheet growth in eurasia owing to adjacent ice dammed lakes large proglacial lakes cool regional summer climate because of their large heat capacity and have been shown to modify precipitation through mesoscale atmospheric feedbacks as in the case of lake agassiz 1 several large ice dammed lakes with a combined area twice that of the caspian sea were formed in northern eurasia about 90 000 years ago during the last glacial period when an ice sheet centred over the barents and kara seas 2 blocked the large northbound russian rivers 3 here we present high resolution simulations with an atmospheric general circulation model that explicitly simulates the surface mass balance of the ice sheet we show that the main influence of the eurasian proglacial lakes was a significant reduction of ice sheet melting at the southern margin of the barents kara ice sheet through strong regional summer cooling over large parts of russia in our simulations the summer melt reduction clearly outweighs lake induced decreases in moisture and hence snowfall such as has been reported earlier for lake agassiz1 we conclude that the summer cooling mechanism from proglacial lakes accelerated ice sheet growth and delayed ice sheet decay in eurasia and probably also in north america

climate change and arctic ecosystems 1 vegetation changes north of 55 n between the last glacial maximum mid holocene and present a unified scheme to assign pollen samples to vegetation types was used to reconstruct vegetation patterns north of 55 n at the last glacial maximum lgm and mid holocene 6000 years b p the pollen data set assembled for this purpose represents a comprehensive compilation based on the work of many projects and research groups five tundra types cushion forb tundra graminoid and forb tundra prostrate dwarf shrub tundra erect dwarf shrub tundra and low and high shrub tundra were distinguished and mapped on the basis of modern pollen surface samples the tundra forest boundary and the distributions of boreal and temperate forest types today were realistically reconstructed during the mid holocene the tundra forest boundary was north of its present position in some regions but the pattern of this shift was strongly asymmetrical around the pole with the largest northward shift in central siberia 200 km little change in beringia and a southward shift in keewatin and labrador 200 km low and high shrub tundra extended farther north than today at the lgm forests were absent from high latitudes graminoid and forb tundra abutted on temperate steppe in northwestern eurasia while prostrate dwarf shrub erect dwarf shrub and graminoid and forb tundra formed a mosaic in beringia graminoid and forb tundra is restricted today and does not form a large continuous biome but the pollen data show that it was far more extensive at the lgm while low and high shrub tundra were greatly reduced illustrating the potential for climate change to dramatically alter the relative areas occupied by different vegetation types

exhumation by debris flows in the 2013 colorado front range storm the relative importance of extreme events in the long term exhumation of landscapes is difficult to determine the degree to which modern records capture long term mean process rates is therefore commonly unknown in september 2013 a massive precipitation event in the front range of colorado usa triggered over 1100 landslides and debris flows in a historically sedate landscape here we employ topographic differencing utilizing repeat aerial lidar to quantify net sediment transport volumes in 120 of these mass movements within an area of 102 km 2 west of boulder colorado comparing our results against published long term erosion rates we find that these mass movements evacuated the equivalent of hundreds to thousands of years of hillslope weathering products we conclude that 1 rare debris flows perform the majority of sediment transport and channel erosion within steep channels along the eastern edge of the front range potentially explaining discrepancies between modern sediment yields and long term erosion rates in such settings and 2 the high spatial density of debris flows along the corridors bounding steep canyons suggests that the landscape switches to debris flow dominance as knickpoints pass headward along the canyons

the siberian loess record and its significance for reconstruction of pleistocene climate change in north central asia abstract the siberian loess represents the most significant terrestrial proxy record of quaternary climatic history in northern asia loess is extensive in southern siberia between the irtysh basin in the west and the angara basin in the east palaeoenvironmental multi proxy data magnetic susceptibility ms grain size caco 3 toc pollen etc from high resolution loess palaeosol sections provide evidence for a strongly fluctuating climatic sequence in north central asia during the late quaternary displaying the globally diagnostic sequences found in the deep sea oxygen isotope records ms provides the most continuous and detailed record encompassing the last two interglacial glacial cycles in loess sections in the minusinsk basin yenisei area and on the northern altai plains evidence for periodic atmospheric shifts is provided by gradual changes in the main vegetation zones with parkland steppe and mixed taiga during warm interglacial interstadial stages being replaced by boreal tundra forest and arid periglacial tundra steppe during stadials climatic pulses from warm intervals to cold are recorded by incipient forest steppe tundra gleysols the occurrence of the highest sediment accumulation rates in glacial stages ois 4 and ois 2 in the southern plains and depressions indicates that the most intensive aeolian dust deposition followed the glacial maxima with the most recent interval dated to ca 19 15 ka bp because of its zonal distribution and pronounced climatic continentality the siberian loess region represents an important data source for reconstructing past climates in the northern hemisphere it provides a key to the correlation of other loess regions within the west east eurasian continental zone

mass balance and equilibrium line altitudes of glaciers in high mountain environments abstract the mass balance characteristics of glaciers in high mountain environments complicate the relationship between glacier equilibrium line altitudes elas and climatic variables such as precipitation and air temperature therefore methods of ela reconstruction employed in low relief environments are commonly not applicable in high mountains or require some modification we review the concept of the ela with reference to the mass balance of a range of glacier types found in high mountain regions we examine the applicability of several commonly used methods of ela reconstruction for different glacier types and propose some general principles to guide the choice of appropriate methods

toward the snowball earth deglaciation the current state of knowledge suggests that the neoproterozoic snowball earth is far from deglaciation even at 0 2 bars of co2 since understanding the termination of the fully ice covered state is essential to sustain or not the snowball earth theory we used an atmospheric general climate model agcm to explore some key factors which could induce deglaciation after testing the models sensitivity to their parameterizations of clouds co2 and snow we investigated the warming effect caused by a dusty surface associated with ash release during a mega volcanic eruption we found that the snow aging process its dirtiness and the ash deposition on the snow free ice are key factors for deglaciation our modelling study suggests that under a co2 enriched atmosphere a dusty snowball earth could reach the deglaciation threshold

representing glaciers in a regional climate model a glacier parameterization scheme has been developed and implemented into the regional climate model remo the new scheme interactively simulates the mass balance as well as changes of the areal extent of glaciers on a subgrid scale the temporal evolution and the general magnitude of the simulated glacier mass balance in the european alps are in good accordance with observations for the period 1958 1980 but the strong mass loss towards the end of the twentieth century is systematically underestimated the simulated decrease of glacier area in the alps between 1958 and 2003 ranges from 17 1 to 23 6 the results indicate that observed glacier mass balances can be approximately reproduced within a regional climate model based on simplified concepts of glacier climate interaction however realistic results can only be achieved by explicitly accounting for the subgrid variability of atmospheric parameters within a climate model grid box

equatorward shift of the subarctic boundary in the northwestern pacific during the last deglaciation 1 we have generated a high resolution record of alkenone sea surface temperature sst between 10 24 ka from core md01 2421 off central japan in the northwestern pacific the cooling by 5 c from 21 ka to 12 8 ka implies the equatorward shift of the subarctic boundary in the northwestern pacific by 2 8 in latitude this shift was a result of the stronger summer okhotsk high the okhotsk high was likely enhanced by the combined effects of el nino like conditions in the tropical pacific and the heating of the land surface of northeastern siberia

regolith thickness instability and the formation of tors in arid environments 1 we present model results suggesting that a physical erosion bedrock weathering feedback is responsible for the development of isolated bedrock knobs tors inselbergs that often punctuate otherwise smooth pediments of homogeneous basement lithology tors and larger more heavily jointed and morphologically complex exposures inselbergs may arise as a consequence of fluctuations in rainfall and sediment transport conditions combined with a bedrock weathering mechanism that depends on regolith thickness hydrogeochemical considerations and field observations in arid granitic environments suggest that the relationship between weathering rate and regolith thickness exhibits a maximum for a finite thickness of cover we have encapsulated this simple erosion weathering feedback in a numerical model simulating arid semiarid landscape evolution that produces low sloping pediments punctuated by tors tors form during periods of higher effective moisture resulting in local base level incision and regolith thinning on pediments invoking a transition in which mantled surfaces lower at rates exceeding the bare bedrock weathering rate this condition favors the emergence and growth of tors in areas covered by regolith thickness less than a threshold value subsequent shifts in climate or local base level that restore sediment surface lowering rates less than the bare bedrock weathering rate will lead to a progressive decrease in tor height and ultimately their disappearance thus according to this model tors in arid environments represent possibly transient features related to fluctuations in climate or local transport conditions rather than palimpsests of an ancient landscape derived from differential subsurface weathering followed by regolith stripping

global regional and local scale factors determining glaciation extent in eastern siberia over the last 140 000 years the aim of this work is to evaluate the effect of variations of greenhouse gas concentrations orbital parameters sea surface conditions vegetation and dust deposition on the extent of east siberian mountain glaciations during the late quaternary an atmosphere only general circulation model is used in a series of 16 sensitivity tests at high spatial resolution over the region of interest to systematically evaluate the relative importance of these different forcing parameters no attempt was made to reproduce in detail the history of late quaternary mountain glaciations in east siberia because given a the temporal and spatial scarcity of available evidence of mountain glaciations in this region and b the large uncertainties concerning the boundary conditions to be prescribed in this model such an exercise must necessarily remain incomplete and partially inconclusive the results of this study suggest that moisture delivery from the atlantic is an important factor determining mountain glacier mass balance in eastern siberia and is very sensitive to the geometry of the west eurasian ice sheet this means that variable moisture blocking by the west eurasian ice sheet during the weichselian is the most important single factor explaining the opposite history of glacier and ice sheet extent in west and east eurasia during the weichselian this work confirms earlier results showing that the large 140 kyr bp west eurasian ice sheet caused regional scale cooling extending towards eastern eurasia nevertheless the simulated response of the regional summer temperature and thus glacier extent because of the strong dependency of glacier mass balance of summer melt rates is to a very large extent directly determined by insolation for the early weichselian this leads to a clear maximum of local glacier extent at 70 kyr bp which is in line with the variations of top of the atmosphere insolation on orbital time scales but to some degree at odds with geological evidence which suggests larger glacier extent at 115 and 90 kyr bp than at 70 kyr bp through snow feedbacks the effects of changes in the prescribed vegetation distribution and dust deposition rate are also substantial in summary it appears that the broad features of late quaternary glaciation history in eastern eurasia can be understood in terms of known forcings

ice free glacial northern asia due to dust deposition on snow during the last glacial maximum lgm 21 kyr bp no large ice sheets were present in northern asia while northern europe and north america except alaska were heavily glaciated we use a general circulation model with high regional resolution and a new parameterization of snow albedo to show that the ice free conditions in northern asia during the lgm are favoured by strong glacial dust deposition on the seasonal snow cover our climate model simulations indicate that mineral dust deposition on the snow surface leads to low snow albedo during the melt season this in turn caused enhanced snow melt and therefore favoured snow free peak summer conditions over almost the entire asian continent during the lgm whereas perennial snow cover is simulated over a large part of eastern siberia when glacial dust deposition is not taken into account

new perspectives on beringian quaternary paleogeography stratigraphy and glacial history abstract aspects of the paleogeography stratigraphy and glacial history of beringia have been greatly revised over the past 15 20 yr access to north east russia in particular has provided the opportunity to evaluate the beringia landscape as a contiguous subcontinent during the quaternary for the first time new research has made clearer the connection between tectonic forces and the submergence of the bering strait during the middle pliocene revisions in the regional stratigraphy of glacial and interglacial deposits in northwest alaska and northeast russia provide a new foundation for assessing the causes for differences in glacial ice extent through time the consensus of all field workers verifies that glacial ice throughout most of beringia was of very limited extent during the last glacial maximum the onset of regional glaciation during the waning stages of the last interglaciation is clearly out of phase with glaciation at lower latitudes despite the lack of much glacial activity during the early holocene alaska contains a rich record of late holocene glacial response to neoglacial cooling changes in the holocene environment of beringia likely had a profound affect on early inhabitants the curiosity driven vision and spirit of both david hopkins and the late troy pewe have had a profound influence on arctic paleoenvironmental research

late quaternary glaciations in northeastern russia a summary of the extent and chronology of quaternary glaciations in ne russia is presented in this paper the complex timing and style of glaciations include asynchronous development of alpine glaciers in the western and eastern part of the area while in the eastern part of ne russia well preserved moraines have been dated to the global last glacial maximum 18 24 ka in the westernmost part of the area no glacial advance took place at this time in general glacial advances were more extensive earlier rather than later in the last glacial cycle although only a handful of studies with reliable absolute ages in the vast area of ne russia exist it is clear that the number of advances throughout the region varies variable glacial response to global climate patterns is attributable to contrasting sources of precipitation an atlantic moisture source dominates in the western part of ne russia while a pacific source influences the eastern part of the region the glacial advances in the interior of ne russia are largely unexplored and further research is needed in order to understand quaternary climate change in the region copyright 2008 john wiley sons ltd

role of orbitally induced changes in tundra area in the onset of glaciation the link between glacial interglacial cycles and changes in insolation due to variations in the earth s orbital parameters is well established1 4 but of the attempts to simulate incipient glaciation using three dimensional general circulation models gcms driven by orbital forcing alone5 10 only one10 has been successful gcm experiments7 11 show that reduced summer insolation 115 000 years ago during an interglacial to glacial climate shift produces sufficient high latitude cooling to cause expansion of tundra at the expense of boreal forest11 which in turn can induce more cooling11 14 here we show using a global climate model that the increase in surface albedo under snow covered conditions that results from a biome model estimate11 of tundra expansion 115 000 years ago is sufficient to induce glaciation over extreme northeastern canada if the additional cooling from this estimated tundra expansion induces further expansion then widespread glaciation occurs at latitudes above 65 n these results suggest that the climate feedback from high latitude tundra expansion might have contributed to the onset of the most recent glaciation

early pleistocene glacial cycles and the integrated summer insolation forcing long term variations in northern hemisphere summer insolation are generally thought to control glaciation but the intensity of summer insolation is primarily controlled by 20 000 year cycles in the precession of the equinoxes whereas early pleistocene glacial cycles occur at 40 000 year intervals matching the period of changes in earth s obliquity the resolution of this 40 000 year problem is that glaciers are sensitive to insolation integrated over the duration of the summer the integrated summer insolation is primarily controlled by obliquity and not precession because by kepler s second law the duration of the summer is inversely proportional to earth s distance from the sun

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

palaeoglacial and palaeoclimatic conditions in the nw pacific as revealed by a morphometric analysis of cirques upon the kamchatka peninsula abstract the distribution of glacial cirques upon the kamchatka peninsula far eastern russia is systematically mapped from satellite images and digital elevation model data a total of 3758 cirques are identified 238 of which are occupied by active glaciers the morphometry of the remaining 3520 cirques is analysed these cirques are found to show a very strong n bias in their azimuth orientation likely resulting from aspect related variations in insolation the strength of this n bias is considered to indicate that former glaciation upon the peninsula was often marginal and mainly of cirque type with peaks extending little above regional equilibrium line altitudes this is supported by the fact that s and se facing cirques are the highest in the dataset suggesting that glacier cover was rarely sufficient to allow s and se facing glaciers to develop at low altitudes the strength of these azimuth related variations in cirque altitude is thought to reflect comparatively cloud free conditions during former periods of glaciation it is suggested that these characteristics of marginal glaciation and comparatively cloud free conditions reflect the region s former aridity which was likely intensified at the global last glacial maximum and during earlier periods of ice advance as a result of the development of negative pressure anomalies over the north pacific driven by the growth of the laurentide ice sheet combined with other factors including an increase in the extent and duration of sea ice a reduction in global sea levels cooler sea surface temperatures and the localised growth of mountain glaciers there is published evidence to suggest extensive glaciation of the kamchatka peninsula at times during the late quaternary yet the data presented here appear to suggest that such phases were comparatively short lived and that smaller cirque type glaciers were generally more characteristic of the period

late weichselian ice sheets in arctic and pacific siberia abstract interpretation of space images coupled with field data on glacial geomorphology and glacial geology of northern eurasia have provided compelling evidence for a continuous late weichselian ice sheet covering the entire arctic margin of the continent in addition to the scandinavian ice sheet three ice sheets of the same order the karan east siberian and beringian are identified within the major eurasian ice sheet also there is evidence and other considerations suggesting a former ice sheet in the sea of okhotsk ice spreading centers of the ice sheets were situated on the continental shelves off the siberian coasts thus we can term the ice sheets siberian so far the conventional stratigraphic approach to the problem of siberian glaciation has proven fruitless and yielded nothing but uncertainty while geomorphological studies have discovered a wealth of glacial landforms in arctic siberia it was these landforms and their spacing that made the existence of former siberian ice sheets evident the east siberian ice sheet rested on the shelves of the eastern laptev and east siberian seas and its flow was directed radially including up the yana and indigirka rivers the beringian ice sheet was grounded on the chukchi bering and beaufort sea shelves overriding the chukchi and seward peninsulas from the north and flowing through the bering strait it was continued by a thick floating ice shelf buttressed by the submarine aleutian commander ridge the okhotsk ice sheet was grounded on the okhotsk shelf specific gemorphic signatures of marine ice sheets the glacially cut corners have been identified on all promontories jutting out into the bering and okhotsk seas the beringian and okhotsk ice sheets are consistent with the results of deep sea drilling in the adjacent north pacific during leg 145 of d v joides resolution

late quaternary glaciations in far ne russia combining moraines topography and chronology to assess regional and global glaciation synchrony during various periods of late quaternary glaciation small ice sheets caps fields and valley glaciers occupied the mountains and uplands of far ne russia including the verkhoyansk suntar khayata and chersky mountains the kolyma anyuy and koryak highlands and much of the kamchatka and chukchi peninsulas here the margins of former glaciers across this region are constrained through the comprehensive mapping of moraines from remote sensing data landsat 7 etm satellite images aster global digital elevation model gdem2 and viewfinder panorama dem data a total of 8414 moraines are mapped and this record is integrated with a series of published age estimates n 25 considered to chronologically constrain former ice margin positions geomorphological and chronological data are compiled in a geographic information system gis to produce best estimate reconstructions of ice extent during the global last glacial maximum glgm and to a lesser degree during earlier phases of glaciation the data reveal that much of far ne russia 1 092 427 km 2 preserves a glaciated landscape i e is bounded by moraines but there is no evidence of former ice masses having extended more than 270 km beyond mountain centres suggesting that during the late quaternary the region has not been occupied by extensive ice sheets during the glgm specifically glaciers occupied 253 000 km 2 and rarely extended more than 50 km in length during earlier pre glgm periods glaciers were more extensive though the timing of former glaciation and the maximum quaternary extent appears to have been asynchronous across the region and out of phase with ice extent maxima elsewhere in the northern hemisphere this glacial history is partly explained through consideration of climatic forcing particularly moisture availability solar insolation and albedo though topographic controls upon the former extent and dynamics of glaciers are also considered as are topographic controls upon moraine deposition and preservation ultimately our ability to understand the glacial and climatic history of this region is restricted when the geomorphological record alone is considered particularly as directly dated glacial deposits are few and topographic and climatic controls upon the moraine record are difficult to distinguish 2012 elsevier ltd