New evidence suggests wildfires devastated terrestrial ecosystems during the end-Permian mass extinction

The end-Permian mass extinction (EPME) that occurred approximately 252 million years ago was a catastrophic event, resulting in the devastating loss of approximately 81% of marine species and 89% of terrestrial species.

New research conducted by a collaboration between the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences (NIGAPS), Nanjing University, and Yunnan University has provided valuable insights into the collapse of terrestrial ecosystems and changes in vegetation during the Permian-Triassic (P-T) transition period. This joint research group confirmed the occurrence of large-scale, high-temperature wildfire events through precise analysis of biomarker compounds known as polycyclic aromatic hydrocarbons (PAHs). Their findings were published in Earth and Planetary Science Letters.

The EPME was triggered by intense volcanic activity in the Siberian Traps large igneous province and the formation of a large continental arc. These volcanic activities led to the release of massive amounts of greenhouse gases and poisonous gases, causing global warming, aridification, and frequent wildfires. PAHs, which are indicative of incomplete combustion of organic matter at high temperatures, serve as useful markers for investigating wildfire activity in geological history.

While previous studies have mainly focused on marine records during the P-T transition, research on terrestrial records has been relatively limited. This study specifically examined the high-resolution PAH content in a non-marine P-T transitional sequence obtained from the HK-1 drill core in the Lengqinggou section of Southwest China. The analysis revealed a consistent and significant enrichment of PAHs during the P-T transitional period. This enrichment was coupled with negative organic carbon isotope anomalies, indicating the occurrence of large-scale, high-temperature wildfire events under hot and arid paleoclimate conditions during this period.

Furthermore, the presence of low-molecular-weight compounds, such as Dibenzofuran (DBF), suggested the biodegradation of terrestrial plant polysaccharides and lignin. In the HK-1 drill core, the unusually high concentration of DBF compounds, along with their co-variation with combustion-derived PAHs, indicated that the PAHs primarily originated from high-temperature wildfires involving terrestrial plants. The tropical rainforest vegetation systems during the P-T transition provided ample fuel for these large-scale wildfires.

The Lower Triassic period exhibited low PAH contents, indicating a scarcity of fuel following mass deforestation. Moreover, the significant changes in PAH ratios indicated a profound impact on the terrestrial ecosystem after the EPME.

Based on these PAH records, it can be inferred that the vegetation type transitioned from a dense and diverse gigantopterid-dominated tropical rainforest ecosystem to an isoetalean-dominated herbaceous heathland-like ecosystem.

Source: Chinese Academy of Sciences

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