Asthenospheric ice-load effects in a global dynamical-system model of the Pleistocene climate

Abstract

In a previous dynamical model the late Cenozoic climate variations were simulated, taking into account free and forced variations of atmospheric carbon dioxide acting in concert with changes in global ice mass and the deep ocean thermal state, all under the influence of the known earth-orbital radiative changes. This model is now extended by adding another relevant variable, bedrock/asthenosphere depression, including its associated ice-calving effects. Within the context of this extended model we (1) demonstrate the main results of previous bedrock/ice sheet models in what we believe is the simplest possible manner, (2) show how these previous models can exhibit the mid-Pleistocene transition with the inclusion of CO2 effects, (3) discuss the limitations of these previous bedrock models, and (4) illustrate the possibility of removing some of these limitations and accounting for further aspects of the paleoclimate record by using the full dynamical system that includes forced and free effects of CO2, as well as effects of bedrock depression and Milankovitch forcing. As one example of a new possibility, with bedrock effects included in the full system we can obtain a solution characterized by irregularly spaced, intermittent episodes in which the behavior is dominated either by near-40 kyr period oscillations or by near-100 kyr periods (such as prevailed over the Pleistocene).