Estimating Antarctic Grounding Zone Ice Flexure with ICESat-2 Data

Antarctic ice shelves, the floating extensions of the Antarctic Ice Sheet, occupy 75% of the Antarctic coastline and account for about 10% of the total area of meteoric ice. Changes in extent, thickness and rheology of ice shelves have profound effects on grounded-ice loss that leads to sea level rise. The ice shelves are partitioned from the grounded ice sheet by grounding zones that are typically a few ice thicknesses wide. Within these zones, ice flexure occurs as the ice transitions from fully grounded to floating in hydrostatic balance with the ocean. Variability of ocean height due to ocean tides, inverse barometer effect, ocean circulation, and long-term sea level change drives time-varying flexural response of ice in the grounding zones, which can be directly measured using satellite altimeters and synthetic aperture radar. Here, we use measurements from the Ice Cloud and land Elevation Satellite-2 (ICESat-2), NASA's next generation laser altimeter, in combination with tidal predictions from the Circum-Antarctic Tidal Simulation (CATS2008) model, to estimate the local flexure of Antarctic grounding zones. Although the tidal signal is highly aliased due to the 91-day repeat cycle and does not resolve all major tidal constituents, we show that the offshore and onshore edges of the flexural boundary can be identified, and the ratio of ice shelf surface amplitude to hydrostatic amplitude can be mapped. These estimates of ice-shelf flexure will help inform and extend the next generation of ocean tide models under ice shelves into the grounding zones. We demonstrate how flexure maps can help improve the ICESat-2 gridded land-ice height products (ATL14/15) by providing empirical corrections to existing tide models used in evaluating ice sheet surface height changes over the ICESat-2 mission.