ABSTRACT
Physical and chemical oceanographic data were obtained by seasonal monitoring along a transect (Transect N) in the northern South China Sea (nSCS) during 1976-2004. Fluctuations of dissolved inorganic nitrogen (DIN), seawater temperature (SST and Tav-average temperature of the water column), N:P ratio and salinity (Sav and S200-– alinity at the 200 m layer) exhibited an increasing trend, while those of T200, dissolved oxygen (DO), P, Si, Si:N, and SSS exhibited a decreasing trend. The annual rates of change in DIN, DO, T, and S revealed pronounced changes, and the climate trend coefficients, which was defined as the correlation coefficient between the time series of an environmental parameter and the nature number (namely 1,2,3, . . . . . .n), were 0.38-0.89 and significant (p ≤ 0.01-0.05). Our results also showed that the ecosystem has obviously been influenced by the positive trends of both sea surface temperature (SST) and DIN, and negative trends of both DO and P. For example, before 1997, DIN concentrations in the upper layer were very low and N:P ratios were less than half of the Redfield ratio of 16, indicating potential N limitation. However after 1997, all Si:P ratios were >22 and the Nav:Pav was close to the Redfield ratio, indicating potential P limitation, and therefore N limitation has been reduced after 1997.
