Climatic and environmental implications from n-alkanes in glacially eroded lake sediments in Tibetan Plateau: An example from Ximen Co

Gas chromatography-mass spectrometry was used to identify a series of n-alkanes in the sediments of a typical glacially eroded lake in the eastern Tibetan Plateau. By comparing the distribution patterns of n-alkanes in lake sediments, surface soils and cow manure, it was shown that n-C-27-n-C-33 alkanes in the soil ecosystem of Ximen Co are derived from vascular plant species and that the distribution pattern of n-C-27-n-C-33 alkanes remains unchanged during the feeding and digestion processes of herbivores. The relative percentage of C-27, C-29 and C-31 n-alkanes decreased from the bottom to the top of the sediment core showing a trend of degradation of higher plants in the Ximen Co lake region during the formation of the 44 cm core. Pb-210 dating, combined with pre-existing AMS C-14 dating results showed that the depositional core reflects climatic and environmental variations since about 900 years before present. The n-alkane indexes (ACL(27-33), P (aq), P (wax)) are comparable with regional temperature variation, especially recording the Little Ice Age event (LIA). This study highlights that n-alkanes are valid proxies for paleo-climate and paleo-environment reconstruction, despite the same distribution patterns in n-alkane molecular fossils derived from a typical glacially eroded lake.