Atmosphere-ocean changes in the Pacific Southern Ocean over the past 1 Million years and implications for global climate

• Main Authors: Lamy, Frank, Arz, Helge, Esper, Oliver, Gersonde, Rainer, Hall, Ian, Harada, Naomi, Jaeschke, Andrea, Kaiser, Jerome, Kilian, Rolf, Kuhn, Gerhard, Lambert, Fabrice, Lange, Carina B., Lembke-Jene, Lester, Martínez-García, Alfredo, Tiedemann, Ralf, Winckler, Gisela, Wu, Shuzhuang
• Format: Conference Object
• Language: unknown
• Published: SCAR 2017
• Subjects: Antarc*; Antarctic; Drake Passage; Scotia Sea; Southern Ocean
• Online Access: https://epic.awi.de/id/eprint/46273/; https://epic.awi.de/id/eprint/46273/1/PAIS17_Lamy_et_al_3.pdf; https://hdl.handle.net/10013/epic.b87f9ac8-fbdd-4ea3-9488-8d0fa845e12f

Atmosphere-ocean interactions play an important role for understanding processes and feedbacks in the Southern Ocean (SO) and are relevant for changes in Antarctic ice-sheets and atmospheric CO2 concentrations. The most important atmospheric forcing at high and mid-latitudes of the Southern Hemisphere is the westerly wind belt (SWW), which strongly affects the strength and extension of the Antarctic Circumpolar Current (ACC), upwelling of deep-water masses, and controls the back-flow of intermediate waters to the tropics. In order to address orbital and millennial-scale changes of the SWW and the ACC, we present sediment proxy records from the Pacific SO including the Chilean Margin and the Drake Passage. The Drake Passage (DP) represents the most important oceanic gateway along the ACC. Based on grain-size and geochemical properties of sediment records from the southernmost continental margin of South America, we reconstruct changes in DP throughflow dynamics over the past 65,000 years. In combination with published sediment records from the Scotia Sea and preliminary sediment records from the central Drake Passage (Polarstern cruise PS97, 2016), we argue for a considerable total reduction of DP transport and reveal an up to ~40% decrease in flow speed along the northernmost ACC pathway entering the DP during glacial times. Superimposed on this long-term decrease are high-amplitude millennial-scale variations, which parallel Southern Ocean and Antarctic temperature patterns. The glacial intervals of strong weakening of the ACC entering the DP imply a reduced Pacific-Atlantic exchange via the DP (“cold-water route”). The reduced Drake Passage glacial throughflow was accompanied by a pronounced northward extension of the Antarctic cold-water sphere in the Southeast Pacific sector and stronger export of northern ACC water into the South Pacific gyre. These oceanographic changes are consistent with reduced SWW within the modern maximum wind strength zone over the subantarctic ACC and reduced wind forcing due to ...