Rapid subtropical North Atlantic salinity oscillations across Dansgaard–Oeschger cycles

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 climate3,4,5. 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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Figure 1: Idealized North Atlantic surface (red arrows) and deep water (blue arrow) circulation during MIS 3 stadial events.
Figure 2: Temperature and salinity variation at site 1060 during MIS 3.

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Acknowledgements

We thank the Ocean Drilling Program for core samples. Funding for this research was provided by JOI-ODP Schlanger Ocean Drilling Fellowships to M.W.S. and by a US National Science Foundation grant to H.J.S. Laboratory assistance from D. Pak and mass spectrometer operation by G. Paradis and D. Winter were critical to the success of this study. Elemental analyses were conducted in D. Lea's laboratory at the University of California, Santa Barbara. We also thank A. Russell and D. Lea for discussions and comments.

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Correspondence to Matthew W. Schmidt.

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Schmidt, M., Vautravers, M. & Spero, H. Rapid subtropical North Atlantic salinity oscillations across Dansgaard–Oeschger cycles. Nature 443, 561–564 (2006). https://doi.org/10.1038/nature05121

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