Postglacial rebound in a non-Newtonian spherical Earth

Using finite-elements we study the postglacial rebound in an axisymmetric E arth with a non-Newtonian rheology. Our approach allows for the first time a self-consistent study of the effect of a power-law creep on the long-wave length deformations, which cannot be performed using flat models. We show t hat, for a non-Newtonian upper mantle, the time-variations of the low-degre e Stokes coefficients become largely insensitive to the viscosity of the lo wer mantle. This is in contrast with previous evidence based on Newtonian m odels, which emphasized the importance of the low degree signatures for con straining the lower mantle viscosity.