Study on the mechanisms of biogenic basalt alteration by synchrotron-based X-ray microscopy

2018 Fiscal Year Final Research Report

• Project/Area Number: 15H05330
• Research Category: Grant-in-Aid for Young Scientists (A)
• Allocation Type: Single-year Grants
• Research Field: Environmental dynamic analysis
• Research Institution: Ehime University
• Principal Investigator: Mitsunobu Satoshi 愛媛大学, 農学研究科, 准教授 (70537951)
• Research Collaborator: Makita Hiroko
• Project Period (FY): 2015-04-01 – 2019-03-31
• Keywords: 海洋地殻 / 生物的風化 / XAFS / 鉄酸化反応 / バクテリア

Outline of Final Research Achievements

The weathering of oceanic basalt has a significant impact on Earth's climate on a geological timescale by providing a sink for atmospheric CO2 through carbonization of oceanic basalts. The fresh basalt rock contains abundant Fe and its major species is Fe(II). Recent previous studies have reported that oceanic microorganisms would play a significant role to the oxidation of Fe(II) in the basalt. In this study, we investigated the mechanisms of the biogenic Fe(II) oxidation in basalt weathering by synchrotron X-ray spectrocopic techniques. We appliyed the techniques into the basalt samples prepared by in situ incubation of fresh basalt at deep seafloor in Izu-Ogasawara bonin. Our analysis of the sample clearly showed that microbial Fe(II) oxidation is more rapid reaction than abiotic Fe(II) oxidation and that the biotic Fe(II) oxidation promotes the whole basalt weathering. These findings would be an important knowledge to understand mechanism of biogenic weathering of oceanic crust.

Free Research Field

地球化学

Academic Significance and Societal Importance of the Research Achievements

上述の通り、海洋地殻である玄武岩の酸化風化は海洋のCO2固定を促進するため、地球規模の炭素循環を考える上でも重要な反応である。本研究では、ナノスケールの空間分解能を有する先端的X線顕微鏡を利用して、鉱物－微生物細胞界面における鉄、酸素、炭素の元素分布さらには化学種分析をおこない、海底下微生物が玄武岩風化を促進させる分子レベルでの証拠を得た。これらの知見は、地球規模の炭素循環に果たす海底下微生物の影響を再考するきわめて重要な知見となる。