Stable oxygen isotope record and Mg/Ca ratios at the Mid-Pleistocene Climate Transition, ODP Site 181-1123

Over this time, an increase occurred in the amplitude of change of deep ocean foraminiferal oxygen isotopic ratios, traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep-ocean temperature.

We have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios. Our results suggest that the MPT was initiated by an abrupt increase in Antarctic ice volume at 900 ka. We see no evidence of a pattern of gradual cooling but near-freezing temperatures occur at every glacial maximum.