| Summary: | 碩士 === 國立臺灣大學 === 海洋研究所 === 89 === The East China Sea (ECS) has large continental shelf which receives large quantities of terrigenous materials from the east Asia. To understand the biogeochemistry cycle of carbon and nitrogen in the ECS shelf, we used stable isotopes as tools to trace the origin of organic carbon and nitrogen in the suspended particles and to explore processes of biogeochemical cycle. The d13Corg and d15N values of suspended particles in the southern ECS ranged from -24.4 to -17.3 ‰ and from -2.6 to 4.9 ‰, respectively. The isotopic compositions indicate that there were 3 end-members representing the terrestrial and the marine organic matter and the N-fixers. The heavier d15N values observed in the inner shelf indicates a marine dominated origin associated with coastal upwelling. Outside the inner shelf, d15N values were lower and some rather low d15N values (<1 ‰) occurred in the outer shelf, indicating that nitrogen fixation played an important role in this region.
In the Tanshui River, the d13Corg values of suspended particles during Typhoon Bilis ranged from -25 to -24 ‰, increasing with time. The lower d13C values observed at the beginning of typhoon period suggested a higher fraction of fresh biogenic materials. When the concentration of total suspended matter (TSM) shot up, the d15N values increased from -2~-3 ‰ to 2~3 ‰, suggesting that the organic matter of these suspended particles had a higher degree of degradation. After typhoon, the isotopic shift suggested growth of aquatic plants in the water body, probably due to decreasing turbidity.
During non-typhoon period, the d13Corg values of suspended particles in the Tanshui River ranged from -25.5 to -19 ‰, increasing with salinity. For salinity below 30, the d15N values of suspended particles were -3~-2 ‰, suggesting a larger fraction of terrestrial organic matter. For salinity above 30, the d15N values of suspended particles ranged from -16 to 4 ‰, suggesting production of biogenic organic nitrogen from complicated biogeochemical pathways.
Concentrations of POC and PN during typhoon period were 10 times higher than those of the non-typhoon period. Therefore, the exported particulate materials during typhoon period could represent the exported terrestrial end-member. The weighted mean d13C and d15N values were -24.4 ‰ and 2.0 ‰, respectively.
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