Intense mixing of the Faroe Bank Channel overflow

[1] The continuous, swift flow of cold water across the sill of the Faroe Bank Channel, the deepest passage from the Nordic Seas to the North Atlantic Ocean, forms a bottom-attached dense plume (overflow). The amount and distribution of entrainment and mixing that the overflow encounters during its descent influence the ventilation of the deep North Atlantic, however, remain poorly known due to lack of direct measurements. Using the first direct turbulence measurements, we describe the dynamic properties and mixing of the overflow plume as it descends toward the Iceland Basin. The vigorously turbulent plume is associated with intense mixing and enhanced turbulent dissipation near the bottom and at the plume-ambient interface, but with a quiescent core. Our measurements show a pronounced transverse circulation consistent with rotating plume dynamics, a strong lateral variability in entrainment velocity, and a vertical structure composed of order 100 m thick stratified interface and comparably thick well-mixed bottom boundary layer with significant transport and entrainment.