Over a decade of autonomous GNSS and seismic observations across West Antarctica reveal surprising complexities in both crustal deformation patterns and lateral Earth structure beneath the West Antarctic Ice Sheet (WAIS). Crustal motion patterns derived from GNSS are unlike motions predicted from glacial isostatic adjustment (GIA) models that use Last Glacial Maximum ice histories to load globally representative 1-D Earth models. Broad regions of West Antarctica are inferred to have very low mantle viscosities, approximating those of the Iceland hotspot. Relaxation times following removal (or addition) of ice loads are short, and modeling shows that there can be both elastic and viscoelastic displacements on decadal timescales where the Earth structure has such a ‘weak’ profile. In the absence of observational constraints, GIA modeling studies must currently use ‘ice history scenarios’, thus data-constrained ice sheet histories over short time scales are urgently needed for West Antarctica. Given regional differences in Earth structure across relatively small spatial scales, it is also essential to incorporate 3-D earth structure to model the GIA response in West Antarctica. Quantification of the degree of influence of Earth-Ice feedbacks on future WAIS evolution and contributions to global sea level requires a range of new observational and modeling efforts for Antarctica.
