Dynamical Impact of the Mekong River Plume in the South China Sea

Abstract

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

Reconstructing three-dimensional salinity field of the South China Sea from satellite observations

“…At a depth of 5 m, the relatively large error is mainly located in two coastal regions, but their values are still less than 0.3 psu. The regions correspond to the generation and extension of the Pearl River and Mekong River plumes that have a significant impact on the salinity field of the coastal and upper waters of the SCS (Chen et al, 2016;Zeng et al, 2022). The larger error near the Mekong River estuary is particularly notable in the upper 10 m, while the error near the Pearl River estuary is mainly distributed in the top layer.…”

“…The larger error near the Mekong River estuary is particularly notable in the upper 10 m, while the error near the Pearl River estuary is mainly distributed in the top layer. This might be associated with larger pulse of riverine flow into the SCS via the Mekong River, which results in a stronger halocline near the estuary (Gan et al, 2009;Zeng et al, 2022).…”

“…In summer, the RMSE within the top three layers is larger near the Pearl River and Mekong River estuaries than that in the other parts of the SCS. This might be related to the large amount of river discharge caused by the monsoon and wide extension of the river plumes to the SCS (Ou et al, 2007;Zeng et al, 2022). The southwest monsoon will bring a lot of precipitation over the ocean, thus increasing the river discharge.…”

Seasonal variability of satellite-derived primary production in the South China Sea from an absorption-based model

“…The seasonal cycle of NPP in the VE region is the same as in the NC region, resulting in a higher NPP in summer than in winter. In addition to the upwelling driven by the alongshore wind stress (Wyrtki, 1961), nutrients transported by the Mekong River were also found to have a crucial impact on the summer peak of NPP (Zeng et al, 2022). Quartile diagrams of similarity index between the seasonal variation of NPP for each year (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019)(2020) and monthly climatology mean in typical regions: The local dynamical processes are more complex in region LS.…”

“…High values of CHL (> 2 mg m -3 ) generally occur near the coast, while offshore concentrations are lower (< 0.3 mg m -3 ) (Yu et al, 2019). Ecological processes in the SCS are strongly affected by atmospheric depositions driven by season monsoons (e.g., Lin et al, 2007), in addition to alterations driven by river discharge (Zhang et al, 2012;Zeng et al, 2022), coastal upwelling (Shaw et al, 1996;Jing et al, 2009;Yan et al, 2015), and Kuroshio invasion (Li L et al, 2020). During certain specific periods, NPP in the SCS responds to environmental events such as forest fires (Xiao et al, 2020) and climatic events such as ENSO (Liao et al, 2012).…”