Glacial isostatic adjustment in Fennoscandia with a three-dimensional viscosity structure as an inverse problem

Glacial isostatic adjustment data are commonly used to invert for the radial viscosity structure of the mantle. However, the effects of lateral variations in mantle viscosity in such inversions are not yet accounted for. Here we analysed synthetic sea-level data for the Fennoscandian region, which are derived from a three-dimensional (3D) earth model with realistic lateral and vertical viscosity variations deduced from seismological and geological information. The inversion of the 3D synthetic data for a best-fitting 1D viscosity profile reveals that (i) lateral lithospheric thickness variations can be detected with 1D model predictions, if the data are grouped into regional subsets, (ii) combined lateral variations in lithospheric thickness and asthenospheric viscosity are not properly resolved with 1D model predictions, and (iii) the spatial and temporal distribution of observational data strongly affects the resulting 1D viscosity profile.