Mean seasonal cycle of isothermal depth in the South China Sea

[1] The mean seasonal cycle of isothermal depth is examined using all available temperature profiles in the South China Sea. On the annual average, the isothermal depth has two deep cores (> 45 m). One extends westward from the Luzon Strait along the continental slope south of China, and the other in the deep basin of the southern South China Sea. Harmonic analysis shows that the seasonal variation of isothermal depth is predominantly annual in the northern South China Sea, exceeding 70 m in winter and falling below 20 m in summer near the continental slope south of China. The annual variation is weaker in the southern South China Sea, where the isothermal depth approaches its seasonal maximum (> 55 m) in fall and minimum (< 35 m) in spring. The semiannual variation is most prominent in the southern South China Sea, being of comparable strength with the annual variation. Among others, local Ekman pumping appears to be an important process responsible for the semiannual variation in the southern South China Sea. A detailed description of the month-to-month variations is provided, to set a basic background for further understanding the South China Sea mixed layer dynamics and thermodynamics.