Scattering of the M2 Internal Tide in a Selection of Continental Slope Canyons

Robert Nazarian, Fairfield University, Physics, Fairfield, CT, United States, Sonya Legg, Princeton University, Princeton, NJ, United States, Madeleine Marie Hamann, Scripps Institution of Oceanography, Physical Oceanography, La Jolla, CA, United States and Amy Frances Waterhouse, Scripps Institution of Oceanography, La Jolla, CA, United States
Submarine canyons comprise approximately ten percent of the global continental slope and are responsible for a host of coastal processes. Numerous observations and numerical simulations have shown that continental slope canyons can be regions of intense internal tide-driven mixing. Here, we undertake a modeling process study of tidally-generated internal wave scattering in realistic submarine canyons to understand the processes responsible for enhanced mixing and to determine whether observations of mixing in canyons can be explained by scattering of low-mode internal waves. We perform high-resolution numerical simulations of remotely-generated, M2 tidal-frequency, mode-1 internal waves interacting with three realistic canyon topographies that represent a variety of observed canyon bathymetries. We compare the simulations with observations from within these canyons as a means of validating the numerical simulations and determining the processes responsible for observed mixing in submarine canyons. Simulations agree with existing observations in the magnitude and spatial distribution of dissipation, with some differences in the vertical. Energy loss within these realistic canyon simulations is consistent with that in simulations of idealized canyons with similar bottom slope and aspect ratio, despite the complexity of the realistic topography. While internal wave focusing and other processes have been found to lead to enhanced levels of dissipation in observations and simulations of canyons, we find that the frictional bottom boundary layer is an additional, important dissipative process in submarine canyons. The relative agreement between the mixing in the idealized simulations of M2 internal tides and the observations, where multiple tidal frequencies and harmonics are present, is encouraging and may provide the basis for parameterizations of mixing in canyons in ocean models.