| 其他摘要 | This past is the key to understand the present and to predict the future. The study on the Holocene climatic and environmental change is of great significance, not only for its nearest epoch but also for the understanding of the interrelation between human and the earth. The Mongolian Plateau, situated at the climate sensitive region, is a very important channel for global energy’s transformation. Furthermore, the climate and environment changes there are controlled by three global-scale climate systems: winter monsoon, summer monsoon, and westerlies. Therefore, the high resolution records of the past climatic changes in the Mongolian Plateau should provide us the critical regional evidence for Holocene global changes. However, limited by the research conditions, most studies on the Mongolian Plateau are concentrated on the southern part, which is in China, while the northern part is under very poor attention.
For the reasons above, we have studied the sediments of Gun Nuur Lake, northern Mongolia, systematically discussed the great values in paleoenvironmental reconstruction of carbonate content, δ13C and δ18O of carbonates, total organic carbon, and the δ13C of organic matter, etc. The main conclusions we have obtained are as follows:
1. The carbonate content in the sediments of Gun Nuur Lake was controlled by the summer temperature. When the temperature rose, the solubilities of carbonate and CO2 decreased, thus resulting in more deposited carbonates.
2. The δ18O values of carbonates in the Gun Nuur Lake mainly reflect the ratio of precipitation/ evaporation thus can indicate lake level changes: higher δ18O value suggested smaller ratio of precipitation/ evaporation, and lower lake level; lower δ18O value indicated the bigger ration of precipitation/ evaporation, and higher lake level.
3. Temperature and its consequential the rate of evaporation, as well as biologic processes in the lake influenced the δ13C of carbonates, resulting its insensitive indication of climate changes.
4. The δ13C of organic matter can reflect the paleo- productivity of the lake, which meant that the higher δ13C value, the higher productivity; the lower δ13C values, the lower lake productivity.
5. The TOC of the lake sediment can be representative of the local winter temperature or the duration of the winter in history, thus could be a good index of the East Asia winter monsoon. |
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