Determination of mass variation in Northern Europe from GRACE data

Abstract

In Northern Europe the region of Fennoscandia is characterised by present-day uplift caused by glacial isostatic adjustment (GIA). The uplift effect reaches up to 11 mm/year at the Earth’s surface. This effect can be observed geometrically, e.g. by GPS or spirit levelling, and gravitationally by absolute gravimetry. A new challenge is the determination of the GIA-induced gravity changes by the satellite mission GRACE. During the mission duration of GRACE (more than five years), a temporal gravity change of about 100 nm/$s^2$ is expected in the centre of the Fennoscandian land uplift area (the Bothnian Bay). The configuration of GRACE is basically suited to determine this magnitude of variation. But the GRACE observations contain the integral signal of various geophysical processes such as atmospheric, oceanic and hydrological effects which may conceal the uplift signal. In this study, we determine secular and periodic gravity changes in Fennoscandia from the GRACE monthly solutions as provided by CSR, University of Texas, and Geoforschungszentrum Potsdam (GFZ) for the first 4 years of the GRACE mission. We compare the resulting variations with hydrological models and match the GRACE derived signals with those obtained from a simple uplift model based on geophysical predictions.