On the Canyon-Induced Dissipation of the Internal Tides

The breaking of tidally-generated internal gravity waves (hereafter internal tides) is a significant driver of ocean mixing, and observations and model simulations show that a non-negligible amount of this internal tide-driven mixing occurs in submarine canyons. While previous studies have used single observations of canyon mixing to estimate the global magnitude of internal tide-driven mixing within canyons, there is still significant uncertainty in these estimates. To address this question, we have constructed an algorithm based on the modelled energy loss in idealized simulations to calculate the magnitude of mixing in each submarine canyon and to determine the percentage of the global internal tide energy budget that is dissipated in canyons. The algorithm utilizes the Harris et al. 2014 analysis of the SRTM30_PLUS global bathymetry map to provide the geometrical properties of each canyon and a high-resolution, tidally-forced HYCOM simulation to determine the internal tide field. Preliminary calculations show that the canyons geometrical properties as well as local hydrographic properties have significant effects on the magnitude of mixing. Specifically, canyons that are tall relative to the depth of the water column and long relative to the incoming internal tides wavelength dissipate approximately 100% of the incoming waves energy. Our estimate of the globally-integrated energy dissipation in canyons, taking into account geometric properties of each canyon, is two to three times larger than prior global estimates extrapolated from observations of individual canyons. Furthermore, our research highlights canyon hotspots of internal tide-driven mixing in the global ocean, for which observations do not presently exist. These results raise larger questions about the location of internal tide dissipation and the inclusion of such dissipation in global ocean models.