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Circulation around and atop the Seychelles Plateau
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  • Alma Carolina Castillo-Trujillo,
  • Isabella Beatriz Arzeno,
  • Sarah Nicole Giddings,
  • Geno Pawlak,
  • Julie L McClean,
  • Luc Rainville
Alma Carolina Castillo-Trujillo
Scripps Institution of Oceanography

Corresponding Author:[email protected]

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Isabella Beatriz Arzeno
University of California, San Diego
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Sarah Nicole Giddings
University of California, San Diego
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Geno Pawlak
University of California, San Diego
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Julie L McClean
Scripps Institution of Oceanography
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Luc Rainville
School of Oceanography, Seattle
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Abstract

The ocean circulation around and over the Seychelles Plateau is characterized using 35 months of temperature and velocity measurements and a numerical model of the region. The results here provide the first documented description of the ocean circulation atop the Seychelles Plateau. The Seychelles Plateau is an unusually broad (~200 km), shallow (~50 m) plateau, dropping off steeply to the abyss. It is situated in a dynamic location (3.5-5.5S, 54-57$E) in the south-western tropical Indian Ocean where northwesterly winds are present during austral summer and become southeasterly in austral winter, following the reversal of the Indian monsoon winds. Measurements around the Inner Islands, on the Seychelles Plateau, have been carried out since 2015. Velocity measurements show that most of the depth-averaged current variance on the Seychelles Plateau arises from near-inertial oscillations and lower-frequency variability. Lower-frequency variability encompasses seasonal and intraseasonal variability, the latter of which includes the effects of mixed Rossby-gravity waves and mesoscale eddies. A global 0.1-deg numerical ocean simulation is used in conjunction with these observations to describe the regional circulation around and on the Seychelles Plateau. Atop the SP, circulation is dominated by ageostrophic processes consistent with Ekman dynamics, while around the SP, both geostrophic and ageostrophic processes are important and vary seasonally. Stratification responds to the sea surface height semiannual signal which is due to Ekman pumping-driven upwelling (related to the Seychelles-Chagos Thermocline Ridge) and the arrival of an annual downwelling Rossby wave.
Feb 2021Published in Journal of Geophysical Research: Oceans volume 126 issue 2. 10.1029/2020JC016593