Abstract
A 794-cm section and core from Tengger Nuur (42°27´N, 110°42´E) in the Inner Mongolia Plateau had been collected. 8 effective AMS 14C data had been determined to set an age-depth model after minus about 1920 years carbon reservoir effective. Based on the multi-proxies grain size, carbonate-content, TOC-content, ratios of Mg/Ca and Sr/Ca, and carbonate carbon and oxygen isotope, palaeoenvironmental change had been reconstructed since the last deglacial. Tengger Nuur was very shallow during the last deglacial under cool and wet climate, especially much shallower at interval cold YD event. Although, temperature and humidity increased from the early Holocene ~10500 to 8750 cal a BP, low lake-level indicated that summer monsoon did not strengthen the modern monsoon boundary in Inner Mongolia. High monsoon precipitation made lake to expand during 8750~5000 cal a BP, but lake-level oscillated in a shallow state under higher evaporation. A low lake-level event interrupted with the cold-wet climate at interval 5450~5100 cal a BP. Summer monsoon receded gradually to keep a deep lake under high effective humidity during 5000~2000 cal a BP, and low lake-level events punctuated at intervals 4300~3980 cal a BP and 3700~2750 cal a BP. Lakes shrank gradually to be salinization or completely desiccation in the cold and dry westerly after 2000 cal a BP, but oscillated much lower lake-levels at four periods of 1900~1740 cal a BP, 1500~1050 cal a BP, 550~400 cal a BP (Little Ice Age), 100 cal a BP ~AD 1985. A weak eastern summer monsoon was in the early Holocene, and lake-level oscillation was controlled by the effective humidity in the arid and semi-arid area.
Highlights
The region of mid and eastern Mongolia, which lies at the boundary of the modern summer monsoon, is controlled by the winter, summer monsoon, and westerlies
The fragile ecological system at the monsoon boundary is sensitive to the monsoon, and a large number of lake-filling events triggered by the summer monsoon precipitation record the paleoenvironmental change
In the past several decades, several lakes at the modern eastern monsoon boundary of Inner Mongolia, i.e., Daihai Lake (Li et al, 1992; Xiao et al, 2004; Zheng et al, 2010; Zeng et al, 2013), Wulagai Lake (Yu et al, 2014), Baahar Nuur Lake (Guo et al, 2007), Dali Nor Lake (Wang et al, 2004), Haolaihure Paleolake (Liu et al, 2018), Diaojiao Lake (Song et al, 1996; Yang et al, 1997; Yang, 1998), Huangqihai (Li et al, 1992), Hulun Lake (Yang and Wang, 1996; Zhang and Wang, 2000; Wen et al, 2010), Dabusu Lake (Jie et al, 2001), and Angulinao (Zhai et al, 2000), had been used to reconstruct paleoenvironmental changes based on pollen and geochemical proxies
Summary
The region of mid and eastern Mongolia, which lies at the boundary of the modern summer monsoon, is controlled by the winter, summer monsoon, and westerlies. About >757 cm (∼10,920 cal a BP), fine-grained sediment layer, low Mg/Ca and Sr/Ca ratios indicate a shallow lake with freshwater formed under a cool climate and much higher water supply than evaporation and rudimentary vegetation.
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