Modelling Sea-Level Fingerprints of Glaciated Regions with Low Mantle Viscosity

Abstract

Abstract. Sea-level fingerprints define the spatially varying relative sea-level response to changes in grounded ice distribution. These fingerprints are a key component in generating regional sea-level projections. Calculation of these fingerprints is commonly based on the assumption that the isostatic response of the Earth is dominantly elastic on century time scales. While this assumption is accurate for regions underlain my mantle material with viscosity close to that of global average estimates, recent work focusing on the Antarctic region has shown that this assumption can led to significant error when the viscosity departs significantly from typical average values. Here we test this assumption for fingerprints associated with glaciers and ice caps. We compare output from a (1D) elastic Earth model to that of a 3D viscoelastic model which includes low viscosity mantle in three glaciated regions: Alaska, southwestern Canada and the southern Andes (Randolph Glacier Inventory (RGI) regions 1, 2 & 17, respectively). This comparison indicates that the error incurred by ignoring the non-elastic response is generally less than 1 cm over the 21st century but can reach magnitudes of up to several 10s of centimetres in low viscosity areas. This error can have large spatial gradients where crustal uplift in ice covered (or previously ice covered) areas changes into subsidence when moving away from the loading centres to areas peripheral to the mass loss. The existence of these large gradients indicates the need for loading models with high spatial resolution to accurately simulate sea-level fingerprints in these regions. We conclude that sea-level projections for Alaska, southwestern Canada and the southern Andes should not be based on elastic Earth models.