Spatial Variability along the Mud Belt between the Mouth of Changjiang and northern Taiwan Strait

• Main Authors: Cheng-Chan Chien, 簡呈展
• Other Authors: James T. Liu
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/84qrh8

碩士 === 國立中山大學 === 海洋科學系研究所 === 106 === From the mouth of Changjiang along the coast of Zhejiang and Fujian to the northern part of the Taiwan Strait, over a distance of 1000 km, the primary sediment source of the mud belt is Changjiang. Rivers in Zhejiang, Fujian and the Zhuoshui River in Taiwan also contribute to the sediment source. The sediment transport in this mud belt sediment is mainly affected by seasonally changing ocean currents and river plume. In winter, the northeast monsoon enhances the southwestern China Coastal Currents. In the summer, the southwest monsoon enhances the northward Taiwan Warm Current. This study uses sediment trap, surface sediments and sediment cores for data acquisition. Various methods (MSCL, clay mineral analysis, grain size analysis, 210Pbex activity analysis, 7Be/210Pbex activity ratio and EOF) were used to explore the spatial variation characteristics of sediments from source to sink during the muddy belt in winter. The sediment grain size analysis of the surface sediment and the box core shows that the sediment in the mud belt is mainly mud, while the sediment of the Zhuoshui River mouth is mainly sand. The 7Be/210Pbex activity ratio of the surface sediment along the mud belt indicates that the fresh terrestrial sediments from the Changjiang are transported to southwestward into the Taiwan Strait. The results of clay mineral analysis show that the clay mineral composition on the mud belt is closely affected by the Changjiang source. From the measurements of MSCL, spectrophotometer, grain size analysis and 210Pbex activity analysis of the box cores samples that the value of γ-density is smaller along the mud belt, because of the lower sediment density due to high water content. While the value of γ-density is the highest in G3 (Zhuoshui River mouth), because of the sand content.The value of L* is higher along the mud belt. The surface color of the sediment is brighter and its composition is mainly mud. The value of L* is lower at the G3 (near Zhuoshui River mouth), indicating that the surface brightness of the sediment is dim, and its composition is mainly sand. The Changjiang river mouth (lower color a* value is mainly affected by long-term weathering during river transport) and the MSI along the coast of Zhejiang and Fujian (color a* gradually decreases from the Oujiang River mouth to the northern part of the Taiwan Strait), indicating its magnetic minerals are mainly magnetite, while the MSI of the G3 is low, indicating that its magnetic minerals are mainly pyrrhotite. From the results of b* that if the surface color of the sediment is yellow, it suggests that it is subject to long-term weathering, which means that the sedimentary environment is more dynamic. When the surface color of the sediment is darker, it indicates that it is not weathered. It suggests that its sediment environment is less dynamic.