Formation of ferromanganese crust in Western Pacific Magellan Seamount: Variations in redox state of Fe/Mn

Kiho Yang1, Hanbeom Park1, Jinwook Kim1, Hionsuck Baik2, Jonguk Kim3, kyeong Ryang Park4 and Junbeom Yoon4, (1)Yonsei University, Seoul, Korea, Republic of (South), (2)KBSI Korea Basic Science Institute, Seoul, Korea, Republic of (South), (3)KIOST Korea Institute of Ocean Science and Technology, Busan, South Korea, (4)Hannam University, Daegeon, Korea, Republic of (South)
Abstract:
Redox reaction is a ubiquitous process in the formation of ferromanganese crust that may reflect one of paleoenvironments, particularly variations of Fe/Mn redox states and microbial diversity in the crust suggests the unique biogeochemical reactions when the crust formed in the ocean sediment.

Samples were dredged from the seamounts in the western Pacific Magellan Seamount (OSM11) to investigate the biotic/abiotic redox reaction in the formation of the crust that consists of five well-defined layers from the rim (layer 1) to the core (layer 5). Mineralogy, morphology and Fe/Mn oxidation state in each layer were determined by X-ray Diffractometer (XRD), Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED) pattern, Energy Dispersive X-ray spectrometer (EDX), and Electron Energy Loss Spectroscopy (EELS). Fe-rich vernadite was detected in all layers while quartz, feldspar, and hematite only appeared in layer 1, and carbonate fluorapatite (CFA) were observed in layers 4 and 5. The oxidation states of Fe in Fe-rich vernadite measured by EELS showed a distinct change between layers ranging 26 – 60 % of Fe3+/Fetot. Analyses of Restriction Fragment Length Polymorphism (RFLP) indicated the presence of functional gene (CumA) association with Mn oxidizer suggesting that the biotic Mn oxidation may promote the formation of the Fe-Mn crust.

The present study collectively showed a process of ferromanganese crust formation, secondary phase mineral precipitation such as CFA, and a distinct changes in Fe-redox states implying the biotic/abiotic associations such as biotic local reduction of Fe or uplift-subsidence of sea mounts, inducing the variations redox conditions in the formation of the crust.

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