abstract.txt

Antarctica's ice shelves, the floating extensions of the ice sheet, exert an important dynamic constraint on the flow of ice from the grounded ice sheet to the ocean, and hence on changes in global sea level. Thinning of an ice shelf reduces its ability to restrain the ice discharge from the grounded ice-sheet interior. Since the ice sheet responds to perturbations in the ice shelves, predicting sea-level rise requires that we understand how ice-shelf processes couple ice-sheet changes to climate variability. Yet our understanding of these processes is still too rudimentary to allow prediction of ice-sheet change under projected future climate states. In this dissertation, we present improved procedures to construct 18-year time series of ice-shelf height around the entire Antarctic continent, merging data from multiple overlapping satellite radar altimeter missions (ERS-1, ERS-2, and Envisat). We introduce improved procedures for trend analysis, and propose a more accurate alternative for uncertainty estimation to the standard error propagation approach. We analyze ice-shelf height variability using orthogonal-component decomposition of multivariate time series, spectral estimation and background-noise statistical tests. The derived data set and method allow us to estimate, reliably, the temporal progression and spatial structure of changes in ice-shelf height and volume in Antarctica between 1994 and 2012. The results reveal that, overall, Antarctic ice-shelf volume loss is accelerating; and significant interannual variability in the Amundsen Sea ice shelves is strongly correlated with the low-frequency mode of El Ni\~no-Southern Oscillation. These findings may ultimately allow us to improve our models for predicting future ice loss.