The South China Sea (SCS) is the largest marginal sea in Southeast Asia. It occupies the region from the equator to 23°N and from 99°E to 121°E with a maximum depth of over 5,000 m. It connects to the Sulu and Java Seas in the south through several shallow passages, and with the Pacific Ocean through the deep (∼2,000 m) Luzon Strait in the north. Exchange of shelf waters between the South China Sea and the East China Sea occurs through the Taiwan Strait at a sill depth of 60 m. Two broad shelves with depth shallower than 200 m are located on the northwestern and southwestern SCS, bordering the central, bowl-shaped deep basin (Hu et al., 2000). The SCS circulation is strongly influenced by the monsoonal winds (Daryabor et al., 2016). In winter, northeasterly winds prevail over the whole region with an average magnitude of 9 ms −1 and the coastal upwelling off the coast of Vietnam is suppressed due to the wind-driven cyclonic circulation cell (Chao et al., 1996). In contrast, the weaker southwest summer monsoon winds from June to September, with an average magnitude of 6 ms −1 , induce coastal upwelling that brings colder and saltier water to the surface (Wang et al., 2015). As a result of the wind upwelling, two distinct circulation cells are visible during this season (Dippner et al., 2011). The summer monsoon also brings intense rainfall over the ocean and Indochina, which drives large pulses of riverine flow into the SCS via the Mekong River (Shaw & Chao, 1994). The Mekong River originates in the Tibetan Plateau in China, drains a nearly 800,000 km 2 watershed and discharges into the SCS at the Mekong Delta in Vietnam with an annual mean