Observations of turbulence on the shelf and slope of northern South China Sea

• Direct measurements of turbulence over the continental shelf and slope of the northern South China Sea are presented.
• Spatial structure and temporal variability of turbulent dissipation and mixing are investigated.
• Potential mechanisms for this microstructure pattern are explored.

Using the data collected in 2004 from a microstructure profiler, we present measurements of turbulence along a section across the continental shelf and slope in the northern South China Sea. The results show that energetic turbulence occurred over the shelf with an average dissipation rate (εε) and diapycnal diffusivity (κκ) at 2.8×10−7 W kg−1 and 1.6×10−3 m2 s−1, respectively; over the slope, they are about one order smaller, at 3.6×10−8 W kg−1 and 5.2×10−4 m2 s−1, respectively. In addition, the dissipation rate varied diurnally within the mixed layer on both the shelf and the slope. Below the mixed layer, εε shows six-hour variability over the shelf and peaked at 10−6 W kg−1 near the ocean bottom. We show that the shear instabilities from semidiurnal and diurnal tides are responsible for the turbulent dissipation of intermediate water over the shelf. On the slope, high εε reaching 10−7 W kg−1 prevailed within the pycnocline during the observation period, due to the shear instability caused by Kuroshio intrusion. This work facilitates the exploration of spatial structure and temporal variability of small-scale mixing and its impacts on large-scale processes in the South China Sea.