| Summary: | 碩士 === 國立中山大學 === 海洋地質及化學研究所 === 88 === Abstract
In this study, we have analyzed systematically the oxygen isotopic compositions of South China Sea (SCS) and Luzon Strait (LS) seawater so that a comprehensive interpretation of their temporary and spatial variability can be delineated. The oxygen isotopic compositions of the samples collected in the two areas were determined using the Epstein-Mayeda technique, and the overall precision of the d18OSMOW measurements is +0.1 ?. Our data suggest that LS seawater is a mixture of SCS and Kuroshio waters. The precipitation (1.5 mm) on SCS in April 1998 (during ORI517 cruise) is much less than that (169.5 mm) in April 1999 (during ORI546 cruise). As LS and SCS waters are concerned, the profiles of d18OSMOW generally share the same trend as those of salinity. The d18OSMOW values of the SCS surface water decrease toward the south, while those of the LS surface water decrease toward the west. These suggest that the effect of the Kuroshio water decreases are it moves from northeast toward southwest after its intrusion through LS. The salinity of Kuroshio water reaches the maximum at 34.92 with the corresponding d18OSMOW value of 0.42 ?, whereas the salinity of the representative SCS surface water is 33.34 and the corresponding d18OSMOW is -0.25 ?. As these two data were selected as end members, the estimated proportion of the intruding Kuroshio water in the composition of LS water could be high up to 80 % at 121.5o E. The plot of d18OSMOW versus salinity for cruises OR517 and 546 shows a difference between the slopes of the two regression lines, indicating the effect of variability in precipitation and the depth of the mixed layer. The average d18OSMOW value for surface water decreases toward the west as the water moves from Western Philippine Sea (WPS) to LS and SCS. The average d18OSMOW values for the surface, subsurface, intermediate, and deep waters are listed in the corresponding order in parentheses preceded by the studied area as follows: WPS (0.29 ?, 0.25 ?, -0.06 ?, -0.10 ?); LS (0.15 ?, 0.17 ?, -0.02 ?, -0.08 ?); SCS (-0.03 ?, 0.18 ?, -0.05 ?, -0.08 ?).
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