Science 363, 516–521 (2019)

The Atlantic Meridional Overturning Circulation (AMOC) is projected to slow down in the twenty-first century. Observations across the Atlantic basin, at different latitudes, are needed to understand changes in the MOC, which led to the Overturning in the Subpolar North Atlantic Program (OSNAP). This observing system has two sections — the west section covers the southeast Labrador Shelf to the southwest tip of Greenland, and the east section covers the southeast tip of Greenland to the Scottish shelf — and was deployed in the boreal summer, 2014.

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Colin Varndell / Alamy Stock Photo

Susan Lozier and Feili Li of Duke University, United States, and their co-authors analyse the first 21 months of data (to April 2016) to show that the transport of heat and freshwater across the observing line is primarily a result of the overturning circulation. The authors depart from the previous view that AMOC variability is controlled by Labrador Sea deep-water formation. They suggest that the conversion of warm, salty, shallow Atlantic waters to colder, fresher, deep waters north of the OSNAP line (from Greenland to Scotland) drives the overturning and its variability in the subpolar region.