Regional Antarctic Ice Sheet Acceleration from Satellite Gravimetry

The Antarctic Ice Sheet is subject to increasing atmospheric and ocean temperatures due to changes in large-scale circulation patterns in the Southern Hemisphere. These climatological changes vary regionally and have the potential to trigger a range of processes leading to ice sheet disintegration and global sea level rise. Currently, significant ice mass loss and acceleration of ice flow are observed in the Amundsen Sea Embayment in West Antarctica. In East Antarctica, such processes have so far been spatially restricted to smaller regions, such as to glaciers feeding the Amery Ice Shelf. The present behavior of the ice is critical to understand its associated contribution to future global sea level rise. In this context, we aim to quantify the ice-dynamic acceleration in Antarctica based on differencing GRACE/GRACE-FO and ERA5-SMB for the period 2002 to 2020. This indirect method presents an alternative to estimates that quantify ice stream acceleration based on satellite observations of the surface-ice velocity, and is justified by the excellent agreement of GRACE/GRACE-FO and SMB at interannual time scales. Our estimate identifies the Amundsen Sea Embayment and Bellingshausen Sea region in West Antarctica as the dominant source of dynamic losses and potential instability, in-line with direct observations. We find that uncertainties of the SMB estimate limit the accuracy of our discharge estimate most, compared to other uncertainty sources. The uncertainties in our estimate can be reduced by further improving regional climate models. In conclusion, we provide an alternative to previous dynamic acceleration methods that can be considered for future assessments on the state of the Antarctic Ice Sheet. Including acceleration of the ice sheet mass loss in the projection of sea level rise results in a contribution more than twice that of linear extrapolation to 2100.