ИСТИНА

The permafrost zone of Siberia is extremely vulnerable to environmental changes. Our paleoecological study is focused on one of the palsa mires located at the eastern edge of the West Siberian Lowlands (Yenisei Siberia) in the forest-tundra ecotone. Perennial frost mounds, often called as palsas and peat plateaus, are the dominant landscape type in this region. The reconstruction of the Holocene climate and environmental history is based on high resolution multy-proxy paleoecological evidence included pollen, plant macrofossils, stable isotope, macroscopic charcoal and loss on ignition data and detailed AMS radiocarbon dating from a 8 m long peat sequence, obtained from the palsa mire situated near the town of Igarka (N 67°31’53.77’ E 86°38’05.65’). The obtained results provide important new data on fire, vegetation, climate and peatland interrelations during the last 6500 cal yr BP. The obtained data show that peat inception in the studied mire occurred at about 6200 cal yr BP during the Holocene Thermal Maximum. The time interval between 6500 and 5360 cal yr BP was characterized by warm and dry climate conditions and the highest charcoal accumulation rate throughout the Mid and late Holocene. The fire return period was 70-120 years that is shorter then at present. Vegetation cover was formed by larch (Larix sibirica) and pine-spruce-larch (Pinus sibirica, Picea obovata) forest with admixture of fir (Abies sibirica). Nowadays the northern limit of Abies geographical range is situated about 100 km south from the study area. The main stages of palsa uplift occurred at about 5360 cal yr BP and 2250 cal yr BP and coincided with the periods of climatic cooling and moistening and permafrost aggradation in the Russian Arctic region. Since 5360 cal yr BP charcoal accumulation in the palsa decreased significantly and in some time interval ceased. The fire return period extended to 1500-1800 years. The dense forests were replaced by open larch woodlands with small proportion of birch, pine and spruce and peatlands. Radiocarbon dating and plant macrofossil analysis of the upper part of peat sequences in the mire under study indicated suppression of peat accumulation in the palsa during the last 2000 years, but it is most likely that the uppermost peat layer has been lost due to water erosion and fires. The increase of the charcoal accumulation rate in the peat profile occurred at the end of 14th – beginning 15th centuries C.E. and then charcoal input declined. We supposed that human induced fires led to the biomass burning. According to historical data the Russian colonization of this part of Siberia began in the 17th century, but the first Russian settlers already found a local hunter population in the area of Igarka. The settlement lies on the banks of the Yenisei River, historically one of the main trading routes in Siberia. During the 20th century wood-using industry and a river harbor were developed in Igarka, was obviously accompanied by active deforestation that led to some reducing the forest fire occurrence. The study was supported by the Russian Science Foundation (grant 20-17-00043).