Paleoclimate changes of the past 30 cal ka BP inferred from lipid biomarkers and geochemical records from Qionghai Lake, southwest China

Abstract

Multi-proxy records of paleoclimate changes spanning the past 30 cal ka BP were obtained from Qionghai Lake sediment core, Sichuan Province, southwest China, where southwest summer monsoon prevails. The core was studied for molecular compositions of n-alkanes, stable carbon isotope ratios (δ13C) of organic matter (OM), total organic carbon (TOC), total nitrogen (TN) and trace elements. Evidence from n-alkanes, cross chart of C/N-δ13C values and trace elements indicated the organic matter derived from a mixed source composed of autochthonous aquatic organisms and allochthonous terrestrial plants, and the sediments mainly deposited in reducing conditions, which is in favor of preservation and accumulation of OM. Variations of n-alkanes biomarker proxies, δ13C of organic matter and Mo concentrations reflected three stages of paleoclimate evolution during the past 30 cal ka BP: a relatively warm and humid climate between 29.1 and 22.9 cal ka BP, corresponding to a strong southwest summer monsoon; climate shifted towards cold and dry condition during the period of 22.9–15.7 cal ka BP, in response to the reduced insolation and weakened southwest summer monsoon; temperature and humidity gradually increased in the Holocene with fluctuations, broadly track the strengthening trend of southwest summer monsoon. Our findings further confirm that variations in solar activity may primarily affect the strength of southwest summer monsoon, resulting in the shifts of paleoclimate conditions. Further studies are needed to better constrain the detailed forcing drivers which may amplify the intensity of southwest summer monsoon particularly in the Holocene period.