Fire, permafrost, and people: Late Holocene fire regimes and their impacts on lake systems in Yakutia, Siberia

The Republic of Sakha (Yakutia), the coldest permanently inhabited region on Earth, is characterized by unique ecological relationships between larch forest, permafrost, and wildfires. Together, they can stabilize each other, preserving the larch-dominated biome. Abundant lakes have important cultural and subsistence-related functions and are dynamically connected to warming permafrost processes. Recently intensified wildfire seasons, however, raised questions regarding the causes and impacts of long-term (centennial to millennial) fire regime changes. Despite recent progress, eastern Siberia is still sparsely covered by reconstructions of long-term fire history. This also limits any evaluation of fire regime impacts on permafrost lake development and catchment erosion. Past studies have shown the benefit of combining paleoecological fire reconstructions with geochemical data to shed light on fire regime changes and their impacts on lake catchments, as well as traces of potential human land use. We present nine new records of Late Holocene wildfire activity, based on macroscopic charcoal in lake sediments (including information on charcoal particle sizes, morphologies, and length to width ratios), accompanied by sediment geochemistry data from high-resolution XRF core scanning. The studied lakes are located in the Lena-Amga interfluve of the Central Yakutian Lowlands, the Verkhoyansk Mountains, and the Oymyakon Highlands. The new data cover both thermokarst and glacial lakes, and a range from remote to rural settings and low to high elevations. Charcoal concentration in the lowland lakes is on average three times as high as in the highland lakes. Contrary to our hypothesis, charcoal concentration in most lakes is negatively correlated to many XRF-derived lithogenic elements indicating detrital input from catchment erosion (e.g., Ti, K). Reminiscent of earlier findings [1], multiple lowland sites share a signal of sharply decreasing biomass burning around 1300 CE. This coincides with the initial settlement of the Sakha people and increased catchment erosion. The new fire reconstructions allow for the evaluation of potential human impacts on past fire regime changes in Yakutia, while improving the region’s representation in global synthesis studies. [1]  Glückler R. et al. (2021): Wildfire history of the boreal forest of south-western Yakutia (Siberia) over the last two millennia documented by a lake-sediment charcoal record. Biogeosciences 18 (13): 4185–4209. https://doi.org/10.5194/bg-18-4185-2021.