Internal-wave convection and shear near the top of a deep equatorial seamount
In: Pure and Applied Geophysics. Birkhäuser: Basel. ISSN 0033-4553; e-ISSN 1420-9136, more
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| Author keywords |
Unnamed equatorial deep Atlantic seamount; high-resolution temperature sensors moored between [0.4 56.4] m; turbulence values constant between 2–56 m above seafloor; dominant convection in lower 2–12 m above seafloor |
| Abstract |
The near-equatorial ocean experiences particular dynamics because the Coriolis force is weak. One modelled effect of these dynamics is strong reduction of turbulent mixing in the ocean interior. Unknowns are effects on internal wave breaking and associated turbulent mixing above steeply sloping topography. In this paper, high-resolution temperature observations are analyzed from sensors that were moored near the top of a deep Ceará Basin seamount for one week. A vertical string held sensors between 0.4 and 56.4 meters above the seafloor. The observations show common semidiurnal-periodic internal wave breaking, with tidal- and 56-m mean turbulence values that are not significantly different from those observed near the top of 1000-m shallower mid-latitude Great Meteor Seamount, despite the twice lower vertical density stratification. Profiles of 6-day mean turbulence values yield vertically uniform values except for a small decrease in the lower 2 m above the seafloor. The lower 2-m show a distinct departure from turbulent inertial subrange in temperature variance spectra. In 10-m higher-up, spectral slopes indicate dominant turbulent convection with reduced flow and turbulence, except when a primary tidal bore is present. Further-up than 15 m, shear dominates (stratified) turbulence. The lack of Coriolis force is not found to be important for internal wave-induced turbulence above steeply sloping topography, except that Kelvin–Helmholtz instabilities seem somewhat less chaotic and more organized roll-up than at mid-latitudes. |
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