Lipid and lignin/cutin compounds in Lake Baikal sediments over the last 37 kyr: implications for glacial–interglacial palaeoenvironmental change

A stratigraphic study of total organic carbon (TOC) concentration, carbon isotopic composition of total organic matter (TOM), lipids (n-alkanes, n-alkanols, n-alkanoic acids and sterols) and lignin/cutin compounds has been conducted for a Lake Baikal core (323-PC1) over the last glacial/interglacial. TOC concentrations (mg g−1 dry sediment) are low (2–4) in the glacial sections, but high (10–29) in the interglacial ones. The concentrations of land plant-derived compounds such as n-C14 to C28 ω-hydroxyalkanoic acids, lignin phenols (p-hydroxyl, vanillyl and syringyl), total cutin acids, normalized to TOC in the interglacial, are 5–6 times higher than those in the glacial. Carbon isotopic compositions of TOM are −24 ± 0.9‰ in the glacial, while they are −27 ± 1.3‰ in the interglacial. The heavy isotope composition of TOM in the glacial might be due to a contribution from submerged plants and/or grasses. The light isotopic composition of TOM for the interglacial may be due to a contribution from both land plant- and phytoplankton (mainly diatom)-derived OM. Autochthonous organic carbon contents were estimated from the C/N ratio corrected for the effect of inorganic nitrogen and based on the assumption of C/N values of 8 for autochthonous and 25 for allochthonous OM. The estimation indicates that autochthonous OC comprises 74 ± 6% of TOC for the glacial and 72 ± 9% for the interglacial, respectively. Primary palaeoproductivity was estimated to be below 20 gC m−2 y−1 in the glacial (before 18 ka), but high (100–120 gC m−2 y−1) in the interglacial (11–8 ka), which is 10–30% higher than the modern values.