Wildfire response to rapid climate change during the Permian-Triassic biotic crisis

Abstract

Char and polycyclic aromatic hydrocarbons (PAHs), which can serve as proxies for wildfire frequency and/or intensity, are widely present in Permian-Triassic boundary (PTB) strata, providing information on volcanism or on climatic control of fuel availability (linked to vegetation type and density) or combustibility (linked to aridity). Here, we present evidence to separate temporal from geographic signals of climate impact on wildfire during the Permian-Triassic (P-Tr) transition. Geographically, char and pyrolytic PAHs for wildfire are concentrated in temperate and tropical regions and show a connection with forest distribution as reflected by occurrences of Upper Permian coals. Temporally, the subtropical terrestrial Dalongkou section of northwestern China provides evidence of two intervals of increased pyrolytic PAHs of combustion origin. The first interval was linked to climatic hyperwarming during the latest Permian, whereas the second interval was associated with rapid climatic drying, as recorded by spore-to-pollen ratios (S/P), during the P-Tr transition. This record suggests that rapid climate change during the P-Tr transition increased wildfire frequency. A climate link is also shown by turnovers of ostracods, conchostracans, and charophytes in conjunction with greater wildfire frequency. The trigger for enhanced wildfires and biotic changes is inferred to have been volcanically induced climatic warming and aridification. Our data thus document important links between wildfires, climate change, volcanism, and mass extinction during the P-Tr transition.