Journal Article

Pathways to Turbulent Dissipation in a Submarine Canyon

Voet, Gunnar, Bellerjeau, Charlotte, Le Boyer, Arnaud, Naveira Garabato, Alberto, Dematteis, Giovanni, Couto, Nicole, Alford, Matthew H., Wynne‐Cattanach, Bethan L.

2025

Overview

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. Plain Language Summary Winds and tides contribute energy to the ocean which is either used to move deep water toward the surface or dissipated at small scales. It is important to understand the fate of ocean energy, so it can be properly incorporated into global models. To get to the small scales where dissipation occurs, energy undergoes a series of transfers through intermediate scales. The pathways energy takes on its way to dissipation are better understood in the open ocean than in areas near steep topography where dissipation is commonly the strongest, leaving a gap in our understanding. We use velocity data to examine the pathways that energy takes before being dissipated in a highly energetic environment, where waves created by the tide break on a canyon slope. The method we use has never been applied to small‐scale ocean observations before, but we are able to because of our closely spaced moorings and direct observations of small turbulent motions. This new approach reveals faster energy transfer (hours rather than days) than predictions from existing methods designed for the open ocean. By observing dissipation in areas where it is strongest, we can do a better job of estimating its impact on global systems in ocean‐climate models. Key Points Kinetic energy cascade from the internal tide to dissipation is mapped using velocity observations from a tidally active submarine canyon The timescale of energy flux to dissipation is 6 hr near the canyon floor, faster than previous open‐ocean estimates of many days A method allowing strong nonlinearity reveals energy flux to dissipation from frequencies lower than those predicted by weakly nonlinear methods

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Canyons / Climate / Climate models / Deep water / Dissipation factor / Dynamical systems / Energy / Energy flux / Energy transfer / Fluxing / Granulation / Internal tides / Kinetic energy / Mooring / Nonlinear dynamics / Nonlinear systems / Nonlinearity / Ocean circulation / Ocean models / Oceans / Parameterization / Spatial distribution / Submarine canyons / Topographic waves / Turbulence / Upwelling / Velocity / Wave breaking / Winds