Changes of the Earth's rotation axis owing to advection of mantle density heterogeneities

Polar wander, the secular motion of the Earth's rotation axis relative to its surface, has been studied for many years. Dynamical arguments(1-3) show that polar wander can arise from the redistribution of mass in a plastic deformable Earth, the rate depending on both the rate of mass redistribution and the rate at which the Earth's rotational bulge can readjust to the changing geoid modelling(4), a mantle flow field consistent with tomographic anomalies(5), and time-dependent lithospheric plate motions(6) to calculate the advection of mantle density heterogeneities and corresponding changes in the degree-two geoid during the Cenozoic era. We show that the rotation axis will follow closely any imposed changes of the axis of maximum non-hydrostatic moment of inertia. The resulting path of the rotation axis agrees well with palaeomagnetic results(7), with the model predicting a current rate of polar motion that explains 40% of that observed geodetically(8).