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    Turbulent mixing in a deep fracture zone on the Mid-Atlantic Ridge

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    jpo-d-16-0264.1.pdf (3.385Mb)
    Date
    2017-07-13
    Author
    Clément, Louis  Concept link
    Thurnherr, Andreas M.  Concept link
    St. Laurent, Louis C.  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/9235
    As published
    https://doi.org/10.1175/JPO-D-16-0264.1
    DOI
    10.1175/JPO-D-16-0264.1
    Keyword
     Abyssal circulation; Bottom currents/bottom water; Diapycnal mixing 
    Abstract
    Midocean ridge fracture zones channel bottom waters in the eastern Brazil Basin in regions of intensified deep mixing. The mechanisms responsible for the deep turbulent mixing inside the numerous midocean fracture zones, whether affected by the local or the nonlocal canyon topography, are still subject to debate. To discriminate those mechanisms and to discern the canyon mean flow, two moorings sampled a deep canyon over and away from a sill/contraction. A 2-layer exchange flow, accelerated at the sill, transports 0.04–0.10-Sv (1 Sv ≡ 106 m3 s−1) up canyon in the deep layer. At the sill, the dissipation rate of turbulent kinetic energy ε increases as measured from microstructure profilers and as inferred from a parameterization of vertical kinetic energy. Cross-sill density and microstructure transects reveal an overflow potentially hydraulically controlled and modulated by fortnightly tides. During spring to neap tides, ε varies from O(10−9) to O(10−10) W kg−1 below 3500 m around the 2-layer interface. The detection of temperature overturns during tidal flow reversal, which almost fully opposes the deep up-canyon mean flow, confirms the canyon middepth enhancement of ε. The internal tide energy flux, particularly enhanced at the sill, compares with the lower-layer energy loss across the sill. Throughout the canyon away from the sill, near-inertial waves with downward-propagating energy dominate the internal wave field. The present study underlines the intricate pattern of the deep turbulent mixing affected by the mean flow, internal tides, and near-inertial waves.
    Description
    Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 47 (2017): 1873-1896, doi:10.1175/JPO-D-16-0264.1.
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    • Physical Oceanography (PO)
    Suggested Citation
    Journal of Physical Oceanography 47 (2017): 1873-1896
     

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