Spatial Variability of Diapycnal Mixing in the South China Sea Inferred from Density Overturn Analysis

The 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 epsilon and diapycnal diffusivity K-z between 100 and 1500 m indicated that the strongest mixing occurred in the Luzon Strait and Dongsha Plateau regions, with epsilon similar to 3.0 X 10(-8)W kg(-1)(epsilon(z)(ma)(x) = 5.3 X 10(-6) W kg(-1))and K-z similar to 3.5 X 10(-4)m(2) s(-1) (K-z(ma)x = 4.2 X 10(-2) m(2) s(-1)). The weakest mixing occurred in the thermocline of the central basin, with epsilon similar to 6.2 X 10(-)(10) W kg(-1) and K-z similar to 3.7 X 10(-6) m(2) s(-1). The epsilon and K-z in the continental slope indicated that the mixing in the northern part [O(10(-8)) W kg(-1) and O(10(-4)) m(2) s(-1), respectively] was comparatively stronger than that in the Xisha and Nansha regions [O(10(-)(9))W kg(-1) and O(10(-5)) m(2) s(-1), respectively]. The K-z 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 K-z = 3.3 X 10(-4) [1 + (1 - D/H)/0.22](-2) - 6.0 X 10(-6) m(2) s(-1). The vertically integrated energy dissipation was nominally 15.8 mW m(-2) for all data and 25.6 mW m(-2) for data at stations H < 2000 m. This was about one order of magnitude higher than that in the open oceans (3.0-3.3 mW m(-2)), which confirmed the active mixing state in the SCS.

Automated summary

The study reveals that the strongest mixing in the South China Sea occurs in the Luzon Strait and Dongsha Plateau regions, while the weakest mixing occurs in the thermocline of the central basin. Mixing in the northern continental slope region is comparatively stronger than that in the Xisha and Nansha regions.