Dynamics of permafrost thaw in Western Siberia - a 200 years multi-proxy and high-resolution reconstruction from Khanymei peatlands

Abstract

Western Siberian peatlands are one of the biggest peatland complexes in the world. Despite playing an essential role in regulating global climate, these ecosystems still remain understudied. A lack of long-term multi-proxy studies comprehensively examining the dynamics between permafrost thaw and peatland ecosystems in Siberia makes it difficult to determine how these areas will be affected by future climate change. Our research covers the history of the Khanymei peatlands (63°43’N, 75°57’E), located in the discontinuous permafrost zone in the last 200 years (from the end of the Little Ice Age to modern times). In this study, we applied multi-proxy analysis (testate amoebae, plant macrofossil, pollen, micro and macro charcoal, LOI and XRF) on two cores from a transect between a peat mound and a thermokarst lake. A newly developed by Halaś et al. (2023) testate amoebae calibration data set based on samples from the Khanymei peatlands complex was used to reconstruct past changes in peatland hydrology. In the last 200 years, we observed constant drying of studied peatlands with events of wetting caused by thawing permafrost. Reconstructed changes in peatland vegetation indicate that lichens (genus Cladonia) dominate during stable permafrost phases. We discovered that peatland drying in recent decades caused the expansion of shrubs onto Khanymei peatlands, which is also widely observed in other parts of Arctic tundra. The increase in peatland moisture after thawing is noted only in the initial period and in a limited area. Thawing led to high Sphagnum growth and change in the structure of testate amoebae communities, with an increase of mixotrophic species like Placocista spinosa. Species with organic and idiosomic tests started to dominate in the community replacing species with agglutinated shells. We discovered that permafrost thawing resulted in a short-term increase of peat accumulation and carbon sequestration, increased abundance of fungal communities, and promotion of oxic conditions. Initially, positive effects of thawing (like carbon accumulation) quickly weakened as favorable moisture conditions disappeared. As permafrost continues to thaw, these processes will occur on an increasingly larger scale. According to climate change predictions, this region in Western Siberia may become unsuitable for the functioning of permafrost peatlands in their current form.