A Study On The Spatial And Temporal Chl-α Distribution In The South China Sea And A Response To The South China Sea Monsoon

The present study mainly analyzed spatial and temporal variations of Chlorophyll-a (Chl-a) concentration in the South China Sea (SCS), based on the in situ historical cruises observation data of Chl-a concentration, NCEP / NCAR (Reanalysis) daily average sea surface global re-analysis of wind data, in situ historical cruises observation data of water temperature and conductivity. Combining the characteristics of East Asia Monsoon, the relationship between the change of the Chl-a concentration and the intensity of the wind are discussed in the SCS.Using the data in the historical literatures since the 1980's and 11 cruises observation data of Chl-a concentration in the SCS , the seasonal distribution of Chl-a is analyzed in Nansha Islands sea area. In winter, the SCS northeast monsoon was strengthened to achieve strongest in December, and the Chl-a distribution was mainly high at the north-western coast of the island of Kalimantan and the south-eastern Vietnamese coast close to the Mekong River estuary, maximum up to 0.13 mg/m3. In spring, the intensity of the monsoon in the SCS became weak, and Chl-a concentration also started to decline. The high-value area in south-eastern coast of Viet nam's disappeared, only the north-west Kalimantan Island area exist, maximum up to 0.11 mg/m3. In summer, the southwest monsoon generally breaks out. With the wind strengthener, the sea surface temperatures rise, and the sunlight enhance, the Chl-a concentration increases rapidly, maximum up to 0.28 mg/m3. In fall, southwest monsoon become weak, the Chl-a concentration began to reduce over the whole region, maximum only up to 0.1 mg/m3 . Meanwhile, the Chl-a concentration in the north of SCS is obvious higher than thet in the south of SCS in Sep and Dec, the max. is 0.8 mg/m3.In general, the surface Chl-a content is higher in summer and winter than that in spring and fall, and higher in the coastal area than that in the center sea area.The vertical profile of Chl-a showed that the maximum Chl-a concentration in SCS does not appear in the surface, but at the sub-surface with the depth 25-75m. Comparing of the northern SCS area in September 2004, 2005 and 2006, the vertical distribution changes of Chl-a concentration in the three cruises in trend is relatively consistent. The maximum Chl-a concentration is in the depth of 25-75m. From the sea surface to the sub-surface maximum, the Chl-a concentration increases with depth, and then decreases rapidly. The seasonal and inter-annual variability of wind stress is prominent in the SCS. By analyzing NCEP / NCAR (Reanalysis) daily average sea surface global re-analysis data, the SCS prevails north-easterly wind in winter (from Dec to Feb), but south-westerly wind in summer (from June to Aug). Since the intensity of the monsoon in each year is not same, the monsoon index is defined to the strength of the monsoon.The wind effect on the phytoplankton growth in the SCS could have a lag. By using the existing 11 cruises data of Chl- a concentration and the NCEP / NCAR (Reanalysis) daily average sea surface global re-analysis of wind data shows that Chl- a distribution changes lags 5 days around after the sea surface wind in spring and summer and 2days around in autumn and winter.