[1] A coupled three-dimensional physical model and a nitrogen-based dissolved inorganic nitrogen, phytoplankton, zooplankton, and detritus (NPZD) ecosystem model was used to study the ecosystem responses to the wind-driven summer upwelling and to the Pearl River plume over a distinctly widened shelf in the northeastern South China Sea (NSCS). Forced with an idealized, but representative, upwelling-favorable wind and the river discharge for the purpose of process-oriented study, we identified two high chlorophyll centers that are typically observed over the NSCS shelf and stimulated by nutrient enrichment from intensified upwelling over the widened shelf and from the river plume. The nutrient enrichment has strong along-shore variability involving the variable cross-isobath nutrient transport between the middle and the inner widened shelf during the upwelling and an eastward expansion of the nutrient-rich plume. About 20% of the upwelled nutrientrich deep water from the outer shelf reaches the inner shelf where algal blooms occur. Nutrient enrichment in the plume stretches over a broad extent of the shelf and produces significant biomass on the NSCS shelf. The plume is physically governed by intensified surface Ekman dynamics that leads to a strong offshore nutrient transport and eventually offsets the shoreward transport caused by the upwelling in the NSCS. Biological forcing and circulation dynamics of the surface Ekman layer jointly form the spatial dislocation and temporal variation of NO 3 , phytoplankton, and zooplankton biomasses in the upwelled and plume waters. The simulated results qualitatively resemble field and satellite measurements and demonstrate the physically modulated biological responses to the intensified upwelling and plume-influenced NSCS shelf.

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We examined diurnal variations of surface seawater pCO 2 (partial pressure of CO 2 ) in a suite of coastal marine environmental systems in the vicinity of the South China Sea (SCS) from inshore and nearshore settings in Xiamen Bay, Shenhu Bay, and the southwestern Taiwan Strait, to offshore sites in the basin and on the slope of the northern South China Sea as well as in a coral reef system at Xisha Islands in the middle of the SCS. There were significant diurnal changes of surface pCO 2 , ranging from 1.0 Pa to 1.6 Pa (10-16 matm) in the offshore and oligotrophic sites, ,4.1 Pa in the Taiwan Strait, 5.1-15.2 Pa in Xiamen Bay and Shenhu Bay, to as high as 60.8 Pa in the coral reef system at Xisha Islands. Processes that modulate these pCO 2 diurnal variations were temperature, tide or current, and biological controls. Temperature was a major driver of the pCO 2 diurnal variability in the oligotrophic regions, while tidal effects were important in the nearshore. In the coral reef system, biological metabolism dominated variability. Diurnal variability could have a potentially important implication on the estimate of air-sea CO 2 fluxes, which may result in an uncertainty of 60.48-0.77 mmol C m 22 d 21 for the offshore sites in the SCS. Such uncertainties were larger in nearshore settings.

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