Carbon concentration and isotope composition of black carbon in the topsoil of the central and southeastern Qinghai-Tibetan Plateau, and their environmental significance

The carbon concentration and carbon isotope of black carbon (BC) have been widely used to reconstruct fire history and vegetation change. In order to establish the relationship between BC, contemporary vegetation and climate at the high altitudes of the Qinghai-Tibetan Plateau (QTP), we investigated the carbon concentration and carbon isotope composition of BC and soil organic carbon (SOC) (%BC, %SOC, delta C-13(BC) and delta C-13(SOC)) in 29 topsoil samples from the central and southeastern QTP. In general, the %SOC and %BC of topsoil show generally similar variations, indicating a common controlling factor for SOC and BC production, i.e., vegetation. The relatively small BC/SOC ratios fall in the range of BC/OC for pyrogenic particles from biomass burning, indicating a minor contribution of BC from fossil fuel combustion. The delta C-13(SOC) of topsoil can effectively indicate local vegetation in the QTP. The delta C-13(BC) and delta C-13(SOC) are positively correlated, whereas the delta C-13(BC) values are more negative than those of delta C-13(SOC). This could due to fire season and fractionation processes during post-deposition, but not carbon isotope fractionation during combustion or exogenous BC input. Therefore, BC in topsoil of the QTP mainly records 'local' environmental information, and the delta C-13(BC) can be used in paleovegetation reconstruction in combination with the local climate.