High-resolution paleoclimatic records spanning the past 30 cal ka BP inferred from Qionghai Lake sediments in south-west China: Insights from geochemical investigations and grain-size characteristics

摘要

There have been few high-resolution investigations covering the last glacial and Holocene from Sichuan, Yunnan, or south Asia area in the south-west monsoon domain region. High-resolution analyses of lake sediments retrieved from Qionghai Lake, Sichuan Province, were conducted using a combination of variables including total organic carbon (TOC) and total nitrogen (TN) concentration, low frequency magnetic susceptibility (chi(LF)), particle size, carbonate content, and delta C-13 value of organic matter (delta C-13(org)), to provide a new perspective on the detailed paleoclimate history of south-west China spanning the past 30 cal ka BP. Our findings suggest that organic matter in the Qionghai Lake was mainly derived from microorganisms, aquatic macrophytes, and terrestrial C-3 plants. From 29.1 to 23.2 cal ka BP, low carbonate contents, high median grain size (Md values), and chi(LF) values indicated a warm and wet climate. During the period 23.2 to 15.4 cal ka BP, low chi(LF), Md values, and high carbonate contents suggested a decrease in temperature and humidity. The cold and dry Last Glacial Maximum (LGM) and Heinrich 1 event (H1) were captured between 21.6 and 19.4 cal ka BP and 17.6 and 15.8 cal ka BP, respectively. During the interval 15.4 to 9.7 cal ka BP, low level of chi(LF) values and Md values, together with relatively high carbonates, demonstrated that a dry climate prevailed in this period. Since 9.7 cal ka BP, the climate was warm and humid in the early to mid-Holocene and shifted towards cold and dry condition in the late Holocene. A cold and dry period at 8.5 to 8.1 cal ka BP and warm and wet interval at 6.6 to 4.6 cal ka BP were identified, corresponding to the 8.2-ka cold event and Holocene climatic optimum (HCO), respectively. These climate changes may reflect variations of the intensity of the south-west summer monsoon, primarily in response to the Northern Hemisphere solar insolation on a millennial scale induced by orbital forcing. The positio