Determination of Paleoenvironmental Changes by Using δ13C, 14C Dating and Rb/Sr Ratio in Critical Karst Area of Yunnan-Guizhou Plateau, Southwestern China

Abstract

Paleosols preserve archives of vegetation history, environmental changes, and sedimentary systems. The changes in vegetation history and environmental conditions in karst areas of the Yunnan–Guizhou plateau of southwestern China since the late Pleistocene were analyzed using δ13C, 14C and the Rb/Sr ratio. Our δ13C results reveal the coexistence of C3 and C4 plants (−10.91 to −30.45‰) in soil organic matter, something that is consistent with the present field vegetation assessment. The large vertical difference in the δ13C value (>4‰) is related to the cultivation of agricultural crops and to changes in environmental conditions. Furthermore, the variation in δ13C values was influenced by the summer monsoon climate of the Indian Ocean and east Asia. We found that total organic carbon (TOC) concentration decreased exponentially with soil depth, indicating high carbon loss. In addition, 14C apparent age of the soil profiles ranged from modern times to 20,605 (±63) years before the present (yrs. BP) and is positively correlated with soil depth. The combined results indicate that, since the late Pleistocene era, environmental conditions in the study area have changed intermittently on a scale of millennia from hot-humid to cold-dry conditions. We speculate that there may have been extreme climate events in the study area 14,750 years BP, which are marked by a drastic change in δ13C and in the Rb/Sr ratio.