antarctic outlet glacier mass change resolved at basin scale from satellite gravity gradiometry the orbit and instrumental measurement of the gravity field and steady state ocean circulation explorer goce satellite mission offer the highest ever resolution capabilities for mapping earth s gravity field from space however past analysis predicted that goce would not detect changes in ice sheet mass here we demonstrate that goce gravity gradiometry observations can be combined with gravity recovery and climate experiment grace gravity data to estimate mass changes in the amundsen sea sector this refined resolution allows land ice changes within the pine island glacier pig thwaites glacier and getz ice shelf drainage systems to be measured at respectively 67 7 63 12 and 55 9 gt yr over the goce observing period of november 2009 to june 2012 this is the most accurate pure satellite gravimetry measurement to date of current mass loss from pig known as the weak underbelly of west antarctica because of its retrograde bed slope and high potential for raising future sea level

volume loss from antarctic ice shelves is accelerating the floating ice shelves surrounding the antarctic ice sheet restrain the grounded ice sheet flow thinning of an ice shelf reduces this effect leading to an increase in ice discharge to the ocean using 18 years of continuous satellite radar altimeter observations we have computed decadal scale changes in ice shelf thickness around the antarctic continent overall average ice shelf volume change accelerated from negligible loss at 25 64 cubic kilometers per year for 1994 2003 to rapid loss of 310 74 cubic kilometers per year for 2003 2012 west antarctic losses increased by 70 in the past decade and earlier volume gain by east antarctic ice shelves ceased in the amundsen and bellingshausen regions some ice shelves have lost up to 18 of their thickness in less than two decades

sustained increase in ice discharge from the amundsen sea embayment west antarctica from 1973 to 2013 we combine measurements of ice velocity from landsat feature tracking and satellite radar interferometry and ice thickness from existing compilations to document 41 years of mass flux from the amundsen sea embayment ase of west antarctica the total ice discharge has increased by 77 since 1973 half of the increase occurred between 2003 and 2009 grounding line ice speeds of pine island glacier stabilized between 2009 and 2013 following a decade of rapid acceleration but that acceleration reached far inland and occurred at a rate faster than predicted by advective processes flow speeds across thwaites glacier increased rapidly after 2006 following a decade of near stability leading to a 33 increase in flux between 2006 and 2013 haynes smith pope and kohler glaciers all accelerated during the entire study period the sustained increase in ice discharge is a possible indicator of the development of a marine ice sheet instability in this part of antarctica key points sustained ase mass flux increase 77 since 1973 thwaites accelerated by 33 during the last 6 years speed changes are pervasive and rapid major implications for ice flow modeling 2014 american geophysical union all rights reserved

mass balance reassessment of glaciers draining into the abbot and getz ice shelves of west antarctica we present a reassessment of input output method ice mass budget estimates for the abbot and getz regions of west antarctica using cryosat 2 derived ice thickness estimates the mass budget is 8 6 gt yr 1 and 5 17 gt yr 1 for the abbot and getz sectors respectively for the period 2006 2008 over the abbot region our results resolve a previous discrepancy with elevation rates from altimetry due to a previous 30 overestimation of ice thickness for the getz sector our results are at the more positive bound of estimates from other techniques grounding line velocity increases up to 20 between 2007 and 2014 alongside mean elevation rates of 0 67 0 13 m yr 1 between 2010 and 2013 indicate the onset of a dynamic thinning signal mean snowfall trends of 0 33 m yr 1 water equivalent since 2006 indicate recent mass trends are driven by both ice dynamics and surface processes

coupled thermo hydro mechanical processes in the near field of a high level radioactive waste repository in clay formations the present paper provides an overview of key coupled thermo hydro mechanical thm processes in clay formations that would result from the development of a high level radioactive waste repository here in this paper clay formations include plastic clay such as the boom clay of belgium as well as more indurated clay such as the callovo oxfordian and upper toarcian of france and opalinus clay of switzerland first we briefly introduce and describe four major underground research laboratories urls that have been devoted to clay repository research over the last few decades much of the research results in this area have been gained through investigations in these urls and their supporting laboratory and modeling research activities then the basic elements in the development of a waste repository in clays are presented in terms of four distinct stages in repository development for each of these four stages key processes and outstanding issues are discussed a summary of the important areas of research needs and some general remarks then conclude this paper

antarctic ice shelf thickness from satellite radar altimetry ice shelf thickness is an important boundary condition for ice sheet and sub ice shelf cavity modelling it is required near the grounding line to calculate the ice flux used to determine ice sheet mass balance by comparison with the upstream accumulation in this mass budget approach the accuracy of the ice thickness is one of the limiting factors in the calculation we present a satellite retrieval of the ice thickness for all antarctic ice shelves using satellite radar altimeter data from the geodetic phases of the european remote sensing satellite ers 1 during 1994 95 supplemented by icesat data for regions south of the ers 1 latitudinal limit surface elevations derived from these instruments are interpolated on to regular grids using kriging and converted to ice thicknesses using a modelled firn density correction the availability of a new spatial variable firn density correction significantly reduces the error in ice thickness as this was previously the dominant error source comparison to airborne data shows good agreement particularly when compared to soar casertz data on the largest ice shelves biases range from 13 0 m for areas where the assumption of hydrostatic equilibrium breaks down to 53 4 m in regions where marine ice may be present

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

acceleration of the contribution of the greenland and antarctic ice sheets to sea level rise 1 ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques over different time periods and at various levels of spatial detail considerable disparity remains between these estimates due to the inherent uncertainties of each method the lack of detailed comparison between independent estimates and the effect of temporal modulations in ice sheet surface mass balance here we present a consistent record of mass balance for the greenland and antarctic ice sheets over the past two decades validated by the comparison of two independent techniques over the last 8 years one differencing perimeter loss from net accumulation and one using a dense time series of time variable gravity we find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss in 2006 the greenland and antarctic ice sheets experienced a combined mass loss of 475 158 gt yr equivalent to 1 3 0 4 mm yr sea level rise notably the acceleration in ice sheet loss over the last 18 years was 21 9 1 gt yr2 for greenland and 14 5 2 gt yr2 for antarctica for a combined total of 36 3 2 gt yr2 this acceleration is 3 times larger than for mountain glaciers and ice caps 12 6 gt yr2 if this trend continues ice sheets will be the dominant contributor to sea level rise in the 21st century

increased ice losses from antarctica detected by cryosat 2 we use 3 years of cryosat 2 radar altimeter data to develop the first comprehensive assessment of antarctic ice sheet elevation change this new data set provides near continuous 96 coverage of the entire continent extending to within 215 km of the south pole and leading to a fivefold increase in the sampling of coastal regions where the vast majority of all ice losses occur between 2010 and 2013 west antarctica east antarctica and the antarctic peninsula changed in mass by 134 27 3 36 and 23 18 gt yr 1 respectively in west antarctica signals of imbalance are present in areas that were poorly surveyed by past missions contributing additional losses that bring altimeter observations closer to estimates based on other geodetic techniques however the average rate of ice thinning in west antarctica has also continued to rise and mass losses from this sector are now 31 greater than over the period 2005 2010

petrographic studies of refractory inclusions from the murchison meteorite textural and mineral chemical data on freeze thaw disaggregated refractory inclusions from the murchison meteorite are reported the data were obtained with neutron activation analysis sem and spectroscopy the study revealed corundum bearing inclusions spinel hibonite aggregates and spherules and spinel pyroxene and elivine pyroxene inclusions one of the three spinel pyroxene forsterite rich inclusions had an amoeba shaped spinel pyroxene core implying vapor to solid condensation and therefore crystallization from a melt it is concluded that the meteorite formation encompassed diverse nebular materials and that further studies of the meteorite will enhance the data base on the planetary nebular processes

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

hydrologic issues associated with nuclear waste repositories significant progress in hydrology especially in subsurface flow and solute transport has been made over the last 35 years because of sustained interest in underground nuclear waste repositories the present paper provides an overview of the key hydrologic issues involved and to highlight advances in their understanding and treatment because of these efforts the focus is not on the development of radioactive waste repositories and their safety assessment but instead on the advances in hydrologic science that have emerged from such studies work and results associated with three rock types which are being considered to host the repositories are reviewed with a different emphasis for each rock type the first rock type is fractured crystalline rock for which the discussion will be mainly on flow and transport in saturated fractured rock the second rock type is unsaturated tuff for which the emphasis will be on flow from the shallow subsurface through the unsaturated zone to the repository the third rock type is clay rich formations whose permeability is very low in an undisturbed state in this case the emphasis will be on hydrologic issues that arise from mechanical and thermal disturbances i e on the relevant coupled thermo hydro mechanical processes the extensive research results especially those from multiyear large scale underground research laboratory investigations represent a rich body of information and data that can form the basis for further development in the related areas of hydrologic research

increasing rates of ice mass loss from the greenland and antarctic ice sheets revealed by grace 1 we use monthly measurements of time variable gravity from the grace gravity recovery and climate experiment satellite gravity mission to determine the ice mass loss for the greenland and antarctic ice sheets during the period between april 2002 and february 2009 we find that during this time period the mass loss of the ice sheets is not a constant but accelerating with time i e that the grace observations are better represented by a quadratic trend than by a linear one implying that the ice sheets contribution to sea level becomes larger with time in greenland the mass loss increased from 137 gt yr in 2002 2003 to 286 gt yr in 2007 2009 i e an acceleration of 30 11 gt yr2 in 2002 2009 in antarctica the mass loss increased from 104 gt yr in 2002 2006 to 246 gt yr in 2006 2009 i e an acceleration of 26 14 gt yr2 in 2002 2009 the observed acceleration in ice sheet mass loss helps reconcile grace ice mass estimates obtained for different time periods

analysis of the railway heave induced by soil swelling at a site in southern france in order to better understand the heave observed on the railway roadbed of the french high speed train tgv at chabrillan in southern france the swelling behaviour of the involved expansive clayey marl taken from the site by coring was investigated the aim the study is to analyse the part of heave induced by the soil swelling first the swell potential was determined by flooding the soil specimen in an oedometer under its in situ overburden stress on the other hand in order to assess the swell induced by the excavation undertaken during the construction of the railway a second method was applied the soil was first loaded to its in situ overburden stress existing before the excavation it was then flooded and unloaded to its current overburden stress after the excavation the swell induced by this unloading was considered finally the experimental results obtained were analyzed together with the results from other laboratory tests performed previously and the data collected from the field monitoring this study allowed estimating the heave induced by soil swelling subsequently the part of the heave due to landslide could be estimated which corresponds to the difference between the monitored heave and the swelling heave

on the thm behaviour of a sheared boom clay sample application to the behaviour and sealing properties of the edz abstract in this study the effect of the temperature increase on the hydro mechanical properties of sheared boom clay samples is investigated two samples of boom clay are resaturated in a new hollow cylinder triaxial cell with a short drainage path and then sheared by performing an axisymmetric triaxial loading the effect of the undrained heating under deviatoric stress is studied on the first sample it is shown that undrained temperature increase leads to an increase of pore water pressure and consequently to a decrease of the effective mean stress which brings the sample to failure for an initially sheared sample the failure occurs along the existing shear band which behaves as a weakness plane in the sample the responses of the local strain measurement transducers clearly show the sliding of rigid blocks when failure occurs in the sample the effect of the presence of a shear band on the permeability of the other boom clay sample is investigated at ambient temperature and at 80 c it is shown that the presence of a shear band does not affect significantly the permeability these results confirm the good self sealing properties of boom clay at ambient and at high temperature

lower satellite gravimetry estimates of antarctic sea level contribution a new model of glacial isostatic adjustment used in conjunction with grace satellite data suggests that ice loss from antarctica is contributing 0 19 millimetres per year to global mean sea level which is substantially less than previous grace based estimates estimates for recent mass loss from antarctica vary widely making it difficult to calculate any subsequent contributions to sea level rise one prominent approach uses the grace gravity recovery and climate experiment satellites to detect changes in gravity but the final estimates are dependent on the modelled response of the continent to changes in ice loading over time and to changes in lithospheric elastic rebound matt king and colleagues apply a new model of this glacial isostatic adjustment to the grace data and estimate antarctic mass loss between 2002 and 2010 to be about 69 gigatonnes per year much lower than previous estimates and equivalent to an annual sea level rise of about 0 2 millimetres recent estimates of antarctica s present day rate of ice mass contribution to changes in sea level range from 31 gigatonnes a year gt yr 1 ref 1 to 246 gt yr 1 ref 2 a range that cannot be reconciled within formal errors3 time varying rates of mass loss2 4 5 6 contribute to this but substantial technique specific systematic errors also exist3 in particular estimates of secular ice mass change derived from gravity recovery and climate experiment grace satellite data are dominated by significant uncertainty in the accuracy of models of mass change due to glacial isostatic adjustment7 8 gia here we adopt a new model of gia developed from geological constraints which produces gia rates systematically lower than those of previous models and an improved fit to independent uplift data9 after applying the model to 99 months from august 2002 to december 2010 of grace data we estimate a continent wide ice mass change of 69 18 gt yr 1 0 19 0 05 mm yr 1 sea level equivalent this is about a third to a half of the most recently published grace estimates2 5 which cover a similar time period but are based on older gia models plausible gia model uncertainties and errors relating to removing longitudinal grace artefacts destriping confine our estimate to the range 126 gt yr 1 to 29 gt yr 1 0 08 0 35 mm yr 1 sea level equivalent we resolve 26 independent drainage basins and find that antarctic mass loss and its acceleration is concentrated in basins along the amundsen sea coast outside this region we find that west antarctica is nearly in balance and that east antarctica is gaining substantial mass

suction effects in deep boom clay block samples extensive investigations have been and are being carried out on a stiff clay from an underground research laboratory located at mol belgium called boom clay in the context of research into deep nuclear waste disposal suction effects in deep boom clay block samples were investigated through the characterisation of the water retention and of the swelling properties of the clay the data obtained allowed an estimation of the sample initial suction that was reasonably compatible with the in situ state of stress at a depth of 223 m the relationship between suction and stress changes during loading and unloading sequences were also examined by running oedometer tests with suction measurements a rather wide range of the ratio s v being s the suction and v the effective vertical stress was obtained 0 61 1 different from that proposed by bishop et al 1974 finally the effect of suction release under an isotropic stress close to the estimated sample suction was investigated a slight swelling 1 7 was observed and further compression provided a satisfactory value of the overconsolidation ratio confirming the suggestions of taking some precautions before putting a swelling sample in contact with water as suggested by graham et al 1987 the various experimental data gathered in this study finally evidenced a relatively good state of conservation of the block sample used

drying induced shrinkage of boom clay an experimental investigation drying induced shrinkage of geomaterials may have a strong effect on geostructure stability and deformation the settlement of foundations and fracture openings in slopes roads and tunnel walls may be due to drying shrinkage however there is still a lack of knowledge concerning shrinkage evolution with time and shrinkage propagation within the material in this study the shrinkage of a specific clayey rock boom clay under drying conditions is investigated experimentally this rock is a deep geological formation which is under study for high level and long term radioactive waste storage in belgium two experimental campaigns are presented the first based on the vapour equilibrium drying technique and coupled with sample size manual measurement aims to characterize the material shrinkage in balanced states the second based on the convective drying technique and coupled with shape monitoring using x ray tomography aims to analyse how shrinkage develops before reaching a steady state both app

the water retention properties of a natural unsaturated loess from northern france the water retention properties of a natural loess from northern france were investigated on intact block samples that were excavated along a high speed train line tgv that experienced stability problems during heavy rain episodes suction measurements were made by using the filter paper method and an in house constructed high capacity tensiometer hct so as to determine the water retention curve of the loess the results showed that an alternative approach using a previously wetted filter paper could fruitfully be used with suction values reasonably compatible with the hct measurements the water retention curve obtained exhibited a peculiar form with no hysteresis observed around the natural water content 14 4 and two hysteresis loops on both the wet and dry sides of the curve it is hypothesised that this zone with no hysteresis corresponds to the natural variations of the water content under seasonal changes providing a range of natural suction between 20 and 80 kpa and it is suggested that th

impact of excavation damage on the thermo hydro mechanical properties of natural boom clay abstract boom clay has been considered as a potential host rock for the geological radioactive waste disposal in belgium in this context it is important to well understand the thermo hydro mechanical behaviour of this clay around the disposal galleries in this study the effect of excavation damage on the thermo hydro mechanical properties of natural boom clay around the connecting gallery excavated in 2002 in the mol underground research laboratory hades high activity disposal experimental site was investigated several samples taken from a horizontal borehole drilled in july 2012 were tested the thermal conductivity in three different orientations perpendicular parallel and 45 to the bedding plane was measured using the needle probe method the results show a cross anisotropy of natural boom clay and an impact of the excavation damage on the thermal property of samples near the gallery to further investigate the anisotropy behaviour bender element tests were carried out under unconfined conditions to determine the small strain shear modulus also in three different orientations the obtained results confirm the anisotropic behaviour of boom clay moreover the evolution of small strain shear modulus with the distance from the gallery axis r was found to be similar to that of thermal conductivity the values in the zone near the gallery are lower than those in the far field from these experimental data an extent of the excavation damaged zone edz of 4 m from the connecting gallery axis was determined further investigations on the microstructure of several samples taken at different distances r by mercury intrusion porosimetry mip and scanning electron microscope sem methods were carried out macro pores of diameter 5 m were identified in the samples near the gallery the identified macro pores were related to the effect of excavation damage and a damage variable was thus defined allowing a damage model to be developed the values of the two model parameters have been determined from the observed relationship between macro porosity and thermal conductivity comparisons between the predicted and experimental results in terms of small strain shear modulus and hydraulic conductivity show a reasonable agreement

corrigendum calving fluxes and basal melt rates of antarctic ice shelves nature 502 89 92 2013 doi 10 1038 nature12567 in this letter a reference citation to a previously published paper1 on a similar topic was omitted from the fifth paragraph of the main body of the paper where it should have been cited details on the differences between the two studies are discussed in the supplementary information of the original manuscript

combined grace and insar estimate of west antarctic ice mass loss 1 we estimate the mass balance of eight drainage basins in west antarctica from the gravity recovery and climate experiment grace data gfz rl04 gsm level 2 using a constrained inverse gravimetric approach we consider insar observations of ice surface velocity as an indication of mass change assuming that large mass loss occurs in areas of fast glacier flow from these mass distribution functions we construct forward models of the geoid height change and their spatial correlations for each drainage basin then the difference between the grace data and the forward model is minimized by adjusting the total amount of mass change within each drainage basin to overcome the ambiguity inherent in this inverse problem we constrain its solution by including a priori estimates based on the insar mass budget method however unconstrained grace only mass change estimates can be recovered for three to four combined drainage basins differences between grace and insar values exist mainly for the pine island glacier and getz ice shelf region resulting in a lower unconstrained grace total of 91 0 3 5 gt yr for the years 2002 2008 compared to the insar estimate of 116 6 19 0 gt yr outflow measurement for the years 1992 1996 and 2006 there is evidence that this difference arises from anomalously large accumulation within the grace time interval august 2002 to august 2008 in the amundsen sea sector and possibly from an overestimation of ice thickness for parts of the bellinghausen sea sector underlying the insar mass budget values

dynamic thinning of glaciers on the southern antarctic peninsula growing evidence has demonstrated the importance of ice shelf buttressing on the inland grounded ice especially if it is resting on bedrock below sea level much of the southern antarctic peninsula satisfies this condition and also possesses a bed slope that deepens inland such ice sheet geometry is potentially unstable we use satellite altimetry and gravity observations to show that a major portion of the region has since 2009 destabilized ice mass loss of the marine terminating glaciers has rapidly accelerated from close to balance in the 2000s to a sustained rate of 56 8 gigatons per year constituting a major fraction of antarctica s contribution to rising sea level the widespread simultaneous nature of the acceleration in the absence of a persistent atmospheric forcing points to an oceanic driving mechanism

yielding and plastic behaviour of boom clay an underground research laboratory url has been excavated in a deposit of boom clay at a depth of 223 m by the sck cen belgian organisation near the city of mol this url is devoted to research into nuclear waste disposal this paper presents the results of an investigation carried out in the triaxial apparatus on specimens that were trimmed from blocks extracted during excavation sequences in the url in order to characterise the mechanical behaviour of the natural boom clay and to examine the effect of initial and induced anisotropy on its constitutive behaviour two series of triaxial tests were carried out special attention was devoted to the yield behaviour and the effects of stress history experimental results showed a clear relation between the shape of yield curves and stress history the yield curve of the clay in its initial state was oriented along the k0 line illustrating the anisotropy of fabric that was generated during the soil deposition subsequent isotropic compression up to 9 mpa

mass balance of the antarctic ice sheet the antarctic contribution to sea level rise has long been uncertain while regional variability in ice dynamics has been revealed a picture of mass changes throughout the continental ice sheet is lacking here we use satellite radar altimetry to measure the elevation change of 72 of the grounded ice sheet during the period 1992 2003 depending on the density of the snow giving rise to the observed elevation fluctuations the ice sheet mass trend falls in the range 5 85gt yr 1 we find that data from climate model reanalyses are not able to characterise the contemporary snowfall fluctuation with useful accuracy and our best estimate of the overall mass trend growth of 27 29 gt yr 1 is based on an assessment of the expected snowfall variability mass gains from accumulating snow particularly on the antarctic peninsula and within east antarctica exceed the ice dynamic mass loss from west antarctica the result exacerbates the difficulty of explaining twentieth century sea level rise

study on the hydraulic conductivity of boom clay the hydraulic conductivity is a parameter in geotechnical engineering practice that is key in seepage and consolidation analysis experimental results show that the hydraulic conductivity is mainly governed by the soil porosity and correlations with void ratio are usually proposed the validity of these correlations has been verified for soft clays and sands however few studies have included stiff clays in this work the hydraulic conductivity of boom clay a stiff clay taken from the essen site in belgium was determined from both consolidation and constant head percolation tests the data obtained was then analyzed to evaluate the existing correlations to predict the hydraulic conductivity in addition as these correlations usually require a referred hydraulic conductivity at a known void ratio the existing methods are often difficult to use in practice thus a new method was developed allowing the prediction of hydraulic conductivity without the referred value which was based on two existing co

stress release undrained storage and reconsolidation in simulated underwater clay triaxial testing has examined the influence of storage time and reconsolidation procedures on normally consolidated and overconsolidated samples of reconstituted clay prepared with high pore water pressures to simulate underwater deposits samples of illite were consolidated one dimensionally off loaded without drainage stored undrained reconsolidated and sheared undrained the storage times were 15 min 1 day and 7 days reconsolidation pressures were 1 isotropic to 2 isotropic to and 3 anisotropic to the results were compared with specimens that had not been off loaded different undrained storage times had no effect on the strengths after reconsolidation but the strengths were affected by the reconsolidation pressures anisotropic reconsolidation produced the best agreement between the control specimens and samples in terms of their strengths and af values the duration of storage time did affect stress strain parameters such as the undrained compression modulus e50 and the pore

estimation of in situ stresses using anisotropic elasticity and suction measurements sampling and specimen preparation produce changes in mean effective stresses and pore water pressures even with perfect sampling the paper takes an existing simplified three parameter cross anisotropic elastic model and uses it to model these changes the required ratio of cross anisotropic parameters j 3g can be obtained from standard ciu triaxial tests if measurements are also made of suctions in unloaded specimens in the laboratory then a combination of j 3g the measured suction and the effective overburden pressure permits an estimation of the horizontal effective pressure and the k0 at rest coefficient this can be helpful in numerical modelling that needs to start from in situ conditions and in planning pressure levels for reconsolidation of clay specimens in the laboratory tests were done on belfast upper boulder clay from a depth of 28 m values of horizontal in situ effective stress estimated from these measurements compare favorably with conventional estimates of the at rest coef

distribution of marine ice beneath the amery ice shelf we present a map of the marine ice accreted to the base of the amery ice shelf ais east antarctica this map is obtained by converting a digital elevation model dem of the ais generated from satellite radar altimeter data to an ice thickness map assuming hydrostatic equilibrium and subtracting from that a second ice thickness map derived from airborne radio echo sounding res measurements the res signal does not penetrate the marine ice so the measurement is only to the meteoric marine ice boundary and therefore the difference between the two maps is the marine ice thickness the marine ice is up to 190 m thick and accounts for about 9 of the shelf volume it is concentrated in the northwest of the shelf a result of the clockwise ocean circulation in the cavity below

antarctic ice sheet loss driven by basal melting of ice shelves accurate prediction of global sea level rise requires that we understand the cause of recent widespread and intensifying glacier acceleration along antarctic ice sheet coastal margins atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves potentially limiting their ability to buttress the flow of grounded tributary glaciers indeed recent ice shelf collapse led to retreat and acceleration of several glaciers on the antarctic peninsula but the extent and magnitude of ice shelf thickness change the underlying causes of such change and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum antarctic pattern of ice shelf thinning through increased basal melt we deduce that this increased melt is the primary control of antarctic ice sheet loss through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow the highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of antarctic ice shelves through ocean upwelling in the amundsen and bellingshausen seas and atmospheric warming on the antarctic peninsula this implies that climate forcing through changing winds influences antarctic ice sheet mass balance and hence global sea level on annual to decadal timescales

creep and consolidation of a stiff clay under saturated and unsaturated conditions in this paper the one dimensional 1d time dependent behaviour of natural and reconstituted london clay samples under saturated and unsaturated conditions is studied for this purpose a set of 1

mass gains of the antarctic ice sheet exceed losses during 2003 to 2008 the mass gain of the antarctic ice sheet from snow accumulation exceeded the mass loss from ice discharge by 49 gt yr 2 5 of input as derived from icesat laser measurements of elevation change the net gain 86 gt yr over the west antarctic wa and east antarctic ice sheets wa and ea is essentially unchanged from revised results for 1992 to 2001 from ers radar altimetry imbalances in individual drainage systems ds are large 68 to 103 of input as are temporal changes 39 to 44 the recent 90 gt yr loss from three ds pine island thwaites smith and marie bryd coast of wa exceeds the earlier 61 gt yr loss consistent with reports of accelerating ice flow and dynamic thinning similarly the recent 24 gt yr loss from three ds in the antarctic peninsula ap is consistent with glacier accelerations following breakup of the larsen b and other ice shelves in contrast net increases in the five other ds of wa and ap and three of the 16 ds in east antarctica ea exceed the increased losses alternate interpretations of the mass changes driven by accumulation variations are given using results from atmospheric model re analysis and a parameterization based on 5 change in accumulation per degree of observed surface temperature change a slow increase in snowfall with climate warming consistent with model predictions may be offsetting increased dynamic losses

a laboratory investigation of thermally induced pore pressures in the callovo oxfordian claystone in the framework of research into radioactive waste disposal it was decided to investigate the thermally induce pore pressure occurring in the callovo oxfordian claystone a possible host rock in which the andra underground laboratory of bure east of france has been excavated thermal pore pressures appear in low permeability soils and rocks because the thermal expansion coefficient of water is significantly higher than that of the solid grains campanella and mitchell 1968 1 ghabezloo and sulem 2009 2 this phenomenon has clearly been observed in various in situ heating tests conducted in opalinus claystone in the mont terri underground research laboratory url in switzerland he d test and in callovo oxfordian cox claystone in the bure url in france ter test wileveau and su 2007 3 the processes of coring transportation storage and specimen trimming induce some desaturation in the sample due to the very low permeability 10 20 m2 of the cox claystone a long period of time is necessary to properly resaturate the sample a mandatory condition to satisfactorily investigate thermal pressurisation particular emphasis was hence put on the previous saturation procedure that was carried out under in situ effective stress condition thermal pressurization has been investigated by performing undrained heating tests while measuring pore pressures changes in a specially adapted thermal isotropic compression cell special care was devoted to calibration procedures to account for the effects of the system on the pore pressure measurements the thermal pressurization coefficient measured appeared to change with temperature mainly because of the changes with temperature of both the water thermal expansion coefficient of water and the drained compression coefficient of the claystone

calving fluxes and basal melt rates of antarctic ice shelves iceberg calving has been assumed to be the dominant cause of mass loss for the antarctic ice sheet with previous estimates of the calving flux exceeding 2 000 gigatonnes per year1 2 more recently the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front3 4 5 so far however no study has reliably quantified the calving flux and the basal mass balance the balance between accretion and ablation at the ice shelf base for the whole of antarctica the distribution of fresh water in the southern ocean and its partitioning between the liquid and solid phases is therefore poorly constrained here we estimate the mass balance components for all ice shelves in antarctica using satellite measurements of calving flux and grounding line flux modelled ice shelf snow accumulation rates6 and a regional scaling that accounts for unsurveyed areas we obtain a total calving flux of 1 321 144 gigatonnes per year and a total basal mass balance of 1 454 174 gigatonnes per year this means that about half of the ice sheet surface mass gain is lost through oceanic erosion before reaching the ice front and the calving flux is about 34 per cent less than previous estimates derived from iceberg tracking1 2 7 in addition the fraction of mass loss due to basal processes varies from about 10 to 90 per cent between ice shelves we find a significant positive correlation between basal mass loss and surface elevation change for ice shelves experiencing surface lowering8 and enhanced discharge9 we suggest that basal mass loss is a valuable metric for predicting future ice shelf vulnerability to oceanic forcing

mass changes of the greenland and antarctic ice sheets and shelves and contributions to sea level rise 1992 2002 changes in ice mass are estimated from elevation changes derived from 10 5 years greenland and 9 years antarctica of satellite radar altimetry data from the european remote sensing satellites ers 1 and 2 for the first time the dh dt values are adjusted for changes in surface elevation resulting from temperature driven variations in the rate of firn compaction the greenland ice sheet is thinning at the margins 42 2g t a 1 below the equilibrium line altitude ela and growing inland 53 2g t a 1 above the ela with a small overall mass gain 11 3g t a 1 0 03 mm a 1 sle sea level equivalent the ice sheet in west antarctica wa is losing mass 47 4g t a 1 and the ice sheet in east antarctica ea shows a small mass gain 16 11 gt a 1 for a combined net change of 31 12 gt a 1 0 08 mm a 1 sle the contribution of the three ice sheets to sea level is 0 05 0 03 mm a 1 t he antarctic ice shelves show corresponding mass changes of 95 11 gt a 1 in wa and 142 10 gt a 1 in ea thinning at the margins of the greenland ice sheet and growth at higher elevations is an expected response to increasing temperatures and precipitation in a warming climate the marked thinnings in the pine island and thwaites glacier basins of wa and the totten glacier basin in ea are probably ice dynamic responses to long term climate change and perhaps past removal of their adjacent ice shelves the ice growth in the southern antarctic peninsula and parts of ea may be due to increasing precipitation during the last century