A global inversion for sea-level contributions from satellite data: towards improving Antarctica's representation

Variations in sea level are a globally comprehensively measurable indicator of the effect of climate change on the Earth system. Satellite geodesy provides data with global coverage to analyze sea level changes in space and time, but also to investigate the individual contributions to sea level from the subsystems oceans, continental hydrology, glaciers, ice sheets, and the solid Earth. Particularly valuable for this purpose are time-variable satellite gravity, realized by the GRACE and GRACE-FO missions, and satellite altimetry over the oceans, realized, e.g., by the Jason-1/-2/-3 and Sentinel-6 reference missions. However, previous studies show that the uncertainty of the estimated Antarctic Ice Sheet’s contribution to sea level remains large, primarily due to errors in the glacial isostatic adjustment (GIA) correction. We use a global fingerprint inversion method that evaluates GRACE and ocean altimetry data in a globally consistent framework and enables the quantification of individual contributions to sea level on a monthly basis on global grids. The inversion is additionally supplemented by observations from Argo floats. The parametrization of the contributions from steric effects, ice sheets, glaciers, hydrology, and GIA are realized by time-invariant sea-level fingerprints obtained from a priori information. This includes, e.g., the locations of mass changes or statistically obtained information from geophysical model simulations. In a methodological advancement of the inversion method, we have implemented a new parametrization of the ice mass changes (IMC) of the Antarctic ice sheet. Previously, IMC and corresponding sea level change has been estimated only on basin level for 27 large ice catchment areas, so-called drainage basins. However, this coarse parametrization of IMC prevents the inversion method from better resolving errors in the GIA correction in upcoming inversion implementations. We have therefore introduced a high-resolution parametrization based on individual grid points with a resolution of up to 50 km, resulting in up to 4755 Antarctic mass balance parameters to be estimated in a globally consistent way. In order to solve this inverse problem, we introduced altimetry over ice sheets as an additional observation at a 10 km spatial and a monthly temporal resolution. We present and discuss results from different variants of parametrization of IMC and different variants of implementation of ice altimetry observations. This methodological advancement presented here is a necessary step towards minimizing GIA-related errors when determining the sea level budget utilizing this global framework in the future.