Tracing the Mid-Pleistocene Transition using SST and Sea Ice Proxies in the Sub-Arctic Pacific.

Abstract:

The Middle Pleistocene Transition (MPT) is defined as a dramatic change in the Earth’s climate when glacial/interglacial cyclicity switched from a 41-kyr orbital obliquity to 100-kyr precessional forcing. The cause of the 100-kyr cycle emergence in the absence of any change in orbital forcing remains unknown. High latitude sites, such as the Bering Sea, can provide important data as the timing and mechanisms behind this major climatic shift. This work will present high resolution alkenone-derived SST and diatom data from core U1340A collected during IODP Expedition 323. Preliminary results reveal a broad intensification of cold surface water conditions averaging 2-4^oC and increased sea ice duration at ca. 0.8-1.1 Ma. Diatom assemblages reveal a marked downturn in Alaskan Stream water masses and greater influence of western basin waters after this period. These results suggest both an intensification of glacial/interglacial cycles and increased isolation of the basin during glacial periods