Holocene Envrionmental Change Inferred By Pollen And Charcoal Records From The Zoige Basin

The Zoige Basin is located at the margin of the monsoonal region on the northeastern Tibetan Plateau. Ecosystems in the study area are sensitive to climate change. In this dissertation, we reconstruct the Holocene vegetation climatic change and fire history in the Zoige Basin under reliable chronology, employing high-resolution pollen-charcoal analysis (resolution of78years) based on peat cores collected from the study area. The loss on ignition (LOI%) results show that at10.3-3ka (1ka=1000cal yr BP), the organic matter content reach up to60-80%; at3-1.3ka, organic matter content started to decrease with two peak fluctuations; at1.3-0.5ka, organic matter content declined to the lowest level. Combining analysis on ash-free bulk density, it suggests that the climate condition is relatively moist at10.3-3ka, with the interval of6.5-4.7ka being the wettest period since the Holocene; after3ka, a drying trend was recorded. Since the Holocene, average carbon accumulation rate in the study area was30.6gC/m2/yr and it increased after2ka. Result of fossil pollen analysis shows that sedge meadow and coniferous forest (dominated by Picea) are major vegetation in the study area since the Holocene. Tree pollen in the study area is likely to reflect the changes in temperature. Percentage of tree pollen had high fluctuations (3-34%) in the early Holocene, peaked and relatively stabilized in the mid-Holocene, quickly decreased after3.3ka. Charcoal analysis presented a fire history in the study area since the Holocene:intensified fire intervals include10.3-6.5,4.7-3.3ka and around1.5ka. A Multi-Taper analysis on charcoal concentration shows that there is a period of226year for fire history in the study area, which may be related with solar activities. Integrated analysis on multiple proxies indicate that the warmest and wettest climate prevailed in the mid-Holocene, while the late Holocene was characterized by cold and dry climate conditions and the impact of human activities become more and more evident. We speculate that vegetation dynamics in the Zoige Basin are mainly influenced by temperature changes.