4.7 Article

On Internal Tides Driving Residual Currents and Upwelling on an Island

Journal

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
Volume 127, Issue 7, Pages -

Publisher

AMER GEOPHYSICAL UNION
DOI: 10.1029/2021JC018261

Keywords

internal tides; residual currents; upwelling; island; temperature; internal wave

Categories

Funding

  1. ONR [N00014-22-1-2040, N00014-15-1-2287, N00014-16-1-2256, N00014-20-1-2707]
  2. NSF [OCE-1753317]

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This study presents a modeling study of internal tides propagating around an idealized island. It shows that subcritical slope has the greatest potential for creating favorable conditions for benthic organisms through enhanced upwelling. These findings are important for understanding the propagation of internal waves and the characteristics of water flow around islands.
We present a modeling study of an idealized island with sloping sides in a stratified ocean with internal tides propagating through the domain, which transform into nonlinear internal waves as they encounter shallow depths. In the base condition, representative of a mid-latitude island with relatively steep super critical slopes, the nonlinear internal waves shoaling on the island wrap around the island, scatter, and create an asymmetric wavefield. Radiation stress gradients from this wavefield and rotation are balanced by pressure gradients and turbulent vertical diffusion in the momentum equations which drive residual mean currents around the island. We explore the effects of different physical parameters including no rotation, higher Froude number, subcritical slope, addition of barotropic tides, larger excursion number, and addition of large-scale mean currents. All simulations showed formation of residual currents of varying intensity, upwelled deep waters in shallow regions, and cooler waters on the side of the island consistent with the direction of incoming internal tides. While the no rotation and strong mean flow conditions created some upwelling, of all the modeled conditions, the subcritical slope has the greatest potential for creating favorable conditions for benthic organisms through enhanced upwelling. Areas of the world's oceans with stratified waters sufficient to sustain internal tide motions, strong internal tide energy, and local subcritical bottom slopes are likely to have cooler waters and more upwelled deep waters than the surrounding areas, and potentially serve as thermal refugia from future ocean warming.

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