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)

• Published in: Journal of geophysical research. Oceans 2013-06, Vol.118 (6), p.2774-2792
• Main Authors: Sheen, K. L., Brearley, J. A., Naveira Garabato, A. C., Smeed, D. A., Waterman, S., Ledwell, J. R., Meredith, M. P., St. Laurent, L., Thurnherr, A. M., Toole, J. M., Watson, A. J.
• Format: Article
• Language: English
• Subjects: Antarctic Circumpolar Current; Computational fluid dynamics; Dissipation; Earth, ocean, space; Exact sciences and technology; External geophysics; Geophysics; internal wave; Internal waves; Lee waves; Marine; Mixing; Ocean floor; Parametrization; Physics of the oceans; Sea beds; Southern Ocean; Spatial distribution; Turbulence; turbulent dissipation; Wave energy
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1002/jgrc.20217

The spatial distribution of turbulent dissipation rates and internal wavefield characteristics is analyzed 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(1×10−10Wkg −1) in the Southeast Pacific to O(1×10−9Wkg −1) in the Scotia Sea, typically reaching 3×10−9Wkg −1 within a kilometer of the seabed. Enhanced levels of turbulent mixing are associated with strong near‐bottom flows, rough topography, and regions where the internal wavefield 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 mW m−2 in the Southeast Pacific and 14 mW 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. Key Points Turbulence increases by an order of magnitude between SE Pacific & Scotia Sea Lee waves play a pivotal role in Southern Ocean diapycnal mixing and circulation 10‐30 % of Southern Ocean predicted lee wave energy is dissipated locally