Estimation of ice shelf thinning derived from surface depression of an ice rumple

Abstract

Ice rumples are locally-grounded features of flowing ice shelves, elevated tens of meters above the surrounding surface. These features may significantly impact the dynamics of ice-shelf grounding lines, which are strongly related to shelf stability. However, the observation of such surface feature was hardly carried out due to its small size. The present study was designed to observe and better understand the transient nature of the ice rumple surface elevation. We used DLR's TanDEM-X and TerraSAR-X bi-static SAR data to construct high-resolution DEMs of the Thwaites ice shelf in West Antarctica from 2011 to 2013. During the period 2011-2013, the deformation maps showed the presence of an ice rumple and its recent fading. The ice rumple may have appeared sometime between the observations of a grounding line of the Thwaites glacier using Double-Differential Interferometric SAR (DDInSAR) in 1996 and 2011. The observed degradation of the ice rumple during 20112013 may be related to a loss of contact with the underlying bathymetry caused by the thinning of the ice shelf. We used a viscoelastic deformation model with a finite spherical pressure source to interpret the surface changes in terms of pressure changes at the bottom of the ice shelf. Global optimization allowed us to fit the model to the observed deformation map, producing reasonable estimates of the ice thickness at the center of the pressure source. Then, we calculated the thickness change using the estimated thicknesses from the viscoelastic deformation model. The thinning rate was much higher than that of previously reported levels, suggesting strong melting at a local pinning point. We conclude that combining the use of multiple high-resolution DEMs and the simple viscoelastic deformation model is feasible for observing and understanding the transient nature of small ice rumples, with implications for monitoring ice shelf stability.