Comparative Geochemistry of 234Th, 210Pb, and 210Po n the Hung-Tsai Trough
Date Issued
2008
Date
2008
Author(s)
Chou, Lin-Hwa
Abstract
Large-volume seawater samples were collected from three locations during 6~8 March 2006 (OR1-784) in the Hung-Tsai Trough off Southwestern Taiwan for the determinations of dissolved and particulate 234Th,210Pb, and 210Po. Along with profiles of nutrients, particulate organic carbon, and other hydrographic parameters, the geochemical behaviors of the three radionulides were compared. Detailed profiles of dissolved and particulate 234Th,210Pb, and 210Po activities showed no significant difference among the three sampling stations. By comparing the distributions of 234Th/238U and 210Po/210Pb ratios at the same station obtained from three cruises (OR1-784, OR1-742, and OR1-744), no seasonal variability for the disequilibria was found. However, the 210Pb/226Ra ratio showed an excess in the spring and deficient in the winter. In the entire water column of the Hung-Tsai Trough, 234Th is deficient relative to 238U, and 210Pb is excessive relative to 226Ra. 210Po is deficient in the surface layer but is excessive in the intermediate layer relative to 210Pb. The distribution coefficients of 234Th,210Pb, and 210Po show the order of the affinity toward particulate matter is 210Po > 234Th ~ 210Pb in the Hung-Tsai Trough. This study uses box model incorporating the horizontal advection to estimate the residence times of the three radionulides. The residence times of dissolved and particulate are 8 and 5 days, 15 and 4 days, and total 15 days, respectively, for 234Th, 210Po, and 210Pb in the water column of the Hung-Tsai Trough. By using 234Th and 210Po as proxies of particulate organic carbon to estimate the export flux from the upper 80 m in the Hung-Tsia Trough, the export flux are 40 mmolC/m2/d and 64 mmolC/m2/d, respectively. The results show that the two approaches are similar.
Subjects
Hung-Tsai Trough
residence time
particulate organic carbon
Type
thesis
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