Vertical Land Motion Determined by Satellite Altimetry and Tide-Gauge Data in Fennoscandia

Present-day vertical land motion in Fennoscandia reaches values up to around 1 cm/year. The primary cause of the uplift is Glacial Isostatic Adjustment , i.e., the ongoing response of the Earth and the ocean to the melting of late-Pleistocene ice sheets. Additional signals caused, e.g., by the elastic rebound from contemporary melting of glaciers, tectonics, and hydrology contribute less. The relation between relative sea-level change (Sdot), change in the sea surface height (Ndot), and vertical land motion (Udot) is given by Sdot = Ndot – Udot. All three
quantities can be observed directly by means of tide gauges, satellite altimetry, and Global Navigation Satellite Systems (GNSS), respectively. Alternatively, Udot may be estimated from observations of Sdot and Ndot. In the present study, we combine satellite altimetry and tide-gauge data to determine vertical land motion at tide gauges in Fennoscandia. Considering the discrepancies in the spatial sampling of conventional altimeters, where the mean distance between conventional altimetry sites and tide gauges along the Norwegian coast is 53 km, we take advantage of the CryoSat-2 geodetic orbit. The European Space Agency's CryoSat-2 satellite is the first to carry a synthetic aperture interferometric radar altimeter, resulting in
higher range precision and along-track resolution. This allows us to get closer to the coast, with observations of the sea surface at the tide-gauge stations as a main benefit when combining altimetry and tide-gauge data. In turn, we compare the estimated vertical land motion rates with the independent semi-empirical land uplift model NKG2016LU for the Nordic-Baltic region, based on GNSS and levelling.