Distribution of n‐alkan‐2‐ones in Qionghai Lake sediments, southwest China, and its potential for late Quaternary paleoclimate reconstruction

Studies on long‐chain n‐alkan‐2‐ones from lake sediments remain sparse. In this study, we present an n‐alkan‐2‐one record from Qionghai Lake, southwest China, to assess the paleoclimate significance of variations in their compositions. A homologous series of n‐alkan‐2‐ones ranging from C21 to C35 were identified, with maximum concentrations of the C29 or C31 chain lengths and a strong odd‐over‐even predominance. This type of n‐alkan‐2‐one is considered to derive mainly from microbial oxidation of the corresponding n‐alkanes, and partial inputs from plants. The n‐alkan‐2‐one‐derived average chain length (ACL) and carbon preference index (CPI) values changed significantly over the past 28k cal a bp, consistent with the sediment grain size and n‐alkane proxies from the same core. Generally, the high CPI27‐33‐ket and low ACL27‐33‐ket values indicated cold and dry climates such as for the Last Glacial Maximum (23.2–19.7k cal a bp), Heinrich 1 event (17.6–15.6k cal a bp) and Younger Dryas (12.8–11.6k cal a bp), but low CPI27‐33‐ket and high ACL27‐33‐ket values denoted a warm and humid Holocene Climatic Optimum (7.0–4.3k cal a bp). Therefore, n‐alkan‐2‐ones have great paleoclimatic potential and can be applied together with other biomarkers to reconstruct a reliable paleoclimate record in lake sediments.