Oxygen Isotope Compositions of the Sea Water

• Main Authors: Lin, Shih-chao, 林士超
• Other Authors: David D. Sheu
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/07844340914479383827

碩士 === 國立中山大學 === 海洋地質及化學研究所 === 87 === As a result of preliminary study on the distribution of salinity, temperature and d18O in the East China Sea (ECS) water between China Coastal Current and Kuroshio in four seasons (December, 1997, and March, July, November, 1998), the water in the ECS may be considered as a mixture which results from a two end-member mixing between the saline (S>34) and isotopically heavier (d18O> 0.3 per mil) Kuroshio Surface Water and the fresher (S<33) and lighter (d18O< 0 per mil) Changjiang Dilute Water (CDW). The ECS water becomes isotopically more heavier as seaward, so that the ECS could be regarded as an extended estuary of the Changjiang. The CDW appeared as two plumes: one extending eastward into the ECS north of 31oN off the mouth of Changjiang, and the other hugging the coast south of 30 N. The intruding Kuroshio Surface Water formed a wedge between these two plumes. The values of d18O in the surface waters in ECS were strongly and linearly correlated with salinity in each season, both of d18O and salinity are generally conservative tracers of seawater. However, there were small inter-seasonal variations in these linear relationships mostly as a result of the changes in the composition of CDW while the composition of Kuroshio Surface Water remained essentially the same. In the T-S and the d18O-S diagrams at a deep station in the Okinawa Trough, similar features could be found so that d18O may be used as a tracer for distinguishing the Kuroshio Surface Water from the upwelling Kuroshio Subsurface Water in the ECS. The box model calculation indicates that about 1.5x10^4 km^3/y of the Kuroshio Surface Water and a similar volume of the upwelling Kuroshio Subsurface Water were imported into the ECS when 3.1x10^4 km^3/y of the ECS Water was exported to the Kuroshio and the Japan Sea. Of the exported water, about 40 % enters the Japan Sea while the remaining 60 % comes back to the Kuroshio. The year-round upwelling center at the shelf edge northeast of Taiwan supplys for 40 % of the upwelling water. Thus, there may be other upwelling along the shelf edge of the ECS. During exchange between the Kuroshio and the ECS, there was a net water loss of 1.2x10^4 km^3/y from the Kuroshio.