Karst-ecological changes during the middle and late Holocene in Southwest China revealed by δ18O and δ13C records in a stalagmite

Rocky desertification is a major environmental problem in the karst regions of Southwest China and seriously impacts ecological and socioeconomic development. Human activities and climate change have been proposed as the main factors responsible for the development and expansion of rocky desertification, but more evidence is needed to support this hypothesis. In this study, the history of the Asian summer monsoon (ASM) since 6200 yr BP is reconstructed based on 230Th dating and delta O-18 and delta C-13 data of a stalagmite from Feilong Cave in Guizhou Province of Southwest China. Positive delta O-18 and delta C-13 excursions record eleven interdecadal-centennial weak summer monsoon events at 1000-870, 1660-1460, 2040-1900, 2780-2460, 3020-2860, 3250-3120, 3650-3370, 4273-3980, 4820-4480, 5370-5180, and 5840-5560 yr BP. These weak ASM events were controlled by a southward shift of the Intertropical Convergence Zone and frequent El Ni (n) over tildeo events. Changes in the delta C-13 values of this stalagmite were mainly driven by changes in vegetation coverage and type, soil microbial activity, and regional hydrogeological conditions. The simultaneous positive excursions of delta O-18 and delta C-13 at similar to 5500, 4200, and 2800 yr BP indicate a degradation of the karst ecological environment in response to the weak summer monsoon. In addition, frequent dynasty changes in China since 3000 yr BP profoundly influenced the karst ecological environment. During the Medieval Warm Period, the Jing-Kang event (JK event) resulted in the fall of the Northern Song Dynasty and led to a large-scale migration into southern China. As a consequence, the population increase in the Yangtze River basin enhanced land use, accelerated the disappearance of forests, and finally resulted in the deterioration of the regional environment. We conclude that climate change and anthropogenic activity may have jointly triggered and/or exacerbated rocky desertification in Southwest China.