Abstract

The summer air temperature that regulates the ice margin covaries with the sea surface temperature but precedes the ice volume during glacial cycles, suggesting that the ocean is the intermediary of the orbital forcing of the ice sheet. We formulate a minimal model to elucidate the ocean role in the genesis of glacial cycles. We show that, because of the atmospheric coupling, an eddying ocean exhibits bistates of maximum entropy production, which would translate to ice bistates of polar ice cap and Laurentide ice sheet, enabling large ice-volume signal when the bistable interval is crossed by the forcing. Since this bistable interval is set by the global convective flux, it is lowered during Pleistocene cooling, whose interplay with the ice-albedo feedback may account for the mid-Pleistocene transition from 41-ky obliquity cyles to 100-ky ice-age cycles paced by eccentricity. Quantitative tests of the theory and its parsimony in resolving myriad glacial puzzles suggest that the theory has captured the governing physics of the Pleistocene glacial cycles.