Evidence for elevated wildfire activity during Cretaceous OAE 2 from eastern Tethys

Abstract

Intensified frequency and scale of wildfires due to global warming has been increasingly recorded in recent years. Studies of wildfire activity during deep time greenhouse climate states are crucial for evaluating their likely impacts on the global environment and ecosystems in the future. Oceanic anoxic event 2 (OAE 2, ∼94 Ma), which was characterized by extremely high global temperature and a reduced equator-pole temperature gradient, could provide insights into our understanding of present-day global change processes. Here we provide data on polycyclic aromatic hydrocarbon (PAH) abundance from the Qiangdong section in the Tethyan Himalaya of southern Tibet to investigate wildfire behavior and its impact on the environment during OAE 2. Our results indicate a significant increase in the frequency of wildfires during the early part of OAE 2, followed by a rapid weakening. The change of PAH composition through OAE 2 in Qiangdong shares a similar trend to that previously found in the Western Interior Seaway (North America), indicating potentially globally elevated wildfire frequency during the early part of OAE 2. We also document a rapid increase in chemical index of alteration values in Qiangdong. These data, coupled with other proxies for weathering intensity through OAE 2, suggest that increased weathering during OAE 2 can be attributed at least in part to the effects of vegetation loss caused by wildfire. As such, we suggest that frequent wildfires during OAE 2 promoted the flux of nutrients to the oceans, thereby stimulating productivity that, in turn, increased the area of oceanic anoxia and organic carbon burial.