Orbital variability and high latitude circulation and climate change during the Pliocene-Pleistocene.

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This project aims to investigate deep- and intermediate-water mass exchange between the Arctic Ocean, the Nordic Seas and the high North Atlantic Ocean of the past 5 million years focusing on the period between 3 and 1 million years ago. These dense water masses have strongly affected Atlantic Meridional Overturning Circulation (AMOC), which, in turn, has had a strong impact on global climate. We propose to reconstruct changes in the sources, strength and mixing of these water masses, and in the sediment they carried, from measurements of their radiogenic isotope signatures. Our investigation will focus on an as quantitative as possible reconstruction of the water mass dynamics on timescales from millions of years to glacial/interglacial variability during the climatically highly relevant periods of the major Intensification of Northern Hemisphere Glaciation (INHG) and the Mid-Pleistocene Transition (MPT). We propose to work on samples from four ODP/IODP sediment cores forming a northsouth transect; one in the high North Altantic (Site 984 or 607), one in the Greenland- Norwegian Sea (Site 907), one in the Fram Strait on the Yermak Plateau (Site 911), and the central Arctic ACEX core (IODP Leg 302). For each core, we will determine the paleo variability of the radiogenic neodymium (Nd), lead (Pb) and strontium (Sr) isotope compositions of deep waters from the authigenic metal oxide phase, as well as Nd isotope compositions from foraminiferal calcite. Bulk sediment radiogenic isotope compositions will provide information on changes in source areas of the sediments transported by the water masses. These proxy data will allow us to unravel changes in both exchange of water masses between the three basins, as well as in erosional provenance in and around these basins during the initiation of Quaternary. Our main goal is to improve our understanding of the role of changes in circulation and glaciation in controlling and responding to climate. The results will offer deeper insight into broader climate control mechanisms as compared to those only seen in Late Quaternary records, and will contribute to the refinement of models of both past and future climatic change.