van Haren, Hans; Gostiaux, Louis
Journal of Marine Research, Volume 74, Number 3, May 2016, pp. 161-173(13)
A 2.4 km long deep-sea mooring was deployed for 14 months in the Puerto Rico Trench, the deepest part of the Atlantic Ocean. Below its top buoyancy package, the mooring line held a 200 m long string of high-resolution temperature sensors and a current meter. Over the instrumented range between 6,004 and 6,204 m, waters are very weakly stratified, with local buoyancy frequency equaling about 1.9 times the semidiurnal tidal frequency.
Besides quiescent waters, the detailed observations show regular vertical turbulent overturning associated with periodic warming and driven by internal tidal and inertial waves. During such episodes, the 4-day and 200 m vertically averaged dissipation rate increases from approximately 10–11 up to 10–9 m2 s–3, and eddy diffusivity increases from 5 × 10–5 up to 4 × 10–3 m2 s–1. No large-scale shear-driven Kelvin-Helmholtz billows are observed, and free convection seems the dominant primary turbulent overturning mechanism affecting material redistribution and life in the weakly stratified environment.