Although the Kuroshio and the South China Sea (SCS) waters flow in and out of the Luzon Strait near surface, the SCS water mainly flows out of the SCS at mid-depth between 350 and 1350 m in all seasons and years that we studied. The eastward flowing SCS intermediate water is blocked by and joins the northward flowing Kuroshio at about 122°E. Thus the Kuroshio Intermediate Water is composed of the West Philipping Sea (WPS) proper water on the east, while on the west is the mixed water of the SCS and WPS. The nutrient-rich SCS Intermediate Water, which retains its signature in the Okinawa Trough, upwells onto the East China Sea shelf and becomes a major source of nutrients to the shelf water.