Dynamic mantle support beneath West Antarctica's Ice Sheets: Insights from geophysical and geochemical observations

Transient mantle processes generate and maintain topographic variations which cannot be accounted for by crustal isostatic effects.  Accurately constraining the importance of dynamic topography across Antarctica will yield valuable insights into spatial and temporal patterns of mantle convection that inform studies of key boundary conditions for ice sheet models, such as heat flux and palaeotopography. Global studies largely neglect Antarctica because of complications associated with ice cover. In contrast, regional studies tend to oversimplify the problem by exploiting gridded datasets that ignore crustal density variations. Residual elevations, calculated by isolating and removing isostatic contributions to observed topography, enable the amplitude and wavelength of dynamic support to be gauged. Here, the results of analysing legacy (i.e. refraction) and modern (i.e. wide-angle) seismic experiments, onshore receiver functions, as well as a regional shear-wave crustal tomographic model are presented. In this way, a comprehensive suite of spot measurements (n = 195) across West Antarctica are calculated which, in conjunction with a recently augmented database of residual depths in the surrounding Southern Ocean (n = 1106), permit spatial variations of residual topography to be quantified. Positive residual anomalies (1 - 2 km) from the Transantarctic Mountains, Marie Byrd Land and the Antarctic Peninsula are consistent with regions of slow shear-wave velocity anomalies within the upper mantle, positive free-air gravity anomalies, and Cenozoic intraplate basaltic volcanism, indicating that topographic support is attributable to mantle convective processes. Lithospheric thicknesses derived from inverse modelling of basaltic rare-earth element concentrations show that elevated topography coincides with thinned lithosphere, further attesting to the relationship between positive residual elevation and mantle convective upwelling. Steepened geothermal gradients associated with regions of plate thinning have significant implications for the delivery of heat flux to the base of the West Antarctic Ice Sheet.