A snapshot of turbulence in the Northeastern Magellan Strait

Abstract

First-ever measurements of the turbulent kinetic energy (TKE) dissipation rate in the northeastern Strait of Magellan (Segunda Angostura region) taken in March 2019 are reported here. At the time of microstructure measurements, the magnitude of the reversing tidal current ranged between 0.8 and 1.2 ms⁻¹. The probability distribution of the TKE dissipation rate in the water interior above the bottom boundary layer was lognormal with a high median value \({\varepsilon }_{med}^{MS}=1.2\times {10}^{-6}\) Wkg⁻¹. Strong vertical shear, \(\left(1-2\right)\times {10}^{-2}\) s⁻¹, in the weakly stratified water interior ensued a sub-critical gradient Richardson number \(Ri<{10}^{-1}-{10}^{-2}\). In the bottom boundary layer (BBL), the vertical shear and the TKE dissipation rate both decreased exponentially with the distance from the seafloor \(\xi\), leading to a turbulent regime with an eddy viscosity \({K}_{M}\sim {10}^{-3}\) m²/s, which varied with time and location, while being independent of the vertical coordinate in the upper part of BBL (for \(\xi >\sim 2\) meters above the bottom).