Ice Sheets, Sea Level and the Dynamic Earth, Geodyn. Ser., pp. 233-256, ed. Mitrovica, J. X., and L. L. A. Vermeersen, AGU, Washington, DC., 2002.

The Convective Mantle Flow Signal in Rates of True Polar Wander

Bernhard Steinberger and Richard J. O'Connell


Abstract

We investigate changes of the rotation axis caused by mantle convection. In the first part, the coupled problem of viscoelastic deformation and rotational dynamics is solved for simple Earth models in order to compute how the rotation axis changes following emplacement of non-hydrostatic excess masses. It is shown that both direct integration and a computationally more effective ``quasi-static integration'' give virtually identical results. With the latter method, results of eigenmode and time domain approach were compared, with little difference found. Although the number of viscoelastic relaxation eigenmodes is infinite, for an adiabatic Earth mantle only two eigenmodes need be considered for an approximately correct description, and an even simpler steady-state solution can be used. The results indicate that for our best estimates of present-day mantle properties, the maximum speed of polar motion is about 1 degree per million years, and during Cenozoic times the rotation axis has always followed closely the axis of maximum non-hydrostatic moment of inertia imposed by advection of mantle density heterogeneities. The latter was calculated for a number of tomographic models and inferred flow fields. Results indicate on average a slow motion of about 5 degrees in 60 Ma roughly towards Greenwich, which is not in conflict with paleomagnetic results. Only one of the models additionally predicted a faster motion prior to about 80 Ma in a direction similar to what is inferred from paleomagnetism.