March 9, 2020: Ocean Circulation and Climate Dynamics Colloquium

11:00 h, Large Conference Room [R.075], Düsternbrooker Weg 20

The Atlantic Meridional Overturning Circulation (AMOC), a key mechanism in the climate system, transforming warm and salty waters from the subtropical gyre into colder and fresher waters in the subpolar gyre and Nordic Seas. To measure the AMOC and its variability at subpolar latitudes, the Overturning in the Subpolar North Atlantic Program (OSNAP) array was deployed in the summer of 2014. The array runs from Newfoundland to West Greenland (OSNAP West) and from the south east tip of Greenland to Scotland (OSNAP East). Based on observations through May 2016, the majority of the light‐to‐dense water conversion (15.6 ± 0.8 Sv) takes place north of the OSNAP East section. In this study, we quantify the processes transforming waters in the area located between the Greenland-Scotland Ridge and the OSNAP East section, not easily attributed to the overflow transports through the Greenland-Scotland Ridge. From the OSNAP and trans-ridge fluxes, the mean overturning within this area is estimated to be 6.9 ± 1.3 Sv across σMOC = 27.55 kg m-3, the isopycnal that separates the northward and southward flows. This mean overturning estimate is in close agreement with a value of 6.5 ± 1 Sv derived from water mass transformation theory and air-sea buoyancy fluxes from atmospheric reanalysis. However, the monthly variability of the transformation rates leads to an accumulation of dense water during winter and to its progressive export the following five months.

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