Internal tide driven tracer transport across the continental slope

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  • Carl Spingys
    University of Southampton
  • Richard Williams
    University of Liverpool
  • Joanne Hopkins
    National Oceanography Centre, Liverpool
  • Rob Hall
    University of East Anglia
  • Mattias Green
  • Jonathan Sharples
    University of Liverpool
The role of the internal tide in driving tracer transport across the continental slope is examined using simplified layered theory, channel model experiments and observational diagnostics of near shelf‐edge moorings. The effect of the internal tide is interpreted in terms of its Stokes' drift, which is separated into two distinct components: a bolus component, driven by the co‐variance of layer thickness and the velocity; and a shear component, driven by the velocity following the movement of an interface. For a three layer ocean, in the model experiments and observations, the onshore propagation of an internal tide drives a Stokes' transport directed onshore in the surface and the bottom layers, and directed offshore in the pycnocline. This reversing structure is due to the bolus component dominating near the boundaries, while the shear component dominates at the pycnocline. In the observational diagnostics, the Stokes' transport is not cancelled by the Eulerian transport, which is mainly directed along bathymetric contours. The Stokes' drift of the internal tide then provides a systematic on shelf tracer transport if there is a tracer sink on the shelf, carried in the surface or bottom layers. Conversely, the tracer transport is directed offshore if there is a tracer source on the shelf with plumes of shelf tracer expected to be carried offshore along the pycnocline. This tracer transport as a result of the internal tide is diagnosed for heat, salt and nitrate. The depth‐integrated nitrate flux is directed onto the shelf supplying nutrients to the productive shelf seas.

Keywords

  • exchange, internal tide, moorings, nitrate, shelf edge, Stokes' transport
Original languageEnglish
Article numbere2019JC015530
JournalJournal of Geophysical Research: Oceans
Volume125
Issue number9
Early online date3 Sep 2020
DOIs
Publication statusPublished - 17 Sep 2020
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