Global abyssal mixing inferred from lowered ADCP shear and CTD strain profiles

Abstract

Internal wave-wave interaction theories and observations support a parameterization for the turbulent dissipation rate ε and eddy diffusivity K that depends on internal wave shear (Vz2) and strain (ξz2) variances. Its latest incarnation is applied to about 3500 lowered ADCP/CTD profiles from the Indian, Pacific, North Atlantic, and Southern Oceans. Inferred diffusivities K are functions of latitude and depth, ranging from 0.03 × 10-4 m2 s-1 within 2° of the equator to (0.4-0.5) × 10-4 m2 s-1 at 50°-70°. Diffusivities K also increase with depth in tropical and subtropical waters. Diffusivities below 4500-m depth exhibit a peak of 0.7 × 10-4 m2 s-1 between 20° and 30°, latitudes where semidiurnal parametric subharmonic instability is expected to be active. Turbulence is highly heterogeneous. Though the bulk of the vertically integrated dissipation ∫ε is contributed from the main pycnocline, hotspots in ∫ε show some correlation with small-scale bottom roughness and near-bottom flow at sites where strong surface tidal dissipation resulting from tide-topography interactions has been implicated, Average vertically integrated dissipation rates are 1.0 mW m-2, lying closer to the 0.8 mW m-2 expected for a canonical (Garrett and Munk) internal wave spectrum than the global-averaged deep-ocean surface tide loss of 3.3 mW m-2. © 2006 American Meteorological Society.