The southern Greenland Deep Western Boundary Current (DWBC) advects major components of North Atlantic Deep Water. Turbulent diapycnal mixing rates of ∼10⁻⁴ m² s⁻¹ commonly occur in the DWBC. These diffusivities, estimated with an internal wave strain-based parameterisation, are independently confirmed by budgets of density and dissolved O₂. “Moderate” mixing rates (∼10⁻⁴ m² s⁻¹) over the DWBC path between Denmark Strait and Cape Farewell (∼1000 km) drive a similar net increase in volume transport by diapycnal entrainment to the more intense (∼10⁻³ m² s⁻¹), localised mixing rates found near the Denmark Strait overflow sill. Therefore turbulent mixing associated with the DWBC south of Denmark Strait is instrumental in establishing the magnitude of the North Atlantic Meridional Overturning Circulation. Elevated mixing rates are also seen in the East and West Greenland Currents; this may be significant in preconditioning seasonal restratification of the intermediate layers of the Irminger and Labrador basins.