The destiny of the North Pacific Intermediate Water in the South China Sea

The previous studies show that the spreading path of the subtropical salinity minimum of the North Pacific Intermediate Water （NPIW） is southwestward pointing to the Luzon Strait. Based on the P -vector method and generalized digital environmental model （GDEM） data, the volume transport of NPIW through Luzon Strait and the upward transport on the NPIW lower and upper boundaries are calculated to examine the destiny of NPIW in the South China Sea （SCS）. On the annual mean, the estimation of NPIW transport into the SCS through the Luzon Strait is 1.72 Sv （1Sv=10 6 m 3 /s）. The upward transport over the SCS is 0.31 Sv on the NPIW upper boundary and 1.31 Sv on the NPIW lower boundary. There is no strait or passage deeper than the surface for the NPIW to extend, except for the Luzon Strait. For the volume balance in the SCS NPIW, the volume transport of 2.72 Sv has to flow out of the SCS NPIW layer through the Luzon Strait.

A quasi-synoptic interpretation of water mass distribution and circulation in the western North Pacific:I.Water mass distribution

With high-resolution conductivity-temperature-depth （CTD） observations conducted in Oct.-Nov. 2005, this study provides a detailed quasi-synoptic description of the North Pacific Tropic Water （NPTW）, North Pacific Intermediate Water （NPIW） and Antarctic Intermediate Water （AAIW） in the western North Pacific. Some novel features are found. NPTW enters the western ocean with highest-salinity core off shore at 15°-18°N, and then splits to flow northward and southward along the western boundary. Its salinity decreases and density increases outside the core region. NPIW spreads westward north of 15°N with lowest salinity off shore at 21°N, but mainly hugs the Mindanao coast south of 12°N. It shoals and thins toward the south, with salinity increasing and density decreasing. AAIW extends to higher latitude off shore than that in shore, and it is traced as a salinity minimum to only 10°N at 130°E. Most of the South Pacific waters turn northeastward rather than directly flow northward upon reaching to the Mindanao coast, indicating the eastward shift of the Mindanao Undercurrent （MUC）.

A preliminary study on the intermediate water masses in the tropical West Pacific

Based on the CTD data of China's first WOCE cruise in winter of 1991, and those of the first and second Chinese TOGA cruises in the winters of 1985 and 1986, we apply the classical method of T-S diagram analysis to identify intermediate water masses in the tropical West Pacific and study their distribution feature. Results of these analyses show that there are mainly two kinds of intermediate water masses, namely, the mouth Pacific intermediate Water (SPIW) and the North Pacific intermediate Water (NPIW) in the tropical West Pacific. The NPIW extends from north to south with its southern boundary generally at about 8° N. However, it is westwards intensified near the coast of Mindanao Island where it extends further south to about 5° N with more distinctive characteristics of low salinity and low temperature. The SPIW extends from south to north with its northern boundary at about 12° N. In the zonal area between 0° and 4° N various intermediate waters interact. The analysis also shows the existence of interannual variations of NPIW in the tropical West Pacific.