Ice-age cycles: Earth's rotation instabilities and sea-level changes

Abstract

A new class of multilayered, viscoelastic Earth models based on PREM is applied to the modeling of Earth's rotation instabilities and associated sea-level changes, induced by the occurrence of Pleistocene ice-age cycles that match the oxygen isotope records over the last 0.8 Myr. The novelty of our approach stands on the usage, for the first time in post-glacial rebound induced sea-level studies, of a fully analytical scheme based on normal mode theory that allows to deal with complexities of the real Earth, such as lithospheric and mantle layering, sphericity and self-gravitation. The ice models are based on ICE-3G. Our results show that differences in true polar wander (TPW) and TPW-induced sea-level changes between Earth models with a few layers and models having enough layers so that saturated continuum limits are reached, can amount factors 2 to 3. This may change conclusions derived from some earlier studies on polar wander induced changes in climate, that were based on Earth models with a limited amount of layers. The results indicate that models containing about 15 layers with a stratified lower mantle and transition zone have reached saturated continuum responses for both TPW and TPW-induced sea-level changes. Stratification of the lithosphere is not important. This is in contrast with the sensitivity of post-seismic deformation models. This difference in sensitivity on the radial profile of the Earth model can be explained with simple arguments on the dependence on zonal degree. Copyright 1997 by the American Geophysical Union.