Particle Scavenging in the Deep Water of Southern Okinawa Trough: Application of 234Th/238U Disequilibria

• Main Authors: Yu-Ching Jang, 張雨青
• Other Authors: 魏慶琳
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/18882137434505471273

碩士 === 國立臺灣大學 === 海洋研究所 === 87 === Nepheloid plume in the deep water of Southern Okinawa Trough is con-sidered the mechanism of particulate matter exportation from East China Sea shelf. Submarine canyons on the slope off northeastern Taiwan may be the main path for particulate transport. In this research, transmissometer was used to represent the spatial distribution of total suspended matter(TSM) concentra-tion in the water column of the study area. Activities of Th-234 in the dis-solved and particulate phases were also measured and used to calculate distri-bution coefficients (Kd) and residence times. Beam attenuation (BA), derived from transmission, has a good correlation to the TSM concentration measured by large-volume filtration. Transport of particulate plume from East China Sea to southern Okinawa Trough is most evident over the Keelung canyon and the Mien-hwa canyon. From the cross-section of BA, several TSM maxima lying in different isopycnal surfaces were observed, among which the nepheloid plume at the σθ.=27.07 is most evident. Th-234 profiles at stas 7 and 13 showed that high scavenging and removal rates were found in the deep water of the Okinawa Trough. Scavenging rate at sta 13 is higher than that of sta 7 due to resuspension of organic-rich sediments. Residence times of dissolved Th-234 at sta 7 and sta 13 are 40 and 38 days and particulate Th-234 residence times at sta 7 and 13 are 49 and 110 days, respec-tively.