Internal-Wave Convection and Shear Near the Top of a Deep Equatorial Seamount

The near-equatorial ocean experiences particulardynamics because the Coriolis force is weak. One modelled effectof these dynamics is strong reduction of turbulent mixing in theocean interior. Unknowns are effects on internal wave breaking andassociated turbulent mixing above steeply sloping topography. Inthis paper, high-resolution temperature observations are analyzedfrom sensors that were moored near the top of a deep Ceara Basinseamount for one week. A vertical string held sensors between 0.4and 56.4 meters above the seafloor. The observations show com-mon semidiurnal-periodic internal wave breaking, with tidal- and56-m mean turbulence values that are not significantly differentfrom those observed near the top of 1000-m shallower mid-latitudeGreat Meteor Seamount, despite the twice lower vertical densitystratification. Profiles of 6-day mean turbulence values yield ver-tically uniform values except for a small decrease in the lower 2 mabove the seafloor. The lower 2-m show a distinct departure fromturbulent inertial subrange in temperature variance spectra. In 10-mhigher-up, spectral slopes indicate dominant turbulent convectionwith reduced flow and turbulence, except when a primary tidal boreis present. Further-up than 15 m, shear dominates (stratified) tur-bulence. The lack of Coriolis force is not found to be important forinternal wave-induced turbulence above steeply sloping topogra-phy, except that Kelvin-Helmholtz instabilities seem somewhatless chaotic and more organized roll-up than at mid-latitudes