Pathways to Turbulent Dissipation in a Submarine Canyon

Velocity and turbulence observations are used to estimate the forward cascade of kinetic energy from the internal tide to dissipation within a steep canyon. Two methods for computing cross-frequency kinetic energy flux are compared to observed dissipation. One method, coarse graining, allows strongly nonlinear dynamics while the other assumes weak nonlinearity. Fluxes from both methods agree within a factor of 3 with dissipation estimates from a finescale parameterization which is often used in climate-scale ocean models. Coarse graining predicts 68% of energy fluxing to dissipation from frequencies lower than 8cpd, while the weakly nonlinear method predicts 34%. The weighting of energy flux toward lower frequencies supports a shorter frequency-space pathway to dissipation in the presence of topographic wave breaking than assumed by parameterizations. Enhanced near-boundary mixing and upwelling has implications for the rate and spatial distribution of the upwelling branch of the global overturning circulation.