Intrusion of the North Pacific waters into the South China Sea

Water mass distribution was studied by analyzing historical hydrographic da ta in the South China Sea. Despite considerable modification of characteris tics as a result of mixing, waters of both salinity maximum and minimum of the North Pacific origin were traced on the density surfaces around 25.0 an d 26.73 sigma(theta), respectively. In the salinity maximum layer, property distribution suggests an intrusion into the South China Sea all year-round through the Luzon Strait. The seasonal variation of the intrusion contains a pronounced semiannual signal, with greater strength in winter and summer than in spring and fall. From spring to fall, the intrusion water from the Pacific is narrowly confined in the continental slope south of China; only in winter, when the northeast monsoon becomes fully developed, can it spre ad in the southern South China Sea. In the salinity minimum layer, water en ters the South China Sea only in spring, when the intrusion in the salinity maximum layer is weakest. A combined use of the "island rule" with climato logical data suggests a mean Luzon Strait transport of the order 4 Sv (1 Sv = 10(6) m(3) s(-1)).