spatial and temporal evolution of pine island glacier thinning 1995 2006 we use ers 2 and envisat satellite radar altimetry to examine spatial and temporal changes in the rate of thinning of the pine island glacier west antarctica during the period 1995 to 2006 we show that the pattern of thinning has both accelerated and spread inland to encompass tributaries flowing into the central trunk of the glacier within the 5 400 km 2 central trunk the average rate of volume loss quadrupled from 2 6 0 3 km 3 yr 1 in 1995 to 10 1 0 3 km 3 yr 1 in 2006 the region of lightly grounded ice at the glacier terminus is extending upstream and the changes inland are consistent with the effects of a prolonged disturbance to the ice flow such as the effects of ocean driven melting if the acceleration continues at its present rate the main trunk of pig will be afloat within some 100 years six times sooner than anticipated citation wingham d j d w wallis and a shepherd 2009 spatial and temporal evolution of pine island glacier thinning 1995 2006 geophys res lett 36 l17501 doi 10 1029 2009gl039126

recent antarctic ice mass loss from radar interferometry and regional climate modelling observed estimates of ice losses in antarctica combined with regional modelling of ice accumulation in the interior suggest that east antarctica is close to a balanced mass budget but large losses of ice occur in the narrow outlet channels of west antarctic glaciers and at the northern tip of the antarctic peninsula

long term change of mass balance and the role of radiation the effect of climate change in the 20th century is investigated based on measured mass balance data annual winter and summer mass balances on claridenfirn switzerland since 1914 15 storglaciaren sweden since 1945 46 storbreen norway since 1948 49 glacier de sarennes france since 1948 49 and vernagtferner austria since 1965 66 are studied with air temperature at high altitude stations and the longest records of solar global radiation in europe the mean mass balances of these glaciers during the 20th century were mostly negative except for the first two decades the fluctuating mass balance reaches the minimum largest loss and maximum almost equilibrium around 1940 and 1980 respectively with a drastic loss in the last 15 years these variations are mostly steered by the variation in summer mass balance the change in the summer mass balance is determined to 72 by temperature and the remaining 28 by solar radiation during the colder period e g 1960 80 the reduction in solar radiation counteracted the warming trend due to the greenhouse effect since 1990 the greenhouse effect of terrestrial radiation and the global brightening effect of solar radiation have both been acting to accelerate the melt resulting in the unprecedented mass loss of the observational era the glacier mass balance during the 20th century clearly reacted towards temperature and solar radiation changes which reflected the greenhouse effect and aerosol and cloud variations

mass balance of himalayan glaciers using aar and ela methods the accumulation area ratio aar for himalayan glaciers representing zero mass balance is substantially lower than for north america and europe regression analysis suggests 0 44 for the aar representing zero mass balance in the western himalaya a good correlation was observed when this method was applied to individual glaciers such as gara and gor garang in himachal pradesh india the correlation coefficients r using 6 and 7 years of data respectively were 0 88 and 0 96 for gara and gor garang glaciers respectively however when data from six western himalayan glaciers were correlated the correlation was 0 74 the aar was also estimated by using landsat images which can be useful in obtaining a trend in mass balance for a large number of himalayan glaciers for which very little information exists a higher correlation was observed between equilibrium line altitude ela and mass balance the field data from gara and gor garang glaciers shows a high correlation coefficient i e 0 92 and 0 94 respectively the ela values obtained from the landsat satellite images combined with topographic maps suggest positive mass balance for the year 1986 87 and negative for 1987 88

evaluation of the representation of arctic sea ice in the u k hadley centre gcm the amount of arctic sea ice predicted by the hadley centre global climate model gcm is evaluated using 15 years of passive microwave data while the hadley model reproduces the seasonal cycle reasonably well it underestimates the total area of sea ice by more than 3 x 10 6 km 2 for most of the year in the winter months most of the underestimate in ice area results from the prediction of far too little ice in hudson bay and the sea of okhotsk leading to an excess of up to 0 2 pw heat input to the atmosphere from hudson bay alone the surface energy budget of hudson bay is investigated using a mixture of surface observations poles satellite data atsr ssm i and isccp and output from the goddard data assimilation office analysis flux adjustments of the order of 200 wm 2 resulting from anomalously high sea surface temperatures in the levitus 1982 climatology are found to be the cause of the model s underestimation of sea ice in both hudson bay and the sea of okhotsk the fact that flux adjustments based on an inaccurate climatology will produce errors even if the model physics is correct underlines the need both for improved climatologies and for models accurate enough not to require flux adjustment

temperature and precipitation climate at the equilibrium line altitude of glaciers expressed by the degree day factor for melting snow several authors relate accumulation or precipitation at the glacier equilibrium line altitude ela to summer mean temperature using exponential or power law functions i analyze the accumulation temperature relation at the ela with a degree day model using data from the 1992 paper by a ohmura and others the dataset includes estimates at the ela of winter balance and of winter balance plus summer precipitation which represent respectively low and high estimates of annual accumulation which is seldom measured the ohmura dataset only lists summer mean temperature but i recover monthly temperatures for the whole year for 66 of the glaciers by assuming sinusoidal temperature variation through the year and using annual temperature range from a gridded climatology monthly degree day sums are then estimated from monthly mean temperature and summed to give annual totals so degree day factors for melting snow at the ela are obtained the degree day factors fall close to those reported in the literature for glacier snowmelt with averages of 3 5 1 4 and 4 6 1 4 mm d 1 k 1 for low and high accumulation estimates on the 66 glaciers the degree day model gives a family of accumulation temperature curves that depend upon the annual temperature range representing the contrast between maritime and continental climates

identification of snow ablation rate ela aar and net mass balance using transient snowline variations on two arctic glaciers identification of the transient snowline tsl from high spatial resolution landsat imagery on lemon creek glacier lcg southeast alaska usa and mittivakkat gletscher mg southeast greenland is used to determine snow ablation rates the equilibrium line altitude ela and the accumulation area ratio aar the rate of rise of the tsl during the ablation season on a glacier where the balance gradient is known provides a measure of the snow ablation rate on both lcg and mg snow pits were completed in regions that the tsl subsequently transects this further provides a direct measure of the snow ablation rates for a particular year tsl observations from multiple dates during the ablation season from 1998 to 2011 at lcg and 1999 to 2012 at mg were used to explore the consistency of the tsl rise and snow ablation rate on lcg and mg the satellite derived mean tsl migration rates were 3 8 0 6 and 9 4 9 1md 1 respectively the snow ablation rates were 0 028 0 004 m w e d 1 for lcg and 0 051 0 018 m w e d 1 for mg estimated by applying a tsl mass balance gradient method and 0 031 0 004 and 0 047 0 019 m w e d 1 by applying a snow pitsatellite method illustrating significant agreement between the two different approaches for both field sites also satellite derived ela and aar and estimated net mass balance ba conditions were in agreement with observed ela aar and ba conditions for lcg and mg

flow of the west antarctic ice sheet on the continental margin of the bellingshausen sea at the last glacial maximum geophysical data show that during the last glaciation the west antarctic ice sheet wais drained to the continental shelf edge of the bellingshausen sea through a cross shelf bathymetric trough belgica trough as a grounded fast flowing ice stream the drainage basin feeding this ice stream probably encompassed southwestern palmer land parts of southern alexander island and the bryan coast of ellsworth land with an area exceeding 200 000 km2 on the inner continental shelf streamlined bedrock and drumlins mapped by swath bathymetry show that the ice stream was fed by convergent ice flow draining from eltanin bay and bays to the east as well as by ice draining the southern part of the antarctic peninsula ice sheet through the ronne entrance the presence of a paleoice stream in belgica trough is indicated by megascale glacial lineations formed in soft till and a trough mouth fan on the continental margin grounding zone wedges on the inner and midshelf record ice marginal stillstands during deglaciation and imply a staggered pattern of ice sheet retreat these new data indicate an extensive wais at the last glacial maximum lgm on the bellingshausen sea continental margin which advanced to the shelf edge in conjunction with ice sheet reconstructions from the antarctic peninsula and pine island bay this implies a regionally extensive ice sheet configuration during the lgm along the antarctic peninsula bellingshausen sea and amundsen sea margins with fast flowing ice streams draining the wais and antarctic peninsula ice sheet to the continental shelf edge

ice and ocean processes in the bellingshausen sea antarctica 1 in the vicinity of the antarctic peninsula observations show diminishing sea ice and a rapid warming of atmosphere and ocean these changes have led to the collapse of ice shelves and retreat acceleration and thinning of inland ice however ocean observations in the center of the nearby bellingshausen sea are spatially and temporally coarse in this study ocean and sea ice models forced by atmospheric reanalyses are used to investigate this data gap by simulating processes in the bellingshausen sea for the years 1979 2007 the model suggests flow features in the region and predicts the basal melting of local ice shelves modeled ocean conditions are found to be less variable than in the nearby amundsen sea which is situated closer to foci of annual and interannual atmospheric variability melt rates beneath george vi ice shelf are investigated in detail concluding that the ice shelf may have been melting out of balance and therefore thinning for decades the melt rate contains significant interannual variability that the model links to variation in sea ice conditions offshore of the southern end of the ice shelf this stands in contrast to the amundsen sea where models suggest that ice shelf melting is controlled by variable transport of circumpolar deep water onto the continental shelf

topographic controls on post oligocene changes in ice sheet dynamics prydz bay region east antarctica within the general trend of post eocene cooling the largest and oldest outlet of the east antarctic ice sheet underwent a change from ice cliff to ice stream and or ice shelf dynamics with an associated switch from line source to fan sedimentation available geological data reveal little about the causes of these changes in ice dynamics during the miocene epoch or the subsequent effects on pliocene pleistocene ice sheet history icesheet numerical modeling reveals that bed morphology was probably responsible for driving changes in both ice sheet extent and dynamics in the lambert amery system at prydz bay the modeling shows how the topography and bathymetry of the lambert graben and prydz bay control ice sheet extent and flow the changes in bathymetric volume required for shelf edge glaciation correlate well with the prydz channel fan sedimentation history this suggests a negative feedback between erosion and glaciation whereby the current graben is overdeepened to such an extent that shelf edge glaciation is now not possible even if a last glacial maximum environment recurs we conclude that the erosional history of the lambert graben and prydz bay in combination with the uplift histories of the surrounding mountains are responsible for the evolution of this section of the east antarctic ice sheet once the necessary initial climatic conditions for glaciation were achieved at the start of the oligocene epoch

upper air model of summer balance on mount rainier usa in 2003 07 summer balance was measured at altitudes between 1700 and 3382 m a s l on two glaciers on mount rainier washington state usa 46 85 n 121 72 w 4400 m a s l south facing nisqually glacier and east northeast facing emmons glacier upper air temperatures at the nearest gridpoint in the ncep ncar reanalysis database are used in a distributed over altitude positive degree day pdd model for each glacier the model used the same coefficients at all altitudes for all years the rms model error was 0 65 r 2 0 87 and 0 78 m a 1 w e r 2 0 93 for nisqually and emmons glaciers respectively although pdd work generally uses different coefficients for snow and ice surfaces and the duration of exposure of those surfaces varies with altitude error in this single coefficient model is nearly uncorrelated with altitude values of coefficients obtained are within the range of those found in other pdd work the degree day coefficient however differs markedly between the two glaciers and is shown to be controlled by the difference between them in vertical gradient of measured summer balance it is smaller for nisqually glacier where solar radiation is a stronger contributor to melt and larger for emmons glacier where it is a weaker contributor over 1948 2007 when the model calibrated over 2003 07 was applied to the upper air temperatures estimated summer balance was 0 4 m a 1 less negative over 1962 83 than before and 0 6 m a 1 less negative than after corresponding roughly with changes of the northeast pacific sea surface temperatures

new boundary conditions for the west antarctic ice sheet subglacial topography beneath pine island glacier 1 predictions about future changes in the amundsen sea sector of the west antarctic ice sheet wais have been hampered by poorly known subglacial topography extensive airborne survey has allowed us to derive improved subglacial topography for the pine island glacier basin the trunk of this glacier lies in a narrow 250 km long 500 m deep sub glacial trough suggesting a long lived and constrained ice stream two tributaries lie in similar troughs others lie in less defined shallower troughs the lower basin of the glacier is surrounded by bedrock which after deglaciation and isostatic rebound could rise above sea level this feature would impede ice sheet collapse initiated near the grounding line of this glacier and prevent its progress into the deepest portions of wais the inland slope of the bed beneath the trunk of the glacier however confirms potential instability of the lower basin containing sufficient ice to raise global sea by 24 cm

glacier extent and climate in the maritime alps during the younger dryas we would like to acknowledge prof rea and dr pellitero for fruitful discussions on various aspects of this work and in particular on the use of glacier reconstruction and ela gis tools and extraction of climatic variables at a glacier ela dr ortu for kindly providing easy access to pollen data and for discussions on the climate of the younger dryas across the alps prof edwards for discussions on pollen analyses and prof federici for inspiring glaciological research in this beautiful region the constructive and useful feedback provided by dr monegato and an anonymous reviewer is greatly appreciated l cignoni is thanked for reviewing the english ms acknowledges support from nerc ciaf 9092 1010

the loch lomond readvance on the isle of mull scotland glacier reconstruction and palaeoclimatic implications geomorphological mapping of mull provides evidence for an icefield 143 km2 in area flanked by six corrie glaciers with a total area of ca 13 km2 the absence of lateglacial periglacial features shorelines and pollen sites from the area occupied by this readvance together with radiocarbon dating of shell fragments confirm that it occurred during the loch lomond younger dryas stade the thickness of glacigenic deposits within the area of the readvance is attributed to reworking of paraglacial sediments up valley continuity of recessional moraines indicates that the ice remained active and near to equilibrium during retreat consistent with slow warming following the coldest part of the stade reconstructed equilibrium line altitudes elas imply vigorous snow blowing by westerly winds and are consistent with a general southwestwards decline in elas across the scottish highlands an ela of 250 m was calculated for the mull icefield using an ablation accumulation balance ratio abr approach palaeotemperature and palaeoprecipitation estimates were derived by calculating a theoretical regional ela from meteorological data and assuming that the combination of temperature and precipitation implied by the theoretical ela approximates conditions at 250 m on mull during the loch lomond stade the result indicates a mean july sea level temperature of 5 7 0 5 c and a mean annual precipitation at 250 m of ca 2700 3800 mm best estimate 3200 mm indicating higher precipitation totals than at present owing to more vigorous atmospheric circulation copyright 2002 john wiley sons ltd

ice sheet grounding line dynamics steady states stability and hysteresis 1 the ice sheet ice shelf transition zone plays an important role in controlling marine ice sheet dynamics as it determines the rate at which ice flows out of the grounded part of the ice sheet together with accumulation this outflow is the main control on the mass balance of the grounded sheet in this paper we verify the results of a boundary layer theory for ice flux in the transition zone against numerical solutions that are able to resolve the transition zone very close agreement is obtained and grid refinement in the transition zone is identified as a critical component in obtaining reliable numerical results the boundary layer theory confirms that ice flux through the grounding line in a two dimensional sheet shelf system increases sharply with ice thickness at the grounding line this result is then applied to the large scale dynamics of a marine ice sheet our principal results are that 1 marine ice sheets do not exhibit neutral equilibrium but have well defined discrete equilibrium profiles 2 steady grounding lines cannot be stable on reverse bed slopes and 3 marine ice sheets with overdeepened beds can undergo hysteresis under variations in sea level accumulation rate basal slipperiness and ice viscosity this hysteretic behavior can in principle explain the retreat of the west antarctic ice sheet following the last glacial maximum and may play a role in the dynamics of heinrich events

climatic controls on the equilibrium line altitudes of scandinavian cirque glaciers abstract the equilibrium line altitudes elas of reconstructed palaeoglaciers have been widely used to assess palaeoclimatic conditions yet this concept has rarely been tested using modern glaciers to address this shortcoming correlations between the elas of 513 modern cirque glaciers and present day climatic and topographic variables across scandinavia as well as regional trends in ela and climate are analysed elas are calculated using the area altitude balance ratio method with a ratio of 1 5 0 4 results indicate that glacier elas are strongly correlated with distance from the coast this reflects the present day precipitation pattern of the region characterised by high precipitation near the sea and demonstrates a climate dominated by a maritime continental transition temperature explains differences in glacier ela regional trends as well as ela changes with latitude following standard meteorological convention scandinavia is divided into two macro climate regions and analyses are run within the macro regions as well as the complete dataset the strength of correlations between ela and precipitation increases when the study is divided into northern and southern macro regions these results test long held assumptions about relationships between climate and cirque glacier ela which is of particular relevance to palaeoclimatic studies based on the reconstruction of former cirque glaciers

accumulation at the equilibrium line altitude of glaciers inferred from a degree day model and tested against field observations we extrapolate temperature data from a gridded climatology to the equilibrium line altitude ela of a glacier and tune a degree day model by adjusting precipitation to give zero mass balance at the ela we verify the tuned model by comparing modelled accumulation with winter balance where this has been measured presently for 180 glaciers the modelled accumulation naturally depends upon the vertical lapse rate vlr for temperature and the degree day factor ddf for snowmelt both are somewhat uncertain in high mountain areas but modelled accumulation and measured winter balance are in reasonable agreement for most glaciers the degree day model predicts a non linear relation between accumulation and summer temperature at the ela as assumed by many workers but we find a family of curves rather than a single universal curve maritime glaciers with low annual temperature range have proportionally more accumulation than continental glaciers with high annual temperature range for a similar summer mean temperature averages of winter balance for the five main geographical regions where mass balance data are available agree well with annual accumulation from the degree day model

a re analysis of the 58 year mass balance record of storglaciaren sweden the use of glacier mass balance records to assess the effects of glacier volume change from climate change requires high quality data the methods for measuring glacier mass balance have been developed in tandem with the measurements themselves which implies that the quality of the data may change with time we have investigated such effects on the mass balance record of storglaciaren sweden by re analyzing the records using a better map base and applying successive maps over appropriate time periods our results show that errors 10 year oscillations the pseudo cyclic signal must thus be explained by factors other than cyclically occurring phenomena although the record may still be too short to establish significant signals we strongly recommend re analysis of long mass balance records in order to improve the mass balance records used for other analyses

basement control on past ice sheet dynamics in the amundsen sea embayment west antarctica abstract the development of landscapes and morphologies follows initially the tectonic displacement structures of the basement and sediments such fault zones or lineaments are often exploited by surface erosional processes and play therefore an important role in reconstructing past ice sheet dynamics observations of bathymetric features of the continental shelf of the amundsen sea embayment and identification of tectonic lineaments from geophysical mapping indicate that the erosional processes of paleo ice stream flows across the continental shelf followed primarily such lineaments inherited from the tectonic history since the cretaceous break up between new zealand and west antarctica three major ice flow trends correspond to different tectonic phases in east west northwest southeast and north south directions east west oriented basement trends correlate with coastline trends and overlay tectonic lineaments caused by former rift activities directional trends with northwest southeast orientation are observed for the glacial troughs of the western embayment outer shelf the western pine island bay coastal zones and the inner pine island glacial trough and are associated with a distributed southern plate boundary zone of the former bellingshausen plate the north south trend of the main pine island glacial trough and the north northeast trend of the abbot ice shelf trough on the outer shelf follow the predicted lineation trend of an eastern branch of the west antarctic rift system extending from the thwaites drainage basin northward into pine island bay an understanding of this context helps better constrain the geometries and sea bed substrate conditions for regional paleo ice sheet models

climate at the equilibrium line of glaciers the relationships between temperature precipitation and radiation on glacier equilibrium lines are investigated using 70 glaciers for which the mass balance and meteorological observations have been carried out for sufficiently long periods it is found that the characteristic climate at glacier equilibrium lines can be described using the summer 3 months temperature in a free atmosphere annual total precipitation and the sum of global and long wave net radiation all of these are measured at or very near the equilibrium line altitudes then it is shown how the shift of the equilibriumline will occur as a result of a climatic change finally the effect of the shift of the equilibrium line on the annualmean specific mass balance is analytically derived and compared with observations the present results make it possible to identify the altitudes in climate models where glacierization should begin and to evaluate the mass balance changes as a result of possible future changes in the climate

inland thinning of west antarctic ice sheet steered along subglacial rifts current ice loss from the west antarctic ice sheet wais accounts for about ten per cent of observed global sea level rise1 losses are dominated by dynamic thinning in which forcings by oceanic or atmospheric perturbations to the ice margin lead to an accelerated thinning of ice along the coastline2 3 4 5 although central to improving projections of future ice sheet contributions to global sea level rise the incorporation of dynamic thinning into models has been restricted by lack of knowledge of basal topography and subglacial geology so that the rate and ultimate extent of potential wais retreat remains difficult to quantify here we report the discovery of a subglacial basin under ferrigno ice stream up to 1 5 kilometres deep that connects the ice sheet interior to the bellingshausen sea margin and whose existence profoundly affects ice loss we use a suite of ice penetrating radar magnetic and gravity measurements to propose a rift origin for the basin in association with the wider development of the west antarctic rift system the ferrigno rift overdeepened by glacial erosion is a conduit which fed a major palaeo ice stream on the adjacent continental shelf during glacial maxima6 the palaeo ice stream in turn eroded the belgica trough which today routes warm open ocean water back to the ice front7 to reinforce dynamic thinning we show that dynamic thinning from both the bellingshausen and amundsen sea region is being steered back to the ice sheet interior along rift basins we conclude that rift basins that cut across the wais margin can rapidly transmit coastally perturbed change inland thereby promoting ice sheet instability

stronger ocean circulation and increased melting under pine island glacier ice shelf the ice shelf buttressing antarctica s pine island glacier has been melting rapidly observations taken between 1994 and 2009 show that meltwater production has increased by about 50 since 1994 as a result of a stronger circulation below the ice shelf

palaeo ice streams in the foxe baffin sector of the laurentide ice sheet in this paper we describe mapping of palaeo ice streams in the foxe baffin sector of the laurentide ice sheet by means of geomorphological interpretation of high resolution satellite images our interpretations were guided by a glaciological inversion scheme aided by digital elevation models publicly available sonar surveys and field studies as a result we produced a map depicting the location geometry and relative temporal changes of palaeo ice streams and analysed their palaeoglaciological implications for the foxe baffin sector we conclude that in the period between the last glacial maximum and approximately 7 0 kyr bp the foxe baffin sector was largely drained by topographically controlled outlet glaciers and ice streams which were organized in a relatively stable pattern during this time large areas of melville peninsula and central baffin island were subject to cold based conditions between 7 0 and 6 0 kyr bp the foxe baffin sector collapsed catastrophically in the foxe basin after which its remnant portion became confined to baffin island during this collapse rapid successions of small transient ice streams occurred along wide loosely defined topographical corridors in two sectors of baffin island the presently available landform archive on emerged land is not sufficient to conclusively support the existence of fully scaled ice streams along the whole length of hudson strait as an alternative solution we propose that topographically controlled ice streams might have occurred along the deepest parts of hudson strait with attendant cold based ice zones on marginal areas and islands at the head of the strait

an enhanced temperature index glacier melt model including the shortwave radiation balance development and testing for haut glacier d arolla switzerland an enhanced temperature index glacier melt model incorporating incoming shortwave radiation and albedo is presented the model is an attempt to combine the high temporal resolution and accuracy of physically based melt models with the lower data requirements and computational simplicity of empirical melt models represented by the degree day method and its variants the model is run with both measured and modelled radiation data to test its applicability to glaciers with differing data availability five automatic weather stations were established on haut glacier d arolla switzerland between may and september 2001 reference surface melt rates were calculated using a physically based energy balance melt model the performance of the enhanced temperature index model was tested at each of the four validation stations by comparing predicted hourly melt rates with reference melt rates predictions made with three other temperature index models were evaluated in the same way for comparison the enhanced temperature index model offers significant improvements over the other temperature index models and accounts for 90 95 of the variation in the reference melt rate the improvement is lower but still significant when the model is forced by modelled shortwave radiation data thus offering a better alternative to existing models that require only temperature data input

glacier changes since the little ice age maximum in the western qilian shan northwest china and consequences of glacier runoff for water supply based on aerial photographs topographical maps and the landsat 5 imidge data we have analyzed fluctuations of glaciers in the western qilian shan northwest china from the little ice age lia to 1990 the areas and volumes of glaciers in the whole considered region decreased 15 and 18 respectively from the lia maximum to 1956 this trend of glacier shrinkage continued and accelerated between 1956 and 1990 these latest decreases in area and volume were about 10 in 34 years the recent shrinkage may be due either to a combination of higher temperatures and lower precipitation during the period 1956 66 or to continuous warming in the high glacicrized mountains from 1956 to 1990 as a consequence glacier runoff from ice wastage between 1956 and 1990 has increased river runoff by 6 2 km 3 in the four river basins under consideration besides the equilibrium line altitude ela rise estimated from the mean terminus retreat of small glaciers 1 km long is 46 m which corresponds to a 0 3 c increase of mean temperatures in warm seasons from the lia to the 1950s

influence of subglacial geology on the position of a west antarctic ice stream from seismic observations ice streams drain much of the interior west antarctic ice sheet and buffer the main ice reservoir from oceanic influences1 2 the slow flowing interior feeds the floating ross ice shelf with ice via fast flowing ice streams3 that are believed to modulate sea level change through their control of inland ice storage understanding ice stream behaviour and predicting the response to climate change4 requires a better knowledge of the subglacial geology5 6 it is known that a thawed ice bed and high pressure basal water are necessary but not sufficient conditions to cause ice streaming7 8 moreover it has been hypothesized that a soft sedimentary bed is also required because of its intrinsic low frictional resistance to flow9 and owing to its high erodibility so as to generate till that can deform and lubricate ice motion10 11 or to bury rough features and smooth the bed for sliding here we use seismic observations to provide evidence that one margin of the upglacier part of an ice stream is directly above the boundary of a basin with such sedimentary fill the ice stream is within the basin and the ice outside the basin is slow flowing the basin fill presents an order of magnitude lower frictional resistance to ice flow than the subglacial material outside the basin we conclude that the ice stream position is dependent on subglacial geology

effects of climatic perturbations on the equilibrium line altitude west greenland perturbation analysis is applied to the heat balance at the egig line west greenland with respect to climatic changes the shift of the equilibrium line altitude is obtained for perturbations of temperature absolute humidity cloudiness and annual accumulation the total net ice ablation at the egig line increases by 45 with a perturbation of 1 k

numerical modeling of the development of u shaped valleys by glacial erosion the steep sided valleys and overdeepened basins of alpine landscapes are well known products of glaciation yet relatively little is known about how the dynamics of ice flow and glacial erosion interact to give rise to such landforms by linking a finite element model for ice flow through a glacier cross section with an erosion model it is possible to investigate the development of one of the most striking glacial landforms the u shaped valley in addition to providing a detailed understanding of landform development such modeling provides a way to test current understanding of the controls on glacial sliding and erosion to simulate valley development i first model flow through an initial glacier cross section and calculate the glaciological parameters that govern erosion i then numerically simulate erosion to produce a modified transverse profile for which a new flow field and erosion pattern are computed a number of iterations permits examination of the progressive transformation of cross section form which can be compared with field data model predictions of the cross section flow field are in close accord with data from the athabasca glacier and include marked lateral variations in sliding velocity with an erosion law dependent on basal velocity the model predicts the rapid transformation of a v shaped cross section into a recognizably glacial form over a time period on the order of 10 4 yr and the eventual development of a steady state quasi parabolic glacier cross section better agreement with empirical data from glaciated valleys is obtained by including temporal variations in ice discharge in order to mimic the characteristics of 100 000 yr glacial cycles the high discharge phase dominates form development and at low discharges cross section form is essentially inherited from the central part of the form that developed during the preceding high discharge phase

glaciers dominate eustatic sea level rise in the 21st century ice loss to the sea currently accounts for virtually all of the sea level rise that is not attributable to ocean warming and about 60 of the ice loss is from glaciers and ice caps rather than from the two ice sheets the contribution of these smaller glaciers has accelerated over the past decade in part due to marked thinning and retreat of marine terminating glaciers associated with a dynamic instability that is generally not considered in mass balance and climate modeling this acceleration of glacier melt may cause 0 1 to 0 25 meter of additional sea level rise by 2100