Geoscience Reference
In-Depth Information
Figure 4.
Variation trends in Si concentrations in the nSCS during 1989-2004. (a), (b), and (c) show
the annual means of sea surface Si (SSSi), water column average Si in the upper 200 m (Siav) and Si
in the 200 m layer (Si200), respectively. The lines are linear regressions.
Decreasing Trends and the Response of the Ecosystem
The decreasing trends in SSS may be related to the increase in the freshwater dis-
charge into the nSCS since 1990 and less vertical mixing, because of the presence of a
permanent thermocline (Shi et al., 2001; Yuan and Deng, 1997a, b). It has previously
been observed that the occurrence of low SSS often corresponded to abnormally high
discharge of the Pearl River (Xie and Zhang, 2003; Xu et al., 2008). During the pe-
riod of 1990-2000, the Pearl River runoff increased by 22.5% in comparison with the
mean discharge for 1960-1999 (Lei et al., 2003). In the 1990s (i.e., 1994, 1995, 1996,
1997, 1999) and 2002, SSS in the nSCS was especially low (Figure 5a), which was
induced by the Pearl River floods (Lei et al., 2003). Particularly in 2002, the strongest
