Buoyancy flux and mixing efficiency from direct, near-bottom turbulence measurements in a submarine canyon

Alford, Matthew H. ORCID: https://orcid.org/0000-0002-6318-0737; Wynne-Cattanach, Bethan; Le Boyer, Arnaud; Couto, Nicole; Voet, Gunnar; Spingys, Carl P.; Fernandez Castro, Bieito; Forryan, Alex; Naveira Garabato, Alberto C.; van Haren, Hans. 2025 Buoyancy flux and mixing efficiency from direct, near-bottom turbulence measurements in a submarine canyon. Journal of Physical Oceanography, 55 (2). 97-118. 10.1175/JPO-D-24-0005.1

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Abstract/Summary

Turbulent kinetic energy and thermal variance dissipation rates ϵ and χ , buoyancy flux J b , diffusivity κ ρ , and mixing coefficient , which is simply related to the mixing efficiency , are estimated from highly resolved microstructure measurements collected in a submarine canyon that has been previously shown to be experiencing near-bottom diapycnal upwelling. It is demonstrated that turbulence arises primarily from the convective instability of the internal tide. Twelve tidally resolving stations (12–48 h long) were conducted, wherein profiles were collected from between 5–15 m and 400 m above the bottom every 13–15 min using a custom turbulence vehicle. Turbulent buoyancy flux is estimated using the Osborn and Winters and D’Asaro methods, allowing direct estimation of the mixing coefficient as a function of time, temperature, and height above bottom. Turbulent dissipation and buoyancy flux generally increase toward the seafloor. The associated turbulent diapycnal diffusivity is 10 −4 –10 −2 m 2 s −1 . Observed is ∼0.2 ± 0.05 near the top of our measurement range, as expected in the ocean interior, and increases to 0.3–0.7 approaching the bottom, consistent with turbulence generated by convective instability.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1175/JPO-D-24-0005.1
ISSN:	0022-3670
Additional Keywords:	Abyssal circulation, Diapycnal mixing, Mixing, Thermohaline circulation
Date made live:	26 Feb 2025 21:15 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/538971

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