Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

M (Multidisciplinary and Interdisciplinary) » M-ZZ Others

[M-ZZ41] Marine manganese deposits: from basic to applied sciences

Wed. May 23, 2018 10:45 AM - 12:15 PM A11 (Tokyo Bay Makuhari Hall)

convener:Akira Usui(Marine Core Research Center, Kochi University), Yoshio Takahashi(Department of Earth and Planetary Science, Graduate School of Science, The 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, 共同), Takashi Ito(Faculty of Education, Ibaraki University), Chairperson:Usui Akira, Suzuki Katsuhiko(JAMSTEC), Takahashi Yoshio(東京大学)

11:00 AM - 11:15 AM

[MZZ41-02] Nanomineralogical Evidence of Microbial Formation of Deep-Sea Ferromanganese Crust

*Yohey Suzuki1 (1.Graduate School of Science, The University of Tokyo)

Keywords:Microbial precipitation, Biofilm formation

Since the Late Paleocene, ferromanganese crust (Fe-Mn crust) has been deposited extensively on the surface of seamounts or plateaus at 400 to 6000 meters below sea level (mbsl) with a thickness range of 1 to 20 cm. Although cosmogenic nuclide and paleomagnetic dating unambiguously revealed the exceedingly slow growth rates (1 to 10 mm/Myr), the formation process of Fe-Mn crusts is poorly understood. Mn(II) oxidation to Mn(III) is mediated by superoxide formation by oxygen respiration by microbes, whereas Mn(III) oxidation to a Mn(IV) oxide phase is kinetically hindered by a reverse reaction by peroxide produced aerobically in oxygenated circumneutral seawater. Microbial consumption of peroxide is speculated to be involved in the formation of Fe-Mn crusts, but no direct evidence has been presented to date. In this study, the surface of Fe-Mn crust obtained from a depth of 3000 mbsl at Takuyo Daigo Seamount was characterized by a confocal laser microscope, and the dense colonization of microbial cells stained by SYBR Green I was observed on the crust surface. An ultrathin section fabricated by focus ion beam (FIB) was characterized by a transmission electron microscope (TEM) equipped with energy dispersive spectroscopy (EDS). TEM-EDS analysis revealed that microbial cells were enrobed in Fe- and Mn-bearing precipitates. Selected area electron diffraction (SAED) patterns showed that Fe- and Mn-bearing precipitates were amorphous or poorly crystalline. High-Angle Annular Dark Field Scanning TEM (HAADF-STEM) analysis of Fe- and Mn-bearing precipitates around microbial cells and inside the Fe-Mn crust demonstrated that the compositions and nanomineralogical features were identical. It is therefore suggested that the formation of Fe-Mn crust is mediated by microbial activities on the crust surface.