To better understand eddy‐induced heat and salt transport, a targeted joint hydrographic investigation focusing on an anticyclonic eddy was carried out in July 2017 in the northern South China Sea. In situ and satellite observations together with Hybrid Coordinate Ocean Model (HYCOM) output show the transport of subsurface saline Kuroshio water into the northern South China Sea by an anticyclonic eddy. Subsurface high‐salinity cores are consistent with the anticyclonic eddy centers. The transport of saline Kuroshio water occurs in two stages accompanied by eddy shedding. First, saline Kuroshio water is trapped within the anticyclonic eddy at its generation location. Then, although the salinity within the eddy gradually weakens as the eddy carries the saline water westward, the quantity of saline water (>34.70 psu) shows a sharp increase, dominated by eddy‐induced salinity advection. A diagnosis of the salinity budget further confirms that the contribution of eddy flow advection is greater than that of mean flow advection. The saline Kuroshio water is trapped and conveyed in this anticyclonic eddy, providing vital evidence and important implications for eddy‐induced salt transport and water exchange.

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.