5:15 PM - 6:45 PM
[MIS01-P04] The Middle and Late Holocene environmental history, fire dynamics and climate changes in Yenisei Siberia revealed by a high-resolution peat archive
Keywords:The Middle and Late Holocene environmental history, Yenisei Siberia, fire dynamics, climate changes, high-resolution peat archive
High-latitude ecosystems are particularly vulnerable to environmental change. 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 environmental history is based on high resolution (up to decadal) palaeoecological evidence based on detailed AMS radiocarbon dating, plant macrofossils, macroscopic charcoal, testate amoebae, loss on ignition, peat humification, elemental and stable isotopic records 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 comparison of the obtained multy-proxy paleoecological evidence with pollen data from this peatland and regional paleoclimatic reconstruction provides important new data on fire, climate and peatland interrelations during the last 6500 cal yr BP.
The obtained data show that the peatland initiation occurred at about 6350 cal yr BP by paludification of a larch forest in the conditions of climate warming and high surface wetness, possibly, due to permafrost thaw. 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. The pollen record showed an expansion of middle taiga forests of Larix sibirica, Pinus sibirica, Picea obovata and Abies sibirica. Climate warming caused a northward shift of vegetation zone boundaries in Yenisei Siberia and an expansion of the range of Abies sibirica by about 200 km to the north compared to the present day. The increased frequency of fires and biomass burning during warm periods may promote the melting of the local permafrost, thereby enhancing the tree growth and regeneration.
The first sign of palsa formation occurred about 5360 cal yr BP and coincided with the temperature decrease, wetter and anoxic conditions in peatland. After several phases of uplifts (and relatively dryer conditions) and partial thawing and subsidence of its surface (wetter conditions) between 5360 and 2250 cal yr BP, the continuous rise of the perennial frost mound (up to the height of 5 m) accomplished by drying its surface and colonization by drought-resistant plant species, evidently, encouraged by the climate cooling and permafrost aggradation during the last two millennia. The high-resolution analyses of elemental (C and N) and stable isotope content (d13C and d15N) of the peat sequence revealed the strong linkages between the plant composition and mineralization/humification processes. Our multi-proxy study revealed detailed features of peat accumulation patterns driven by multiple interrelated allogenic and autogenic forcings, influencing changes in peat macroelement content and stable isotope composition.
According to the pollen data from the Igraka peatland the forest canopy was gradually reduced from 5360 cal yr BP, the middle taiga vegetation was replaced by larch woodlands with spruce, pine and some herbaceous plants that are typical for the northern taiga. The vegetation pattern of the region became close to the modern one around 2700 cal yr BP. 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 increase of the charcoal accumulation rate in the peatland under study occurred at the end of 14th – beginning 15th centuries 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 studies were funded by the State assignment for the Institute of Geography RAS FMWS-2024-0005.
The obtained data show that the peatland initiation occurred at about 6350 cal yr BP by paludification of a larch forest in the conditions of climate warming and high surface wetness, possibly, due to permafrost thaw. 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. The pollen record showed an expansion of middle taiga forests of Larix sibirica, Pinus sibirica, Picea obovata and Abies sibirica. Climate warming caused a northward shift of vegetation zone boundaries in Yenisei Siberia and an expansion of the range of Abies sibirica by about 200 km to the north compared to the present day. The increased frequency of fires and biomass burning during warm periods may promote the melting of the local permafrost, thereby enhancing the tree growth and regeneration.
The first sign of palsa formation occurred about 5360 cal yr BP and coincided with the temperature decrease, wetter and anoxic conditions in peatland. After several phases of uplifts (and relatively dryer conditions) and partial thawing and subsidence of its surface (wetter conditions) between 5360 and 2250 cal yr BP, the continuous rise of the perennial frost mound (up to the height of 5 m) accomplished by drying its surface and colonization by drought-resistant plant species, evidently, encouraged by the climate cooling and permafrost aggradation during the last two millennia. The high-resolution analyses of elemental (C and N) and stable isotope content (d13C and d15N) of the peat sequence revealed the strong linkages between the plant composition and mineralization/humification processes. Our multi-proxy study revealed detailed features of peat accumulation patterns driven by multiple interrelated allogenic and autogenic forcings, influencing changes in peat macroelement content and stable isotope composition.
According to the pollen data from the Igraka peatland the forest canopy was gradually reduced from 5360 cal yr BP, the middle taiga vegetation was replaced by larch woodlands with spruce, pine and some herbaceous plants that are typical for the northern taiga. The vegetation pattern of the region became close to the modern one around 2700 cal yr BP. 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 increase of the charcoal accumulation rate in the peatland under study occurred at the end of 14th – beginning 15th centuries 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 studies were funded by the State assignment for the Institute of Geography RAS FMWS-2024-0005.