Measurements of the Turbulence in an Abyssal Boundary Layer

Abstract

Electromagnetic sensors have been used to measure the turbulent current fluctuations 50 cm above the sea bed at a depth exceeding 4000 m on an abyssal plain. Bursts of turbulent energy typically 1asted for about 50 s and showed a peak instantaneous −uw perturbation product of about 0.25 cm² s⁻². The horizontal and vertical integral length scales were estimated to be around 150 and 30 cm, respectively, in a mean flow of about 3 cm s⁻¹. The eddy correlation method gave estimates for the friction velocity of around 0.12 cm s⁻¹ and the bottom drag coefficient was estimated to be 1.9 × 10⁻³. When normalized by variance, height above bottom and wave number the spectra agree with the similarity scaling suggested by Soulsby, and the statistics of the turbulence are consistent with existing results obtained from atmospheric and shallow water boundary layers.