Salinification in the South China Sea Since Late 2012: A Reversal of the Freshening Since the 1990s

Salinification has occurred in the South China Sea from late 2012 to the present, as shown by satellite Aquarius/Soil Moisture Active Passive data and Argo float data. This salinification follows a 20 year freshening trend that started in 1993. The salinification signal is strongest near the surface and extends downward under the seasonal thermocline to a depth of 150 m. The salinification occurs when the phase of the Pacific Decadal Oscillation switches from negative to positive. Diagnosis of the salinity budget suggests that an increasing net surface freshwater loss and the horizontal salt advection through the Luzon Strait driven by the South China Sea throughflow contributed to this ongoing salinification. In particular, a decrease in precipitation and enhanced Luzon Strait transport dominated the current intense salinification. Of particular interest is whether this salinification will continue until it reaches the previous maximum recorded in 1992. Plain Language Summary A significant salinification is taking place in the South China Sea starting from late 2012 to the present, as seen in satellite and Argo float data. The temperature, in contrast, exhibits no significant change. The salinification is mainly associated with switches in the Pacific Decadal Oscillation from negative to positive phase from late 2012 to the present. A decrease in precipitation and enhanced Luzon Strait transport dominated the current intense salinification. After a freshening period that lasted 20 years, we are particularly interested in whether the salinification will continue in the future. Key Points Salinification has occurred in the South China Sea from late 2012 to the present Both surface freshwater forcing and horizontal advection through the Luzon Strait contribute to the salinification Sharp fall in precipitation and enhanced Luzon Strait transport dominated the current intense salinification