GFZ German Research Centre for Geosciences, Potsdam, Germany.
Department of Microbiology and Immunology, University of British Columbia, Vancouver, Canada.
Nat Commun. 2021 Apr 13;12(1):2216. doi: 10.1038/s41467-021-22453-0.
Deposition of ferruginous sediment was widespread during the Archaean and Proterozoic Eons, playing an important role in global biogeochemical cycling. Knowledge of organic matter mineralization in such sediment, however, remains mostly conceptual, as modern ferruginous analogs are largely unstudied. Here we show that in sediment of ferruginous Lake Towuti, Indonesia, methanogenesis dominates organic matter mineralization despite highly abundant reactive ferric iron phases like goethite that persist throughout the sediment. Ferric iron can thus be buried over geologic timescales even in the presence of labile organic carbon. Coexistence of ferric iron with millimolar concentrations of methane further demonstrates lack of iron-dependent methane oxidation. With negligible methane oxidation, methane diffuses from the sediment into overlying waters where it can be oxidized with oxygen or escape to the atmosphere. In low-oxygen ferruginous Archaean and Proterozoic oceans, therefore, sedimentary methane production was likely favored with strong potential to influence Earth's early climate.
在太古代和元古代，铁质沉淀物的沉积广泛存在，在全球生物地球化学循环中发挥了重要作用。然而，对于这种沉积物中有机质矿化的认识在很大程度上仍然是概念性的，因为现代的铁质类似物基本上没有得到研究。在这里，我们表明，在印度尼西亚的托乌蒂富铁湖中，尽管存在大量稳定的针铁矿等反应性三价铁相，但产甲烷作用主导了有机质矿化。因此，即使存在易降解的有机碳，三价铁也可以在地质时间尺度上被埋藏。三价铁与毫摩尔浓度的甲烷共存进一步表明不存在依赖铁的甲烷氧化作用。由于甲烷氧化作用可以忽略不计，甲烷从沉积物中扩散到上覆水中，在那里可以被氧气氧化或逸出到大气中。因此，在低氧的太古代和元古代富铁海洋中，沉积物中的甲烷生成可能很有利，并有很强的潜力影响地球的早期气候。
