Internal wave–turbulence pressure above sloping sea bottoms

Abstract

An accurate bottom pressure sensor has been moored at different sites varying from a shallow sea strait via open ocean guyots to a 1900 m deep Gulf of Mexico. All sites show more or less sloping bottom topography. Focusing on frequencies (sigma) higher than tidal, the pressure records are remarkably similar, to within the 95% statistical significance bounds, in the internal gravity wave continuum (IWC) band up to buoyancy frequency N. The IWC has a relatively uniform spectral slope: log(P(sigma)) = -alpha log(sigma), alpha = 2 +/- 1/3. The spectral collapse is confirmed from independent internal hydrostatic pressure estimate, which suggests a saturated IWC. For sigma > N, all pressure-spectra transit to a bulge that differs in magnitude. This bulge is commonly attributed to long surface waves. For the present data it is suggested to be due to stratified turbulence-internal wave coupling, which is typically large over sloping topography. The bulge drops off at a more or less common frequency of 2-3 x 10(-2) Hz, which is probably related with typical turbulent overturning scales.