Abstract. Vertical distributions of dissolved and particulate 210 Pb and 210 Po 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 210 Pb, 379 ± 43 × 10 3 dpm m −2 , from the secular equilibrium was found within the 3500 m water column. On the other hand, a smaller deficiency of 210 Po, 100 ± 21 × 10 3 dpm m −2 , relative to 210 Pb was found in the water column. Time-series data showed insignificant temporal variability of the 210 Pb and 210 Po profiles. To balance these deficiencies, the removal fluxes for 210 Pb and 210 Po via particle settling ranging from 45 to 51 dpm m −2 d −1 and from 481 to 567 dpm m −2 d −1 , respectively, are expected at 3500 m. The 210 Pb removal flux is comparable with, whereas the 210 Po removal flux is much higher than, the flux directly measured by moored sediment traps. The discrepancy between the modeled 210 Po flux and the measured flux suggests that sporadic events that enhance 210 Po removal via sinking ballast may occur in the water column at the site.