Glacial isostatic adjustment of Scandinavia and northwestern Europe and the radial viscosity structure of the Earth's mantle

Abstract

During the last glacial maximum (LGM), large ice sheets covered Scandinavia, the Barents Sea and the Northern British Isles. Subsequent to the LGM, the ice sheets disappeared and the solid Earth readjusted towards a new isostatic equilibrium. The glacial isostatic adjustment process is documented in numerous observations, for example, palaeoshorelines covering the last deglaciation phase, and ongoing crustal deformations monitored by GPS stations, for example, the BIFROST project. In this study, we use palaeoshoreline data from Scandinavia, the Barents Sea and northwestern Europe (NW) as well as radial crustal velocities from the BIFROST campaign to infer the radial viscosity structure of the Earth's mantle underneath Scandinavia and NW Europe. A global inverse procedure based on the Neighbourhood Algorithm allows us to explore the hypothesis of a low-viscosity zone in the upper mantle, which has been proposed in the literature. Our results indicate a low-viscosity zone underneath the Barents Sea, with viscosities between 1019 and 1020 Pa s in a depth interval of 160-200 km. No such low-viscosity zone is found underneath Scandinavia, and no clear indication for such a zone underneath NW Europe. The thickness of the rheological lithosphere increases from 60 to 70 km underneath NW Europe and the Barents Sea towards values exceeding 120 km underneath Scandinavia.