iceberg calving flux and mass balance of the austfonna ice cap on nordaustlandet svalbard 1 satellite radar interferometry 60 mhz airborne ice penetrating radar data and visible band satellite imagery were used to calculate the velocity structure ice thickness and the changing ice marginal extent of austfonna 8000 km2 and 2500 km3 the largest ice cap in the eurasian arctic ice cap motion is generally less than about 10 m a 1 except where faster flowing curvilinear features with velocities of several tens to over 200 m a 1 are present most drainage basins of austfonna have undergone ice marginal retreat over the past few decades at an average of a few tens of meters per year integrating margin change around the whole ice cap gives a total area loss of about 10 km2 a 1 iceberg flux from the marine margins of austfonna is about 2 5 0 5 km3 a 1 water equivalent about 45 of the total calving flux from the whole svalbard archipelago when mass loss by iceberg production is taken into account the total mass balance of austfonna is negative by between about 2 5 and 4 5 km3 a 1 this iceberg flux represents about 33 5 of total annual mass loss from austfonna with the remainder lost through surface ablation iceberg flux should be included in calculations of the total mass balance of the many large arctic ice caps including those located in the russian and canadian arctic that end in tidewater the neglect of this term has led to underestimates of mass loss from these ice caps and thus to underestimates of the contribution of arctic ice caps to global sea level rise

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

surface deformation induced by present day ice melting in svalbard summary the vertical movement of the earth s surface is the result of a number of internal processes in the solid earth tidal forces and mass redistribution in the atmosphere oceans terrestrial hydrosphere and cryosphere close to ice sheets and glaciers the changes in the ice loads can induce large vertical motions at intraseasonal to secular timescales the global positioning system gps and very long baseline interferometry vlbi antennas in ny a u lesund svalbard that started observations in 1991 and 1995 respectively observe vertical uplift rates on the order of 8 2m m yr 1 which are considerably larger than those predicted by postglacial rebound pgr models order 2 mm yr 1 the observations also indicate increased uplift rates starting some time in 2000 a local gps campaign network that has been reoccupied annually since 1998 reveals a tilting away from the neighbouring glaciers the svalbard glaciers have been undergoing melting and retreat during the last century with increased melting since about 2000 we compared the observed vertical motion to the motion predicted by loading models using a detailed ice model with annual time resolution as forcing the model predictions correlate well with the observations both with respect to the interannual variations and the spatial pattern of long term trends the regression coefficients for predicted and observed interannual variations in height is 1 08 0 38 whereas the regression coefficient for the predicted and observed spatial pattern turns out to be 1 26 0 42 estimates of the predicted secular trend in height due to pgr and present day melting are on the order of 4 8 0 3 mm yr 1 and thus smaller than the observed secular trend in height this discrepancy between predictions and observations is likely caused by the sum of errors in the secular rates determined from observations due to technique dependent large scale offsets and incomplete or erroneous models unaccounted tectonic vertical motion errors in the ice load history scale errors in the viscoelastic pgr models and the elastic models for present day melting

the origin and mode of emplacement of lujavrites in the ilimaussaq alkaline complex south greenland abstract lujavrites are rare meso to melanocratic agpaitic nepheline syenites that are characterized by elevated contents of elements such as li be zr ree nb th and u they are the most evolved members of the three large composite agpaitic complexes lovozero kola peninsula russia pilansberg south africa and ilimaussaq south greenland and are inferred to stem from the same deep fractionating magma sources that fed the earlier members of the complexes the composition of the melts that evolved into lujavrites is however not well known the agpaitic part of the ilimaussaq complex is divided into a roof series a floor series of cumulates and an intermediate series of lujavrites sandwiched between the two in the traditional view the lujavrites formed from residual melts left between the downward crystallizing roof series and the floor cumulates new field observations and geochemical data suggest that the floor cumulates and the main mass of lujavrites constituted a separate intrusive phase which was emplaced into the already consolidated roof series rocks largely by piecemeal stoping studies of the contact facies of the floor cumulates indicate that the initial magma of the floor cumulate lujavrite sequence was peralkaline nepheline syenitic with enhanced contents of zr hf hree y nb ta f ba and sr subsequent crystallization in a closed system resulted in the formation of the floor cumulates and lujavrites chemical analyses of dykes within and outside the complex represent stages in the magmatic evolution of the agpaitic rocks

fluid production rate during the regional metamorphism of a pelitic schist phase equilibria modeling of the pressure temperature p t path of regional metamorphism and associated fluid expulsion combined with constraints on the timescale of garnet growth by sm nd geochronology elucidates the fluid production rate and fluid flux during barrovian metamorphism of pelitic rocks from townshend dam vt usa this modeling builds on a published companion study that utilized sm nd geochronology of concentric growth zones in multiple garnet grains to constrain the duration of garnet growth in a large sample of schist at townshend dam to 3 8 2 2 million years gatewood et al chem geol 401 151 168 2015 p t pseudosections combined with observed mineral compositions constrain garnet growth conditions and were utilized to construct p t path dependent thermodynamic forward models these models determine that garnet growth was initiated at 0 6 gpa and 525 c with a roughly linear loading and heating p t trajectory to 0 8 gpa and 610 c loading and heating rates of 2 4 km myear 1 with a range of 1 6 to 5 8 km million year 1 and 23 c million year 1 with a range of 14 to 54 c million year 1 respectively are consistent with model estimates and chronologic constraints for tectono metamorphic rates during orogenesis phase equilibria modeling also constrains the amount of water release during garnet growth to be 0 7 wt or 2 vol largely resulting from the complete consumption of chlorite coupling this estimate with calculated garnet growth durations provides a fluid production rate of 5 2 kg m 3 million year 1 with a range of 3 2 to 12 2 kg m 3 million year 1 and when integrated over the overlying crustal column a regional scale fluid flux of 0 07 0 37 kg m 2 million year 1 this range of values is consistent with those derived by numerical models and theory for regional scale pervasive fluid flow this study signifies the first derivation of a fluid production rate and fluid flux in regional metamorphism using a direct chronology of water producing garnet forming reactions and can provide a framework for future studies on elucidating the nature and timescales of fluid release

deglacial land emergence and lateral upper mantle heterogeneity in the svalbard archipelago i first results for simple load models summary the glacial isostatic adjustment following the removal of the pleistocene ice sheets furnishes basic information on the thickness of the earth s lithosphere and the viscosity of the subjacent mantle paper i is concerned with an elementary interpretation of the post glacial land emergence observed at a restricted set of six locations in the svalbard archipelago the interpretation is based on a three layer incompressible maxwell viscoelastic earth model which is forced by a time dependent load distribution simulating the deglaciation history of the svalbard archipelago and the barents sea in view of inconclusive geomorphological evidence suggesting either total or partial glaciation of the area at glacial maximum two simple load models barents t1 and barents p1 are considered in the first instance a comparison between the calculated and observed values of land emergence suggests increases in lithosphere thickness and asthenosphere viscosity with increasing distance of the location from the continental margin the trends are qualitatively insensitive to the load model load thickness or load cross section used for load model barents t1 with parabolic cross section an initial load thickness of 1 50 km and a relaxed fitting criterion the lateral variations are only weak if a more restrictive fitting criterion is employed the variations become more prominent and suggest increasing values of lithosphere thickness from below 80 km to above 140 km and of asthenosphere viscosity from below 3 1018 pa s to above 2 1019 pa s over a distance of about 300 km in paper ii kaufmann wolf 1995 a high resolution load model and an extended set of land emergence observations are used to study further the possibility of resolving lateral heterogeneity in the upper mantle below the svalbard archipelago

effects of diffusional modification of garnet growth zoning on p t path calculations the effect of intragranular diffusion on chemical zoning in garnet and on p t paths calculated from that zoning was evaluated using a numerical model of multicomponent diffusion in combination with simulations of garnet growth syn and post growth diffusion of mg fe mn ca species in garnet was calculated for a model pelitic assemblage over a range of temperatures from 485 to 635 c compositions from zoned garnet as modified by diffusion hypothetical inclusions of plagioclase within garnet and matrix phases were used to reconstruct pressure temperature p t paths from isobaric and polybaric model histories p t path calculations based on numerical simulations conducted over an input isobaric heating path that reached peak temperatures between 585 and 635 c show that relaxation of garnet compositional gradients by diffusion can induce modest to appreciable curvature in the inferred paths retrieved paths also indicated somewhat smaller overall temperature changes relative to the actual temperature difference of the input path the magnitude of these distortions is shown to depend upon the heating and cooling rate and garnet crystal size as well as the actual peak temperature condition the effect of diffusion on path trajectories in simulations with thermal histories that also included cooling were comparable to heating only models that reached peak temperatures approximately 15 30 c higher compositions of garnets with radii less than 1 mm that reached actual peak temperatures of 605 c along temperature time histories characteristic of regional metamorphism experienced sufficient diffusional relaxation to introduce errors of hundreds of bars to in excess of one kilobar in path trajectories path distortions were significant at heating cooling rates less than 10 c ma but rapidly diminished for rates faster than this in polybaric simulations diffusion effects were least noticeable when the actual pressure temperature conditions changed in a clockwise sense i e convex to higher p and higher t but apprecciable modification was seen in path models that underwent counterclockwise changes in p and t reequilibration of garnet rim compositions occurred during cooling on all paths and temperature maxima obtained from garnet biotite geothermometry underestimated actual peak conditions by 40 to 70 c calculations suggest that p t path trajectories calculated from garnets of at least 1 mm size and that experienced actual thermal maxima below 585 c are not likely to be distorted by diffusional effects during regional metamorphism however p t path reconstructions based on garnet zonation with smaller grains or higher temperatures may lead to misinterpretation of crystallization history the partitioning record of peak metamorphic temperatures may be destroyed by diffusional reequilibration of garnet rim compositions during cooling seriously complicating the task of quantitatively estimating diffusion effects on path calculations

vertical land motion from present day deglaciation in the wider arctic vertical land motion vlm from past and ongoing glacial changes can amplify or mitigate ongoing relative sea level change we present a high resolution vlm model for the wider arctic that include

atmospheric effects and spurious signals in gps analyses improvements in the analyses of global positioning system gps obser vations yield resolvable mm to sub mm di erences in coordinate estimates thus provid ing su cient resolution to distinguish subtle di erences in analysis methodologies here we investigate the e ects on site coordinates of using di erent approaches to modelling atmospheric loading deformation atml and handling of tropospheric delays the rig orous approach of using the time varying vmf1 mapping function yields solutions with lower noise at a range of frequencies compared with solutions generated using empiri cal mapping functions this is particularly evident when atml is accounted for some improvement also arises from using improved a priori zenith hydrostatic delays zhd with the combined e ect being site speci c importantly inadequacies in both mapping functions and a priori zhds not only introduce time correlated noise but signi cant pe riodic terms at solar annual and semi annual periods we nd no signi cant di erence between solutions where non tidal atml is applied at the observation level rather than as a daily averaged value but failing to model diurnal and semi diurnal tidal atml at the observation level can introduce anomalous propagated signals with periods that closely match the gps draconitic annual 351 4 d and semi annual period 175 7 d ex acerbated by not xing ambiguities these signals are evident in both stacked and sin gle site power spectra with each tide contributing roughly equally to the dominant semi annual peak the amplitude of the propagated signal reaches a maximum of 0 8 mm with a clear latitudinal dependence that is not correlated directly with locations of maximum tidal amplitude this is the first evidence of aliased signals being produced from tidal atml deformations

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

atmospheric pressure and gravity summary gravity green s functions for a column load of a model atmosphere on a spherical elastic earth are presented and they are used to evaluate the contribution of global atmospheric pressure variations to local gravity the green s functions are found to be relatively insensitive to the details of the model atmosphere but they are dependent on the temperature at the base of the column and on the relative height difference between the base of the column and the gravity station the total signal that global pressure systems contribute to gravity is about 30 gal of which about 90 per cent is produced by the atmosphere within 50 km of the gravity station a zone between 50 and 1000km from the gravity station contributes a couple of gal as does the remainder of the globe this pattern the coherence scale of pressure fluctuations the time and spatial scales appropriate to the hydrostatic approximation and the distance of the gravity station from the oceans suggest a division of the globe into local regional and global zones data requirements processing details and the reliability of the computed signal are different in each zone the local zone is within about 50 km of the gravity station within this zone pressure changes rapidly in time but is spatially coherent so that hourly observations of pressure and temperature at the gravity site alone are sufficient to compute an accurate correction except when a front is passing through the regional zone extends from the edge of the local zone to between several hundred and a thousand kilometres the signal from this zone is small and is only weakly coherent with the signal from the central zone so that a rather sparse array of hourly samples of pressure and temperature are required the gravity signal from the global zone can reach about a gal it varies on a time scale of days and is influenced by the response of the oceans to pressure variations previously reported observations that the admittance between local pressure and gravity residuals depends on epoch frequency or site are most probably due to incorrect modelling a proper local regional temperature and global correction can adequately account for the gravity signal from the atmosphere to within a few tens of ngal in the diurnal band and about 100 ngal in the days to seasonal band except during extreme weather conditions the application of the local correction lowers the power spectral density of the gravity residuals in every band from seasonal to hourly the regional global and temperature corrections lower the residual noise in the seasonal and synoptic bands but are not consistently effective at periods less than about half a day

separation of the geodetic consequences of past and present ice mass change influence of topography with application to svalbard norway polar regions such as greenland svalbard and antarctica are deforming today because of both the present day ice mass pdim change of glaciers and the glacial isostatic adjustment gia following the pleistocene deglaciation observations handled in these areas contain both the contributions from the pdim change and gia this study aims at separating them by considering two specific gravity variation to vertical displacement ratios we first review the case of the viscoelastic rebound gia subsequent to the pleistocene deglaciation leading to a ratio c v the outcome of previous studies is that c v is approximately equal to 0 15 gal mm and almost independent of the deglaciation history ice geometry and viscosity profile of the mantle similarly we consider the elastic deformation resulting from pdim change which leads to a second ratio c e n several studies have shown that c e n approx 0 26 mu gal mm if one assumes that the changing glaciers are thin layers over the surface of a spherical earth model in this case we show that the separation between the contributions from pdim change and gia is unique if both gravity and height changes observations are available at the same station next we focus on c e n and show that according to the deglaciation glaciation context and from colocated gravity variation and ground vertical velocity measurements one can deduce a range of possible values for c e n studying the influence of the topography on c e n we first show that it tends to positive values if most of surrounding ice mass changes above the altitude of the observation site and to values lower than 0 26 gal mm if changes are below we next apply our general formalism to the case of the past and pdim changes in svalbard norway we compute the ratio c e n at the geodetic observatory at ny alesund and show the influence of the topography of the surrounding glaciers on the measured gravity and uplift rates we show that if the ice mass change is spatially uniform c e n does not depend on the speed of ice mass change and hence the separation of the contributions from pdim changes and gia can still be done univocally however if the ice mass change is not spatially uniform c e n depends on both the speed of ice mass change and the volume of ice change rate

glacier volume changes using aster satellite stereo and icesat glas laser altimetry a test study on edgeoya eastern svalbard currently one of the major methodological gaps in the observation of glaciers from space is the measurement of volume changes of mountain glaciers and ice caps in this paper we present a case study of comparing a digital elevation model derived from advanced spaceborne thermal emission and reflection radiometer aster satellite optical stereo elevation data derived from ice cloud and land elevation satellite geoscience laser altimeter system glas laser altimetry and contour lines from a topographic map from the 1970s for two ice caps in eastern svalbard kvalpyntfonna and digerfonna we obtain an overall elevation change of 0 55 or 0 61 m year between 1970 and 2002 aster or glas 2006 respectively from comparison of different methods and from different quality checks we estimate the error of this numbers to be on the order of 5 this paper demonstrates that and on how long term glacier volume changes can be observed from space over a large number of ice caps and glaciers

a geophysical interpretation of the secular displacement and gravity rates observed at ny alesund svalbard in the arctic effects of post glacial rebound and present day ice melting summary we have analysed the ny alesund very long baseline interferometry vlbi data over the period 1994 august to 2004 may and we obtain secular displacement rates relative to a nnr nuvel 1a reference frame of 0 2 0 5 mm yr 1 1 7 0 5 mm yr 1 and 4 8 1 1 mm yr 1 for the north east and vertical directions respectively the corresponding global positioning system gps station displacement rates relative to the same reference frame for the north east and vertical directions are 0 2 0 6 mm yr 1 2 3 0 6 mm yr 1 and 6 4 1 5 mm yr 1 at nya1 and 0 1 0 5 mm yr 1 1 6 0 5 mm yr 1 and 6 9 0 9 mm yr 1 at nall where these gps rates were derived from the itrf2000 velocity solution of heflin from the comparison at 25 globally distributed collocated sites we found that the difference in uplift rate between vlbi and gps at ny alesund is mainly due to a gps reference frame scale rate error corresponding to 1 6 mm yr 1 in the gps vertical rates the uplift rate was estimated to be 5 2 0 3 mm yr 1 from the analysis of the tide gauge data at ny alesund hence the uplift rates obtained from three different kinds of data are very consistent each other the absolute gravity ag measurements at ny alesund which were carried out four times period 1998 2002 by three different fg5 absolute gravimeters lead to a decreasing secular rate of 2 5 0 9 gal yr 1 1 gal 10 8 ms 2 in this analysis the actual data obtained from a superconducting gravimeter at ny alesund were used in the corrections for the gravity tide including the ocean tide effect and for the air pressure effect we have

gravity and uplift rates observed in southeast alaska and their comparison with gia model predictions gravity change rates unit mgal yr 1 mgal 10 8 ms 2 over the 6 sites are estimated to be 4 50 0 76 and 4 30 0 92 by only using our data and also using the 1987 data respectively we computed the uplift and gravity rates predicted by ice load models for three different time intervals last glacial maximum lgm little ice age lia and present day pd except for 1 2 examples the predictions recover the observed rates within the observation errors we also estimated the viscous portion of the ratio unit mgal mm of the observed gravity rate to the uplift rate by correcting for the effects of the present day ice mass change pdimc two pdimc models are compared which are called here as uaf05 and uaf07 mean ratios are estimated to be 0 205 0 089 and 0 183 0 052 for the cases using uaf05 and uaf07 respectively the predicted mean ratios are 0 166 0 001 and 0 171 0 002 for the cases using both the lga and lia ice models and only using the lia ice model respectively we have confirmed that our ag and gps observations detect the rates and ratios reflecting an early stage of viscoelastic relaxation mainly due to the unloading effects after the lia

displacements of the earth s surface due to atmospheric loading effects on gravity and baseline measurements atmospheric mass loads and deforms the earth s crust by performing a convolution sum between daily global barometric pressure data and mass loading green s functions we estimate the time dependent effects of atmospheric loading including those associated with short term synoptic storms on surface point positioning measurements and surface gravity observations we calculate the response for both an oceanless earth and an earth with an inverted barometer ocean load responses for near coastal stations are significantly affected by the inclusion of an inverted barometer ocean peak to peak vertical displacements are frequently 15 20 mm with accompanying gravity perturbations of 3 6 gal baseline changes can be as large as 20 mm or more the perturbations are largest at higher latitudes and during winter months these amplitudes are consistent with the results of rabbel and zschau 1985 who modeled synoptic pressure disturbances as gaussian functions of radius around a central point deformation can be adequately computed using real pressure data from points within about 1000 km of the station knowledge of local pressure alone is not sufficient rabbel and zschau s hypothesized corrections for these displacements which use local pressure and the regionally averaged pressure prove accurate at points well inland but are in general inadequate within a few hundred kilometers of the coast

study of the atmospheric pressure loading signal in very long baseline interferometry observations 1 redistribution of air masses due to atmospheric circulation causes loading deformation of the earth s crust which can be as large as 20 mm for the vertical component and 3 mm for horizontal components rigorous computation of site displacements caused by pressure loading requires knowledge of the surface pressure field over the entire earth surface a procedure for computing three dimensional displacements of geodetic sites of interest using a 6 hourly pressure field from the national centers for environmental prediction numerical weather models and the ponte and ray 2002 model of atmospheric tides is presented we investigated possible error sources and found that the errors of our pressure loading time series are below the 15 level we validated our model by estimating the admittance factors of the pressure loading time series using a data set of 3 5 million very long baseline interferometry observations from 1980 to 2002 the admittance factors averaged over all sites are 0 95 0 02 for the vertical displacement and 1 00 0 07 for the horizontal displacements for the first time horizontal displacements caused by atmospheric pressure loading have been detected the closeness of these admittance factors to unity allows us to conclude that on average our model quantitatively agrees with the observations within the error budget of the model at the same time we found that the model is not accurate for several stations that are near a coast or in mountain regions we conclude that our model is suitable for routine data reduction of space geodesy observations

a reconciled estimate of glacier contributions to sea level rise 2003 to 2009 glaciers distinct from the greenland and antarctic ice sheets are losing large amounts of water to the world s oceans however estimates of their contribution to sea level rise disagree we provide a consensus estimate by standardizing existing and creating new mass budget estimates from satellite gravimetry and altimetry and from local glaciological records in many regions local measurements are more negative than satellite based estimates all regions lost mass during 2003 2009 with the largest losses from arctic canada alaska coastal greenland the southern andes and high mountain asia but there was little loss from glaciers in antarctica over this period the global mass budget was 259 28 gigatons per year equivalent to the combined loss from both ice sheets and accounting for 29 13 of the observed sea level rise

spectral finite element approach to viscoelastic relaxation in a spherical compressible earth application to gia modelling summary the choice of the physical model of postglacial rebound plays a decisive role to derive information about the mantle rheology and viscosity from observed data in models for the mantle rheology an incompressible maxwell material is often assumed in spite of seismic observations showing that the earth s mantle is composed of compressible material in this study in order to assess the influence of compressibility on glacial isostatic adjustment gia the spectral finite element approach proposed by martinec is extended to incorporate the effect of compressibility using this approach the present day velocity field is computed for peltier s ice5g vm2 earth model glaciation history combination considering the sea level equation in the formulation of hagedoorn et al the results show that the effect of compressibility on the vertical displacement rate is small whereas the horizontal rates are markedly enhanced for example the rate around fennoscandia and laurentide becomes twice as large when compressibility is considered this large difference between the compressible and incompressible models can be reduced by adjusting the elastic rigidity of the incompressible model so that the flexural rigidity becomes approximately the same as that in the compressible model however differences of 1 mm yr 1 still remain for wavelengths longer than 8000 km these findings show that when modelling horizontal motion induced by gia the influence of compressibility cannot be neglected

determining p t paths from garnet zoning using a brute force computational method reconstructing metamorphic pressure temperature p t paths through petrographic textures mineral assemblages and compositions is fundamental to the understanding of orogenesis we present a new method to derive the p t path of a rock from mineral zoning using perple x connolly in earth planet sci lett 236 1 2 524 541 2005 and a matlab script we forward model garnet zoning parageneses and mineral modes for an arbitrary set of possible p t paths and then compare the calculated results to mineral modes textures and zoning preserved in rocks the best fit p t path is determined by comparing the calculated zoning to the measured zoning using the sum of squares the results indicate that combining mg ca and mn zoning in garnet with mineral modes can yield precise constraints on the p t path of a rock

svalbard glacier elevation changes and contribution to sea level rise 1 we compare satellite altimetry from the ice cloud and land elevation satellite icesat 2003 2007 to older topographic maps and digital elevation models 1965 1990 to calculate long term elevation changes of glaciers on the svalbard archipelago results indicate significant thinning at most glacier fronts with either slight thinning or thickening in the accumulation areas except for glaciers that surged which show thickening in the ablation area and thinning in the accumulation areas the most negative geodetic balances occur in the south and on glaciers that have surged while the least negative balances occur in the northeast and on glaciers in the quiescent phase of a surge cycle geodetic balances are related to latitude and to the dynamical behavior of the glacier the average volume change rate over the past 40 years for svalbard excluding austfonna and kvitoya is estimated to be 9 71 0 55 km3 yr 1 or 0 36 0 02 m yr 1 w equivalent for an annual contribution to global sea level rise of 0 026 mm yr 1 sea level equivalent

geodetic secular velocity errors due to interannual surface loading deformation geodetic vertical velocities derived from data as short as 3 yr are often assumed to be representative of linear deformation over past decades to millennia we use two decades of surface loading deformation predictions due to variations of atmospheric oceanic and continental water mass to assess the effect on secular velocities estimated from short time series the interannual deformation is time correlated at most locations over the globe with the level of correlation depending mostly on the chosen continental water model using the most conservative loading model and 5 yr long time series we found median vertical velocity errors of 0 5 mm yr 1 over the continents 0 3 mm yr 1 globally exceeding 1 mm yr 1 in regions around the southern tropic horizontal velocity errors were seven times smaller unless an accurate loading model is available a decade of continuous data is required in these regions to mitigate the impact of the interannual loading deformation on secular velocities

some effects of lateral heterogeneities in the upper mantle on postglacial land uplift close to continental margins summary we investigate the effects of lateral heterogeneities in the upper mantle on the calculation of postglacial land uplift for the model calculations we use a commercial finiteelement code which enables us to solve the equations governing a layered isotropic incompressible maxwell viscoelastic half space with laterally varying layer thicknesses and physical properties following previous investigations performed by sabadini yuen portney 1986 and gasperini sabadini 1989 we extend their results using a more realistic loading history and different earth models we then focus our attention on the question whether lateral heterogeneities in the upper mantle can be modelled correctly using a set of homogeneous earth models to this end a comparison of model calculations using both laterally homogeneous and heterogeneous earth models is performed we find that lateral heterogeneities in the upper mantle significantly influence the calculated postglacial land uplift the resolving power of relative sea level observations for the prescribed lateral heterogeneities used in this study is mainly focused on observations around the load margin and outside the glaciated areas where differences in predicted land uplift between individual models are large enough to be resolved by observations we can qualitatively determine lateral heterogeneities in the upper mantle using a set of laterally homogeneous earth models if the geological structure for example a continental margin is known however in order to infer the correct values of lithospheric thickness and asthenospheric viscosity we need to use laterally heterogeneous models

the last glacial maximum of svalbard and the barents sea area ice sheet extent and configuration abstract the timing extent and configuration of the late weichselian barents ice sheet has been debated for several decades this debate has arisen largely because of the limited or conflicting field evidence on which most models have been based in particular reconstruction of the marine parts of the former barents ice sheet has been controversial this paper aims to review the geological observations and interpretations regarding the size and timing of the late weichselian ice sheet combined with numerical modelling of its formation in order to produce a reconstruction of ice sheet extent and behaviour sub glacial till with overlying glacimarine deposits dated to the late weichselian is found over most of the barents sea floor and the continental shelf west of svalbard glacially induced debris flow deposits on the large bjonoya and isfjorden trough mouth fans strongly support the idea of ice sheet extension to the shelf edge during maximum glaciation isobase maps show a centre of post glacial uplift in the north central barents sea and glaciological and isostatic modelling suggest that the ice sheet was 2000 3000 m thick in this area the ice sheet was confluent with ice over the kara sea but the interaction between the barents and kara ice sheets is not yet fully understood the deglaciation of the barents ice sheet started ca 15 ka probably by calving within the deeper troughs by 12 ka most of the central barents sea was ice free and ice remained over the svalbard franz josef land and novaja zemlya archipelagos and adjacent shallow shelf areas the coasts and fjords of these islands were ice free by 10 ka

decadal geodetic variations in ny alesund svalbard role of past and present ice mass changes the geodetic rates for the gravity variation and vertical uplift in polar regions subject to past and present day ice mass changes pdimcs provide important insight into the rheological structure of the earth we provide an update of the rates observed at ny alesund svalbard to do so we extract and remove the significant seasonal content from the observations the rate of gravity variations derived from absolute and relative gravity measurements is 1 39 0 11 gal yr 1 the rate of vertical displacements is estimated using gps and tide gauge measurements we obtain 7 94 0 21 and 8 29 1 60 mm yr 1 respectively we compare the extracted signal with that predicted by gldas noah and era interim hydrology models we find that the seasonal gravity variations are well represented by local hydrology changes contained in the era interim model the phase of seasonal vertical displacements are due to non local continental hydrology and non tidal ocean loading however a large part of the amplitude of the seasonal vertical displacements remains unexplained the geodetic rates are used to investigate the asthenosphere viscosity and lithosphere asthenosphere thicknesses we first correct the updated geodetic rates for those induced by pdimcs in svalbard using published results and the sea level change due to the melting of the major ice reservoirs we show that the latter are at the level of the geodetic rate uncertainties and are responsible for rates of gravity variations and vertical displacements of 0 29 0 03 gal yr 1 and 1 11 0 10 mm yr 1 respectively to account for the late pleistocene deglaciation we use the global ice evolution model ice 3g the little ice age lia deglaciation in svalbard is modelled using a disc load model with a simple linear temporal evolution the geodetic rates at ny alesund induced by the past deglaciations depend on the viscosity structure of the earth we find that viscous relaxation time due to the lia deglaciation in svalbard is more than 60 times shorter than that due to the pleistocene deglaciation we also find that the response to past and pdimcs of an earth model with asthenosphere viscosities ranging between 1 0 and 5 5 10 18 pa s and lithosphere resp asthenosphere thicknesses ranging between 50 and 100 km resp 120 and 170 km can explain the rates derived from geodetic observations

shallow upper mantle rheology and secular ice sheet fluctuations on time scales from decades to centuries continental cryospheric forcing in response to climate change constitutes a major source of isostatic disequilibrium that may influence future regional sea level variations current vertical displacements and gravity field variations are often estimated neglecting rheological effects and thus assuming a fully elastic response of the earth in this study we adopt a more general point of view aiming at describing ongoing surface movements resulting from recent glacial instabilities also taking into account the effects associated with shallow upper mantle and crustal rheologies our computations are based on the post widder laplace inversion formula which permits the straightforward computation of load deformation coefficients for steady state and transient rheologies up to very high harmonic degrees using a surface load with a simple geometry and time history we compare the classical elastic solutions to those obtained considering the rheological response of the shallow upper mantle while at the center of the ice sheet rheology only magnifies the elastic response the pattern and time history of vertical displacement at the ice sheet margins show a greater complexity mainly due to the development of lateral forebulges whose shape and amplitude are particularly sensitive to the rheology of the shallow upper mantle in this region assuming an elastic rheology is generally appropriate on a century time scale but significant deviations from a purely elastic response both sign and amplitude are observed at longer time scales or when a low viscosity zone with maxwell rheology is taken into account

postglacial sea level change on a rotating earth summary we present a complete derivation of the equation governing long term sea level variations on a spherically symmetric self gravitating maxwell viscoelastic planet this new sea level equation extends earlier work by incorporating in a gravitationally self consistent manner both a time dependent ocean continent geometry and the in uence of contemporaneous perturbations to the rotation vector of the planet we also outline an e cient pseudo spectral numerical methodology for the solution of this equation and present a variety of predictions based on a suite of earth models of relative sea level rsl variations due to glacial isostatic adjustment gia these results show that the contribution to the predicted rsl signal from gia induced perturbations to the rotation vector can reach 7 8 m over the postglacial period in geographic regions where the rotationally induced signal is a maximum this result is sensitive to variations in the adopted lower mantle viscosity and is relatively insensitive to variations in the adopted lithospheric thickness we also show that the rotationally induced component of rsl change is su cient to in uence previous estimates of late holocene melting events and ongoing sea level change due to giawhich were based on a rsl theory for a non rotating earth in particular estimates of antarctic melting over the last 5 kyr based on the amplitude of sea level highstands from the australian region may require an adjustment downwards of the order of 0 5 m of equivalent sea level rise furthermore present day rates of sea level change are perturbed by as much as 0 2 mm yr 1 by the rotational component of sea level change and this has implications for gia corrections of the global tide gauge record over the period from the last glacial maximum to the present we predict a distinctly non monotonic variation in the rotation induced component of rsl this is in agreement with our previous preliminary study milne mitrovica 1996 but contrasts signi cantly with predictions presented by han wahr 1989 and bills james 1996 we demonstrate that the disagreement arises as a consequence of approximations adopted in the latter studies we furthermore refute an assertion by bills james 1996 that previously published constraints on mantle viscosity and ice sheet histories which did not incorporate a rotation induced rsl component are largely invalidated by this omission

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

deglacial land emergence and lateral upper mantle heterogeneity in the svalbard archipelago ii extended results for high resolution load models summary in paper i breuer wolf 1995 a preliminary interpretation of the postglacial land emergence observed at a restricted set of six locations in the svalbard archipelago was given the study was based on a simple model of the barents sea ice sheet and suggested increases in lithosphere thickness and asthenosphere viscosity with increasing distance from the continental margin in the present paper the newly developed high resolution load model barents 2 and land uplift observations from an extended set of 25 locations are used to study further the possibility of resolving lateral heterogeneity in the upper mantle below the northern barents sea a comparison of the calculated and observed uplift values shows that the lithosphere thickness is not well resolved by the observations although values above 110 km are most common for this parameter in contrast to this there are indications of a lateral variation of asthenosphere viscosity whereas values in the range 10 8 1020 pa s are inferred for locations close to the continental margin 1020 102 pa s are suggested further away from the margin a study of the sensitivity of the values found for lithosphere thickness and asthenosphere viscosity to modifications of load model barents 2 shows that such modifications can be largely accommodated by appropriate changes in lithosphere thickness whereas the suggested lateral variation of asthenosphere viscosity is essentially unaffected an estimate of the influence of the fennoscandian ice sheet leads to the conclusion that its neglect results in an underestimation of the thickness of the barents sea ice sheet by about 10 per cent

past and present day ice mass variation on svalbard revealed by superconducting gravimeter and gps measurements 1 we use superconducting gravimeter sg and global positioning system gps measurements from ny alesund svalbard to infer changes in ice mass loss between september 1999 and september 2010 we find that during this period the gravity rate and vertical crustal velocities are changing with time adding to evidence about varying rates of ice mass loss the gravity rate varies through 10 years of observation 0 23 gal yr in 2000 2002 3 22 gal yr in 2002 2005 and 1 10 gal yr in 2005 2010 the gravity changes agree well with the observed uplift rates measured by gps which are 4 4 11 3 and 7 4 mm yr over the same periods in addition we generate model predictions which account for past and present day ice mass variation we find that the models under predict both the observed uplift rates and gravity changes

decoding the origins of vertical land motions observed today at coasts in recent decades geodetic techniques have allowed detecting vertical land motions and sea level changes of a few millimetres per year based on measurements taken at the coast tide gauges on board of satellite platforms satellite altimetry or both global navigation satellite system here contemporary vertical land motions are analysed from january 1993 to july 2013 at 849 globally distributed coastal sites the vertical displacement of the coastal platform due to surface mass changes is modelled using elastic and viscoelastic green s functions special attention is paid to the effects of glacial isostatic adjustment induced by past and present day ice melting various rheological and loading parameters are explored to provide a set of scenarios that could explain the coastal observations of vertical land motions globally in well instrumented regions predicted vertical land motions explain more than 80 per cent of the variance observed at scales larger than a few hundred kilometres residual vertical land motions show a strong local variability especially in the vicinity of plate boundaries due to the earthquake cycle significant residual signals are also observed at scales of a few hundred kilometres over nine well instrumented regions forming observation windows on unmodelled geophysical processes this study highlights the potential of our multitechnique database to detect geodynamical processes driven by anthropogenic influence surface mass changes surface loading and glacial isostatic adjustment and tectonic activity including the earthquake cycle sediment and volcanic loading as well as regional tectonic constraints future improvements should be aimed at densifying the instrumental network and at investigating more thoroughly the uncertainties associated with glacial isostatic adjustment models

agpaitic nepheline syenites a potential source of rare elements abstract the agpaitic nepheline syenites may with regard to their elevated contents of a number of rare elements be compared with the complex granite pegmatites both rock types form highly evolved magmas under closed system conditions which prevent volatiles from escaping agpaitic rocks are peralkaline nepheline syenites characterized by the presence of complex rare element minerals such as eudialyte and mosandrite instead of the simple minerals such as zircon and ilmenite uranium deposits have been found in agpaitic rocks in brazil pocos de caldas china saima and greenland ilimaussaq nb and apetite deposits in russia lovozero and khibina the type locality of agpaitic rocks the ilimaussaq complex in south greenland is characterized by elevated contents of elements such as zr ree y be li nb u th and f not only in pegmatites late veins and contact fenites but also in some of the rocks especially lujavrite and kakortokite the most important rare element containing minerals are eudialyte zr ree y nb steenstrupine u th ree rinkite nb ree y u pyrochlore and perovskite nb ta li mica li chkalovite be and villiaumite f occurrences of eudialyte rich kakortokite and lujavrite are presently being explored in the ilimaussaq complex as sources of zr ree y and nb

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

pressure temperature paths from p t pseudosections and zoned garnets potential limitations and examples from the zanskar himalaya nw india the extraction of p t histories from metamorphic rocks provides a valuable dataset for the elucidation of the tectonic mechanisms for orogeny while continued re equilibration frequently obliterates early information garnet zonation and inclusion assemblages can often surmount this problem the task is more difficult in high variance assemblages or if inclusions are not preserved but one approach is to use pseudosections that are specific to the bulk composition of a given rock in the latter case the compositions and abundances of all the minerals are fixed at a given p t point such that if the effective bulk composition is known the garnet composition alone can be used to reconstruct the history here we explore this approach using examples from the zanskar himalaya nw india pseudosections have been calculated for four pelitic to semipelitic rocks from the zanskar himalaya and have been contoured for garnet composition the calculations adequately model the mineral assemblages in the rocks and predict the presence of chlorite in the early assemblage where chlorite is found as inclusions within garnet moreover the pseudosections successfully model the garnet core compositions with all three independent compositional contours overlapping at a single pressure and temperature this occurs at 550 c and at pressures varying from 3 7 kbar for the four rocks studied we have been less successful however at modelling garnet compositions beyond the cores because fractionation of the effective bulk composition is caused by garnet growth itself however in this case a combination of the pseudosection and conventional thermobarometry using fe ti inclusions and matrix phases allows us to reconstruct the entire p t history the resulting p t paths record burial of 3 5 kbar without significant temperature increase followed by isobaric heating of 50 100 c this evolution is consistent with himalayan collision in the early tertiary but a combination of the p t data presented here and published geochronological data suggests renewed thrusting south of the suture zone in the oligocene in addition the data demonstrate that no extra heat source is required to cause melting of the himalayan crust in the miocene while melting could have occurred both by dehydration during decompression or in the presence of a fluid the lack of garnet resorption does suggest decompression was rapid and followed quickly by cooling this scenario favours melting by decompression

recent elevation changes of svalbard glaciers derived from icesat laser altimetry abstract we have tested three methods for estimating 2003 2008 elevation changes of svalbard glaciers from multi temporal icesat laser altimetry a linear interpolation of crossover points between ascending and descending tracks b projection of near repeat tracks onto common locations using digital elevation models dems and c least squares fitting of rigid planes to segments of repeat track data assuming a constant elevation change rate the two repeat track methods yield similar results and compare well to the more accurate but sparsely sampled crossover points most glacier regions in svalbard have experienced low elevation thinning combined with high elevation balance or thickening during 2003 2008 the geodetic mass balance excluding calving front retreat or advance of svalbard s 34 600 km2 glaciers is estimated to be 4 3 1 4 gt y 1 corresponding to an area averaged water equivalent w e balance of 0 12 0 04 m w e y 1 the largest ice losses have occurred in the west and south while northeastern spitsbergen and the austfonna ice cap have gained mass winter and summer elevation changes derived from the same methods indicate that the spatial gradient in mass balance is mainly due to a larger summer season thinning in the west and the south than in the northeast our findings are consistent with in situ mass balance measurements from the same period confirming that repeat track satellite altimetry can be a valuable tool for monitoring short term elevation changes of arctic glaciers

acceleration in thinning rate on western svalbard glaciers 1 geodetic measurements indicate that a number of glaciers in western svalbard ranging in size from 5 1000 km2 are losing mass at an accelerating rate the average thinning rate for midtre lovenbreen the glacier with the best data coverage has increased steadily since 1936 thinning rates for 2003 2005 are more than 4 times the average for the first measurement period 1936 1962 and are significantly greater than presented previously on slakbreen thinning rates for the latest measurement period 1990 2003 are more than 4 times that of the period 1961 1977 thinning of several glaciers along a previously measured airborne lidar profile in wedel jarls land has also increased doubling between the period 1990 1996 and 1996 2002 our results imply an increased sea level contribution from svalbard in addition the mass loss is an important influence on measured rates of rebound on western svalbard and should be factored into analysis of grace results

horizontal and vertical velocities derived from the ids contribution to itrf2014 and comparisons with geophysical models in the context of the 2014 realization of the international terrestrial reference frame the international doris doppler orbitography radiopositioning integrated by satellite service ids has delivered to the iers a set of 1140 weekly sinex files including station coordinates and earth orientation parameters covering the time period from 1993 0 to 2015 0 from this set of weekly sinex files the ids combination centre estimated a cumulative doris position and velocity solution to obtain mean horizontal and vertical motion of 160 stations at 71 doris sites the main objective of this study is to validate the velocities of the doris sites by comparison with external models or time series horizontal velocities are compared with two recent global plate models geodvel 2010 and nnr morvel56 prior to the comparisons doris horizontal velocities were corrected for global isostatic adjustment from the ice 6g vm5a model for more than half of the sites the doris horizontal velocities differ from the global plate models by less than 2 3 mm yr 1 for five of the sites arequipa dionysos gavdos manila and santiago with horizontal velocity differences with respect to these models larger than 10 mm yr 1 comparisons with gnss estimates show the veracity of the doris motions vertical motions from the doris cumulative solution are compared with the vertical velocities derived from the latest gps cumulative solution over the time span 1995 0 2014 0 from the university of la rochelle solution at 31 co located doris gps sites these two sets of vertical velocities show a correlation coefficient of 0 83 vertical differences are larger than 2 mm yr 1 at 23 percent of the sites at thule the disagreement is explained by fine tuned doris discontinuities in line with the mass variations of outlet glaciers furthermore the time evolution of the vertical time series from the doris station in thule show similar trends to the grace equivalent water height

recent contributions of glaciers and ice caps to sea level rise satellite measurements of earth s gravity field show that the mass loss of glaciers and ice caps contributed to sea level rise by approximately 0 4 millimetres per year between 2003 and 2010 the extent to which mass loss from ice covered land areas contributes to sea level rise is not known accurately in part because previous global estimates use different techniques for glaciers ice caps and ice sheets the gravity recovery and climate experiment grace satellite has provided monthly measurements of the global gravity field since 2002 using grace data jacob et al assess regional mass loss between 2003 and 2010 and conclude that mass loss from ice covered land areas contributed almost 1 5 mm per year to the sea level rise estimated mass loss from the high mountains of asia was negligible in contrast to some other reports glaciers and ice caps gics are important contributors to present day global mean sea level rise1 2 3 4 most previous global mass balance estimates for gics rely on extrapolation of sparse mass balance measurements1 2 4 representing only a small fraction of the gic area leaving their overall contribution to sea level rise unclear here we show that gics excluding the greenland and antarctic peripheral gics lost mass at a rate of 148 30 gt yr 1 from january 2003 to december 2010 contributing 0 41 0 08 mm yr 1 to sea level rise our results are based on a global simultaneous inversion of monthly grace derived satellite gravity fields from which we calculate the mass change over all ice covered regions greater in area than 100 km2 the gic rate for 2003 2010 is about 30 per cent smaller than the previous mass balance estimate that most closely matches our study period2 the high mountains of asia in particular show a mass loss of only 4 20 gt yr 1 for 2003 2010 compared with 47 55 gt yr 1 in previously published estimates2 5 for completeness we also estimate that the greenland and antarctic ice sheets including their peripheral gics contributed 1 06 0 19 mm yr 1 to sea level rise over the same time period the total contribution to sea level rise from all ice covered regions is thus 1 48 0 26 mm 1 which agrees well with independent estimates of sea level rise originating from land ice loss and other terrestrial sources6

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

greenland uplift and regional sea level changes from icesat observations and gia modelling we study the implications of a recently published mass balance of the greenland ice sheet gris derived from repeated surface elevation measurements from nasa s ice cloud and land elevation satellite icesat for the time period between 2003 and 2008 to characterize the effects of this new high resolution gris mass balance we study the time variations of various geophysical quantities in response to the current mass loss they include vertical uplift and subsidence geoid height variations global patterns of sea level change or fingerprints and regional sea level variations along the coasts of greenland long wavelength uplifts and gravity variations in response to current or past ice thickness variations are obtained solving the sea level equation which accounts for both the elastic and the viscoelastic components of deformation to capture the short wavelength components of vertical uplift in response to current ice mass loss which is not resolved by satellite gravity observations we have specifically developed a high resolution regional elastic rebound er model the elastic component of vertical uplift is combined with estimates of the viscoelastic displacement fields associated with the process of glacial isostatic adjustment gia according to a set of published ice chronologies and associated mantle rheological profiles we compare the sensitivity of global positioning system gps observations along the coasts of greenland to the ongoing er and gia in notable contrast with past reports we show that vertical velocities obtained by gps data from five stations with sufficiently long records and from one tide gauge at the gris margins can be reconciled with model predictions based on the ice 5g deglaciation model and the er associated with the new icesat derived mass balance

influences of reaction history and chemical diffusion on p t calculations for staurolite schists from the littleton formation northwestern new hampshire geothermometry from staurolite grade pelitic assemblages may fail to reflect peak temperatures of metamorphism because of 1 prograde gamet consuming reactions and 2 diffusional reequilibration during cooling in response to retrograde reactions gamet dissolution during staurolite formation leads to sharp compositional gradients within a few micrometers of garnet rims these gradients may then be modified by diffusion on cooling and lead to anomalous temperature estimates calculated from thermo barometers involving garnet numerical simulations of mineral growth and diffusion were used to examine these effects for a prograde metamorphic sequence from the salmon hole brook syncline northwestern new hampshire in higher grade assemblages mineral textures indicate that staurolite grew by the consumption of gamet and gamet biotite temperature estimates fall in the range 515 t 30 c interbedded layers containing garnet and biotite but not staurolite yield temperature estimates of 565 t 25 c in the eastern portion of the syncline rocks containing kyanite staurolite garnet biotite assemblages indicate temperatures of 550 t 25 c hypothetical growth and reaction histories that adhere to the modal mineralogical and known geochronological constraints were developed using a thermodynamically rigorous treatment of mineral modes and compositions incorporating calculations for multicomponent diffusion in garnet these models demonstrate that temperature estimates from staurolite schists may underestimate actual thermal maxima by more than 50 c gamet growth accompanying the reaction staurolite kyanite biotite garnet can lead to higher absolute temperature estimates but these may still be at least 50 c lower than actual peak temperatures simulations also demonstrate that fe enrichment in biotite accompanying retrograde production of chlorite may lead to calculated temperatures that are 10 50 c higher than would occur where only diffusional exchange operated on cooling evidence from additional metamorphic terranes suggests that this reaction model has wide applicability