TC The Cryosphere TC The Cryosphere 1994-0424 Copernicus Publications Göttingen, Germany 10.5194/tc-8-1375-2014 Constraining the recent mass balance of Pine Island and Thwaites glaciers, West Antarctica, with airborne observations of snow accumulation Medley B. https://orcid.org/0000-0002-9838-3665 1 2 Joughin I. 2 Smith B. E. https://orcid.org/0000-0002-1118-7865 2 Das S. B. 3 Steig E. J. https://orcid.org/0000-0002-8191-5549 1 4 Conway H. https://orcid.org/0000-0003-4634-3474 1 Gogineni S. 5 Lewis C. 5 Criscitiello A. S. https://orcid.org/0000-0002-8741-709X 3 6 McConnell J. R. https://orcid.org/0000-0001-9051-5240 7 van den Broeke M. R. https://orcid.org/0000-0003-4662-7565 8 Lenaerts J. T. M. https://orcid.org/0000-0003-4309-4011 8 Bromwich D. H. 9 Nicolas J. P. 9 Leuschen C. 5 Earth and Space Sciences, University of Washington, Seattle, WA, USA Polar Science Center, Applied Physics Lab, University of Washington, Seattle, WA, USA Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, USA Quaternary Research Center, University of Washington, Seattle, WA, USA Center for Remote Sensing of Ice Sheets, University of Kansas, Lawrence, KS, USA MIT/WHOI Joint Program in Oceanography/Applied Ocean Sciences and Engineering, Woods Hole Oceanographic Institution, Woods Hole, MA, USA Desert Research Institute, Nevada System of Higher Education, Reno, NV, USA Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, the Netherlands Polar Meteorology Group, Byrd Polar Research Center, and Atmospheric Sciences Program, Department of Geography, The Ohio State University, Columbus, OH, USA 31 07 2014 8 4 1375 1392 Copyright: © 2014 B. Medley et al. 2014 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/8/1375/2014/tc-8-1375-2014.html The full text article is available as a PDF file from https://tc.copernicus.org/articles/8/1375/2014/tc-8-1375-2014.pdf

In Antarctica, uncertainties in mass input and output translate directly into uncertainty in glacier mass balance and thus in sea level impact. While remotely sensed observations of ice velocity and thickness over the major outlet glaciers have improved our understanding of ice loss to the ocean, snow accumulation over the vast Antarctic interior remains largely unmeasured. Here, we show that an airborne radar system, combined with ice-core glaciochemical analysis, provide the means necessary to measure the accumulation rate at the catchment-scale along the Amundsen Sea coast of West Antarctica. We used along-track radar-derived accumulation to generate a 1985–2009 average accumulation grid that resolves moderate- to large-scale features (>25 km) over the Pine Island–Thwaites glacier drainage system. Comparisons with estimates from atmospheric models and gridded climatologies generally show our results as having less accumulation in the lower-elevation coastal zone but greater accumulation in the interior. Ice discharge, measured over discrete time intervals between 1994 and 2012, combined with our catchment-wide accumulation rates provide an 18-year mass balance history for the sector. While Thwaites Glacier lost the most ice in the mid-1990s, Pine Island Glacier's losses increased substantially by 2006, overtaking Thwaites as the largest regional contributor to sea-level rise. The trend of increasing discharge for both glaciers, however, appears to have leveled off since 2008.

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