Mapping geodetically inferred Antarctic ice height changes into thickness variations: a sensitivity study

Abstract. Determining recent Antarctic ice volume changes from satellite altimeter measurements of ice height requires a correction for contemporaneous vertical crustal deformation. This correction must consider two main sources of crustal deformation: (1) ongoing glacial isostatic adjustment (GIA), that is, the deformational, gravitational and rotational response to late Pleistocene and Holocene ice and ocean mass changes; and (2) modern ice mass flux. In this study, we seek to quantify the uncertainties associated with each of these corrections. Corrections of ice height changes for (1) have generally involved the adoption of global models of GIA defined by some preferred combination of ice history and mantle viscoelastic structure. We have computed the GIA correction generated from a coupled ice sheet – sea level model and a realistic earth model incorporating three-dimensional viscoelastic structure. Integrating the difference between this correction and those from recent GIA analyses widely adopted in the literature yields an uncertainty in total present-day ice volume change equivalent to approximately 10 % of Antarctic ice mass loss inferred for the previous decade. This reinforces earlier work indicating that ice histories characterized by relatively high excess ice volume at the Last Glacial Maximum may be introducing significant error in estimates of modern melt rates. Regarding correction (2), a spatially invariant scaling has commonly been used to convert GIA-corrected ice height changes obtained from satellite altimetry into ice volume estimates. We adopt modeling results based on a projection of Antarctic ice mass flux over the next 40 years to demonstrate a spatial variability in the scaling of up to 10 % across the ice sheet. Furthermore, using these calculations, we find an error in the projected net ice volume change of up to 4.5 mm GMSL equivalent forty years after present, with most of the difference arising in areas of West Antarctica above mantle zones of low viscosity.