Spatial variability of diapycnal mixing in the South China Sea inferred from density overturn analysis

Abstract

AbstractThe nominal spatial distribution of diapycnal mixing in the South China Sea (SCS) is obtained with Thorpe-scale analysis from 2004 to 2020. The inferred dissipation rate ε and diapycnal diffusivity Kz between 100 and 1500 m indicated that the strongest mixing occurred in the Luzon Strait and Dongsha Plateau regions, with ε ~ 3.0 × 10-8 W/kg (εmax = 5.3 × 10-6 W/kg) and Kz ~ 3.5 × 10-4 m2/s (Kz max = 4.2 = 10-2 m2/s). The weakest mixing occurred in the thermocline of the central basin, with ε ~ 6.2 × 10-10 W/kg and Kz ~ 3.7 × 10-6 m2/s. The ε and Kz in the continental slope indicated that the mixing in the northern part [O(10-8) W/kg, O(10-4) m2/s] was comparatively stronger than that in the Xisha and Nansha regions [O(10-9) W/kg, O(10-5) m2/s]. The Kz in the continental slope region (200–2000 m) decayed at a closed rate from the ocean bottom to the main thermocline when the measured depth D was normalized by the ocean depth H as D/H, whether in the shallow or deep oceans. The diapycnal diffusivity was parameterized as Kz = 3.3 × 10−4 (1 + )−2 − 6.0 × 10−6 m2/s. The vertically integrated energy dissipation was nominally as 15.8 mW/m2 for all data and 25.6 mW/m2 for data at stations H < 2000 m. This was about one order higher than that in the open oceans (3.0–3.3 mW/m2), which confirmed the active mixing state in the SCS.