Accurate glacial isostatic adjustment (GIA) models are required for correcting measurements of mass change in Antarctica and for improving knowledge of the sub-surface, especially in areas of large current ice loss such as the Amundsen Sea Embayment (ASE). Regionally, seismic and gravity data suggests lateral differences in viscosity (3D). Furthermore, mantle flow laws allow for a stress-dependent effective viscosity which changes over time (3D-s). In this study we investigate whether models with 3D/3D-s have significant effects on the uplift in the region. We use a finite element model with composite rheology consisting of diffusion and dislocation creep, forced by an ice deglaciation model starting in 1900. We use its uplift predictions as synthetic observations to test the performance of 1D model inversion in the presence of viscosity variations. Stress-dependent rheology results in lower viscosity beneath the load and a more localized uplift pattern. We demonstrate that the background stress from earlier ice load changes can both increase or decrease the influence of stress-induced effective viscosity changes. For the ASE, fitting 1D models to 3D model uplift results in a best fitting model with viscosity that represents the average of a large area, while for 3D-s rheology, local viscosity is more influential. 1D models are statistically indistinguishable from 3D/3D-s viscosity with current GPS stations. However, 3D and 3D-s models should be taken into account when accurate uplift and gravity rate patterns are needed, as uplift can differ up to 45% compared to 1D models in between existing GPS stations.

In this study we combine seismological and petrological models with satellite gravity gradient data to obtain the thermal and compositional structure of the Antarctic lithosphere. Our results indicate that Antarctica is largely in isostatic equilibrium, although notable anomalies exist. A new Antarctic Moho depth map is derived that fits the satellite gravity gradient anomaly field and is in good agreement with independent seismic estimates. It exhibits detailed crustal thickness variations also in areas of East Antarctica that are poorly explored due to sparse seismic station coverage. The thickness of the lithosphere in our model is in general agreement with seismological estimates, confirming the marked contrast between West Antarctica (<100 km) and East Antarctica (up to 260 km). Finally, we assess the implications of the temperature distribution in our model for mantle viscosities and glacial isostatic adjustment. The upper mantle temperatures we model are lower than obtained from previous seismic velocity studies. This results in higher estimated viscosities underneath West Antarctica. When combined with present-day uplift rates from GPS, a bulk dry upper mantle rheology appears permissible.

In the ESA Support to Science Element GOCE+Antarctica, we study the influence of the lithospheric structure on estimates of GIA. From recent geophysical, especially seismological, studies new insights on the deep structure of the Antarctic continents are available. However, the seismological models differ in resolution and do not provide a consistent image of the lithosphere. This is critical in analysing the feedback between the lithosphere and glacial loading or unloading. To reduce such ambiguities, we combine the latest seismological models with gravity gradient data derived from the GOCE satellite mission. The gradients are in particular sensitive to the geometry and density variations of the main lithospheric layers, i.e. ice and sediment thickness, the Moho depth and the temperature and composition of the upper mantle. Initial results indicate that differences exist in the mode of compensation for West and East Antarctica related to different mantle properties. The impact of an improved lithospheric model on GIA modelling is estimated by testing the sensitivity to the new temperature and density distribution and by comparing 1D and 3D viscosity models, especially in areas of low viscosity as in the Amundsen Sea sector.