A 35kyr record of organic matter composition and δ13C of n-alkanes in bog sediments close to Lake Baikal: Implications for paleoenvironmental studies

We characterized the compositions of organic compounds in a Cheremushka bog sediment core (deposited over the last 35 kyr), located at the eastern coast of Lake Baikal, to obtain basic information about the terrestrial organic matter (OM) which contributed to Lake Baikal sediments. The bog sediment was analyzed for the molecular composition of n -alkanes, lignin phenols and n -C 24 to C 30 alkanoic acids, as well as the carbon isotopic composition of plant wax derived n -C 27 to C 33 alkanes. Concentrations of lignin phenols [vanillyl (V) plus syringyl (S) phenols] normalized to total organic carbon (TOC) in the Holocene are twice those for the last glacial maximum (LGM), while concentrations of TOC-normalized n -C 24 to C 30 alkanoic acids do not change markedly in this period. Thus, the ratio of lignin phenols to n -C 24 to C 30 alkanoic acids increases from the LGM to the Holocene. This result is essentially consistent with pollen analysis indicating an expansion of woody plants in the Holocene and a prevailing herb-abundant environment for the LGM. The δ 13 C values of n -C 27 to C 33 alkanes (e.g. −29‰ to −33‰ for C 31 ) indicate the presence of C 3 -dominant plants throughout the core. The contribution of terrestrial OM to Lake Baikal sediments was estimated using the biomarkers, on the assumption that the OM in the bog sediments is a representative of the terrestrial OM around the lake. Hence, the estimation using lignin phenol or n -C 24 to C 30 alkanoic acid parameters indicates that 11–24% of the TOC in the Academician Ridge sediments is land-derived for both the Holocene and the LGM, which is similar to the estimates from C/N values of bulk OM. However, the estimates for terrestrial OM using the n -C 27 to C 33 alkane parameter are generally higher than those using lignin phenol or n -C 24 to C 30 alkanoic acid parameters. The difference is thought to be associated with the difference in source and behavior of these biomarkers.