antarctic snow accumulation mapped using polarization of 4 3 cm wavelength microwave emission different parts of antarctica receive different amounts of snowfall each year in this paper we map the variations of the mean annual snow accumulation across the ice sheet we also quantify the uncertainty in our estimates more objectively than has been possible for earlier maps the new map is produced using observations from satellites and ground based measurements after a logarithmic transformation these are combined using the geostatistical method of continuous part universal kriging to give an estimate of the snow accumulation within each cell of a rectangular grid covering antarctica we also derive spatial averages over the major drainage systems of the ice sheet along with their confidence intervals we obtain a value of 143 4 kg m 2 a 1 for the average rate of snow accumulation upon the grounded ice sheet of antarctica

modis based mosaic of antarctica moa data sets continent wide surface morphology and snow grain size abstract we present digital image mosaics of surface morphology and optical snow grain size for the antarctic continent and surrounding islands assembled from 260 moderate resolution imaging spectroradiometer modis images the products are derived from modis band 1 red light 647 nm and band 2 infrared 857 nm orbit swath data acquired during the 2003 2004 austral summer multiple images of all areas are combined in a data cumulation scheme to improve spatial resolution and increase radiometric content of the mosaics the component images were de striped geo registered and re sampled to the projection grid using the modis swath to grid toolbox ms2gt software a 125 m ground equivalent polar stereographic projection was used identical to previous radar image mosaics and similar to several other continent wide data sets geo location accuracy of the final mosaics is better than 125 m swath acquisition times were limited to the range 05 00 13 30 ut to provide broad but uniform mosaic illumination regions of cloud cover blowing snow and intense forward scattering were masked prior to compositing the moa snow grain size data set image provides the first continent wide semi quantitative map of mean summer snow firn and blue ice grain size optical grain size radius was determined using a normalized difference index derived from modis band 1 and band 2 rad values atmospheric correction adjustments for directional reflectance variation and snow grain size estimation were accomplished by a look up table generated by a combination of published models of snow spectral reflectance and atmosphere radiative transfer validation of the snow grain size image is provided by in situ spectra of snow covered sea ice made in october 2003 we use the new data sets to determine major ice shelf areas and shelf edge coastline and ice grounding line vector files and determine areas of selected blue ice regions these data sets are available for download at http nsidc org data moa

southeast greenland high accumulation rates derived from firn cores and ground penetrating radar despite containing only 14 of the greenland ice sheet by area the southeastern sector has the highest accumulation rates and hence receives 30 of the total snow accumulation we present accumulation rates obtained during our 2010 arctic circle traverse derived from three 50 m firn cores dated using geochemical analysis we tracked continuous internal reflection horizons between the firn cores using a 400 mhz ground penetrating radar gpr gpr data combined with depth age scales from the firn cores provide accumulation rates along a 70 km transect we followed an elevation gradient from 2350 to 1830m to understand how progressive surface melt may affect the ability to chemically date the firn cores and trace the internal layers with gpr from the firn cores we find a 52 0 43 m w e a 1 increase in average snow accumulation and greater interannual variability at the lower site than the upper site the gpr profiling reveals that accumulation rates are influenced by topographic undulations on the surface with up to 23 variability over 7 km these measurements confirm the presence of high accumulation rates in the southeast as predicted by the calibrated regional climate model polar mm5

past and future grounding line retreat of the west antarctic ice sheet the history of deglaciation of the west antarctic ice sheet wais gives clues about its future southward grounding line migration was dated past three locations in the ross sea embayment results indicate that most recession occurred during the middle to late holocene in the absence of substantial sea level or climate forcing current grounding line retreat may reflect ongoing ice recession that has been under way since the early holocene if so the wais could continue to retreat even in the absence of further external forcing

variability in accumulation rates from gpr profiling on the west antarctic plateau isochronal layers in firn detected with ground penetrating radar gpr and dated using results from ice core analyses are used to calculate accumulation rates along a 100 km across flow profile in west antarctica accumulation rates are shown to be highly variable over short distances elevation measurements from global positioning system surveys show that accumulation rates derived from shallow horizons correlate well with surface undulations which implies that wind redistribution of snow is the leading cause of this variability temporal changes in accumulation rate over 25 185 year intervals are smoothed to along track length scales comparable to surface undulations in order to identify trends in accumulation that are likely related to changes in climate results show that accumulation rates along this profile have decreased in recent decades which is consistent with core derived time series of annual accumulation rates measured at the two ends of the radar profile these results suggest that temporal variability observed in accumulation rate records from ice cores and gpr profiles can be obscured by spatial influences although it is possible to resolve temporal signals if the effects of local topography and ice flow are quantified and removed

static grounding lines and dynamic ice streams evidence from the siple coast west antarctica 1 grounding line dynamics are key to our understanding of marine ice sheets such as the west antarctic ice sheet wais we present an accurate and rapid method for locating grounding lines using glas icesat laser altimetry data we then apply this technique to the siple coast region of the wais our technique exploits the high surface slope at the grounding line relative to the adjacent flat ice streams and ice shelf the technique is validated by ground based observations comparisons between the current grounding line and earlier measured locations demonstrate that the siple coast s grounding line has been largely static over the last two decades this is important as the ice streams have been undergoing considerable variations over this period we conclude that ice stream flow speeds can vary while the grounding line remains stable we suggest that grounding lines may migrate abruptly and then stabilize rather than undergoing continuous retreat

wind borne redistribution of snow across an antarctic ice rise redistribution of snow by the wind can drive spatial and temporal variations in snow accumulation that may affect the reconstruction of paleoclimate records from ice cores in this paper we investigate how spatial variations in snow accumulation along a 13 km transect across lyddan ice rise antarctica are related to wind borne snow redistribution lyddan ice rise is an approximately two dimensional ridge which rises about 130 m above the surrounding ice shelves local slopes on its flanks never exceed 0 04 despite this very smooth profile there is a pronounced gradient in snow accumulation across the feature accumulation is highest on the ice shelf to the east climatologically upwind of the ice rise and decreases moving westward with the lowest accumulation seen to the west climatologically downwind of the ice rise crest superimposed on this broad scale gradient are large 20 30 localized variations in accumulation on a scale of around 1 km that appear to be associated with local variations in surface slope of less than 0 01 the broad scale accumulation gradient is consistent with estimates of wind borne redistribution of snow made using wind speed observations from three automatic weather stations the small scale variability in accumulation is reproduced quite well using a snow transport model driven by surface winds obtained from an airflow model providing that both the wind shear and static stability of the upwind flow are taken into account we conclude that great care needs to be exercised in selecting ice core sites in order to avoid the possibility of blowing snow transport confounding climate reconstructions

radar characterization of the basal interface across the grounding zone of an ice rise promontory in east antarctica radar power returned from the basal interface along a 42 km long profile over an ice rise promontory and the adjacent roi baudouin ice shelf dronning maud land east antarctica is analyzed to infer spatial variations in basal reflectivity and hence the basal environment extracting basal reflectivity from basal returned power requires an englacial attenuation model we estimate attenuation in two ways 1 using a temperature dependent model with input from thermomechanical ice flow models and 2 using a radar method that linearly approximates the geometrically corrected returned power with ice thickness the two methods give different results we argue that attenuation calculated using a modeled temperature profile is more robust than the widely used radar method especially in locations where depth averaged attenuation varies spatially or where the patterns of basal reflectivity correlate with the patterns of the ice thickness

dating ice flow change near the flow divide at roosevelt island antarctica by using a thermomechanical model to predict radar stratigraphy 1 radar detected internal layering contained in some ice divides shows upwarped arches termed raymond bumps the distribution of their amplitude with height can date the onset of divide flow reflecting changes in the basin structure of the ice sheet the distribution depends on rheology surface geometry accumulation rate and temperature conway et al 1999 used an isothermal parameterized ice flow model to estimate a date of 3200 years b p with no error estimate for the onset of divide flow in roosevelt island ross ice shelf which they associated with grounding line retreat of the west antarctic ice sheet no other retreat dating exists for an area of the ross ice shelf distant from geological exposures employing a full thermomechanically coupled transient model we use a direct search to determine which ice rheology best fits the observed bump distribution and surface profile estimating the sensitivity of the dating to model parameters and exploring possible reasons for the observed asymmetry of the surface profile our main results are as follows 1 a best estimate of the date of grounding line retreat near roosevelt island is 3000 years b p bounded by 2300 and 4200 years b p 2 standard rheology power n 3 can only match the observed bump distribution for unrealistic isothermal models 3 for thermomechanically coupled models a high power n 4 in glen s law is required 4 low power rheologies and wind scouring cannot produce correct bump amplitude distributions 5 asymmetric accumulation cannot explain the observed asymmetry of the surface profile 6 modeling isochrones in flanking regions also indicates changes in flow around 3000 years b p

variability in horizontal current velocities in the central and eastern equatorial atlantic in 2002 1 near surface current velocity data from the pilot research moored array in the tropical atlantic at 23 w in the year 2002 were re examined and compared to simultaneous unpublished velocity data at 10 w near the surface strong 7 day period fluctuations were observed in the zonal velocity component and in temperature records at 23 w the large temperature fluctuations near the thermocline depth suggest a vertical velocity component at the same 7 day period the 7 day period signals occurred in june july simultaneously with the seasonal upwelling the meridional velocity component presented similar spectral contents at 23 w and at 10 w two distinguishable quasiperiodic signals were observed in the meridional component at both locations the first signal occurred in the spring had a periodicity of about 14 days was subsurface intensified and had the characteristics of a mixed rossby gravity wave the second signal occurred three times in the year once in winter 2001 2002 another in summer and another during fall 2002 had a periodicity of about 20 days was strongest close to the surface and was the result of the passage of tropical instability waves tiws satellite sea surface temperature sst data show the same periodicities as the meridional velocity records and present a spatial structure in accordance with the tiw sst signature the summer of 2002 showed different tiw sst patterns depending upon location suggesting the existence of different types of tiws overall variability in the current meter data for the year 2002 was mainly due to current instabilities except around boreal spring where intraseasonal variability in surface winds was strongest

sedimentation beneath ice shelves the view from ice stream b abstract ice shelf development is favored by rapid flow of cold ice from outlet glaciers or ice streams into protected embayments with localized high spots basal melting of ice shelves is rapid near the ice front and may occur near the grounding line ice from outlet glaciers may contain significant englacial debris that is deposited as a dropstone diamicton in regions of basal melting englacial debris is sparse or absent in ice streams evidence from ice stream b draining into the ross ice shelf of west antarctica suggests that the rapid ice velocity arises from deformation of a several meter thick water saturated basal till layer that is eroding an unconformity on sediments beneath and that has deposited a till delta tens of meters thick and tens of kilometers long at the grounding line sea level fall would cause conveyor belt recycling of this till delta and grounding line advance across the ross sea to the edge of the continental shelf forming an ice sheet with a low ice stream profile resting on a several meter thick deforming till layer eroding an unconformity the modern ross sea is characterized by a regional unconformity overlain by a diamicton of probable latest pliocene pleistocene age measuring several meters to tens of meters thick we hypothesize that this diamicton is a deformed glacial till and that the ross sea sediments record one or more expansions of the till lubricated west antarctic ice sheet to the edge of the continental shelf

characterizing the glaciological conditions at halvfarryggen ice dome dronning maud land antarctica we present a comprehensive approach including field data remote sensing and an anisotropic ice flow model to characterize halvfarryggen ice dome in coastal dronning maud land antarctica this is a potential drill site for the international partnerships in ice core sciences which has identified the need for ice cores covering atmospheric conditions during the last few millennia we derive the surface topography the ice stratigraphy from radar data and accumulation rates which vary from 400 to 1670 kg m 2 a 1 due to preferred wind directions and changing surface slope the stratigraphy shows anticlines and synclines beneath the divides we transfer dansgaard johnsen age depth scales from the flanks along isochrones to the divide in the upper 20 50 of the ice thickness and show that they compare well with the results of a full stokes anisotropic ice flow model which predicts 1 11 ka bp ice at 90 of the ice thickness 2 a temporally stable divide for at least 2700 4500 years 3 basal temperatures below the melting point 12 degrees c to 5 degrees c and 4 a highly developed crystal orientation fabric cof we suggest drilling into the apices of the deep anticlines providing a good compromise between record length and temporal resolution and also facilitating studies of the interplay of anisotropic cof and ice flow

isochrones and isotherms beneath migrating ice divides we use simple numerical and analytical models of ice flow and heat flow to characterize the shape of isochrones and isotherms beneath moving ice divides both non linear ice flow and reduced accumulation wind scouring at a divide can cause reduced downward flow in a region about one ice thickness wide under a divide greater downward velocities on the flanks cause isochrones and isotherms to become arched at depth the magnitudes and shapes of these arches depend on the history of divide position arch amplitudes decrease by approximately e for each increase in migration rate of 3 5 times the accumulation rate the arches become asymmetric with steeper leading edges and more gentle trailing edges and the arch apex lags behind the divide isochrone and isotherm shapes can be used to infer past divide motions in advection dominated ice sheets isochrone shapes record a longer history of divide position than do isotherm shapes the opposite is true for diffusion dominated ice sheets in which a spatial array of ice temperature measurements might extend the recorded history of divide position

a spatially adjusted elevation model in dronning maud land antarctica based on differential sar interferometry in this paper a new digital elevation model dem is derived for the ice sheet in western dronning maud land antarctica it is based on differential interferometric synthetic aperture radar sar from the european remote sensing 1 2 ers 1 2 satellites in combination with icesat s geoscience laser altimeter system glas a dem mosaic is compiled out of 116 scenes from the ers 1 ice phase in 1994 and the ers 1 2 tandem mission between 1996 and 1997 with the glas data acquired in 2003 that served as ground control using three different sar processors uncertainties in phase stability and baseline model resulting in height errors of up to 20 m are exemplified atmospheric influences at the same order of magnitude are demonstrated and corresponding scenes are excluded for validation of the dem mosaic covering an area of about 130 000 km2 on a 50 m grid independent icesat heights 2004 2007 ground based kinematic gps 2005 and airborne laser scanner data als 2007 are used excluding small areas with low phase coherence the dem differs in mean and standard deviation by 0 5 10 1 1 1 6 4 and 3 1 4 0 m from icesat gps and als respectively the excluded data points may deviate by more than 50 m in order to suppress the spatially variable noise below a 5 m threshold 18 of the dem area is selectively averaged to a final product at varying horizontal spatial resolution apart from mountainous areas the new dem outperforms other currently available dems and may serve as a benchmark for future elevation models such as from the tandem x mission to spatially monitor ice sheet elevation

snowfall in coastal west antarctica much greater than previously assumed 1 a new antarctic accumulation distribution based on regional model output calibrated with 1900 in situ observations is used to re assess accumulation in 24 antarctic ice drainage basins when compared to the previous compilation good agreement is found for 19 of the 24 basins representing 93 of the ice sheet that is reasonably well covered with observations in contrast the amundsen sea sector of west antarctica and the western antarctic peninsula both data sparse regions are found to receive 80 96 more accumulation than previously assumed for the pine island and thwaites glaciers west antarctica which have recently undergone rapid acceleration and thinning this means a downward adjustment of their contribution to global sea level rise from 0 24 to 0 14 mm per year model time series do not show a significant change in antarctic accumulation over the period 1980 2004

temporal and spatial variation of stable isotope ratios and accumulation rates in the hinterland of neumayer station east antarctica four firn cores were retrieved in 2007 at two ridges in the area of the ekstrom ice shelf dronning maud land coastal east antarctica in order to investigate the recent regional climate variability and the potential for future extraction of an intermediate depth core stable water isotope analysis tritium content and electrical conductivity were used to date the cores for the period 1981 2006 a strong and significant correlation between the stable isotope composition of firn cores in the hinterland and mean monthly air temperatures at neumayer station was r 0 54 0 71 no atmospheric warming or cooling trend is inferred from our stable isotope data for the period 1962 2006 the stable isotope record of the ice firn cores could expand well beyond the meteoro logical record of the region no significant temporal variation of accumulation rates was detected however decreasing accumulation rates were found from coast to hinterland as well as from east halvfarryggen to west sorasen the deuterium excess d exhibits similar differences higher d at sorasen lower d at halvfarryggen with a weak negative temporal trend on halvfarryggen 0 04 a 1 probably implying increasing oceanic input we conclude that halvfarryggen acts as a natural barrier for moisture carrying air masses circulating in the region from east to west

the role of atmospheric rivers in anomalous snow accumulation in east antarctica recent heavy snow accumulation events over dronning maud land dml east antarctica contributed significantly to the antarctic ice sheet surface mass balance smb here we combine in situ accumulation measurements and radar derived snowfall rates from princess elisabeth station pe located in the dml escarpment zone along with the european centre for medium range weather forecasts interim reanalysis to investigate moisture transport patterns responsible for these events in particular two high accumulation events in may 2009 and february 2011 showed an atmospheric river ar signature with enhanced integrated water vapor iwv concentrated in narrow long bands stretching from subtropical latitudes to the east antarctic coast adapting iwv based ar threshold criteria for antarctica by accounting for the much colder and drier environment we find that it was four and five ars reaching the coastal dml that contributed 74 80 of the outstanding smb during 2009 and 2011 at pe therefore accounting for ars is crucial for understanding east antarctic smb

numerical simulations of major ice streams in western dronning maud land antarctica under wet and dry basal conditions we study the presence and effect of subglacial water on the motion of the inland ice in western dronning maud land a full stokes model including three routing schemes for a thin film of subglacial water and a modification of a weertman type sliding relation to account for higher sliding velocities under wet basal conditions were used to perform 200 ka spin up simulations on a 2 5 km grid subsequent 30 ka simulations with wet and dry basal conditions were analysed for the effects of sliding on the thermal regime and velocities the occurrence of the major ice streams in this area is mainly controlled by the ice and bedrock geometry smaller glaciers only appear as pronounced individual glaciers when subglacial water is taken into account the thermal regime is affected by creep instabilities produced by an ice rheology including a microscopic water content leading to a cyclic behaviour on millennial time scales of the ice flow and occurrence of temperate ice at the base

recent snowfall anomalies in dronning maud land east antarctica in a historical and future climate perspective 1 enhanced snowfall on the east antarctic ice sheet is projected to significantly mitigate 21st century global sea level rise in recent years 2009 and 2011 regionally extreme snowfall anomalies in dronning maud land in the atlantic sector of east antarctica have been observed it has been unclear however whether these anomalies can be ascribed to natural decadal variability or whether they could signal the beginning of a long term increase of snowfall here we use output of a regional atmospheric climate model evaluated with available firn core records and gravimetry observations and show that such episodes had not been seen previously in the satellite climate data era 1979 comparisons with historical data that originate from firn cores one with records extending back to the 18th century confirm that accumulation anomalies of this scale have not occurred in the past 60 years although comparable anomalies are found further back in time we examined several regional climate model projections describing various warming scenarios into the 21st century anomalies with magnitudes similar to the recently observed ones were not present in the model output for the current climate but were found increasingly probable toward the end of the 21st century

in situ measurements of antarctic snow compaction compared with predictions of models 1 we describe in situ measurements of the compaction of antarctic snow at three different sites in antarctica the rate of compaction was measured hourly over various depth intervals for up to two years these measurements show that compaction at each of the sites occurs through slow viscous deformation of the snowpack with no significant contribution from sudden collapse of weak layers the measured rates of compaction at the coldest site exhibit a strong seasonality consistent with a temperature dependent sintering mechanism having activation energy of 70 kj mol 1 at the two warmer sites activation energies of 80 and 120 kj mol 1 provide slightly better agreement with the observations published models of snow compaction underestimate the temperature sensitivity a good match to our observations is provided by a semi empirical model based on rate equations for lattice diffusion nabarro herring creep of material around pores combined with normal grain growth this model also provides a theoretical basis for a widely used empirical model of snow compaction the rate coefficient for lattice diffusion inferred from our measurements is considerably higher than published values however and other creep mechanisms cannot be ruled out

melting and refreezing beneath roi baudouin ice shelf east antarctica inferred from radar gps and ice core data indicate that this reflector pattern is best fit by including basal melting of at least 15 cm a 1 this rate of melting is low compared with rates observed on larger ice shelves in both west and east antarctica ice cores extracted from a rift system close to the ice rise promontory show several meters of marine ice accreted beneath the shelf these observations of low rates of basal melting and limited distribution of accreted marine ice suggest that either antarctic surface water may reach the ice shelf base or that circulation beneath the shelf is likely dominated by the production of high salinity shelf water rather than the incursion of circumpolar deep water implying a weak sub shelf circulation system here many of the ice shelves located along the coast of dronning maud land are like roi baudouin ice shelf characterized by frequent ice rises and promontories therefore it is highly likely that these are also of shallow bathymetry and are subject to similarly weak side shelf basal melting and refreezing

precipitation sublimation and snow drift in the antarctic peninsula region from a regional atmospheric model 1 a regional atmospheric model with a horizontal grid spacing x of 14 km is used to study the surface mass balance components precipitation sublimation and snow drift in the region of the antarctic peninsula ap an integration is performed for the 7 year period 1987 1993 using a realistic forcing at the lateral model boundaries and at the sea surface output from this integration indicates that the precipitation reaches its maximum value on the northwestern slope of the ap where the upward motion in the atmosphere is largest uplift occurs upstream of the barrier affecting the precipitation distribution over sea the effect of the barrier on the precipitation distribution over the bellingshausen sea might have important implications for the ocean circulation in this region the mean precipitation over the grounded ice of the ap 1 20 m water eq yr 1 is 6 times larger than the mean value over all the grounded ice of antarctica our estimates for the surface sublimation and wind transport of snow over the grounding line toward the sea are 9 and 6 1 of the precipitation respectively in situ data of the wind distribution at three coastal sites located on the northern eastern and western sides of the ap are used to evaluate the modeled wind field which is important for the snow drift calculations for two of the three sites considered the prevailing wind direction and bimodal wind distribution are correctly represented by the model the calculated distribution of accumulation and ablation due to snow drift shows a complex pattern the wind removes snow from the spine of the ap where the near surface flow field diverges whereas deposition occurs mainly on the eastern slopes where the near surface flow field converges an intercomparison between two 7 year integrations at different horizontal resolution x 14 km and x 55 km shows that the precipitation on the northwestern slope is very sensitive to the model resolution in the x 14 km integration precipitation on the northwestern slope is higher than in x 55 km because of higher vertical velocities resulting in a 35 increase in average precipitation over the grounded ice of the ap

observations beneath pine island glacier in west antarctica and implications for its retreat thinning ice in west antarctica is currently contributing about 10 of the observed rise in global sea level observations obtained from an autonomous underwater vehicle operating beneath pine island glacier west antarctica reveal that the glacier was recently grounded on a transverse ridge in the sea floor but now warm sea water flows through the widening gap above the ridge thinning ice in west antarctica resulting from acceleration in the flow of outlet glaciers is at present contributing about 10 of the observed rise in global sea level1 pine island glacier in particular has shown nearly continuous acceleration2 3 and thinning4 5 throughout the short observational record the floating ice shelf that forms where the glacier reaches the coast has been thinning rapidly6 driven by changes in ocean heat transport beneath it as a result the line that separates grounded and floating ice has retreated inland7 these events have been postulated as the cause for the inland thinning and acceleration8 9 here we report evidence gathered by an autonomous underwater vehicle operating beneath the ice shelf that pine island glacier was recently grounded on a transverse ridge in the sea floor warm sea water now flows through a widening gap above the submarine ridge rapidly melting the thick ice of the newly formed upstream half of the ice shelf the present evolution of pine island glacier is thus part of a longer term trend that has moved the downstream limit of grounded ice inland by 30 km into water that is 300 m deeper than over the ridge crest the pace and ultimate extent of such potentially unstable retreat10 are central to the debate over the possibility of widespread ice sheet collapse triggered by climate change11 12

ice shelf density reconstructed from optical televiewer borehole logging 1 optical televiewer luminosity logs are compared with densities measured gravimetrically on 520 snow firn and ice samples from two locations of similar annual temperature 14 c and contrasting accumulation rates 0 23 and 0 43 m water equivalent per year on the roi baudouin ice shelf antarctica at the scale of 10 1 m an inverse exponential relationship r2 0 96 is recorded between density and luminosity indicating i that optical televiewing luminosity provides an effective proxy for density at such ice shelves and ii that densities may be reconstructed from boreholes drilled elsewhere by hot water without the need for core material our analysis also suggests that this relationship may hold for newly formed ice as well as for snow and firn at the scale of 10 1 m both luminosity and density show similar patterns but precise correlation is confounded by detailed differences between the two records

inference of accumulation rate patterns from deep layers in glaciers and ice sheets the spatial pattern of accumulation rate can be inferred from internal layers in glaciers and ice sheets non dimensional analysis determines where finite strain can be neglected shallow layer approximation or approximated with a local one dimensional flow model local layer approxima tion and where gradients in strain rate along particle paths must be included deep layers we develop a general geophysical inverse procedure to infer the spatial pattern of accumulation rate along a steady state flowband using measured topography of the ice sheet surface bed and a deep layer a variety of thermomechanical ice flow models can be used in the forward problem to calculate surface topography and ice velocity which are used to calculate particle paths and internal layer shapes an objective tolerance criterion prevents over fitting the data after making site specific simplifications in the thermomechanical flow algorithm we find the accumulation rate along a flowband through taylor mouth a flank site on taylor dome antarctica using a layer at approximately 100 m depth or 20 of the ice thickness accumulation rate correlates with ice surface curvature at this site gradients along flow paths critically impact inference of both the accumulation pattern and the depth age relation in a 100 m core

physical stratigraphy and sedimentology of the late pleistocene holocene tiber delta depositional sequence the tiber delta lies on the passive continental margin of central western italy the tiber delta is a late pleistocene holocene sedimentary succession and constitutes an incomplete high frequency depositional sequence 4th or 5th order which developed from the last post glacial rise in sea level to the present stillstand it is bound by a type 1 basal unconformity which cuts pleistocene deposits five depositional systems have been identified 1 coastal barrier lagoon 2 shelf transition 3 fluvial braided 4 tiber lagoonal deltas t1 t2 t3 and 5 tiber wave dominated delta the first four systems constitute the transgressive system tract tst which is characterized by a retrogradational parasequences set while the fifth system represents the highstand system tract hst characterized by only one parasequence progradational the evolution of these depositional systems has been mostly controlled by sea level rise which was not continuous but punctuated by eight minor stillstands and rapid rises this mechanism of sea level change led to the formation of parasequences that developed within the depositional systems from a palaeogeographical point of view the present tiber delta area was mainly characterized by a coastal barrier lagoon and tiber lagoonal deltas t1 t2 t3 which migrated landwards during the sea level rise throughout the time of the present stillstand the t3 lagoonal delta prograded rapidly into the lagoon reaching the coastal barrier and the lagoon was replaced first by marshes and then by the alluvial plain finally the tiber river overcame the littoral barrier supplying the coast giving rise to the present wave dominated delta

evolution of derwael ice rise in dronning maud land antarctica over the last millennia ice rises situated in the ice shelf belt around antarctica have a spatially confined flow regime with local ice divides beneath the divides ice stratigraphy often develops arches with amplitudes that record the divide s horizontal residence time and surface elevation changes to investigate the evolution of derwael ice rise dronning maud land antarctica we combine radar and gps data from three consecutive surveys with a two dimensional full stokes thermomechanically coupled transient ice flow model we find that the surface mass balance smb is higher on the upwind and lower on the downwind slopes near the crest the smb is anomalously low and causes arches to form in the shallow stratigraphy observable by radar in deeper ice arches are consequently imprinted by both smb and ice rheology raymond effect the data show how arch amplitudes decrease as along ridge slope increases emphasizing that the lateral positioning of radar cross sections is important for the arch interpretation using the model with three rheologies isotropic with n 3 4 5 and anisotropic with n 3 we show that derwael ice rise is close to steady state but is best explained using ice anisotropy and moderate thinning our preferred albeit not unique scenario suggests that the ice divide has existed for at least 5000 years and lowered at approximately 0 03 m a 1 over the last 3400 years independent of the specific thinning scenario our modeling suggests that derwael ice rise has exhibited a local flow regime at least since the mid holocene

high variability of climate and surface mass balance induced by antarctic ice rises ice rises play key roles in buttressing the neighbouring ice shelves and potentially provide palaeoclimate proxies from ice cores drilled near their divides little is known however about their influence on local climate and surface mass balance smb here we combine 12 years 2001 12 of regional atmospheric climate model racmo2 output at high horizontal resolution 5 5 km with recent observations from weather stations ground penetrating radar and firn cores in coastal dronning maud land east antarctica to describe climate and smb variations around ice rises we demonstrate strong spatial variability of climate and smb in the vicinity of ice rises in contrast to flat ice shelves where they are relatively homogeneous despite their higher elevation ice rises are characterized by higher winter temperatures compared with the flat ice shelf ice rises strongly influence smb patterns mainly through orographic uplift of moist air on the upwind slopes besides precipitation drifting snow contributes significantly to the ice rise smb the findings reported here may aid in selecting a representative location for ice coring on ice rises and allow better constraint of local ice rise as well as regional ice shelf mass balance

modelling of kealey ice rise antarctica reveals stable ice flow conditions in east ellsworth land over millennia flow at ice divides their shape size and internal structure depend not only on local conditions but also on the flow regimes and past histories of the surrounding ice masses here we use field data from kealey ice rise ellsworth land west antarctica in combination with flow modelling to investigate any possible signs of transients in the flow of the surrounding ice masses kealey ice rise shows linear surface features running parallel to its ridge in satellite imagery and a conspicuous layering in the ground penetrating radar data known as double peaked raymond bumps through numerical modelling by using an anisotropic full stokes thermomechanical flow solver we analyse the evolution of kealey ice rise and the timescales involved we conclude that the features observed in the stratigraphy of kealey ice rise require at least 3 ka of near stationary flow conditions however we cannot exclude the possibility of a recent flow reorganization in the last century we stress that the signs of stationary flow in radar stratigraphy observed in kealey ice rise have been observed in other ice divides in the east ellsworth land area suggesting stationary flow conditions over a millennial timescale in the region

ground based measurements of spatial and temporal variability of snow accumulation in east antarctica the east antarctic ice sheet is the largest highest coldest driest and windiest ice sheet on earth understanding of the surface mass balance smb of antarctica is necessary to determine the present state of the ice sheet to make predictions of its potential contribution to sea level rise and to determine its past history for paleoclimatic reconstructions however smb values are poorly known because of logistic constraints in extreme polar environments and they represent one of the biggest challenges of antarctic science snow accumulation is the most important parameter for the smb of ice sheets smb varies on a number of scales from small scale features sastrugi to ice sheet scale smb patterns determined mainly by temperature elevation distance from the coast and wind driven processes in situ measurements of smb are performed at single points by stakes ultrasonic sounders snow pits and firn and ice cores and laterally by continuous measurements using ground penetrating radar smb for large regions can only be achieved practically by using remote sensing and or numerical climate modeling however these techniques rely on ground truthing to improve the resolution and accuracy the separation of spatial and temporal variations of smb in transient regimes is necessary for accurate interpretation of ice core records in this review we provide an overview of the various measurement techniques related difficulties and limitations of data interpretation describe spatial characteristics of east antarctic smb and issues related to the spatial and temporal representativity of measurements and provide recommendations on how to perform in situ measurements

field studies of bottom crevasses in the ross ice shelf antarctica analyse des crevasses observees par sondages radar aeriens et terrestres localisation de leurs points de formation

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