Eddy- and Wind-Driven Circulation in the Enclosed Basins of the Norwegian Sea Evaluated Using a Model and Absolute Geostrophic Flow From Argo

Cyclonic flow in enclosed basins arises from cyclonic vorticity input from either winds or eddies. Previous observations show winds account for about half of the circulation (integral of parallel velocity around a closed isobath) in the Lofoten Basin of the Norwegian Sea, implying a comparable contribution from eddies. In contrast, in the Norwegian Basin, winds explain much of the circulation. We use Argo data from 2012 to 2022, a linear wind-forced and bottom friction-regulated model, and a primitive equation model to investigate how winds and eddies drive the circulation. While Argo cannot resolve individual eddies, it does resolve mesoscale spatial variability. Absolute geostrophic velocities to 2,000 m are calculated by referencing geostrophic shear from objective maps of the profile data to the trajectories at 1,000 m. The time-mean shear is anticyclonic. However, the flow is mostly cyclonic, bottom-intensified, and isobath following. The linear model explains less than half of the observed circulation, suggesting a contribution from an unobserved eddy flux. This interpretation is supported by a numerical model with 800-m horizontal resolution, which resolves the 10–15-km deformation radius. In this model, the difference between the full and linear response comes from an eddy-driven vorticity flux, which produces a largely cyclonic circulation. This result is consistent with the observed global prevalence of positive topostrophy (anticyclonic flow around elevations and cyclonic flow around basins). The observations also show a seasonal shift in the eddy flux, which maybe related to a decadal-scale fresh inflow that alters the density gradient and influences eddy production.