4th International Submarine Canyon Symposium (INCISE2018)

5-7 November 2018, Shenzhen, CHINA

View Abstract

This is the detail of Low-mode internal tide energy loss at a canyon topographic “pinch point” leads to intense stratified mixing layers and a focused region of lateral flow between near-boundary and offshore waters

< Back to List Version: 1019:1024 Status: Approved Edit Time: 2018/9/17 13:36:00


Author
Erika McPhee-Shaw
Co-Author(s)
Eric Kunze, James Girton, Jingping Xu, Amy Waterhouse
Abstarct Title
Low-mode internal tide energy loss at a canyon topographic “pinch point” leads to intense stratified mixing layers and a focused region of lateral flow between near-boundary and offshore waters
Abstarct Body
Energetic internal waves have long been recognized as a dominant dynamic feature in submarine canyons around the world. Here we discuss recent findings from studies over the past decade in canyons on the US west coast focused on understanding internal tide propagation and dissipation within canyons. Observational experiments from two canyons have shown dissipation to cause intense stratified mixing layers, and evidence of along-isopycnal exchange between boundary-layer and offshore waters. Monterey Canyon, Central California, USA, is characterized by low-mode semidiurnal internal wave energy from the outer ocean funneling into the outer canyon and propagating shoreward, causing intense tidal currents over the deep thalweg and stratified turbulent layers with elevated turbulent dissipation extending 200 to 600 meters above the seafloor. Wave energy is lost as propagation progresses up-canyon, and a bottleneck occurs where the canyon undergoes abrupt topographic change at a bend between about 1000 and 700-m depth, a site where topography steepens and two tributary canyon branches meet. 80% of incident low-mode internal wave energy flux is lost passing over this large-scale feature. Much of this energy loss goes to water column mixing. Yet the water column does not gain potential energy and instead appears to continuously re-stratify. One outcome of the re-stratification process is persistent exchange between near-boundary and offshore waters, and the formation of spatially persistent and recurrent intermediate nepheloid layers. Offshore exchange of mixed near-boundary waters was also found to affect the distribution of oxygen within the deep oxygen minimum zone offshore of the region of intense mixing. The Eel River Canyon, in northern California, is characterized by similar internal wave energetics, flux convergence, and intense stratified mixing layers extending hundreds of meters above the seafloor. Both canyons are important sinks for internal wave energy and the implications for canyon shape feeding back into abyssal mixing, internal tide energy loss, and boundary-interior exchange are discussed.
INCISE Theme
Session 1: Canyon processes in space and time (formation, evolution, circulation)
Presentation Type
Oral Presentation
Keywords
internal waves, boundary layer, turbulence, sediment, intermediate nepheloid layer

< Back to List