Satellite data reveal details of glacial isostatic adjustment in the Amundsen Sea Embayment, West Antarctica

Abstract. The instability of the West Antarctic ice sheet (WAIS) is a tipping element in the climate system and it is mainly dictated by changes in the ice flow behavior of the outflow glaciers in the Amundsen Sea Embayment (ASE). Recent studies postulated that vertical uplift of bedrock can delay the collapse of glaciers in this region. In West Antarctica, bedrock motion is largely caused by a fast viscoelastic response of the upper mantle to changes in ice loads during the last centuries. This glacial isostatic adjustment (GIA) effect is poorly understood so far, since Earth's rheology and the ice-loading history are both subject to large uncertainties in simulations. Moreover, results from data-driven approaches have not yet resolved GIA at a sufficient spatial resolution. We present a data-driven GIA estimate, based on data from GRACE/GRACE-FO, CryoSat-2 altimetry, regional climate modelling, and firn modelling, that is the first to agree with independent GNSS-derived vertical velocities in West Antarctica. Our data combination yields a maximum GIA bedrock-motion rate of 43 ± 7 mm a^-1 in the Thwaites Glacier region and agrees within uncertainties of the GNSS-derived rate. The data-driven present-day GIA result may be used in future simulation runs to quantify a potential delay of the collapse of the West Antarctic ice sheet due to the stabilization effects induced by GIA. Furthermore it may be used for testing rheological models with a low upper-mantle viscosity in conjunction with centennial loading histories.