Century Temperature Reconstruction And Holocene Climate Change Cycle Analysis In Lugu Lake Area

The Holocene climate is an unstable time series with the characteristics of periodic fluctuations and alternating changes of cold and warm.The study of the Holocene climate change has become an important aspect of global climate change research.Tree rings and lake sediments are carriers of climate records with different resolutions.An in-depth analysis of them can provide a more comprehensive understanding of the regional climate change situation,find the driving causes of climate change and the connection with global change;at the same time,you can use the regional climate background and change laws to guide the prevention and control of geological disasters,and arrange local production and construction.It is of great significance for scientific research and economic production.It is very rare that the year-resolutin climate reconstruction in the Lugu Lake area and it is also lacking that the analysis of the driving factors of climate change Based on this,this study makes use of tree-ring cores of Picea likiangensis that are collected from the northern part of Lugu Lake,and the minimum temperature of the past 119 years have been reconstructed in this region,using the method of Dendroclimatology.Moreover,the established Ca CO₃ sedimentary sequence of Lugu Lake and the reconstructed minimum temperature sequence are conducted Ensemble Empirical Mode Decomposition respectively,then the cycles of Lugu Lake in different time scales since Holocene are obtained,also the periodic driven is discussed.At the same time,it also briefly discusses the impact of Neotectonics on regional climate change This study achieved the following results,?1?Through correlation analysis of tree-ring width chronology and instrumental data,it was found that before 2000 A.D.,the minimum temperature in winter and spring was the most important factor for limiting the radial growth of Picea likiangensis in Lugu Lake.There was no significant effect brought about by water on the radial growth of trees.After 2000 A.D.,this kind of correlation has mutated,showing obvious growth ring-climate"divergence problem".Then,this phenomenon is further discussed,the result displays that the differentiation between tree growth and measured data is an objective ecological phenomenon;after 2000 A.D.,the main controlling factor may be affected by the combination of the minimum temperature,the maximum temperature or the relative humidity in summer.But the new controlling factor is not clear because of the short time occurred by this phenomenon.?2?Through correlation analysis of chronology-climate,and referring to the general treatment method after the occurrence of"divergence problem",we reconstructs the changing history of minimum temperature in winter and spring?prior October to current May?in Lugu Lake during the reliable chronology period of1882?2000 A.D..The reconstructed sequence exhibits two warm periods?1911?1927A.D.and 1992?2018 A.D.?and one cold period?1940?1991 A.D.?.At the same time,three warm periods 1888?1895 A.D.,1900?1904 A.D.,1931?1939 A.D.and four cold periods 1883?1887 A.D.,1896?1899 A.D.,1905?1910 A.D.,1928?1930 A.D.have also been found.This reconstructed sequence is basically the same as the temperature fluctuation of CRU lattice sequence and the tree ring reconstruction sequence in northwest Yunnan.It also has a strong corresponding relationship with the paleopigment records of Lugu Lake Sediments and the glacial advance and retreat records.At the same time,each cold and warm period has corresponding historical records of meteorological disaster events.Spatial field correlation analysis obtained that the field correlation ranges between Lugu Lake reconstruction and measuring temperature before 2000 A.D.are basically the same.However,after 2000 A.D.,the height-related area of temperature field is mainly around the northern part of Bay of Bengal,and there is no correlation with the areas located by samples.?3?The Ensemble Empirical Mode Decomposition?EEMD?is carried out by adopting the Ca CO₃ sedimentary sequence that can reflect the variation history of monsoon rainfall in Lugu Lake area and the reconstructed 100-year minimum temperature sequence in Lugu Lake,respectively.The result shows that there are change periods of 2?4 a,8 a,11 a and 23 a existing in the minimum temperature sequence,while the Ca CO₃ sequence has change periods of 72 a,189 a,303 a,1006 a,2222 a,6667 a and 10000 a,in which the existence and stability of 6667 a and 10000a can not be determined.?4?The plateau uplift and the tectonic landform of northwest Yunnan caused by the neotectonics have strengthened the Asian Winter Monsoon and facilitated the influence brought about by the Indian monsoon on southwest China.Therefore,it has become the tectonic-circulation background of climate change in plateau area formed after the Holocene Age and Lugu Lake region that locates in the periphery of plateau.Since the Holocene,solar activity has been the most important driving factor of climate change at various time scales in Lugu Lake.In particular,solar activity plays a stable and important role in climate cycle change on a millennial scale.To sum it up,the shorter the climate change cycle,the more complex the influential factors.Ice floating debris in North Atlantic,El Ni?o Southern Oscillation?ENSO?,and Total Solar Irradiance?TSI?are main driving factors to control the climate change during100-year and millennial scales in Lugu Lake.But at the inter-annual and inter-decadal scales,the influential factors are numerous and complex,North Atlantic Oscillation?NAO?,North Pacific Oscillation?PDO?,relative number of sunspots,Kuroshio and so on may be the influential factors of the high frequency periodic variability of Lugu Lake.