Atmospheric depositional fluxes of cosmogenic ~(35)S and ~7Be: Implications for the turnover rate of sulfur through the biosphere

摘要

The wet depositional fluxes of cosmogenic ~(35)S and ~7Be, together with~210Pb, were measured in Seoul, Korea, from April 2004 to April 2005. Approximately half of the annual fluxes occurred in summer, during which about 60% of the precipitations occurred. Our simple box model shows that the theoretical scavenging ratio of ~(35)S/~7Be to the ground is approximately 0.013, which accounts for the decay for the duration of oxidation and settling. However, we observed ~50% higher ~(35)S/~7Be activity ratios than the theoretical removal ratio over the entire sampling period, with particularly higher (~ 133%) ratios during November 2004—April 2005. These higher ratios in the winter cannot be explained by sudden incursions of the stratospheric air or longer aerosol residence times, on the basis of ~7Be/~210Pb ratios. We hypothesize that the ratios could occur owing to biomass burning or as plants go dormant and dry during the autumn and winter. Based on this hypothesis, we developed a ~(35)S/~7Be mass balance model which yields the turnover rate of sulfur in the atmosphere through the biosphere to be 0.015 ± 0.007 d-1. Such a rapid sulfur turnover rate should be applied to the prediction model of sulfur inventory changes.