Observations of Tidally Driven Turbulence over Steep, Small-Scale Topography Embedded in the Tasman Slope. Marques, O. B., Alford, M. H., Pinkel, R., MacKinnon, J. A., Voet, G., Klymak, J. M., & Nash, J. D. J. Phys. Oceanogr., 54(2):601–615, 2024.
doi  abstract   bibtex   
Abstract Enhanced diapycnal mixing induced by the near-bottom breaking of internal waves is an essential component of the lower meridional overturning circulation. Despite its crucial role in the ocean circulation, tidally driven internal wave breaking is challenging to observe due to its inherently short spatial and temporal scales. We present detailed moored and shipboard observations that resolve the spatiotemporal variability of the tidal response over a small-scale bump embedded in the continental slope of Tasmania. Cross-shore tidal currents drive a nonlinear trapped response over the steep bottom around the bump. The observations are roughly consistent with two-dimensional high-mode tidal lee-wave theory. However, the alongshore tidal velocities are large, suggesting that the alongshore bathymetric variability modulates the tidal response driven by the cross-shore tidal flow. The semidiurnal tide and energy dissipation rate are correlated at subtidal time scales, but with complex temporal variability. Energy dissipation from a simple scattering model shows that the elevated near-bottom turbulence can be sustained by the impinging mode-1 internal tide, where the dissipation over the bump is O (1%) of the incident depth-integrated energy flux. Despite this small fraction, tidal dissipation is enhanced over the bump due to steep topography at a horizontal scale of O (1) km and may locally drive significant diapycnal mixing. Significance Statement Near-bottom turbulent mixing is a key element of the global abyssal circulation. We present observations of the spatiotemporal variability of tidally driven turbulent processes over a small-scale topographic bump off Tasmania. The semidiurnal tide generates large-amplitude transient lee waves and hydraulic jumps that are unstable and dissipate the tidal energy. These processes are consistent with the scattering of the incident low-mode internal tide on the continental slope of Tasmania. Despite elevated turbulence over the bump, near-bottom energy dissipation is small relative to the incident wave energy flux.
@Article{	  marquesetal24,
  Title		= {Observations of {{Tidally Driven Turbulence}} over
		  {{Steep}}, {{Small-Scale Topography Embedded}} in the
		  {{Tasman Slope}}},
  Author	= {Marques, Olavo B. and Alford, Matthew H. and Pinkel,
		  Robert and MacKinnon, Jennifer A. and Voet, Gunnar and
		  Klymak, Jody M. and Nash, Jonathan D.},
  Year		= {2024},
  Journal	= {J. Phys. Oceanogr.},
  Volume	= {54},
  Number	= {2},
  Pages		= {601--615},
  DOI		= {10.1175/JPO-D-23-0038.1},
  URLDate	= {2025-10-10},
  Abstract	= {Abstract Enhanced diapycnal mixing induced by the
		  near-bottom breaking of internal waves is an essential
		  component of the lower meridional overturning circulation.
		  Despite its crucial role in the ocean circulation, tidally
		  driven internal wave breaking is challenging to observe due
		  to its inherently short spatial and temporal scales. We
		  present detailed moored and shipboard observations that
		  resolve the spatiotemporal variability of the tidal
		  response over a small-scale bump embedded in the
		  continental slope of Tasmania. Cross-shore tidal currents
		  drive a nonlinear trapped response over the steep bottom
		  around the bump. The observations are roughly consistent
		  with two-dimensional high-mode tidal lee-wave theory.
		  However, the alongshore tidal velocities are large,
		  suggesting that the alongshore bathymetric variability
		  modulates the tidal response driven by the cross-shore
		  tidal flow. The semidiurnal tide and energy dissipation
		  rate are correlated at subtidal time scales, but with
		  complex temporal variability. Energy dissipation from a
		  simple scattering model shows that the elevated near-bottom
		  turbulence can be sustained by the impinging mode-1
		  internal tide, where the dissipation over the bump is O
		  (1\%) of the incident depth-integrated energy flux. Despite
		  this small fraction, tidal dissipation is enhanced over the
		  bump due to steep topography at a horizontal scale of O (1)
		  km and may locally drive significant diapycnal mixing.
		  Significance Statement Near-bottom turbulent mixing is a
		  key element of the global abyssal circulation. We present
		  observations of the spatiotemporal variability of tidally
		  driven turbulent processes over a small-scale topographic
		  bump off Tasmania. The semidiurnal tide generates
		  large-amplitude transient lee waves and hydraulic jumps
		  that are unstable and dissipate the tidal energy. These
		  processes are consistent with the scattering of the
		  incident low-mode internal tide on the continental slope of
		  Tasmania. Despite elevated turbulence over the bump,
		  near-bottom energy dissipation is small relative to the
		  incident wave energy flux.},
  copyright	= {http://www.ametsoc.org/PUBSReuseLicenses},
  Keywords	= {jmkrefereed},
  File		= {/Users/jklymak/Zotero/storage/WT6YEYE8/Marques et al. -
		  2024 - Observations of Tidally Driven Turbulence over
		  Steep, Small-Scale Topography Embedded in the Tasman.pdf}
}
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