LATE PLEISTOCENE CLIMATIC TRAJECTORY IN THE PHASE-SPACE OF GLOBAL ICE, OCEAN STATE, AND CO2 - OBSERVATIONS AND THEORY

We consider the evolution of three main slow-response variables descri bing the state of the climate system during the late Pleistocene (glob al ice mass, atmospheric carbon dioxide, and the ocean state) as measu red, respectively, by the SPECMAP delta(18)O record, the Vostok CO2 re cord, and the North Atlantic sea surface temperature record at 50(0)N (core K708-1), which is coherent with other ocean state properties. Th eir coevolution is portrayed in the form of a trajectory in the phase space of the three variables and its projections on its three phase pl anes. The oscillatory nature and phase lags of the variables are clear ly illustrated suggesting a ''physical process'' scenario that can acc ount for the observations. The basic element of this scenario is a fre e, near-100 kyr period, oscillation driven by internal instability, in volving feedbacks between all three variables under the influence of E arth-orbital (Milankovitch) forcing and long-term tectonic CO2 forcing . It is shown that a phenomenological theory advanced by the authors, emphasizing the role of CO2, provides a credible account of the phase- space trajectory.