Ocean Loading Effects on Predictions of Uplift and Gravity Changes due to Glacial Isostatic Adjustment in Antarctica

The effect of relatively high fidelity regional ocean loading in Antarctica on predicted rates of glacial isostatic adjustment (GIA) is quantified for the IJ05 surface loading history. The recently developed IJ05 model was designed to incorporate the growing compilation of geological and glaciological constraints on the evolution of the Antarctic ice sheet that has emerged in the last decade. IJ05 defines its surface load history relative to the present-day surface load, rather than specifying an absolute, or total, loading history. Thus, IJ05 implicitly includes the 'water dumping' effect described by Milne, and the addition of explicit ocean loading only introduces a perturbative change to the calculated response. As a consequence, the changes in predicted GIA rates when regional ocean loading is included are greatly muted compared to the widely used ICE-3G model, which specifies an absolute load history. For example, the IJ05 uplift and gravity rates change at most by +1 mm/yr and +0.25 cm/yr water equivalent for Ivins and James' [2005] "average" viscosity structure (1021, 1022, and 8×1022 Pa s for the upper, middle and lower mantle, respectively). The changes for ICE-3G have much larger magnitude at -8 mm/yr and -3 cm/yr w.e., respectively. Thus, the conclusions of previous studies that used IJ05 predictions with implicit ocean loading are relatively robust. Future calculations, however, will include the full regional ocean loading effect in order to provide the best possible GIA correction for analysis of GRACE observations to determine present-day Antarctic mass balance and for interpretation of the growing body of GPS crustal motion observations.