Linkages between climate, fire and vegetation in southwest China during the last 18.5Â ka based on a sedimentary record of black carbon and its isotopic composition

Fires are sensitive to climate changes, and in addition they have a major influence on the global carbon cycle, land-surface properties, and chemical composition of the atmosphere, which in turn can affect the climate system. Projecting the impacts of future climate changes on fire-mediated biogeochemical processes requires understanding of how various climatic factors influence regional fire regimes. However, long-term variations in fire activity and their controls are poorly known. In this study, we report the concentration of black carbon (BC) and its isotopic composition (δ13CBC) in an upland lake sediment core from southwest China in order to elucidate linkages between changes in fire regime, climate and vegetation over the past 18.5 ka. The results show that the sedimentary BC content recorded variations in fire activity and exhibits a close negative correlation with the amount of precipitation delivered by the Indian Summer Monsoon (ISM). During Heinrich Event 1(18.5-15.0 cal ka BP), the Younger Dryas (12.8-11.1 cal ka BP) and the mid- to late-Holocene, the weakening of the ISM led to greatly increased fire activity in southwest China. In the last 1.0 ka, the BC record may have been affected by human activity in the catchment which may have caused an increased influx of minerogenic material to the lake thereby diluting the sedimentary BC concentration. The general trend of changing vegetation compositions inferred from the δ13CBC values also tracks the variations of the ISM, suggesting a change from mixed C3/C4-plant ecosystems during the last glacial maximum to C3-plant-dominated forest during the Holocene. However, the abundance of C4 plants may be overestimated during the Bølling-Allerød warm interval and the early Holocene due to the fact that fires were probably limited to the savanna ecosystem in the valleys and low-lying basins.