snow megadune fields on the east antarctic plateau extreme atmosphere ice interaction large dune fields occupy more than 500 000 km 2 of the east antarctic plateau the megadunes or long wavelength surface ripples have amplitudes of only a few meters wavelengths of a few kilometers and parallel crests which can extend one hundred kilometers they occur in areas characterized by low accumulation extensively recrystallized snow and strong scattering of the microwave part of the spectrum dune crests are oriented perpendicular to the regional katabatic wind direction snow megadunes are unlikely to be formed by simple wind transport of snow particles

on the use of tide gauges to determine altimeter drift topex measurements of sea level variability have been compared to tide gauge measurements from 40 sites and to dynamic topography measurements computed from temperatures recorded at 23 tropical ocean global atmosphere toga tropical atmosphere ocean tao buoys in the eastern pacific and mean temperature salinity profiles buoy data in the western pacific were not used because of large long term slopes in the data that appear to be due to interannual salinity variations the relative drift between topex and the two different in situ sets of data agree within 1 mm yr 1 with a weighted average of 2 6 mm yr 1 and an estimated uncertainty of 1 5 mm yr 1 if values from an internal calibration of the topex altimeter are applied the consistency of the two relative drifts suggests that the slope is due at least in part to a drift in the topex measurement a substantial portion of this drift may be due to a drift in the topex microwave radiometer tmr since comparisons with three independent external measurements indicate a drift in sea level due to the tmr measurement of about 2 mm yr 1

undulating topography on the antarctic ice sheet revealed by noaa avhrr images undulating topography on the east antarctic ice sheet was clearly revealed by noaa avhrr the following three patterns of undulating topography were detected by using high pass filtered images from the visible to thermal infrared channels in coastal regions below 2000 m a s l undulation can be clearly detected by the fluctuation of reflectance in visible channel it has wavy structure with spacing less than 10 km and alignment at a right angle to the ice flow lines in the katabatic zone from 2000 m a s to 3000 m a s well defined fluctuations of albedo stpectrum can be seen with spacing from 10km to 20km aligned at right angles to the ice flow lines or prevailing katabatic wind direction ground survey data show that the undulating topography is associated with large variations of net accumulation rate on the inland plateau above 3000 m a s l undulation can be clearly seen in the fluctuation of thermal infrared channel in winter ground survey data show that the signal corresponds to the undulating topography the alignment of the undulation is at a right angle to the ice flow lines and the spacing is longer than 20 km the characteristics of these undulations represent the ice flow dynamics and

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

the ellsworth subglacial highlands inception and retreat of the west antarctic ice sheet antarctic subglacial highlands are where the antarctic ice sheets first developed and the pinning points where retreat phases of the marine based sectors of the ice sheet are impeded due to low ice velocities and limited present day change in the ice sheet interior west antarctic subglacial highlands have been overlooked for detailed study these regions have considerable potential however for establishing the locations from which the west antarctic ice sheet originated and grew and its likely response to warming climates here we characterize the subglacial morphology of the ellsworth subglacial highlands west antarctica from ground based and aerogeophysical radio echo sounding res surveys and the moderate resolution imaging spectroradiometer modis mosaic of antarctica we document well preserved classic landforms associated with restricted dynamic marine proximal alpine glaciation with hanging tributary valleys feeding a significant overdeepened trough the ellsworth trough cut by valley tidewater glaciers fjord mouth threshold bars down ice of two overdeepenings define both the northwest and southeast termini of paleo outlet glaciers which cut and occupied the ellsworth trough satellite imagery reveals numerous other glaciated valleys terminating at the edge of deep former marine basins e g bentley subglacial trench throughout the ellsworth subglacial highlands these geomorphic data can be used to reconstruct the glaciology of the ice masses that formed the proto west antarctic ice sheet the landscape predates the present ice sheet and was formed by a small dynamic ice field s similar to those of the present day antarctic peninsula at times when the marine sections of the west antarctic ice sheet were absent the ellsworth subglacial highlands represent a major seeding center of the paleo west antarctic ice sheet and its margins represent the pinning point at which future retreat of the marine based west antarctic ice sheet would be arrested

spatiotemporal variations of snowmelt in antarctica derived from satellite scanning multichannel microwave radiometer and special sensor microwave imager data 1978 2004 1 we derived the extent onset date end date and duration of snowmelt in antarctica from 1978 to 2004 using satellite passive microwave scanning multichannel microwave radiometer smmr and special sensor microwave imager ssm i data a wavelet transform based method was developed to determine and characterize melt occurrences about 9 12 of the antarctic surface experiences melt annually this is more than twice the surface melt extent measured in greenland seasonally surface melt primarily takes place in december january and february and peaks in early january regression analysis over the 25 year period of study reveals a negative interannual trend in surface melt nevertheless the trend inference is not statistically significant large year to year fluctuations characterize the interannual variability extremely high melt occurred in the 1982 1983 and 1991 1992 summers while extremely weak melt occurred in the 1999 2000 summer a strong correlation with air temperature suggests that the melt index can serve as a diagnostic indicator for regional temperature variations periodic melting has been observed over ross ice shelf ronne filchner ice shelf the west antarctic ice streams and outlet glaciers in the transantarctic mountains the antarctic peninsula west ice shelf shackleton ice shelf amery ice shelf and the ice shelf along the princess ragnhild coast experienced the most persistent and intensive melt and should be closely monitored for their stability in the future given the recent disintegration of the larsen ice shelf a and b

flow of the brunt ice shelf antarctica derived from landsat images 1974 85 satellite images recorded in 1973 1974 and 1985 of the brunt ice shelf are compared there are sufficient identifiable features moving with the ice shelf to show flow patterns over an area of 10000 km 2 velocities vary from 500 m a i in the west near the dawson lambton ice stream to 1300 m a i in the east within the stancomb wills ice stream

multi track extraction of two dimensional surface velocity by the combined use of differential and multiple aperture insar in the amery ice shelf east antarctica abstract glaciers and ice streams drain the ice from the ice sheets to the ice shelves and contribute to global sea level changes therefore ice velocity is an essential parameter for the assessment of mass balance in this paper we propose an approach for the multi track extraction of two dimensional ice surface velocity by the combined use of multiple aperture interferometry mai and differential synthetic aperture radar interferometry dinsar the azimuth and ground range ice movements of each individual track are first estimated by the use of mai and dinsar respectively a seamless two dimensional ice velocity map is then achieved by calibration and mosaicking of the estimated velocity of the multi temporal and multi track measurements over a large area finally the dynamic behavior of the amery ice shelf is analyzed by formulating a long term series of ice flow velocities consisting of historical surface velocities 1968 1990 the estimated surface velocity by the proposed method with ers 1 2 data 1996 existing surface velocity products such as the radarsat 1 antarctic mapping project ramp velocities 1997 2000 and rignot s results 2007 2010 as well as the estimated velocities obtained by the use of the offset tracking method from landsat 8 images 2013 2014 the results show that the estimated velocity obtained by the use of the proposed method is superior to the other methods and the long term series of ice velocity measurements shows that the ice velocity in the amery ice shelf has hardly changed over the past 45 years 1968 2014 we conclude that the ice flow velocity of the amery ice shelf has showed a slight deceleration over the past 45 years

spectral bidirectional reflectance of antarctic snow measurements and parameterization the bidirectional reflectance distribution function brdf of snow was measured from a 32 m tower at dome c at latitude 75 s on the east antarctic plateau these measurements were made at 96 solar zenith angles between 51 and 87 and cover wavelengths 350 2400 nm with 3 to 30 nm resolution over the full range of viewing geometry the brdf at 900 nm had previously been measured at the south pole the dome c measurement at that wavelength is similar at both locations the natural roughness of the snow surface causes the anisotropy of the brdf to be less than that of flat snow the inherent brdf of the snow is nearly constant in the high albedo part of the spectrum 350 900 nm but the angular distribution of reflected radiance becomes more isotropic at the shorter wavelengths because of atmospheric rayleigh scattering parameterizations were developed for the anisotropic reflectance factor using a small number of empirical orthogonal functions because the reflectance is more anisotropic at wavelengths at which ice is more absorptive albedo rather than wavelength is used as a predictor in the near infrared the parameterizations cover nearly all viewing angles and are applicable to the high parts of the antarctic plateau that have small surface roughness and at viewing zenith angles less than 55 elsewhere on the plateau where larger surface roughness affects the brdf at larger viewing angles the root mean squared error of the parameterized reflectances is between 2 and 4 at wavelengths less than 1400 nm and between 5 and 8 at longer wavelengths

in situ sampled snow particle sizes of the east antarctic ice sheet and their relation to physical and remotely sensed snow surface parameters knowledge of snow properties across antarctica is important in estimating how climate could potentially influence the mass balance of the antarctic ice sheet however measuring these variables has proven to be challenging because appropriate techniques have not yet been developed and extensive datasets of field estimates are lacking the goal of this study was to estimate the relationship between field observed snow particle size parameters from across the east antarctic ice sheet and a suite of spatial datasets i e topography remote sensing data using a principal component analysis pca five snow particle size parameters were correlated to spatial datasets of the following five groups 1 relief properties such as elevation and slope 2 remote sensing data from moderate resolution imaging spectroradiometer modis and synthetic aperture radar sar sensors 3 spatially interpolated data i e 10 m maps of temperature and approximate snow accumulation in kg m 2 a 1 4 field retrieved data on surface roughness and 5 in situ elevation and distance from the coast the results show that the relief parameter slope correlated best with the snow particle length and area r 0 76 r 0 80 further the pca indicated that the different remote sensing parameters correlated differently with the size parameters and that the most common parameter in visual analysis particle length grain diameter is not always the optimal parameter to characterize the snow particle size as for example area correlates better to slope and aspect than length

constructing improved decadal records of antarctic ice shelf height change from multiple satellite radar altimeters abstract antarctica s ice shelves the floating extensions of the ice sheet exert an important dynamic constraint on the flow of ice from the grounded ice sheet to the ocean and therefore on changes in global sea level thinning of an ice shelf reduces its ability to restrain the ice discharge from the grounded ice sheet however our understanding of how ice shelf processes couple ice sheet changes to climate variability is still rudimentary in part this is due to the brevity and low temporal resolution of surveys of ice shelf thickness relative to the broad range of time scales on which ice sheet mass fluctuates here we present improved procedures to construct 18 year 1994 2012 time series of antarctic ice shelf surface height at high spatial resolution 30 km by merging data from three overlapping satellite radar altimeter missions ers 1 ers 2 and envisat we apply an averaging scheme to enhance the signal to noise ratio of height changes over the floating ice shelves and extract low order polynomial trends using a robust approach regularized regression with cross validation that accounts for both bias and variance in the fit we construct formal confidence intervals by bootstrap resampling of the residuals of the fit the largest source of height error arises from the interaction of the radar signal with the snow and firn surface on annual time scales changes in surface and sub surface scattering and radar penetration lead to apparent height changes that are larger than the true surface height change arising from densification our 18 year time series of surface height provide an insight into how ice shelves respond to the changing atmospheric and oceanic conditions our methods could also be applied to grounded portions of the ice sheets both in antarctica and greenland

ice shelf grounding zone structure from icesat laser altimetry 1 we present a technique for investigating the grounding zone gz of antarctic ice shelves using laser altimetry from the ice cloud and land elevation satellite icesat most surface height variability in the gz is easily resolved by the icesat laser s 65 m footprint and 172 m along track spacing comparisons of repeated tracks sampled at different phases of the ocean tide identify the landward and seaward limits of tide forced ice flexure providing gz location and width information for each track using icesat data in the institute ice stream region of southern ronne ice shelf we demonstrate that the location of the gz based on feature identification in satellite imagery or digital elevation models may be in error by several km our results show that icesat will contribute significantly to improving knowledge of gz structure and to studies requiring accurate gz locations e g ice mass balance calculations and ice sheet ocean modeling

properties of a marine ice layer under the amery ice shelf east antarctica the amery ice shelf east antarctica undergoes high basal melt rates near the southern limit of its grounding line where 80 of the ice melts within 240 km of becoming afloat a considerable portion of this later refreezes downstream as marine ice this produces a marine ice layer up to 200 m thick in the northwest sector of the ice shelf concentrated in a pair of longitudinal bands that extend some 200 km all the way to the calving front we drilled through the eastern marine ice band at two locations 70 km apart on the same flowline we determine an average accretion rate of marine ice of 1 1 0 2 m a 1 at a reference density of 920 kg m 3 between borehole sites and infer a similar average rate of 1 3 0 2 m a 1 upstream the deeper marine ice was permeable enough that a hydraulic connection was made whilst the drill was still 70 100 m above the ice shelf base below this marine close off depth borehole video imagery showed permeable ice with water filled cavities and individual ice platelets fused together while the upper marine ice was impermeable with small brine cell inclusions we infer that the uppermost portion of the permeable ice becomes impermeable with the passage of time and as more marine ice is accreted on the base of the shelf we estimate an average closure rate of 0 3 m a 1 between the borehole sites upstream the average closure rate is faster at 0 9 m a 1 we estimate an average porosity of the total marine ice layer of 14 20 such that the deeper ice must have even higher values high permeability implies that sea water can move relatively freely through the material and we propose that where such marine ice exists this renders deep parts of the ice shelf particularly vulnerable to changes in ocean properties

grounding line migration from 1992 to 2011 on petermann glacier north west greenland we use satellite radar interferometry to investigate changes in the location of the petermann glacier grounding line between 1992 and 2011 the grounding line location was identified in 17 quadruple difference interferograms produced from european remote sensing ers 1 2 data the most extensive time series assembled at any ice stream to date there is close agreement 20 6 cm between vertical displacement of the floating ice shelf and relative tide amplitudes simulated by the arctic ocean dynamics based tide model 5 aodtm 5 arctic tide model over the 19 a period the groundling line position varied by 470 m on average with a maximum range of 7 0 km observed on the north east margin of the ice stream although the mean range 2 8 km and variability 320 m of the grounding line position is considerably lower if the unusually variable north east sector is not considered our observations demonstrate that large isolated movements cannot be precluded thus sparse temporal records should be analysed with care the grounding line migration observed on petermann glacier is not significantly correlated with time r 2 0 22 despite reported ice shelf thinning and episodes of large iceberg calving which suggests that unlike other ice streams on the south west margin of the greenland ice sheet petermann glacier is dynamically stable

integrating satellite observations with modelling basal shear stress of the filcher ronne ice streams antarctica using inverse methods constrained by recent satellite observations we have produced a comprehensive estimate of the basal shear stress beneath the filchner ronne ice streams the inversions indicate that a weak bed approx 4 20 kpa underlies much of these ice streams compared to the ross ice streams the distribution of weak subglacial till is more heterogeneous with sticky spots providing much of the resistance to flow a weak bed beneath recovery ice stream extends several hundred kilometres inland with flow along this ice stream discrepancies between thickness measurements and flux estimates suggest the existence of a deep 1400 m trough not resolved by existing maps of subglacial topography we hypothesize that the presence of this and other deep troughs is a major influence on this sector of the ice sheet that is not fully incorporated in current models of ice sheet evolution

on the formation of blue ice on byrd glacier antarctica blue ice areas bias cover 1 of the east antarctic ice sheet and are visual evidence of persistent ablation in these regions more snow is sublimated and or eroded than is accumulated the physical processes driving the formation of bias are poorly understood here we combine a firndensification model with high resolution 5 5 km maps of surface mass balance and ice velocity to simulate the build up and removal of a firn layer along an ice flowline passing byrd glacier a bia is formed once the complete firn layer is removed feedback processes which enhance blue ice formation through the difference in surface characteristics of snow and ice are examined using sensitivity simulations the presence of blue ice on byrd glacier is found to be mainly determined by 1 ice velocity 2 surface mass balance and 3 the characteristics thickness mass of the firn layer prior to entering the ablation area with a moderate decrease of the surface mass balance the location and extent of the simulated bia on byrd glacier is found to be in good qualitative agreement with modis optical imagery

a decade of west antarctic subglacial lake interactions from combined icesat and cryosat 2 altimetry we use cryosat 2 interferometric satellite radar altimetry over the mercer and whillans ice streams west antarctica to derive surface elevation changes due to subglacial lake activity at monthly resolution for the period 2010 to 2013 we validate cryosat 2 elevation measurements trends and spatial patterns of change using satellite image differencing and in situ vertical movement from global positioning system gps data two subglacial lake discharge events occur in the same subglacial hydrological catchment within a 9 month period using gps measurements that are spanning the gap between the ice cloud and land elevation satellite and cryosat 2 missions we cross calibrate the two missions to establish the efficacy of cryosat 2 altimetry to measure dynamic changes on the ice sheets

major ice sheet change in the weddell sea sector of west antarctica over the last 5 000 years until recently little was known about the weddell sea sector of the west antarctic ice sheet in the last 10 years a variety of expeditions and numerical modelling experiments have improved knowledge of its glaciology glacial geology and tectonic setting two of the sector s largest ice streams rest on a steep reverse sloping bed yet despite being vulnerable to change satellite observations show contemporary stability there is clear evidence for major ice sheet reconfiguration in the last few thousand years however knowing precisely how the ice sheet has changed in the past and when would allow us to better understand whether it is now at risk two competing hypotheses have been established for this glacial history in one the ice sheet retreated and thinned progressively from its last glacial maximum position retreat stopped at or very near the present position in the late holocene alternatively in the late holocene the ice sheet retreated significantly upstream of the present grounding line and then advanced to the present location due to glacial isostatic adjustment and ice shelf and ice rise buttressing both hypotheses point to data and theory in their support yet neither has been unequivocally tested or falsified here we review geophysical evidence to determine how each hypothesis has been formed where there are inconsistencies in the respective glacial histories how they may be tested or reconciled and what new evidence is required to reach a common model for the late holocene ice sheet history of the weddell sea sector of west antarctica

greenland ice sheet surface properties and ice dynamics from ers 1 sar imagery c band synthetic aperture radar sar imagery from the european space agency s ers 1 satellite reveals the basic zonation of the surface of the greenland ice sheet the zones have backscatter signatures related to the structure of the snowpack which varies with the balance of accumulation and melt at various elevations the boundaries of zones can be accurately located with the use of this high resolution imagery the images also reveal a large flow feature in northeast greenland that is similar to ice streams in antarctica and may play a major role in the discharge of ice from the ice sheet

velocity and strain rates derived from insar analysis over the amery ice shelf east antarctica we use displacements derived from matching complex synthetic aperture radar data using maximum coherence to generate a dense network of velocity estimates over the amery ice shelf from these velocities we generate the horizontal strain rate components and resolve them with respect to the local flow direction we present the spatial distributions of velocity and transverse shear strain rate and use them to investigate features of the flow regime for the shelf from the southern end of the shelf velocity decreases from a high of about 800ma 1 to around 300 ma 1 and then increases to a maximum of about 1350ma 1 at the centre of the front strain rates vary systematically across and along the shelf the pattern of the transverse shear strain rate clearly identifies the shear margins where values exceed 0 1 a 1 in the southern section of the shelf the pattern also shows longitudinal bands of enhanced shear strain rate containing ice with a strong preferred crystal fabric that was advected from shear margins upstream in the northern section of the shelf significant values of longitudinal and traverse stresses lead to enhanced shear deformation through their effect on the octahedral shear stress term

blue ice areas in antarctica derived from noaa avhrr satellite data we have mapped antarctic blue ice areas using the u s national oceanic and atmospheric administration noaa advanced very high resolution radiometer avhrr antarctica cloud free image mosaic established by the united states geological survey the mosaic consists of 38 scenes acquired from 1980 to 1994 our results show that approximately 60 000 km2 of blue ice exist for each of the two main types of blue ice melt induced and wind induced normally the former type is located on slopes in coastal areas where climate conditions i e persistent winds and temperature together with favourable surface orientation sustain conditions for surface and near surface melt the latter blue ice category occurs near mountains or on outlet glaciers often at higher elevations where persistent winds erode snow away year round and combined with sublimation creates areas of net ablation furthermore we have identified an additional area of 121 000 km2 as having potential for blue ice however in these areas features such as mixed pixels glazed snow surfaces crevasses and or shadows make interpretation more uncertain in conclusion a conservative estimate of antarctic blue ice area coverage by this method is found to be 120 000 km2 0 8 of the antarctic continent with a potential maximum of 241 000 km2 1 6 of the antarctic continent

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

effect of sastrugi on snow bidirectional reflectance and its application to modis data 1 snow surface roughness such as sastrugi on the antarctic ice sheet can be a cause of error for remote sensing of snow parameters the effect of sastrugi on snow bidirectional reflectance was assessed by a field experiment model simulations and satellite measurements the hemispherical directional reflectance factor hdrf of artificial sastrugi like linear ridges measured at nakasatsunai hokkaido japan exhibited different patterns from that of a flat surface with the difference of more than 50 for some geometries a 3 d monte carlo radiative transfer model mc model reproduced both the hdrf measurements for the artificial ideal sastrugi and previous measurements for natural sastrugi at the south pole furthermore the sastrugi effect was applied to remote sensing failure to include the surface roughness in models for developing snow grain size lookup tables can lead to order of magnitude retrieval errors using the mc model and multiangle data derived from the moderate resolution imaging spectrometer over the south pole during the 2003 2004 summer the sastrugi and snow parameters were retrieved the height to width ratio of sastrugi reduced from 0 1 to 0 02 whereas the azimuth angle was nearly constant within the range of 0 30 during the summer the snow grain size showed a seasonal variation which depended on the spectral channel these retrieved parameters were consistent with existing ground measurements the results suggest that a combination of multiangle data and a 3 d radiative transfer model can be used to quantitatively estimate surface roughness along with snow grain size on ice sheets

a glaciological map of filchner ronne ice shelf antarctica a set of landsat 5 multispectral scanner mss images of filchner ronne ice shelf was commissioned by the institut fur angewandte geodasie and recorded over a short period in early 1986 a mosaic of digitally enhanced images was constructed using all available ground control in due course it is planned to use the data for the production of a series of digital image maps at a scale of 1 1 000 000 meanwhile a line map has been prepared at a scale of 1 2 000 000 to show the principal glaciological features the new mosaic shows much more detail than earlier landsat images and extends coverage to higher latitudes more of the poorly known southern boundary of the ice shelf can be identified but floating ice still extends beyond the limit of coverage extensive ice rumples are revealed many of them undetected in earlier imagery flow bands can be tracked without a break from their ice stream source to the ice front over distances of up to 800 km even minor tributaries and sheet flow from the inland ice sheet between the ice streams yield narrow but identifiable flow bands ice thickness velocity and mass flux data are reviewed in order to underline their dependence on good mapping

improving avhrr resolution through data cumulation for mapping polar ice sheets abstract data cumulation is a digital image processing technique in which several scenes of the same area taken under similar viewing conditions are combined into a single image of enhanced spatial and radiometric resolution this is effected by the reduction of aliasing in the along scan and along track sampling of scenes and by the reduction of noise content in the combined scene the technique hinges on two key steps accurate image coregistration to a precision significantly better than 1 pixel and cumulation of multiple image data grids derived from the individual images into a single image we report here on the development and initial results of the application of data cumulation using advanced very high resolution radiometer avhrr satellite images of the polar ice sheets the process can improve the real spatial resolution of avhrr data in the along scan direction from 1000 m to 650 m and in the along track direction from 1400 m to 700 m justifying a decrease in pixel size to about 500 m the technique is demonstrated in an image of a portion of the ross ice shelf in antarctica

ice velocity mapping of ross ice shelf antarctica by matching surface undulations measured by icesat laser altimetry abstract we present a novel method for estimating the surface horizontal velocity on ice shelves using laser altimetry data from the ice cloud and land elevation satellite icesat 2003 2009 the method matches undulations measured at crossover points between successive campaigns elevation measurements are first relocated into a time varying moving coordinate system using an initial velocity e g from velmap and then crossover height differences are minimized with an adjustment vector errors in geolocation of the icesat tracks result in some error in the adjustment vectors but these are small relative to the velocity adjustment for fast moving ice shelves we use the algorithm to estimate changes in the ice velocity of ross ice shelf between an earlier mapping from velmap and the icesat period the new velocity field is compared with velocities from in situ measurements and satellite radar interferometry the slowdown of 98 34 m yr 1 23 is observed in the ice shelf downstream of whillans ice stream and the deceleration rate is 3 1 1 1 m yr 2 during last three decades the method can be expanded to the simultaneous mapping of ice horizontal velocity ice thickness change and surface deformation for antarctic ice shelves as well as a more accurate mapping using future icesat 2 measurements

contact spectroscopy for determination of stratigraphy of snow optical grain size we present a technique for in situ measurement of the vertical and spatial stratigraphic distribution of snow optical grain size with a coupled contact illumination probe and field spectroradiometer accurate measurements of optical equivalent grain size are critical for modeling radiative properties of snow such as spectral albedo and microwave emission measurements of the spectral reflectance of the snow pit surface are made at 2 cm intervals in the vertical plane under constant illumination and view geometries we invert the integral of the continuum normalization of the ice absorption feature with maximum at 1 03 mm wavelength for optical equivalent grain size using the validated model of nolin and dozier 2000 that has accuracy of 10 50 mm across the grain size range 50 900 mm results are presented for an alpine site in southwest colorado usa across the ablation season and for a greenland ice sheet site at the onset of snowmelt these results suggest that traditional measurements of grain size using a hand lens are nearly accurate only for rounded grains r 2 0 41 rmse 160 mm for polycrystals and faceted grains the hand lens approach is very inaccurate r 2 0 03 and 0 24 rmse 1206 and 1010 mm respectively we demonstrate an order of magnitude improvement in modeling of shortwave spectral albedo and net shortwave flux with contact spectroscopy measurements of grain size stratigraphy over those from a hand lens

quantifying vulnerability of antarctic ice shelves to hydrofracture using microwave scattering properties abstract recent ice shelf disintegrations on the antarctic peninsula and subsequent increases in ice sheet mass loss have highlighted the importance of tracking ice shelf stability with respect to surface melt ponding and hydrofracture in this study we use active microwave scatterometry in time series to estimate melt season duration and winter backscatter levels as a proxy for relative concentration of refrozen ice lenses in antarctic ice shelf firn we demonstrate a physical relationship between melt days and firn ice backscatter using scatterometry and field data from greenland and apply the observed relationship to derive and map a vulnerability index for antarctica s ice shelves the index reveals that some remaining antarctic peninsula ice shelves have already reached a firn state that is vulnerable to hydrofracture we also show that the progression of an ice shelf towards vulnerability is affected by many factors such as surface mass balance internal stresses and ice shelf geometry

analysis of velocity field mass balance and basal melt of the lambert glacier amery ice shelf system by incorporating radarsat sar interferometry and icesat laser altimetry measurements 1 by incorporating recently available remote sensing data we investigated the mass balance for all individual tributary glacial basins of the lambert glacier amery ice shelf system east antarctica on the basis of the ice flow information derived from sar interferometry and icesat laser altimetry we have determined the spatial configuration of eight tributary drainage basins of the lambert amery glacial system by combining the coherence information from sar interferometry and the texture information from sar and modis images we have interpreted and refined the grounding line position we calculated ice volume flux of each tributary glacial basin based on the ice velocity field derived from radarsat three pass interferometry together with ice thickness data interpolated from australian and russian airborne radio echo sounding res surveys and inferred from icesat laser altimetry data our analysis reveals that three tributary basins have a significant net positive imbalance while five other subbasins are slightly positive or close to zero balance overall in contrast to previous studies we find that the grounded ice in lambert glacier amery ice shelf system has a positive mass imbalance of 22 9 4 4 gt a 1 the net basal melting for the entire amery ice shelf is estimated to be 27 0 7 0 gt a 1 the melting rate decreases rapidly from the grounding zone to the ice shelf front significant basal refreezing is detected in the downstream section of the ice shelf the mass balance estimates for both the grounded ice sheet and the ice shelf mass differ substantially from other recent estimates

thwaites glacier grounding line retreat influence of width and buttressing parameterizations major ice loss has recently been observed along coastal outlet glaciers of the west antarctic ice sheet mainly due to increased melting below the ice shelves however the behavior of this marine ice sheet is poorly understood leading to significant shortcomings in ice sheet models attempting to predict future sea level rise the stability of a marine ice sheet is controlled by the dynamics at the grounding line the boundary between the grounded ice stream and the floating ice shelf one of the largest contributors to current sea level rise is the fast flowing thwaites glacier which flows into the amundsen sea here we use an ice stream ice shelf model and perform a number of experiments along a central flowline to analyze the sensitivity of its grounding line on centennial timescales in the absence of width and buttressing effects we find that the grounding line retreats by 300 km in 200 years from the present day rate of 1 5 km a 1 with variable glacier width implemented in the model flow convergence slows the retreat of thwaites grounding line at 0 3 1 2 km a 1 the parameterization of ice shelf buttressing according to different observed scenarios further reduces the glacier retreat and can even lead to a slight advance in the most buttressed case

west antarctic ice stream discharge variability mechanism controls and pattern of grounding line retreat west antarctic ice streams show pronounced flow variability in their downstream reaches with changes stranding formerly fast flowing ice and redirecting discharge a simple model in which the temperature gradient in basal ice provides control of fast sliding in the downstream reach can explain this behavior downstream thinning steepens the temperature gradient near the bed increasing upward heat flow and the tendency toward basal freezing the basal temperature gradient is steepest and the tendency toward basal freezing the strongest in ice that has experienced the most rapid downstream thinning that is the fastest flowing ice the most successful rapid outflows are regions where basal water from elsewhere is likely to be consumed freezing here leads to episodic slow downs and redirections of flow the history of which appears in satellite imagery as ice rises distorted streaklines and margin jumps created when discharge migrates to areas with more favorable basal conditions one compelling consequence of this process is that it makes catastrophic collapse less likely if discharge currents are forced to slow when they become too fast thin then there may be an upper bound on the retreat rate and discharge flux of the west antarctic ice sheet wais ice stream system under the present climate

2001 2009 elevation and mass losses in the larsen a and b embayments antarctic peninsula we investigate the elevation and mass balance response of tributary glaciers following the loss of the larsen a and b ice shelves antarctic peninsula in 1995 and 2002 respectively our study uses modis imagery to track ice extent and aster and spot5 digital elevation models dems plus atm and icesat laser altimetry to track elevation changes spanning the period 2001 09 the measured larsen b tributary glaciers hektoria green evans punchbowl jorum and crane lost up to 160 m in elevation during 2001 06 and thinning continued into 2009 elevation changes were small for the more southerly flask and leppard glaciers which are still constrained by a larsen b ice shelf remnant in the northern embayment continued thinning of 3 m a 1 on drygalski glacier 14 years after the larsen a ice shelf disintegrated suggests that mass losses for the exposed larsen b tributaries will continue for years into the future grounded ice volume losses exceed 13 km 3 for crane glacier and 30 km 3 for the hektoria green evans glaciers the combined mean loss rate for 2001 06 is at least 11 2 gt a 1 our values differ significantly from published mass budget based estimates for these embayments but are a reasonable fraction of grace derived rates for the region 40 gt a 1

tides of the northwestern ross sea and their impact on dense outflows of antarctic bottom water abstract moored and depth profile measurements of hydrography and currents during the 2003 2005 antarctic slope anslope program on the shelf slope region near drygalski trough sill in the northwest ross sea have revealed an energetic benthic outflow of cold dense antarctic bottom water aabw produced near the shelf break this outflow couples dense water production processes on the continental shelf to ventilation of the global deep ocean we use time series of bottom pressure and currents on the anslope moorings and a high resolution three dimensional primitive equation numerical model to explore the hypothesis that the tidal currents near the shelf break have a significant impact on outflow volume transport and hydrographic properties tidal currents exceed 1 m s 1 at spring tide over the outer shelf and upper slope tidal advection at spring tide carries water parcels 20 km across slope during a half tidal cycle sufficient to advect water from northern drygalski trough across the sill to the shelf break or similarly from the shelf break 500 m water depth down to the 1600 m isobath a tidally rectified lagrangian mean flow of order 0 05 0 1 m s 1 over the outer shelf and upper slope accompanies the spring tide thickness and water mass properties of the benthic layer over the sill and upper slope exhibit pronounced tidal cycles due to advection of hydrographic gradients and to energetic mixing that can extend more than halfway up from the seabed to the ocean surface maximum parameterized diapycnal diffusivity in the benthic layer at spring tides approaches 1 m 2 s 1 the addition of tides has a profound effect on time averaged outflows of aabw primarily through an increase in benthic layer thickness during spring tide downslope volume fluxes of aabw over the slope averaged over a tidal cycle are 2 5 times larger at spring tide than at neap indicating a need to include the effect of tides in large scale ocean models attempting to represent shelf water contributions to the global ocean circulation

a millennium of variable ice flow recorded by the ross ice shelf antarctica an enhanced composite advanced very high resolution radiometer avhrr image is used to map flow stripes and rifts across the ross ice shelf antarctica the patterns of these flow related features reveal a history of discharge variations from the ice streams feeding the eastern part of the shelf the most profound variations are visible in the track of rifts downstream of crary ice rise flow stripe bends to the west of this ice rise and adjacent to steershead ice rise and changes in the northern margin of ice stream b the track of rifts downstream of crary ice rise indicates that the ice rise has existed for at least 700 years the character of this track changes about 350 km downstream indicating a rearrangement of flow patterns about 550 years ago the large bulge in the flow stripes to the west of crary ice rise is shown in detail with bent flow stripes extending for several hundred kilometers along flow this feature formed from the south possibly due to a change in the discharge of ice stream a the avhrr image documents a complex history associated with the shutdown of ice stream c with changes in the margins of ice stream c and the northern margin of ice stream b and the grounding of steershead ice rise with an associated bending and truncation of flow stripes landsat imagery shows a region that appears to be actively extending just downstream of the ice rise as the shelf continues to respond to recent changes in ice stream discharge we present a four stage flow history which accounts for the features preserved in the ice shelf

arise antarctic remote ice sensing experiment in the east 2003 validation of satellite derived sea ice data products preliminary results are presented from the first validation of geophysical data products ice concentration snow thickness on sea ice hs and ice temperature ti from the nasa eos aqua amsr e sensor in east antarctica in september october 2003 the challenge of collecting sufficient measurements with which to validate the coarse resolution amsr e data products adequately was addressed by means of a hierarchical approach using detailed in situ measurements digital aerial photography and other satellite data initial results from a circumnavigation of the experimental site indicate that at least under cold conditions with a dry snow cover there is a reasonably close agree ment between satellite and aerial photo derived ice concentrations i e 97 2 3 6 for nt2 and 96 5 2 5 for bba algorithms vs 94 3 for the aerial photos in general the amsr e concentration represents a slight overestimate of the actual concentration with the largest discrepancies occurring in regions containing a relatively high proportion of thin ice the amsr e concentrations from the nt2 and bba algorithms are similar on average although differences of up to 5 occur in places again related to thin ice distribution the amsr e ice temperature ti product agrees with coincident surface measurements to approximately 0 58c in the limited dataset analyzed regarding snow thickness the amsr hs retrieval is a significant underestimate compared to in situ measurements weighted by the percentage of thin ice and open water present for the case study analyzed the underestimate was 46 for the overall average but 23 compared to smooth ice measurements the spatial distribution of the amsr e hs product follows an expected and consistent spatial pattern suggesting that the observed difference may be an offset at least under freezing conditions areas of discrepancy are identified and the need for future work using the more extensive dataset is highlighted

extensive retreat and re advance of the west antarctic ice sheet during the holocene to predict the future contributions of the antarctic ice sheets to sea level rise numerical models use reconstructions of past ice sheet retreat after the last glacial maximum to tune model parameters 1 reconstructions of the west antarctic ice sheet have assumed that it retreated progressively throughout the holocene epoch the past 11 500 years or so 2 4 here we show however that over this period the grounding line of the west antarctic ice sheet which marks the point at which it is no longer in contact with the ground and becomes a floating ice shelf retreated several hundred kilometres inland of today s grounding line before isostatic rebound caused it to re advance to its present position our evidence includes first radiocarbon dating of sediment cores recovered from beneath the ice streams of the ross sea sector indicating widespread holocene marine exposure and second ice penetrating radar observations of englacial structure in the weddell sea sector indicating ice shelf grounding we explore the implications of these findings with an ice sheet model modelled re advance of the grounding line in the holocene requires ice shelf grounding caused by isostatic rebound our findings overturn the assumption of progressive retreat of the grounding line during the holocene in west antarctica and corroborate previous suggestions of ice sheet re advance 5 rebound driven stabilizing processes were apparently able to halt and reverse climate initiated ice loss whether these processes can reverse present day ice loss 6 on millennial timescales will depend on bedrock topography and mantle viscosity parameters that are difficult to measure and to incorporate into ice sheet models

antarctic ice shelf calving triggered by the honshu japan earthquake and tsunami march 2011 we use european space agency envisat data to present the first observational evidence that a northern hemisphere tsunami triggered antarctic ice shelf calving more than 13 000 km away the honshu tsunami of 11 march 2011 traversed the pacific ocean in 46 years this event further illustrates the growing evidence of ocean wave impact on antarctic calving and emphasizes the teleconnection between the antarctic ice sheet and events as far away as the northern hemisphere

impacts of warm water on antarctic ice shelf stability through basal channel formation the antarctic ice sheet is buttressed by floating ice shelves remote sensing data show extensive basal channels particularly in west antarctica which grow quickly in response to warm water intrusion antarctica s ice shelves provide resistance to the flow of grounded ice towards the ocean if this resistance is decreased as a result of ice shelf thinning or disintegration1 acceleration of grounded ice can occur increasing rates of sea level rise loss of ice shelf mass is accelerating especially in west antarctica where warm seawater is reaching ocean cavities beneath ice shelves2 here we use satellite imagery airborne ice penetrating radar and satellite laser altimetry spanning the period from 2002 to 2014 to map extensive basal channels in the ice shelves surrounding antarctica the highest density of basal channels is found in west antarctic ice shelves within the channels warm water flows northwards eroding the ice shelf base and driving channel evolution on annual to decadal timescales our observations show that basal channels are associated with the development of new zones of crevassing suggesting that these channels may cause ice fracture we conclude that basal channels can form and grow quickly as a result of warm ocean water intrusion and that they can structurally weaken ice shelves potentially leading to rapid ice shelf loss in some areas

investigating tidal flexure on an ice shelf using kinematic gps the positions of ice stream grounding zones are uniquely sensitive to changes in the mass balance of the ice sheet present methods for locating groundingzone features are either imprecise or require considerable effort in interpretation and so are of little value for change studies we present a new method which uses the kinematic gps technique to locate the position of the limit of tidal flexure the method involves the collection of at least two surface elevation profiles along the same track through the grounding zone at different times during the tidal cycle the elevation profiles obtained coincide upstream of the limit of flexure but diverge downstream of the limit of flexure subtracting the profiles produces a tidal def1ection profile which shows directly the response of the ice shelf to the tidal forcing we present two examples of the use of this method both on rutford ice stream antarctica the first is across the grounding zone and shows that the method is capable of measuring grounding positions to around 200 m precision the second taken across an active shear margin shows a tidal deflection profile with an absence of steps that would indicate the presence of fracture planes penetrating from the ice base to sea level

wissard at subglacial lake whillans west antarctica scientific operations and initial observations a clean hot water drill was used to gain access to subglacial lake whillans slw in late january 2013 as part of the whillans ice stream subglacial access research drilling wissard project over 3 days we deployed an array of scientific tools through the slw borehole a downhole camera a conductivity temperature depth ctd probe a niskin water sampler an in situ filtration unit three different sediment corers a geothermal probe and a geophysical sensor string our observations confirm the existence of a subglacial water reservoir whose presence was previously inferred from satellite altimetry and surface geophysics subglacial water is about two orders of magnitude less saline than sea water 0 37 0 41 psu vs 35 psu and two orders of magnitude more saline than pure drill meltwater 0 002 psu it reaches a minimum temperature of 0 558c consistent with depression of the freezing point by 7 019 mpa of water pressure subglacial water was turbid and remained turbid following filtration through 0 45 mm filters the recovered sediment cores which sampled down to 0 8 m below the lake bottom contained a macroscopically structureless diamicton with shear strength between 2 and 6 kpa our main operational recommendation for future subglacial access through water filled boreholes is to supply enough heat to the top of the borehole to keep it from freezing

a new inventory of mountain glaciers and ice caps for the antarctic periphery although the glaciers in the antarctic periphery make up a large fraction of all mountain glaciers and ice caps on earth a detailed glacier inventory of the region is lacking we compile such an inventory recording areas area altitude distributions terminus characteristics and volume estimates glaciers on the mainland are excluded the inventory is derived from the antarctic digital database and some manual digitization we additionally rely on satellite imagery digital elevation models and a flowshed algorithm to classify ice bodies we find 1133 ice caps and 1619 mountain glaciers covering a total of 132 867 6643 km 2 estimated total volume corresponds to 0 121 0 010 m sea level equivalent of the total glacier area 99 drains either into ice shelves 63 or into the ocean 36 the inventory will provide a database for glacier mass balance assessments modelling and projections and help to reduce the uncertainties in previous studies

ocean excited plate waves in the ross and pine island glacier ice shelves ice shelves play an important role in buttressing land ice from reaching the sea thus restraining the rate of grounded ice loss long period gravity wave impacts excite vibrations in ice shelves that can expand pre existing fractures and trigger iceberg calving to investigate the spatial amplitude variability and propagation characteristics of these vibrations a 34 station broadband seismic array was deployed on the ross ice shelf ris from november 2014 to november 2016 two types of ice shelf plate waves were identified with beamforming flexural gravity waves and extensional lamb waves below 20 mhz flexural gravity waves dominate coherent signals across the array and propagate landward from the ice front at close to shallow water gravity wave speeds 70 m s 1 in the 20 100 mhz band extensional lamb waves dominate and propagate at phase speeds 3 km s 1 flexural gravity and extensional lamb waves were also observed by a 5 station broadband seismic array deployed on the pine island glacier pig ice shelf from january 2012 to december 2013 with flexural wave energy also detected at the pig in the 20 100 mhz band considering the ubiquitous presence of storm activity in the southern ocean and the similar observations at both the ris and the pig ice shelves it is likely that most if not all west antarctic ice shelves are subjected to similar gravity wave excitation

flow of the ross ice shelf antarctica is modulated by the ocean tide the ice streams feeding the ross ice shelf antarctica have large tidally modulated sinusoidal and stick slip flow but the interaction with the ice shelf is poorly understood we show that the flow of the ross ice shelf front up to 650 km from the ice streams exhibits smooth sinusoidal motions corresponding to tidal modulation these observations suggest a possible linking of the ice shelf with the ice streams to form a unified system that responds to small perturbations in stresses associated with ocean tides if this is the case the presence of the sinusoidal motion but the absence of stick slip motion suggests there is damping of very high frequency signals the dissimilar signatures of the motions observed in the ice streams and at the front of the ice shelf present challenges to model development aimed at understanding the dynamics of coupled ice stream ice shelf flow and the movement of ice across grounding lines

ocean variability contributing to basal melt rate near the ice front of ross ice shelf antarctica basal melting of ice shelves is an important but poorly understood cause of antarctic ice sheet mass loss and freshwater production we use data from two moorings deployed through ross ice shelf 6 and 16 km south of the ice front east of ross island and numerical models to show how the basal melting rate near the ice front depends on sub ice shelf ocean variability the moorings measured water velocity conductivity and temperature for 2 months starting in late november 2010 about half of the current velocity variance was due to tides predominantly diurnal components with the remainder due to subtidal oscillations with periods of a few days subtidal variability was dominated by barotropic currents that were large until mid december and significantly reduced afterward subtidal currents were correlated between moorings but uncorrelated with local winds suggesting the presence of waves or eddies that may be associated with the abrupt change in water column thickness and strong hydrographic gradients at the ice front estimated melt rate was 1 2 0 5 m a 1 at each site during the deployment period consistent with measured trends in ice surface elevation from gps time series the models predicted similar annual averaged melt rates with a strong annual cycle related to seasonal provision of warm water to the ice base these results show that accurately modeling the high spatial and temporal ocean variability close to the ice shelf front is critical to predicting time dependent and mean values of meltwater production and ice shelf thinning

a synthesis of remote sensing data on wilkins ice shelf antarctica wilkins ice shelf has an area of 16000 km2 and lies off the west coast of the antarctic peninsula bounded by alexander latady charcot and rothschild islands several ice shelves including wilkins exist close to a climatic limit of viability the recent disintegration of the neighbouring wordie ice shelf has been linked to atmopsheric warming observed on the antarctic peninsula the limit of ice shelf viability thus appears to have migrated south should this continue the question arises how long will wilkins ice shelf survive compared with the other ice shelves on the antarctic peninsula few surface glaciological data have been collected on wilkins ice shelf we compare contrast and combine a variety of remotely sensed data the recently declassified geosat geodetic mission altimetry landsat mss and tm imagery and radio echo sounding data res to study its structure and mass balance regime we find that this shelf has an unusual mass balance regime and relies heavily for sustenance on in situ accumulation its response to a continued atmospheric warming may be significantly different from that of wordie ice shelf wordie ice shelf was fed by several dynamic outlet glaciers which accelerated the disintegration process when the ice shelf fractured wilkins ice shelf by contrast is almost stagnant and is expected to respond by normal calving at the ice front changes in the accumulation rate or basal melt rate may however dominate any dynamic effect over the last two decades the ice front positions have remained stable

improving antarctic tide models by assimilation of icesat laser altimetry over ice shelves 1 assimilation of laser altimeter data from the ice cloud and land elevation satellite icesat significantly improves the accuracy of ocean tide models for the ross ice shelf ris for the most energetic tidal harmonic k1 assimilation reduces the root mean square error rmse between the model and a set of 16 independent tide records on and near the ris from 6 0 to 2 8 cm and the combined rmse for the six most energetic tidal harmonics from 7 7 to 5 4 cm when only the six most recent and highest quality tide records are considered the combined rmse is 4 8 cm this value is close to the uncertainty expected from tidal analyses of the short 1 2 month validation records indicating that assessing further improvements in tide model accuracy will require development of a higher quality validation data set

structure of southeastern antarctic peninsula ice shelves and ice tongues from synthetic aperture radar imagery examination of synthetic aperture radar data collected over the southeastern antarctic peninsula shows that features sometimes mapped as ice shelves are more likely composed of numerous ice tongues interspersed within a matrix of fast ice and icebergs the tongues are formed by the seaward extension of numerous small mountain glaciers that drain from the antarctic peninsula once afloat the tongues intermingle with a matrix of fast ice and brash examination of 1997 radarsat 1 image mosaics shows that southeastern antarctic peninsula composite ice shelves covered an area of about 3500 km 2 like ice tongues around the rest of antarctica these features are highly fragmented and likely to be susceptible to mechanical failure one such composite shelf located between new bedford and wright inlets was observed to decrease in area by 1200km 2 between 1997 and 2000

antarctic firn compaction rates from repeat track airborne radar data i methods while measurements of ice sheet surface elevation change are increasingly used to assess mass change the processes that control the elevation fluctuations not related to ice flow dynamics e g firn compaction and accumulation remain difficult to measure here we use radar data from the thwaites glacier west antarctica catchment to measure the rate of thickness change between horizons of constant age over different time intervals 2009 10 2010 11 and 2009 11 the average compaction rate to approximately 25m depth is 0 33ma exp 1 with largest compaction rates near the surface our measurements indicate that the accumulation rate controls much of the spatio temporal variations in the compaction rate while the role of temperature is unclear due to a lack of measurements based on a semi empirical steady state densification model we find that surveying older firn horizons minimizes the potential bias resulting from the variable depth of the constant age horizon our results suggest that the spatiotemporal variations in the firn compaction rate are an important consideration when converting surface elevation change to ice mass change compaction rates varied by up to 0 12ma exp 1 over distances less than 6km and were on average greater than 20 larger during the 2010 11 interval than during 2009 10

snow dunes and glazed surfaces in antarctica new field and remote sensing data as part of the international trans antarctic scientific expedition project the italian antarctic programme undertook two traverses from the terra nova station to talos dome and to dome c along the traverses the party carried out several tasks drilling glaciological and geophysical exploration the difference in spectral response between glazed surfaces and snow makes it simple to identify these areas on visible near infrared satellite images integration of field observation and remotely sensed data allows the description of different mega morphologic features wide glazed surfaces sastrugi glazed surface fields transverse dunes and megadunes topography global positioning system ground penetrating radar and detailed snow surface surveys have been carried out providing new information about the formation and evolution of mega morphologic features the extensive presence up to 30 of glazed surface caused by a long hiatus in accumulation with an accumulation rate of nil or slightly negative has a significant impact on the surface mass balance of a wide area of the interior part of east antarctica the aeolian processes creating these features have important implications for the selection of optimum sites for ice coring because orographic variations of even a few metres per kilometre have a significant impact on the snow accumulation process remote sensing surveys of aeolian macro morphology provide a proven high quality method for detailed mapping of the interior of the ice sheet s prevalent wind direction and could provide a relative indication of wind intensity

continental scale simulation of the antarctic katabatic wind regime abstract katabatic winds are a common feature of the lower antarctic atmosphere although these drainage flows are quite shallow there is increasing evidence that the low level circulations are an important component in establishing large scale tropospheric motions in the high southern latitudes three dimensional numerical simulations of the antarctic katabatic wind regime and attendant tropospheric circulations have been conducted over the entire continent to depict the topographically forced drainage patterns in the near surface layer of the atmosphere results of the simulation enable a mapping of katabatic wind potential and identification of coastal regions which may experience anomalously intense katabatic winds a large upper level cyclonic circulation forms rapidly in response to the evolving katabatic wind structure in the lower atmosphere suggesting that the drainage circulations are an important component in prescribing the resulting resulting circumpolar vortex these results imply that som

interannual changes of the floating ice shelf of petermann gletscher north greenland from 2000 to 2012 petermann gletscher northwest greenland drains 4 of the greenland ice sheet into nares strait its floating ice shelf retreated from 81 to 48 km in length during two large calving events in 2010 and 2012 we document changes in the three dimensional ice shelf structure from 2000 to 2012 using repeated tracks of airborne laser altimetry and ice radio echo sounding icesat laser altimetry and modis visible imagery the recent ice shelf velocity measured by tracking surface features between flights in 2010 and 2011 is 1 25 km a 1 15 30 faster than estimates made before 2010 the steady state along flow ice divergence represents 6 3 gt a 1 mass loss through basal melting 5 gt a 1 and surface melting and sublimation 1 0 gt a 1 airborne laser altimeter data reveal thinning both along a thin central channel and on the thicker ambient ice shelf from 2007 to 2010 the ice shelf thinned by 5 m a 1 which represents a non steady mass loss of 4 1 gt a 1 we suggest that thinning in the basal channels structurally weakened the ice shelf and may have played a role in the recent calving events

variable basal melt rates of antarctic peninsula ice shelves 1994 2016 we have constructed 23 year 1994 2016 time series of antarctic peninsula ap ice shelf height change using data from four satellite radar altimeters ers 1 ers 2 envisat and cryosat 2 combining these time series with output from atmospheric and firn models we partitioned the total height change signal into contributions from varying surface mass balance firn state ice dynamics and basal mass balance on the bellingshausen coast of the ap ice shelves lost 84 34 gt a 1 to basal melting compared to contributions of 50 7 gt a 1 from surface mass balance and ice dynamics net basal melting on the weddell coast was 51 71 gt a 1 recent changes in ice shelf height include increases over major ap ice shelves driven by changes in firn state basal melt rates near bawden ice rise a major pinning point of larsen c ice shelf showed large increases potentially leading to substantial loss of buttressing if sustained

the surface topography of large ice masses from landsat imagery les images de landsat mss de l antarctique et du svalbard ont ete comparees a des mesures altimetriques effectuees a partir d avion

the supply of subglacial meltwater to the grounding line of the siple coast west antarctica recent satellite studies have shown that active subglacial lakes exist under the antarctic ice streams and persist almost to their grounding lines when the lowest lying lakes flood the water crosses the grounding line and enters the sub ice shelf cavity modeling results suggest that this additional freshwater influx may significantly enhance melting at the ice shelf base we examine the spatial and temporal variability in subglacial water supply to the grounding lines of the siple coast ice streams by combining estimates for lake volume change derived from ice cloud and land elevation satellite icesat data with a model for subglacial water transport our results suggest that subglacial outflow tends to concentrate towards six embayments in the siple coast grounding line although mean grounding line outflow is 60m3 s 1 for the entire siple coast maximum local grounding line outflow may temporarily exceed 300 m3 s 1 during the synchronized flooding of multiple lakes in a hydrologic basin variability in subglacial outflow due to subglacial lake drainage may account for a substantial portion of the observed variability in freshwater flux out of the ross ice shelf cavity the temporal variability in grounding line outflow results in a net reduction in long term average melt rate but temporary peak melting rates may exceed the long term average by a factor of three

observations of buried lake drainage on the antarctic ice sheet between 1992 and 2017 the antarctic ice sheet ais lost ice equivalent to 7 6 3 9 mm of sea level rise ais mass loss is mitigated by ice shelves that provide a buttress by regulating ice flow from tributary glaciers however ice shelf stability is threatened by meltwater ponding which may initiate or reactivate preexisting fractures currently poorly understood processes here through ground penetrating radar gpr analysis over a buried lake in the grounding zone of an east antarctic ice shelf we present the first field observations of a lake drainage event in antarctica via vertical fractures concurrent with the lake drainage event we observe a decrease in surface elevation and an increase in sentinel 1 backscatter finally we suggest that fractures that are initiated or reactivated by lake drainage events in a grounding zone will propagate with ice flow onto the ice shelf itself where they may have implications for its stability

antarctic analog for dilational bands on europa europa s surface shows signs of extension which is revealed as lithospheric dilation expressed along ridges dilational bands and ridged bands ridges the most common tectonic feature on europa comprise a central crack flanked by two raised banks a few hundred meters high on each side together these three classes may represent a continuum of formation in tufts dilational model ridge formation is dominated by daily tidal cycling of a crack which can be superimposed with regional secular dilation the two sources of dilation can combine to form the various band morphologies observed new gps data along a rift on the ross ice shelf antarctica is a suitable earth analog to test the framework of tufts dilational model as predicted by tufts dilational model tensile failures in the ross ice shelf exhibit secular dilation upon which a tidal signal can be seen from this analog we conclude that tufts dilational model for europan ridges and bands may be credible and that the secular dilation is most likely from a regional source and not tidally driven

grounding line retreat of totten glacier east antarctica 1996 to 2013 2015 american geophysical union all rights reserved totten glacier east antarctica a glacier that holds a 3 9 m sea level change equivalent has thinned and lost mass for decades we map its grounding line positions in 1996 and 2013 using differential radar interferometry insar data and develop precise high resolution topographies of its ice surface and ice draft using nasa operation icebridge data insar data and a mass conservation method we detect a 1 to 3 km retreat of the grounding line in 17 years the retreat is asymmetrical along a two lobe pattern where ice is only grounded a few 10 m above sea level or ice plain which may unground further with only modest amounts of ice thinning the pattern of retreat indicates ice thinning of 12 m in 17 years or 0 7 0 1 m yr at the grounding line on average sustained thinning will cause further grounding line retreat but may not be conducive to a marine instability key points grounding line of totten glacier is retreating not as fast as west antarctica retreat pattern explained by the newly inferred bed geometry if ice thinning maintains bed geometry conducive to further retreat

combination of hi net and kik net data for deconvolution interferometry abstract application of deconvolution interferometry to wavefields observed by kik net a strong motion recording network in japan is useful for estimating wave velocities and s wave splitting in the near surface at the location of the borehole accelerometer of each kik net station a velocity sensor is also installed as a part of a high sensitivity seismograph network hi net i present a technique that uses both hi net and kik net records for computing deconvolution interferometry the deconvolved waveform obtained from the combination of hi net and kik net data is similar to the waveform computed from kik net data only this similarity in the waveforms indicates that one can use hi net wavefields for deconvolution interferometry because hi net records have a high signal to noise ratio snr and high dynamic resolution snr and quality of amplitude and phase of deconvolved waveforms can be improved with hi net data these advantages are especially important for short time moving window seismic interferometry and deconvolution interferometry using coda waves