Climatic control of orbital time-scale wildfire occurrences since the late MIS 3 at Qinghai Lake, monsoon marginal zone

摘要

Wildfires play an important role in earth climate systems, with influences on the atmosphere, vegetation distributions, and human survival. Considerable debate persists with regard to the relationship between wildfire occurrence and climate. Some records indicate relatively fewer wildfires during glacial times as compared to the Holocene, while others support the opposite view. These contradictory views need to be resolved to fully understand the relationship and controlling mechanisms that relate biomass burning to climate. In this study, black carbon (BC), including both char and soot, is used to reconstruct wildfire history over the past 32 ka from Qinghai Lake. BC, especially as micrometer-size soot, is mainly transported via the atmosphere, and can carry evidence of wildfires over long distances. Qinghai Lake's position on the northeastern edge of the Tibet Plateau is especially well-suited to such long-distance transport, with a potentially global climatic impact. We observed a significantly positive relationship between char and soot fluxes that suggest that the Qinghai Lake BC record is dominated by material transported through the atmosphere in large-scale wildfires. We find that relatively more wildfires occurred during cold-dry late glacial time (32.8-11.7 ka), and fewer wildfires during the warm-humid Holocene. Our study demonstrates that drought is the key factor that determines wildfire occurrences on an orbital time-scale. These fundamental and persistent patterns can assist in our understanding of climate-wildfire interactions and in the assessment of feedbacks on the global climate system, for example, through the well-known relationship between soluble iron and atmospheric CO2.