Climate variability at the Middle Pleistocene Transition 900 kyr ago (CLIM900K)

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The prolongation and intensification of glacial cycles over the course of the Middle Pleistocene Transition (MPT; ~1.25-0.65 Ma) remains one of the major unsolved mysteries of Quaternary ice ages. Within the MPT, the interval from Marine Isotope Stage (MIS) 25 to 21 (~0.965-0.850 Ma) is thought to represent a fundamental shift in the mode of glacial cycles, with the appearance of a 100-kyr glacial cycle culminating in the first major Northern Hemisphere glaciation, but there is considerable uncertainty over the extent of ice volume increase. Moreover, while prominent debates centre on the causes of the transition, we are still lacking an adequate description and understanding of the evolution of climate variability over this interval. We propose to provide a comprehensive assessment of orbital- and millennial-scale climate changes during MIS 25-21, through joint pollen and foraminiferal isotopic and Mg/Ca analyses at unprecedented resolution from Site U1385 on the Portuguese Margin, a key location for linking changes in the ocean, atmosphere and biosphere. Results will transform our understanding of the magnitude of ice volume increase, the interaction of orbital- and millennial-scale variability and its role in glaciation and deglaciation, and impacts on plant biodiversity during this interval and will provide a benchmark for future studies on the transition into the 100-kyr world.