1. Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, B3H 4J1 Canada
2. Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia, V6T 1Z4 Canada
3. Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
4. Alfred-Wegener Institute for Polar and Marine Research, 27570 Bremerhaven, Germany, and Department of Geosciences, University of Bremen, 28359 Bremen, Germany
5. College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA

Correspondence to: Markus Kienast¹ Correspondence and requests for materials should be addressed to M.K. (Email: markus.kienast@dal.ca).

Surface ocean conditions in the equatorial Pacific Ocean could hold the clue to whether millennial-scale global climate change during glacial times was initiated through tropical ocean–atmosphere feedbacks or by changes in the Atlantic thermohaline circulation¹. North Atlantic cold periods during Heinrich events and millennial-scale cold events (stadials) have been linked with climatic changes in the tropical Atlantic Ocean and South America^{2, 3, 4}, as well as the Indian and East Asian monsoon systems^{5, 6}, but not with tropical Pacific sea surface temperatures⁷. Here we present a high-resolution record of sea surface temperatures in the eastern tropical Pacific derived from alkenone unsaturation measurements. Our data show a temperature drop of 1 °C, synchronous (within dating uncertainties) with the shutdown of the Atlantic meridional overturning circulation during Heinrich event 1, and a smaller temperature drop of 0.5 °C synchronous with the smaller reduction in the overturning circulation during the Younger Dryas event. Both cold events coincide with maxima in surface ocean productivity as inferred from ²³⁰Th-normalized carbon burial fluxes, suggesting increased upwelling at the time. From the concurrence of equatorial Pacific cooling with the two North Atlantic cold periods during deglaciation, we conclude that these millennial-scale climate changes were probably driven by a reorganization of the oceans' thermohaline circulation, although possibly amplified by tropical ocean–atmosphere interaction as suggested before⁸.

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