Climate Evolution Of Holocene In East Aisa And Its Quantitative Analyses

Based on analysis of the climate proxy data, reconstruction of the wetness in Tibetan Plateau, East China, and Mongolia Plateau are made; also the evolution and intensity of Indian monsoon and East Asian monsoon are analyzed in millennial scale in Holocene. Quantitative reconstruction of mean July temperature and annual precipitation is based on both pollen percentage content from surface and stratum pollen samples and vertical meteorological observations across 700-2800m in Dajiuhu, Shennongjia. Finally, tree-rings are used to deposit the temporal and spatial changes in the Medieval Warm Period and Little Ice Age, and the annual PDO index are reconstructed. The major conclusions are as followings:1. Evolution of Indian monsoon and East Asian monsoon in Holocene.Lake status and high resolution climate records depicted the millennial-scale variability of Indian monsoon and East Asian monsoon. Indian summer monsoon strengthened at about 11.5 kaBP, and controlled the whole Tibetan Plateau at 0.5ka. Then, it spread through Southwest China, South China and Yangtze River catchment for 2-3ka. The wettest period ended at 9 kaBP in Qaidam Basin and western Tibetan Plateau, and about 8 kaBP in South China meanwhile Indian summer monsoon weaken in middle part of Tibetan Plateau. After 7 kaBP the monsoon front returned to mid-Tibetan Plateau from western part. Another millennial weakening took place at 6-5 kaBP in east and northeast of the Plateau, together with the ending of warm-wet period in middle part. There's a weakening event of summer monsoon at 2.5-2.4 kaBP from the records of Yidun Lake, Haiden Lake and Rencuo.East Asian summer monsoon had arrived in Northeast China, middle Inner Mongolia and eastern Loess Plateau at 11.5 kaBP, which caused a short warm-wet climate period. It might reach eastern Loess Plateau and east part of Northwest China at 10 kaBP. Beginning of strong summer monsoon precipitation was at 9.8-9.4 kaBP in mountain area of Northeast China,9.2-9 kaBP in eastern Inner Mongolia,8.5 kaBP in middle and east part and 8.5-8.2 kaBP in western Loess Plateau,8 kaBP in middle Inner Mongolia and east part of Northwest China, and 8-7.2 kaBP from east to west in Xinjiang province. Ending of warm-wet period started in Northwest China at 6.5 kaBP, while at 6 kaBP in Northeast Plain, eastern Inner Mongolia and Loess Plateau. The transition of wet to dry was at 5-4 kaBP in middle Inner Mongolia,4.2 kaBP in Northeast China and western Loess Plateau, then 3.1 kaBP of Loess Plateau.2. Reconstruction of humidity change in East Asia in Holocene. Result of semi-quantitative reconstruction of humidity in southern Tibetan Plateau, East China and Mongolia showed that it kept wet in Tibetan Plateau in whole Holocene, and the wettest period occurred at 8-6 kaBP. After about 6-5 kaBP it turned dry. The severe aridity events appeared around 4 and 2 kaBP. The warmest and wettest period was 8-5.5 kaBP in East China, with a warming and wetting early Holocene and droughty late Holocene. There's the largest fluctuation of humidity in Mongolia, and it's in heavy drought condition when wettest age occurred in East summer monsoon controlling area.3. Quantitative reconstruction of mean July temperature and annual precipitation in Dajiuhu, Shennongjia based on pollen-climate response surface.Quantitative reconstruction was based on pollen percentage content from surface and stratum pollen samples and vertical meteorological observations across 700-2800m. Canonical correspondence analysis and robust locally weighted regression of surface pollen samples gave the relationship between plants and climate, which helped us to build the nine pollen-climate response surface models. Reconstructed results of the stable type assemblage depicted the climate evolution from Late Glacial period credibly, including the B(?)lling-Aller(?)d warm period, Younger Drays, climatic optimum, cold events of 8 and 4 kaBP. Combination of temperature and humidity illustrates that climatic optimum with high temperature and precipitation occurred during early-Holocene and former mid-Holocene. Sensitivity analysis of pollen factors revealed that woody plants with high quantity were insensitive to abrupt climate change, herb and fern were more sensitive to climatic fluctuation, and recorded the extreme climatic events remarkably.4. Moistiness change in East Asia for past 2ka.Climate records of tree-rings, icecores and stalagmites indicate the wetness change in northeast Tibetan Plateau, East China and Mongolia. Stronger winter monsoon in South China responded to the decreasing of summer monsoon precipitation, and cooling in North China could be compared with wetter period in Mongolia, which pictured the general Little Ice Age. Medieval Warm Period appeared early in Tibetan Plateau, then gradually late along latitude in East China and Mongolia. Warming trend was remarkable in high latitude and not significant in lower latitude area. Global warming after 18th in East China displayed similar characteristics.5. Reconstruction of PDO index in terms of tree-rings.There're significant relationship between interdecadal climate change in East Asia and Pacific Decadal Oscillation, especially in high latitude area. Reconstruction of PDO since 1613 AD showed the interdecadal characteristics of the semi-20yr period. Change of reconstructed PDO was smaller than that of observation, and represented acute fluctuation from later part of 18th to early 19th. Our result is comparable with other's that had similar low frequency changing trend. Historical records confirm the truth of the change of wetness in the catchments of Yellow River and Yangtze River, which showed negative and positive relationship to PDO index, respectively.