A preliminary study on the response of marine primary production to monsoon variations in the South China Sea Basic characteristics

Seasonal, interannual and interdecadal variations of monsoon over the South China Sea (SCS) directly influence the ocean circulation and the mass transport process, etc., especially the changes of horizontal circulation pattern and upwelling area. These changes directly influence the nutrient transport and the photosynthesis of phytoplankton, which induce the change of the marine ecosystem in the SCS, including the change of marine primary production in this sea area. On the basis of climatic data for long-time series and primary production estimated by remote sensing, the multi-time scale variations of monsoon, seasonal and interannual variations of primary production, and the response of primary production to monsoon variations were analyzed. Furthermore, the spatio-temporal variations of primary production in different sea areas of the SCS and their relations to the monsoon variations were given. The results showed that the strong southwesterly prevailed over the SCS in summer whereas the vigorous northeasterly in winter. The seasonal primary production in the entire sea area of the SCS also produced a strong peak in winter and a subpeak in summer. And the seasonal primary production distributions displayed different characteristics in every typical sea area. The variations of the annual and summer averaged primary production in the entire sea area of the SCS showed almost the same rising trend as the intensity of the summer monsoon. Especially for 1998, the summer monsoon reached almost the minimum in the past 54 a when the primary production was also found much lower than any other year (1999-2005). The responses of annual primary production to monsoon variation were displayed to different extent in different sea areas of the SCS; especially it was better in the deep sea basin. Such research activities could be very important for revealing the response of marine ecosystem to the monsoon variations in the SCS.