The Arrested Ekman Layer Escapes! Ventilation of the Bottom Boundary Layer by Internal Swash. I. N/f ~ 4 and N / slope f ~ O(1)

Moored data downstream of Orkney Passage, a small gap in the submarine extension of the Western Antarctic Penninsula through which > 25% of the total AABW crossing the Southern Boundary of the AAC passes, are presented. Subinertial flows of $O(0.2$ m s${}^{-1}$) are in the sense of Kelvin wave propagation, and support a downwelling Ekman layer with reduced near-boundary stratification. The moored data document cross-slope and vertical buoyancy fluxes dominated by a frequency band that includes diurnal and inertial frequencies and that extends to about an order of magnitude larger than inertial. We refer to this frequency band as internal swash, and to the region of reduced stratification at the bottom boundary exhibiting these fluxes as the internal swash zone. Vertical fluxes of cross-slope momentum associated with internal swash band frequencies are large and of similar order of magnitude as the drag associated with the viscous no-flow bottom boundary condition on the cross-slope subinertial current. Mixing efficiencies within the internal swash zone are large ($\Gamma \sim 0.8$). Similar mixing efficiencies at mixing levels $O\left(1000\right)$ times background extend well above (thousands of meters above) the internal swash zone. This enhanced turbulence appears to be sourced by high-frequency internal waves radiating from the swash zone.