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

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-SG. 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.