Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox
Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox
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DOI：
10.1073/pnas.0903518106
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发表时间：
2009-09
期刊：
影响因子：
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通讯作者：
Y. Ueno;Matthew S. Johnson;S. Danielache;Carsten Eskebjerg;A. Pandey;N. Yoshida
中科院分区：
文献类型：
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作者：
Y. Ueno;Matthew S. Johnson;S. Danielache;Carsten Eskebjerg;A. Pandey;N. Yoshida
如果能够定量地描述产生同位素效应的机制，地质样品中硫同位素的分布将提供大气成分的记录。测定了~(32)SO_2、~(33)SO_2和~(34)SO_2的紫外吸收光谱，并用它们来解释地质记录。计算的SO2光解同位素分馏系数给出了与质量无关的分布，这些分布对大气中O2、O3、CO2、H2O、CS2、NH3、N2O、H2S、OCS和SO2本身的浓度高度敏感。考虑了不同的紫外线屏蔽情况，我们得出结论，在太古宙硫酸盐沉积物中观察到的负Δ33S只能用接触网屏蔽来解释。在相关的太古宙气体中，OCS具有独特的能力，可以防止λ>；202 nm处的阳光光解二氧化硫。使用光化学盒子模型运行的情景显示，OCS的ppm水平将在富含CO的太古代大气中积累。由于这种水平的OCS，辐射强迫能够解决微弱的年轻太阳悖论。此外，大气OCS的下降可能是造成太古宙晚期冰川的原因。
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 32SO2, 33SO2, and 34SO2 and use them to interpret the geological record. The calculated isotopic fractionation factors for SO2 photolysis give mass independent distributions that are highly sensitive to the atmospheric concentrations of O2, O3, CO2, H2O, CS2, NH3, N2O, H2S, OCS, and SO2 itself. Various UV-shielding scenarios are considered and we conclude that the negative Δ33S observed in the Archean sulfate deposits can only be explained by OCS shielding. Of relevant Archean gases, OCS has the unique ability to prevent SO2 photolysis by sunlight at λ >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.