Late Holocene Environmental Changes Revealed By Peat Records In The Eastern Tibetan Plateau

Pollen, charcoal and LOI data from peat sections ZB08-S4 and ZB08-S9 in the Zoige Basin were obtained to examine vegetation and climatic change in the eastern Tibetan Plateau. The chronology of the peat sections were controlled by 14C dates on bulk samples. Loss-on-ignition analysis (LOI) and charcoal records were also used as climate indicators in this study.The fossil pollen and LOI records of S4 indicate the environmental changes over the last～1400 years in the Zoige Basin:during 1400～700 cal yr BP, AP and dry bulk density are relatively high (mean values are 9.5% and 0.47 g/cm3), Cyperaceae percentage is low (～76.5%). The subalpine meadow and peatland may be the main vegetation types with the small forest growing on the surrounding mountain, suggesting the warm climate during 1400～700 cal yr BP. After 700 cal yr BP, AP (3.3%) and dry bulk density (0.16 g/cm3) decreased significantly while Cyperaceae increased (81.3%), suggesting the climate turned cold.Section S9 shows stablely high Cyperaceae and low AP over the last 3200 years, indicating the vegetation was consistently dominated by Cyperaceae in both lowalnd and highland. LOI results possibly indicate the climatic change in the study region:at 3150～2000 cal yr BP, low dry bulk density (～0.27 g/cm3) indicates relatively cold climate; at 2000～650 cal yr BP higher dry bulk density (～0.33 g/cm3) suggests warmer climate; dry bulk density is low (～0.22 g/cm3) and the climate change to cold after 650 cal yr BP. The peak concentration of charcoal and the war events represent some coincidences suggesting human activities have likely affected charcoal concentration value.Both Section S4 and Section S9 show that～700 cal yr BP is a transitional period from warmer climate to colder climate, which is consistent with the results fromδ13C data of Hongyuan Peat andδ18O data of Wanxiang Cave nearby Zoige. The climate change may be influenced by Asia Monsoon and human activities in the Zoige Basin.