Black carbon records in Chinese Loess Plateau over the last two glacial cycles and implications for paleofires

To study the temporal and spatial changes in paleofires over the Chinese Loess Plateau, black carbon concentrations were analyzed on the loess-paleosol samples from three sections along a north-south transect. Using the orbitally tuned time scales of the sections, the black carbon mass sedimentation rates (BCMSR) were calculated. Results show that in the last two glacial cycles, the BCMSR values in glacial periods are 2-3 times higher than in interglacial periods, and the BCMSR variability has a relatively strong precession-associated 23 ky period, suggesting that the glacial cold-dry climate conditions were apt to induce natural fires over the Loess Plateau. Comparison of the BCMSR records among the three loess sections demonstrates that natural fire occurrence was much more intensive and frequent in the northern Loess Plateau than in the southern part, coinciding with the previous conclusion that the northern Plateau has experienced a drier climate regime in both glacial and interglacial periods. The substantial increase in BCMSR of the upper S0 relative to the lower S0 at Lingtai and Weinan indicates that human activities have exerted a significant influence on fire regimes in the middle and southern Loess Plateau during late Holocene due to the relatively intensive agricultural usage of land.