Climate And Environment Variation Recorded In The Sediment Of Qinghai Lake In Tengchong Since2000a BP

Research on climate change over the past2000is one of the core concerns ofglobal change research, the most significant weather events in this period is theMedieval Warm Period (MWP) and the Little Ice Age (LIA), which is the most recentwarm period and cold periods from modern. Period of2ka BP. is an important timewindow which connecting geologic records and instrumental literature and thenpredicting the future changes of the environment human lived. Human activities onthe global environment exerted the most profound since2ka BP., and humanactivities and nature changes superimposed on each other, constitute a complex globalenvironment and ecosystems. As an important information carrier of continentalclimate change, lake sediment has the characteristics: good continuity deposition, thedeposition rate, high resolution, rich information content, and can be faithfullyrecorded information about climate and environment changes, with status witch otherclimate record carrier cannot be replaced. Yunnan plateau is located in the intersectionzone of southwest monsoon and southeast monsoon. The climate mainly due to thesouthwest monsoon climate and is also affected by the Westerly Jet and the TibetanPlateau local climate, resulting in complexity and diversity climate in differentregions in Yunnan Province. In historical periods especially in the last2,000years, therelations between climate change and human activities is more closely. So researchingYunnan lake sediments, revealing its climate change and understanding the impact ofhuman activities on the environment is very important. In Yunnan lakes study, thepaleoclimate reconstruction basin lake sediments have become more mature, but thereis little research on the Qinghai, Tengchong. There is almost no research involved itspaleoclimate reconstruction, except for the study of its water quality. Therefore, thisstudy will reveal the Qinghai lake sediments response to watershed environment,climate change and human activities. This will both provide new information for thesouthwest region of the evolution of the characteristics of past climate evolution, andprovide a scientific basis for predicting future change in the region from2ka BP.Based160cm long core of Qinghai lake sediment, we established the chronology from2ka BP by using14C dating, tested and comprehensive analyzed the indicators whichare organic matter, carbonates, particle size and magnetic, and reconstructed the climate evolution of Qinghai watershed since2ka BP. Our main conclusions are asfollows:(1) The organic matters and carbonates in Qinghai sediment mainly come from thelake itself. Autogenic carbonate content and organic matter in lake sediments areclosely related to development and environment of the lake, they are robust indicatorsof climate change. High autogenic organic content indicates high temperature andhigh plant productivity level and the large amount contribution to the organic matterin the lake; otherwise it will be low productivity, and contribute a small amount oforganic matter. Under normal circumstances, the lake’s autogenic carbonate content isclosely related to the ratio between freshwater and salt water, and indicate effectivemoisture level indirectly. But in some stages, carbonate content is affected by organicmatter content, for example, the two curves showed the same direction at Ⅲ, Ⅳ stage.The proportion of sediment particle size can be well reveal the size of the lake runoffand indicate that there is how much precipitation in the lake. Heavy proportion clay(<4m) which bring large amount of fine particle for deep water indicate largeamount of runoff; on the contrary, low proportion clay indicate little precipitation.(2) Through a comprehensive analysis of relevant indicators, we got thereconstruction of the ancient environment near the lake since2ka, which is as follows:stage Ⅰ, the climate was warm and dry at2004a BP～1453a BP; stage Ⅱ, theclimate was slant warm-humid but was obvious cold humid fluctuations at1453aBP～853a BP; stage Ⅲ, it was warm-dry at853a BP～373a BP; stage Ⅳ, it wascold-humid at373a BP～1969AD; it was warm-dry at1969AD～2003AD.Since2kaBP, it suggests that the climatic succession type in the region is the warm-dry and thecold-humid alternatively. Compared with historical records, the third fourth and fifthstage of Qinghai Environment was respectively similar with Medieval Warm Period,the Little Ice Age and20th century warming on climatic characteristics and start-stoptime. It may indicate that Tengchong Basin has been response to these climatic eventssince2ka.(3) Through a comprehensive analysis of relevant indicators, we got thereconstruction of the ancient environment near the lake since2ka, which is as follows:stage Ⅰ, the climate was warm and dry at2004a BP～1453a BP; stage Ⅱ, theclimate was slant warm-humid but was obvious cold humid fluctuations at1453aBP～853a BP; stage Ⅲ, it was warm-dry at853a BP～373a BP; stage Ⅳ, it wascold-humid at373a BP～1969AD; it was warm-dry at1969AD～2003AD.Since2ka BP, it suggests that the climatic succession type in the region is the warm-dry and thecold-humid alternatively. Compared with historical records, the third fourth and fifthstage of Qinghai Environment was respectively similar with Medieval Warm Period,the Little Ice Age and20thcentury warming on climatic characteristics and start-stoptime. It may indicate that Tengchong Basin has been response to these climatic eventssince2ka.