Variability of chlorophyll-a concentration and sea surface wind in the South China Sea associated with the El Niño-Southern Oscillation

Abstract

In this paper, the seasonal and interannual variability of the chlorophyll-a concentration (Chl-a) and sea surface wind (SSW) fields in the South China Sea (SCS) are analyzed using Orbview-2/SeaWiFS, and ERS-1/2 and QuikSCAT satellite data. The mode 1 results of the empirical orthogonal function (EOF) analysis for Chl-a indicate the higher Chl-a is mainly along the coastal areas in the SCS, while the EOF mode 2 results show a summer-winter oscillation of the Chl-a distribution in the SCS. Through the comparison between EOF mode 2 results of the Chl-a anomaly and Nino 3.4 index, it is found that the Chl-a variation in the SCS is highly related to the El Nino-Southern Oscillation (ENSO) events. The SSW EOF mode 1 results indicate that the northeasterly monsoon in winter is much stronger than the southwesterly monsoon in summer. The SSW EOF mode 2 results show the zonal line near 15o N can be a boundary to separate the wind pattern into two parts in fall, the northeasterly wind is in its north and southwesterly wind in its south. The EOF results of the SSW anomaly show the weaker monsoon occurring during the 1997/1998 El Nino winter. Comparing Chl-a EOF mode 2 and SSW EOF mode 1 results, we can find that Chl-a in the SCS is mainly influenced by the monsoon wind, wind-induced coastal upwelling makes the Chl-a increasing along the western SCS in summer but along the eastern SCS in winter.