Cosmogenic ¹⁰Be and ²⁶Al exposure dating of Nam Co lake terraces since MIS 5, southern Tibetan Plateau

Lake paleo-shorelines can be used to reconstruct lake level fluctuations, which serve as sensitive indicators of climate change. The Tibetan Plateau (TP) contains the highest areal proportion of lakes in China, and dramatic past lake level changes have led to the formation of numerous relict shorelines. Here, we present 24 ¹⁰Be and ²⁶Al exposure-ages for five of seven lake terraces situated north of Nam Co, on the southern TP. The ages of four high stands marked by terraces (T7, T6, T5, and T4) are 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, correlates with periods of enhanced Indian summer monsoon (ISM) and supports an MIS 5 maximum lake expansion on the TP, as opposed to MIS 3. Ages of two lower terraces (T5 and T4) possibly correspond to Melt Water Pulse (MWP) events. We also evaluate different possible sources of uncertainty from geologic processes on ¹⁰Be exposure ages of lake terraces. Subaerial erosion following terrace exposure has the most significant influence on ¹⁰Be exposure ages on ancient high terraces (for example > 80 ka), while inherited ¹⁰Be from prior exposure and partial shielding by shallow water, beach or talus are the most important geological source error of ¹⁰Be exposure ages for relatively low and young terraces (for example < 15 ka).