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Strong transport and mixing of deep water through the Southwest Indian Ridge

Nature Geoscience volume 1, pages 755758 (2008) | Download Citation

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Abstract

The Indian Ocean harbours an important but poorly understood part of the global meridional ocean overturning circulation, which transports heat to high latitudes1. Understanding heat exchange in the Indian Ocean requires knowledge of the magnitudes and locations of both meridional deep-water transport and mixing, but in particular the latter is poorly constrained at present2,3. Here we present detailed measurements of transport and mixing in the Atlantis II fracture zone in the Southwest Indian Ridge, one of the main conduits for equatorward-flowing deep water4,5. We observe a northward jet of deep and bottom water extending 1,000 m vertically with a transport rate of 3×106 m3 s−1. Turbulent diffusivity within the jet was up to two orders of magnitude above typical deep ocean levels in our measurements. Our results quantify the flow through this narrow fracture zone to 20 to 30% of the total meridional overturning circulation in the Indian Ocean, and provide an example of elevated turbulence in a deep sheared flow that is not hydraulically controlled, in contrast to many other fracture zones6,7,8,9.

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Acknowledgements

We are greatly indebted to the expertise, helpful attitude and hard work of R/V Revelle’s captain, D. Murline, and crew. We thank K. Speer and P. Lazarevich for the generous loan of their ADCP. The work could not have been completed without the hard work of T. Aja, G. Carter, M. Goldin, T. Hughen, T. Huussen, D. Lucas, S. Nguyen and O. Sun. High-resolution bathymetry near the SWIR was obtained from multibeam instruments and provided by A. Scheirer at USGS. This work was supported by NSF grant OCE-0726783 and the University of California Ship Funds program.

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  1. Scripps Institution of Oceanography, La Jolla, California 92093, USA

    • J. A. MacKinnon
    • , T. M. S. Johnston
    •  & R. Pinkel

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Correspondence to J. A. MacKinnon.

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https://doi.org/10.1038/ngeo340

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