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

Abstract

The wet depositional fluxes of cosmogenic 35S 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 35S/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 35S/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 35S/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.