[U-03] Advanced understanding of Quaternary and Anthropocene hydroclimate changes in East Asia

[U03-07] A zonal mode over the tropical Indian Ocean during Heinrich Stadial 1

★Invited Papers

*Xiaojing Du^1,2, James M Russell^1,2, Zhengyu Liu³, Bette L Otto-Bliesner⁴, Delia W Oppo⁵, Mahyar Mohtadi⁶, Chenyu Zhu⁷, Valier V Galy⁸, Enno Schefuß⁶, Yan Yan⁹, Yair Rosenthal¹⁰, Nathalie Dubois^11,12, Jennifer Arbuszewski⁵, Yu Gao¹³ (1.Department of Earth, Environmental, and Planetary Sciences, Brown University, 2.Institute at Brown for Environment and Society, Brown University, 3.Atmospheric Science Program, Department of Geography, The Ohio State University, 4.Climate and Global Dynamics Laboratory, National Center for Atmospheric Research, 5.Geology and Geophysics Department, Woods Hole Oceanographic Institution, 6.MARUM-Center for Marine Environmental Sciences, University of Bremen, 7.Frontier Science Center for Deep Ocean Multispheres and Earth System (FDOMES) and Physical Oceanography Laboratory, Ocean University of China, 8.Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 9.State Key Laboratory of Isotope Geochemistry, CAS Center for Excellence in Deep Earth Science, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 10.Department of Marine and Coastal Sciences and Department of Earth and Planetary Sciences, Rutgers, State University of New Jersey, 11.Department of Surface Waters Research and Management, Eawag, 12.Department of Earth Sciences, ETH Zürich, 13.Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University)

Keywords:Tropical Indian Ocean , AMOC, Heinrich stadial 1, ITCZ

Heinrich stadial 1 (HS1) involves the largest Atlantic Meridional Overturning Circulation (AMOC) reduction in recent geological time. Such abrupt changes in AMOC are thought to impact tropical hydroclimate via adjustments of the latitudinal position of the intertropical convergence zone (ITCZ). However, proxy records suggest zonal anomalies over the tropical Indian Ocean, featuring intense and widespread drought in tropical East Africa and generally wet but heterogeneous conditions in the Maritime Continent. Here we synthesize proxy data and an isotope-enabled transient deglacial simulation and show an intensified Walker circulation across the tropical Indian Ocean in response to the North Atlantic meltwater forcing during HS1. We propose that the southward ITCZ shift over the eastern Indian Ocean, in response to North Atlantic cooling strengthens the Indian Ocean Walker circulation, triggering an east-west precipitation dipole across the basin during HS1. This dipole reverses the zonal precipitation anomalies caused by the exposure of Sunda and Sahul shelves due to the glacial lower sea level. Our study illustrates how zonal modes of atmosphere-ocean circulation can amplify or reverse global climate anomalies. Given the potential for reduced AMOC under global warming, this work highlights the importance of the zonal modes of atmosphere-ocean circulation for future climate change.