Tracing tropical and intermediate waters from the South China Sea to the Okinawa Trough and beyond

Intermediate waters with a salinity minimum from 350 to 1350 m depths have been reported to flow out of the South China Sea (SCS) through the Luzon Strait. This eastward flowing SCS Intermediate Water (SCSIW) is blocked by the northward flowing Black Stream (Kuroshio) southeast of Taiwan and is forced to turn to the north. The SCSIW subsequently enters and occupies the western half of the Okinawa Trough. Because of strong upwelling in the SCS basin, the SCSIW contains more nutrients than does the Kuroshio Intermediate Water in the Philippine Sea. One of the major purposes of this note is to reconfirm that the SCSIW actually does upwell onto the East China Sea (ECS) shelf and to show that the South China Sea Tropical Water (SCSTW), with a salinity maximum of 50-150 m in depth, follows the same pathway as the SCSIW and similarly occupies the western half of the Okinawa Trough. Part of these relatively nutrient-rich subsurface waters upwell, thereby supplying nutrients to the ECS shelves. The remaining SCSIW and SCSTW flow along with the Kuroshio and can be traced as far east as 140 degrees E, south of Japan. This is just around the region where the Oyashio joins the Kuroshio to form the North Pacific Intermediate Water.