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Rates and mechanisms of turbulent dissipation and mixing in the Southern Ocean: Results from the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES)

Sheen, K.L.; Brearley, J.A.; Naveira Garabato, A.C. ; Waterman, S.; Smeed, D.A.; Ledwell, J.R.; Meredith, M.P.; St. Laurent, L.; Thurnherr, A.M.; Toole, J.M.; Watson, A.J.. 2013 Rates and mechanisms of turbulent dissipation and mixing in the Southern Ocean: Results from the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). Journal of Geophysical Research: Oceans, 118 (6). 2774-2792. 10.1002/jgrc.20217

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Abstract/Summary

The spatial distribution of turbulent dissipation rates and internal wave field characteristics is analysed across two contrasting regimes of the Antarctic Circumpolar Current (ACC), using microstructure and finestructure data collected as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). Mid-depth turbulent dissipation rates are found to increase from O (1×10-10 W kg-1) in the Southeast Pacific to O (1×10-9 W kg-1) in the Scotia Sea, typically reaching 3×10-9 W kg-1 within a kilometre of the seabed. Enhanced levels of turbulent mixing are associated with strong near-bottom flows, rough topography, and regions where the internal wave field is found to have enhanced energy, a less-inertial frequency content and a dominance of upward-propagating energy. These results strongly suggest that bottom-generated internal waves play a major role in determining the spatial distribution of turbulent dissipation in the ACC. The energy flux associated with the bottom internal wave generation process is calculated using wave radiation theory, and found to vary between 0.8 mWm-2 in the Southeast Pacific and 14 m W m-2 in the Scotia Sea. Typically, 10-30% of this energy is found to dissipate within 1 km of the seabed. Comparison between turbulent dissipation rates inferred from finestructure parameterizations and microstructure-derived estimates suggests a significant departure from wave-wave interaction physics in the near-field of wave generation sites.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1002/jgrc.20217
Programmes: BAS Programmes > Polar Science for Planet Earth (2009 - ) > Polar Oceans
ISSN: 21699275
Date made live: 14 May 2013 12:30 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/501905

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