1. Department of Geology, University of California, Davis, California 95616, USA
2. Department of Geological Sciences and Marine Science Institute, University of California, Santa Barbara, California 93106, USA

Correspondence to: Matthew W. Schmidt¹ Email: schmidt@geology.ucdavis.edu

Abstract

Variations in the strength of the North Atlantic Ocean thermohaline circulation have been linked to rapid climate changes¹ during the last glacial cycle through oscillations in North Atlantic Deep Water formation and northward oceanic heat flux^{2, 3, 4}. The strength of the thermohaline circulation depends on the supply of warm, salty water to the North Atlantic, which, after losing heat to the atmosphere, produces the dense water masses that sink to great depths and circulate back south². Here we analyse two Caribbean Sea sediment cores, combining Mg/Ca palaeothermometry with measurements of oxygen isotopes in foraminiferal calcite in order to reconstruct tropical Atlantic surface salinity^{5, 6} during the last glacial cycle. We find that Caribbean salinity oscillated between saltier conditions during the cold oxygen isotope stages 2, 4 and 6, and lower salinities during the warm stages 3 and 5, covarying with the strength of North Atlantic Deep Water formation⁷. At the initiation of the Bølling/Allerød warm interval, Caribbean surface salinity decreased abruptly, suggesting that the advection of salty tropical waters into the North Atlantic amplified thermohaline circulation and contributed to high-latitude warming.

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