Big Ice

International Polar Year Collaborative Research: Constraining the Mass-Balance Deficit of the Amundsen Coast's glaciers

Summary

The West Antarctic Ice Sheet is losing mass, in large part because of rapid thinning of the Amundsen Coast glaciers. Estimates of Amundsen Coast thinning range from 46 to 86 Gtons/yr, with the 40-Gton/yr difference in estimates being nearly equivalent to the combined outflow of Mercer, Whillans, Kamb, and Bindschadler ice streams (46 Gtons/yr). While warmer ocean temperatures may drive this thinning, the large uncertainties in the current mass balance estimates largely arise from poor knowledge of the snowfall accumulation over Pine Island, Thwaites, Smith, Pope and Kohler glaciers. This International Polar Year project is determining accumulation rates in this vastly under-sampled region to remove the large uncertainties in current mass balance estimates.

The first year (2009/10) field effort will collect a series of airborne accumulation radar profiles to map internal layers and ice thickness. Near-surface radar layers will be dated using age-depth profiles derived from shallow ice cores that will be drilled during the second season (2010/11). The combination of these data will yield multiple transects of decadal-scale average accumulation rates extending back through the last century. Spatially complete, annually-resolved maps of accumulation will be obtained from these data using EOF-based interpolation schemes guided by weather hindcast results (i.e. NCEP, ECMWF, Polar MM5 output). Comparison of the basin-averaged accumulation with ice discharge determined using Interferometric Synthetic Aperture Radar (InSAR) velocity data will provide improved mass-balance estimates. Study of changes in flow speed will produce a record of mass balance over the last three decades. Analysis of the satellite altimeter record in conjunction with annual accumulation estimates also will provide estimates of changes and variability in mass balance. Finally, these data will constrain a modeling effort to determine how coastal changes propagate inland, to allow better prediction of future change.