Propagation and dissipation of the internal tide in upper Monterey Canyon

Abstract

Submarine canyons are sites of intense turbulence and mixing. Monterey Canyon cuts into the continental shelf off California, and is defined by its sinuous nature. Temperature, salinity, and current velocity measurements were made over 21 days in April 2009 with a depth-cycling towed body to understand internal tide propagation and dissipation through the canyon bends. Cross-canyon transects reveal complex flow patterns that follow large-scale bathymetry on scales greater than 5 km. Changes in thalweg direction deflect baroclinic energy flux, but the bends in the measurement region are too sharp for the flux to follow the thalweg. Ridges that form the bends in the canyon act as obstacles to the flow, and turbulent dissipation rates greater than 1 × 10 -5 m2 s-3 were observed on their flanks, especially at the largest meander (the Gooseneck). The canyon-integrated baroclinic energy flux increased from 2.7 MW at the most western section to 3.7 MW at the Gooseneck Ridge, which has a nearly critical bottom slope with respect to the semidiurnal baroclinic tide on the western side; baroclinic energy flux was 50% less on the eastern side of the ridge. While measured dissipation near the Gooseneck Meander was sufficient to explain the flux divergence, turbulence near the Gooseneck may have been undersampled. Between the Gooseneck Ridge and the most eastern cross-canyon transect, dissipation may account for the decrease in the energy flux; though a local energy balance does not hold, the energy budget is balanced over the larger scale of the measurement region east of the Gooseneck Ridge. Key Points Barotropic flow in the canyon was weak compared to the baroclinic. Flow was driven by the semidiurnal tide and followed the large-scale bathymetry. Turbulent hotspots were associated with ridges, shear flows, and critical slopes ©2013. American Geophysical Union. All Rights Reserved.