Surface-Forced Variability in the Nordic Seas Overturning Circulation and Overflows

Water mass transformation in the Nordic Seas and the associated overflow of dense waters across the Greenland-Scotland Ridge (GSR) acts to maintain the lower limb of the Atlantic meridional overturning circulation. Here, we use ocean and atmospheric reanalysis to assess the temporal variability in the Nordic Seas overturning circulation between 1950 and 2020 and its relation to surface buoyancy forcing. We find that variable surface-forced transformation of Atlantic waters in the eastern Nordic Seas can explain variations in overflow transport across the GSR. The production of dense water masses in the Greenland and Iceland Seas is of minor importance to overflow variability. The Nordic Seas overturning circulation shows pronounced multidecadal variability that is in phase with the Atlantic Multidecadal Variability (AMV) index, but no long-term trend. As the AMV is currently transitioning into its negative phase, the next decades could see a decreased overflow from the Nordic Seas.

Automated summary

Water mass transformation and overflow of dense waters across the Greenland-Scotland Ridge play a crucial role in maintaining the Atlantic meridional overturning circulation. The variability in Nordic Seas overturning circulation between 1950 and 2020 is found to be related to surface buoyancy forcing in the eastern Nordic Seas. The multidecadal variability in the Nordic Seas overturning circulation is in phase with the Atlantic Multidecadal Variability index, but there is no long-term trend.