AMOC: Densification and Overturning in the Iceland Basin and Irminger Sea

The Atlantic Meridional Overturning Circulation (AMOC), a key mechanism in the climate system, transforms warm and salty waters from the subtropical gyre into colder and fresher waters in the subpolar gyre and Nordic Seas. To measure the mean AMOC and its variability at subpolar latitudes, the Overturning in the Subpolar North Atlantic Program (OSNAP) array was deployed in the summer of 2014. Based on observations through May 2016, the majority of the light‐to‐dense water conversion takes place north of the OSNAP East line, which runs from the southeast tip of Greenland to the Scottish shelf. In this study, we assess the transformation of dense waters in the area located between the Greenland-Scotland Ridge and the OSNAP East section. From 2014 to 2016, the mean overturning over this area is estimated at 7.6 Sv across σ₀= 27.55 kg m^-3, which separates the northward and southward flows. This mean overturning estimate matches predictions using air-sea buoyancy forcing from atmospheric reanalysis. However, the large monthly variability of the overturning (standard deviation of 4.1 Sv) cannot easily be attributed to the buoyancy forcing or to the overflow variability through the Greenland-Scotland Ridge. We explore possible mechanisms that can account for this variability and discuss differences between the Iceland Basin and the Irminger Sea in the transformation process.