Contrasting Behaviors Of Pb-210 And Po-210 In The Productive Shelf Water Versus The Oligotrophic Water

We measured the total, truly dissolved (<10 kDa), colloidal (10 kDa-0.2 mu m), and particulate phases (>0.2 mu m) of Pb-210 and Po-210 in the East China Sea (ECS) shelf water and the East Sea (Japan Sea). In order to examine the behaviors of Pb-210 and Po-210 in different marine environments, we compiled our results with previously reported data in the same region and in the northwestern Pacific Ocean (NWPO). The proportions of the truly dissolved, colloidal, and particulate phases in the shelf water were 32, 27, and 41% for Pb-210 and 49, 32, and 19% for Po-210, respectively. Based on a steady-state scavenging model, Pb-210 and Po-210 showed higher (3.0 +/- 0.6 year(-1)) and lower (0.3 +/- 0.2 year(-1)) scavenging rates, respectively, in the shelf water than those in the NWPO and the East Sea. A non-steady-state model, accounting for the residence time of the shelf water, also showed twice more efficient removal rate of Pb-210 in the shelf water than that in the NWPO and the East Sea. In contrast, there was the net input of Po-210 in the shelf water relative to the large removal in the NWPO and the East Sea. The large proportions of total dissolved (truly dissolved + colloidal) Po-210 (>80%) in the shelf water indicate active regeneration of Po-210 from the sinking particles and the surface sediments. Our results suggest that the ECS shelf is the source for Po in the northwestern Pacific marginal seas, a proxy for sulfur group elements (S, Se, and Te), whereas it is the efficient sink for Pb, together with other particle-reactive trace elements.