Reduced early Holocene moisture availability inferred from δD values of sedimentary n-alkanes in Zigetang Co, Central Tibetan Plateau

Abstract

An 885-cm-long laminated sediment core was retrieved from Zigetang Co, a non-glacial meltwater-fed lake in the central Tibetan Plateau, and analyzed for n-alkanes as well as their hydrogen isotopes to trace the regional climatic and environmental history spanning the last 13.8 cal. ka BP. The short-chain n-alkanes C15/16/17, likely derived from aquatic algae, plankton, and photosynthetic bacteria, dominate the n-alkane composition in this lake. This unusual distribution pattern might be attributed to the meromictic lake system that is characterized by a rapid salinity increase and an abrupt decrease in dissolved oxygen in the lake water with depth, as well as anoxic conditions at the bottom. n-Alkane indicator ratios (e.g. carbon preference index (CPI), average chain length (ACL), and aquatic/terrigenous ratio (ATR)) and δD values reveal that higher effective moisture availability at Zigetang Co occurred in the middle (5.8–2.7 cal. ka BP) rather than the early Holocene. This contradicts palaeoclimate records from neighboring lakes (e.g. Nam Co, Siling Co, and Paru Co). We suggest that in the Zigetang Co catchment where glacial meltwaters are not available, the temperature-induced evaporation would outweigh the monsoonal precipitation and, therefore, result in lower effective moisture displayed by the increasing δD values during the early Holocene. The local recycling of air masses could also have an important impact on the lake level and moisture availability and cannot be excluded. Our record provides further evidence for the complex relationship of insolation-induced temperature, evaporation, and precipitation affecting the regional climate changes on the Tibetan Plateau.