Gulf Stream hydrography during the Late Pliocene/Early Pleistocene: low versus high latitude forcing of the Atlantic Meridional Overturning Circulation

• Applicant: Anne Osborne, Ph.D.
• Subject Area: Palaeontology ; Mineralogy, Petrology and Geochemistry ; Oceanography
• Term: from 2015 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 279458136

The goal of this project is to reconstruct the hydrography of the Gulf Stream during the final stages of the closure of the Central American Seaway (CAS) in the Late Pliocene/Early Pleistocene. We propose to use material from ODP Sites 1006 and 1000 in the Florida Straits and central Caribbean to test the hypothesis that there was a direct link between CAS closure, warming and increased salinity of the Gulf Stream, and a major strengthening of the Atlantic Meridional Overturning Circulation (AMOC), which led to the present day Atlanticcirculation and climate system. It is proposed to first establish an age model for Site 1006 (658 m water depth), based on the stable isotope composition of oxygen and carbon in benthic foraminifera. An age-model for this key site, positioned ideally at the start of the Gulf Stream, will be the basis for a whole range of paleoceanographic research efforts. The radiogenic isotope composition of neodymium (Nd) in the Fe-Mn coatings of uncleaned foraminifera will be measured to trace intermediate water mass mixing and the strengthof the AMOC during repeated episodes of CAS closure and re-opening caused by sea level changes. Upper water column hydrography will be reconstructed from the stable isotope composition of oxygen measured in mixed-layer and thermocline dwelling planktonic foraminifera. Together, these millennial resolution records will give us insight into the importance of low versus high latitude forcings of the strength of the AMOC. This willnot only significantly improve our understanding of the mechanisms driving past changes in ocean circulation in response to major tectonic changes but will also provide information relevant to future climate perturbations as a consequence of changing sea surface salinity of the Gulf Stream influencing the functioning of the North Atlantic circulation.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 527: Bereich Infrastruktur - "International Ocean Discovery Program" (IODP)
• Co-Investigator: Professor Dr. Martin Frank