• DOI:10.1038/nature12432
• Corpus ID: 1624477

Rapid cross-density ocean mixing at mid-depths in the Drake Passage measured by tracer release

@article{Watson2013RapidCO,
  title={Rapid cross-density ocean mixing at mid-depths in the Drake Passage measured by tracer release},
  author={Andrew J. Watson and James R. Ledwell and Marie-Jos{\'e} Messias and Brian A. King and Neill Mackay and Michael P. Meredith and Benjamin J. W. Mills and Alberto Naveira Garabato},
  journal={Nature},
  year={2013},
  volume={501},
  pages={408-411}
}

• A. Watson, J. Ledwell, +5 authors A. N. Garabato
• Published 19 September 2013
• Environmental Science
• Nature

Diapycnal mixing (across density surfaces) is an important process in the global ocean overturning circulation. Mixing in the interior of most of the ocean, however, is thought to have a magnitude just one-tenth of that required to close the global circulation by the downward mixing of less dense waters. Some of this deficit is made up by intense near-bottom mixing occurring in restricted ‘hot-spots’ associated with rough ocean-floor topography, but it is not clear whether the waters at mid-depth, 1,000 to 3,000 metres, are returned to the surface by cross-density mixing or by along-density flows. Here we show that diapycnal mixing of mid-depth (∼1,500 metres) waters undergoes a sustained 20-fold increase as the Antarctic Circumpolar Current flows through the Drake Passage, between the southern tip of South America and Antarctica. Our results are based on an open-ocean tracer release of trifluoromethyl sulphur pentafluoride. We ascribe the increased mixing to turbulence generated by the deep-reaching Antarctic Circumpolar Current as it flows over rough bottom topography in the Drake Passage. Scaled to the entire circumpolar current, the mixing we observe is compatible with there being a southern component to the global overturning in which about 20 sverdrups (1 Sv = 106 m3 s−1) upwell in the Southern Ocean, with cross-density mixing contributing a significant fraction (20 to 30 per cent) of this total, and the remainder upwelling along constant-density surfaces. The great majority of the diapycnal flux is the result of interaction with restricted regions of rough ocean-floor topography.