2007). Hierarchical CA was used on standardized data, applying Ward’s method with correlation. The low and high nutrient stations were determined from hierarchical CA using linkage

distance. PCA extracted eigenvalues and eigenvectors from the covariance matrix of the original variables, then produced new GS-7340 nmr orthogonal variables known as PCs through VARIMAX rotation, which are linear combinations of the original variables. PCs provide information on the most meaningful parameters that describe a whole data set, allowing data reduction with minimum loss of original information. They are unobservable, hypothetical, latent variables (Vega et al. 1998, Helena et al. 2000, Pekey et al. 2004, Singh et al. 2004, Wu & Wang 2007, Zhou et al. 2007). All the mathematical and statistical computations were performed using MATLAB R2008b (Mathworks Inc., USA) and ArcGIS 9.3 (ESRI Inc., USA). MODIS-Aqua satellite images (4-km Level 3 HDF) covering the SCS were obtained from NASA. Weekly (8-day) composite sea surface temperature (SST) data from 14 to 21 September were used owing to the heavy cloud coverage around this region during the cruise. The SeaDAS package was used to process the SST imagery. The horizontal distributions of parameter concentrations at the surface are shown in Figure 2. The horizontal distributions of surface NO2-N reveal that there are two

high concentration regions: one is near the Pearl River Estuary in signaling pathway the north-west, the other is near the Luzon Strait in the

south-east (Figure 2a). The NO3-N distribution shows four high nutrient regions: near the Pearl River, in the south-west, south-east Histamine H2 receptor and north-east of the PIS (Figure 2b). The NH4-N concentration is high in the north-west, north-east and south-east of the PIS (Figure 2c). SiO3-Si is distributed in three regions: (1) around and to the north-east of the PIS, (2) in the west of the PIS and (3) near the perennial cold cyclonic eddy (Figure 2d). The PO4-P distribution shows horizontal variations with increases from the southern to the northern regions; it is also found in the same three regions where silicate is distributed (Figure 2e). The distributions of DO and Chl a are similar: high near the coast and low in offshore waters. The offshore DO concentration is equal to 6.64 m ol dm−3. In contrast, Chl a shows three small, high-concentration regions in the Pearl River Estuary, the locations of which are similar to those of silicate ( Figures 2f–g). The temperature distribution is significantly low in the north-east and the west of the PIS, and low at 114°E–115°E in the south ( Figure 2h). The horizontal distributions of SiO3-Si and temperature show three upwelling regions: (1) the north-east of the PIS, (2) the west of the PIS and (3) the regions of the perennial cold cyclonic eddy.