Landscape and climatic conditions in the Eastern Sayan Foothills in the Holocene according to the study of the Sosnovka Mire

This study is devoted to the vegetation dynamics, hydroclimatic conditions and fires research in the northwestern macroslope foothills of the Eastern Sayan. The results of palaeoecological reconstruction obtained based on AMS dating, pollen, macrofossils, macrocharcoal and malacofaunal analyses of the Sosnovka mire deposits (right bank of the Yenisei River, southern part of the Rybinskaya Depression) covering the last ≈ 11,000 calendar years are presented. The grain size analysis of the mineral deposits underlying peat was performed and minerals of different size fractions were studied using scanning electron microscopy. The data show that about 10, 000 calendar yeas ago, a shallow water body experiencing periodic shallowing were formed in the floodplain of the Kan River. The process of mire formation began ≈9,700–8,500 cal. yr BP at the optimum of heat and moisture supply, when the dry valleys were covered with a mixed siberian pine-spruce-fir forest dominated by spruce and fir. During the Holocene Thermal Optimum (7,500–6,000 years ago) a reduction in spruce and fir in the composition of the forest stand, increased fire activity, clearing of forests, beginning of mire formation in the floodplains of rivers with catchments in the western part of the Eastern Sayan foothills occurred. The periods of decreased heat supply and increased humidity occurred at 5,500–5,200, 3,560–2,960, 2,300–2,000, 1,800–1,300 cal. yr BP. This, among other things, caused the expansion of the range of dark coniferous forests, with the most significant response in the range of 1,360–1,300 cal. yr BP. Changes in climatic conditions towards aridization and increased continentality 7,500–6,000 cal. yr BP, 3,800–3,600 and 2,000–1,800 cal. yr BP contributed to the rise of the lower boundary of dark coniferous forests and increased fire activity. The last 800 years have been characterized by strengthening of continentality, expansion of forests with Pinus sylvestris and the highest fire activity (in the last 100 years the rate of accumulation of macroscopic charcoal has been 80 particles/cm2 per year).

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