TC The Cryosphere TC The Cryosphere 1994-0424 Copernicus Publications Göttingen, Germany 10.5194/tc-5-569-2011 Getting around Antarctica: new high-resolution mappings of the grounded and freely-floating boundaries of the Antarctic ice sheet created for the International Polar Year Bindschadler R. 1 Choi H. 2 Wichlacz A. 2 Bingham R. 3 Bohlander J. 4 Brunt K. 5 Corr H. 6 Drews R. 7 Fricker H. 8 Hall M. 9 Hindmarsh R. 6 Kohler J. 10 Padman L. 11 Rack W. 12 Rotschky G. 10 Urbini S. 13 Vornberger P. 2 Young N. 14 Code 614.0, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA SAIC, NASA Goddard Space Flight Center, Greenbelt MD 20771, USA School of Geosciences, University of Aberdeen, Aberdeen, AB24 3FX, UK National Snow and Ice Data Center, University of Colorado, Boulder CO 80309-0449, USA Code 614.1, NASA Goddard Space Flight Center, Greenbelt MD 20771, USA British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK Alfred Wegener Institut for Polar and Marine Research, Postfach 12 01 61, 27515 Bremerhaven, Germany Scripps Institute of Oceanography, University of California at San Diego, 9500 Giman Drive, La Jolla CA 92093, USA Climate Change Institute, University of Maine, Orono ME 04469, USA Norwegian Polar Institute, Polar Environmental Centre, 9296 Tromso, Norway Earth and Space Research (ESR), 3350 SW Cascade Ave., Corvallis, OR 97333-1536, USA Gateway Antarctica, University of Canterbury, Private Bag, Christchurch 8140, New Zealand Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, 605, 00143 Rome, Italy Australian Antarctic Division, University of Tasmania, Kingston, Tasmania 7050, Australia 18 07 2011 5 3 569 588 Copyright: © 2011 R. Bindschadler et al. 2011 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://tc.copernicus.org/articles/5/569/2011/tc-5-569-2011.html The full text article is available as a PDF file from https://tc.copernicus.org/articles/5/569/2011/tc-5-569-2011.pdf

Two ice-dynamic transitions of the Antarctic ice sheet – the boundary of grounded ice features and the freely-floating boundary – are mapped at 15-m resolution by participants of the International Polar Year project ASAID using customized software combining Landsat-7 imagery and ICESat/GLAS laser altimetry. The grounded ice boundary is 53 610 km long; 74 % abuts to floating ice shelves or outlet glaciers, 19 % is adjacent to open or sea-ice covered ocean, and 7 % of the boundary ice terminates on land. The freely-floating boundary, called here the hydrostatic line, is the most landward position on ice shelves that expresses the full amplitude of oscillating ocean tides. It extends 27 521 km and is discontinuous. Positional (one-sigma) accuracies of the grounded ice boundary vary an order of magnitude ranging from ±52 m for the land and open-ocean terminating segments to ±502 m for the outlet glaciers. The hydrostatic line is less well positioned with errors over 2 km. Elevations along each line are selected from 6 candidate digital elevation models based on their agreement with ICESat elevation values and surface shape inferred from the Landsat imagery. Elevations along the hydrostatic line are converted to ice thicknesses by applying a firn-correction factor and a flotation criterion. BEDMAP-compiled data and other airborne data are compared to the ASAID elevations and ice thicknesses to arrive at quantitative (one-sigma) uncertainties of surface elevations of ±3.6, ±9.6, ±11.4, ±30 and ±100 m for five ASAID-assigned confidence levels. Over one-half of the surface elevations along the grounded ice boundary and over one-third of the hydrostatic line elevations are ranked in the highest two confidence categories. A comparison between ASAID-calculated ice shelf thicknesses and BEDMAP-compiled data indicate a thin-ice bias of 41.2 ± 71.3 m for the ASAID ice thicknesses. The relationship between the seaward offset of the hydrostatic line from the grounded ice boundary only weakly matches a prediction based on beam theory. The mapped products along with the customized software to generate them and a variety of intermediate products are available from the National Snow and Ice Data Center.

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