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Fei Huang 1, Lisa Kealhofer 2, Shang-Fa Xiong 3, Feng-Bao Huang 1 1 Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing, 210008, China. fhuang@nigpas.ac.cn 2 Anthropology and Sociology Department, Santa Clara University, CA, USA 95053 3 Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China The study area is situated at the northwestern limit of East Asian summer monsoon region, which is sensitive to monsoon change. It is also located in the central eastern Inner Mongolian grassland where grasses can serve as good indicators of past climatic changes. However, the processes of grassland in Inner Mongolia under the changing monsoon are not well investigated. Most previous pollen research on Holocene vegetation history in Inner Mongolia comes from lakes and peat bogs in forested regions. Palynological evidence from these Holocene palaeosol sequences usually obscures the dynamics of Holocene vegetation change. However, phytolith analysis provides an alternate means for studying long-term in situ vegetation in grassland ecosystems and for interpreting grassland vegetation change in response to large-scale climatic controls. In our study, we present Holocene pollen and phytolith records from a 1.4m-deep trench profile at the central eastern Inner Mongolia, and attempt to interpret anthropogenic- and natural- induced changes in the grassland communities of Inner Mongolia, in order to add to existing records of monsoon variations during Holocene. The Taipusi Banner paleosol profile (41°58′30″N, 115°10′32″E, 1340m asl) consists mainly of sandy soil, 140 cm thick. The profile shows no sign of either erosional hiatuses or aeolian sand layers. The bottom of the sequence is underlain by loess and sand layers. Besides two samples from the loess and sand layers, 28 pollen and phytolith samples were collected at the Taipusi Banner profile, with an interval of 5 cm. Radiocarbon samples were dated at the Institute of Geology, China Seismology Bureau. Three 14C age are measured. The bottom of the profile is estimated to date to ca. 10000 cal yr B.P. The ages of sampled horizons were interpolated between radiocarbon-dated horizons. Pollen and phytolith records from Taipusi Banner paleosol profile indicated that the abruptness moist/arid transition at ~5000 cal yr B.P. is one of the main factors leading to grassland degeneration in Inner Mongolia. At the beginning of Holocene, a winter monsoon regime still prevailed. From 8700 cal yr B.P., summer monsoon influence began to increase, and reached a maximum from 7000 to 5000 cal yr B. P., with a significant spread of C4 grasses in the grassland. Correspondence analysis also supports the climate during this period was uniquely warmer and wetter than present-day, though there is no modern analogue. After 5000 cal yr B.P., summer monsoon influence declined dramatically, with the gradual invasion of dry, salt-resistant and psammophilous plants, the components of the grassland significantly varied. During 3000 and 2100 cal yr B.P., Echinops-type plants and some C4 grasses expansion ascribed to summer monsoon oscillation. The cultivation practices in the study area occurred much earlier, but negative impacts on the grasslands can only be directly linked to anthropogenic factors in the Taipusi profile from ca. 2100 cal yr B.P., and then human disturbance accelerated the process of grassland degeneration.
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