Ice-ocean mass balance during the Late Pleistocene glacial cycles in view of CHAMP and GRACE satellite missions

Abstract

During the last glacial cycles, global sea level dropped several times by about 120 m and large ice sheets covered North America, northern Europe and Antarctica during the glacial stages. The changes in the ice-ocean mass balance have displaced mantle material mainly via viscous flow, and the perturbation of the equilibrium figure of the Earth by glacial isostatic adjustment is still observable today in time-dependent changes of gravitational and rotational observations. Contemporary ice-ocean mass balance from volume changes of polar ice caps also contributes to secular variations of the Earth's gravitational field. In the near future, several satellite gravity missions will significantly improve the accuracy of the observed time-dependent gravitational field. In view of the expected improvements in the observations, we predict glacially induced perturbations of the gravitational field, induced by Late Pleistocene and contemporary ice volume changes, for a variety of radial mantle viscosity profiles. We assess the degree of uncertainty for the glacially induced contributions to gravitational and rotational parameters, both in the spectral and the spatial domain. Predictions of power spectra for the glacially induced free-air gravity and geoid anomalies are about one order of magnitude lower than the observed values, and uncertainties arising from different plausible viscosity profiles are around 0.15-0.4 mGal and 0.2-1.5 m, respectively. Uncertainties from different ice models are of secondary importance for the predicted power spectra. Predicted secular changes in geoid anomalies in formerly glaciated areas are mainly controlled by the viscosity profile and contemporary ice volume changes. We also show that the simple three-layer viscosity profiles currently employed for the majority of postglacial rebound studies represent a limited subset for model predictions of the time-dependent gravitational field.