secular changes in the solar semidiurnal tide of the western north atlantic ocean 1 an analysis of twentieth century tide gauge records reveals that the solar semidiurnal tide s2 has been decreasing in amplitude along the eastern coast of north america and at the mid ocean site bermuda in relative terms the observed rates are unusually large of order 10 per century periods of greatest change however are inconsistent among the stations and roughly half the stations show increasing amplitude since the late 1990s excepting the gulf of maine lunar tides are either static or slightly increasing in amplitude a few stations show decreases large changes in solar but not lunar tides suggest causes related to variable radiational forcing but the hypothesis is at present unproven

sedimentological characteristics of small rivers with loessic headwaters in the chaco south america some sedimentological characteristics of uvial environments located in the northeastern region of the chaco pampa plain were analysed in order to determine the possible in uence of the loessic headwaters of local basins concentrations of suspended sediments as well as grain size of the river beds were compared unexpectedly it was found that the suspended load has an inverse relationship with the hydrometric levels with the exception of highly saline streams conductivity values between 4300 and 11 000 l sc m 1 the mean concentration of suspended sediments was 63 1 and 206 3 mg l 1 in ood and low water periods respectively the grain size of bed sediments was relatively homogeneous along the whole hydrological cycle sandy silty bottoms predominate in channels followed by silty sandy and clayey silty bottom types sediment transport mainly occurs in accelerating ow suspension overcoming the critical erosion velocity during ood periods some parameters exceeded by 70 the values recorded during the low water phase 2000 elsevier science ltd and inqua all rights reserved

accelerated ice mass depletion revealed by low degree gravity field from satellite laser ranging greenland 1991 2011 1 we detect the acceleration of ice mass depletion in greenland for the period 1991 2011 from the low degree gravity field up to degree and order 4 derived from the satellite laser ranging slr data between 2003 and 2011 during the era when the grace gravity recovery and climate experiment satellite data are available our slr results of gravity changes agree well with grace showing significant negative patterns in greenland prior to that the slr linear trend maps show a near balance in greenland ice mass during 1991 2002 after the glacial isostatic adjustment is accounted for using model values we further confirm the consistency of our slr results with the vertical crustal uplift of the region observed by the global positining system gps which manifests ice mass loading unloading thus the slr data series constitute a continuous benchmark for the time history of the greenland ice mass changes for over two decades

a method for estimating ice mass loss from relative insar observations application to the vatnajokull ice cap iceland 1 we present a new method for estimating ice mass loss from glaciers and ice sheets using interferometric synthetic aperture radar insar time series data we use a linear inversion method based on observations of nearby bedrock uplift and a solution for surface loading of an elastic half space the method assumes that mass loss is focused on lower elevation terminal regions of the glacier or ice sheet and that there is an exponential decrease in thinning rate toward the higher elevation interior we apply the method to uplift rates between 1995 and 2009 near vatnajokull iceland the data reveal up to 13 mm yr relative line of sight los velocity around the south western edge of vatnajokull we find an ice mass loss rate of 6 8 0 7 0 8 gt yr in approximate agreement with other estimates ice loss since 1995 is twice as fast as the loss rate estimated for the rest of the 20th century

crustal deformation associated with glacial fluctuations in the eastern chugach mountains alaska the changes of the solid earth in south central alaska in response to two major glacial fluctuations on different temporal and spatial scales have been estimated and we evaluated their influence on the stress state and ongoing tectonic deformation of the region during the recent 1993 1995 bering glacier surge a large transfer of ice from the bagley ice field to the bering glacier terminus region occurred we estimated the elastic displacement of the solid earth due to ice mass redistribution from global positioning system gps measurements at sites near the surging glacier we can account for these displacements by transfer of an ice volume of about 14 km3 from the surge reservoir area to the terminus region we examined the background seismicity ml 2 5 before during and after the surge we found that the occurrence of small earthquakes ml 4 0 in the surge reservoir region increased during the surge time interval possibly in response to a decrease in ice mass this suggests that a small decrease in the vertical stress 3 could be enough to modulate the occurrence of small shallow earthquakes in this dominantly thrust fault setting during this century the southern alaska coastal glaciers have been undergoing an overall decrease in volume based on our compilation of changes in the extent and thickness of the coastal glaciers between the malaspina and bering we calculated surface displacements due to the earth s viscoelastic response to annual thinning and to the cumulative retreat over the last 100 years the uplift of the region due to an average annual thinning rate of 1 6 m yr in the ablation region is 1 12 mm yr for our reference model with a viscosity of 5 1019 pa s for depths between 40 and 200 km the total viscoelastic response due to the retreat over the last century may be as much as a couple of meters within the coastal ablation zone near icy bay the maximum decrease in v between 0 and 10 km was 1 0 mpa which is significant in relation to the stress drops in recent earthquakes 2 to 10 mpa but small in relation to the estimated tectonic stress magnitude therefore the occurrence of an earthquake such as the st elias 1979 ms 7 2 may have been advanced in time however most of the ongoing stress accumulation would be primarily due to tectonic forces

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

sea level rise and tidal power plants in the gulf of maine 1 the response of the bay of fundy and gulf of maine to large scale tidal power plants and future sea level rise is investigated using an established numerical tidal model free stream tidal turbines were simulated within the bay of fundy by implementing an additional bed friction term kt the present day maximum tidal power output was determined to be 7 1 gw and required kt 0 03 extraction at this level would lead to large changes in the tidal amplitudes across the gulf of maine with future slr implemented the energy available for extraction increases with 0 5 1 gw per m slr slr simulations without tidal power extraction revealed that the response of the semidiurnal tides to slr is highly dependent on how changes in sea level are implemented in the model when extensive flood defenses are assumed at the present day coast line the response to slr is far larger than when land is allowed to permanently flood for example within the bay of fundy itself the m2 amplitude increases with nearly 0 12 m per m slr without flooding but it changes with only 0 03 m per m slr with flooding we suggest that this is due to the flooding of land cells changing the resonant properties of the basin

annual variation of coastal uplift in greenland as an indicator of variable and accelerating ice mass loss 1 seasonal melting of the coastal part of the greenland ice sheet is investigated using gps vertical displacement data from coastal stations combined with data on atmospheric and ocean temperatures using a high pass filter and cubic spline models we estimate five variables describing seasonal uplift a proxy for proximal mass loss including duration of the melt season and the amount of summer uplift our analysis shows both temporal and spatial variations of uplift southern coastal greenland experienced anomalously large uplift in summer 2010 implying significant melting that year however the northwest coast did not experience significant change in uplift at that time our data suggest that a combination of warm summer air temperature and warm sub surface ocean water temperature drove the large mass losses in 2010 using the uplift pattern of 2008 2010 and comparing to atmospheric data and ocean water temperature data we show that warm irminger water iw exerted significant influence on coastal melting in southeastern southern and southwestern greenland reaching about 69 n in 2010 north of this iw did not exert significant influence in effect defining the northward limit of the sub polar gyre for that year thus short term variability in the coastal gps uplift signal can be used to infer an oceanographic parameter that has a critical influence on greenland ice sheet health

greenland glacial history and local geodynamic consequences summary space time reconstructions of the continental ice sheets that existed at last glacial maximum lgm have previously been produced using two entirely independent methodologies one based upon the use of theoretical models of ice sheet accumulation and flow and one based upon the geophysical inversion of relative sea level rsl histories from previously ice covered regions the analyses described in this paper demonstrate the significant advantages that derive from the simultaneous application of both methods to the particular case of greenland we thereby show that the ice 4g reconstruction of the glaciation history of this region from lgm to present which was based upon the geophysical inversion of rsl data alone was reasonably accurate in the peripheral regions where rsl data were available but inaccurate in the interior of the ice sheet which was unconstrained by such information we test the new model of greenland glacial history determined by the simultaneous application of the constraints that derive from ice sheet modelling and the geophysical inversion of rsl data by employing recently published geodetic inferences of mass balance over the entire interior region of the ice sheet and of gps measurements of vertical crustal motion these observations which were not employed to constrain the ice sheet reconstruction provide significant support for the new glacial history for greenland that our analyses have led us to infer

observation of glacial isostatic adjustment in stable north america with gps 1 motions of three hundred and sixty global positioning system gps sites in canada and the united states yield a detailed image of the vertical and horizontal velocity fields within the nominally stable interior of the north american plate by far the strongest signal is the effect of glacial isostatic adjustment gia due to ice mass unloading during deglaciation vertical velocities show present day uplift 10 mm yr near hudson bay the site of thickest ice at the last glacial maximum the uplift rates generally decrease with distance from hudson bay and change to subsidence 1 2 mm yr south of the great lakes the hinge line separating uplift from subsidence is consistent with data from water level gauges along the great lakes showing uplift along the northern shores and subsidence along the southern ones horizontal motions show outward motion from hudson bay with complex local variations especially in the far field although the vertical motions are generally consistent with the predictions of gia models the horizontal data illustrate the need and opportunity to improve the models via more accurate descriptions of the ice load and laterally variable mantle viscosity

the use of gps horizontals for loading studies with applications to northern california and southeast greenland received 23 august 2012 revised 15 january 2013 accepted 20 january 2013 published 25 april 2013 1 we describe how gps measurements of horizontal crustal motion can be used to augment vertical crustal motion measurements to improve and extend gps studies of surface loading we show that the ratio of the vertical displacement to the horizontal displacement combined with the direction of the horizontal motion can help determine whether nearby loading is concentrated in a small region for example in a single lake or glacier and where that region is we illustrate this method by applying it to two specific cases an analysis of gps data from northern california to monitor the level of lake shasta and the analysis of data from a single gps site in southeast greenland to determine mass variability of two large nearby outletglaciers helheim glacier and midgaard glacier the californiaexampleserves largely as a proof of concept where the results can be assessed by comparing with independent observations lake shasta tide gauge data in this case our greenland results show that both helheim and midgaard have experienced notable interannual variations in mass loss rate over the last decade helheim sm ass loss accelerated rapidly in mid 2003 decelerated in late 2005 and increased again in 2008 2009 before returning to about its pre 2003 rate in late 2010 midgaard s mass loss accelerated in mid 2004 and remained more or less constant before returning to its pre 2003 rate in late 2008

a gis based method for evaluating sediment storage and transport in large mining affected river systems currently the evaluation of sediment storage and transport for large river systems with variable flow has proven to be a challenge that often requires complex numerical models to be applied and sometimes costly direct data acquisition to be made the present study proposes a low cost widely available gis based method through which an initial assessment can be made on areas of sediment storage transport and deposition as well as possible environmental risks that the accumulation of contaminated material may pose to riverine communities along the rivers channel the method mainly relies on satellite imagery and elevation data to devise a quick model of the channel the model has been successfully applied to study the bolivian sector of the well known mining contaminated rio pilcomayo the analysis shows that the portion of the channel from villamontes to d orbigny accounts for more than half of the total c 314 km2 sedimentation area of the pilcomayo in bolivia and that the most environmentally problematic area is centreed around puente sucre where agriculture is practiced on the contaminated floodplain combined with supplementary bathymetric data on the depth of the river in various points around the channel the method could offer further insight into the sediment fluxes and transport capacity of the pilcomayo in various sectors and could thus be successfully used to assess other large mining contaminated river channels around the world

using gps and absolute gravity observations to separate the effects of present day and pleistocene ice mass changes in south east greenland measurements of vertical crustal uplift from bedrock sites around the edge of the greenland ice sheet gris can be used to constrain present day mass loss interpreting any observed crustal displacement around the gris in terms of present day changes in ice is complicated however by the glacial isostatic adjustment gia signal with gps observations alone it is impossible to separate the uplift driven by present day mass changes from that due to ice mass changes in the past wahr et al 1995 demonstrated that viscoelastic surface displacements were related to the viscoelastic gravity changes through a proportionality constant that is nearly independent of the choice of earth viscosity or ice history model thus by making measurements of both gravity and surface motion at a bedrock site the viscoelastic effects could be removed from the observations and we would be able to constrain present day ice mass changes alternatively we could use the same observations of surface displacements and gravity to determine the gia signal in this paper we extend the theory of wahr et al 1995 by introducing a constant z that represents the ratio between the elastic changes in gravity and elastic uplift at a particular site due to present day mass changes further we combine 20 yrs of gps observations of uplift with eight absolute gravity observations over the same period to determine the gia signal near kulusuk a site on the southeastern side of the gris to experimentally demonstrate the theory we estimate that the gia signal in the region is 4 49 1 44mm yr and is inconsistent with most previously reported model predictions that demonstrate that the gia signal here is negative however as there is very little in situ data to constrain the gia rate in this part of greenland the earth model or the ice history reconstructions could be inaccurate khan et al 2016 improving the estimate of gia in this region of greenland will allow us to better determine the present day changes in ice mass in the region e g from grace

space geodetic constraints on glacial isostatic adjustment in fennoscandia analysis of global positioning system gps data demonstrates that ongoing three dimensional crustal deformation in fennoscandia is dominated by glacial isostatic adjustment our comparison of these gps observations with numerical predictions yields an earth model that satis es independent geologic constraints and bounds both the average viscosity in the upper mantle 5 x 10 20 to 1 x 10 21 pascal seconds and the elastic thickness of the lithosphere 90 to 170 kilometers we combined gps derived radial motions with fennoscandian tide gauge records to estimate a regional sea surface rise of 2 1 0 3 mm year furthermore ongoing horizontal tectonic motions greater than 1 mm year are ruled out on the basis of the gps derived three dimensional crustal velocity field

nodal variations and long term changes in the main tides on the coasts of china the long term changes in the main tidal constituents o1 k1 m2 n2 and s2 along the coasts of china and in adjacent seas are investigated based on 17 tide gauge records covering the period 1954 2012 the observed 18 61 year nodal modulations of the diurnal constituents o1 and k1 are in agreement with the equilibrium tidal theory except in the south china sea the observed modulations of the m2 and n2 amplitudes are smaller than theoretically predicted at the northern stations and larger at the southern stations the discrepancies between the theoretically predicted nodal variations and the observations are discussed the 8 85 year perigean cycle is identifiable in the n2 parameters at most stations except those in the south china sea the radiational component of s2 contributes on average 16 of the observed s2 except in the gulf of tonkin on the south coast where it accounts for up to 65 we confirmed the existence of nodal modulation in s2 which is stronger on the north coast the semidiurnal tidal parameters show significant secular trends in the bohai and yellow seas on the north coast and in the taiwan strait the largest increase is found for m2 for which the amplitude increases by 4 7 mm yr in the yellow sea the potential causes for the linear trends in tidal constants are discussed

spatial and temporal variations in greenland glacial earthquake activity 1993 2010 1 glacial earthquakes are anomalous earthquakes associated with large ice loss events occurring at marine terminating glaciers primarily in greenland they are detectable teleseismically and a proper understanding of the source mechanism may provide a remote sensing tool to complement glaciological observations of these large outlet glaciers we model teleseismic surface wave waveforms to obtain locations and centroid single force source parameters for 121 glacial earthquakes occurring in greenland during the period 2006 2010 we combine these results with those obtained by previous workers to analyze spatial and temporal trends in glacial earthquake occurrence over the 18 year period from 1993 2010 we also examine earthquake occurrence at six individual glaciers comparing the earthquake record to independently obtained observations of glacier change our findings confirm the inference that glacial earthquake seismogenesis occurs through the capsize of large newly calved icebergs we find a close correspondence between episodes of glacier retreat thinning and acceleration and the timing of glacial earthquakes and document the northward progression of glacial earthquakes on greenland s west coast over the 18 year observing period our results also show that glacial earthquakes occur when the termini of the source glaciers are very close to the glacier grounding line i e when the glaciers are grounded or nearly grounded

the influence of decadal to millennial scale ice mass changes on present day vertical land motion in greenland implications for the interpretation of gps observations 1 we show predictions of present day vertical land motion in greenland using a recently developed glacial isostatic adjustment gia model calibrated using both relative sea level rsl observations and geomorphological constraints on ice extent predictions from our gia model are in agreement with the relatively small number of gps measurements of absolute vertical motion from south and southwest greenland this suggests that our model of ice sheet evolution over the holocene period is reasonably accurate the uplift predictions are highly sensitive to variations of upper mantle viscosity thus depending on the earth model adopted different periods of ice loading change dominate the present day response in particular regions of greenland we also consider the possible influence of more recent changes in the ice sheet by applying a second ice model specifically a surface mass balance smb model which covers the period 1866 to 2005 predictions from this model suggest that decadal scale smb changes over the past 140 years play only a small role in determining the present day viscous response at the sub mm yr level in most locations for a range of earth model parameters high rates of peripheral thinning from 1995 to 2005 predicted using the smb model produce large elastic uplift rates 6 mm yr in west and southwest greenland this suggests that in some areas close to the ice margin modern surface mass balance changes have a dominant control on present day vertical land motion

calving seasonality associated with melt undercutting and lake ice cover a detailed understanding of calving processes at the lacustrine margins of the greenland ice sheet is necessary for accurately forecasting its dynamic response to ongoing climate change however existing data sets of lacustrine calving are limited to summer seasons and to alpine glaciers here we use an integrated time lapse and structure from motion approach to generate the first continuous year round volumetric record of calving processes at a lacustrine ice sheet margin we identify two distinct calving regimes that are associated with melt undercutting and lake ice cover we also find that calving rates respond rapidly to sudden lake drainage given that lake temperature lake ice cover and sudden lake drainages are controlled by air temperature and ice margin thinning we suggest that climate change manifested in lengthening summer seasons will accelerate rates of mass loss and terminus recession at lacustrine ice margins in greenland

jtrf2014 the jpl kalman filter and smoother realization of the international terrestrial reference system we present and discuss jtrf2014 the terrestrial reference frame trf the jet propulsion laboratory constructed by combining space geodetic inputs from very long baseline interferometry vlbi satellite laser ranging slr global navigation satellite systems gnss and doppler orbitography and radiopositioning integrated by satellite submitted for the realization of itrf2014 determined through a kalman filter and rauch tung striebel smoother assimilating position observations earth orientation parameters and local ties jtrf2014 is a subsecular time series based trf whose origin is at the quasi instantaneous center of mass cm as sensed by slr and whose scale is determined by the quasi instantaneous vlbi and slr scales the dynamical evolution of the positions accounts for a secular motion term annual and semiannual periodic modes site dependent variances based on the analysis of loading displacements induced by mass redistributions of terrestrial fluids have been used to control the extent of random walk adopted in the combination with differences in the amplitude of the annual signal within the range 0 5 0 8 mm jtrf2014 derived center of network to center of mass cm cn is in remarkable agreement with the geocenter motion obtained via spectral inversion of gnss gravity recovery and climate experiment grace observations and modeled ocean bottom pressure from estimating the circulation and climate of the ocean ecco comparisons of jtrf2014 to itrf2014 suggest high level consistency with time derivatives of the helmert transformation parameters connecting the two frames below 0 18 mm yr and weighted root mean square differences of the polar motion polar motion rate in the order of 30 as 17 as d

geodetic measurements of postglacial adjustments in greenland 1 we analyze data from seven continuous global positioning system gps receivers and one tide gauge all located along the edge of the greenland ice sheet to determine vertical uplift rates we compare our results with predictions based on the ice 5g deglaciation model of peltier 2004 results from the gps receiver at kellyville 1 2 1 1 mm a and from the tide gauge at nuuk 2 2 1 3 mm a indicate that ice 5g overestimates the subsidence rates at those locations by 2 1 and 1 1 mm a respectively kellyville and nuuk are located along the southwestern margin of the greenland ice sheet and the observed negative uplift rates are consistent with independent evidence that the ice margin along the southwestern edge readvanced during the last 8 ka to its current position the ice 5g glaciation deglaciation history includes a readvance between the latitudes of 62 n and 72 n the gps measurements suggest the ice 5g readvance may be too large or mistimed our gps results at qaqortoq located at the southern tip of greenland suggest a secular subsidence rate of 0 3 1 1 mm a while ice 5g predicts an uplift rate of 1 0 mm a ice 5g assumes no ice sheet readvance in south greenland including no readvance of the qassimiut lobe the difference of 1 3 1 1 mm a can tentatively be explained as due to a 33 km readvance of the qassimiut lobe during the last 3 ka for the other gps sites the observed predicted uplift rates are 3 6 1 1 0 1 mm a at thule 0 0 1 1 2 0 mm a at scoresbysund and 0 4 1 1 1 7 mm a at kulusuk for thule kulusuk and scoresbysund the differences between the observed and predicted rates are on the order of 1 3 3 7 mm a though with opposite signs and indicate that ice 5g does not exactly reproduce the correct rebound signal at those locations

two layer tidal modeling of the yellow and east china seas with application to seasonal variability of the m2 tide 1 the baroclinic response of tide and tidal currents in the yellow and east china seas is investigated using a two layer numerical model seasonal variability in the m2 tide especially the smaller summer amplitudes prevailing along the korea tsushima strait kang et al 1995 is investigated by a series of numerical experiments with varying degrees of stratification specific to winter and summer model results show that the summer amplitudes of the m2 tide around the southwestern tip of the korean peninsula and korea tsusima strait decrease with a peak decrease of about 14 cm off the southwestern tip of the korean peninsula while the summer amplitudes in other coastal regions tend to increase this seasonal variability generally coincides with the observations these models results indicate that seasonal stratification has several noticeable effects on the tides including varying degrees of current shear varying frictional dissipation and varying barotropic energy flux in particular it drives complicated seasonal variability in the m2 tide with a peak amplitude modulation of nearly 5 off the southwestern tip of the korean peninsula the seasonal variation of barotropic m2 energy flux through the eastern entrance of the yellow sea is thought to induce the corresponding variability in the m2 amplitude in the korea tsusima strait with smaller amplitudes found in the summer

collapse of the pilcomayo river the pilcomayo river flows south eastwards from the bolivian andes across the chaco plains setting the border between argentina and paraguay it flows down along 1000km in principle to finally join the paraguay river it spills over the plains during the rainy season from january to march the sediment load of the pilcomayo is one of the largest in the world 140milliontons per year which is mostly wash load from the upland andes the mean concentration of suspended sediment is 15g l the maximum recorded concentration is as high as 60g l the river has built a large fan covering a surface of 210 000km2 with many abandoned channels today it is a river prone to avulsion raising border disputes between the two lowland countries argentina and paraguay moreover the very special feature of pilcomayo river is that it does not actually flow into the paraguay river very far upstream of the mouth in the paraguay the channel blocks itself with sediment and wood debris forcing water and sediment to spread across the plains moreover the point of blockage has moved hundreds of kilometers upstream throughout the 20th century many environmental issues arise because of this collapse channel discontinuity not the least of them is the migration of fish the future of the river concerns bolivia and the two lowland countries 2012 elsevier b v

bedrock displacements in greenland manifest ice mass variations climate cycles and climate change the greenland gps network gnet uses the global positioning system gps to measure the displacement of bedrock exposed near the margins of the greenland ice sheet the entire network is uplifting in response to past and present day changes in ice mass crustal displacement is largely accounted for by an annual oscillation superimposed on a sustained trend the oscillation is driven by earth s elastic response to seasonal variations in ice mass and air mass i e atmospheric pressure observed vertical velocities are higher and often much higher than predicted rates of postglacial rebound pgr implying that uplift is usually dominated by the solid earth s instantaneous elastic response to contemporary losses in ice mass rather than pgr superimposed on longer term trends an anomalous pulse of uplift accumulated at many gnet stations during an approximate six month period in 2010 this anomalous uplift is spatially correlated with the 2010 melting day anomaly

influence of anthropogenic groundwater unloading in indo gangetic plains on the 25 april 2015 mw 7 8 gorkha nepal earthquake groundwater usage in the indo gangetic plains exceeds replenishment of aquifers leading to substantial reduction in the mass such anthropogenic crustal unloading may promote long term fault slip or may modulate seismic activity in the adjoining himalayan region our simulation using gravity recovery and climate experiment data and hydrological models of such a process indicates that the thrust earthquakes on the main himalayan thrust mht including the recent 25 april 2015 mw 7 8 gorkha nepal earthquake are probably influenced by the anthropogenic groundwater unloading process in the gangetic plains the groundwater withdrawal leading to crustal unloading in the gangetic plains causes a significant component of horizontal compression which adds to the secular interseimic compression at the seismogenic depth 5 20 km on the mht beneath the himalayan arc and at hypocentral depth of the 2015 gorkha nepal earthquake this effect enhances the coulomb stress on the locked zone of mht

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

modeling deformation induced by seasonal variations of continental water in the himalaya region sensitivity to earth elastic structure strong seasonal variations of horizontal and vertical positions are observed on gps time series from stations located in nepal india and tibet china we show that this geodetic deformation can be explained by seasonal variations of continental water storage driven by the monsoon for this purpose we use satellite data from the gravity recovery and climate experiment to determine the time evolution of surface loading we compute the expected geodetic deformation assuming a perfectly elastic earth model we consider green s functions describing the surface deformation response to a point load for an elastic homogeneous half space model and for a layered nonrotating spherical earth model based on the preliminary reference earth model and a local seismic velocity model the amplitude and phase of the seasonal variation of the vertical and horizontal geodetic positions can be jointly adjusted only with the layered earth model while an elastic half space model fails emphasizing the importance of using a realistic earth elastic structure to model surface displacements induced by surface loading we demonstrate based on a formal inversion that the fit to the geodetic data can be improved by adjusting the layered earth model therefore the study also shows that the modeling of geodetic seasonal variations provides a way to probe the elastic structure of the earth even in the absence of direct measurements of surface load variations

a new glacial isostatic adjustment model of the innuitian ice sheet arctic canada abstract a reconstruction of the innuitian ice sheet iis is developed that incorporates first order constraints on its spatial extent and history as suggested by regional glacial geology studies glacial isostatic adjustment modelling of this ice sheet provides relative sea level predictions that are in good agreement with measurements of post glacial sea level change at 18 locations the results indicate peak thicknesses of the innuitian ice sheet of approximately 1600 m up to 400 m thicker than the minimum peak thicknesses estimated from glacial geology studies but between approximately 1000 to 1500 m thinner than the peak thicknesses present in previous gia models the thickness history of the best fit innuitian ice sheet model developed here termed sjd15 differs from the ice 5g reconstruction and provides an improved fit to sea level measurements from the lowland sector of the ice sheet both models provide a similar fit to relative sea level measurements from the alpine sector the vertical crustal motion predictions of the best fit iis model are in general agreement with limited gps observations after correction for a significant elastic crustal response to present day ice mass change the new model provides approximately 2 7 m equivalent contribution to global sea level rise an increase of 0 6 m compared to the innuitian portion of ice 5g sjd15 is qualitatively more similar to the recent ice 6g ice sheet reconstruction which appears to also include more spatially extensive ice cover in the innuitian region than ice 5g

changes in the velocity structure of the greenland ice sheet using satellite radar interferometry observations of greenland we detected widespread glacier acceleration below 66 north between 1996 and 2000 which rapidly expanded to 70 north in 2005 accelerated ice discharge in the west and particularly in the east doubled the ice sheet mass deficit in the last decade from 90 to 220 cubic kilometers per year as more glaciers accelerate farther north the contribution of greenland to sea level rise will continue to increase

accelerating uplift in the north atlantic region as an indicator of ice loss vertical motions of the rocky margins of greenland and antarctica respond to mass changes of their respective ice sheets but these motions can be obscured by ancient episodes of glacial advance or retreat an analysis of the acceleration of vertical motion indicates that accelerated ice loss in western greenland started in the late 1990s vertical motions of the rocky margins of greenland and antarctica respond to mass changes of their respective ice sheets1 2 however these motions can be obscured by episodes of glacial advance or retreat that occurred hundreds to thousands of years ago3 4 5 6 which trigger a delayed response because of viscous flow in the underlying mantle here we present high precision global positioning system gps data that describe the vertical motion of the rocky margins of greenland iceland and svalbard we focus on vertical accelerations rather than velocities to avoid the confounding effects of past events our data show an acceleration of uplift over the past decade that represents an essentially instantaneous elastic response to the recent accelerated melting of ice throughout the north atlantic region our comparison of the gps data to models for glacial isostatic adjustment suggests that some parts of western coastal greenland were experiencing accelerated melting of coastal ice by the late 1990s using a simple elastic model we estimate that western greenland s ice loss is accelerating at an average rate of 8 7 3 5 gt yr 2 whereas the rate for southeastern greenland based on limited data falls at 12 5 5 5 gt yr 2

influence of a meteorological cycle in mid crustal seismicity of the nepal himalaya abstract the process of interseismic strain accumulation across the nepal himalaya is associated with micro seismicity also called mid crustal seismicity which occurs along the mid crustal ramp on the main himalayan thrust mht the seismicity shows strong annual periodicity in response to the annual stress variation of hydrological loads we report dominance of annual periodicity in the eastern nepal as compared to that of western nepal and overall annual periodicity dominance in the small magnitude earthquakes mw 0 3 rainfall seismicity cross correlation is significantly higher in the eastern nepal region as compared to that of western nepal with a prominent phase lag of 5 6 months with respect to the occurrence of monsoonal rainfall seasonal modulation can be explained by coulomb failure stress model and fault resonance hypothesis induced by meteorological cycle this new observation upholds the existing hypothesis that evaporation induced unloading in the himalayan foothills and adjacent indo gangetic plains during the post monsoon period i e during winter add significant component of horizontal compression to the interseismic contraction at the mht which is the main driving mechanism for the seasonal modulation

elastic uplift in southeast greenland due to rapid ice mass loss this is the publisher s version also available electronically from http onlinelibrary wiley com

mean sea level variability in the north sea processes and implications mean sea level msl variations across a range of time scales are examined for the north sea under the consideration of different forcing factors since the late 19th century we use multiple linear regression models which are validated for the second half of the 20th century against the output of a tide surge model to determine the barotropic response of the ocean to fluctuations in atmospheric forcing we find that local atmospheric forcing mainly initiates msl variability on time scales up to a few years with the inverted barometric effect dominating the variability along the uk and norwegian coastlines and wind controlling the msl variability in the south from belgium up to denmark on decadal time scales msl variability mainly reflects steric changes which are largely forced remotely a spatial correlation analysis of altimetry observations and gridded steric heights suggests evidence for a coherent signal extending from the norwegian shelf down to the canary islands this fits with the theory of longshore wind forcing along the eastern boundary of the north atlantic causing coastally trapped waves to propagate over thousands of kilometers along the continental slope implications of these findings are assessed with statistical monte carlo experiments it is demonstrated that the removal of known variability increases the signal to noise ratio with the result that i linear trends can be estimated more accurately ii possible accelerations as expected e g due to anthropogenic climate change can be detected much earlier such information is of crucial importance for anticipatory coastal management engineering and planning

constraints on the greenland ice sheet since the last glacial maximum from sea level observations and glacial rebound models abstract geomorphological descriptions of changes in the extent of the greenland ice sheet gis have been combined with glacial isostatic adjustment models to reproduce the sea level history of greenland since the last glacial maximum lgm the contribution to past sea level change around greenland due to ice load changes outside of that region has been considerable 10 s of meters while still contributing a rise of several mm yr 1 today the isostatic contribution to relative sea level around greenland from changes in the gis is found by iteratively perturbing preliminary ice models with different lgm extents and deglaciation starting times the resulting first order model that provides the best agreement between observed and predicted sea level contributes 3 1 and 1 9 m water equivalent of additional ice relative to present day ice volumes at the lgm and younger dryas respectively the gis in most areas does not appear to have extended far onto the continental shelf the exceptions being southern most southwest greenland and northern east greenland as well as at the coalescence of the northwest greenland and innuitian ice sheets changes in ice thickness since the lgm were 500 m along the present day outer coast and 1500 m along some parts of the present day ice margin the observed mid to late holocene fall in sea level to below the present day level and the subsequent transgression seen in some areas implies that the gis retreated behind the present day margin by distances of the order of 40 km before readvancing

sediment yield along the andes continental budget regional variations and comparisons with other basins from orogenic mountain belts abstract we assess the sediment yield at 119 gauging stations distributed from colombia to patagonia covering the different morphotectonic and morphoclimatic settings of the andes the most productive areas are the meta river basin within the northern andes and the bolivian and northern argentina chaco systems which produce an average of 3345 4909 and 2654 t km2 y 1 of sediment respectively the rivers of the northern and central andes excluding the pacific watersheds of peru northern chile and central argentina have a weighted mean sediment yield of 2045 t km 2 y 1 and produce 2 25 gty 1 of total sediment a major constraint estimating the andean continental budget of sediment yield lies in the lack of gauging data for the peruvian region using the available gauge stations the regional sediment yield appears underestimated assuming a higher value of sediment yield for the peruvian andes the total budget for the whole central andes could range between 2 57 gt y 1 and 3 44 gt y 1 a minimum of 0 55 gt y 1 and a probable maximum of 1 74 gt y 1 of sediment are deposited in the intramontane and surrounding proximal sedimentary basins the magnitude of sediment yield in the andes is comparable to other rivers draining orogenic belts around the world

progressive increase in ice loss from greenland 1 laser altimeter measurements over greenland show increasing thickening rates above 2000 m reflecting increasing snowfall in a warming climate but near coastal thinning rates have increased substantially since the mid 1990s and net mass loss more than doubled from an average of 4 50 gt yr 1 between 1993 4 and 1998 9 to 57 105 gt yr 1 between 1998 9 and 2004 this increasing trend is very similar to findings from independent mass budget studies but differs widely from ers radar altimeter results this may result from limitations associated with the large ers footprint over sloping and undulating surfaces that typify fast narrow glaciers where thinning is most pronounced

the raft of the saint jean river gaspe quebec canada a dynamic feature trapping most of the wood transported from the catchment abstract the rivers of the gaspe peninsula quebec canada a coastal drainage system of the st lawrence river receive and transport vast quantities of large wood the rapid rate of channel shifting caused by high energy flows and noncohesive banks allows wood recruitment that in turn greatly influences river dynamics the delta of the saint jean river has accumulated wood since 1960 leading to frequent avulsions over that time period the wood raft there is now more than 3 km in length which is unusual but natural this jam configuration allows a unique opportunity to estimate a wood budget at the scale of a long river corridor and to better understand the dynamics of large wood lw in rivers a wood budget includes the evaluation of wood volumes i produced by bank erosion input ii still in transit in the river corridor deposited on sand bars or channel edges and iii accumulated in the delta output the budget is based on an analysis of aerial photos dating back to 1963 as well as surveys carried out in 2010 all of which were used to locate and describe large wood accumulations along a 60 km river section the main results of this paper show that the raft formation in the delta is dynamic and can be massive but it is a natural process considering the estimated wood volume trapped in the delta from 1963 to 2013 25 000 m3 two important points are revealed by the quantification of the wood recruitment volume from 1963 to 2004 27 000 m3 400 m3 and of the wood volume stored on the bars in 2010 5950 m3 first the recruitment of large wood from lateral migration for the 40 year period can account for the volume of large wood in the delta and in transit second the excess wood volume produced by lateral migration and avulsion represents a minimum estimation of the large wood trapped on the floodplain owing to wood volume that has decomposed and large wood that exited the river system rafts are major trapping structures that provide good potential sites to monitor wood delivery from the catchment through time and allow estimations of lw residence time while in transit these results contribute to understanding the interannual large wood dynamics in the saint jean river and can assist river managers in determining sustainable solutions for coping with the issue of wood rafts in rivers

active tectonics in northern victoria land antarctica inferred from the integration of gps data and geologic setting accepted for publication in journal of geophysical research copyright 2010 american geophysical union

geodetic gps measurements in south iceland strain accumulation and partitioning in a propagating ridge system 1 gps observations in south iceland between 1994 and 2003 are compared with two dimensional elastic half space and viscoelastic coupling models for two parallel rift zones representing the western and eastern volcanic zones wvz evz gps data from the hreppar block between the wvz and evz fit a rigid block model within uncertainties spreading rates across the wvz increase from 2 6 0 9 mm yr in the northeast to 7 0 0 4 mm yr in the southwest conversely spreading rates in the evz decrease from 19 0 2 0 mm yr in the northeast to 11 0 0 8 mm yr in the southwest the direction of ridge propagation summed extension rates across the two rift zones are approximately constant and equal to the total plate rate 18 20 mm yr consistent with a simple propagating ridge model whereby the wvz is deactivating in the direction of evz propagation the coupling model confirms results from the simple elastic half space model including relatively shallow locking depths 5 km beneath the rift zones and allows for an estimate of mean viscosity 1019 1020 pa s beneath the elastic layer the location of maximum surface velocity gradient in the evz presumably the locus of subsurface magma accumulation and future rifting does not coincide with the 1783 1784 lakagigar fissure eruption but is 20 km to the west on the bar abunga veidivotn fissure swarm this had a small volume eruption in 1862 1864 but a major eruption in 1477 a d

rapid change in semi diurnal tides in the north atlantic since 1980 1 an anomalously large trend of m2 and s2 amplitudes and phases beginning in the early 1980s is observed in the north atlantic harmonic analysis of long term sea level records from tide gauge stations along the north american atlantic coast and european atlantic coast shows a large decrease in m2 and s2 amplitudes and an increase in phase lag the characteristics of the evolution of m2 and s2 tides are similar but not fully conclusive which may suggesting different causes in general the trends may be due to global warming which significantly increased in the early 1980s in the north atlantic region several climate related driving mechanisms for the observed changes in tides are discussed

nodal modulation of the lunar semidiurnal tide in the bay of fundy and gulf of maine observations numerical modeling and theoretical calculations show how the 18 6 year modulation of the main lunar semidiurnal tide in the bay of fundy and gulf of maine is reduced from its astronomical value of 3 7 percent to 2 4 percent by the effects of friction and resonance the agreement of the three approaches increases confidence in model predictions of widespread changes in the tidal regime resulting from development of tidal power

on the resonance and influence of the tides in ungava bay and hudson strait 1 the tides of leaf basin in ungava bay may be the world s highest an analysis of the frequency dependence of the response to outside forcing a normal mode analysis and a study of the damped oscillation of an initial disturbance suggest that the ungava bay hudson strait region has a natural period of about 12 7 hours and so is close to resonance with the tidal forcing the implications for regional and global tides in the present past and future are explored

geodetic measurements in greenland and their implications we describe results from an ongoing experiment in greenland in which we are using absolute gravity and continuous global positioning system gps measurements to study vertical crustal motion at two locations along the edge of the ice sheet kellyville located about one third of the way up the western ice margin and kulusuk located along the eastern ice margin at about the same latitude as kellyville the gps measurements suggest average crustal uplift rates of 5 8 1 0 mm yr at kellyville and 2 1 1 5 mm yr at kulusuk there have not yet been enough absolute gravity occupations to permit useful secular gravity solutions at either location the negative uplift rate at kellyville is consistent with independent archeological and historical evidence that the southwestern edge of the continent has been subsiding over the last 3000 years but it is inconsistent with estimates of the earth s continuing viscoelastic response to melting ice during the early holocene which predict that kellyville is likely to be uplifting rather than subsiding by 2 0 3 5 mm yr the resulting 7 8 3 6 mm yr discrepancy between the observed and predicted uplift rates is too large to be caused by loading from present day changes in nearby ice however it is consistent with independent suggestions that the western ice sheet margin in this region may have advanced by 50 km during the past 3000 4000 years if this advance did occur and if the crustal subsidence it induces is not removed from altimeter measurements of greenland ice sheet elevations then the altimeter solutions could underestimate the true snow ice thickness change by 5 10 mm yr along portions of the western margin of the ice sheet

annual variations in gps measured vertical displacements near upernavik isstrom greenland and contributions from surface mass loading in response to present day ice mass loss on and near the greenland ice sheet steady crustal uplifts have been observed from the network of global positioning system gps stations mounted on bedrock in addition to the secular uplift trends the gps time series also show prominent annual variability here we examine the annual changes of the vertical displacements measured at two gps stations srmp and upvk near upernavik isstrom in western greenland we model elastic loading displacements due to various surface mass loading including three non ice components atmospheric pressure ocean bottom pressure continental water storage and one ice component i e surface mass balance smb we find that the contribution from atmospheric pressure changes can explain 46 and 78 of the annual amplitude observed in the gps verticals at srmp and upvk respectively we also show that removing the predicted loading displacements due to smb adversely increases the annual variance of the gps residuals however using the gps data alone we cannot identify the exact cause s of this discrepancy because the annual loading displacements are sensitive to the smb changes from over 85 of the ice sheet area alternatively by differencing vertical displacements between the two stations we find a good agreement between the modeled differential smb loading displacements and the gps residuals after removing non ice components our study highlights the necessity of correcting for non ice loading contributions in the gps measurements of crustal deformation to infer ice mass changes in greenland at annual periods

universal relation with regime transition for sediment transport in fine grained rivers fine grained sediment grain size under 2 000 m builds floodplains and deltas and shapes the coastlines where much of humanity lives however a universal physically based predictor of sediment flux for fine grained rivers remains to be developed herein a comprehensive sediment load database for fine grained channels ranging from small experimental flumes to megarivers is used to find a predictive algorithm two distinct transport regimes emerge separated by a discontinuous transition for median bed grain size within the very fine sand range 81 to 154 m whereby sediment flux decreases by up to 100 fold for coarser sand bedded rivers compared to river with silt and very fine sand beds evidence suggests that the discontinuous change in sediment load originates from a transition of transport mode between mixed suspended bed load transport and suspension dominated transport events that alter bed sediment size near the transition may significantly affect fluviocoastal morphology by drastically changing sediment flux as shown by data from the yellow river china which over time transitioned back and forth 3 times between states of high and low transport efficiency in response to anthropic activities

present day antarctic ice mass changes and crustal motion the peak vertical velocities predicted by three realistic but contrasting present day scenarios of antarctic ice sheet mass balance are found to be of the order of several mm a one scenario predicts local uplift rates in excess of 5 mm a these rates are small compared to the peak antarctic vertical velocities of the ice 3g glacial rebound model which are in excess of 20 mm a if the holocene antarctic deglaciation history portrayed in ice 3g is realistic and if regional upper mantle viscosity is not an order of magnitude below 10 exp 21 pa s then a vast geographical region in west antarctica is uplifting at a rate that could be detected by a future global positioning system gps campaign while present day scenarios predict small vertical crustal velocities their overall continent ocean mass exchange is large enough to account for a substantial portion of the observed secular polar motion omega m bar and time varying zonal gravity field j sub 1

grace observes small scale mass loss in greenland using satellite gravity data between february 2003 and january 2008 we examine changes in greenland s mass distribution on a regional scale during this period greenland lost mass at a mean rate of 179 25 gt yr equivalent to a global mean sea level change of 0 5 0 1 mm yr rates increase over time suggesting an acceleration of the mass loss driven by mass loss during summer the largest mass losses occurred along the southeastern and northwestern coast in the summers of 2005 and 2007 when the ice sheet lost 279 gt and 328 gt of ice respectively within 2 months in 2007 a strong mass loss is observed during summer at elevations above 2000 m for the first time since the start of the observations

the elastic response of the earth to interannual variations in antarctic precipitation measurements of elastic displacements of the bed rock surrounding large ice sheets have been proposed as a means to detect mass changes in these ice sheets however ac cumulation of glacial mass on the ice sheets is a noisy process subject to large spatial and temporal variations in precipita tion we simulated the response of the antarctic continent to a stochastic model of interannual precipitation variations and found that interannual variations in the elastic response of the earth are large when compared to the long term mean of dis placements produced by an assumed average ice mass imbal ance of 10 if as some scientists predict antarctic ice mass changes in the future become dramatic the long term signal should be large enough to be detected by a few years of geo detic measurements despite climatic noise

climate driven vertical acceleration of icelandic crust measured by continuous gps geodesy earth s present day response to enhanced glacial melting resulting from climate change can be measured using global positioning system gps technology we present data from 62 continuously operating gps instruments in iceland statistically significant upward velocity and accelerations are recorded at 27 gps stations predominantly located in the central highlands region of iceland where present day thinning of the iceland ice caps results in velocities of more than 30 mm yr and uplift accelerations of 1 2 mm yr2 we use our acceleration estimates to back calculate to a time of zero velocity which coincides with the initiation of ice loss in iceland from ice mass balance calculations and arctic warming trends we show through a simple inversion a direct relationship between ice mass balance measurements and vertical position and show that accelerated unloading is required to reproduce uplift observations for a simple elastic layer over viscoelastic half space model

grace era secular trends in earth rotation parameters a global scale impact of the global warming process 1 recent trends in the two primary anomalies in the rotational state of the planet are analyzed in detail namely those associated with the speed and direction of polar wander and with the non tidal acceleration of the rate of axial rotation via the measurement of the changing oblateness of the earth s shape it is demonstrated that a significant change in the secular trends in both of these independent parameters became evident subsequent to approximately 1992 it is suggested that both parameters might have come to be substantially influenced by mass loss from both the great polar ice sheets and from the very large number of small ice sheets and glaciers that are also being influenced by the global warming phenomenon the modern values for the secular drifts in those parameters that we estimate are appropriate to the period during which measurements have been made by the satellites of the gravity recovery and climate experiment grace thesechangesinsecularratesmightgreatly assist in understanding why the grace inferred values of the time derivatives of the degree two and order one stokes coefficients differ so significantly from those associated with late quaternary ice age influence citation roy k and w r peltier 2011 grace era secular trends in earth rotation parameters a global scale impact of the global warming process geophys res lett 38 l10306 doi 10 1029 2011gl047282

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

evolution of tidal amplitudes in the eastern pacific ocean 1 global sea level gsl rise is well documented however changes in high waters including the tidal contribution are sometimes more relevant than gsl rise analysis of 34 long tidal records from the eastern pacific ocean shows that k1 and m2 amplitudes k1 and m2 are increasing except for m2 in the gulf of panama north of 18 n k1 and m2 are both growing at 2 2 century 1 the mean increase in total tidal amplitude 0 59 mmyr 1 is less than the present gsl rise 1 7 mmyr 1 however mean sea level is nearly constant in the ne pacific so tidal evolution plays a major regional role in changes in high water levels the spatial pattern of tidal evolution suggests the influence of large scale processes and the similarity in spatial patterns for k1 and m2 excludes mechanisms with strong frequency dependence increasing tidal amplitudes may impact ocean mixing nutrient supply primary production fisheries and coastal erosion

volcano deformation at active plate boundaries deep magma accumulation at hekla volcano and plate boundary deformation in south iceland volcano deformation at active plate boundaries deep magma accumulation at hekla volcano and plate boundary deformation in south iceland

kalref a kalman filter and time series approach to the international terrestrial reference frame realization the current international terrestrial reference frame is based on a piecewise linear site motion model and realized by reference epoch coordinates and velocities for a global set of stations although linear motions due to tectonic plates and glacial isostatic adjustment dominate geodetic signals at today s millimeter precisions nonlinear motions due to earthquakes volcanic activities ice mass losses sea level rise hydrological changes and other processes become significant monitoring these sometimes rapid changes desires consistent and precise realization of the terrestrial reference frame trf quasi instantaneously here we use a kalman filter and smoother approach to combine time series from four space geodetic techniques to realize an experimental trf through weekly time series of geocentric coordinates in addition to secular periodic and stochastic components for station coordinates the kalman filter state variables also include daily earth orientation parameters and transformation parameters from input data frames to the combined trf local tie measurements among colocated stations are used at their known or nominal epochs of observation with comotion constraints applied to almost all colocated stations the filter smoother approach unifies different geodetic time series in a single geocentric frame fragmented and multitechnique tracking records at colocation sites are bridged together to form longer and coherent motion time series while the time series approach to trf reflects the reality of a changing earth more closely than the linear approximation model the filter smoother is computationally powerful and flexible to facilitate incorporation of other data types and more advanced characterization of stochastic behavior of geodetic time series

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

on the modification of tides in a seasonally ice covered sea 1 new observations from eight moorings located in foxe basin hudson strait and hudson bay are used to study the seasonal variability of the m 2 tide significant seasonal variations of the m 2 surface elevation are found in all these regions and at all seasons the largest variations occur during winter while both elevation increase hudson strait and decrease hudson bay foxe basin are observed these variations are found recurrent at the stations where multiyear observations are available observations from a velocity profiler are consistent with a seasonal damping of the tides because of friction under ice numerical simulations with a sea ice ocean coupled model and realistic forcing qualitatively reproduce most of the features of the observed variability the simulations show that the winter m 2 variations are essentially caused by the under ice friction albeit with strong regional differences under ice friction mostly occurs in a limited region foxe basin and can account for both increased and decreased m 2 elevations during winter

glacio isostatic deformation around the vatnajokull ice cap iceland induced by recent climate warming gps observations and finite element modeling 1 glaciers in iceland began retreating around 1890 and since then the vatnajokull ice cap has lost over 400 km 3 of ice the associated unloading of the crust induces a glacio isostatic respo

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

toward a global horizontal and vertical elastic load deformation model derived from grace and gnss station position time series we model surface displacements induced by variations in continental water atmospheric pressure and nontidal oceanic loading derived from the gravity recovery and climate experiment grace for spherical harmonic degrees two and higher as they are not observable by grace we use at first the degree 1 spherical harmonic coefficients from swenson et al 2008 https doi org 10 1029 2007jb005338 we compare the predicted displacements with the position time series of 689 globally distributed continuous global navigation satellite system gnss stations while gnss vertical displacements are well explained by the model at a global scale horizontal displacements are systematically underpredicted and out of phase with gnss station position time series we then reestimate the degree 1 deformation field from a comparison between our grace derived model with no a priori degree 1 loads and the gnss observations we show that this approach reconciles grace derived loading displacements and gnss station position time series at a global scale particularly in the horizontal components assuming that they reflect surface loading deformation only our degree 1 estimates can be translated into geocenter motion time series we also address and assess the impact of systematic errors in gnss station position time series at the global positioning system gps draconitic period and its harmonics on the comparison between gnss and grace derived annual displacements our results confirm that surface mass redistributions observed by grace combined with an elastic spherical and layered earth model can be used to provide first order corrections for loading deformation observed in both horizontal and vertical components of gnss station position time series

geomorphology and late quaternary of the chaco south america the chaco is a large tropical plain located in the interior of south america consisting of parts of argentina paraguay and bolivia it is 840 000 km2 in area and is characterized by forests savannas and extensive swamps which give it a marked climatic and biogeographic identity it encompasses five huge alluvial fans built by the major rivers which cross the region salado bermejo pilcomayo parapeti and grande the fans are composed of several sedimentary units deposited during different times of the late quaternary under diverse climates two fluvial terraces appear at the apex of each fan the older one is probably late pleistocene in age the second was formed in postglacial times humid climates such as the present one favoured the generation of soils and stable fluvial belts drier climates led to widespread sedimentation along small ephemeral channels and large spill outs during two intervals on in the late quaternary glacial maximum and the late holocene dry climates occurred in the region leading to the formation of dune fields and loess mantles

sustained water loss in california s mountain ranges during severe drought from 2012 to 2015 inferred from gps drought struck california during 7 of the 9 years from 2007 to 2015 reducing the state s available water resources pumping of central valley groundwater has produced spectacular land subsidence uplift of the adjacent sierra nevada mountains has been proposed to be either tectonic uplift or solid earth s elastic response to unloading of central valley groundwater we find that of the 24 mm of uplift of the sierra nevada from october 2011 to october 2015 just 5 mm is produced by central valley groundwater loss less than 2 mm is tectonic uplift and 17 mm is solid earth s elastic response to water loss in the sierra nevada we invert gps vertical displacements recording solid earth s elastic response to infer changes in water storage across the western u s from january 2006 to october 2017 we find water changes to be sustained over periods of drought or heavy precipitation the sierra nevada lost 15 19 km3 of water during drought from october 2006 to october 2009 gained 18 14 km3 of water during heavy precipitation from october 2009 to october 2011 and lost 45 21 km3 of water during severe drought from october 2011 to october 2015 95 confidence limits such large changes are not in hydrology models snow accumulation in october is negligible and long term soil moisture change is small we infer that there must be large loss of either deep soil moisture or groundwater in river alluvium and in crystalline basement in the sierra nevada the results suggest there to be parching of water in the ground during the summer of years of drought and seeping of melting snow into the sierra nevada in the spring of years of heavy precipitation

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

mass changes of the greenland and antarctic ice sheets and shelves and contributions to sea level rise 1992 2002 changes in ice mass are estimated from elevation changes derived from 10 5 years greenland and 9 years antarctica of satellite radar altimetry data from the european remote sensing satellites ers 1 and 2 for the first time the dh dt values are adjusted for changes in surface elevation resulting from temperature driven variations in the rate of firn compaction the greenland ice sheet is thinning at the margins 42 2g t a 1 below the equilibrium line altitude ela and growing inland 53 2g t a 1 above the ela with a small overall mass gain 11 3g t a 1 0 03 mm a 1 sle sea level equivalent the ice sheet in west antarctica wa is losing mass 47 4g t a 1 and the ice sheet in east antarctica ea shows a small mass gain 16 11 gt a 1 for a combined net change of 31 12 gt a 1 0 08 mm a 1 sle the contribution of the three ice sheets to sea level is 0 05 0 03 mm a 1 t he antarctic ice shelves show corresponding mass changes of 95 11 gt a 1 in wa and 142 10 gt a 1 in ea thinning at the margins of the greenland ice sheet and growth at higher elevations is an expected response to increasing temperatures and precipitation in a warming climate the marked thinnings in the pine island and thwaites glacier basins of wa and the totten glacier basin in ea are probably ice dynamic responses to long term climate change and perhaps past removal of their adjacent ice shelves the ice growth in the southern antarctic peninsula and parts of ea may be due to increasing precipitation during the last century

secular trends in ocean tides observations and model results 1 during the last century the response of the oceans to tidal forces has changed significantly this study focuses on an analysis of long term sea level records located in the atlantic and pacific primarily in the northern hemisphere it shows that changes of tidal amplitude and or phase have taken place over large scales the principal solar semidiurnal s2 tide shows the largest trends at some locations the change in the mean tidal range due to tidal trends is significant compared with the trend in mean sea level thus it might be advisable to consider these changes in studies of the impact of rising sea level numerical simulations of the principal lunar semidiurnal tide m2 demonstrate a model sensitivity in the north atlantic to changes in glacial isostatic adjustment and sea level rise which captures 30 40 of the magnitude of the trends in observations however the spatial patterns do not agree well with those inferred from observations suggesting that forward global models are currently useful for qualitative but not quantitative understanding of the observed trends a global free oscillation synthesis indicates that sea level rise due to glacial isostatic adjustment leads to decreasing global resonant periods and increasing damping in the system and a coupled oscillator model shows that changes in sea level on the shelf are much more effective at perturbing shelf and ocean tides than sea level changes in the deep ocean