The Atmospheric Input of Dissolvable Pb Based on the Radioactive 210 Pb Budget in the Equatorial Western Indian Ocean.

To estimate the atmospheric deposition flux of ²¹⁰Pb in the equatorial western Indian Ocean, we determined the dissolved (<0.45 μm) and particulate ²¹⁰Pb (>0.45 μm) in the water column. In addition, we calculated the atmosphere-derived dissolvable Pb in seawater using the budget of ²¹⁰Pb. The dissolved ²¹⁰Pb and total ²¹⁰Pb were higher in the surface layer and, overall, showed a decreasing distribution with depth. In particular, radioactive ²¹⁰Pb activities in the surface-to-upper layer (<1000 m depth) were 1.5 to 2 times higher than those reported in the 1970s (in nearby regions), suggesting that there has been additional ²¹⁰Pb input in recent years. Based on the mass balance of the total ²¹⁰Pb budget in the water column, we estimated the atmospheric deposition flux of ²¹⁰Pb and the residence time of Pb for the first time in this region. The atmospheric deposition flux of ²¹⁰Pb was estimated to be 0.1–0.5 dpm cm⁻² yr⁻¹, and these values agreed with the general global estimations for the major oceans (0.1–0.7 dpm cm⁻² yr⁻¹). Considering the residence time of ²¹⁰Pb (29–41 years) in the water column (estimated from the ²¹⁰Pb inventory and ²³⁴Th-based Pb scavenging rate), the atmospheric input of seawater-dissolvable Pb was quantified to be 0.08–0.1 nmol cm⁻² yr⁻¹, which is about eight times higher than the estimated input in the early 1990s in the region. Therefore, these results imply that radioactive ²¹⁰Pb could be a useful tracer for quantifying Pb flux in seawater. [ABSTRACT FROM AUTHOR]