Ning et al. (2004) found that the mean concentrations of NO3, PO4, and SiO3 were higher basin wide in winter than summer in the SCS, corresponding to higher phytoplankton stock in the winter compared to the summer. A distinct seasonal pattern of phytoplankton biomass and primary production in the euphotic layer with a winter maximum was also observed accompanying the seasonal change of nutrients (N, P) in the mixed layer (Tseng et al., 2005) at the South East Asian Time- series Study (SEATS) station, located 0.5 degrees to the south of station SCS-N. Tseng et al. (2005) pointed out that winter max- imum of phytoplankton production and nutrient was a result of enhanced vertical mixing over a shallow and relatively less variable nutricline