Wildfire, ecosystem, and climate interactions in the Early Triassic.

Wildfires are a key component of Earth system dynamics with respect to carbon cycling. Thus, reconstructing past wildfire dynamics is crucial for understanding potential future climate change as related to (paleo)environmental feedbacks. Here, we explore wildfire during the Early Triassic (Smithian and Spathian, ca. 250 million years ago) - a time interval characterized by scarce fire evidence, perturbation of the carbon cycle, climatic oscillations, vegetation succession and biotic radiation-extinction pulses - using polyaromatic hydrocarbons, which are an organic (geo)chemical fire indicator in sediments. Hydrocarbon abundances in shales from Spitsbergen show a prominent increase after the Smithian-Spathian boundary. Diagnostic ratios of hydrocarbons suggest that these compounds were derived from relatively unaltered biomass as opposed to soil erosion and petrogenic carbon inputs or coal combustion vis-à-vis a coincidental Siberian Trap volcanism. Our data indicates that as temperatures decline during the late Smithian, coeval hydrological conditions become less intense and changing vegetation successions become more amenable to wildfire activity. We hypothesize that changing regional wildfire regimes influenced biogeochemical cycles, potentially affecting long-term carbon sequestration. The observed coupled behavior in water-vegetation-wildfire systems amid key perturbations in Earth's history provides new insights into imminent future climate change consequences.