Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

B (Biogeosciences) » B-CG Complex & General

[B-CG09] Decoding the history of Earth: From Hadean to the present

Tue. May 22, 2018 1:45 PM - 3:15 PM 101 (1F International Conference Hall, Makuhari Messe)

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(国立研究開発法人海洋研究開発機構・海底資源研究開発センター), Chairperson:Fujisaki Wataru(Japan Agency for Marine-Earth Science and Technology)

2:00 PM - 2:15 PM

[BCG09-08] Total pressure dependence of sulfur mass-independent fractionation by SO2 photolysis

*Yoshiaki Endo1, Yuichiro Ueno1,2,3, Miho Oinuma4, Sebastian Oscar Danielache2,4 (1.Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2.Earth-Life Science Institute, 3.Department of Subsurface Geobiological Analysis and Research (D-SUGAR), Japan Agency for Marine-Earth Science and Technology (JAMSTEC, 4.Faculty of Science and Technology, Sophia University)

Keywords:Archean atmosphere, Sulfur isotopes, Mass-independent fractionation, Self-shielding

Sulfur mass-independent fractionation (S-MIF) in Archean sedimentary rocks is a useful proxy for atmospheric chemistry. Archean S-MIF signatures typically show that Δ36S/Δ33S values are close to −1. We have succeeded to reproduce the Δ36S/Δ33S slope experimentally (Endo et al., 2016). Based on the experimental results, we suggested that Archean S-MIF can be explained by a combination of two effects: (1) self-shielding of SO2 photolysis (Δ36S/Δ33S ~ −2.4) and (2) intersystem-crossing in excited SO236S/Δ33S ~ +0.7). However, several results of previous photochemical experiments cannot be explained only by the two effects (Ono et al. 2013, Masterson et al. 2011). Total pressure may cause an additional effect on the S-MIF, though the mechanism is poorly understood. Here, we conducted SO2 photolysis experiments under various total pressures from 0.1 bar to 1.7 bar and measured sulfur isotope fractionations. Measured Δ36S/Δ33S values changed depending on total pressure. We discuss the mechanism of total pressure dependence of S-MIF by SO2 photolysis in terms of pressure broadening effect (Lyons et al., 2018) and present an implication for the total pressure of the Archean atmosphere.