Holocene Sedimentary Characteristics And Signal Records Of Yunnan Lakes Based On Wavelet Analysis

Based on the characteristics of environmental multi-proxy indicators of Lugu Lake and Xingyun Lakes, the environmental and climate change of the lake basin and the evolution of the Asian Southwest monsoon and its mechanism were discussed, with the AMS14 C datings and wavelet theory. The analysis is leads to the following conclusion:1. The 1000 a, 500 a and 250 a quasi-cycles of the environmental and climate change in the study area are exisiting in the records of climate and environment proxies of Lugu Lake and Xingyun Lakes by the wavelet analysis. The intensity of Asian Southwest monsoon shows the periodic variations from weak, strong to weak, and the 1000 a cycle of various cycles is particularly noticeable in the environmental and climatic records during the Holocene.2. The characteristics of climatic and environmental change of Lugu Lake and Xingyun Lake are different under the interaction of the global and regional change. During the early Holocene(10000-8000 cal a BP), the periodic signals of climate change which in Lugu Lake and Xingyun Lake are obviously, and the 1000 a quasi-cycles is especially prominent. From 8000 cal a BP, the signal of Lugu and Xingyun Lake have appeared unsynchronization.There have remained signal differences in the climate change of Lugu and Xingyun Lake during the climate periodic signal of Lugu Lake only has 1000 a cycle and relatively weak. Lasting from 8000-4000 cal a BP. However, the cycles of 1000 a and 500 a cycles exist in theenvironmental signals of Xingyun Lake during 8000-5000 cal a BP, and 500 a quasi-cycle is significantly more than 1000 a. From the middle to late Holocene(4000-0 cal a BP), the climate proxies of Lugu Lake sediment are exist 1000 a, 500 a, and 250 a cycles, and the signals is obviously. However, these features in the Xingyun Lake are recorded between 5000 and 2000 cal a BP. The periodic signal of environmental records of Xingyun Lake is influenced because of the strong human activities in the middle of Yunnan since 2000 cal a BP.3. Through the comparison of the regional environmental records, the results show that millennium scale signals of climate and environment evolution in the study area since the Holocene are mainly controll by the solar radiation. 500 a qusi-cycle is linked to the thermohaline circulation, which is a harmonic of the millennium cycle, and 250 a cycle is related to the solar activity cycle about 210 a.4. The climate and environment evolution of the Asian Southwest monsoon region is fluctuation by the interaction of external driving factor(solar activity) and internal driving factor(the thermohaline circulation). During the early Holocene, the obvious 1000 a periodic signal shows that the climatic fluctuation of Yunnan Plateau is mainly influenced by the increase of solar radiation, and the Asian Southwest monsoon is weakly in this time. During the middle Holocene, the climate was stable and 1000 a periodic signal became weak, the Asian Southwest monsoon has been strengthed. During the late Holocene, the Asian Southwest monsoon became weak, the obvious 1000 a periodic signal shows that the climate was influenced primarily by decrease of solar radiation, and the climate events are happening with increasing frequency.