Sulfate in antarctic snow: Spatio-temporal distribution

Abstract

Delmas and Boutron (1978) may have measured sulfate deposition from a major volcanic eruption recorded in Antarctic snow, and this involved concentrations of some 20 x 10^(-9) gg^(-1) sulfur superimposed on a background of 20 x 10^(-9) gg^(-1) sulfur. They suggest that this type of sulfate contribution may be superimposed on backgrounds of both marine and anthropogenic contributions in those snows. Their observations define upper limits to contributions of substances to polar snows by volcanic emissions. That is, major eruptions do not contribute more than sporadic additions of sulfate equal in amount to background concentrations. In normal polar regions we can assume for the maximum case that half the sulfate is contributed from volcanic sources while the remainder originates from marine and anthropogenic sources. On the basis of the sulfate data of Unni et al. (1978) and Herron et al. (1977), this would yield a sulfur concentration of 10 x 10^(-9) gg^(-1) sulfur from volcanoes in snow. Herron et al. (1977) claim that concentrations of lead in 1000-yr old arctic snows at levels of 0.05 x 10^(-9) gg^(-1) are not anthropogenic but originate from natural sources such as volcanic emissions. The Pb/S ratio in volcanic gas has been measured (Duce et al., 1978) and is found to be < 1 x 10^(-7) wt fraction. The amount of lead contributed to arctic snow from volcanic sources would therefore be on the order of 1 x 10^(-15) gg^(-1) lead in snow which is infinitesimally smaller than the concentrations they report to have been derived from natural sources. Such concentrations in fact did not exist in prehistoric times since, concentrations slightly less than 10^(-12) gg^(-1) lead are observed in 3000-yr old Arctic snow (Murozumi eta!., 1969).

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