Search

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 Atlantic meridional overturning circulation (AMOC) and the subpolar gyre (SPG) are important elements in mechanisms for multidecadal variability in models in the North Atlantic Ocean. In this study, a 2000-year long global ocean model integration forced with the atmospheric patterns associated with a white noise North Atlantic Oscillation (NAO) index is shown to have three distinct timescales of North Atlantic Ocean variability. First, an interannual timescale with variability shorter than 15 years, that can be related to Ekman dynamics. Second, a multidecadal timescale, on the 15- to 65-year range, that is mainly concentrated in the SPG region and is controlled by constructive interference between density anomalies around the gyre and the changing NAO forcing. Finally, the centennial timescales, with variability longer than 65 years, that can be attributed to the ocean being in a series of quasi-equilibrium states. The relationship between the ocean's response and the NAO index differs for each timescale; the 15-year and shorter timescales are directly related to the NAO of the same year, 15- to 65-year timescales are dependent on the NAO index in the last 25-30 years in a sinusoidal sense while the 65-year and longer timescales relate to a sum of the last 50-80 years of the NAO index. [ABSTRACT FROM AUTHOR]

The article highlights trends in meridional overturning circulation (MOC) in the North Atlantic Ocean in 2013. Topics discussed include the mean variability of the MOC, the variability of transported properties, and the strength of the MOC. The lack of consistent trend in the MOC during the year is noted.

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.