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typhoon rain storm resulted in the historically greatest flood of the Pearl River, and
therefore, which induced in the lowest SSS (32.2) in the nSCS during that study period
(Lei et al., 2003; Xie and Zhang, 2003). In 1999, the SSS was below normal due to the
influence of frequent typhoon rain storms (total of 28 typhoons, including 7 landed
ones). Furthermore, in the summer of 1999, the Dongsha upwelling (Station 3-6) was
weak and the depth of the 20°C isopleth was deeper than 105 m. However in 1998,
although large floods of the Pearl River occurred, the SSS did not decrease, due to the
strong upwelling as indicated by shallow (84 m) depth of the 20°C isopleths. Chai et
al. (2001) pointed out that the strength of upwelling can be indicated by the depth of
20°C temperature isopleth in the SCS. In this study, the range depth of 20°C isopleths
is 84-150 m. However, the high SSS in 1993 was probably due to the reduced Pearl
River discharge (Lei et al., 2003).
Figure 5.
The spatial-temporal distributions of the DINav (mean concentrations in the water
column). The shadow shows the area and period of time which exceeded the low limit of suitable N
concentration for diatom growth (5.71 μmol l
−
1, Chu, 1949).
