Precession-scale climate forcing of peatland wildfires during the early middle Jurassic greenhouse period

As an important terrestrial carbon reservoir, peatland has the potential to influence the global carbon cycle and global climate. In recent decades, the frequency and extent of peatland wildfires in boreal and tropical regions are increasing owing to climate change and human activity. However, the processes that govern changes in peatland wildfire are poorly understood over long timescales, particularly on the orbital scales. We analyzed coal petrology and geochemistry in coal seams of the Aalenian Yan'an Formation in Ordos Basin to identify peatland wildfire records based on the co-occurrence of charcoal and pyrolytic polycyclic aromatic hydrocarbons (PAHs). In addition, the presence of widespread peatland wildfires has suggested that atmospheric oxygen concentration at the time should be substantially higher than the minimum needed for sustained combustion. Spectral analysis of vitrinite/inertinite (V/I) and inertinite reflectance data demonstrate that peatland wildfires were controlled by precession cycles owing to a shift in the seasonal contrast and amount of rainfall. Our results provide essential context for understanding the importance of peatland wildfires carbon emissions in a coupling of orbital forcing, climate, and the carbon cycle.