Low‐salinity water off West Luzon Island in summer

Low-salinity water with two cores is found off West Luzon Island in the South China Sea (SCS) during summer. A series of salinity observations and model results show that the low-salinity water begins to appear in June, reaches its lowest salinity in September, and disappears after October. Rainfall associated with the summer monsoon impinging on the Philippine mountain ranges plays an important role in the formation of the low-salinity water, while upward Ekman pumping of high-salinity subsurface water caused by the strong winter monsoon is important for its disappearance. Variation in mixed layer depth is responsible for the formation of the two cores of the low-salinity water, while advection also contributes. The study further demonstrates that the low-salinity water has considerable interannual variability associated with El Nino-Southern Oscillation (ENSO): during the summer of the decaying year of an El Nino, an anticyclonic wind anomaly occurs in the SCS. The anticyclonic wind anomaly is associated with a northeasterly anomaly south of 18°N, reducing precipitation and causing salting of the low-salinity water off West Luzon Island. The situation is reversed during the summer of the decaying year of a La Nina.