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Abstract

Annually laminated sediments of Lake Sihailongwan (SHL) in northeast China preserve a high resolution record of past climatic and environmental changes. Thin sections of varved early Holocene sediments were analyzed using light optical and scanning electron microscopic methods. Sediment micro-facies and geochemical analyses reveal two different seasonal clastic layer types: spring snow melt and dust layers. Dust layers distinctly differ from snow melt layers through their finer grain size, better sorting, higher Al and lower Mg and Ca contents. In contrast to recent Lake SHL sediments, during the early Holocene silt-sized dust has been deposited after spring snow melt and after pronounced spring diatom blooms. For the time interval between 11,580 and 7060 varve years BP dust layers were quantified at annual resolution. Highest intensities and frequencies of dust accumulation are observed in the period from 11,100 to 8200 varve years BP, in good agreement with dry conditions in this time interval documented by palaeoclimatic records derived from lake sediments and loess in central Asia and northern China. Based on modern meteorological observation of dust storms in China, the dust accumulation record mirrors mainly the variation in climatic conditions governing generation of cyclone and cold air surges in the arid and semi-arid mid-latitude regions of China and Mongolia. On multidecadal and centennial time scales, solar activity might have been an additional forcing factor for dust accumulation frequency in the early Holocene. Spectral analyses reveal 205-years and 88-years periodicities in variations of dust accumulation frequency that likely reflect the de Vries (Suess) and the Gleissberg solar cycles.