Millennial-aged pyrogenic carbon in high-latitude mineral soils

Wildfires in the Arctic are producing pyrogenic carbon as product of incomplete biomass combustion. The storage and distribution of pyrogenic carbon in soils is poorly known, especially in carbon rich permafrost-affected mineral soils. Here, we extracted pyrogenic carbon in mineral soils from eleven forest sites across the North Canadian permafrost regions by hydrogen pyrolysis. We found pyrogenic carbon with millennial-scale ages that were older in continuous (1960-12,690 calibrated years before present) than in discontinuous (510-3560 calibrated years before present) permafrost-affected soils. In all cases, pyrogenic carbon showed longer residence times compared to bulk soil organic carbon. The proportions of pyrogenic carbon on total soil organic carbon were consistent at 6.9 +/- 0.5% of total soil organic carbon. Thus, pyrogenic carbon forms a significant component of the total soil organic carbon and climatic as well as soil factors control the long residence times of pyrogenic carbon in vulnerable high-latitude forest mineral soils. Pyrogenic carbon in mineral soils has longer residence times than bulk soil organic carbon and constitutes 6.9 +/- 0.5% of the total soil organic carbon pool, according to analysis of mineral soils from forest sites across eleven North Canadian permafrost regions.