Biogeochemical evidence for freshwater periods during the Last Glacial Maximum recorded in lake sediments from Nam Co, south-central Tibetan Plateau

Abstract

Improved knowledge of deglaciation processes during the termination of the Last Glacial Maximum on the Tibetan Plateau can provide important information for understanding deglaciations in climate-sensitive high-altitude ecosystems. Little, however, is known about this time interval because most lacustrine sediment records from the Tibetan Plateau are younger than 19,000 years. This study focused on a lake sediment record from Nam Co, south-central Tibetan Plateau, covering the interval from *23.7 to 20.9 cal ka BP. We analysed the distribution and compound-specific hydrogen isotope composition (dD) of sedimentary n-alkanes, as well as the bulk sediment TOC, TN, d13 C org and d 15 N composition, to infer lake system development. Pronounced changes in environmental conditions between *21.6 and 21.1 cal ka BP, as well as between 23.1 and 22.5 cal ka BP (Greenland Interstadial 2), were inferred from increased aquatic nalkane amounts and decreased dD n-C23 values within these time intervals, respectively. Freshwater inputs, which most likely resulted from enhanced glacier melting, caused these changes. Our results suggest that mountain glacier retreat on the Tibetan Plateau started earlier than previously assumed. The required energy for thawing was probably provided by temperature changes caused by reorganization of atmospheric circulation, which has also been recorded in Greenland ice records.

Climatic and associated cryospheric, biospheric, and hydrological changes on the Tibetan Plateau: a review

“…The TP boasts the greatest concentration of high‐altitude inland lakes in the world. With a total area of 41 800 km 2 , it has been estimated that more than 1000 lakes distributed on TP are larger than 1 km 2 (Ma et al ., ; Witt et al ., ). Glacier melt has greatly supported the development of many inland TP lakes because these are fed by glaciers located in their catchments (Yao et al ., ; Zhu et al ., ; Günther et al ., ).…”