The Holocene East Asian Monsoon Record From Tenger Nuur Of Monsoon Boundary In The Southern Mongolia Plateau

Study on the Holocene climate and environment are of great significance not only for its near past but also for the understanding of the inter-correlation between human and earth environment. Research on Asian monsoon evolution is very important because the monsoon system provide primary moisture and influence the Holocene climate and environment change in eastern Asia. Further more, the marginal monsoon area is more sensitive to climate change, palaeoclimate records and associated research are helpful to understanding the dynamics of the evolution of the East Asian Monsoon.Based on radiocarbon dates, we provide continual sedimentary geophysical and geochemical records of the Tenger Nuur, which located at the monsoon marginal area in southern Mongolian Plateau, reconstruct the regional Holocene climate and environment change sequences. Conclusions were made through synthesis and comparison of the palaeoclimate records distributed at adjacent area and its southern marginal monsoon area.1. The regional Holocene climate could be divided into three phases: during 8777-3390 ¹⁴C a BP(400-100cm), paleoclimate proxies such as grainsize, carbonate content, Rb/Sr ratio, Fe/Mn ratio and Mg/Ca ratio disclosed the climate might be warm and wet. This can be well related to the Holocene climate optimum; from 3390 to 1193 ¹⁴C a BP, above proxies display negative patterns relative to Holocene climate optimum, the climate deteriorated into cold and dry; after 1193 BP¹⁴C a BP(26cm-0), the climate ameliorated, this might be a signal of the Medieval Warm Period.2. Through synthesis and comparison with the adjacent paleoclimate records, we conclude that time span of the Holecene climate optimum increased from north to south, i.e., the time span increased from 8777-5174 ¹⁴C a BP in Tenger nuur to 8200-4000 ¹⁴C a BP in Hunagqihai lake, 8500-3100 ¹⁴C a BP in southern loess plateau(Tongwei county, catchment of Zuli river and Xi'an). That is to say, the sustained time of the summer monsoon prolonged from north to south.Temperature varied more intensively in east relative to west at the same latitude, distance from ocean and continentality account for this difference. Summarize in all, the intensity and the time span of the summer monsoon influence gradually decreased from the southeast to the northwest.On the occurred time of the monsoon records distributed at different areas, we can deduce the spatial pattern of the monsoon evolution. The farthest boundary influenced by summer monsoon might be the national boundary between China and Mongolia, which outreach the modern monsoon area.3. The proxy of grainsize might have different climate and environment indication in different sedimentary and climatic environment. On the reference of other climate proxies, we analyze the grain size records of Tenger nuur, conclude that high value of grain size in Tenger nuur profile was mainly induced by the enhancement of the river transport capability which caused by increase of regional precipitation. Therefore, the increase of the grain size in Tenger nuur could indicate well moisture condition.4. The content of organic matter is susceptible to grain size because organic matter preserved poorly in coarse sediment for low absorbability. The variability of Rb/Sr ratio indicates the weather intensity in lake catchments, Fe/Mn ratio directly denotes the lake level, and increased Mg/Ca ratio indicates the enhancement of the salinization.