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To provide an observational basis for the Intergovernmental Panel on Climate Change projections of a slowing Atlantic meridional overturning circulation (MOC) in the 21st century, the Overturning in the Subpolar North Atlantic Program (OSNAP) observing system was launched in the summer of 2014. The first 21-month record reveals a highly variable overturning circulation responsible for the majority of the heat and freshwater transport across the OSNAP line. In a departure from the prevailing view that changes in deep water formation in the Labrador Sea dominate MOC variability, these results suggest that the conversion of warm, salty, shallow Atlantic waters into colder, fresher, deep waters that move southward in the Irminger and Iceland basins is largely responsible for overturning and its variability in the subpolar basin. [ABSTRACT FROM AUTHOR]

The article reports on the first retrieval of data from the 53 moorings in an array called the Overturning in the Subpolar North Atlantic Program (OSNAP) which stretches from Labrador to Greenland to Scotland. Topics discussed include the array's measurements of ocean temperature, salinity, and current velocity, the efforts to understand the Atlantic Meridional Overturning Circulation (AMOC), and the scientists' attempt to study the pull in the Southern Ocean that grids Antarctica.