The Holocene Climate And Environment Changes In The Mongolian Plateau

Holocene is important periods of past globle climatic and environmental changes. One strategy of Holocene climatic changes research is to select the key sentive study area. Therefore, it is great important to reconstruct the paleoclimate changes of the Mongolian Plateau, which is situated at the core of the east-central Asia and controlled by three global-scale climate systems. The paleoclimate changes reconstrcution in the Mongolian Plateau should significantly improve our understanding of the mechanisms and processes of the Holocene climate changes.This dissertation focuses one lake core (Gun Nuur) in the Northern Mongolian Plateau and another lake core (Qigai Nuur) in the Ordos, souther Mongolian Plateau. Analyses of geophysics and geochemistry were conducted in an attempt to retrieve the Holocene chronosequence of climatic and environmental changes based on AMS ¹⁴C-dated chronology. The main conclusions are as follows:1. The data from the Gun Nuur 9.28m lake core provided high-resolution records of the Holocene climate and environment changes Northern Monglian Plaeteau. The data show that cold and dry climatic conditions occurred between 9.27 and 8.46 ka BP, and warm and wetter conditions prevailed between 8.46 and 7.1 ka BP, followed by warm and dry conditions between 6.9 and 5.6 ka BP. The second half of the Holocene flucuate frequently with cooler-wetter spelles: 5.6-4.9, 4,1-3.65, 3.2-2.7, 1.8-1.4 0.76-0 .55 ka BP and wamrer-drier spells: 4.9-4.1, 3.65-3.2, 2.3-2.0, 1.2-0.76ka BP.2. The data from the Qigai Nuur 8.2m lake core revealed the detailed climate change history of Ordos during the past 12 ka BP: cool-humid cliamte condtions followed by slighter warmer and humid conditiond between 11.4-10.2 ka BP; then the climate deterioated badly correspond to YD evnet. Between 9.2 -6.8 ka BP, climate is generally cold-dry with several shift; between 5.6-2.9 ka BP, the condition is warm-wet refered as the Holocene optimal period;over the past 2.9 ka BP,the cliamte is generally cool and dry.3. The Holocene climate and environment change records retrieved both from Gun Nuur Northern Mongolian Plateau and Qigai Nuur are consistent but not in synchronism. Warmer Bolling/Allerod climate happened earlier in the Northern Mongolian than that of the Southern Mongolian Plateau, the YD event is much significant in Ordos than that in the Northern Mongolian. The cool-humid temperature and water combination in the Northern Mongolian different from the warm-humid combination in the Ordos.4. The humid climate period retrieved from the Gun Nuur lake core are consitent with the paleosol formed in the eolian sequence Northern Mongolian Plateau. While the Paleosol developed in the Ordos Southern Mongolian Plateau well matched with the humid period retrieved from the Qigai Nuur lake core.5. The data of the Qigai Nuur indicated the delayed Holocene beginning in the Ordos about 9.2 ka BP, which is different from the eolian-wetland records from the neighbourhood area.6. The proxies of the Gun Nuur show it developed at 8.4kaBP, synchronism with the humid interval indicated by the Qigai Nuur data.