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

Abstract

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, 210Pb 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 Sci., 20, 411-423, doi: 10.3319/TAO.2008.01.09.01(Oc) IN TRO DUC TIONThe con vey ance of par ti cle-re ac tive el e ments from the up per wa ter col umn to sed i ments sig nif i cantly re lies on the set tling of par tic u late mat ter. The three most par ti cle-re active radionulides of Po have been ex ten sively used as pow er ful trac ers for the study of par ti cle dy nam ics in the ocean. With a proper mass bal ance setup based on the fact that the ra dio ac tive dis equi lib rium be tween long-lived par ent and short-lived daugh ter radionuclides re flects the ver ti cal fluxes out of the sys tem, ex port fluxes can then be quantitatively estimated.Pro duced con stantly from

Nearshore scavenging phenomenon elucidated by 234th/238u disequilibrium in the coastal waters off Western Taiwan

“…The flow field derived from the sb-ADCP data in the vicinity of JWR agreed with the direct current measured by current meter deployments at the JWR river mouth (our station D19) by Liu et al (2000). The average current at the southernmost station is to the southeast (Table 2, Wei et al, 2008a). Consequently, the DTh and PTh, 0.55 and 0.30 dpm L -1 , respectively, measured at S2 in the northern Luzon Strait were used (Fig.…”

“…In this region, most (50~80%) of TTh is in the dissolved phase. As pointed out by Wei et al (2008a), this region is affected by southeastward transport of South China Sea water.…”

Seasonal distributions and fluxes of <sup>210</sup>Pb and <sup>210</sup>Po in the northern South China Sea

“…Seawater was immediately pressure-filtered with compressed air through a pre-weighed 142 mm Nuclepore filter (0.45 µm) mounted in a Plexiglas filter holder. The analytical procedures described in Wei et al (2009) were followed. In short, the filtrate from the 210 Po sample was acidified with about 10 ml concentrated HCl and spiked with 2.2 dpm of 209 Po and 30 mg of Fe carrier.…”

Particle-reactive radionuclides (<sup>234</sup>Th, <sup>210</sup>Pb, <sup>210</sup>) as tracers for the estimation of export production in the South China Sea

“…Seawater was immediately pressure-filtered by compressed air through a pre-weighed 142 mm Nuclepore filter (0.45 µm) mounted in a Plexiglas filter holder. Filtrate and particles retained on the filter were processed and analyzed for 234 Th, 210 Pb, and 210 Po activities following the procedures described in Wei et al (2009).…”