Abstract
Abstract. Vertical distributions of dissolved and particulate 210Pb and 210Po in the water column at the SouthEast Asian Time-series Study (SEATS, 18°00´ N and 116°00´ E) station in the northern South China Sea were determined from four cruises between January 2007 and June 2008. A large deficiency of 210Pb, 379 ± 43 × 103 dpm m−2, from the secular equilibrium was found within the 3500 m water column. On the other hand, a smaller deficiency of 210Po, 100 ± 21 × 103 dpm m−2, relative to 210Pb was found in the water column. Time-series data showed insignificant temporal variability of the 210Pb and 210Po profiles. To balance these deficiencies, the removal fluxes for 210Pb and 210Po via particle settling ranging from 45 to 51 dpm m−2d−1 and from 481 to 567 dpm m−2d−1, respectively, are expected at 3500 m. The 210Pb removal flux is comparable with, whereas the 210Po removal flux is much higher than, the flux directly measured by moored sediment traps. The discrepancy between the modeled 210Po flux and the measured flux suggests that sporadic events that enhance 210Po removal via sinking ballast may occur in the water column at the site.
Highlights
Within the context of carbon sequestration and elemental cycling, material conveyance through particle settling from the surface layer to the deep ocean is an important pathway of elemental removal in the ocean
Vertical profiles of total suspended matter (TSM) concentration measured from the four cruises are shown in Fig. 2a, d, g, and k
The TSM falls in a small range of 0.1–0.5 mg L−1 throughout the water column
Summary
Within the context of carbon sequestration and elemental cycling, material conveyance through particle settling from the surface layer to the deep ocean is an important pathway of elemental removal in the ocean. The distributions of 210Pb (t1/2 = 22.3a) and 210Po (t1/2 = 138d) have been used extensively by marine chemists to determine the removal rates of particles and associated elements from the ocean (Bacon et al, 1976; Nozaki et al, 1990). Both 210Pb and 210Po are particle reactive, there exist subtle differences in the geochemical behaviour of the two radionuclides in the ocean.
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