Effect of different types of El Nino on primary productivity in the South China Sea

More than ten years of satellite-derived net primary production (NPP) data were used to investigate the interannual variations of NPP associated with two different types of El Nino in the South China Sea (SCS). Results of the empirical orthogonal function analysis (EOF) showed that the first two modes had significant interannual variations and were sensitive to two types of El Nino. The first mode is highly correlated to the canonical El Nino. This mode is characterized by basin-scale decreased NPP during the canonical El Nino years, predominantly diminished off the east coast of Vietnam and the northwest coast of Luzon. The second mode is well correlated to the El Nino Modoki, showing increased NPP in the central and eastern SCS during the El Nino Modoki years. The interannual NPP variability is linked to anomalous atmospheric and oceanic conditions associated with these two types of El Nino. During the developing phase of El Nino Modoki, enhanced western North Pacific summer monsoon and moderate northeasterly wind divergence gave rise to the positive wind stress curl anomalies in the central and eastern SCS, inducing strong Ekman upwelling and increased upward nutrient supply. The moderate Ekman upwelling in the mature phase of El Nino Modoki also sustained the ocean primary productivity. Basin-scale decreased NPP in the SCS was attributed to anomalous weakened wind and abnormal warm sea surface temperature throughout the period of canonical El Nino.