Analysis of Glacial Isostatic Adjustment in Fennoscandia: Comparison of Model Results and Observational Evidence

摘要

Glacial isostatic adjustment is the ongoing response of the Earth and the ocean to the melting of Pleistocene ice sheets. This unloading initiated an uplift of the crust close to the centers of former ice sheets. Today, vertical surface velocities in Fennoscandia reach values up to around 1 cm/year and are dominated by post-glacial rebound, while additional signals caused, e.g., by the elastic rebound from contemporary melting of glaciers, tectonic processes or hydrological loading contribute less. Using ice histories from the ICE-x series (specifically ICE-5G and ICE6G_C) along with the related rheological profiles (VMx), we predict vertical velocity fields as well as time series of relative sea level change (RSL). Computations are performed with the open source sea level equation solver (SELEN) and validated against external data, namely the semi-empirical land-uplift model NKG2016LU_abs (representing present-day vertical crustal velocities) and geological RSL reconstructions. Because NKG2016LU_abs fits the actual vertical velocity field best, we also use the underlying rheological profiles as alternatives to the VMx profiles. In order to quantify the significance of some of the assumptions and approximations in SELEN, we compare our processing results with published grids of vertical velocities derived by other authors with other software solutions.In general, all software solutions agree on a ～1 mm/yr level with NKG2016LU_abs in terms of standard deviations of differences. The agreement between predictions from SELEN and external data is highly dependent on the implemented ice model. We find that all vertical velocity fields as well as RSL predictions calculated with ICE6G_C show a considerably better fit to NKG2016LU_abs and RSL data than model results of ICE-5G, which confirms the improvement within the ICE-x series. For both ice models, predictions of present-day vertical velocities based on VMx rheological profiles agree better with observations (NKG2016LU_abs) than predictions based on NKG rheologies. Considering predictions of RSL between the last glacial maximum and present day, the opposite holds true. Here, predictions with NKG rheologies, on average, fit better to RSL data than predictions with VMx rheologies.