Hopanoid Distributions Differ in Mineral Soils and Peat: A Re-Evaluation of Hopane-Based PH Proxies

作者：Gordon N. Inglis, Cindy De Jonge, Christoph Häggi, Sarah J. Feakins, Jingjing Guo, Gerd Dercon, Dailson José Bertassoli, Thomas Kenji Akabane, McKenzie R. Bentley, Emily J. Beverly, B. David A. Naafs, Richard D. Pancost · 发表于：Advances in Geochemistry and Cosmochemistry · 年份：2025 · DOI：10.33063/agc.v1i2.755 · 被引用次数：4 · 研究领域：Geology and Paleoclimatology Research、Geochemistry and Geologic Mapping、Mineralogy and Gemology Studies

Hopanoids are produced by bacteria and are commonly found in terrestrial and marine environments. In modern environments, hopanoids mostly occur in the biological 17β,21β(H) configuration. Over geological time (106 to 108 years), thermal degradation changes their stereochemistry to the thermally mature 17α,21β(H) configuration. However, in modern acidic peat-forming environments, the ‘thermally mature’ C31 17α,21β(H)-homohopane dominates over the biological ββ stereoisomer, with an increase in the relative abundance of the αβ stereoisomer at lower pH. Based on this pH dependency, hopane isomerisation ratios have been used to reconstruct pH in ancient peat-forming environments. However, the environmental controls on hopane isomerisation remain poorly constrained and it is unclear whether this proxy is also applicable in mineral soils. Here, we analysed hopane distributions in mineral soils characterised by a wide range of mean annual temperature and pH. We show that mineral soils are dominated by diploptene, an unsaturated C30 hopanoid synthesised by a wide range of bacteria. In our soil dataset, there are relatively few thermally mature αβ hopanes – even within acidic mineral soils – and there is no relationship between hopane isomerisation ratios and pH. We propose that mineral protection in these soil environments selectively protects hopanoids from rapid degradation and subsequent isomerisation in modern samples. This provides a plausible explanation for the lack of 17α,21...