[M-IS14] Paleoclimatology and paleoceanography

[MIS14-10] Changes in the Southern Hemisphere Westerlies in response to Heinrich events

*Takuto Kasuya^1,2, Kana Nagashima², Hitoshi Hasegawa³, Yusuke Okazaki¹, Yuta Kuniyoshi⁴, Ayako Abe-Ouchi⁴, Shinya Iwasaki⁵, Frank Lamy⁶, Helge W. Arz⁷, Julia R. Hagemann⁶, Carina B. Lange⁸, Masafumi MURAYAMA⁹, Naomi Harada⁴ (1.Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University, 2.Japan Agency for Marine-Earth Science and Technology, Research Institute for Global Change, 3.Faculty of Science and Technology, Kochi University, 4.The University of Tokyo, 5.Graduate School of Environmental Science, Hokkaido University, 6.Marine Geology Section, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, 7.Department of Marine Geology, Leibniz Institute for Baltic Sea Research, 8.Departamento de Oceanografía and Centro de Investigación Oceanográfica en el Pacífico Suroriental (Coastal), Universidad de Concepción, 9.Faculty of Agriculture and Marine Science, Kochi University)

Keywords:Atlantic Meridional Overturning Circulation (AMOC), millennial scale, Patagonian Icesheet, Southern Hemisphere

During the last glacial period, millennial-scale iceberg discharges in the North Atlantic, known as Heinrich Events (HEs), could have shifted the Southern Hemisphere Westerly Wind Belt (SWW) poleward and potentially led upwelling-driven CO₂ outgassing from the Southern Ocean. However, direct evidence of SWW poleward shift in response to HEs remains limited. Based on detrital elements, minerals, and grain-size records in well-dated sediment core MR16-09 PC03 (46°24.32′, 77°19.45′, 3082 m water depth), from off western Patagonia at ~46°S, we found abrupt onsets in the discharge of medium-to-coarse silt-sized detritus during the latter half of each HEs (HE 3, 4, 5, 5a, and 6) originating from the Patagonian Batholith exposed in the coastal area of western Patagonia. Such abrupt discharges are unique events south of ~46°S and probably reflect the extension of glacial erosion into the western fjords related to a pronounced positive anomaly in the glacial surface mass balance of the western-central Patagonian ice sheet. The impact of HE on climate of the southern mid-to-high latitudes has been proposed to change precipitation via southward SWW shifts. Our climate model (MIROC4m) hosing experiment suggests that the SWW and precipitation belt along the Chilean coast migrated poleward over a thousand years after the onset of HE, which is consistent timing with our core records. Thus, increased precipitation south of 46°S following the poleward-SWW shift most likely drove the positive anomaly of the western-central PIS mass balance and abrupt detritus discharges. These findings provide critical evidence of abrupt climate changes propagating from the North Atlantic to the southern midlatitudes via the large-scale reorganization of the atmospheric and ocean circulations.