1. Department of Geology, University of California, Davis, California 95616, USA
2. Godwin Laboratory for Palaeoclimate Research, University of Cambridge, Cambridge CB2 3EQ, UK
3. †Present addresses: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia 30332, USA (M.W.S.); British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK (M.J.V.)

Correspondence to: Matthew W. Schmidt^1,3 Correspondence and requests for materials should be addressed to M.W.S. (Email: mschmidt@eas.gatech.edu).

Abstract

Geochemical and sedimentological evidence suggest that the rapid climate warming oscillations of the last ice age, the Dansgaard–Oeschger cycles¹, were coupled to fluctuations in North Atlantic meridional overturning circulation through its regulation of poleward heat flux². The balance between cold meltwater from the north and warm, salty subtropical gyre waters from the south influenced the strength and location of North Atlantic overturning circulation during this period of highly variable climate^{3, 4, 5}. Here we investigate how rapid reorganizations of the ocean–atmosphere system across these cycles are linked to salinity changes in the subtropical North Atlantic gyre. We combine Mg/Ca palaeothermometry and oxygen isotope ratio measurements on planktonic foraminifera across four Dansgaard–Oeschger cycles (spanning 45.9–59.2 kyr ago) to generate a seawater salinity proxy record from a subtropical gyre deep-sea sediment core. We show that North Atlantic gyre surface salinities oscillated rapidly between saltier stadial conditions and fresher interstadials, covarying with inferred shifts in the Tropical Atlantic hydrologic cycle⁶ and North Atlantic overturning circulation. These salinity oscillations suggest a reduction in precipitation into the North Atlantic and/or reduced export of deep salty thermohaline waters during stadials. We hypothesize that increased stadial salinities preconditioned the North Atlantic Ocean for a rapid return to deep overturning circulation and high-latitude warming by contributing to increased North Atlantic surface-water density on interstadial transitions.

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