Evidence for biogenic processes during formation of ferromanganese crusts from the Pacific Ocean: Implications of biologically induced mineralization |
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| Authors: | Xiao-hong Wang Ute Schlo?macher Filipe Natalio Heinz C. Schr?der Stephan E. Wolf Wolfgang Tremel Werner E.G. Müller |
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| Affiliation: | 1. Center for Marine Core Research Institute, Kochi University, Japan;2. Institute for Industrial Science, University of Tokyo, Japan;3. R & D Center for Marine Resources, JAMSTEC, Japan;4. Metals Exploration Dept., JOGMEC, Japan;5. Division of Chemistry, Tsukuba University, Japan;6. Geological Survey of Japan, National Inst. Advanced Industrial Science and Technology (AIST), Japan;7. Tokyo University of Pharmacy and Life Sciences, Japan;8. Emeritus Professor, University of Tokyo, Japan;1. Earth and Space Sciences, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany;2. U.S. Geological Survey, 400 Natural Bridges Dr., Santa Cruz, CA 95060, USA;3. Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, 30655 Hannover, Germany;4. Department of Natural Environmental Science, Kochi University, 2-5-1 Akebono, Kochi 780-8520, Japan;1. Department of Geology, Graduate School of Integrated Arts and Sciences, Kochi University, Japan;2. Department of Geology, Kochi University, Japan;3. Sumiko Resources Exploration and Development, Co., Japan;4. Center for Advanced Marine Core Research, Kochi University, Japan;1. Geological Survey of Spain, (IGME), C/Ríos Rosas, 23, 28003 Madrid, Spain;2. Crystallography and Mineralogy Department, Complutense University of Madrid, C/Jose Antonio Novais, 2, 28040 Madrid, Spain;3. Instituto de Geociencias IGEO (CSIC, UCM), Madrid, Spain;4. Instituto Español de Oceanografía, C.O. de Málaga, Puerto Pesquero s/n, 29649 Fuengirola, Spain |
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| Abstract: | Ferromanganese [Fe/Mn] crusts formed on basaltic seamounts, gain considerable economic importance due to their high content of Co, Ni, Cu, Zn and Pt. The deposits are predominantly found in the Pacific Ocean in depths of over 1000 m. They are formed in the mixing layer between the upper oxygen-minimum zone and the lower oxygen-rich bottom zone. At present an almost exclusive abiogenic origin of crust formation is considered. We present evidence that the upper layers of the crusts from the Magellan Seamount cluster are very rich in coccoliths/coccolithophores (calcareous phytoplankton) belonging to different taxa. Rarely intact skeletons of these unicellular algae are found, while most of them are disintegrated into their composing prisms or crystals. Studies on the chemical composition of crust samples by high resolution SEM combined with an electron probe microanalyzer (EPMA) revealed that they are built of distinct stacked piles of individual compartments. In the center of such piles Mn is the dominant element, while the rims of the piles are rich in Fe (mineralization aspect). The compartments contain coccospheres usually at the basal part. Energy dispersive X-ray spectroscopy (EDX) analyses showed that those coccospheres contain, as expected, CaCO3 but also Mn-oxide. Detailed analysis displayed on the surface of the coccolithophores a high level of CaCO3 while the concentration of Mn-oxide is relatively small. With increasing distance from the coccolithophores the concentration of Mn-oxide increases on the expense of residual CaCO3. We conclude that coccoliths/coccolithophores are crucial for the seed/nucleation phase of crust formation (biomineralization aspect). Subsequently, after the biologically induced mineralization phase Mn-oxide deposition proceeds “auto”catalytically. |
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