The Mid-Quaternary Climatic Transition as the Free Response of a Three-Variable Dynamical Model

Abstract

A simplified version of a previously described dynamical model governing global ice mass, atmospheric carbon dioxide, and mean ocean temperature (that may also be a proxy for some other CO2?controlling oceanic variable, e.g., nutrient supply) is shown to possess solutions, in a realistic parameter range, that can replicate the main features of the climatic variations implied by the full, two million years, Quarternary δ18O record. These variations include a major ?transition? between a low-ice (δ18O, low variance mode before roughly 900 kyr BP to a high-ice (near 100 kyr period) variance mode after that time to the present. The model contains only three free parameters in this simplified form. No external earth-orbital forcing is prescribed; i.e., the model represents only internal dynamics. From the previous studies it seems clear that additional variance representing such features as the ?rapid? deglaciation and the phase of the major Quaternary oscillation can be largely explained with no more than four additional parameters representing an internal asymmetry and the external periodic forcing. The present results, therefore, constitute a first-order account for the existence of the ?ice age? fluctuations over the last two million years, including the concomitant variations of atmospheric CO2. The variations of mean ocean temperature (or a related VO2?controlling proxy variable) are also deduced and represent a side prediction of the model.