Mid-depth mixing linked to North Atlantic Current variability

Repeated observations at the subpolar front west of the Mid‐Atlantic Ridge show a link between the position of the North Atlantic Current (NAC) and the spatial distribution of fine‐scale variance, diapycnal diffusivity, and integrated energy dissipation. Observational data were collected during three cruises. A single branch of the NAC was found in 2008, approximately at 50°30′N, and two branches were observed in 2010 and 2011, with alternating intensities. Shear variance was elevated below the core of the NAC in all cases, resulting in an average diapycnal diffusivity that is higher by a factor of 3 compared to the averages north and south of the NAC. The integrated energy dissipation has maxima at or south of the fronts; background dissipation is highest during 2008, also the year with the highest surface eddy kinetic energy. Key Points Observations show enhanced open ocean mixing below North Atlantic Current coreLocation of mixing changes with position of NAC/Mid Atlantic Ridge interactionIntegrated energy dissipation corresponds to surface eddy kinetic energy