Dependence of GIA-induced gravity change in Antarctica on viscoelastic Earth structure

The Antarctic ice mass loss is accelerating due to recent global warming. Changes in Antarctic ice mass have been observed as the gravity change by GRACE (Gravity Recovery and Climate Experiment) satellites. However, the gravity signal includes both the component of the ice mass change and the component of the solid Earth response to surface mass change (Glacial Isostatic Adjustment, GIA). Evaluating the GIA-induced gravity change requires viscoelastic Earth structure and ice history from the last deglaciation.

Antarctica is characterized by lateral heterogeneity of seismic velocity structure. West Antarctica shows relatively low seismic velocities, suggesting low viscosity regions in the upper mantle. On the other hand, East Antarctica shows relatively high seismic velocities, suggesting thick lithosphere. Here we examine the sensitivities of GIA-induced gravity change in Antarctica to upper mantle viscosity and lithosphere thickness using spherically symmetric Earth models.

Results indicate that the gravity field change depends on both the upper mantle viscosity profile and the lithosphere thickness. In particular, the long-wavelength gravity field changes become dominant in the adoption of viscoelastic models with a low viscosity layer beneath the elastic lithosphere. The same trend is also shown in the adoption of viscoelastic models with a thick lithosphere, and there is a trade-off between the structure of the low viscosity layer and the thickness of the lithosphere. This trade-off may reduce the effect of the lateral variations in Earth structure beneath Antarctica on the estimate of Antarctic ice sheet mass change.