Vegetation, climate and human impact since 20 ka in central Yunnan Province based on high-resolution pollen and charcoal records from Dianchi, southwestern China

Abstract

High-resolution pollen and charcoal records from Dianchi in central Yunnan Province, southwestern China are presented in this study and reveal variations in vegetation, fire, lake environments, and climate over the last 20,000 years (20 ka). The results show that the climate during the period 20.0–18.0 ka was relatively cold, and rainfall in winter and early spring was relatively lower than the present, which belongs to the Last Glacial Maximum (LGM) . After 18.0 ka, the temperature increased gradually, indicating the onset of deglacial warming in central Yunnan Province, though the mean annual temperature before 10.8 ka was still at least 1.5 °C lower than today. The climate began to obviously warm from ∼10.8 ka and was at least 2 °C higher than today and relatively humid between 10.0 and 5.4 ka, denoting the early-Holocene Thermal Maximum. A major vegetation change around Dianchi occurred at ∼5.4 ka and was most likely caused by the climate cooling and drying with no obvious evidence for cultivation activities except for some possible evidence of human fire use or selective deforestation from the pollen assemblage. Significant cultivation activities in Yunnan Province indicated by the first obvious increases in Poaceae (>40 μm) and Poaceae (25–40 μm) pollen percentages began at ∼2.4 ka. In central Yunnan Province, there was a continuous deglacial warming that occurred between 18.0 and 12.5 ka without marked interruption during the interval of Heinrich Event 1 (H1). Additionally, the Holocene Thermal Maximum occurred in the early Holocene. The results from this study are different from the western region of southwestern China where the paleoclimate studies have clearly detected the H1, the B/A, and the YD events, and revealed a mid-Holocene climatic optimum. Show more