Mapping the Antarctic Grounding Zone from ICESat-2 Laser Altimetry

Abstract:

The grounding zone is the transition region between the fully grounded ice sheet and the freely floating ice shelf. Knowledge of its position and dynamics are important for mass budget assessments, ice sheet instability monitoring and numerical modelling. The grounding zone is typically mapped from the landward limit of tidal flexure (Point F) and the inshore limit of hydrostatic equilibrium (Point H) using different satellite techniques, such as differential synthetic aperture radar interferometry (DInSAR), ICESat laser altimetry repeat track analysis and CryoSat-2 radar altimetry pseudo crossover analysis. However, these methods have been limited by either spatial or temporal coverage. Launched on 15 September 2018, the ICESat-2 satellite offers the potential to map the grounding zone with high spatio-temporal coverage and accuracy, which can advance our understanding of the structure and dynamics of the Antarctic grounding zone. Here we present a new, fully automated method of mapping Points F and H using a combination of repeat track and crossover analyses of ICESat-2 laser altimeter tracks. The approach was tested on Larsen C Ice Shelf using a ten-month period of ICESat-2 data. Our method recovers a nearly nine-fold increase in the number of grounding zone observed by ICESat. The locations of ICESat-2-derived Point F show good agreement with previous estimates from DInSAR observations, with the mean absolute separation and the standard deviation of 0.39 km and 0.32 km, respectively. Our method also records the mean tidal amplitude, which can be used to study short-term grounding line migration due to ocean tides as more repeat cycles become available. The method is being applied to the whole of the Antarctic continent, and our results demonstrate the improvements in efficiency, sampling density and accuracy that can be achieved with ICESat-2.