| Summary: | 碩士 === 國立臺灣海洋大學 === 海洋環境化學與生態研究所 === 98 === Sediment trap is directly used to determine particulate organic carbon (POC) flux, while the problem of zooplankton and the solubilization of material after collection. 234Th has been increasingly used as a tracer to estimate POC flux in the surface ocean using the product of the POC/ 234Th ratio from sinking particles (e.g. trap-collected) times the 234Th ratio flux. However, the 234Th-derived POC flux may be significantly biased due to two factors : large uncertainties in estimates of the 234Th flux, and the great variability of POC/ 234Th ratio. The POC/ 234Th ratio from large, pump- collected (>50 mm), particles are considered to be representative of sinking particles, but this hypothesis has not been thoroughly tested. In this study, we present POC and 234Th data for various particle size classes (>150, 50-150, 10-50 and 1-10 mm, (here in we defined <50 mm is the “small particle”, >50 mm is the “large particle”) from trap-collected particles in the upwelling region of northeastern Taiwan and the Kuroshio. Within the trap-collected POC pool, the small particles contained the largest proportion of POC (bulk, >1 mm)(26-67%) and 234Th (39-91%) fluxes. SEM images of bulk (without sequential filtration) sinking particles evidence that sinking particles contained many small particles. In variation of POC/ 234Th ratio in the large particle (upwelling area: 1.2~31.1, Kuroshio: 3.2~12.6) was higher than that of POC/ 234Th ratio in the small particle (upwelling area: 0.6~8.0, Kuroshio: 0.8~3.0). The results indicate that 234Th-derived POC flux will be significantly overestimated of POC/ 234Th ratio in the large particle is used. Therefore, we suggest that the POC/ 234Th ratio in bulk sinking particles should be used in estimating POC flux when using the 234Th approach.
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