ABSTRACT

We generated a record of lignin and fatty acid compositions from the TK-2004 core in Takano Basin, central Japan, during 39–162 ka by TMAH-thermochemolysis-GC/MS. We tested lignin and fatty acid compositions in the sediments of a small lake (1.88 km² watershed) as a paleovegetation proxy to understand the responses of terrestrial vegetation in central Japan to global climate change. Variation in terrestrial organic carbon contents estimated by C/N and ∑8 was parallel to the total organic content (TOC) variation, suggesting that the inflow of terrestrial organic matter was a major factor determining the TOC. The ratio of mid-chain C₂₀–C₂₄ n-fatty acids to short-chain C₁₄–C₁₈ n-fatty acids (MFA/SFA ratio) and the ratio of cinnamyl to vanillyl phenols (C/V ratio) of lignin gradually increased from mid-MIS 6 to early MIS 3. The increase in both parameters suggested increase in the contribution of submerged and floating plants as the flats were expanded in the lake margin. The ratio of syringyl to vanillyl phenols (S/V ratio) corresponded to the pollen vegetation index. This correspondence indicated that the S/V ratio reflected the relative abundance of angiosperms to gymnosperms in the Takano Basin. The consistency of the S/V ratio at the site of core TKN-2004 and the other two locations suggests that the S/V ratio in a small basin is a robust proxy for terrestrial vegetation on a regional scale.