In search of laterally heterogeneous viscosity models of glacial isostatic adjustment with the ICE-6G_C global ice history model

Most models of glacial isostatic adjustment (GIA) assume that the Earth is laterally homogeneous. However, seismic and geological observations clearly show that the Earth's mantle is laterally heterogeneous. Previous studies of GIA with lateral heterogeneity mostly focused on its effect or sensitivity on GIA predictions, and it is not clear to what extent can lateral heterogeneity solve the misfits between GIA predictions and observations. Our aim is to search for the best 3-D viscosity models that can simultaneously fit the global relative sea level data, the peak uplift rates (u-dot from the Global Navigation Satellite System) and peak gravity-rate-of-change (g-dot from the Gravity Recovery And Climate Experiment satellite mission) in Laurentia and Fennoscandia. However, the search is dependent on the ice and viscosity model inputs-the latter depends on the background viscosity and the seismic tomography models used. In this paper, the ICE-6G_C ice model, with Bunge and Grand's seismic tomography model and background viscosity models close to VM5 will be assumed. A coupled Laplace-finite element method is used to compute gravitationally self-consistent sea level change with time-dependent coastlines and rotational feedback in addition to changes in deformation, gravity and the state of stress. Several laterally heterogeneous models are found to fit the global sea level data better than laterally homogeneous models. Two of these laterally heterogeneous models also fit the observed peak g-dot and u-dot rates in Laurentia simultaneously. However, even with the introduction of lateral heterogeneity, no model that is able to fit the present-day g-dot and uplift rate data in Fennoscandia has been found. Therefore, either the ice history of ICE-6G_C in Fennoscandia and Barents Sea needs some modifications or the sublitho-spheric property/non-thermal effect underneath northern Europe must be different from that underneath Laurentia.