Vertical mixing in the deep region of the Sunda Strait, Indonesia

Abstract

The characteristics of mixing properties in the Sunda Strait waters were revealed using indirect method, employing the archived CTD datasets of the RCO-BRIN. The mixing properties represented by turbulent kinetic energy dissipation (TKE) rate and vertical eddy diffusivity were inferred using an improved Thorpe Method from gravitationally unstable density profiles measured by CTD in July 2001. This study is aimed to reveal the rate of water mass mixing quantitatively. Vertically, the region was characterized by three distinctive regimes of TKE dissipation rate, i.e. 8.2×10^-8 W/kg in the near-surface and upper thermocline layer, 2.6×10^-7 W/kg in the lower thermocline layer and 9.1×10^-9 W/kg in the intermediate and deep layer. The spatial variability of the dissipation rate is likely related to topography roughness pattern where enhanced dissipation rate mainly occurred in the steep topography region. No specific regime can be clustered from the vertical diffusivity value due to its intermittent pattern, possibly due to the impact of topography roughness and stratification variability in space and time. The maximum enhanced values reached 3×10^-4 m²/s. It was suggested that strong shear due to interaction between sharp changing topography, the strait throughflow and tidal currents controls the mixing rate in this region. This indirect estimates need to be validated against microstructure measurements via a continuously profiling which covers at least one tidal cycle to investigate possible temporal variability