古新世-始新世暖期北半球野火演化研究

古近纪是现代气候和植被形成的关键过渡期, 而野火活动与气候、植被和碳循环等存在耦合关系。开展古新世-始新世(66~34 Ma)3个特征暖期, 即古新世-始新世极热事件(PETM, 约55.9 Ma)、早始新世气候适宜期(EECO, 53.3~49.1 Ma)、中始新世气候适宜期(MECO, 约40.5~40.1 Ma)的野火活动研究, 对于揭示气候和植被变化特征及其影响具有重要意义。本研究基于蒙古高原南部二连盆地古新世-始新世野火记录, 并结合北半球该时段其他12个地点的野火研究数据, 从长尺度地质记录视角, 重建北半球野火活动特征与演变, 并探讨其驱动机制。研究结果显示古新世-始新世不同特征暖期野火发生规模和强度存在差异, PETM极端暖期较EECO和MECO暖期野火强度更大, 但不十分显著。古新世-始新世暖期并没有持续的、大规模的野火发生, 呈现"低野火状态", 总体不支持强调燃烧活动影响全球碳循环的"野火假说"。通过野火发生与温度、降水、植被以及CO2浓度等环境因子之间的关系分析, 对"古近纪低火谜题"进行初探, 认为古新世-始新世气候的季节性并不分明, 较短的干季不利于可燃"燃料"和潜在火源的形成, 很可能是新生代早期"低野火"的主因。

A study of wildfire evolution during the Paleocene-Eocene warm period in the Northern Hemisphere

The Paleocene is a critical transition period for the formation of modern climate and vegetation, and wildfire activities are intrinsically coupled with climate, vegetation and carbon cycle. The study of wildfire evolution during three typical warm periods in the Paleocene-Eocene(66~34 Ma), including the Paleocene-Eocene Thermal Maximum(PETM, ca. 55.9 Ma), the Early Eocene Climate Optimum(EECO, 53.3~49.1 Ma), and the Middle Eocene Climate Optimum(MECO, 40.5~40.1 Ma), is of great significance to reveal climate and vegetation changes and their impacts. Based on the Paleocene-Eocene wildfire data from the Erlian Basin in the southern Mongolian Plateau, 12 other wildfire records from different sites in the Northern Hemisphere during this time period were collected. In terms of the spatial distribution of the study sites, the newly integrated dataset covers the Northern Hemisphere regions of Europe, North America, South Asia and East Asia. Our study reconstructed the characteristics and evolution of wildfire activities in the Northern Hemisphere and explored its driving mechanism from the perspective of long-scale geologic records. The results show that the scale and intensity of wildfires during the warm periods of the Paleocene-Eocene varied, and that wildfires during the extreme warm period of the PETM were more intense than those during the warm periods of the EECO and MECO, but not very significant. The Paleocene-Eocene warm period was not characterized by sustained and large-scale wildfires, and the "low wildfire state" generally does not support the "wildfire hypothesis", which emphasizes the influence of burning activities on the global carbon cycle. The "Paleocene low-wildfire puzzle" has been initially explored through the discussion of the relationship between wildfire occurrence and environmental factors such as temperature, precipitation, vegetation, and CO2 concentration. Our study suggests that the indistinct seasonality of the Paleocene-Eocene climate resulted in short dry seasons, which was not conducive to the formation of combustible "fuels" and potential ignition source, and that this is likely the main cause of the "low wildfire" in the Early Cenozoic.