JpGU-AGU Joint Meeting 2017

Presentation information

[EJ] Oral

B (Biogeosciences) » B-PT Paleontology

[B-PT05] [EJ] Decoding the history of Earth: From Hadean to Modern

Tue. May 23, 2017 3:30 PM - 5:00 PM 201B (International Conference Hall 2F)

convener:Tsuyoshi Komiya(Department of Earth Science & Astronomy Graduate School of Arts and Sciences The University of Tokyo), Yasuhiro Kato(Department of Systems Innovation, Graduate School of Engineering, University of Tokyo), Katsuhiko Suzuki(Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology), Chairperson:Hisashi Asanuma(Tokyo institute of Technology)

3:30 PM - 3:45 PM

[BPT05-07] High-resolution 32/33/34/36SO2 absorption cross-section measurements for revealing Archean atmospheric composition

*Yoshiaki Endo1, Moeko Ogawa2, Masumi Shinkai2, Sebastian Danielache2,3, Yuichiro Ueno1,3,4 (1.Tokyo Institute of Technology, 2.Sophia Univ., 3.ELSI, 4.JAMSTEC)

Keywords:Archean atmosphere, Sulfur isotope, Photochemistry

Many geological and geochemical records suggest a reducing Archean atmosphere. Revealing Archean atmospheric composition is important proxy for the understanding of the origin and evolution of life. The discovery and explanation of sulfur mass-independent fractionation (S-MIF) signatures in Archean sedimentary rocks possess as a key to unravel Archean atmospheric composition. Our SO2 photochemical experiments generated large S-MIF (Δ33S > +5‰) and reproduced basic character of the Archean S-MIF signature (Δ36S/Δ33S = −1) under a specific condition for the first time (Endo et al. 2016). Self-shielding of SO2 photodissociation and intersystem crossing (ISC) form singlet SO2 to triplet SO2 are shown as key mechanisms. Next, we simulated large S-MIF signature (Δ33S > +5‰) in our box numerical model, and we showed that Archean S-MIF trend (Δ36S/Δ33S = −1) can be explained when there are several ppm level of SO2 (like the plume of volcanic gas) and 2% (2 kPa) CO or 3% (3 kPa) CH4 in the atmosphere. But box model’s calculation is not completely correct because photochemical reaction rate and fractionation factor (such as self-shielding) strongly depends on the altitude. Then we need to develop 1-D atmospheric model.
Our group's new 1-D model which focuses on UV spectra because reactions and fractionation factor (such as self-shielding) change delicately as a function of irradiative photon flux. Fractionation factor of photodissociation can be calculated by isotopologue cross-section and irradiative photon flux. Then in order to develop 1-D atmospheric model including sulfur isotopes, SO2 isotopologue cross-sections (32/33/34/36SO2) are necessary. Although SO2 isotopologue cross-section have been measured, they are too low-resolution to estimate self-shielding (Danielache et al. 2008, Endo et al. 2015). Here, we report preliminary results of high resolution (~1cm-1) 32/33/34/36SO2 absorption cross-sections and estimation of fractionation factor including self-shielding effect.

Referces: Endo et al. (2016), EPSL, Danielache et al. (2008), JGR Atmospheres, Endo et al. (2015), JGR Atmospheres