Peatland development reconstruction and complex biological responses to permafrost thawing in Western Siberia

Abstract. Western Siberian peatlands are among the largest peatland complexes in the world and play a crucial role in regulating the global climate. However, a lack of long-term, multi-proxy studies comprehensively examining the interactions between permafrost thaw and peatland ecosystems in Western Siberia hinders the ability to predict their response to future climate change. This research covers two centuries of the Khanymei peatlands history, situated within the discontinuous permafrost zone. In this study, a multi-proxy analysis (testate amoebae, plant macrofossil, pollen, micro- and macrocharcoal, loss on ignition) was conducted on two peat cores – one from a peat plateau and another from the edge of a thermokarst lake. We inferred peatland drying from the end of the Little Ice Age. The elevated peat plateau facilitated the aggradation of permafrost, which began to thaw in recent decades due to rising air temperatures, increasing peat moisture. The lake edge was the most dynamic part of the peatland, where more notable changes in hydrology, vegetation, and microbial composition occurred. Thawing led to significant Sphagnum growth and a shift in the testate amoebae community structure. We reconstructed the effects of permafrost thawing that resulted in a substantial but short-term and local increase in peat and carbon accumulation and an increased abundance of fungal communities. Our study reveals that thaw-induced terrain subsidence was subtle and spatially variable, yet these localized surface changes triggered complex hydrological, vegetational, and microbial responses, highlighting the nonlinear and multifaceted nature of permafrost degradation. The advantage of our research lies in the utilization of multi-proxy high-resolution palaeoecological techniques, enabling us to monitor even relatively minor permafrost transformations and identify early warning signals of climate-induced impacts on this invaluable ecosystem. We anticipate that further warming will contribute to the occurrence of these processes on a larger scale in Western Siberian peatlands, potentially significantly impacting ecosystem conditions and the global climate.