Holocene millennial lake-level fluctuations of Lake Nam Co in Tibet using OSL dating of shorelines

In the past decades, most Tibetan lakes experienced large-scale rises in response to current global warming, conflicting with the limited amplitudes and gradual fluctuation in shoreline-based lake-levels that occurred over the Holocene. The discrepancy is a critical issue in understanding the regional response to global climate. In this study, we reconstructed the Holocene lake-level variations based on high-resolution luminescence ages of thirty-seven samples from fourteen shorelines of Nam Co in interior Tibet. The findings of this work concluded that Nam Co witnessed millennial large-scale lake-level fluctuations with periodical outflows during 11.9–8.3 ka and a broad decrease thereafter. Seven highstand events with ages of ca. 11.9–11.0, 8.3, 6.7, 5.1, 4.2–3.4, 2.4 and 1.1 ka were identified, consistent with the North Atlantic warmer intervals indicating a quick response to global climatic events. In particular, the dramatic lake-level decline during the transition from the Medieval Warm Period to Little Ice Age demonstrated its potential rapid and sensitive response to millennial climatic changes. Our high-resolution OSL dates enabled detection of millennial-scale highstand events. Based on comparison with other global and regional paleoclimatic records, we suggested that Holocene highstands were mainly attributed to the strengthened monsoonal precipitation and increased glacier meltwater that amplifies lake-level fluctuations of glacier-fed lakes, and that paleoclimate and paleo-lake-level reconstruction by core proxies during lake overflow stages could be problematic.