Carbon dioxide and the ?18O record of late-Quaternary climatic change: a global model

Abstract

A dynamical model for the late-Quaternary global variations of δ18O, mean ocean surface tempeature τ, ice mass I, deep ocean temperature θ, and atmospheric carbon dioxide concentration μ, is constructed. This model consists of two diagnostic equations (for δ18O and τ), and three prognostic equations (for I, θ, and μ) of a form studied extensively in previous articles. The carbon dioxide equation includes forcing by a representation of the Milankovitch earth-orbital radiation effects, and contains a basic instability that drives a free oscillation of period near 100,000 years. The system is constrained to conserve mass and energy, contain physically plausible feedbacks including a system time constant no greater than 10.000 years, and be robust (i. e., structurally stable in the presence of expected noise levels and uncertainties in values of coefficients). Within the limits of these constraints, coefficients are chosen such that (i) the solution gives a good fit to the observed SPECMAP δ18O variations, and (ii) the ice mass variations are qualitatively similar to the δ18O variations. The predicted long term variations of sea surface temperature and atmospheric carbon dioxide are in reasonably good agreement with the limited observational evidence available for these quantities, while the predicted variations of deep ocean temperature remain to be verified when paleoclimatic estimates of this quantity become available. The relative contributions of ice mass changes and surface water temperature changes to the variations of δ18O at any time are given by the model.