Polar motion of a viscoelastic Earth due to glacial cycle mass loading

The growth and decay of ice sheets can change the symmetry axis of the global mass distribution and thus excite motion of the rotation axis of the Earth. We develop a simple, normal mode expansion of the operator which converts surface load histories into polar motion histories, and use it to characterize the polar motion response to arbitrary surface loading excitation, in terms of gain and phase, for a wide range of Earth models and excitation time scales. Uncertainties in loading history presently limit the utility of constraints on mantle rheology which can be obtained from matching the present direction and rate of motion of the pole. Because of its magnitude and distance from the pole, the Laurentide ice sheet alone can induce motion of the rotation pole by over 100 km. This will influence the pattern of incident radiation on continents and oceans, and may play a significant role in limiting ice sheet growth. Differential motion of the mantle and core, on a glacial timescale, may also influence the geomagnetic field.