Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox

作者：Ueno Yuichiro; Johnson Matthew S^*; Danielache Sebastian O; Eskebjerg Carsten; Pandey Antra; Yoshida Naohiro

来源：Proceedings of the National Academy of Sciences, 2009, 106(35): 14784-14789.

DOI：10.1073/pnas.0903518106

• mass independent fractionation
• carbonyl sulfide (OCS)
• sulfur dioxide (SO(2))
• photochemistry
• greenhouse gases

Distributions of sulfur isotopes in geological samples would provide a record of atmospheric composition if the mechanism producing the isotope effects could be described quantitatively. We determined the UV absorption spectra of (32)SO(2), (33)SO(2), and (34)SO(2) and use them to interpret the geological record. The calculated isotopic fractionation factors for SO(2) photolysis give mass independent distributions that are highly sensitive to the atmospheric concentrations of O(2), O(3), CO(2), H(2)O, CS(2), NH(3), N(2)O, H(2)S, OCS, and SO(2) itself. Various UV-shielding scenarios are considered and we conclude that the negative Delta(33)S observed in the Archean sulfate deposits can only be explained by OCS shielding. Of relevant Archean gases, OCS has the unique ability to prevent SO(2) photolysis by sunlight at lambda > 202 nm. Scenarios run using a photochemical box model show that ppm levels of OCS will accumulate in a CO-rich, reducing Archean atmosphere. The radiative forcing, due to this level of OCS, is able to resolve the faint young sun paradox. Further, the decline of atmospheric OCS may have caused the late Archean glaciation.

• 出版日期2009-9-1