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While time-variable satellite gravimetry by GRACE and GRACE-FO are directly sensitive to the mass balance of ice sheets, the mass signal caused by glacial isostatic adjustment (GIA) needs to be carefully separated to estimate the ice mass change from the observations. Instead of using forward GIA models this can be achieved by inverse estimation from present day observations, e.g. by combining satellite gravimetry, satellite altimetry and firn model outputs.

We quantify the sensitivity of an inverse GIA estimation approach over Antarctica to the choice of degree-1, C20 products, altimetry missions, time epoch, and uncertainties of firn processes. The latter are characterized empirically using differences between two regional climate model products. The integrated GIA mass change of the Antarctic Ice Sheet varies by 49 Gt a-1. Furthermore we present results applying this signal separation approach over the Greenland Ice Sheet. Our results demonstrate the limitations of combining observations of both geodetic sensors and firn model outputs, e.g. through the reconcilement of spatial resolution of data sets, uncertainties in low-degree harmonics, and firn/ice density assumptions for regional applications.

Moreover, we discuss the signal separation over ice-sheets as a parameter estimation problem with the prospect of global consistency. On that basis we will implement the estimation of the GIA signal from satellite observations in a global fingerprint inversion where it will be co-estimated with all parts of the global sea level budget.