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 (Delta 14C) 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 Delta 14C values of plant-derived (C24, C26, and C28) n-fatty acids (-99%o to -149%o) were considerably lower than the Delta 14C of charred plants (139%o) within the sediments and those of living aquatic plants (-52%o to -58%o) in Lake Yamanaka, suggesting that contributions from pre-aged terrestrial and aquatic plant materials likely affect these acids. Similarly, the Delta 14C of C16 n-fatty acid (-95%o) in surface sediments was much lower than the Delta 14C of modern aquatic plants (-52%o to -58%o), as well as the Delta 14C of dissolved organic carbon (DIC) in surface water (-48%o). 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 Delta 14C of C16 n-fatty acids. Comparing fatty acid Delta 14C 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.