characteristics of the antarctic surface mass balance 1958 2002 using a regional atmospheric climate model temporal and spatial characteristics of the antarctic specific surface mass balance ssmb are presented including its components solid precipitation sublimation deposition and melt for this purpose we use the output of a regional atmospheric climate model racmo2 ant horizontal resolution of 55 km for the period 1958 2002 racmo2 ant uses european centre for medium range weather forecasts ecmwf 40 year re analysis era 40 fields as forcing at the lateral boundaries racmo2 ant underestimates ssmb in the high interior of east and west antarctica and overestimates ssmb on the steep coastal slopes otherwise the modeled spatial pattern of ssmb is in good qualitative agreement with recent compilations of in situ observations large scale patterns like the precipitation shadow effect of the antarctic peninsula are well reproduced and mesoscale ssmb patterns such as the strong precipitation gradients on law dome are well represented in the model the integrated ssmb over the grounded ice sheet is 153mmw e a 1 for the period 1958 2002 which agrees within 5 with the latest measurement compilations sublimation and melt remove 7 and

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

reassessment of net surface mass balance in antarctica abstract recent in situ measurements of surface mass balance and improved calculation techniques are used to produce an updated assessment of net surface mass balance over antarctica a new elevation model of antarctica derived from ers 1 satellite altimetry supplemented with conventional data was used to delineate the ice flow drainage basins across antarctica the areas of these basins were calculated using the recent digital descriptions of coastlines and grounding lines the delineation of drainage basins was achieved using an automatic procedure which gave similar results to earlier hand drawn catchment basins more than 1800 published and unpublished in situ measurements of net surface mass balance from antarctica were collated and then interpolated a net surface mass balance map was derived from passive microwave satellite data being employed as a forcing field to control the interpolation of the sparse in situ observations basinwide integrals of net surface mass balance were calculated using t

restrictions on fluorine depth profiling for exposure age dating in archaeological bones archaeological fragments of bone and teeth that are exposed to a humid environment take up fluorine from the surrounding soil the fluorine ion replaces the hydroxyl group in the mineral phase of the bone forming chemically more stable fluorapatite in cortical parts of the long bone diaphysis a fluorine concentration profile can be observed which decreases from the outer surface and the marrow cavity towards the inner parts of the bone matrix geological time spans are needed for this process to reach equilibrium and for the distribution to become uniform as the shape of the profile which can be described by a diffusion model contains information on the exposure duration of the fossil object several attempts to use fluorine profiling as a dating method have been undertaken the distribution of fluorine in an archaeological sample however is strongly influenced by environmentally induced processes of bone diagenesis i e alteration in the structure and composition of the mineral phase and degradation of organic components that may make the time information indistinct the primary chemical composition of bones can thus be obscured by diagenesis within tens hundreds or thousands of years this depends more on the diagenetic environment than on the geological age to observe the impact of environmental influence on the profile shape samples from several burial sites featuring various soil conditions have been analyzed for their fluorine distribution and preservation state this paper provides an overview on the restrictions that have to be considered when attempts are undertaken to relate a fluorine diffusion pattern to the archaeological age of a bone specimen

positive mass balance of the ross ice streams west antarctica we have used ice flow velocity measurements from synthetic aperture radar to reassess the mass balance of the ross ice streams west antarctica we find strong evidence for ice sheet growth 26 8 gigatons per year in contrast to earlier estimates indicating a mass deficit 20 9 gigatons per year average thickening is equal to 25 of the accumulation rate with most of this growth occurring on ice stream c whillans ice stream which was thought to have a significantly negative mass balance is close to balance reflecting its continuing slowdown the overall positive mass balance may signal an end to the holocene retreat of these ice streams

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

effects of lateral variations in lithospheric thickness and mantle viscosity on glacially induced surface motion on a spherical self gravitating maxwell earth abstract the effects of lateral variations in lithospheric thickness and mantle viscosity on surface motions on a spherical self gravitating incompressible viscoelastic earth are investigated using the coupled laplace finite element method the ice 4g deglaciation model is used together with gravitationally self consistent sea levels in realistic oceans to describe the load lateral variations in mantle viscosities and lithospheric thickness are inferred from seismic tomography model s20a using well known scaling relationships the laterally homogeneous background viscosity has viscosity increases across 670 km and 1330 km depths and is a simplification of peltier s vm2 model the effect of interaction between ice complexes in north america greenland eurasia and antarctica are investigated and found to be significant for tangential motion the predicted motion in laurentide and antarctica are also compared with results obtained with flat earth models and found that there is general agreement between the two types of modeling although spherical earth models are more realistic because they take into account the interaction between ice complexes and there is no problem with edge effects the effects of lateral heterogeneity on uplift rate are found to be large enough to be resolved by current gps technology it confirms that the effect of the reverse viscosity contrast in the transition zone under the laurentian and fennoscandian craton may mask the effect of lateral heterogeneity in the neighboring layers on uplift rate for tangential motion lateral heterogeneity is found to be able to overprint the divergent motion from the centers of rebound predicted in laterally homogeneous models this finding is new for laurentide and is due to the contribution from the deep part of the lower mantle although the contribution from the upper mantle is also important on tangential motion its effects are compromised by the effects from the other layers

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

tide model errors and grace gravimetry towards a more realistic assessment summary the manner in which errors in tide models affect monthly gravity solutions from grace satellite data is re examined we perform a complete simulation of grace gravity estimation including allowance for accelerometer calibrations and satellite state vector adjustment errors in monthly geoid estimates are for most regions of a order of 0 5 mm or roughly 1 cm of equivalent water height when smoothed over radii of 600 km in polar regions where ocean tide models are suspect errors can grow significantly larger over 2 mm in geoid height although over very localized regions errors from diurnal tides tend to cancel but they are not completely eliminated inducing geoid errors of the order of 0 3 mm the currently accepted grace total error budget is roughly an order of magnitude larger than the component arising from tide modelling errors

physical removal of contaminative inorganic material from buried human bone abstract introduction of inorganic contaminants to bone during burial poses a serious problem for the interpretaion of the levels of these elements in terms of ancient diet we have found that the problem of non uniform contamination may be reduced or even eliminated for some elements by removal of 1 3 mm of the surface of the bone by physical abrasion whereas surface contamination on unabraded bone is readily visible in human femurs by scanning electron microscopy sem there is no evidence for contamination according to sem after abrasion this process of surface removal significantly reduces the levels of zn cd k al fe and mn but has no effect on na ca mg sr and ba for these woodland and mississippian samples from west central illinois the latter group of elements apparently survived burial without significant contamination the former group of elements was contaminated by the soil environment but at least for zn cd k and possibly fe surface removal has returned the elemental proportions in the remainder of the bone to close to biogenic levels analysis of variance between subgroups after cleaning shows differences in zn and cu between sexes in ca mg and sr over time and in na and ba based on age at death

a test of diet versus diagenesis at ventana cave arizona abstract eighty two faunal specimens from three stratigraphic levels at ventana cave arizona were analysed for multiple trace elements to investigate the effectiveness of sr and ba as dietary indicators and to assess the extent of diagenetic contamination focusing on predator prey relationships within levels comparisons with modern sonoran desert fauna and elemental correlations the results suggest that ba is a more sensitive paleodietary indicator than sr in a desert environment and that the extent of sr diagenesis is more pronounced than ba through time at the site variations in other elements such as al ca fe mg mn na and p are considered as well

time variability of the earth s gravity field hydrological and oceanic effects and their possible detection using grace the grace satellite mission scheduled for launch in 2001 is designed to map out the earth s gravity field to high accuracy every 2 4 weeks over a nominal lifetime of 5 years changes in the gravity field are caused by the redistribution of mass within the earth and on or above its surface grace will thus be able to constrain processes that involve mass redistribution in this paper we use output from hydrological oceanographic and atmospheric models to estimate the variability in the gravity field i e in the geoid due to those sources we develop a method for constructing surface mass estimates from the grace gravity coefficients we show the results of simulations where we use synthetic grace gravity data constructed by combining estimated geophysical signals and simulated grace measurement errors to attempt to recover hydrological and oceanographic signals we show that grace may be able to recover changes in continental water storage and in seafloor pressure at scales of a few hundred kilometers and larger and at timescales of a few weeks and longer with accuracies approaching 2 mm in water thickness over land and 0 1 mbar or better in seafloor pressure

the sedimentary legacy of a palaeo ice stream on the shelf of the southern bellingshausen sea clues to west antarctic glacial history during the late quaternary a major trough belgica trough eroded by a palaeo ice stream crosses the continental shelf of the southern bellingshausen sea west antarctica and is associated with a trough mouth fan belgica tmf on the adjacent continental slope previous marine geophysical and geological studies investigated the bathymetry and geomorphology of belgica trough and belgica tmf erosional and depositional processes associated with bedform formation and the temporal and spatial changes in clay mineral provenance of subglacial and glaciomarine sediments here we present multi proxy data from sediment cores recovered from the shelf and uppermost slope in the southern bellingshausen sea and reconstruct the ice sheet history since the last glacial maximum lgm in this poorly studied area of west antarctica we combined new data physical properties sedimentary structures geochemical and grain size data with published data shear strength clay mineral assemblages to refine a previous facies classification for the sediments the multi proxy approach allowed us to distinguish four main facies types and to assign them to the following depositional settings 1 subglacial 2 proximal grounding line 3 distal sub ice shelf sub sea ice and 4 seasonal open marine in the seasonal open marine fades we found evidence for episodic current induced winnowing of near seabed sediments on the middle to outer shelf and at the uppermost slope during the late holocene in addition we obtained data on excess pb 210 activity at three core sites and 44 ams c 14 dates from the acid insoluble fraction of organic matter aio and calcareous micro fossils respectively at 12 sites these chronological data enabled us to reconstruct for the first time the timing of the last advance and retreat of the west antarctic ice sheet wais and the antarctic peninsula ice sheet apis in the southern bellingshausen sea we used the down core variability in sediment provenance inferred from clay mineral changes to identify the most reliable aio c 14 ages for ice sheet retreat the palaeo ice stream advanced through belgica trough after similar to 36 0 corrected c 14 ka before present b p it retreated from the outer shelf at similar to 25 5 ka b p the middle shelf at similar to 19 8 ka b p the inner shelf in eltanin bay at similar to 12 3 ka b p and the inner shelf in ronne entrance at similar to 6 3 ka b p the retreat of the wais and apis occurred slowly and stepwise and may still be in progress this dynamical ice sheet behaviour has to be taken into account for the interpretation of recent and the prediction of future mass balance changes in the study area the glacial history of the southern bellingshausen sea is unique when compared to other regions in west antarctica but some open questions regarding its chronology need to be addressed by future work c 2010 elsevier ltd all rights reserved

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 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

elevation changes in antarctica mainly determined by accumulation variability antarctic ice sheet elevation changes which are used to estimate changes in the mass of the interior regions are caused by variations in the depth of the firn layer we quantified the effects of temperature and accumulation variability on firn layer thickness by simulating the 1980 2004 antarctic firn depth variability for most of antarctica the magnitudes of firn depth changes were comparable to those of observed ice sheet elevation changes the current satellite observational period 15 years is too short to neglect these fluctuations in firn depth when computing recent ice sheet mass changes the amount of surface lowering in the amundsen sea embayment revealed by satellite radar altimetry 1995 2003 was increased by including firn depth fluctuations while a large area of the east antarctic ice sheet slowly grew as a result of increased accumulation

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

predictions of antarctic crustal motions driven by present day ice sheet evolution and by isostatic memory of the last glacial maximum detectable crustal motion and secular rate of change of solid surface gravity may be produced by the earth s response to present day and past ice mass changes in antarctica scenarios of present day ice mass balance previously utilized to explore the global geodetic signatures of the antarctic ice sheet produce elastic crustal responses that are typically bounded by uplift rates 5 mm yr horizontal motion 1 mm yr and solid surface gravity change rates 1 gal yr in a restricted locality one scenario produces uplift rates slightly in excess of 10 mm yr and correspondingly enhanced horizontal and gravity rates in contrast the viscoelastic response to ice mass changes occurring since last glacial maximum lgm exceeds 5 mm yr uplift over substantial portions of west antarctica for a wide range of plausible choices of timing and magnitude of deglaciation and mantle viscosity similarly viscoelastic gravity rate predictions exceed 1 gal yr decrease over large regions confirming suggestions that a global positioning system gps and absolute gravity based program of crustal monitoring in antarctica could potentially detect postglacial rebound a published revision to the climap model of the antarctic ice sheet at lgm herein called the d91 model features a substantially altered west antarctic ice sheet reconstruction this revision predicts a spatial pattern of present day crustal motion and surface gravity change that diverges strikingly from climap based models peak d91 crustal rates assuming deglaciation begins at 12 kyr and ends at 5 kyr are around 16 mm yr uplift 2 mm yr horizontal and 2 5 gal yr gravity tabulated crustal response predictions for selected antarctic bedrock sites indicate critical localities in the interior of west antarctica where expected responses are large and d91 predictions differ from climap based models by a factor of 2 or more observations of the postglacial rebound signal in antarctica might help constrain antarctic mass balance and contribution to sea level rise over the past 20 000 years

gsfc00 mean sea surface gravity anomaly and vertical gravity gradient from satellite altimeter data a mean sea surface gsfc00 and its derivatives the altimetry gravity anomaly and vertical gravity gradient fields were computed using sea surface heights of topex ers and geosat satellite altimeter missions provided by the nasa ocean altimeter pathfinder project koblinsky et al 1998 a new estimation method distinct from the gsfc98 mean sea surface computation wang 2000a was explored and used to reduce ocean variability in the mean sea surface heights the gravity anomaly and vertical gravity gradient fields were then computed from the mean sea surface height implied geoid undulations validation of the gsfc00 mean sea surface and gravity anomaly was also performed

vertical deformation and absolute gravity summary crustal deformation in the greenland and antarctic areas is strongly influenced by both postglacial rebound and contemporary mass redistribution we explore the relationship between the displacement field and the gravitational disturbance for a viscoelastic maxwell earth with an arbitrary radial viscosity profile we seek to determine whether the effects of viscous relaxation in the memory of surface mass change can be separated from the effects of present day mass variation by combined measurements of vertical displacement and absolute gravity when the viscosity profile in the earth s interior is unknown our conclusion is positive specifically the non elastic effects can be reduced substantially by combined measurements of displacement and gravity change for a maxwell viscoelastic earth regardless of its radial viscosity profile the underlying physics has nothing to do with the mathematical structure of viscous relaxation modes rather it is due to the fact that the non elastic response of a maxwell earth is nearly incompressible

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

diagenesis in prehistoric bone problems and solutions abstract post depositional chemical alteration or diagenesis in prehistoric human bone is the major problem in the use of trace element analyses for dietary reconstruction following a review of recent studies of diagenesis we discuss means for evaluating post depositional chemical change in bone and for removing such contaminants three different procedures are described which reflect current efforts to evaluate and reduce the effects of diagenesis these include 1 mechanical cleaning 2 chemical cleaning through acid washing and 3 washing with a reducing agent these procedures usually remove major contaminants leaving significant potential of trace element analyses for the investigation of past diet

high resolution interannual mass anomalies of the antarctic ice sheet by combining grace gravimetry and envisat altimetry knowledge of interannual mass variations of the antarctic ice sheet ais associated with its surface mass change is important for correctly interpreting the long term mass trend and evaluating the fidelity of surface mass balance from regional climate models here we revisit the interannual anomalies of mass change from gravity recovery and climate experiment and elevation change from envisat over the ais during 2003 2009 with the objective of obtaining higher resolution interannual mass anomalies based on envisat data high positive correlations 0 6 between the two interannual anomalies are primarily found over the west ais and coastal regions in the east ais occupying more than 40 of the ais by combining the two interannual anomalies we are able to estimate the density of snow ice changing interannually over regions in the ais especially over the amundsen sea sector with significant interannual signals the temporal variability of the density of snow ice associated with interannual anomalies is shown for the first time which agrees with the events of excess snow accumulation and the accelerated ice discharge occurring there furthermore we demonstrate the feasibility of obtaining higher resolution interannual mass anomalies over the west ais based on the density corrected envisat data negative correlations which were also found in a previous study are likely related to errors in the relatively weak interannual signals

variations in the earth s oblateness during the past 28 years 1 analysis of satellite laser ranging slr data indicates that the earth s dynamic oblateness j2 has undergone significant variations during the past 28 years the dominant signatures in the observed variations in j2 are 1 a secular decrease with a rate of approximately 2 75 10 11 yr 1 2 seasonal annual variations with a mean amplitude of 2 9 10 10 3 significant interannual variations with timescales of 4 6 years and 4 a variation with period of 21 years and an amplitude of 1 4 10 10 with minimum in december 1988 two large interannual variations are related to the strong el nino southern oscillation events during the periods of 1986 1991 and 1996 2002 and it appears that another interannual cycle may have started in late 2002 the superposition of the decadal variation on the interannual signal makes the j2 fluctuation appear to be anomalously large during the 1996 2002 period contemporary models of the mass redistributions in the atmosphere ocean and surface water can explain a major part of the 4 to 6 year fluctuations however the cause of the decadal variation remains unknown

reconstructing the antarctic ice sheet at the last glacial maximum abstract a reconstruction of the antarctic ice sheet at the last glacial maximum lgm constrained by geologic data shows expansion across continental shelves accompanied by little inland change this added peripheral ice volume contributed 14 m to the lowering of eustatic sea level at the lgm of the total expansion one third took place in east antarctica and two thirds in west antarctica

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

volume of antarctic ice at the last glacial maximum and its impact on global sea level change abstract the volume of antarctic ice at the last glacial maximum is a key factor for calculating the past contribution of melting ice sheets to late pleistocene global sea level change at present there are large uncertainties in our knowledge of the extent and thickness of the formerly expanded antarctic ice sheets and in the timing of their release as meltwater into the world s oceans this paper reviews the four main approaches to determining former antarctic ice volume namely glacial geology glacio isostatic studies glaciological modelling and ice core analysis and attempts to reconcile these to give a best estimate for ice volume in the ross sea there was a major expansion of grounded ice at the last glacial maximum accounting for 2 3 3 2 m of global sea level at some time in the weddell sea a large grounded ice sheet corresponding to c 2 7 m of global sea level extended to the shelf break however this ice expansion has not yet been confidently dated and may not relate to the last glacial maximum around east antarctica there was thickening and advance offshore of ice in coastal regions ice core evidence suggests that the interior of east antarctica was either close to its present elevation or thinner during the last glacial so the effect of east antarctica on sea level depends on the net balance between marginal thickening and interior thinning suggested east antarctic contributions vary from a 3 5 5 m lowering to a 0 64 m rise in global sea level the antarctic peninsula ice sheet thickened and extended offshore at the last glacial maximum with a sea level equivalent contribution of c 1 7 m thus the antarctic ice sheets accounted for between 6 1 and 13 1 m of global sea level fall at the last glacial maximum this is substantially less than has been suggested by most previous studies but the maximum figure matches well with one modelling estimate the timing of antarctic deglaciation is not well known in the ross sea terrestrial evidence suggests deglaciation may have begun at c 13 000 yr bp 1 but that grounded ice persisted until c 6 500 yr bp marine evidence suggests the western ross sea was deglaciated by c 11 500 yr bp deglaciation of the weddell sea is poorly constrained grounded ice in the northern antarctic peninsula had retreated by c 13 000 yr bp and further south deglaciation occurred sometime prior to c 6 000 yr bp many parts of coastal east antarctica apparently escaped glaciation at the lgm but in those areas that were ice covered deglaciation was underway by 10 000 yr bp with existing data the timing of deglaciation shows no firm relation to northern hemisphere driven sea level rise this is probably due partly to lack of antarctic dating evidence but also to the combined influence of several forcing mechanisms acting during deglaciation

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

estimating geocenter variations from a combination of grace and ocean model output 1 in this study we estimate a time series of geocenter anomalies from a combination of data from the gravityrecoveryandclimateexperiment grace satellitemissionandthe outputfromoceanmodels amatrixequationisderivedrelating totalgeocentervariations to the grace coefficients of degrees two and higher and to the oceanic component of the degree one coefficients we estimate the oceanic component from two state of the art ocean models results are compared to independent estimates of geocenter derived from other satellite data such as satellite laser ranging and gps finally we compute degree one coefficients that are consistent with the processing applied to the grace level 2 gravity field coefficients the estimated degree one coefficients can be used to improve estimates of mass variability from grace which alone cannot provide them directly

predictions of vertical uplift caused by changing polar ice volumes on a viscoelastic earth measurements of crustal uplift from bedrock around the edges of antarctica or greenland could help constrain the mass balance of those ice caps present day changes in ice could cause vertical displacement rates of several mm yr around antarctica and up to 10 15 mm yr around greenland horizontal displacement rates are likely to be about 1 3 the vertical rates the viscoelastic response of the earth to past changes in ice could cause uplift rates that are several times larger by measuring both gravity and vertical displacements it is possible to remove the viscoelastic effects so that the observations can be used to constrain present day thickness changes

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

on postglacial sea level summary an exact method is presented for calculating the changes in sea level that occur when ice and water masses are rearranged on the surface of elastic and viscoelastic non rotating earth models the method is used to calculate the instantaneous elastic and delayed vi scoelastic sea level changes following the partial melting of late quaternary ice sheets we find that there can be large errors in the usual assumption that changes in sea level are uniform over the ocean basins if a quantity of ice equivalent to a uniform 100 m rise in sea level melts from the laurentide and fennoscandian ice sheets then in the south pacific the instantaneous rise in sea level can be as large as 120m in the north atlantic the instantaneous rise is always less than 100 m there is a zone in the north atlantic with almost no sea level change and near greenland and norway the sea level falls rather than rises by over 100 m one thousand years after the melting a forebulge migrating towards the ice loads causes water to flow from the south pacific into the north pacific suggesting that raised beaches should occur in the south pacific the gravitational attraction of an ice mass upon a nearby ocean tends to hold sea level high in the vicinity of the ice this extra load near the ice may have a significant influence on postglacial isostatic adjustment

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

a comparison of different ways of dealing with isostasy examples from modelling the antarctic ice sheet during the last glacial cycle the bedrock isostatic response exerts a strong control on ice sheet dynamics and is therefore always taken into account in ice sheet models this paperreviews the various methods normally used in the ice sheet modeling community to deal with the bedrock response and compares these with a moresophisticated full earth model each of these bedrock treatments five in total are coupled with a three dimensional thermomechanical ice sheet model underthe same forcing conditions to simulate the antarctic ice sheet during the last glacial cycle the outputs of the simulations are compared on the basis of thetime dependent behavior for the total ice volume and the mean bedrock elevation during the cycle and of the present rate of uplift over antarctica thiscomparison confirms the necessity of accounting for the elastic bending of the lithosphere in order to yield realistic bedrock patterns it furthermoredemonstrates the deficiencies inherent to the diffusion equation in modeling the complex deformation within the mantle nevertheless when characteristicparameters are varied within their range of uncertainty differences within one single method are often of the same order as those between the variousmethods this overview finally tries to point out the main advantages and drawbacks of each of these methods and to determine which one is mostappropriate depending on the specific modeling requirements

an ostracod inferred large middle pleistocene freshwater lake in the presently hyper arid qaidam basin nw china abstract exposed sediments of 50 m thickness were investigated in the 120 000 km2 qaidam basin at the northern margin of the tibetan plateau fine grained silty sediments constitute most of the section and were accumulated in a lake intercalated beds of aeolian sand and of fluvial or littoral origin show that the lake experienced periods of desiccation and shallow water levels at the section site the lake sediments provided surprisingly species rich ostracod assemblages with almost all species indicating freshwater to oligohaline conditions the species richness the position of the section in the southern neighbourhood of a topographic rise in the qaidam basin and intercalated layers of fluvial and aeolian sands suggest that a relatively marginal littoral lake setting existed throughout most of the sequence a maximum water depth of several tens of metres may be assumed at least for some parts of the section and a large lake covering about half the size of the qaidam basin may be inferred from our data this inference is in clear contrast to the present day wind shaped topography with salt playas and shallow saline lakes in the lowermost depressions of the qaidam basin dating by optically stimulated luminescence and uranium series measurements did not allow the establishment of a firm chronology for the investigated section however based on infrared stimulated luminescence dates of around 120 140 ka obtained on feldspars and regarded as minimum ages and 230th u ages scattering between 100 and 400 ka a middle pleistocene age between 120 and 400 ka is assumed for the lake formation

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

geomorphological evidence and cosmogenic 10be 26al exposure ages for the last glacial maximum and deglaciation of the antarctic peninsula ice sheet this paper presents the first systematic attempt to map the last glacial maximum lgm configuration of the southern and central parts of the antarctic peninsula ice sheet and to determine the timing of onshore ice sheet retreat geomorphologic evidence shows that the lgm ice sheet expanded to form two ice domes in palmer land and merged with an expanded and thicker west antarctic ice sheet in the weddell sea ice from the antarctic peninsula merged with alexander island ice in george vi sound cosmogenic 10 be and 26 al data from 29 erratics on nunataks yield model ages between 7 2 ka and older than 1 ma the data set contains a high proportion of erratics with evidence of nuclide inheritance once these ages have been excluded the cosmogenic ages suggest that thinning of the west side of the antarctic peninsula ice sheet to near present configuration was almost complete by the early holocene these data combined with previously published 14 c data exclude the possibility that the west side of the antarctic peninsula ice sheet has been thinning throughout the holocene as has been demonstrated for some other sectors of the west antarctic ice sheet on the east side of the antarctic peninsula ice sheet thinning was under way prior to the early holocene but our data do not constrain the ice sheet behavior more recently than 7 2 ka

impact of the choice of bone samples on trace element data in excavated human skeletons abstract the choice of bone samples for trace element analysis of excavated human skeletons is of great influence on trace element data and their interpretation with regard to the reconstruction of ancient diets and palaeoenvironment trace element content in bone specimens from different anatomical sites shows considerable variations even in a single individual primarily due to different metabolic turnover rates in compact and trabecular bone it can be shown that the trace element content in a compact bone sample is well correlated with the total skeletal content of the respective element the use of compact bone from corresponding anatomical sites for trace element analyses is therefore recommended since otherwise any comparison of trace element data of different individuals may produce misleading results