post processing removal of correlated errors in grace data 1 gravity fields produced by the gravity recovery and climate experiment grace satellite mission require smoothing to reduce the effects of errors present in short wavelength components as the smoothing radius decreases these errors manifest themselves in maps of surface mass variability as long linear features generally oriented north to south i e stripes the presence of stripes implies correlations in the gravity field coefficients here we examine the spectral signature of these correlated errors and present a method to remove them finally we apply the filter to a model of surface mass variability to show that the filter has relatively little degradation of the underlying geophysical signals we seek to recover

a community based geological reconstruction of antarctic ice sheet deglaciation since the last glacial maximum a robust understanding of antarctic ice sheet deglacial history since the last glacial maximum is important in order to constrain ice sheet and glacial isostatic adjustment models and to explore the forcing mechanisms responsible for ice sheet retreat such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and sub antarctic islands here we report a new synthesis of those datasets based on an accompanying series of reviews of the geological data organised by sector we present a series of timeslice maps for 20 ka 15 ka 10 ka and 5 ka including grounding line position and ice sheet thickness changes along with a clear assessment of levels of confidence the reconstruction shows that the antarctic ice sheet did not everywhere reach the continental shelf edge at its maximum that initial retreat was asynchronous and that the spatial pattern of deglaciation was highly variable particularly on the inner shelf the deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small antarctic contribution to meltwater pulse 1a we discuss key areas of uncertainty both around the continent and by time interval and we highlight potential priorities for future work the synthesis is intended to be a resource for the modelling and glacial geological community

increased ice loading in the antarctic peninsula since the 1850s and its effect on glacial isostatic adjustment antarctic peninsula ap ice core records indicate significant accumulation increase since 1855 and any resultant ice mass increase has the potential to contribute substantially to present day glacial isostatic adjustment gia we derive empirical orthogonal functions from climate model output to infer typical spatial patterns of accumulation over the ap and by combining with ice core records estimate annual accumulation for the period 1855 2010 in response to this accumulation history high resolution ice sheet modeling predicts ice thickness increases of up to 45 m with the greatest thickening in the northern and western ap whilst this thickening is predicted to affect grace estimates by no more than 6 2 gt yr it may contribute up to 7 mm yr to the present day gia uplift rate depending on the chosen earth model with a strong east west gradient across the ap its consideration is therefore critical to the interpretation of observed gps velocities in the ap

revisiting grace antarctic ice mass trends and accelerations considering autocorrelation previous grace derived ice mass trends and accelerations have almost entirely been based on an assumption that the residuals to a regression model including also semi annual annual and tidal aliasing terms are not serially correlated we consider ice mass change time series for antarctica and show that significant autocorrelation is in fact present we examine power law and autoregressive models and compare them to those that assume white uncorrelated noise the data do not let us separate autoregressive and power law models but both indicate that white noise uncertainties need to be scaled up by a factor of up to 4 for accelerations and 6 for linear rates depending on length of observations and location for the whole of antarctica east antarctica and west antarctica the scale factors are 1 5 1 5 and 2 2 respectively for the trends and for the accelerations 1 5 1 5 and 2 1 substantially lower scale factors are required for offshore time series suggesting much of the time correlation is related to continental mass changes despite the higher uncertainties we find significant 2 sigma accelerations over much of west antarctica overall increasing mass loss and dronning maud land increasing mass gain as well as a marginally significant acceleration for the ice sheet as a whole increasing mass loss

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

potential of the solid earth response for limiting long term west antarctic ice sheet retreat in a warming climate abstract we employ a coupled model for ice sheet dynamics and maxwell viscoelastic solid earth dynamics including a gravitationally consistent description of sea level with this model we study the influence of the solid earth on the future evolution of the west antarctic ice sheet wais starting from steady state conditions close to the present day configuration of the antarctic ice sheet we apply different atmospheric and oceanic forcings and solid earth rheologies in order to analyse the retreat of the wais climate forcing is the primary control on the occurrence of wais collapse for moderate climate forcing and weak solid earth rheologies however we find that the relative sea level rsl fall associated with the viscoelastic solid earth response due to unloading by wais retreat limits the retreat to the amundsen sea embayment on time scales of several millennia whereas stiffer earth structures yield a collapse under these conditions under stronger climate forcing weak earth structures associated with the west antarctic rift system produce a delay of up to 5000 years in comparison to stiffer antarctic average solid earth rheologies furthermore we find that sea level rise from an assumed fast deglaciation of the greenland ice sheet induces wais collapse in the presence of higher asthenosphere viscosities in cases when the climatic forcing is too weak to force wais collapse alone

spatial and temporal antarctic ice sheet mass trends glacio isostatic adjustment and surface processes from a joint inversion of satellite altimeter gravity and gps data we present spatiotemporal mass balance trends for the antarctic ice sheet from a statistical inversion of satellite altimetry gravimetry and elastic corrected gps data for the period 2003 2013 our method simultaneously determines annual trends in ice dynamics surface mass balance anomalies and a time invariant solution for glacio isostatic adjustment while remaining largely independent of forward models we establish that over the period 2003 2013 antarctica has been losing mass at a rate of 84 22 gt yr 1 with a sustained negative mean trend of dynamic imbalance of 111 13 gt yr 1 west antarctica is the largest contributor with 112 10 gt yr 1 mainly triggered by high thinning rates of glaciers draining into the amundsen sea embayment the antarctic peninsula has experienced a dramatic increase in mass loss in the last decade with a mean rate of 28 7 gt yr 1 and significantly higher values for the most recent years following the destabilization of the southern antarctic peninsula around 2010 the total mass loss is partly compensated by a significant mass gain of 56 18 gt yr 1 in east antarctica due to a positive trend of surface mass balance anomalies

ireteba pluton eldorado mountains nevada late deep source peraluminous magmatism in the cordilleran interior abstract the ireteba pluton is a 66 ma documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape mathrm biotite pm mathrm muscovite pm mathrm garnet end document granite emplaced at the eastern edge of the cordilleran plutonic belt in southeastern nevada in common with other cordilleran peraluminous granites its mineralogy major element chemistry isotopic composition and abundant proterozoic zircon inheritance document crustal origin distinctive trace element chemistry field relations and inherited components furth

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

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

the melting history of the late pleistocene antarctic ice sheet spatial and temporal variations in the sea levels of the past 20 000 years around the globe place constraints on the melting history of the major late pleistocene ice sheets the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9 000 6 000 years ago when it may have lagged behind minor melting of the antarctic ice sheet continued throughout the holocene

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

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

glacial isostatic adjustment over antarctica from combined icesat and grace satellite data abstract the glacial history of antarctica during the most recent milankovitch cycles is poorly constrained relative to the northern hemisphere as a consequence the contribution of mass changes in the antarctic ice sheet to global sea level change and the prediction of its future evolution remain uncertain the process of glacial isostatic adjustment gia represents the ongoing response of the solid earth to the late pleistocene deglaciation and therefore provides information about antarctic glacial history moreover insufficient knowledge of gia hampers the determination of present day changes in the antarctic mass balance through satellite gravity measurements previous studies have laid the theoretical foundation for distinguishing between signals of ongoing gia and contemporary ice mass change through the combination of satellite gravimetry and satellite altimetry this distinction is made possible by the fact the gia induced changes involving relatively dense rock will produce a different combination of topography and gravity change than those produced by variations in ice or firn thickness due to the lower density of these materials however no conclusive results have been produced to date here we show that by combining laser altimetry and gravity data from the icesat and grace satellite missions over the period march 2003 march 2008 the gia contribution can indeed be isolated the inferred gia signal over the antarctic continent which represents the first result derived from direct observations by satellite techniques strongly supports late pleistocene ice models derived from glacio geologic studies the gia impact on grace derived estimates of mass balance is found to be 100 67 gt yr

a new hurricane wind retrieval algorithm for sar images a new algorithm for hurricane wind retrieval is developed based on the primary characteristics of hurricane processes by assuming constant wind speeds and equal distant wind directions in three neighboring sub image blocks of any specific concentric circle around the hurricane eye both wind speed and wind direction are resolved without any external information to evaluate the accuracy of the new algorithm a radarsat 1 synthetic aperture radar image of hurricane isabel is studied the retrieved wind speed is compared with quikscat scatterometer winds and in situ winds good consistency is shown since the new algorithm doesn t rely on any external wind information fine resolution wind structures can be retrieved without adding errors due to linear interpolation of the externally derived coarse resolution wind direction

dynamic thinning of antarctic glaciers from along track repeat radar altimetry since 2002 the envisat radar altimeter has measured the elevation of the antarctic ice sheet with a repeat cycle of 35 days this long and regular time series is processed using an along track algorithm to depict in detail the spatial and temporal pattern of elevation change for the whole ice sheet we use this dataset to examine the spatial and temporal pattern of pine island glacier pig thinning and compare it to the neighbouring glaciers we also examine additional areas especially in east antarctica whose mass balance is poorly known one advantage of the finer along track spacing of measurements is that it reveals places of dynamic thinning in regions of rapid ice flow we observe the acceleration of thinning on pig over the entire basin the volume loss increased from 7 km3 a 1 during 2002 06 to 48 km3 a 1 during 2006 10 we also observe accelerated thinning on the lower tens of kilometres of thwaites glacier with a mean thinning of 0 18 m a 1 over its entire basin during our observation period we confirm the dynamic thinning of totten glacier but we do not detect significantly accelerated thinning on any glacier elsewhere than on the coast of the amundsen sea

an assessment of forward and inverse gia solutions for antarctica in this work we assess the most recent estimates of glacial isostatic adjustment gia for antarctica including those from both forward and inverse methods the assessment is based on a comparison of the estimated uplift rates with a set of elastic corrected gps vertical velocities these have been observed from an extensive gps network and computed using data over the period 2009 2014 we find systematic underestimations of the observed uplift rates in both inverse and forward methods over specific regions of antarctica characterized by low mantle viscosities and thin lithosphere such as the northern antarctic peninsula and the amundsen sea embayment where its recent ice discharge history is likely to be playing a role in current gia uplift estimates for regions where many gia models have traditionally placed their uplift maxima such as the margins of filchner ronne and ross ice shelves are found to be overestimated gia estimates show large variability over the interior of east antarctica which results in increased uncertainties on the ice sheet mass balance derived from gravimetry methods

a method for separating antarctic postglacial rebound and ice mass balance using future icesat geoscience laser altimeter system gravity recovery and climate experiment and gps satellite data 5 3 and 19 9 mm yr 1 for postglacial rebound and ice mass trend respectively when smoothed over 250 km scales the largest source of error in the combined signals is the effect of the unknown time variable accumulation on the density of the ice column to estimate this contribution and so obtain better estimates of ice mass trend and postglacial rebound we add global positioning system gps measurements of vertical velocities as additional constraints using an empirical relation between the errors in postglacial rebound and ice mass trend that result from the unknown density variation within the ice column we are able to solve for all three unknowns in the problem ice mass trend postglacial rebound and the snow compaction trend the addition of a plausible distribution of gps measurements reduces the errors in estimates of postglacial rebound and ice mass trend to 3 4 and 15 9 mm yr 1 respectively index terms 1863 hydrology

docking carolina mid paleozoic accretion in the southern appalachians accretion of the extensive carolina zone to laurentia is one of the most critical unresolved problems in southern appalachian tectonics synthesis of southern appalachian tectonism reveals three lines of evidence from across the orogen that indicate a late ordovician to silurian time of accretion a tectonic unconformity in native laurentian rocks an extensive magmatic pulse in the piedmont zone of the orogen and active uplift in the carolina zone are all related to this accretionary event structural geometries in the carolina zone suggest that accretion involved sinistral transpression this new model for carolina accretion is consistent with models for the accretion of northern appalachian peri gondwanan terranes collectively their timing and mode of accretion to laurentia place tectonic constraints on paleozoic global reconstructions

wind speed retrieval from vh dual polarization radarsat 2 sar images recent studies show the promising ability of cross polarization synthetic aperture radar sar for high wind speed monitoring however no dual polarization dual pol geophysical model functions gmfs have thus far been established in this paper we first address the difference between dual pol and quad pol vh radar returns with respect to wind speed and show the necessity of having a vh dual pol gmf for scansar images for remote sensing of mesoscale wind processes such as hurricanes by collocating vh dual pol radarsat 2 sar measurements with in situ buoy winds a vh dual pol gmf was developed after introducing a denoise procedure to increase the signal to noise ratio for sar measurements study results suggest that the vh dual pol radar returns have a linear monotonic piecewise increasing dependence on wind speed with decreasing scatter in high winds successful application of the gmf to high wind speed retrieval for hurricane gustav in 2008 suggests that vh mode sar images do not exhibit signal saturation or the speed ambiguity problem that affects copolarization sar images for high wind speed retrieval this result supports the potential future application of vh dual pol sar images to hurricane monitoring

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

rates of southeast greenland ice volume loss from combined icesat and aster observations 1 repeat satellite laser altimetry is critical for observing the rapidly changing mass balance of the greenland ice sheet however sparse sampling and high surface slopes over rapidly thinning coastal outlet glaciers may result in underestimation of mass loss here we supplement icesat derived surface elevation changes with differenced aster digital elevation models of outlet glaciers in southeastern greenland the region with the largest concentrated change in outlet glacier mass loss we estimate a 2002 2005 regional volume loss rate of 108 km3 yr our results are consistent with drainage scale grace and mass budget estimates when differences in observation periods are taken into account the two largest glaciers kangerdlugssuaq and helheim account for only 28 of the mass loss illustrating the combined importance of smaller glaciers and the need for complete observational coverage additionally we find that rapid concentrated thinning within the outlets represents a small contribution to the total volume change compared to dispersed inland thinning

retreat of the east antarctic ice sheet during the last glacial termination the east antarctic ice sheet retreated at the end of the last glacial period terrestrial and marine data suggest that the retreat began 14 000 years ago indicating that the east antarctic ice sheet probably did not contribute to meltwater pulse 1a 14 700 years ago

a data calibrated distribution of deglacial chronologies for the north american ice complex from glaciological modeling article i nfo past deglacial ice sheet reconstructions have generally relied upon discipline specific constraints with no at tention given to the determination of objective confidence intervals reconstructions based on geophysical inversion of relative sea level rsl data have the advantage of large sets of proxy data but lack ice mechanical constraints conversely reconstructions based on dynamical ice sheet models are glaciologically self consistent but depend on poorly constrained climate forcings and sub glacial processes as an example of a much better constrained methodology that computes explicit error bars we present a dis tribution of high resolution glaciologically self consistent deglacial histories for the north american ice com plex calibrated against a large set of rsl marine limit and geodetic data the history is derived from ensemble based analyses using the 3d mun glacial systems model and a high resolution ice margin chronol ogy derived from geological and geomorphological observations isostatic response is computed with the vm5a viscosity structure bayesian calibration of the model is carried out using markov chain monte carlo methods in combination with artificial neural networks trained to the model results the calibration provides a posterior distribution for model parameters and thereby modeled glacial histories given the observational data sets that takes data uncertainty into account final ensemble results also account for fits between com puted and observed strandlines and marine limits given the model including choice of calibration parameters input and constraint data sets and vm5a earth rhe ology we find the north american contribution to mwp1a was likely between 9 4 and 13 2 m eustatic over a 500 year interval this is more than half of the total 16 to 26 m meltwater pulse over 500 to 700 years with lower values being more probable indicated by the barbados coral record fairbanks 1989 peltier and fairbanks 2006 if one assumes a 5 meter living range for the acropora palmata coral 20 ka ice volume for north america was likely 70 1 2 0 m eustatic or about 60 of the total contribution to eustatic sea level change we suspect that the potentially most critical unquantified uncertainties in our analyses are those related to model structure especially climate forcing deglacial ice margin chronology and earth rheology

dual polarized c and ku band ocean backscatter response to hurricane force winds 1 airborne ocean backscatter measurements at c and ku band wavelengths and h and v polarizations at multiple incidence angles obtained in moderate to very high wind speed conditions 25 65 m s 1 during missions through several tropical cyclones are presented these measurements clearly show that the normalized radar cross sections nrcs response stops increasing at hurricane force winds for both frequency bands and polarizations except for high incidence angles at c band and h polarization the results also show the mean nrcs departing from a power law behavior for all the presented frequency bands polarizations and incidence angles suggesting a reduction in the drag coefficient the overall flattening of the azimuthal response of the nrcs is also very apparent in all cases a new set of geophysical model functions gmfs at c and ku band are developed from these direct ocean backscatter observations for ocean surface winds ranging from 25 to 65 m s 1 the developed gmfs provide a much more accurate characterization of the nrcs versus wind speed and direction and their implementation in operational retrieval algorithms from satellite based scatterometer observations would result in better wind fields the differences between these measurements and other currently available gmfs such as quikscat nscat2 cmod4 and cmod5 are reported the implementation of these gmfs in retrieval algorithms will result in better wind fields from satellite based scatterometers measurements

the march 25 1998 antarctic plate earthquake the march 25 1998 antarctic plate earthquake mw 8 1 occurred 250 km from the nearest plate boundary in oceanic lithosphere with an age of 35 55 my analysis of aftershock patterns shows that the earthquake ruptured a fault or series of strike slip fault segments nearly 300 km long the strike of the fault s is nearly perpendicular to the north south trending fossil fracture zones which are the most marked bathymetric features of this region moment release during the mainshock was concentrated in two large subevents clearly visible in the teleseismic body wave waveforms modeling of these body waves using a finite fault source places the first of the two subevents near the point of rupture initiation on the eastern end of the fault with the second large subevent occurring 220 280 km to the west the two pulses of moment release are found to be separated in time by 65 s comparison of the relative s wave amplitudes of the first and second pulses suggests that a rotation of the focal mechanism by 10 occurred between the two subevents

antarctic contribution to sea level rise observed by grace with improved gia correction antarctic volume changes during the past 21 thousand years are smaller than previously thought and here we construct an ice sheet history that drives a forward model prediction of the glacial isostatic adjustment gia gravity signal the new model in turn should give predictions that are constrained with recent uplift data the impact of the gia signal on a gravity recovery and climate experiment grace antarctic mass balance estimate depends on the specific grace analysis method used for the method described in this paper the gia contribution to the apparent surface mass change is re evaluated to be 55 13 gt yr by considering a revised ice history model and a parameter search for vertical motion predictions that best fit the gps observations at 18 high quality stations although the gia model spans a range of possible earth rheological structure values the data are not yet sufficient for solving for a preferred value of upper and lower mantle viscosity nor for a preferred lithospheric thickness grace monthly solutions from the center for space research release 04 csr rl04 release time series from january 2003 to the beginning of january 2012 uncorrected for gia yield an ice mass rate of 2 9 29 gt yr the new gia correction increases the solved for ice mass imbalance of antarctica to 57 34 gt yr the revised gia correction is smaller than past grace estimates by about 50 to 90 gt yr the new upper bound to the sea level rise from the antarctic ice sheet averaged over the time span 2003 0 2012 0 is about 0 16 0 09 mm yr

sea level changes at the lgm from ice dynamic reconstructions of the greenland and antarctic ice sheets during the glacial cycles abstract new experiments were performed with three dimensional thermomechanical models of the greenland and antarctic ice sheets to simulate their behaviour during the glacial cycles to reconstruct their thickness and extent at the last glacial maximum lgm and to estimate their glacio eustatic contribution to the global sea level stand the calculations used improved ice dynamic and isostatic treatments updated datasets on higher grid resolutions and refined climatic treatments based on newly calibrated transfer functions between ice core records and climatic perturbations results are discussed from a reference run with standard parameters that is compared with available glacial geological observations and from a series of sensitivity experiments focusing on isostatic adjustment thermomechanical coupling climatic forcing mass balance changes and basal melting rates and viscosity changes of antarctic ice shelves for the antarctic ice sheet we find that volume changes are closely linked with grounding line changes of the west antarctic ice sheet at the lgm the grounding line extended close to the continental shelf break almost everywhere ice over central east antarctica was generally thinner than today and varied mainly in accordance with accumulation fluctuations for the greenland ice sheet melting is important only during interglacial periods and the most sensitive period concerns the size of the ice sheet during the eemian at the lgm the greenland ice sheet extended beyond the present coastline to cover at least the inner continental shelf and thinned by up to several hundred meters in central areas for a plausible range of parameters the experiments indicate that at the time of maximum sea level depression 21 kyr bp the antarctic ice sheet contributed 14 18 m to the sea level lowering and the greenland ice sheet 2 3 m significantly less than the older climap reconstructions whereas both ice sheets were at 21 kyr bp close to their maximum extent the experiments also indicate that their maximum volumes were reached only by 16 5 kyr bp greenland and 10 kyr bp antarctica equal to an additional sea level lowering of respectively 0 4 and 3 7 m holocene retreat was essentially complete by 5 kyr bp in greenland but is found to still continue today in west antarctica before reversing to growth during the next millenium the models were found to reproduce gross features of the ice sheet s history since the lgm in reasonably good agreement with available glacial geological data although observational control on ice thickness changes remains very limited

separating geophysical signals using grace and high resolution data a case study in antarctica to fully exploit data from the gravity recovery and climate experiment grace we separate geophysical signals observed by grace in antarctica by deriving high spatial resolution maps for present day glacial isostatic adjustment gia and ice mass changes with the least possible noise level for this we simultaneously i improve the postprocessing of gravity data and ii consistently combine them with high resolution data from ice cloud and land elevation satellite altimeter icesat and regional atmospheric climate model 2 3 racmo we use gps observations to discriminate between various candidate spatial patterns of vertical motions caused by gia the icesat racmo combination determines the spatial resolution of estimated ice mass changes the results suggest the capability of the developed approach to retrieve the complex spatial pattern of present day gia such as a pronounced subsidence in the proximity of the kamb ice stream and pronounced uplift in the amundsen sea sector

ongoing deformation of antarctica following recent great earthquakes antarctica s secular motion is thought to be almost everywhere governed by horizontal rigid plate rotation plus three dimensional deformations due to past and present changes in ice ocean loading known as glacial isostatic adjustment gia we use geodetic data to investigate deformation following the 1998 m 8 2 antarctic intraplate earthquake and show sustained three dimensional deformation along east antarctica s coastline 600 km from the rupture location using a model of viscoelastic deformation we are able to match observed northward velocity changes and either east or height but not all three directions simultaneously apparently partly due to lateral variations in mantle rheology our modeling predicts that much of antarctica may still be deforming with further deformation possible from the 2004 m 8 macquarie ridge earthquake this previously unconsidered mode of antarctic deformation affects geodetic estimates of plate motion and gia its viscous nature raises the prospect of further present day deformation due to earlier great earthquakes

a 3 d coupled ice sheet sea level model applied to antarctica through the last 40 ky abstract we present results from a three dimensional ice sheet shelf model of antarctica coupled to a gravitationally self consistent global sea level model that incorporates maxwell viscoelastic deformation of the solid earth the coupled model captures complex post glacial changes in sea level associated with the gravitational deformational and rotational effects of the evolving surface mass ice plus ocean load over the global ocean including at the grounding lines of marine based ice the simulations are initiated at 40 ka and we focus on ice distributions and sea levels from the last glacial maximum to present our results extend and confirm the key conclusions of earlier work using a simplified 1 d ice sheet model by demonstrating that the sea level coupling has a significant stabilizing influence on marine ice sheet grounding lines the feedback of sea level changes into the ice sheet model acts to slow down the retreat and advance of the grounding line relative to simulations in which the full coupling is not incorporated differences in ice thickness between these simulations can reach 1 km close to the grounding line finally we perform preliminary comparisons of our results to relative sea level rsl histories and gps derived present day uplift rates at sites near the margins of antarctica we find that the coupling improves fits to uplift rates in several regions and that the rsl predictions of the coupled model yield a fit to the observations that is comparable to recent uncoupled simulations in which the underlying earth model was varied to obtain a best fit to the rsl histories

viscous gravitational relaxation summary this paper is concerned with a detailed examination of the response of maxwell models of the planet to surface mass loads particular attention is devoted to an examination of the factors which determine the isostatic response since the understanding of this response is crucial in a number of different geodynamic problems one particular example which we discuss in detail is concerned with the prediction of free air gravity anomalies produced by large scale deglaciation events using the methods developed here we are able to provide the first direct assessment of the importance of initial isostatic disequilibrium on the observed relative sea level variations and free air gravity anomalies forced by the melting of the laurentide ice sheet we are therefore able to estimate the extent to which such initial disequilibrium might influence the inference of mantle viscosity from isostatic adjustment data our calculations establish that free air gravity data although they are sensitive to the degree of initial disequilibrium provide an extremely high quality constraint upon the viscosity of the lower mantle

joint inversion estimate of regional glacial isostatic adjustment in antarctica considering a lateral varying earth structure esa stse project regina a major uncertainty in determining the mass balance of the antarctic ice sheet from measurements of satellite gravimetry and to a lesser extent satellite altimetry is the poorly known correction for the ongoing deformation of the solid earth caused by glacial isostatic adjustment gia although much progress has been made in consistently modelling the ice sheet evolution throughout the last glacial cycle as well as the induced bedrock deformation caused by these load changes forward models of gia remain ambiguous due to the lack of observational constraints on the ice sheet s past extent and thickness and mantle rheology beneath the continent as an alternative to forward modelling gia we estimate gia from multiple space geodetic observations grace envisat icesat and gps making use of the different sensitivities of the respective satellite observations to current and past surface mass ice mass change and solid earth processes we estimate gia based on viscoelastic response functions to disc load forcing we calculate and distribute the viscoelastic response functions according to estimates of the variability of lithosphere thickness and mantle viscosity in antarctica we compare our gia estimate with published gia corrections and evaluate its impact in determining the ice mass balance in antarctica from grace and satellite altimetry particular focus is applied to the amundsen sea sector in west antarctica where uplift rates of several cm yr have been measured by gps we show that most of this uplift is caused by the rapid viscoelastic response to recent ice load changes enabled by the presence of a low viscosity upper mantle in west antarctica this paper presents the second and final contribution summarizing the work carried out within a european space agency funded study regina www regina science eu

widespread complex flow in the interior of the antarctic ice sheet it has been suggested that as much as 90 of the discharge from the antarctic ice sheet is drained through a small number of fast moving ice streams and outlet glaciers fed by relatively stable and inactive catchment areas here evidence obtained from balance velocity estimates suggests that each major drainage basin is fed by complex systems of tributaries that penetrate up to 1000 kilometers from the grounding line into the interior of the ice sheet this finding has important consequences for the modeled or estimated dynamic response time of past and present ice sheets to climate forcing

predictions of secular geoid changes from late pleistocene and holocene antarctic ice ocean mass imbalance summary estimates on ice volume changes in antarctica from both contemporary mass imbalance during the last hundred to thousand years and ice volume changes during the last glacial cycles are difficult to obtain future satellite gravity missions monitoring secular changes in gravity as a proxy of mass changes of the antarctic ice sheet will therefore provide an additional important constraint on the antarctic ice sheet history we assess the contributions from both past ice volume changes during the last glacial cycles and present ice imbalances over antarctica using a variety of published ice models model predictions of secular changes of the geoid anomaly based on plausible mantle viscosity profiles enable us to discuss the importance of past and present ice volume changes and their characteristic signatures while uncertainties arising from the viscosity profile are of secondary importance for model predictions of the secular change of the geoid anomaly we expect significant bias of the observed signal from uncertainties in the timing of the end of deglaciation which is in agreement with previous studies hence the benefit of inferring present day antarctic ice imbalance from satellite gravity missions will depend on improvements to ice models for the last glacial cycle

rapid bedrock uplift in the antarctic peninsula explained by viscoelastic response to recent ice unloading abstract since 1995 several ice shelves in the northern antarctic peninsula have collapsed and triggered ice mass unloading invoking a solid earth response that has been recorded at continuous gps cgps stations a previous attempt to model the observation of rapid uplift following the 2002 breakup of larsen b ice shelf was limited by incomplete knowledge of the pattern of ice unloading and possibly the assumption of an elastic only mechanism we make use of a new high resolution dataset of ice elevation change that captures ice mass loss north of 66 s to first show that non linear uplift of the palmer cgps station since 2002 cannot be explained by elastic deformation alone we apply a viscoelastic model with linear maxwell rheology to predict uplift since 1995 and test the fit to the palmer cgps time series finding a well constrained upper mantle viscosity but less sensitivity to lithospheric thickness we further constrain the best fitting earth model by including six cgps stations deployed after 2009 the larissa network with vertical velocities in the range 1 7 to 14 9 mm yr this results in a best fitting earth model with lithospheric thickness of 100 140 km and upper mantle viscosity of 6 10 17 2 10 18 pa s much lower than previously suggested for this region combining the larissa time series with the palmer cgps time series offers a rare opportunity to study the time evolution of the low viscosity solid earth response to a well captured ice unloading event

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

simultaneous estimation of global present day water transport and glacial isostatic adjustment global water transport between oceans and continents during the transition from glacial to interglacial times has been enormous the viscoelastic solid earth has been responding to this unloading of large ice masses with a rise of the land masses in a process termed glacial isostatic adjustment in addition significant changes in the land ocean water distribution occur at present as both present day changes in the ice water thickness and glacial isostatic adjustment affect space geodetic measurements it is difficult to untangle the relative contributions of these two processes here we combine gravity measurements and geodetic data of surface movement with a data assimilating model of ocean bottom pressure to simultaneously estimate present day water transport and glacial isostatic adjustment we determine their separate contributions to movements in the geocentre which occur in response to changes in the earth s mass distribution with uncertainties below 0 1 mm yr 1 according to our estimates mass losses between 2002 and 2008 in greenland alaska yukon and west antarctica are 104 23 101 23 and 64 32 gt yr 1 respectively our estimates of glacial isostatic adjustment indicate a large geocentre velocity of 0 72 0 06 mm yr 1 in the polar direction we conclude that a significant revision of the present estimates of glacial isostatic adjustments and land ocean water exchange is required present day changes in the thickness of ice sheets and glacial isostatic adjustment both affect space geodetic measurements a combination of gravity measurements and geodetic data of surface movement with a data assimilating model of ocean bottom pressure allows the simultaneous estimation of present day water transport and glacial isostatic adjustment

dual polarization measurements at c band over the ocean results from airborne radar observations and comparison with envisat asar data this paper presents an analysis of measurements of the normalized radar cross section nrcs in vertical and horizontal polarizations over the ocean obtained from the c band airborne radar storm the dataset was collected during the experiment called validation with a polarimetric airborne radar of envisat sar over the ocean valpareso which took place during the calibration validation phase of the envisat advanced synthetic aperture radar asar from this dataset the properties of the polarization ratio are discussed and in particular its dependencies with radar geometry incidence and azimuth angle as well as with meteorological conditions wind and sea state the polarization ratio is found to be dependent on incidence and azimuth angles its dependence with incidence angle is found to be significantly different from empirical models previously proposed in the literature it also exhibits some correlation with surface conditions wind and wave with a more important correlation with significant wave steepness two new analytical formulations are proposed to model the polarization ratio one as a function of incidence angle only the second one with additional dependence with azimuth angle it is shown that it is necessary to consider an azimuth dependent polarization ratio for incidence angles larger than 30 spl deg comparisons with the polarization ratio from envisat asar images are used to assess this model

the impact of lateral variations in lithospheric thickness on glacial isostatic adjustment in west antarctica differences in predictions of glacial isostatic adjustment gia for antarctica persist due to uncertainties in deglacial history and earth rheology the earth models adopted in many gia studies are defined by parameters that vary in the radial direction only and represent a global average earth structure referred to as 1 d earth models oversimplifying the actual earth structure leads to bias in model predictions in regions where earth parameters differ significantly from the global average such as west antarctica we investigate the impact of lateral variations in lithospheric thickness on gia in antarctica by carrying out two experiments that use different rheological approaches to define 3 d earth models that include spatial variations in lithospheric thickness the first experiment defines an elastic lithosphere with spatial variations in thickness inferred from seismic studies we compare the results from this 3 d model with results derived from a 1 d earth model that has a uniform lithospheric thickness defined as the average of the 3 d lithospheric thickness irrespective of the deglacial history and sublithospheric mantle viscosity we find higher gradients of present day uplift rates i e higher amplitude and shorter wavelength in west antarctica when using the 3 d models due to the thinner than 1 d average lithosphere prevalent in this region the second experiment uses seismically inferred temperature as an input to a power law rheology thereby allowing the lithosphere to have a viscosity structure modelling the lithosphere with a powerlaw rheology results in a behaviour that is equivalent to a thinner lithospheremodel and it leads to higher amplitude and shorter wavelength deformation compared with the first experiment we conclude that neglecting spatial variations in lithospheric thickness in gia models will result in predictions of peak uplift and subsidence that are biased low in west antarctica this has important implications for ice sheet modelling studies as the steeper gradients of uplift predicted from the more realistic 3 d model may promote stability in marine grounded regions of west antarctica including lateral variations in lithospheric thickness at least to the level of considering west and east antarctica separately is important for capturing shortwavelength deformation and it has the potential to provide a better fit to global positioning system observations as well as an improved gia correction for the gravity recovery and climate experiment data