The Holocene salinity history of Bosten Lake (Xinjiang, China) inferred from ostracod species assemblages and shell chemistry: Possible palaeoclimatic implications

A sediment core from Bosten Lake, the largest freshwater lake in the Tianshan Mountains and in the northwesternmost province of China provided a high-resolution record of environmental change covering the last ∼8500 cal a BP. Higher salinity levels of Bosten Lake were reconstructed from assemblages, the stable isotope composition and Sr/Ca and Mg/Ca ratios of ostracod shells between ∼7800 and 5600 cal a BP. A period of low and moderate salinities between ∼5600 and 4900 cal a BP was followed by the re-establishment of higher salinities between ∼4900 and 4300 cal a BP. Since then, Bosten Lake has recorded fluctuating conditions with a number of multi-centennial phases of low and moderate salinities. Although the salinity-lake level relationship of Bosten Lake is not fully understood, a higher salinity at the core site seems to correspond to periods of higher lake levels. This contradictory interpretation is explained tentatively by the changing distance of the core site to the freshwater-providing river mouth with changing lake levels and potentially resulting lateral shifts of the salinity-distribution pattern within the lake. Assuming this explanation is correct, the record from Bosten Lake reflects higher moisture availability and a strong climatic influence of the Indian Monsoon in the early mid-Holocene until about 4000 cal a BP, and more unstable drier conditions susceptible to minor changes in the regional circulation patterns and temperature variations afterwards.