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Accurate prediction of global sea-level rise requires that we understand the cause of recent, widespread and intensifying glacier acceleration along Antarctic ice-sheet coastal margins. Floating ice shelves buttress the flow of grounded tributary glaciers and their thickness and extent are particularly susceptible to changes in both climate and ocean forcing. Recent ice-shelf collapse led to retreat and acceleration of several glaciers on the Antarctic Peninsula. However, the extent and magnitude of ice-shelf thickness change, its causes and its link to glacier flow rate are so poorly understood that its influence on the future of the ice sheets cannot yet be predicted. Here we use satellite laser altimetry and modelling of the surface firn layer to reveal for the first time the circum-Antarctic pattern of ice-shelf thinning through increased basal melt. We deduce that this increased melt is the primary driver of Antarctic ice-sheet loss, through a reduction in buttressing of the adjacent ice sheet that has led to accelerated glacier flow. The highest thinning rates (~7 m/a) occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf. Wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of Antarctic ice shelves, through ocean upwelling in the Amundsen and Bellingshausen Seas and atmospheric warming on the Antarctic Peninsula. This implies that climate forcing through changing winds influences Antarctic Ice Sheet mass balance, and hence global sea-level, on annual to decadal timescales.

These data are ICESat GLA12 428 spaceborne laser altimetry data . We have modified the original ICESat data by applying an improved tide model (CATS2008a) as well as the recommended corrections for saturation and surface air pressure (the inverse barometer effect). We provide these data as 9 zipped ArcGIS shapefilesets, split by region.Each zip file contains ArcGIS shapefile sets of ICESat GLA12 428 data in polar stereographic projection grouped typically into 2-year periods denoted by the numbers after the region identifier, e.g. FRIS_67_PS indicates Filchner-Ronne data from 2006 and 2007.The shapefiles contain point data with the following attributes:Attribute Description- daysum: Serial date (decimal days)- year: Year of acquisition- float: Flag 1 or 0 where 1 indicates that the data fell within the domain of CATS2008a tide model. Data flagged 1 are over an ice shelf or ocean.- gain: ICESat processing gain value as defined here http://nsidc.org/data/docs/daac/glas_icesat_l1_l2_global_altimetry.gd.html- ret_energy: ICESat processing return energy value as defined here http://nsidc.org/data/docs/daac/glas_icesat_l1_l2_global_altimetry.gd.html- reflect: ICESat processing reflectivity value as defined here http://nsidc.org/data/docs/daac/glas_icesat_l1_l2_global_altimetry.gd.html- icesvar: ICESat processing waveform spread value as defined here http://nsidc.org/data/docs/daac/glas_icesat_l1_l2_global_altimetry.gd.html- GLASz: The original reported elevation relative to WGS84, as defined here http://nsidc.org/data/docs/daac/glas_icesat_l1_l2_global_altimetry.gd.html- z_corr_WGS: Elevation corrected for saturation and tides where floating (float flag 1).The parameters provided here allow our cloud filtering regime (or a variation) to be applied.

To check the possible presence of a subglacial lake in Isunnguata Sermia, West Greenland we collected two 5 km perpendicular profiles of seismic reflection data. The data revealed a 1.9 km by 450 m and 50 m thick lens-shaped body at the bottom of a subglacial 190 m deep trough, most likely consisting of stratified consolidated sediments possibly overlain by dilatant till. Liquid water seems present at the northern and eastern flank of the subglacial trough. The bed on the northern side of the trough consists of unconsolidated, possibly water containing sediments, whereas on the southern side it consists of more consolidated material.

Accurate prediction of global sea-level rise requires that we understand the cause of recent, widespread and intensifying glacier acceleration along Antarctic ice-sheet coastal margins. Floating ice shelves buttress the flow of grounded tributary glaciers and their thickness and extent are particularly susceptible to changes in both climate and ocean forcing. Recent ice-shelf collapse led to retreat and acceleration of several glaciers on the Antarctic Peninsula. However, the extent and magnitude of ice-shelf thickness change, its causes and its link to glacier flow rate are so poorly understood that its influence on the future of the ice sheets cannot yet be predicted. Here we use satellite laser altimetry and modelling of the surface firn layer to reveal for the first time the circum-Antarctic pattern of ice-shelf thinning through increased basal melt. We deduce that this increased melt is the primary driver of Antarctic ice-sheet loss, through a reduction in buttressing of the adjacent ice sheet that has led to accelerated glacier flow. The highest thinning rates (~7 m/a) occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf. Wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of Antarctic ice shelves, through ocean upwelling in the Amundsen and Bellingshausen Seas and atmospheric warming on the Antarctic Peninsula. This implies that climate forcing through changing winds influences Antarctic Ice Sheet mass balance, and hence global sea-level, on annual to decadal timescales.

Sub-ice shelf circulation and freezing/melting rates in ocean general circulation models depend critically on an accurate and consistent representation of cavity geometry. Existing global or pan-Antarctic data sets have turned out to contain various inconsistencies and inaccuracies. The goal of this work is to compile independent regional fields into a global data set. We use the S-2004 global 1-minute bathymetry as the backbone and add an improved version of the BEDMAP topography for an area that roughly coincides with the Antarctic continental shelf. Locations of the merging line have been carefully adjusted in order to get the best out of each data set. High-resolution gridded data for upper and lower ice surface topography and cavity geometry of the Amery, Fimbul, Filchner-Ronne, Larsen C and George VI Ice Shelves, and for Pine Island Glacier have been carefully merged into the ambient ice and ocean topographies. Multibeam survey data for bathymetry in the former Larsen B cavity and the southeastern Bellingshausen Sea have been obtained from the data centers of Alfred Wegener Institute (AWI), British Antarctic Survey (BAS) and Lamont-Doherty Earth Observatory (LDEO), gridded, and again carefully merged into the existing bathymetry map. The global 1-minute dataset (RTopo-1 Version 1.0.5) has been split into two NetCDF files. The first contains digital maps for global bedrock topography, ice bottom topography, and surface elevation. The second contains the auxiliary maps for data sources and the surface type mask. A regional subset that covers all variables for the region south of 50 deg S is also available in NetCDF format. Datasets for the locations of grounding and coast lines are provided in ASCII format. Supplement to: Timmermann, Ralph; Le Brocq, Anne M; Deen, Tara J; Domack, Eugene W; Dutrieux, Pierre; Galton-Fenzi, Ben; Hellmer, Hartmut H; Humbert, Angelika; Jansen, Daniela; Jenkins, Adrian; Lambrecht, Astrid; Makinson, Keith; Niederjasper, Fred; Nitsche, Frank-Oliver; Nøst, Ole Anders; Smedsrud, Lars Henrik; Smith, Walter (2010): A consistent dataset of Antarctic ice sheet topography, cavity geometry, and global bathymetry. Earth System Science Data, 2(2), 261-273 To enable communication with RTopo-1 users, the author would appreciate a notification when using the dataset or errors are found.