We developed a multi-mission satellite altimetry analysis over the Antarctic Ice Sheet which comprises Seasat, Geosat, ERS-1, ERS-2, Envisat, ICESat and CryoSat-2. After a consistent reprocessing and a stepwise calibration of the inter-mission offsets, we obtained monthly grids of multi-mission surface elevation change (SEC) with respect to the reference epoch 09/2010 (in the format of month/year) from 1978 to 2017. A validation with independent elevation changes from in situ and airborne observations as well as a comparison with a firn model proves that the different missions and observation modes have been successfully combined to a seamless multi-mission time series. For coastal East Antarctica, even Seasat and Geosat provide reliable information and, hence, allow for the analysis of four decades of elevation changes. The spatial and temporal resolution of our result allows for the identification of when and where significant changes in elevation occurred. These time series add detailed information to the evolution of surface elevation in such key regions as Pine Island Glacier, Totten Glacier, Dronning Maud Land or Lake Vostok. After applying a density mask, we calculated time series of mass changes and found that the Antarctic Ice Sheet north of 81.5 • S was losing mass at an average rate of −85 ± 16 Gt yr −1 between 1992 and 2017, which accelerated to −137 ± 25 Gt yr −1 after 2010.

[1] Dual frequency GPS observables only allow the elimination of the 1st -order ionospheric term. Although higher -order ionospheric terms may cause a range bias of several centimeters, accounting for such effects is not yet a common strategy for GPS data analysis. In comparison to previous investigations a rigorous application of 2nd and 3rd -order ionospheric corrections is examined for the estimation not only of receiver positions but of all included parameters. The results reveal a linear dependence of the frame's origin on the integrated electron density. Furthermore, satellite positions are affected at the centimeter level when applying the above -mentioned corrections. Since the ionospheric correction terms show a significant impact on various GPS estimates, their consideration becomes necessary for scientific applications. Hence, the modeling of 2nd and 3rd -order ionospheric correction terms is part of the optimized strategy in an ongoing reprocessing project dealing with a global GPS network and spanning the time period from 1994 up to present time. Citation: Fritsche, M., R.

Land glacier extent and volume at the northern and southern margins of the Drake Passage have been in a state of dramatic demise since the early 1990s. Here time‐varying space gravity observations from the Gravity Recovery and Climate Experiment (GRACE) are combined with Global Positioning System (GPS) bedrock uplift data to simultaneously solve for ice loss and for solid Earth glacial isostatic adjustment (GIA) to Little Ice Age (LIA) cryospheric loading. The present‐day ice loss rates are determined to be −26 ± 6 Gt/yr and −41.5 ± 9 Gt/yr in the Southern and Northern Patagonia Ice Fields (NPI+SPI) and Antarctic Peninsula (AP), respectively. These are consistent with estimates based upon thickness and flux changes. Bounds are recovered for elastic lithosphere thicknesses of 35 ≤ h ≤ 70 km and 20 ≤ h ≤ 45 km and for upper mantle viscosities of 4–8 × 1018 Pa s and 3–10 × 1019 Pa s (using a half‐space approximation) for NPI+SPI and AP, respectively, using an iterative forward model strategy. Antarctic Peninsula ice models with a prolonged LIA, extending to A.D. 1930, are favored in all χ2 fits to the GPS uplift data. This result is largely decoupled from Earth structure assumptions. The GIA corrections account for roughly 20–60% of the space‐determined secular gravity change. Collectively, the on‐land ice losses correspond to volume increases of the oceans equivalent to 0.19 ± 0.045 mm/yr of sea level rise for the last 15 years.

[1] During the 10 years since the official start of the International GNSS Service (IGS) in 1994 considerable improvements in the processing strategies and modeling of global GPS solutions were achieved. Owing to changes at the individual IGS Analysis Centers during these years the resulting time series of global geodetic parameters are very inhomogeneous and inconsistent. A geophysical interpretation of these long series and the realization of a high-accuracy global reference frame are therefore difficult and questionable. In view of these deficiencies, the Technical Universities of Munich and Dresden decided to perform a reprocessing of a global GPS network over the last decade in a joint effort. First results of the reprocessing of 11 years of data show significant improvements in the quality and homogeneity of the estimated parameters and will allow for new geodynamic and geophysical interpretations. In the early years an improvement of the coordinate repeatability by a factor of more than 2 could be achieved. The formal errors of subdaily Earth rotation parameters could be reduced by 30%. Advanced modeling approaches like a mapping function based on numerical weather models, consideration of second-and third-order ionospheric corrections and absolute antenna phase center corrections for receivers and satellites were tested to achieve further improvements.

Height changes of the ice surface above subglacial Lake Vostok, East Antarctica, reflect the integral effect of different processes within the subglacial environment and the ice sheet. Repeated GNSS (Global Navigation Satellite Systems) observations on 56 surface markers in the Lake Vostok region spanning 11 years and continuous GNSS observations at Vostok station over 5 years are used to determine the vertical firn particle movement. Vertical marker velocities are derived with an accuracy of 1 cm/yr or better. Repeated measurements of surface height profiles around Vostok station using kinematic GNSS observations on a snowmobile allow the quantification of surface height changes at 308 crossover points. The height change rate was determined at 1 ± 5 mm/yr, thus indicating a stable ice surface height over the last decade. It is concluded that both the local mass balance of the ice and the lake level of the entire lake have been stable throughout the observation period. The continuous GNSS observations demonstrate that the particle heights vary linearly with time. Nonlinear height changes do not exceed ±1 cm at Vostok station and constrain the magnitude of spatiotemporal lake-level variations. ICESat laser altimetry data confirm that the amplitude of the surface deformations over the lake is restricted to a few centimeters. Assuming the ice sheet to be in steady state over the entire lake, estimates for the surface accumulation, on basal accretion/melt rates and on flux divergence, are derived.

ISI Document Delivery No.: 445BS Times Cited: 33 Cited Reference Count: 61 Cited References: Angermann D, 2007, IAG SYMP, V130, P595 Bentley CR, 2004, MASS BALANCE OF THE CRYOSPHERE: OBSERVATIONS AND MODELLING OF CONTEMPORARY AND FUTURE CHANGES, P459, DOI 10.1017/CBO9780511535659.014 Chen JM, 2006, GEOPHYS RES LETT, V33, DOI 10.1029/2006GL026369 Chen JL, 2007, J GEODESY, V81, P237, DOI 10.1007/s00190-006-0055-7 Chen JL, 2008, EARTH PLANET SC LETT, V266, P140, DOI 10.1016/j.epsl.2007.10.057 Cullather RI, 1998, J CLIMATE, V11, P334, DOI 10.1175/1520-0442(1998)011<0334:SATVOA>2.0.CO;2 Davis CH, 2005, SCIENCE, V308, P1898, DOI 10.1126/science.1110662 Doll P, 2003, J HYDROL, V270, P105, DOI 10.1016/S0022-1694(02)00283-4 FARRELL WE, 1972, REV GEOPHYS SPACE GE, V10, P761, DOI 10.1029/RG010i003p00761 Fenoglio-Marc L, 2006, GEOPHYS RES LETT, V33, DOI 10.1029/2006GL026851 GFZ, 2007, REL NOT GFZ POTSD GR Han SC, 2005, GEOPHYS RES LETT, V32, DOI 10.1029/2005GL024296 Heiskanen W.A., 1967, PHYS GEODESY Helsen MM, 2008, SCIENCE, V320, P1626, DOI 10.1126/science.1153894 HORWATH M, 2007, P GRACE SCI TEAM M D HORWATH M, 2007, THESIS TU DRESDEN FA HORWATH M, 2007, P JOINT CHAMP GRACE Horwath M, 2006, GEOPHYS RES LETT, V33, DOI 10.1029/2005GL025550 Ilk KH, 2008, IAG SYMP, V132, P3 IVINS ER, 2006, ANTARCTIC SCI, V17, P3 Ivins ER, 2005, ANTARCT SCI, V17, P541, DOI 10.1017/S0954102005002968 Koch K.R, 1999, PARAMETER ESTIMATION Kusche J, 2007, J GEODESY, V81, P733, DOI 10.1007/s00190-007-0143-3 LEGRESY B, 2006, ESA SP, V16 LEGRESY B, 2007, P IUGG 24 GEN ASS 20 Llubes M, 2007, EARTH PLANET SC LETT, V260, P127, DOI 10.1016/j.epsl.2007.05.022 Luthcke SB, 2006, SCIENCE, V314, P1286, DOI 10.1126/science.1130776 LUTHCKE SB, 2007, P GRACE SCI TEAM M D Mayer-Gurr T, 2005, J GEODESY, V78, P462, DOI 10.1007/s00190-004-0413-2 Milly PCD, 2002, J HYDROMETEOROL, V3, P283, DOI 10.1175/1525-7541(2002)003<0283:GMOLWA>2.0.CO;2 Monaghan AJ, 2006, PHILOS T R SOC A, V364, P1683, DOI 10.1098/rsta.2006.1795 Moore P, 2008, J GEOPHYS RES-EARTH, V113, DOI 10.1029/2007JF000871 Peltier WR, 2004, ANNU REV EARTH PL SC, V32, P111, DOI 10.1146/annurev.earth.32.082503.144359 Peltier WR, 1998, REV GEOPHYS, V36, P603, DOI 10.1029/98RG02638 Ramillien G, 2006, GLOBAL PLANET CHANGE, V53, P198, DOI 10.1016/j.gloplacha.2006.06.003 Ramillien G, 2004, GEOPHYS J INT, V158, P813, DOI 10.1111/j.1365-246X.2004.02328.x Ramillien G, 2005, EARTH PLANET SC LETT, V235, P283, DOI [10.1016/j.epsl.2005.04.005, 10.1016/j.espl.2005.04.005] Reigber C, 2005, J GEODYN, V39, P1, DOI 10.1016/j.jog.2004.07.001 Rignot E, 2008, NAT GEOSCI, V1, P106, DOI 10.1038/ngeo102 Rodell M, 2004, B AM METEOROL SOC, V85, P381, DOI 10.1175/BAMS-85-3-381 Rowlands DD, 2002, J GEODESY, V76, P307, DOI 10.1007/s00190-002-0255-8 Sasgen I, 2007, EARTH PLANET SC LETT, V264, P391, DOI 10.1016/j.epsl.2007.09.029 Schmidt R, 2006, GLOBAL PLANET CHANGE, V50, P112, DOI 10.1016/j.gloplacha.2004.11.018 Schrama EJO, 2007, J GEOPHYS RES-SOL EA, V112, DOI 10.1029/2006JB004882 Seo KW, 2008, GEOPHYS J INT, V172, P41, DOI 10.1111/j.13...

Mertz Glacier, East Antarctica, is characterized by a 140 km long, 25 km wide floating ice tongue. In this paper, we combine a large number of remotely sensed datasets, including in situ global positioning system measurements, satellite radar altimetry, airborne radio-echo sounding and satellite synthetic aperture radar imagery and interferometry. These various datasets allow us to study the interaction of the ice tongue with the tides and currents. However, the inverse barometer effect needs to be applied to sea-level variations affecting the tongue. We find that the tide-induced currents exert a small lateral pressure on the tongue which, when integrated over the large surface of the tongue, induce a flexure of up to 2 m amplitude per day. Simple elastic modelling of the flexure confirms the observations and helps validate the boundary conditions necessary to explain different eastward and westward tongue deflections. In addition, the along-flow velocity of the tongue does vary daily from 1.9 to 6.8 m d À1 depending on the tidal current.When the current pushes the tongue toward the eastern boundary of the fjord, the tongue is retarded by the drag and the velocity decreases. The accumulated stress is released, allowing the tongue to flow very rapidly when the current pushes the tongue westward. These forcing and boundary conditions on the floating ice flow are important and must be taken into account when studying glacier discharge and calving.

No abstract