The distribution of long-chain n-alkan-2-ones in peat can be used to infer past changes in pH

Yiming Zhang, Xianyu Huang, Ruicheng Wang, B David A Naafs

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Abstract

Long-chain (C21-C33) n-alkan-2-ones are biomarkers ubiquitous in peat deposits. However, their paleoenvironmental significance lacks constraints. Here we evaluate the influence pH exerts on the occurrence of long-chain n-alkan-2-ones in Chinese peats. A comparison of the distribution in a collection (n= 65) of modern peat samples with different pH (pH values 4.4-8.6) from China demonstrates that their distribution is significantly different in acid compared to alkaline peat. This difference can be explained by the pH control on the conversion of n-alkan-2-one precursor compounds (n-alkanes and fatty acids). Transfer functions between pH and n-alkan-2-one ratios were established using linear and logarithmic regression models. We then applied these proxies to reconstruct variations of paleo-pH in the Dajiuhu peat sequence to identify the
history of peatland acidification over the last 13 kyr. We find significant changes in paleo-pH during the deglaciation/early Holocene and relate these to times of dry climate in the region. The drought-induced peat acidification is supported by observations from modern drying events in the peatland. We propose that long-chain n-alkan-2-ones in peats have potential to trace paleo-pH changes across the deglaciation and Holocene, although further research from different peatlands and time periods is still needed.
Original languageEnglish
Article number119622
JournalChemical Geology
Early online date8 Apr 2020
DOIs
Publication statusE-pub ahead of print - 8 Apr 2020

Keywords

  • peatland
  • pH
  • n-alkan-2-one
  • acidification
  • drought

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