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Comparative Geochemistry of 234Th, 210Pb, and 210Po: A Case Study in the Hung-Tsai Trough off Southwestern Taiwan

2009; Springer Nature; Volume: 20; Issue: 2 Linguagem: Inglês

10.3319/tao.2008.01.09.01(oc)

2311-7680

Ching‐Ling Wei, Lin-Hwa Chou, Jing-Ru Tsai, Liang‐Saw Wen, Su‐Cheng Pai,

Radioactive element chemistry and processing

AB STRACTDe tailed pro files of dis solved and par tic u late 234 Th, 210 Pb, and 210 Po ac tiv i ties at three sta tions in the Hung-Tsai Trough off south west ern Tai wan were de ter mined.The to tal 234 Th ac tiv ity is 20 ~ 25% de fi cient from its sec u lar equi lib rium in the en tire wa ter col umn.Ex cept for an ev i dent ex cess of 210 Po at some depths in the mixed layer and in the pycnocline layer, to tal 210 Po ac tiv ity is also lower than to tal 210 Pb ac tiv ity.As a re sult of at mo spheric de po si tion, 210 Pb is about 25% in ex cess of its par ent, 226 Ra, through out the wa ter col umn of the Hung-Tsai Trough.The ra tios of the dis tri bu tion co ef fi cients of 234 Th, 210 Pb, and 210 Po show that the or der of par ti cle af fin ity is Po > Th ~ Pb in the mixed layer and bot tom layer, whereas the or der changes, due to par ti cle re gen er a tion, into Th > Pb > Po in the pycnocline layer of the Hung-Tsai Trough.Mass bal ance equa tions in cor po rat ing hor i zon tal advection are es tab lished to es ti mate the scav eng ing and re moval rates of 234 Th, 210 Pb, and 210 Po.The ver ti cal fluxes of 234 Th, 210 Pb, and 210 Po within the euphotic layer for the Hung-Tsai Trough are 6760, 630, and 400 dpm m -2 d -1 , re spec tively.The res i dence times of the three radionuclides in the euphotic zone are re mark ably close to one an other (within 2 weeks).By us ing 234 Th and 210 Po as prox ies of par tic u late or ganic car bon and ni tro gen, ex port flux from the euphotic layer of the Hung-Tsai is 40 mmol C m -2 d -1 based on the 234 Th ap proach and 64 mmol C m -2 d -1 based on the 210 Po approach.