Relationship between glacial isostatic adjustment and gravity perturbations observed by GRACE

The Gravity Recovery and Climate Experiment space gravity mission provides one of the principal means of estimating present-day mass loss occurring in polar regions. Extraction of the mass loss signal from the observed gravity changes is complicated by the need to first remove the signal of ongoing glacial isostatic adjustment (GIA) since the Last Glacial Maximum. This can be problematic in regions such as Antarctica where the GIA models are poorly constrained by observation and their accuracy is not well known. We present a new methodology that permits the GIA component to be represented mathematically by a simple, linear expression of the ratio of viscoelastic Love numbers that is valid for a broad range of Earth and ice-load models. The expression is shown to reproduce rigorous computations of surface uplift rates to within 0.3 mm/yr, thus providing a means of inverting simultaneously for present-day mass loss and ongoing GIA with all the accuracy of a fully detailed forward model.