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    Temporal characteristics of abyssal finescale motions above rough bathymetry

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    JPO2988.1.pdf (2.667Mb)
    Date
    2007-03
    Author
    Toole, John M.  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/4139
    As published
    https://doi.org/10.1175/JPO2988.1
    DOI
    10.1175/JPO2988.1
    Keyword
     Bathymetry roughness; Finescale motion; Abyssal flows; Turbulent mixing; Shear dispersion 
    Abstract
    Current-meter data from a two-year mooring within a fracture zone on the western flank of the Mid-Atlantic Ridge in the South Atlantic Ocean are reported. The mooring, deployed in conjunction with the Brazil Basin Tracer Release Experiment, was placed in the general area where enhanced diapycnal mixing had previously been inferred. The current-meter data characterize the velocity, temperature, shear, and temperature gradient variability as a function of frequency. Energetic velocities and shears were observed at the mooring at a variety of frequencies. In addition to semidiurnal flows, a significant amount of shear variance derived from near-inertial motions, as has been seen in a recent numerical modeling study of tidal-frequency internal wave radiation and wave–wave interaction. At times, a fortnightly modulation of the total superinertial shear variance was indicated in the data, but this signal did not dominate the records. Wave ray tracing indicates that the deeper current meters may have been placed in a shadow zone for locally generated internal tides. At shallower levels, it is suggested that dispersion, wave–wave interaction, and wave breaking effectively obscured the sources of the finescale energy. Average diapycnal diffusivity estimates inferred from a Richardson-number-based parameterization and from observations of temperature inversions at 4648 m were of the same order of magnitude as those derived from turbulent dissipation estimates and from the rate of diapycnal tracer dispersion. The mooring data thus add additional support to the idea that energetic finescale motions above rough bathymetry support enhanced turbulent diapycnal mixing in these regions.
    Description
    Author Posting. © American Meteorological Society, 2007. 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 37 (2007): 409–427, doi:10.1175/JPO2988.1.
    Collections
    • Physical Oceanography (PO)
    Suggested Citation
    Journal of Physical Oceanography 37 (2007): 409-427
     

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