An examination of the molecular distribution of a tropical lake sediment sequence to assess organic carbon records of climate and environmental changes

Abstract

The bulk organic carbon isotope (δ13C), as the conventional indicator of the C3 and C4 vegetation change, turns relatively contentious in the application of palaeoclimate reconstruction from the lacustrine sediments due to the similar δ13C value between C3 and aquatic plants, particularly in the eutrophic lakes. A long successive lacustrine sequence from Tianyang Maar Lake, locating in the tropical region of South China, has complex organic matter (OM) sources due to relatively high inputs from the aquatic macrophytes and diatoms. We examined the n-alkanes concentration of 80 selected samples from the Tianyangcore, as an additional index to assess the paleovegetation and lake-level changes. The n-alkanes results show some distributional patterns of compounds with carbon numbers ranging from C15 to C39. These patterns indicate differences in OM sources and relative contributions from higher and lower plants, improving the interpretation of δ13C records of changes in climate and depositional conditions. Meanwhile, more details of the aquatic macrophyte and diatom inputs revealed by the n-alkanes based proxies (TAR, Paq) replenish the evidence of the lake-level changes during the evolution history of Tianyang Lake.