Dramatic water-level changes have occurred in most lakes across the Tibetan Plateau (TP), leaving behind a series of paleo-shorelines. However, the timing of maximum lake expansion on the TP remains unclear.

Early radiocarbon dating reveals that maximum lake expansion occurred during MIS 3 (ca. 29-57 ka), while recently, an increasing number of optically stimulated luminescence (OSL) ages have demonstrated that the maximum lake expansion might have occurred during MIS 5 (ca. 71-130 ka).

Other than ¹⁴C and OSL, the amounts of terrestrial in situ cosmogenic nuclides (TCN), including¹⁰Be, ²⁶Al and others, produced by the interaction of secondary cosmic rays with target elements in the upper few meters of earth-surface materials have been proven reliable in dating lake paleo-shorelines ranging from 10² to 10⁶ years with limited number of studies on the TP.

Recently, a study led by Prof. ZHOU Weijian from the Institute of Earth Environment (IEE) of the Chinese Academy of Sciences investigated Nam Co lake terraces based on cosmogenic ¹⁰Be and ²⁶Al exposure dating.

After sensitivity analysis of TCN exposure dating results from geological processes considering both inherited TCN and subaerial erosion, they revealed that the ages of four high Nam Co stands marked by terraces (T7, T6, T5, and T4) were 81.5±9.0 ka, 33.6±1.9 ka, 19.9±1.9 ka, and 15.2±0.4 ka. The topographically highest terrace, T7 supported an MIS 5 maximum lake expansion on the TP.

Comparing with surrounding lakes and paleoclimate archives, they demonstrated that there was no geological evidence to support the existence of a giant East Qiangtang Lake (EQL) that connected Nam Co, Siling Co and other big lakes during MIS 5e.

These findings not only laid a foundation for the assessment of TCN-exposure ages from lake terraces, but also revealed the lake level fluctuations of Nam Co associated with climate change and contributed to a more detailed understanding of maximum lake expansion across the TP.

This work, published in Quaternary Science Reviews, was supported by the Key Research Program of Frontier Sciences, CAS, the International Partnership Program of Chinese Academy of Sciences, and the National Natural Science Foundation of China.