HOLOCENE MONSOON CHANGES INFERRED FROM LAKE SEDIMENT POLLEN AND ISOTOPE IN NORTHERN CHINA

A 1.8m core collected in Lake Bayanchagan, northern China is analyzed for radiometric chronology, pollen and isotope content of authigenic, inorganic carbonate. The core provides a continuous Holocene record. Changes in stable carbon and Oxygen isotopic contents of authigenic carbonates and arboreal pollen percentage reveal significant changes in environmental conditions, induced by climate changes that might have been resulted from East Asian monsoon changes. Quantitative reconstruction of Holocene paleoclimate has being carried out using a model based on pollen data. An increase in arboreal pollen percentage at 9.7 ka BP coincides with a significantly negative shift in oxygen isotopic composition. The quantitative reconstruction shows the precipitation and the mean temperature of the coldest month may increase by ~50-100mm and ~2-4 degrees, respectively. A dry event happened at ~4.6 ka BP, characterized by a rapid decrease in arboreal pollen percentage, and changes of carbon and oxygen isotopic compositions towards more positive values. The precipitation and the mean temperature of the coldest month may decrease by ~100-200mm and ~3-5 degrees, respectively.