Geochemical Behaviors Of²¹⁰Po And²¹⁰Pb And Their Application In The China Marginal Seas

Activity concentrations of210Pb and210Po in China marginal seas, including the Beibu Gulf, the southern Yellow Sea, the East China Sea and the northern South China Sea, were determined. The spatial and temporal distribution of them was depicted. The scavenging and removal rates, residence times, removal flux of210Po and POC export flux were calculated by steady-state (SS) and non-steady-state (NSS) models. The major results we obtained were as follows:1) In the Beibu Gulf, dissolved and total210Pb activity concentrations were higher in spring and summer than those in fall and winter. The seasonal pattern of particulate210Pb was opposite to that of dissolved210Pb. The dissolved and total210Po activity concentrations were the lowest in fall, while particulate210Po activity concentrations were the highest in fall and the lowest in winter. Dissolved210Pb at the bottom layer in most stations increased with distance from the shore, while particulate210Pb decreased. Total210Po/210Pb activity ratios increased with increasing depth, and showed different trends in different seasons at most stations.2) Removal fluxes of210Po estimated by SS model were more reasonable than those by NSS model in the Beibu Gulf. POC export fluxes derived by210Po-210Pb disequilibria were the highest in spring.3) In the southern Yellow Sea and the East China Sea,210Pb and210Po activity concentrations at the mid-layer in the slope region were significantly affected by Kruoshio waters. The particlute210Pb and210Po was the dominate phase in the shelf while dissolved form dominated in the slope. The activity concentrations of210Po and210Pb varied largely with depth in summer, while little vertical variations at stations without the influnce of Kuroshio in fall and winter due to the enhanced water mixing.4) In the southern Yellow Sea and the East China Sea, the scavenging and removal rates and removal fluxes of210Po during summer to winter were lower than those during winter to fall by NSS model, while the residence times of210Po was opposite. The POC export fluxes estimated from210Po/210Pb disequilibria ranged from-258.99to2379.08mmolC/m2/a, with a lower flux from summer to winter than that from winter to fall.5) In the northern South China Sea, the proportions of dissolved210Po to total210Po increased from the inshore to the deep basin, indicating the effect of the particle concentrations.6) The mean residence time of dissolved210Po was slightly lower than that of210Pb in the northern South China Sea, while the mean residence time of particulate210Po was close to or longer than that of210Pb. There was no significant fractionation between dissolved210Po and210Pb during scavenging process, but a significant fractionation between particulate210Po and210Pb was observed during removal process.