Observations of Boundary Mixing Over the Continental Slope

Towed-body observations of mixing over the continental slope reveal the great lateral extent (several km) of continuously turbulent fluid within a few hundred meters of the boundary at 1600 m depth. The largest turbulent dissipation rates were observed over a 5 km horizontal region near a slope critical to the M2 internal tide. Averaged over a submarine landslide oriented perpendicularly to the continental slope, enhanced mixing extended at least 600 m above the boundary, increasing toward the bottom. The resulting vertical divergence of the heat flux near the bottom implies that fluid there must be replenished. Intermediate nepheloid layers detected optically contained fluid with θ-S properties distinct from their surroundings. It is suggested that intermediate nepheloid layers are interior signatures of the boundary layer detachment required by the near-bottom flux divergence.