Vegetation And Climate History Inferred From An Alpine Lake In The Central Tienshan Mountains Since8.5Ka BP

In this paper, we carried out modern surface pollen analysis in the central Tienshan Mountains and obtained core BY10A from Lake Meitiane in the Yourdusi Basin, based on which we analyzed and explained the fossil pollen record. By establishing a reliable age model, we preliminary reconstructed past vegetation and climate history since8.5ka BP in the study area. At8.5-6.6ka, the local vegetation indicated by pollen assemblages was subalpine steppe, suggesting a relatively warm climate. Under this condition, treeline of spruce forest and desert/desert steppe expanded upwards, with ice-snow meltwater increasingly fed the lake, resulting in the rise of the lake level. At6.6ka, the spruce forest area maximized. After that, the treeline descended, reflecting a cooling trend. At6.6-5.5ka and4.5-2.6ka, alpine meadow dominated the local landscape, desert/desert steppe stayed at a low elevation, indicating a generally cool climate, which restricted the amount of meltwater, making the lake evolved into peatland. At5.5-4.5ka, subalpine steppe appreared locally and desert/desert steppe slightly move upwards, showing a relatively warm interval. During this period, with the supply of meltwater, the lake level to some extend rised, promoting the growth of aquatic Myriophyllum and Pediastrum. Since2.6ka, previous alpine meadow surrounding Lake Meitiane was replaced by subalpine steppe, desert/desert steppe expanded upwards, demonstrating a warming trend. With the meltwater increasingly fed the lake, the sedimental lithology gradually changed from peat to lacustrine. After1.7ka, the vegetation zone indistinctively declined, the climate and the lake level relatively remained stable.By making a comparison of our result with the record from Lake Bosten and Guliya ice core, it showed that ice-snow meltwater triggered by temperature changes had an important influence on alpine lake archive. The response of alpine lake to climate changes was characterized by relatively high sensitivity and directness. The low-lying lake, however, was affected by multi-factors, and evaporation may played an important role as records of these lakes tended to reflect the regional relative humidity.