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

在中更新世过渡（MPT; ~1.25-0.65 Ma）过程中，冰川旋回的延长和加剧仍然是第四纪冰期未解之谜之一。在MPT中，从海洋同位素阶段（MIS） 25到21 （~0.965 ~ 0.850 Ma）的间隔被认为代表了冰期旋回模式的根本转变，在北半球第一次主要冰期出现了一个100 kyr的冰期旋回，但冰量增加的程度存在相当大的不确定性。此外，虽然主要的争论集中在这种转变的原因上，但我们仍然缺乏对这段时间内气候变率演变的充分描述和理解。我们建议在葡萄牙边缘的U1385站点（连接海洋、大气和生物圈变化的关键位置），通过联合花粉和有孔虫同位素和Mg/Ca分析，对MIS 25-21期间的轨道和千年尺度的气候变化进行全面评估。结果将改变我们对冰量增加幅度、轨道和千年尺度变率的相互作用及其在冰川和冰川消退中的作用，以及在此期间对植物生物多样性的影响的理解，并将为未来过渡到100 kyr世界的研究提供基准。

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.