Internal Tide-Driven Mixing Above a Rough and Sloping Seafloor

Turbulent mixing is a fundamental process in ocean dynamics, significantly affecting both stratification and circulation. A key component of this mixing is internal tide-driven mixing occurring over rough topography. To investigate the abyssal slope currents generated by tides without the influence of mesoscale eddies, we employ large eddy simulations (LES) with realistic topography from a rough canyon in the Brazil Basin. Our findings reveal a notable difference from previous theories and field campaigns, where upwelling was observed near the bottom boundary and downwelling above it. Instead, we simulated tidal-driven mixing that induces Eulerian mean downwelling within the bottom boundary layer and upwelling in the upper part of the boundary layer and the adjacent interior. The sloping seafloor facilitates restratification, which counterbalances fluid homogenization due to tidal-driven mixing. This interaction allows for the development of a non-transient flow and the potential onset of marginal instability. Internal waves break down into patches of turbulence, driven by mechanisms such as shear instability or convective instability. Our analysis indicates that the bulk mixing coefficient varies with depth and should not be treated as a constant. This depth-dependent variation is crucial for accurately modeling and understanding ocean mixing processes.