Japan Geoscience Union Meeting 2015

Presentation information


Symbol B (Biogeosciences) » B-CG Complex & General

[B-CG28] Interrelation between Life, Water, Mineral, and Atmosphere

Tue. May 26, 2015 6:15 PM - 7:30 PM Convention Hall (2F)

Convener:*Fumito Shiraishi(Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University), Tsubasa Otake(Division of Sustainable Resources Engineering, Faculty of Engineering, Hokkaido University), Yohey Suzuki(Graduate School of Science, The University of Tokyo), Ken Takai(Extremobiosphere Research Center, Japan Agency for Marine-Earth Science & Technology), Yuichiro Ueno(Department of Earth and Planetary Sciences, Tokyo Institute of Technology), Takeshi Naganuma(Graduate School of Biosphere Science), Takeshi Kakegawa(Graduate School of Science, Tohoku University), Tadashi Yokoyama(Department of Earth and Space Science, Graduate School of Science, Osaka University), Kentaro Nakamura(Precambrian Ecosystem Laboratory (PEL), Japan Agency for Marine-Earth Science and Technology (JAMSTEC))

6:15 PM - 7:30 PM

[BCG28-P10] Establishment of iron microelectrode measurement and its application to iron deposit resembling BIF

*Kohei NAKAO1, Fumito SHIRAISHI1 (1.Hiroshima University)

Precambrian banded iron formation (BIF) is important for estimating the redox state of the global environment during that period, and many studies have been conducted until now. In the traditional model, BIF had been considered to be formed by oxidation of Fe(II) by cyanobacteria-released oxygen. However, it has been recently suggested that other microbial metabolisms, such as direct iron oxidation associated with carbon fixation of non-oxygenic Fe(II)-oxidizing phototrophic bacteria, were also involved in the formation. Therefore, its formation process is considered to be complicated much more than previously thought, and detailed investigation about the microbial processes that can potentially form BIF is required. This study aimed to reveal the formation processes of iron deposits found in Sambe hot spring in Shimane Prefecture, and applied both geochemical and geomicrobiological techniques. In previous study, it have been described that this deposit is mainly composed of iron hydroxide (ferrihydrite), and microbial composition at the deposit surface is dominated by iron-oxidizing bacteria (Gallionella sp.) with minor cyanobacteria. In this study, we applied the Fe(II) microelectrode in addition to the pH, redox, O2 microelectrodes in order to accurately evaluate the microbial and inorganic precipitation occurring in the surface. By these microelectrodes, we measured the chemical profiles at the vicinity of deposit surface (about 1 mm from the surface) and found that all chemical profiles were almost the same both in light and dark conditions, indicating that contribution of photosynthesis was negligible. Fe(II) and O2 consumption at the deposit surface implied that iron-oxidizing bacteria (Gallionella sp.) oxidized Fe(II) by using oxygen. This kind of iron precipitation process would provide an important knowledge about the formation process of BIF deposited when the ocean gradually became oxidative by cyanobacteria released oxygen. In addition, measurement method of Fe(II) microelectrode established in this study will be applicative to other types of BIF modern analogs, and it is expected that further details of BIF formation processes will be revealed.