| The aim of global paleoclimatic research is to reveal the natural process of past climate change, probe its mechanisms and forecast the trend of human environment in the future. Last Glacial is a crucial period for exploring the climatic mechanisms. The author collects a stalagmite from a high-altitude cave in the Shen nong jia region, Hubei province, which grew in the Late Last Glacial, and reconstruct the process of winter and summer monsoon circumfluence changes in the middle and lower reaches of the Yangtse River in order to evaluate the status and function of East Asian monsoon in the global climate change.The stalagmite (NO. SL) developed in Tian'e Cave which locates at Songbai borough and its height attains 1570mm. Seven high-precision TIMS dating results show that its growth spans 31 ~ llkaB. P.. Combining with deposition lithofacies research, the author verifies that there is a hiatus occurring at 1010mm from the top in the sample. Therefore, the stalagmite is divided into two sections(0~1010mm from the top and the rest 1010?570mm) to construct time scale applying linear interpolation. The oxygen and carbon isotopic samples are collated at two per mm along the mill finish down the growth axis, and tested at an interval of four samples, get 624 pairs of isotopic data altogether. According to average depositional rate, the resolution of isotopic data before 14474 yrB. P. reaches seven years, but the resolution of the section older than 22200 yrB. P. only attains 30~40 years.The oxygen curves show clearly the millennial-centennial climate events similar to the North Atlantic region, in which include YD event, Boiling, Heinrich events( H2, H3, but excludes HI for growth hiatus), which indicates there is a striking relation of forcing and response between East Asia monsoon and polar region climate. Moreover, the high-resolution climate event sequences of the stalagmite reflect the process and transition features of these catastrophic events. The YD event comprise more than ten cold/warm oscillations lasting 10~30 years. B011ing present a trend of cold and dry to warm and wet as a whole, and its interior structure can be divided into three warm pikes and two cold vales. H2 event show a striking cold vale interlaying a warm pike lasting 500 years. H3 event contains ten centennial scale stepwise cold/warm climate changes. GIS2 is composed of two slightly different in time but equivalently warm pikes. All these decadal climate information has a corresponding relation to GISP2 6 180 record. Further, they verify that high-latitude climate can transfer to East Asia monsoon region via the westerly and Mongolia and Siberian high pressure system.Carbon isotope denoting vegetation evolution has a time-lagging effect on response to the oxygen signal spanning 50?50 years, which denotes climate condition , and influenced by regional factors behaves severalIImatching modes of water and heat, which reveal complexities of local environment change. Combining with the pollen data, the author finds that the hygrophilous xylophyta dominate this region during the warm and cold climate, the herbaceous plants take the second place. Warm and cold climatic events on different intensity affect differently on the ratio of two types of vegetation. The cold event which last long with a large decrease in temperature affect great on the establishment of vegetation visage and resuming process.Spectral analysis on the oxygen and carbon isotope displays a strong periodicity spanning 1380 years which resemble to the "Bond Oscillation" in the high latitude, the other elements such as 42(K 300, 200, 192, 126, 120, 96, 80, 78, 60, 40-50 years all have the distinctive features as sunspot activity, and another one about 36 years apparently like the instrument-measured periodicity. All these reveal that solar radiation is a dominating factor in the evolution of East Asian climatic change and monsoon area in the East Asia has a special response to the global climate, maybe it bears several forcing mechanisms. |
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