Compound-specific radiocarbon analysis of sedimentary fatty acids: Potential as a dating tool for lake sediments of Mt. Fuji volcanic region, Japan

Compound-specific radiocarbon analysis (CSRA) is a promising tool for dating sediment sequences where traditional dating methods are impractical. However, the applicability of CSRA of short-chain fatty acids as a dating tool remains poorly understood, especially in lacustrine settings. Accordingly, we determined the radiocarbon content (Δ¹⁴C) of individual fatty acids in sediments of Lake Yamanaka (central Japan), as well as their stable carbon and hydrogen isotope ratios, to evaluate the potential of CSRA as a dating tool in volcanic lake environments. We found that the Δ¹⁴C values of plant-derived (C₂₄, C₂₆, and C₂₈) n-fatty acids (–99‰ to –149‰) were considerably lower than the Δ¹⁴C of charred plants (139‰) within the sediments and those of living aquatic plants (–52‰ to –58‰) in Lake Yamanaka, suggesting that contributions from pre-aged terrestrial and aquatic plant materials likely affect these acids. Similarly, the Δ¹⁴C of C₁₆ n-fatty acid (–95‰) in surface sediments was much lower than the Δ¹⁴C of modern aquatic plants (–52‰ to –58‰), as well as the Δ¹⁴C of dissolved organic carbon (DIC) in surface water (–48‰). Together with the stable isotope results, we conclude that in addition to autochthonous aquatic sources, contributions from pre-aged terrestrial carbon sources significantly affect the Δ¹⁴C of C₁₆ n-fatty acids. Comparing fatty acid Δ¹⁴C and concentration data across lakes within the Mt. Fuji region suggests that CSRA of the C₁₆ acid provides valid chronological information only when the C₁₆ originates exclusively from autochthonous aquatic sources, with minor allochthonous terrestrial input.