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Open AccessArticle

Petrographical and Geochemical Signatures Linked to Fe/Mn Reduction in Subsurface Marine Sediments from the Hydrate-Bearing Area, Dongsha, the South China Sea

by Xi Xiao 1,2,3,4,†, Qian-Zhi Zhou 1,†, Shao-Ying Fu 3,4, Qian-Yong Liang 3,4, Xiang-Po Xu 1, Yan Li 1,* and Jiang-Hai Wang 1,2,*
1
Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, School of Marine Sciences, Sun Yat-Sen University, Guangzhou 510006, China
2
Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519000, China
3
Guangzhou Marine Geological Survey, Guangzhou 510760, China
4
Gas Hydrate Engineering Technology Center, China Geological Survey, Guangzhou 510075, China
*
Authors to whom correspondence should be addressed.
The authors contributed equally to this work.
Minerals 2019, 9(10), 624; https://doi.org/10.3390/min9100624
Received: 17 September 2019 / Revised: 8 October 2019 / Accepted: 8 October 2019 / Published: 11 October 2019
(This article belongs to the Special Issue Marine Geology and Minerals)
Fe and Mn oxides and (oxy)-hydroxides are the most abundant solid-phase electron acceptors in marine sediments, and dissimilatory Fe/Mn reduction usually links with the anaerobic oxidation of methane (AOM) and organic matter oxidation (OMO) in sediments. In this study, we report the results from subsurface marine sediments in the Dongsha hydrate-bearing area in the South China Sea. The petrological and geochemical signatures show that the Fe/Mn reduction mediated by AOM and OMO might occur in sediments above the sulfate-methane transition zone. X-ray diffraction and scanning electron microscopy analyses of sediments indicate that Fe(III)/Mn(IV)-oxides and authigenic carbonate minerals coexisted in the Fe/Mn reduction zone. The lower δ13C values of dissolved inorganic carbon, coupled with an evident increase in total inorganic carbon contents and a decrease in Ca2+ and Mg2+ concentrations indicate the onset of AOM in this zone, and the greater variation of PO43− and NH4+ concentrations in pore water suggests the higher OMO rates in subsurface sediments. Geochemical and mineralogical analyses suggest that the previously buried Fe(III)/Mn(IV) oxides might be activated and lead to the onset of Fe/Mn reduction induced by AOM and OMO. These findings may extend our understanding of the biogeochemical processes involved in Fe/Mn reduction in continental shelves with abundant methane, organic matter, and terrigenous metal oxides. View Full-Text
Keywords: iron/manganese reduction; anaerobic oxidation of methane; organic matter oxidation; hydrate-bearing area; South China Sea iron/manganese reduction; anaerobic oxidation of methane; organic matter oxidation; hydrate-bearing area; South China Sea
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Xiao, X.; Zhou, Q.-Z.; Fu, S.-Y.; Liang, Q.-Y.; Xu, X.-P.; Li, Y.; Wang, J.-H. Petrographical and Geochemical Signatures Linked to Fe/Mn Reduction in Subsurface Marine Sediments from the Hydrate-Bearing Area, Dongsha, the South China Sea. Minerals 2019, 9, 624.

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