Biogenic Origin of Polymetallic Nodules from the Clarion-Clipperton Zone in the Eastern Pacific Ocean: Electron Microscopic and EDX Evidence |
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Authors: | Xiaohong Wang Ute Schloßmacher Matthias Wiens Heinz C Schröder Werner E G Müller |
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Institution: | Laboratory for Earth Surface Processes, Ministry of Education, Peking University, 100871 Beijing, China. wxh0408@hotmail.com |
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Abstract: | Polymetallic/ferromanganese nodules (Mn-nodules) have been assigned a huge economic potential since they contain considerable
concentrations of manganese, copper, nickel, iron, and cobalt. It has been assumed that they are formed by, besides hydrogenous,
nonbiogenic processes, biogenic processes based on metabolic processes driven by microorganisms. In the present study, we
applied the techniques of digital optical microscopy and high-resolution scanning electron microscopy to search for microorganisms
in Mn-nodules. They were collected from the Clarion-Clipperton Zone in the Eastern Pacific Ocean and are composed of Mn (23.9%),
Cu (0.69%), Ni (1.02%), Fe (10.9%), and Co (0.29%). These Mn-nodules, between 2.3 and 4.8 cm, show a distinct lamination;
they are composed of small-sized micronodules, 100 to 450 μm in size, which are bound together by an interstitial whitish
material. In the micronodules, a dense accumulation of microorganisms/bacteria could be visualized. Only two morphotypes exist:
(1) round-shaped cocci and (2) elongated rods. The cocci (diameter: ≈3.5 μm) are arranged in bead-like chains, while the rods
(≈2 × 0.4 μm) are arranged either as palisades or in a linear row. Energy-dispersive X-ray spectroscopy analyses showed that
the areas rich in microorganisms/bacteria are also rich in Mn, while in regions where no microorganisms are found, the element
Si is dominant. We suggest that growth of the Mn-nodules starts with the formation of “micronodules.” The formation of micronodules
is assumed to be mediated by microorganisms. After accretion of biogenic and additional nonbiogenic minerals, the micronodules
assemble to large nodules on the sea floor through additional inclusion of nonbiogenic material. |
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Keywords: | Manganese nodules Biomineralization Clarion-Clipperton zone Microorganisms Bacteria (cocci) Bacteria (rods) Biogenic manganese |
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