Presentation Abstract

Juan de Fuca Canyon, Washington, which cuts across the continental shelf from the mouth of the Strait of Juan de Fuca to the shelf break, is a likely conduit for deep (below shelf break) Pacific water to enter the Salish Sea. This is important to the Salish Sea ecosystem because the deeper Pacific water has lower pH and dissolved oxygen. Despite its potential importance to Ocean Acidification in the Salish Sea, very few direct observations have been made in the Canyon. Here we report breaking internal lee waves, strong mixing and hydraulic control associated with wind-driven up-canyon flow near the shelf break in Juan de Fuca Canyon. Unlike the flow above the canyon rim, which shows a tidal modulation typical on continental shelves, the flow within the canyon is consistently up-canyon during our observations, with isopycnals tilted consistent with a geostrophic along-canyon momentum balance. As the flow encounters a sill near the canyon entrance at the shelf break, it accelerates significantly and undergoes elevated mixing on the upstream and downstream sides of the sill. On the downstream side, a strong lee wave response is seen, with displacements of O(100 m) and overturns tens of meters high. The resulting diffusivity is sufficient to substantially modify coastal water masses as they transit the canyon.

Session Title

Session S-04A: Frontiers of Ocean Acidification Research in the Salish Sea

Conference Track

Ocean Acidification

Conference Name

Salish Sea Ecosystem Conference (2014 : Seattle, Wash.)

Document Type

Event

Start Date

1-5-2014 8:30 AM

End Date

1-5-2014 10:00 AM

Location

Room 615-616-617

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type

Text

Language

English

Format

application/pdf

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May 1st, 8:30 AM May 1st, 10:00 AM

Observations of Flow and Mixing in Juan de Fuca Canyon

Room 615-616-617

Juan de Fuca Canyon, Washington, which cuts across the continental shelf from the mouth of the Strait of Juan de Fuca to the shelf break, is a likely conduit for deep (below shelf break) Pacific water to enter the Salish Sea. This is important to the Salish Sea ecosystem because the deeper Pacific water has lower pH and dissolved oxygen. Despite its potential importance to Ocean Acidification in the Salish Sea, very few direct observations have been made in the Canyon. Here we report breaking internal lee waves, strong mixing and hydraulic control associated with wind-driven up-canyon flow near the shelf break in Juan de Fuca Canyon. Unlike the flow above the canyon rim, which shows a tidal modulation typical on continental shelves, the flow within the canyon is consistently up-canyon during our observations, with isopycnals tilted consistent with a geostrophic along-canyon momentum balance. As the flow encounters a sill near the canyon entrance at the shelf break, it accelerates significantly and undergoes elevated mixing on the upstream and downstream sides of the sill. On the downstream side, a strong lee wave response is seen, with displacements of O(100 m) and overturns tens of meters high. The resulting diffusivity is sufficient to substantially modify coastal water masses as they transit the canyon.