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Observations and inverse models suggest that small-scale turbulent mixing is enhanced in the Southern Ocean in regions above rough topography. The enhancement extends O(1) km above the topography, suggesting that mixing is supported by the breaking of gravity waves radiated from the ocean bottom. In this study, it is shown that the observed mixing rates can be sustained by internal waves generated by geostrophic motions flowing over bottom topography. Weakly nonlinear theory is used to describe the internal wave generation and the feedback of the waves on the zonally averaged flow. Vigorous inertial oscillations are driven at the ocean bottom by waves generated at steep topography. The wave radiation and dissipation at equilibrium is therefore the result of both geostrophic flow and inertial oscillations differing substantially from the classical lee-wave problem. The theoretical predictions are tested versus two-dimensional highresolution numerical simulations with parameters representative of Drake Passage. This work suggests that mixing in Drake Passage can be supported by geostrophic motions impinging on rough topography rather than by barotropic tidal motions, as is commonly assumed.

Item Type:	Refereed Article
Keywords:	ocean mixing, internal waves, lee waves, eddies, rough topography
Research Division:	Earth Sciences
Research Group:	Oceanography
Research Field:	Physical Oceanography
Objective Division:	Environment
Objective Group:	Climate and Climate Change
Objective Field:	Climate Change Models
Author:	Nikurashin, M (Dr Maxim Nikurashin)
ID Code:	79715
Year Published:	2010
Web of Science® Times Cited:	68
Deposited By:	IMAS Research and Education Centre
Deposited On:	2012-10-01
Last Modified:	2012-11-26
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