Modeling Internal Tides and Mixing Over Ocean Ridges

Observations from the Hawaiian Ocean Mixing Experiment (HOME) survey component suggest an increase in diapycnal mixing events during spring tides in a region above a steep slope. To study possible mixing mechanisms, we utilize numerical simulations of the benthic boundary layer, using a domain on the order of 200 m, with environmental parameters consistent with the conditions during HOME. In model results, when the barotropic tidal flow is upslope, the stratification near the boundary is greatly reduced as denser deep water is advected above the less dense water retained in the boundary layer. This leads to statically unstable situations and persistent strong mixing events that are several tens of meters thick and last for approximately one quarter of the tidal period. Conversely, during the downslope tidal flow, denser fluid remains trapped in the boundary layer as less dense upslope fluid is advected downward, leading to very strong stratification near the boundary, which shuts down vertical mixing over the slope.