Horizontal Eddy Diffusivities and Heat Fluxes in the Norwegian Sea From Argo

Abstract In the Nordic Seas, the main reservoir of heat is in the Lofoten Basin of the Norwegian Sea, where eddies detaching from the slope current bring warm water into the basin. The basin‐mean eddy diffusivity from surface drifters is about 2,000 . Subsurface horizontal diffusivities are calculated from Argo profiling float data with two independent methods to extend previous work. First, temperature anomalies are used to estimate eddy mixing lengths, which are then combined with root‐mean‐squared velocity fluctuations to obtain diffusivities in the upper 2,000 m. Second, diffusivities are calculated based on single particle across‐stream dispersion from the float trajectories at their parking depths near 1,000 m. The mean diffusivity across the Lofoten Basin is about 400 in the upper 1,000 m. With weak stratification, eddy‐driven stirring extends throughout the measured upper 2,000 m. From these diffusivities and the mean temperature gradient, the heat flux is calculated, which is directed into the central Lofoten Basin. Heat flux convergence leads to a mean warming of the Lofoten Basin by about 0.5C , which is comparable to the mean net surface heat flux. This heat is extracted from the poleward flowing Atlantic Water in the Norwegian Atlantic Current. Elevated diffusivities are also found on the slope of the Norwegian Basin, where cooling is noted. Our measurements provide a constraint on the heat budget of the Norwegian Sea.