Improvement of Basal Conditions in Wilkes Land, East Antarctica, Using Data Assimilation

Abstract:

The current global warming seems to have direct consequences on ice-sheet mass loss. Reproducing the responsible mechanisms and forecasting the potential ice-sheets contribution to 21st century sea level rise is one of the major challenges in ice-sheet and ice flow modelling. Such short term projections are very sensitive to model initial state which is usually build from field observations. However, some parameters are not observable on the field, such as the basal drag at the interface between the ice-sheet and the bedrock. Data assimilation methods are widely used to constrain this parameter, using ice surface velocities. However, other parameters remain poorly known, especially the bedrock elevation which is only known along fight tracks often distant from several tens of kilometres from each other. These remaining uncertainties lead to ice flux divergence anomalies affecting the free surface evolution and consequently the model projections.

In this study, we developed two different assimilation algorithms to better constrain both basal drag and bedrock elevation parameters in the Wilkes Land region, East Antarctica. These two algorithms have been implemented in Elmer/Ice and tested beforehand in a twin experiment showing a clear improvement of both parameters knowledge. The application of these algorithms to Wilkes Land reduces the uncertainty on basal conditions in this region showing more accuracy through below outlet glaciers when compared to usually used DEM of bedrock. Reconstruction of both bedrock elevation and basal drag significantly decreases ice flux divergence anomalies and allows to better constrain future contribution to sea level rise.