Zhang
Xiao
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North Atlantic forcing of tropical Indian Ocean climate
Zhang
Xiao
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Preprint
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.