image: (a) δ13CTOC record. (b) δ13CBC record. (c) BC/TOC ratio. (d) Carbonate content. (e) Dolomite/carbonate ratio. (f) Molar Sr/Ca ratios of authigenic carbonates. (g) Molar Mg/Ca ratios of authigenic carbonates. (h) Kaolinite/smectite ratio. (i) Temperature estimates from branched glycerol dialkyl glycerol tetraethers. The gray shadow represents the PETM event.
Credit: ©Science China Press
This study is led by Wang Xueting, Dr. Wang Xu, and Dr. Chen Zuoling from the State Key Laboratory of Lithospheric and Environmental Coevolution, Institute of Geology and Geophysics, Chinese Academy of Sciences. The researchers analyzed black carbon concentration and carbon isotope (δ13C) in sediments from the Beigou section of the Nanyang Basin and the Xilutian section of the Fushun Basin to reconstruct the regional wildfires. To further explore the spatiotemporal evolution and driving mechanisms of wildfires, the researchers integrated paleofire studies from different regions of the Northern Hemisphere during the PETM. The study revealed a " low wildfire activity " in most regions of the Northern Hemisphere during the PETM period.
Specifically, the variation in the BC/TOC (black carbon/ total organic carbon) ratio indicates the frequency and intensity of wildfire activity in both the Nanyang Basin (arid/semi-arid zone) and the Fushun Basin (humid zone) during the PETM. The result shows a sharp decrease in wildfire activity at the onset of the carbon isotope excursion (CIE), which remained low throughout the CIE, except for a brief increase in the Nanyang Basin during the mid-CIE. Subsequently, the wildfire activity gradually intensified during the CIE recovery phase, ultimately returning to pre-PETM levels (Figure 1c and Figure 2c). During the PETM, the global climate was extremely warm and wet. The pollen assemblages in most areas of the Northern Hemisphere indicate a succession of vegetation types during this period, with an increase in angiosperms and wetland plants and a decrease in gymnosperms and ferns. Therefore, they suggest that the low diversity of fire-prone vegetation in most regions of the Northern Hemisphere during the PETM was likely caused by changes in climate and vegetation. During the PETM, excessive rainfall would have increased the moisture content of combustible materials, thereby suppressing the occurrence of wildfires. The warm and humid climate would have promoted vegetation growth and the succession of vegetation types, inhibiting the spatial continuity of combustible materials, and ultimately reducing the occurrence and spread of wildfires. Furthermore, the climate during the PETM was marked by indistinct seasonality, with no obvious dry season, or at the most, a shorter one, conditions unfavorable for the occurrence of wildfires.
Additionally, the results reveal that a significant decrease in BC concentration at the onset of the CIE, indicating reduced burial of inert carbon, with more carbon being stored in the biological-atmospheric surface system. During the CIE recovery phase, the BC concentration increased, indicating an increase in the burial of inert carbon and a shift in carbon from the short-term biological-atmospheric carbon cycle to the long-term geological carbon cycle. This carbon sink transformation process may have contributed to light carbon consumption during the PETM recovery phase, acting as a negative feedback mechanism and impacting regional carbon reservoirs and the global carbon cycle.
See the article:
Wang X T, Chen Z, Cui L, Wang X. 2025. Spatiotemporal evolution of wildfire activity during the Paleocene-Eocene Thermal Maximum in China. Science China Earth Sciences, 68(2): 509–522, https://doi.org/10.1007/s11430-024-1472-5
Journal
Science China Earth Sciences