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Molecular-isotopic stratigraphy of long-chainn-alkanes in Lake Baikal Holocene and glacial age sediments

Organic Geochemistry
Publication Date
DOI: 10.1016/s0146-6380(99)00164-3
  • Lake Baikal
  • Long-Chainn-Alkanes
  • Carbon-Isotopic Compositions
  • Lacustrine Sediments
  • Paleoclimate


Abstract The molecular distribution and the carbon-isotopic composition (δ 13C) of n-alkanes extracted from a Lake Baikal core spanning the last 20 kyr of sediment accumulation have been investigated. A terrestrial origin has been inferred for the odd carbon-numbered long-chain (>C 27) n-alkanes, on the basis of the observed high CPI 27-33 values (range: 8.7–10.8) typical of n-alkanes derived from leaf waxes of higher plants. A shift in the abundance of n-C 27 alkane relative to n-C 31 homologue is observed across the late Pleistocene glacial–Holocene interglacial climate change, perhaps indicative of the climate-induced vegetational change previously deduced from palynological analyses. Compound-specific isotope analyses indicate remarkably uniform δ 13C values in the range of −31.0 to −33.5‰ for the leaf-wax C 27–C 33 n-alkanes in the entire cored sequence. Such an isotopic compositional range is characteristic for n-alkanes biosynthesized by plants utilizing the C 3 photosynthetic pathway. Our data suggest that the observed 13C-enrichment in the bulk organic matter in the glacial age sediments, relative to δ 13C values of total organic carbon in the Holocene section, is therefore unlikely to be attributed to an expansion of C 4-type vegetation in the Baikal watershed during the late Pleistocene glacial interval.

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