Spatio-Temporal Variability of Antarctic Ice Shelf Elevations from Multi-Mission Satellite Radar Altimetry

Antarctica's ice shelves exert a significant dynamic constraint on the flow of ice from the grounded ice sheet to the ocean, and hence on changes in global sea level. Recently, it has been shown that ice shelves are not only susceptible, but can also respond rapidly, to changing atmospheric and oceanic conditions; however, our understanding of how they respond to these changes is still rudimentary. Much of the present knowledge of our understanding of how ice-shelf processes couple ice sheet changes to climate variability comes from analyses of trends in surface elevation change (dh/dt) derived from satellite altimetry data. However, these analyses are usually based on short records from single satellite missions and generally fail to identify neither the significant interannual-to-decadal variability that is present nor the underlying long-term trend. To avoid these limitations, we use improved procedures to integrate data from multiple satellite radar altimeter missions (Geosat, ERS-1, ERS-2, GFO, and Envisat) to derive reliable long-term (>20 years) quasi-continuous records of surface elevation changes for almost all of Antarctica's ice shelf area. We show that there is considerable variability in the elevation change signal on the ice shelves in both space and time. We also show that trends on short time intervals are not representative of the the 20-year trend. By mapping dh/dt in both space and time and analyzing dh time series, we are able to identify spatio-temporal modes of coherent variability in Antarctic ice shelf elevation. Comparison of these modes with known climate indices and observed changes in oceanic and atmospheric conditions will allow us to determine whether the dominant cause of ice shelf change is related to climate or intrinsic ice sheet variability.