North Atlantic forcing of tropical Indian Ocean climate

Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 509 (2014): 76-80, doi:10.1038/nature13196.The response of the tropical climate in the Indian Ocean realm to abrupt climate change events in the North Atlantic Ocean is contentious. Repositioning of the intertropical convergence zone is thought to have been responsible for changes in tropical hydroclimate during North Atlantic cold spells1–5, but the dearth of high-resolution records outside the monsoon realm in the Indian Ocean precludes a full understanding of this remote relationship and its underlying mechanisms. Here we show that slowdowns of the Atlantic meridional overturning circulation during Heinrich stadials and the Younger Dryas stadial affected the tropical Indian Ocean hydroclimate through changes to the Hadley circulation including a southward shift in the rising branch (the intertropical convergence zone) and an overall weakening over the southern Indian Ocean. Our results are based on new, high-resolution sea surface temperature and seawater oxygen isotope records of well dated sedimentary archives from the tropical eastern Indian Ocean for the past 45,000 years, combined with climate model simulations of Atlantic circulation slowdown under Marine Isotope Stages 2 and 3 boundary conditions. Similar conditions in the east and west of the basin rule out a zonal dipole structure as the dominant forcing of the tropical Indian Ocean hydroclimate of millennial-scale events. Results from our simulations and proxy data suggest dry conditions in the northern Indian Ocean realm and wet and warm conditions in the southern realm during North Atlantic cold spells.This study was funded by the German Bundesministerium für Bildung und Forschung (grant 03G0189A) and the Deutsche Forschungsgemeinschaft (DFG grants HE3412/15-1 and STE1044/4-1, and the DFG Research Centre/Cluster of Excellence ‘The Ocean in the Earth System’). D.W.O. is funded by the US NSF, R.D.P.-H. is supported by Chilean FONDAP 15110009/ICM Nucleus NC120066.2014-10-3