use of grace data to detect the present land uplift rate in fennoscandia after more than 13 years of grace monthly data the determined secular trend of gravity field variation can be used to study the regions of glacial isostatic adjustment gia here we focus on fenn

timing and origin of recent regional ice mass loss in greenland within the last decade the greenland ice sheet gris and its surroundings have experienced record high surface temperatures mote 2007 box et al 2010 ice sheet melt extent fettweis et al 2011 and record low summer sea ice extent nghiem et al 2007 using three independent data sets we derive for the first time consistent ice mass trends and temporal variations within seven major drainage basins from gravity fields from the gravity recovery and climate experiment grace tapley et al 2004 surface ice velocities from inteferometric synthetic aperture radar insar rignot and kanagaratnam 2006 together with output of the regional atmospheric climate modelling racmo2 gr ettema et al 2009 and surface elevation changes from the ice cloud and land elevation satellite icesat sorensen et al 2011 we show that changing ice discharge d surface melting and subsequent run off m r and precipitation p all contribute in a complex and regionally variable interplay to the increasingly negative mass balance of the gris observed within the last decade interannual variability in p along the northwest and west coasts of the gris largely explains the apparent regional mass loss increase during 2002 2010 and obscures increasing m r and d since the 1990s in winter 2002 2003 and 2008 2009 accumulation anomalies in the east and southeast temporarily outweighed the losses by m r and d that prevailed during 2003 2008 and after summer 2010 overall for all basins of the gris the decadal variability of anomalies in p m r and d between 1958 and 2010 w r t 1961 1990 was significantly exceeded by the regional trends observed during the grace period 2002 2011 2012 elsevier b v

secular gravity variation at svalbard norway from ground observations and grace satellite data the svalbard archipelago norway is affected by both the present day ice melting pdim and glacial isostatic adjustment gia subsequent to the last pleistocene deglaciation the induced deformation of the earth is observed by using different techniques at the geodetic observatory in ny alesund precise positioning measurements have been collected since 1991 a superconducting gravimeter sg has been installed in 1999 and six campaigns of absolute gravity ag measurements were performed between 1998 and 2007 moreover the gravity recovery and climate experiment grace satellite mission provides the time variation of the earth gravity field since 2002 the goal of this paper is to estimate the present rate of ice melting by combining geodetic observations of the gravity variation and uplift rate with geophysical modelling of both the gia and earth s response to the pdim we estimate the secular gravity variation by superimposing the sg series with the six ag measurements we collect published estimates of the vertical velocity based on gps and vlbi data we analyse the grace solutions provided by three groups csr gfz grgs the crux of the problem lies in the separation of the contributions from the gia and pdim to the earth s deformation to account for the gia we compute the response of viscoelastic earth models having different radial structures of mantle viscosity to the deglaciation histories included in the models ice 3g or ice 5g to account for the effect of pdim we compute the deformation of an elastic earth model for six models of ice melting extension and rates errors in the gravity variation and vertical velocity are estimated by taking into account the measurement uncertainties and the variability of the grace solutions and gia and pdim models the ground observations agree with models that involve a current ice loss of 25 km3 water equivalent yr 1 over svalbard whereas the space observations give a value in the interval 5 18 km3 water equivalent yr 1 a better modelling of the pdim which would include the precise topography of the glaciers and altitude dependency of ice melting is necessary to decrease the discrepancy between the two estimates

antarctic mass rates from grace 1 we estimate mass trends over antarctica using gravity variations observed by the gravity recovery and climate experiment grace satellite mission during its first 3 5 years april 2002 november 2005 an image of surface mass trends is constructed from 1 1 pixels over the entire continent and shows two prominent features a region of mass loss along the coast of west antarctica and one of accumulation in east antarctica after adjusting for bias due to smoothing and to grace s limited spatial resolution and removing post glacial rebound pgr effects the rate in west antarctica is 77 14 km3 year similar to a recent estimate of ice mass loss from satellite altimetry and remote sensing data the prominent east antarctic feature in the enderby land region has a rate of 80 16 km3 year published snow ice mass rates from remote sensing measurements indicate approximate ice mass balance in this region suggesting that this feature is either from unquantified snow accumulation in this region or more likely due to unmodeled pgr

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

grace measurements of mass variability in the earth system monthly gravity field estimates made by the twin gravity recovery and climate experiment grace satellites have a geoid height accuracy of 2 to 3 millimeters at a spatial resolution as small as 400 kilometers the annual cycle in the geoid variations up to 10 millimeters in some regions peaked predominantly in the spring and fall seasons geoid variations observed over south america that can be largely attributed to surface water and groundwater changes show a clear separation between the large amazon watershed and the smaller watersheds to the north such observations will help hydrologists to connect processes at traditional length scales tens of kilometers or less to those at regional and global scales

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

regional ice mass changes and glacial isostatic adjustment in antarctica from grace abstract we infer regional mass changes in antarctica using ca 4 years of gravity recovery and climate experiment grace level 2 data we decompose the time series of the stokes coefficients into their linear as well as annual and semi annual components by a least squares adjustment and apply a statistical reliability test to the stokes potential coefficients linear temporal trends mass changes in three regions of antarctica that display prominent geoid height change are determined by adjusting predictions of glacier melting at the tip of the antarctic peninsula and in the amundsen sea sector and of the glacial isostatic adjustment gia over the ronne ice shelf we use the gfz rl04 cnes rl01c jpl rl04 and csr rl04 potential coefficient releases and show that although all data sets consistently reflect the prominent mass changes differences in the mass change estimates are considerably larger than the uncertainties estimated by the propagation of the grace errors we then use the bootstrapping method based on the four releases and six time intervals each with 3 5 years of data to quantify the variability of the mean mass change estimates we find 95 of our estimates to lie within 0 08 and 0 09 mm a equivalent sea level esl change for the antarctic peninsula and within 0 18 and 0 20 mm a esl for the amundsen sea sector forward modelling of the gia over the ronne ice shelf region suggests that the antarctic continent was covered by 8 4 to 9 4 m esl of additional ice during the last glacial maximum ca 22 to 15 ka bp with regards to the mantle viscosity values and the glacial history used this value is considered as a minimum estimate the mass change estimates derived from all grace releases and time intervals lie within ca 20 amundsen sea sector 30 antarctic peninsula and 50 ronne ice shelf region of the bootstrap estimated mean demonstrating the reliability of results obtained using grace observations

external validation of the grace ggm01c gravity field using gps and doris positioning results 1 we have used the new gravity field model ggm01c derived from grace data to reanalyze doris data from 1993 0 to 2003 2 using the gipsy oasis software and a free network approach we have estimated the position and velocity of each doris station in itrf2000 in order to test the accuracy of these results we have compared them to the positions and velocities of 43 collocated gps stations using local ties and covariance information doris results computed using the ggm01c gravity field instead of the egm96 gravity field show a significantly improved external agreement with gps position agreement of 12 26 mm was reduced to 10 13 mm and velocity agreement of 3 3 3 7 mm yr was reduced to 2 4 3 3 mm yr this can be interpreted as an external test of the accuracy of the new ggm01c gravity field

antarctic circumpolar current transport variability during 2003 05 from grace abstract gravity recovery and climate experiment grace gravity data spanning january 2003 november 2005 are used as proxies for ocean bottom pressure bp averaged over 1 month spherical gaussian caps 500 km in radius and along paths bracketing the antarctic circumpolar current s various fronts the grace bp signals are compared with those derived from the estimating the circulation and climate of the ocean ecco ocean modeling assimilation system and to a non boussinesq version of the regional ocean model system roms the discrepancy found between grace and the models is 1 7 cmh2o 1 cmh2o 1 hpa slightly lower than the 1 9 cmh2o estimated by the authors independently from propagation of grace errors the northern signals are weak and uncorrelated among basins the southern signals are strong with a common seasonality the seasonal cycle grace data observed in the pacific and indian ocean sectors of the acc are consistent with annual and semiannual amplitudes of 3 6 and 0 6 cmh2o 1 1 and 0

the role of subglacial water in ice sheet mass balance subglacial water can significantly affect the velocity of ice streams and outlet glaciers of ice sheets depending on the geometry and capacity of the subglacial hydrologic system increased surface melting in greenland over the coming decades may influence the ice sheet s mass balance furthermore subglacial lakes in antarctica can modulate ice velocities and act as nucleation points for new fast flowing ice streams in the coming decades significant changes in the polar regions will increase the contribution of ice sheets to global sea level rise under the ice streams and outlet glaciers that deliver ice to the oceans water and deformable wet sediments lubricate the base facilitating fast ice flow the influence of subglacial water on fast ice flow depends on the geometry and capacity of the subglacial hydrologic system water moving rapidly through a well connected system of conduits or channels will have little impact on ice sheet velocities but water injected into a spatially dispersed subglacial system may reduce the effective pressure at the base of the ice sheet and thereby trigger increased ice sheet velocities in greenland the form of the subglacial hydrologic system encountered by increasing surface melt water will determine the influence of changing atmospheric conditions on ice sheet mass balance in antarctica subglacial lakes have the capacity to both modulate velocities in ice streams and outlet glaciers and provide nucleation points for new fast ice flow tributaries climate models of ice sheet responses to global change remain incomplete without a parameterization of subglacial hydrodynamics and ice dynamics

the association of australian winter climate with ocean temperatures to the west abstract two general circulation model experiments have been conducted with a view toward determining the sensitivity of australian winter circulation and precipitation to the imposition of idealized sea surface temperature anomalies around the western half of australia in the first a positive anomaly was imposed to the northwest of the continent and a negative anomaly to the southwest while in the second this pattern was reversed in the former major changes were simulated in the circulation over the australian sector and significant precipitation increases were induced over more than half of the continent by contrast the responses to the forcing in the latter experiment were considerably less particularly for precipitation over the continent which showed virtually no change of significance the results taken in concert with those of simmonds suggest the important role played by warm ocean temperatures to the northwest of australia in influencing winter rainfall the results suggest that the a

new insights on intraplate volcanism in french polynesia from wavelet analysis of grace champ and sea surface data in this paper we discuss the origin of superswell volcanism on the basis of representation and analysis of recent gravity and magnetic satellite data with wavelets in spherical geometry we computed a refined gravity field in the south central pacific based on the grace satellite ggm02s global gravity field and the kms02 altimetric grid and a magnetic anomaly field based on champ data the magnetic anomalies are marked by the magnetic lineation of the seafloor spreading and by a strong anomaly in the tuamotu region which we interpret as evidence for crustal thickening we interpret our gravity field through a continuous wavelet analysis that allows to get a first idea of the internal density distribution we also compute the continuous wavelet analysis of the bathymetric contribution to discriminate between deep and superficial sources according to the gravity signature of the different chains as revealed by our analysis various processes are at the origin of the volcanism in french polynesia as evidence we show a large scale anomaly over the society islands that we interpret as the gravity signature of a deeply anchored mantle plume the gravity signature of the cook austral chain indicates a complex origin which may involve deep processes finally we discuss the particular location of the marquesas chain as suggesting that the origin of the volcanism may interfere with secondary convection rolls or may be controlled by lithospheric weakness due to the regional stress field or else related to the presence of the nearby tuamotu plateau

time variable gravity from grace first results eleven monthly grace gravity field solutions are now available for analyses we show those fields can be used to recover monthly changes in water storage both on land and in the ocean to accuracies of 1 5 cm of water thickness when smoothed over 1000 km the amplitude of the annually varying signal can be determined to 1 0 cm results are 30 better for a 1500 km smoothing radius and 40 worse for a 750 km radius we estimate the annually varying component of water storage for three large drainage basins the mississippi the amazon and a region draining into the bay of bengal to accuracies of 1 0 1 5 cm

small scale spatio temporal characteristics of accumulation rates in western dronning maud land antarctica spatio temporal variations of the recently determined accumulation rate are investigated using ground penetrating radar gpr measurements and firn core studies the study area is located on ritscherflya in western dronning maud land antarctica at an elevation range 1400 1560 m accumu lation rates are derived from internal reflection horizons irhs tracked with gpr which are connected to a dated firn core gpr derived internal layer depths show small relief along a 22 km profile on an ice flowline average accumulation rates are about 190 kg m 2 a 1 1980 2005 with spatial variability 1 of 5 along the gpr profile the interannual variability obtained from four dated firn cores is one order of magnitude higher showing 1 standard deviations around 30 mean temporal variations of gpr derived accumulation rates are of the same magnitude or even higher than spatial variations temporal differences between 1980 90 and 1990 2005 obtained from two dated irhs along the gpr profile indicate temporally non stationary processes linked to spatial variations comparison with similarly obtained accumulation data from another coastal area in central dronning maud land confirms this observation our results contribute to understanding spatio temporal variations of the accumulation processes necessary for the validation of satellite data e g altimetry studies and gravity missions such as gravity recovery and climate experiment grace

grace detects coseismic and postseismic deformation from the sumatra andaman earthquake 1 we show that spherical harmonic sh solutions of the gravity recovery and climate experiment grace are now of sufficient quality to observe effects of co seismic and post seismic deformation due to the rupture from the mw 9 3 sumatra andaman earthquake on december 26 2004 and its companion nias earthquake mw 8 7 on march 28 2005 the improved ggm 03 sh level 2 solutions and improved filtering methods provide estimates with spatial resolution comparable to earlier estimates from range rate level 1 grace data the gravityfield disturbance extends over 1800 km along andaman and sunda subduction zones and changes with time following events gravity changes may be due to afterslip viscoelastic relaxation or other processes associated with dilatation satellite gravity measurements from grace provide a unique new measure of deformation and post seismic processes associated with major earthquakes especially in areas which are primarily oceanic citation chen j l c r wilson b d tapley and s grand 2007 grace detects coseismic and postseismic deformation from the sumatraandaman earthquake geophys res lett 34 l13302

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

different modes of variability over the tasman sea implications for regional climate abstracta new approach is used to detect atmospheric teleconnections without being bound by orthogonality such as empirical orthogonal functions this method employs negative correlations in a global dataset to detect potential teleconnections one teleconnection occurs between the tasman sea and the southern ocean it is related to el nino southern oscillation enso the indian ocean dipole iod and the southern annular mode sam this teleconnection is significantly correlated with sam during austral summer fall and winter with iod during spring and with enso in summer it can thus be described as a hybrid between these modes given previously found relationships between iod and enso and iod s proximity to the teleconnection centers correlations to iod are generally stronger than to enso increasing pressure over the tasman sea leads to higher lower surface temperature over eastern australia the southwestern pacific in all seasons and is related to reduced surface temperature over wilkes

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

temporal variations of the marine geoid the effects of temporal changes in the marine geoid on estimates of the ocean dynamic topography is being investigated influences from changes of land hydrology ice sheets post glacial rebound

time variations of land water storage from an inversion of 2 years of grace geoids by delivering monthly maps of the gravity field the grace project allows the determination of tiny time variations of the earth s gravity and particularly the effects of fluid mass redistributions at the surface of the earth however grace data represent vertically integrated gravity measurements thus are the sum of all mass redistributions inside the earth s system atmosphere oceans and continental water storage plus solid earth in this paper we apply a generalized least squares inverse approach previously developed by 1 g ramillien a cazenave o brunau global time variations of hydrological signals from grace satellite gravimetry geophys j int 158 2004 813 826 to estimate from the monthly grace geoids continental water storage variations and their associated uncertainties over a 2 year time span april 2002 to may 2004 tests demonstrating the robustness of the method are presented including the separation between liquid water reservoirs surface waters soil moisture groundwaters and snow pack contributions individual monthly solutions of total land water storage from grace with a spatial resolution of 660 km are presented for the 2 year time span we also derive the seasonal cycle map we further estimate water volume changes over eight large river basins in the tropics and compare with model predictions finally we attempt to estimate an average value of the evapotranspiration over each river basin using the water balance equation which links temporal change in water volume to precipitation evapotranspiration and runoff amplitudes of the grace derived evapotranspiration are regionally consistent to the predictions of global hydrological models

grace estimates of sea surface height anomalies in the gulf of carpentaria australia abstract the gulf of carpentaria in northern australia has a weather driven annual periodic amplitude in sea surface height of 0 4 m such a signal generates a mass variation that is readily detected by the grace mission we used this naturally occurring phenomenon over a region of 2 6 10 5 km 2 to evaluate the accuracy of the grace estimates of temporal mass variation comparison of the groupe de recherche de geodesie spatiale 10 day grace solutions and observations from a nearby tide gauge show a correlation of 0 93 indicating that the grgs grace solutions capture well the regional signal on the other hand the mog2d g barotropic model accounts for only 50 of the non gravitational annual signal suggesting either deficiencies in the model or that some other non barotropic process is occurring

accelerated antarctic ice loss from satellite gravity measurements accurate quantification of antarctic ice sheet mass balance and its contribution to global sea level rise remains challenging gravity recovery and climate experiment data spanning the period april 2002 to january 2009 confirm earlier estimates of ice loss for antarctica and indicate that east antarctica started losing mass in about 2006

grace derived ice mass variations over greenland by accounting for leakage effects 1 after more than 6 years in full operational mode the gravity recovery and climate experiment grace satellite mission provides the opportunity to derive global secular mass changes from space geodetic observations crucial for a reliable estimate of secular mass changes is the ability to correct for spectral and spatial leakage effects in order to account for any leakage signal we present and apply a four step procedure including a validation step based on forward gravity modeling most notably our method is characterized by the separation and quantification of individual leakage sources we test and apply our procedure to the greenland area which exhibits the strongest secular trend signal on the basis of simulation studies we demonstrate that leakage out effects are dominant for the greenland area and if not accounted for mass change rates will be underestimated analyzing time variable grace gravity fields covering 6 whole years august 2002 to july 2008 inclusive we estimate the ice volume loss over greenland to be 177 12 km3 a 1 this value is the average derived from monthly gravity field models provided by csr gfz and jpl with individual contributions of 242 14 km3 a 1 194 24 km3 a 1 and 96 23 km3 a 1 respectively we highlight that without taking leakage effects into account mass change amplitudes over greenland are reduced by a factor of 2 despite the rather large spread of the results among grace processing centers our results are in better agreement with the findings from alternative grace analysis methods and insar observations

antarctic peninsula ice sheet evolution during the cenozoic era the antarctic peninsula region is currently undergoing rapid environmental change resulting in the thinning acceleration and recession of glaciers and the sequential collapse of ice shelves it is important to view these changes in the context of long term palaeoenvironmental complexity and to understand the key processes controlling ice sheet growth and recession in addition numerical ice sheet models require detailed geological data for tuning and testing therefore this paper systematically and holistically reviews published geological evidence for antarctic peninsula ice sheet variability for each key locality throughout the cenozoic and brings together the prevailing consensus of the extent character and behaviour of the glaciations of the antarctic peninsula region major contributions include a downloadable database of 186 terrestrial and marine calibrated dates an original reconstruction of the lgm ice sheet and a new series of isochrones detailing ice sheet retreat following the lgm glaciation of antarctica was initiated around the eocene oligocene transition in east antarctica palaeogene records of antarctic peninsula glaciation are primarily restricted to king george island where glacigenic sediments provide a record of early east antarctic glaciations but with modification of far travelled erratics by local south shetland island ice caps evidence for neogene glaciation is derived primarily from king george island and james ross island where glaciovolcanic strata indicate that ice thicknesses reached 500 850 m during glacials this suggests that the antarctic peninsula ice sheet draped rather than drowned the topography marine geophysical investigations indicate multiple ice sheet advances during this time seismic profiling of continental shelf slope deposits indicates up to ten large advances of the antarctic peninsula ice sheet during the early pleistocene when the ice sheet was dominated by 40 kyr cycles glacials became more pronounced reaching the continental shelf edge and of longer duration during the middle pleistocene during the late pleistocene repeated glacials reached the shelf edge but ice shelves inhibited iceberg rafting the last glacial maximum lgm occurred at 18 ka bp after which transitional glaciomarine sediments on the continental shelf indicate ice sheet retreat the continental shelf contains large bathymetric troughs which were repeatedly occupied by large ice streams during pleistocene glaciations retreat after the lgm was episodic in the weddell sea with multiple readvances and changes in ice flow direction but rapid in the bellingshausen sea the late holocene epoch was characterised by repeated fluctuations in palaeoenvironmental conditions with associated glacial readvances however this has been subsumed by rapid warming and ice shelf collapse during the twentieth century

computations of the viscoelastic response of a 3 d compressible earth to surface loading an application to glacial isostatic adjustment in antarctica and canada s u m m a r y we develop a 3 d finite element model to study the viscoelastic response of a compressible earth to surface loads the effects of centre of mass motion polar wander feedback and selfconsistent ocean loading are implemented to assess the model s accuracy we benchmark the numerical results against a semi analytic solution for spherically symmetric structure we force our model with the ice 5g global ice loading history to study the effects of laterally varying viscosity structure on several glacial isostatic adjustment gia observables including relative sea level rsl measurements incanada and present day time variable gravity and uplift rates in antarctica canadian rsl observations have been used to determine the earth s globally averaged viscosity profile antarcticgps uplift rates have been used to constrainantarcticgia models and gia time variable gravity and uplift signals are error sources for grace and altimeter estimates of present day antarctic ice mass loss and must be modelled and removed from those estimates computinggia results for a 3 d viscosity profile derived from a realistic seismic tomography model and comparing with results computed for 1 d averages of that 3 d profile we conclude that 1 a gia viscosity model based on canadian relative sea level data is more likely to represent a canadian average than a true global average 2 the effects of 3 d viscosity structure on grace estimates of present day antarctic mass loss are probably smaller than the difference between gia models based on different antarctic deglaciation histories and 3 the effects of 3 d viscosity structure on antarctic gps observations of present day uplift rate can be significant and can complicate efforts to use gps observations to constrain 1 d gia models

greenland mass balance from grace 1 we use 22 monthly grace gravity recovery and climate experiment gravity fields to estimate the linear trend in greenland ice mass during 2002 2004 we recover a decrease in total ice mass of 82 28 km3 of ice per year consistent with estimates from other techniques our uncertainty estimate is dominated by the effects of grace measurement errors and errors in our post glacial rebound pg correction the main advantages of grace are that it is sensitive to the entire ice sheet and that it provides mass estimates with only minimal use of supporting physical assumptions or ancillary data

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

antarctic ice mass balance estimates from grace tidal aliasing effects 1 geophysical interpretation of grace gravity fields has provided estimates of antarctic ice mass change such analyses rely on proper consideration of ocean tidal effects through the models csr4 and fes2004 in general mis modeling of tidal constituents with aliasing period less than 30 day will not have significant impact on ice mass change however for constituents such as k1 k2 and s2 the aliasing period is sufficiently large to potentially compromise long term variability studies here we quantify tidal aliasing over antarctica by simulating grace signatures due to differences between csr4 and fes2004 and the best available circum antarctic model tpxo6 2 the s2 simulations are in close agreement with the observed s2 signal from grace simulations of ice mass change show that over 2002 2006 long term k1 and k2 aliasing is equivalent to a rate error of 4 5 1 3 km3 a of ice with csr4 but only 0 2 0 2 km3 a with fes2004 after spatial averaging and destriping k1 plus k2 mis modeling in csr4 fes2004 introduce point wise errors up to 5 2 mm a in equivalent water height over a 3 5 year period with observed mass change equivalent to less than 30 mm a of water height over much of antarctica the simulations show tidal aliasing uncertainty at the 2 3 mm a level for august 2002 january 2006 or 10 of the signal with grace release 04 the revised estimate april 2002 january 2006 of published ice volume decrease is 164 80 km3 a of ice although this value depends very much on the gia model and grace analysis approach

trajectories of the mount st helens eruption plume the plume of the major eruption of mount st helens on 18 may 1980 penetrated 10 to 11 kilometers into the stratosphere attaining heights of 22 to 23 kilometers wind shears rapidly converted the plume from an expanding vertical cone to a thin slightly inclined lamina the lamina was extruded zonally in the stratosphere as the lower part moved eastward at jet stream velocities while the upper part slowly moved westward in the region of nonsteady transition from the westerlies to the summer stratospheric easterlies trajectories computed to position the nasa u 2 aircraft for sampling in the plume are described plume volume after 8 hours of strong volcanic emission is estimated at 2 x 106cubic kilometers only about 1 percent of this volume is attributed to the volcano the rest was entrained from the environment

measurements of time variable gravity show mass loss in antarctica using measurements of time variable gravity from the gravity recovery and climate experiment satellites we determined mass variations of the antarctic ice sheet during 2002 2005 we found that the mass of the ice sheet decreased significantly at a rate of 152 80 cubic kilometers of ice per year which is equivalent to 0 4 0 2 millimeters of global sea level rise per year most of this mass loss came from the west antarctic ice sheet

time variable gravity from space and present day mass redistribution in theearth system abstract since 2002 the us german grace gravity recovery and climate experiment mission has been providing a precise survey of earth s time variable gravity field with unprecedented temporal and spatial sampling grace time variable gravity fields provide a means of measuring temporal and spatial variations of mass redistribution within the earth system the grace mission has launched a new era in studying a series of geophysical problems ranging from deep earth structure to tracking mass redistribution on and near the surface of the earth grace has greatly improved understanding of mass redistribution in various compartments of the climate system atmosphere oceans terrestrial water and cryosphere in this review we use examples to show how grace has fundamentally enriched a number of fields including but not limited to the global water cycle and land hydrology mass balance of polar ice sheets and mountain glaciers ocean mass and global sea level change and solid earth geophysics

rapid sea level rise abstract several global and regional factors contribute to observed sea level change along any particular coast global processes include changes in ocean mass glacio eustasy from ice melt ocean volume steric effects viscoelastic land movements glacioisostatic adjustment gia and changes in terrestrial water storage regional processes often connected to steric and glacial changes include changes in ocean circulation meridional overturning circulation moc glacial melting local gia regional subsidence and others paleoclimate instrumental and modeling studies show that combinations of these factors can cause relatively rapid rates of sea level rise exceeding 3 mm yr 1 over various timescales along particular coasts this paper discusses patterns and causes of sea level rise with emphasis on paleoclimatological records it then addresses the hypothesis of late holocene pre 20th century sea level stability in light of paleoclimatic evidence notably from reconstructions of sea surface temperature and glacial activity for significant climate and sea level variability during this time the practical difficulties of assessing regional sea level sl patterns at submillennial timescales will be discussed using an example from the eastern united states

revisiting sites of the south pole queen maud land traverses in east antarctica accumulation data from shallow firn cores 1 ground based accumulation measurements are scarce on the high east antarctic plateau but highly necessary for model validation and the interpretation of satellite data for the determination of antarctic mass balance here we present accumulation results obtained from four shallow firn cores drilled in the antarctic summer season 2007 2008 the cores were drilled along the first leg of the norwegian us ipy traverse through east antarctica visiting sites like plateau station and pole of relative inaccessibility that have been covered by the south pole queen maud land traverses spqmlt in the 1960s accumulation has been determined from volcanic chronology established from the conductivity records measured by dielectric profiling dep the tambora 1815 unknown 1809 double peak is clearly visible in the conductivity data and serves as a reliable time marker accumulation rates averaged over the period 1815 2007 are in the range of 16 to 32 kg m 2 a 1 somewhat lower than expected from the spqmlt data the spatial pattern is mainly influenced by elevation and continentality three of the firn cores show a decrease of more than 20 in accumulation for the time period 1815 2007 in relation to accumulation rates during the period 1641 1815 the spatial representativity of the firn cores is assessed by ground penetrating radar showing a rather smoothly layered pattern around the drill sites validation of the dep results is utilized by comparison with chemistry data proving the validity of the dep method for dating firn cores the results help understanding the status of the east antarctic ice sheet and will be important for e g future model derived estimates of the mass balance of antarctica

terrestrial and submarine evidence for the extent and timing of the last glacial maximum and the onset of deglaciation on the maritime antarctic and sub antarctic islands this paper is the maritime and sub antarctic contribution to the scientific committee for antarctic research scar past antarctic ice sheet dynamics pais community antarctic ice sheet reconstruction the overarching aim for all sectors of antarctica was to reconstruct the last glacial maximum lgm ice sheet extent and thickness and map the subsequent deglaciation in a series of 5000 year time slices however our review of the literature found surprisingly few high quality chronological constraints on changing glacier extents on these timescales in the maritime and sub antarctic sector therefore in this paper we focus on an assessment of the terrestrial and offshore evidence for the lgm ice extent establishing minimum ages for the onset of deglaciation and separating evidence of deglaciation from lgm limits from those associated with later holocene glacier fluctuations evidence included geomorphological descriptions of glacial landscapes radiocarbon dated basal peat and lake sediment deposits cosmogenic isotope ages of glacial features and molecular biological data we propose a classification of the glacial history of the maritime and sub antarctic islands based on this assembled evidence these include type i islands which accumulated little or no lgm ice type ii islands with a limited lgm ice extent but evidence of extensive earlier continental shelf glaciations type iii seamounts and volcanoes unlikely to have accumulated significant lgm ice cover type iv islands on shallow shelves with both terrestrial and submarine evidence of lgm and or earlier ice expansion type v islands north of the antarctic polar front with terrestrial evidence of lgm ice expansion and type vi islands with no data finally we review the climatological and geomorphological settings that separate the glaciological history of the islands within this classification scheme

glacial isostatic adjustment and nonstationary signals observed by grace 1 changes in hydrologic surface loads glacier mass balance and glacial isostatic adjustment gia have been observed using data from the gravity recovery and climate experiment grace mission in some cases the estimates have been made by calculating a combination of the linear rate of change of the time series and periodic seasonal variations of grace estimates yet the geophysical phenomena are often not stationary in nature or are dominated by other nonstationary signals we investigate the variation in linear rate estimates that arise when selecting different time intervals of grace solutions and show that more accurate estimates of stationary signals such as gia can be obtained after the removal of model based hydrologic effects we focus on north america where numerical hydrological models exist and east antarctica where such models are not readily available the root mean square of vertical velocities in north america are reduced by 20 in a comparison of grace and gps derived uplift rates when the grace products are corrected for hydrological effects using the gldas model the correlation between the rate estimates of the two techniques increases from 0 58 to 0 73 while acknowledging that the gldas model does not model all aspects of the hydrological cycle it is sufficiently accurate to demonstrate the importance of accounting for hydrological effects before estimating linear trends from grace signals we also show from a comparison of predicted gia models and observed gps uplift rates that the positive anomaly seen in enderby land east antarctica is not a stationary signal related to gia

low degree spherical harmonic influences on gravity recovery and climate experiment grace water storage estimates we estimate terrestrial water storage variations using time variable gravity changes observed by the gravity recovery and climate experiment grace satellites during the first 2 years of the mission we examine how treatment of low degree gravitational changes and geocenter variations affect grace based estimates of basin scale water storage changes using independently derived low degree harmonics from earth rotation eop and satellite laser ranging slr observations grace based water storage changes are compared with estimates from nasa s global land data assimilation system gldas results from the 22 grace monthly gravity solutions covering the period april 2002 to july 2004 show remarkably good agreement with gldas in the mississippi amazon ganges ob zambezi and victoria basins combining grace observations with eop and slr degree 2 spherical harmonic coefficient changes and slr observed geocenter variations significantly affects and apparently improves the estimates especially in the mississippi ob and victoria basins

a comparative study of changes in the lambert glacier amery ice shelf system east antarctica during 2004 2008 using gravity and surface elevation observations we present results of a regional comparative study of surface mass changes from 2004 to 2008 based on gravity recovery and climate experiment grace the ice cloud and land elevation satellite icesat and chinare observations over the lambert glacier amery ice shelf system las estimation of the icesat mass change rates benefitted from the density measurements along the chinare traverse and a spatial density adjustment method for reducing the effect of spatial density variations in the high elevation inland region a positive trend was estimated from both icesat and grace data which is in line with the chinare accumulation measurements in the coastal region there were areas with high level accumulations in both icesat and grace trend maps in many high flow speed glacier areas negative mass change rates may be caused by dynamic ice flow discharges that have surpassed the snow accumulation overall the mass change rate estimate in the las of 2004 2008 from the grace icesat and chinare data is 5 41 4 59 gt a 1 indicating a balanced to slightly positive mass trend along with other published results this suggests that a longer term positive mass trend in the las may have slowed in recent years

blast dynamics at mount st helens on 18 may 1980 at 8 32 a m on 18 may 1980 failure of the upper part of the north slope of mount st helens triggered a lateral eruption the blast that devastated the conifer forests in a sector covering 500 km2 north of the volcano i present here a steady flow model for the blast dynamics and propose that through much of the devastated area the blast was a supersonic flow of a complex multiphase solid liquid vapour mixture the shape of the blast zone pressure temperature velocity mach number and density distributions within the flow positions of weak and strong internal shocks and mass flux energy flux and total energy are calculated the shape of blast zone was determined by the initial areal expansion from the reservoir by internal expansion and compression waves including shocks and by the density of the expanding mixture the pressure within the flow dropped rapidly away from the source of the blast until at a distance of 11 km the flow became underpressured relative to the surrounding atmosphere weak shocks within the flow subparallel to the east and west margins coalesced at about this distance into a strong mach disk shock across which the flow velocities would have dropped from supersonic to subsonic as the pressure rose back towards ambient the positions of the shocks may be reflected in differences in the patterns of felled trees at the limits of the devastated area the temperature had dropped only 20 from the reservoir temperature because the entrained solids thermally buffered the flow the dynamic and thermodynamic effects of the admixture of the surrounding atmosphere and the uprooted forest and soils into the flow are not considered the density of the flow decreased with distance until at the limits of the blast zone 20 25 km from the volcano the density became comparable with that of the surrounding dirty atmosphere and the flow became buoyant and ramped up into the atmosphere according to the model the mass flux per unit area at the source was 0 6 104 g s 1 cm 2 and the energy flux per unit area was 2 5 mw cm 2 from the measured total ejected mass 0 25 1015 g the total energy released during the eruption was 1024 erg or 24 megatons the model triggering of the eruption and the transition from unsteady to steady flow and applications to eyewitness observations and atmospheric effects are discussed in ref 1

a deglacial model for antarctica geological constraints and glaciological modelling as a basis for a new model of antarctic glacial isostatic adjustment abstract we present a new reconstruction of the antarctic ice sheets between 20 ka bp and the present day our reconstruction is derived using a numerical model to generate a physically consistent ice surface across the whole of the continent we define the extent of the ice sheet at five time slices 20 15 10 5 and 0 ka bp assuming an equilibrium state for the 20 ka bp time slice and a transient state for the deglacial time slices the evolution of the ice sheet within the numerical model is driven by variations in temperature accumulation rate and relative sea level in order to reconstruct the concave profile of the ice sheet in marine grounded regions such as the ross and weddell seas we force our model to develop channels of faster flow by defining greater basal sliding along the trajectory of former ice streams we find a strong dependence upon the basal sliding parameters and also the position of the grounding line we use an extensive data base of geological and glaciological data to constrain our ice sheet reconstruction grounding line extent is prescribed from marine geological data and we test ice sheet thickness against onshore geological data at 62 sites of the five time slices considered our 20 ka bp reconstruction is the best constrained by data and has an rms misfit of 147 6 m when compared to observations of ice thickness change between 20 ka bp and the present day across all time slices there are large regions of the ice sheet which are poorly constrained especially after 20 ka bp we estimate the spatial distribution of uncertainty in our ice sheet reconstruction and note that the solutions are least reliable in regions of complex topography we predict that the antarctic ice sheets contributed 9 1 5 m of eustatic sea level to the global ocean between 20 ka bp and the present and our reconstruction with minimum misfit contributes 8 m eustatic sea level during this period these values which we argue are an upper bound are lower than many previous estimates the reconstructed pattern of ice unloading can serve as a new input for glacial isostatic models

the sustainability of water resources in high mountain asia in the context of recent and future glacier change high mountain asia contains the largest volume of glacier ice outside the polar regions and contain the headwaters of some of the largest rivers in central asia these glaciers are losing mass at a mean rate of between 0 18 and 0 5 m water equivalent per year while glaciers in the himalaya are generally shrinking those in the karakoram have experienced a slight mass gain both changes have occurred in response to rising air temperatures due to northern hemisphere climate change in the westerly influenced indus catchment glacier meltwater makes up a large proportion of the hydrological budget and loss of glacier mass will ultimately lead to a decrease in water supplies in the monsoon influenced ganges and brahmaputra catchments the contribution of glacial meltwater is relatively small compared to the indus and the decrease in annual water supplies will be less dramatic therefore enhanced glacier melt will increase river flows until the middle of the twenty first century but in the longer term into the latter part of this century river flows will decline as glaciers shrink declining meltwater supplies may be compensated by increases in precipitation but this could exacerbate the risk of flooding

the pole tide and its effect on grace time variable gravity measurements implications for estimates of surface mass variations gravity recovery and climate experiment grace provides monthly solutions for the earth s gravity field in the form of spherical harmonic coefficients these can be used to infer changes in mass at the earth s surface the pole tide the response of the earth and oceans to polar motion causes gravity signals dominated by harmonics of degree 2 order 1 if the pole tide is not removed from grace data it affects the coefficients of those harmonics c21 s21 and introduces errors when using those coefficients to determine surface mass variations the pole tide is partially removed by grace processing centers before solving for the gravity field but long period pole tide signals are not usually included in the grace pole tide correction and so those signals are still present in the grace coefficients we discuss this issue from the standpoint of somebody who uses the grace gravity fields to infer changes in surface mass we arrive at a recommendation for an optimal grace pole tide correction we describe how to modify the c21 s21 coefficients provided by the processing centers so that they conform with our recommendation we discuss the size of the pole tide contributions to c21 s21 compared to those of the direct load induced contributions as an example we show how an incompletely removed pole tide can impact grace results for the trend in ocean mass we consider the impact of mantle anelasticity on long period pole tide corrections and conclude that it is unlikely to affect those corrections by more than 20

the immediate environmental effects of tephra emission the earth s history is punctuated by large explosive eruptions that eject large quantities of magma and silicate rock fragments into the atmosphere these tephra particles can sometimes be dispersed across millions of square kilometres or even entire continents the interaction of tephra with or in receiving environments may induce an array of physical chemical and biological effects the consequences for affected systems and any dependent communities may be chronic and localised in the event of frequent small eruptions while larger and rarer events may have acute regional scale impacts it is therefore necessary to document the range of possible impacts that tephra may induce in receiving environments and any resulting effects in interconnected systems we collate results from many studies to offer a detailed multidisciplinary and interdisciplinary review of the immediate post eruptive effects of tephra emission into the atmosphere onto vegetation soil or ice snow surfaces and in aquatic systems we further consider the repercussions that may be induced in the weeks to years afterwards in the atmosphere tephra can influence cloud properties and air chemistry by acting as ice nuclei in or by offering sites for heterogeneous reactions respectively tephra on vegetation causes physical damage and sustained coverage may elicit longer term physiological responses tephra deposits on soils may alter their capacity to exchange gas water and heat with the atmosphere or may have a specific chemical effect such as nutrient input or acidification on sensitive soils tephra deposition onto snow or ice may affect ablation rates rivers and lakes may experience turbidity increases and changes in their morphology as a result of fallout and prolonged months or years erosion from the tephra covered catchment in the first weeks after deposition tephra leaching may affect river chemistry the abundance and speciation of phytoplankton populations in lakes may be altered by tephra induced changes in water chemistry or sediment water nutrient cycling in the oceans tephra deposition may fertilise fe limited waters with potential impacts on the global carbon cycle embracing the full complexity of environmental effects caused by tephra fall demands a renewed investigative effort drawing on interdisciplinary field and laboratory studies combined with consideration of the interconnectivity of induced impacts within and between different receiving environments

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

closure of the budget of global sea level rise over the grace era the importance and magnitudes of the required corrections for global glacial isostatic adjustment abstract the budget of global sea level rise includes contributions from several distinct factors including thermosteric effects the wasting of small ice sheets and glaciers and the loss of mass by the great polar ice sheets and by the continents due to desiccation since the former contribution may be estimated on the basis of both hydrographic survey data and more recently using argo float data the second may be estimated on the basis of mass balance measurements on existing ice fields and the latter on the basis of modern grace based time dependent gravity field measurements the inputs to the globally averaged rate of sea level rise may be directly constrained since grace also provides a measurement of the rate at which mass is being added to the oceans we are now in a position to ask whether this rate of mass addition to the oceans matches the rate at which mass is being removed from the continents as demonstrated herein the mass component of the budget of global sea level is closed within the observational errors when the mass derived contribution is added to the thermosteric contribution it is furthermore shown that the inference of the net rate of global sea level rise by the altimetric satellites topex poseidon and jason 1 is also reconcilable over the grace era it is noted those individual terms in the budget especially the contribution from small ice sheets and glaciers remains insufficiently accurate it is demonstrated that the lingering influence of the late quaternary ice age upon sea level is profound and that closure of the budget requires an accurate model of its impact

state of the antarctic and southern ocean climate system this paper reviews developments in our understanding of the state of the antarctic and southern ocean climate and its relation to the global climate system over the last few millennia climate over this and earlier periods has not been stable as evidenced by the occurrence of abrupt changes in atmospheric circulation and temperature recorded in antarctic ice core proxies for past climate two of the most prominent abrupt climate change events are characterized by intensification of the circumpolar westerlies also known as the southern annular mode between 6000 and 5000 years ago and since 1200 1000 years ago following the last of these is a period of major trans antarctic reorganization of atmospheric circulation and temperature between ad1700 and 1850 the two earlier antarctic abrupt climate change events appear linked to but predate by several centuries even more abrupt climate change in the north atlantic and the end of the more recent event is coincident with reorganization of atmospheric circulation in the north pacific improved understanding of such events and of the associations between abrupt climate change events recorded in both hemispheres is critical to predicting the impact and timing of future abrupt climate change events potentially forced by anthropogenic changes in greenhouse gases and aerosols special attention is given to the climate of the past 200 years which was recorded by a network of recently available shallow firn cores and to that of the past 50 years which was monitored by the continuous instrumental record significant regional climate changes have taken place in the antarctic during the past 50 years atmospheric temperatures have increased markedly over the antarctic peninsula linked to nearby ocean warming and intensification of the circumpolar westerlies glaciers are retreating on the peninsula in patagonia on the sub antarctic islands and in west antarctica adjacent to the peninsula the penetration of marine air masses has become more pronounced over parts of west antarctica above the surface the antarctic troposphere has warmed during winter while the stratosphere has cooled year round the upper kilometer of the circumpolar southern ocean has warmed antarctic bottom water across a wide sector off east antarctica has freshened and the densest bottom water in the weddell sea has warmed in contrast to these regional climate changes over most of antarctica near surface temperature and snowfall have not increased significantly during at least the past 50 years and proxy data suggest that the atmospheric circulation over the interior has remained in a similar state for at least the past 200 years furthermore the total sea ice cover around antarctica has exhibited no significant overall change since reliable satellite monitoring began in the late 1970s despite large but compensating regional changes the inhomogeneity of antarctic climate in space and time implies that recent antarctic climate changes are due on the one hand to a combination of strong multi decadal variability and anthropogenic effects and as demonstrated by the paleoclimate record on the other hand to multi decadal to millennial scale and longer natural variability forced through changes in orbital insolation greenhouse gases solar variability ice dynamics and aerosols model projections suggest that over the 21st century the antarctic interior will warm by 3 4 1oc and sea ice extent will decrease by 30 ice sheet models are not yet adequate enough to answer pressing questions about the effect of projected warming on mass balance and sea level considering the potentially major impacts of a warming climate on antarctica vigorous efforts are needed to better understand all aspects of the highly coupled antarctic climate system as well as its influence on the earth s climate and oceans

sea level changes since the last glacial maximum an appraisal of the ipcc fourth assessment report the ipcc fourth assessment report ar4 stated that global sea level rose by about 120 m between the last glacial maximum lgm and 3 2 ka and did not rise again until the late 19th century a review of relevant literature demonstrates that the rise may have been larger by 10 15 m that the timing of stabilisation is poorly constrained within the last 7 ka bp and that the onset of modern rates of sea level rise is not synchronous and uniform across the globe the lgm lowstand as defined in the ar4 is based on the classic barbados sea level history but the sea level curve from this island may not be an accurate eustatic approximation if glacial isostatic adjustment gia processes were significant as suggested by various authors the barbados sea level curve revealed the existence of meltwater pulse mwp 1a at around 14 000 cal a bp questions about the source and causal mechanism of mwp 1a are still being explored by field scientists and gia modellers these problems have direct relevance for contemporary measurements of ice mass changes because space geodetic measurements rely on information provided by gia models to separate land motion from ice mass changes global patterns of holocene sea level change are controlled by regional sea level variability not only through isostatic and tectonic processes but also through steric effects longer wavelength gravitational changes produced by changing ice ocean mass flux and hemispheric scale perturbations in the earth s rotation eustasy is therefore merely a concept not a measurable quantity constraining the late holocene ice melt contribution to global sea level rise and determining regional sea level rise patterns in the 18th and 19th centuries are important future tasks for sea level scientists these will establish the baseline contributions to 20th and 21st century sea level rise and will help to determine the causes of modern rates of sea level rise constraining historical sea level accelerations and short term ice mass flux will aid models of ice sheet dynamics and help to reduce current uncertainties in future sea level predictions the ar4 shows that regional sea level variability is clearly present in sea level change patterns for the past 50 a and an important challenge for the next ipcc assessment is to incorporate this variability into regional future sea level rise scenarios copyright 2009 john wiley sons ltd

isolating the pgr signal in the grace data impact on mass balance estimates in antarctica and greenland summary redistribution of mass over the earth and within the mantle changes the gravity field whose variations are monitored at high spatial resolution by the presently flying grace space gravity mission from nasa or at longer wavelengths by the satellite laser ranging slr constellation in principle grace data allow one to study the time evolution of various earth phenomena through their gravitational effects the correct identification of the gravitational spatial and temporal fingerprints of the individual hydrologic atmospheric oceanographic and solid earth phenomena is thus extremely important but also not trivial in particular it has been widely recognized that the gravitational estimates of present day ice mass loss in greenland and antarctica and the related effect on sea level changes depend on an accurate determination of the postglacial rebound pgr after pleistocene deglaciation which in turn depends on the assumed solid earth parameters and deglaciation model here we investigate the effect of the uncertainty of the solid earth parameters viscosity litospheric thickness and of different deglaciation processes on pgr in greenland and antarctica we find that realistic constraints to the trend in ice mass loss derived from grace data determine a range of variation substantially wider than commonly stated ranging from an important ice loss of 209 gt yr 1 to an accumulation of 88 gt yr 1 in antarctica and greenland ablation at a rate between 122 and 50 gt yr 1 however if we adopt the set of most probable earth parameters we infer a substantial mass loss in both regions 171 39 and 101 22 gt yr 1 for antarctica and greenland respectively

large scale ocean circulation from the grace ggm01 geoid 1 the grace gravity model 01 ggm01 computed from 111 days of grace k band ranging kbr data is differenced from a global mean sea surface mss computed from a decade of satellite altimetry to determine a mean dynamic ocean topography dot as a test of the ggm01 gravity model large scale zonal and meridional surface geostrophic currents are computed from the topography and are compared with those derived from a mean hydrographic surface reduction in residual rms between the two by 30 60 and increased correlation indicates that the ggm01 geoid represents a dramatic improvement over older geoid models which were developed from multiple satellite tracking data altimetry and surface gravity measurements for the first time all major current systems are clearly observed in the dot from space based measurements

accelerated sea level rise from west antarctica recent aircraft and satellite laser altimeter surveys of the amundsen sea sector of west antarctica show that local glaciers are discharging about 250 cubic kilometers of ice per year to the ocean almost 60 more than is accumulated within their catchment basins this discharge is sufficient to raise sea level by more than 0 2 millimeters per year glacier thinning rates near the coast during 2002 2003 are much larger than those observed during the 1990s most of these glaciers flow into floating ice shelves over bedrock up to hundreds of meters deeper than previous estimates providing exit routes for ice from further inland if ice sheet collapse is under way

a joint analysis of gps displacement and grace geopotential data for simultaneous estimation of geocenter motion and gravitational field this work is funded by the university of newcastle to support nasa s grace and grace follow on projects as an international science team member to the missions and by australian research council dp170100224 as well as nasa support to j sauber as a science team member

time variations in ocean bottom pressure from a few hours to many years in situ data numerical models and grace satellite gravimetry in situ ocean bottom pressure obp obtained from 154 different locations irregularly scattered over the globe is carefully processed to isolate signals related to the ocean general circulation and large scale sea level changes comparison against a global numerical ocean model experiment indicates poor correspondence for periods below 24 hr possibly related to residual tidal signals and small timing errors in the atmospheric forcing applied to the ocean model correspondence increases rapidly for periods between 3 and 10 days where wind driven dynamics are already well understood and consequently well implemented into numerical models coherence decreases again for periods around 30 days and longer where processes not implemented into ocean general circulation models as barystatic sea level changes become more important correspondence between in situ data and satellite based obp as obtained from the gravity recovery and climate experiment grace german research centre for geosciences rl05a gravity fields critically depends on the postprocessing of level 2 stokes coefficients that also includes the selection of appropriate averaging regions for the grace based mass anomalies the assessment of other available grace level 2 products indicates even better fit of more recent solutions as itsg grace2016 and the center for space research and jet propulsion laboratory rl05 mascons in view of the strong high frequency component of obp however a higher temporal resolution of the oceanic grace products would be rather advantageous

space borne gravimetric satellite constellations and ocean tides aliasing effects summary ocean tides redistribute mass at high temporal frequencies satellite missions that aim to observe medium to low frequency mass variations need to take into account this rapidly varying mass signal correcting for the effects of ocean tides by means of imperfect models might hamper the observation of other temporal gravity field signals of interest this paper explores different methods for mitigating aliasing errors for the specific example of observing mass variations due to land hydrology including temporal filtering of time series of gravity solutions spatial smoothing and the use of satellite constellations for this purpose an earth system model esm was constructed which included state of the art time varying components for ocean atmosphere solid earth hydrology ice sheets and ocean tides using the esm we simulated the retrieval of the hydrologically driven gravity field changes using a number of different satellite constellations we find that 1 the ocean tide aliasing strongly depends on the satellite constellation the choice of orbital parameters and the length of the data span 2 the aliasing effect manifests itself differently for different geographical regions 3 the aliasing causes a peculiar striping pattern along the ground track of the satellite orbits 4 optimizing the choice of orbital parameters of a single grace type tandem can be more effective at reducing the aliasing of ocean tide model errors than flying more tandems finally we corroborate the experiences with grace data analysis that appropriate post processing techniques can significantly improve the quality of the retrieved gravity changes

bioindication of volcanic mercury hg deposition around mt etna sicily mt etna is a major natural source of hg to the mediterranean region total mercury concentrations hg tot in castanea sativa sweet chestnut leaves sampled 7 13 km from etna s vents during six campaigns in 2005 2011 were determined using atomic absorption spectroscopy hg tot in c sativa was greatest on etna s se flank reflecting hg deposition from the typically overhead volcanic plume hg tot also showed hg accumulation over the growing season increasing with leaf age and recent eruptive activity hg tot in c sativa was not controlled by hg tot in soils which instead was greatest on etna s nw flank and was correlated with the proportion of organic matter in the soil org an elevated hg tot org ratio in soils on etna s se flank is indicative of increased hg deposition this ratio was also found to decrease with local soil ph suggesting that hg deposited to the low ph and organic poor soils on etna s se flank may not be retained but will instead be released to groundwater or re emitted to the atmosphere these results show that the deposition of volcanic hg

deglacial history of the west antarctic ice sheet in the weddell sea embayment constraints on past ice volume change the retreat history of the west antarctic ice sheet wais since the last glacial maximum is important for understanding the process of rapid deglaciation constraining models that seek to predict the future trajectory of the ice sheet and for estimating rates of sea level change here we report new glacial geologic data from the southwestern weddell sea embayment that demonstrate that this part of the wais was thinner than previously suggested and that there was progressive thinning of the ice sheet by 230 480 m since ca 15 ka we use geomorphological data and a numerical ice sheet model to reconstruct the ice sheet in the weddell sea at the last glacial maximum the volume of this ice would have added between 1 4 and 2 0 m to postglacial sea level rise and would not have been sufficient to contribute significantly to meltwater pulse 1a a rapid rise in sea level 14 200 yr ago

antarctic regional ice loss rates from grace abstract using recent improved time variable gravity solutions from the gravity recovery and climate experiment grace we estimate rates of antarctic ice mass change for the period january 2003 through september 2006 combined improvements in data and filtering techniques allow observation of ice loss in the northern antarctic peninsula ap and along the coast of the west and central amundsen sea embayment ase in west antarctica there is also evidence of ice loss along the coast near the stancomb wills sta and jutulstraumen jut glaciers in queen maud land apparent rates are adjusted for influences of limited spatial resolution filtering and estimated postglacial rebound pgr to obtain ice loss rates for the northern ap coastal ase and sta jut of 28 8 7 9 81 17 and 16 7 9 7 km3 yr respectively this is the first estimate for the northern ap from satellite gravity data the ase estimate 81 17 km3 yr is consistent with a previous value 77 14 km3 yr using an earlier grace data release these results indicate significant improvement in grace data quality increased spatial resolution and applicability of grace data to a wider class of problems than previously possible

signal and error in mass change inferences from grace the case of antarctica summary this paper examines mass changes from gravity recovery and climate experiment grace monthly spherical harmonic gravity field solutions focusing on the application to the antarctic ice sheet regional integration approaches are investigated and compared with an alternative technique of fitting predefined mass change patterns the main thrust of this new analysis is to better define error sources and error bounds on mass changes of the antarctic ice sheet toward this purpose we examine the release 4 grace products by the geoforschungszentrum potsdam although errors related to the correction for glacial isostatic adjustment are significant both leakage and grace error effects are also important in particular the details of how mass change interior to the antarctic continent is weighted and scaled is crucially linked to the end result mass trend solution accounting for error correlations in the grace monthly solutions it is shown that the corresponding errors in antarctic mass changes are about two times larger than predicted by uncorrelated error propagation our ice mass trend estimate for the grounded ice sheet in the period from 08 2002 to 01 2008 is 109 48 gt yr 1 equivalent to a mean eustatic sea level rise of 0 30 0 13 mm yr 1 w e also provide estimates for 16 individual drainage basins mass losses concentrate in the coastal regions of west antarctica and on the antarctic peninsula with together 105 35 gt yr 1 t he amundsen sea sector alone contributes 60 8 gt yr 1 although these findings agree with independent observations grace trends deduced from a short time series come with the cautioning footnote that the strength of interannual variations remains undetermined we finally discuss directions of methodological improvements

ice sheet mass balance assessment attribution and prognosis contrary to prior expectations that warming would cause mass addition averaged over the greenland and antarctic ice sheets and over the next century the ice sheets appear to be losing mass at least partly in response to recent warming with warming projected for the future additional mass loss appears more likely than not

monthly gravity field models derived from grace level 1b data using a modified short arc approach in this study a new time series of gravity recovery and climate experiment grace monthly solutions complete to degree and order 60 spanning from january 2003 to august 2011 has been derived based on a modified short arc approach our models entitled tongji grace01 are available on the website of international centre for global earth models http icgem gfz potsdam de icgem the traditional short arc approach with no more than 1 h arcs requires the gradient corrections of satellite orbits in order to reduce the impact of orbit errors on the final solution here the modified short arc approach has been proposed which has three major differences compared to the traditional one 1 all the corrections of orbits and range rate measurements are solved together with the geopotential coefficients and the accelerometer biases using a weighted least squares adjustment 2 the boundary position parameters are not required and 3 the arc length can be extended to 2 h the comparisons of geoid degree powers and the mass change signals in the amazon basin the antarctic and antarctic peninsula demonstrate that our model is comparable with the other existing models i e the centre for space research rl05 jet propulsion laboratory rl05 and geoforschungszentrum rl05a models the correlation coefficients of the mass change time series between our model and the other models are better than 0 9 in the antarctic and antarctic peninsula the mass change rates in the antarctic and antarctic peninsula derived from our model are 92 7 38 0 gt yr and 23 9 12 4 gt yr respectively which are very close to those from other three models and with similar spatial patterns of signals

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

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

optimized smoothing of gravity recovery and climate experiment grace time variable gravity observations 1 high degree and high order spherical harmonics of time variable gravity fields observed by the gravity recovery and climate experiment grace gravity mission are dominated by noise we develop two smoothing methods that suppress these high degree and high order errors with results superior to more commonly used gaussian smoothing these optimized smoothing methods considerably improve signal to noise levels of grace terrestrial water storage estimates relative to residual signal and noise over the oceans and show significantly better spatial resolution and lower leakage error on the basis of analysis using an advanced land surface model the equivalent spatial resolution from these optimized smoothing estimates is about 500 km compared to the roughly 800 1000 km gaussian smoothing that is required to suppress high degree noise in the grace fields

southern hemisphere synoptic behavior in extreme phases of sam enso sea ice extent and southern australia rainfall abstract the association between southern hemisphere cyclones and anticyclones and the el nino southern oscillation enso southern annular mode sam antarctic sea ice extent sie and rainfall in perth and melbourne is explored those cities are respectively located in the southwestern and southeastern corners of australia where substantial decreasing rainfall trends have been observed over the last decades the need for a more unified understanding of large scale anomalies in storm indicators associated with the climate features itemized above has motivated this study the main aim is to identify cyclone anomalous areas that are potentially important in characterizing continental rainfall anomalies from a hemispheric perspective focusing on midlatitude australia the study covers the satellite era from 1979 to 2003 and was conducted for the southern winter when midlatitude rainfall is predominantly baroclinic the results indicate a well organized hemispheric cyclone pattern associated with en

mercury content of equisetum plants around mount st helens one year after the major eruption the mercury content of young equisetum plants collected around mount st helens was higher in the direction of yakima and toppenish washington northeast to east northeast than at any other compass heading and was about 20 times that measured around portland oregon the increase in substratum mercury was not as pronounced as that in plants but was also higher toward the northeast the direction taken by the may 1980 volcanic plume

application of avhrr imagery and grace measurements for calculation of actual evapotranspiration over the quaternary aquifer lake chad basin and validation of groundwater models the paper presents an application of noaa avhrr and grace data for studying the regional hydrogeology of the quaternary aquifer in the lake chad basin the actual evapotranspiration et over the phreatic aquifer is computed using the s sebi algorithm and then compared to the et estimates derived from the grace land water solutions both the grace solutions and the s sebi results are similar in description of the actual et over the lake chad basin avhrr data helped to overcome non uniqueness in the modelling of the piezometry anomalies particularly in regional groundwater models the harr piezometric dome appeared to be an area of relatively high effective recharge while the chari baguirmi and the kadzell piezometric depressions and bahr el gahzal were probably areas of excess et over recharge

mass balance of polar ice sheets recent advances in the determination of the mass balance of polar ice sheets show that the greenland ice sheet is losing mass by near coastal thinning and that the west antarctic ice sheet with thickening in the west and thinning in the north is probably thinning overall the mass imbalance of the east antarctic ice sheet is likely to be small but even its sign cannot yet be determined large sectors of ice in southeast greenland the amundsen sea embayment of west antarctica and the antarctic peninsula are changing quite rapidly as a result of processes not yet understood

the antarctic palaeo record and its role in improving predictions of future antarctic ice sheet change this paper reviews the ways in which the palaeo record of antarctic ice sheet change can be used to improve understanding of contemporary ice sheet behaviour and thus enhance predictions of future sea level change the main areas where the palaeo ice sheet record can contribute are understanding long term ice sheet trajectory providing data against which ice sheet models can be tested to identify and understand the range and types of natural ice sheet behaviour to balance the global water budget to correct contemporary glaciological measurements of mass change and to understand the relationship between polar ecosystems and the ice sheet i review each in turn and argue that research priorities include understanding past west antarctic ice sheet collapse and its timing a focus on the palaeo record of rapid retreat events and how these unfolded in the geological past improving the number and range of ice sheet reconstructions particularly through the holocene continuing to investigate the potential for using sediments and landforms to parameterise basal conditions in ice sheet models and understanding past east antarctic ice sheet dynamics particularly the evidence for partial deglaciation copyright 2009 john wiley sons ltd