Bibliographic Details
| Title: |
Methanogenic Archaea as Catalysts for Magnetite Formation in Iron‐Rich Marine Sediments. |
| Authors: |
Lin, Zhiyong, Lin, Haixin, Strauss, Harald, Roberts, Andrew P., Niu, Mingyang, Fang, Yunxin, Yang, Tao, Sun, Xiaoming, Birgel, Daniel, Peckmann, Jörn |
| Source: |
Journal of Geophysical Research. Solid Earth; Jun2024, Vol. 129 Issue 6, p1-18, 18p |
| Subject Terms: |
MARINE sediments, IRON, GOETHITE, MAGNETITE, MAGNETITE crystals, ARCHAEBACTERIA, TURBIDITY currents, TURBIDITES |
| Abstract: |
Fine‐grained authigenic magnetite has been recognized increasingly in iron‐rich marine environments affected by methane seepage and is a major sedimentary magnetization source. However, it is unknown whether this magnetite forms via microbial or abiotic processes. We report here abundant fine magnetite crystals, in close association with goethite, within coarse‐grained sediments from two adjacent methane seepage sites in the South China Sea. The magnetite‐ and goethite‐rich horizons have sharply increased Zr/Ti, Zr/Rb, Ti/Al, and Fe/Al ratios, probably reflecting deposition by turbidity currents. Deeper intervals have elevated pyrite content, positive δ34S excursions of chromium reducible sulfur, and low magnetic susceptibilities, which is consistent with past sulfate‐driven anaerobic oxidation of methane in environments with dynamically variable seepage intensity. In magnetically extracted aggregates (>63 μm), magnetite particles are mainly clustered euhedral crystals with 0.2–0.8 μm sizes, which will likely impact sedimentary magnetic signals. The fine, euhedral crystalline nature of the magnetite suggests formation in sulfide‐free, ferrous iron‐rich sedimentary environments. Based on 16S rRNA gene sequences, anaerobic methanotrophic archaea coincide with pyrite rich horizons. In contrast, two co‐occurring methanogenic archaea groups of the Methanomicrobia class (mainly Methanosarcina and Methanocella) are particularly abundant in turbidites but have low abundance in all other horizons. Increased Methanomicrobia abundances suggest that this class of archaea may be involved in microbial iron reduction in turbidites with abundant goethite as a reactive iron source, and that they apparently trigger magnetite formation. Our findings provide new clues to microbial magnetite formation in iron‐rich marine sediments. Plain Language Summary: Magnetite is a key source of sedimentary magnetic signals. Understanding the origin of magnetite in sediments is critical for proper interpretation of paleomagnetic records. Fine‐grained authigenic magnetite has been recognized increasingly in iron‐rich continental margin environments with high methane flux and represents a further important magnetization source in marine sediments. However, it is unknown whether this magnetite forms via microbial or abiotic processes. Here, we identify abundant fine magnetite crystals within iron‐rich subseafloor horizons from two adjacent methane seepage sites in the South China Sea. From magnetic, mineralogical, geochemical, and genomic analyses, we provide new constraints for understanding magnetite formation in iron‐rich sediments, where methanogenic archaea apparently perform microbial iron reduction and trigger magnetite formation. Key Points: We identify abundant fine magnetite crystals within subseafloor iron‐rich layers from methane seepage impacted sitesMethanogenic archaea coincide with magnetite‐rich horizons and are considered potential drivers of microbial iron reduction and magnetite formationOur findings have profound implications for the nature of paleomagnetic signals recorded in iron‐rich sediments, and for iron cycling in marine sediments [ABSTRACT FROM AUTHOR] |
|
Copyright of Journal of Geophysical Research. Solid Earth is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) |
| Database: |
Complementary Index |
