Summer Monsoon Impacts on Chlorophyll-a Concentration in the Middle of the South China Sea: Climatological Mean and Annual Variability

Climatological mean and annual variations of Chlorophyll-a (Chl-a) distribution, sea surface wind (SSW), and sea surface temperature (SST) from 1998 to 2008 were analyzed in the middle of the South China Sea (SCS), focusing on the typical region off the east coast of Vietnam (8.5-14 degrees N, 109.5-114 degrees E). Based on remote sensing data and SCS summer monsoon index (SCSSMI) data, high Chl-a concentrations in the middle of the SCS in the southwest summer monsoon season (June. September) may be related to strong Ekman pumping and strong wind stress. The maximum of the monthly averaged climatological Chl-a in the summer appeared in August. According to the annual variation, there was a significant negative correlation (r=-0.42) between the SCSSMI and SST, a strongly positive correlation (r=0.61) between the SCSSMI and Chl-a, and a strongly negative correlation (r=-0.74) between the SST and Chl-a in the typical region off the east coast of Vietnam during 1998-2008. Due to the El Nino event specifically, the phenomena of a low Chl-a concentration, high SST and weak SCSSMI were extremely predominant in the summer of 1998. These relationships imply that the SCSSMI associated with the SST could be used to predict the annual variability of summer Chl-a in the SCS.