The deterministic excitation paradigm and the late Pleistocene glacial terminations

A deterministic excitation (DE) paradigm is formulated, according to which the late Pleistocene glacial terminations correspond to the excitation, by the orbital forcing, of nonlinear relaxation oscillations (ROs) internal to the climate system in the absence of any stochastic parameterization. Specific threshold crossing rules parameterizing the activation of internal climate feedbacks leading to RO excitations are derived according to the DE assumption. They are then applied to an energy balance model describing the fluctuations induced by realistic orbital forcing on the glacial state. The timing of the glacial terminations thus obtained in a reference simulation is found to be in good agreement with proxy records. A sensitivity analysis insures the robustness of the timing. The potential irrelevance of noise allowing DE to hold is discussed, and a possible explanation of the 100-kyr cycle problem based on DE is outlined. In conclusion, the DE paradigm characterizes in one of the simplest possible ways the link between orbital forcing and glacial terminations implied by the Milankovitch hypothesis.