4.5 Article

Turbulent mixing and internal tides in Gaoping (Kaoping) Submarine Canyon, Taiwan

Journal

JOURNAL OF MARINE SYSTEMS
Volume 76, Issue 4, Pages 383-396

Publisher

ELSEVIER SCIENCE BV
DOI: 10.1016/j.jmarsys.2007.08.005

Keywords

Turbulent mixing; Internal tides; Sediment Flux; Submarine Canyon

Funding

  1. R.O.C. National Science Council (NSC) [NSC87-2611-M-110-002, NSC88-2611-M-110-001, NSC89-2611-M-110-015, NSC90-2611-M-110-007, NSC 92-2611-M-110-012]

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Turbulent overturning on scales greater than 10 m is observed near the bottom and in mid-depth layers within the Gaoping (formerly spelled Kaoping) Submarine Canyon (KPSC) in southern Taiwan. Bursts of strong turbulence coexist with bursts of strong sediment concentrations in mid-depth layers. The turbulence kinetic energy dissipation rate in some turbulence bursts exceeds 10(-4) W kg(-1), and the eddy diffusivity exceeds 10(-1) m(2) s(-1). Within the canyon, the depth averaged turbulence kinetic energy dissipation rate is similar to 7 x 10(-6) W kg(-1), and the depth averaged eddy diffusivity is similar to 10(-2) m(2) s(-1). These are more than two orders of magnitude greater than typical values in the open ocean, and are much larger than those found in the Monterey Canyon where the strong turbulent mixing has also been. The interaction of tidal currents with the complex topography in Gaoping Submarine Canyon is presumably responsible for the observed turbulent overturning via shear instability and the breaking of internal tides and internal waves at critical frequencies. Strong 1st-mode internal tides exist in KPSC. The depth averaged internal tidal energy near the canyon mouth is similar to 0.17 m(2) s(-2). The depth integrated internal tidal energy flux at the mouth of the canyon is similar to 14 kW m(-1), propagating along the axis of the canyon toward the canyon head. The internal tidal energy flux in the canyon is 3-7 times greater than that found in Monterey Canyon, presumably due to the more than 10 times larger barotropic tide in the canyon. Simple energy budget calculations conclude that internal tides alone may provide energy sufficient to explain the turbulent mixing estimated within the canyon. Further experiments are needed in order to quantify the seasonal and geographical distributions of internal tides in Gaoping Submarine Canyon and their effects on the sediment flux in the canyon. (C) 2008 Elsevier B.V. All rights reserved.

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