Holocene lake level variations of Dagze Co in central Tibetan Plateau revealed by OSL dates on palaeoshorelines

Abstract

Lakes in the Tibetan Plateau (TP) provide indications of the past global climate change over this vast elevated highland. However, the patterns of Holocene lake-level variations in the central TP and their relevance to climate change are still unclear, especially for the middle and late Holocene. Located in the central TP, Dagze Co presents a number of distinct palaeoshorelines, thus making it ideal for investigating these patterns. In this study, we first identified these shorelines using remote sensing images, and then dated these shorelines using optically stimulated luminescence (OSL) dating. The results showed that high-resolution remote sensing images can successfully identify palaeoshorelines, alluvial fans, and remnant river channels surrounding the lake, which enhances our understanding of regional geomorphic processes. The OSL dating results showed that Dagze Co flowed westward to Cuowa Lake during a lake expansion stage in the early Holocene. The highest palaeoshoreline (40.6 m above the present lake level) formed between 6.1 and 5.5 ka, and the lake area was 2.8 times larger than present. The lake level declined between 5.5 and 3.4 ka in response to the weakened Indian summer monsoon (ISM) with substantially reduced summer rainfall. The lake level rose again and was sustained between 3.4 and 2.2 ka owing to slightly increased rainfall and increased water supply from glacial melt water. The lake level rapidly declined since 2.2 ka in response to decreased ISM rainfall and reduced meltwater supply. The lake level variations of Dagze Co was in a long-term decline pattern since the mid Holocene, similar to several other lakes in the TP influenced by the Asian Summer Monsoon (ASM).