Establishment And Climatic Reconstruction Of The Tree-ring Width Chronology For The Last 400 Years In Haizi Mountain, Daocheng

Daocheng Haizi Mountain is located between Litang County and Daocheng County in the Ganzi Tibetan Autonomous Prefecture of Sichuan Province.It belongs to the southern part of Shaluli Mountain in the Hengduan Mountain System.The Haizi Mountain plateau is 4500-4700m above sea level,which is higher than the forest line of the vertical vegetation zone of the river valley.Affected by the last glacier movement,the area is widespread with glacier boulders,but there are also Sabina saltuaria(SS)distributed sparsly in the form of isolated trees or small patches.These Sabina saltuaria are distributed on the Haizishan sensitively respond to regional climate changes,and therefore become an ideal carrier for the dendroclimatology research.Based on the fundamental principles and methods of dendroclimatology,103 tree cores of 43 individuals of SS in Haizi Mountain Daocheng were obtained with increment borers,dried and sanded in the laboratory,cross-dated with skeleton drawing and quality controlled by using COFECHA program.Consequently,three ring width(TRW)chronology of SS from 1645 to 2019 were established using ARSTAN program.The past nearly 400a high-resolution annual average temperature(AMT_p4-c3)time series was established based on the TRW chronology of AMT_p4-c3.Using correlation analysis,regression analysis,power spectrum and wavelet analysis and other statistical methods,this paper preliminarily discussed the dominant cycle of regional temperature changes on a hundred-year scale.On this basis,the internal variability of the climate system and the influence of external forcing factors(e.g.,volcanic activity)on the region are further discussed,and the following conclusions were concluded:(1)The response of the SS growth in this region to the monthly mean temperature and the monthly mean minimum temperature is conspicuous.But in general,the monthly mean temperature is more likely to be the main limiting factor for the SS growth in this region.The"lag effect"of the impact of temperature on the SS growth is evident.The correlation between mean temperature from last April to current March(AMT_p4-c3)and the STD chronology is statistically significant(r=0.58,p<0.01),and the correlation is consistent with the biological characteristics of tree growth.(2)According to the response relationship between AMT_p4-c3and the STD chronology,a simple one-variable linear regression equation was established,thereby the annual mean temperature variation in the Haizishan area of Daocheng was reconstructed.The reconstruction results show that the colder years experienced in this area are 1645,1663,1732,1743,1817,1872,1851,1926,1968 and 1979respectively;the warmer years are 1652,1688,1800,1828,1889,1947,1957 and2007 respectively.Based on the annual mean temperature,the study years is divided into 4 cold periods and 5 warm periods,of which the colder periods are:1730-1750,1810-1825,1860-1880 and 1960-1980;the warmer periods are:1645-1660,1680-1700,1780-1810,1940-1960 and 1980-2019.(3)In accordance with the reconstructed annual mean temperature series,an apparent 29.4-year multi-decadal periodic signals and a high-frequency periodic oscillations with 2-3 year cycle are revealed.Through correlation analysis,the reconstructed series is positively correlated with the AMO index(Atlantic Multidecadal Oscillation)and north Atlantic SSTA(Sea Surface Temperature Anomaly)at 99%confidence level(the correlation coefficient is 0.33 and 0.20,respectively).In addition,the warm/cold phases of AMO and SSTA are coincide with the positive/negative anomalies of reconstructed air temperature,especially in the recent 120 years,such as A.D.1690-1710,A.D.1800-1820,A.D.1930-1960,A.D.1960-1980 and A.D.1990-2019.The results indicate that the Atlantic SSTA may indirectly affect the temperature changes in the southeast of Qinghai-Tibet Plateau by strengthening its influence on the East Asian monsoon system.(4)The temperature change in the study area may be affected by solar activity.The results show that the warm/cold period in the reconstructed AMT_p4-c3is closely matched with the strong/weak solar activity.The cold period is A.D.1790-1830 and the warm period is A.D.1925-1960,corresponding to the Dalton Minimum and Modern Maximum respectively.The sunspots numbers present valleys and peaks respectively in these two periods.(5)The cooling effect of the Tambora volcano eruption in Indonesia in 1815 is captured on the basis of the reconstruction temperature series.The extreme cold period from 1810 to 1825 is closely related to the cold effect caused by the volcanic eruption.The extremely cold year in the series appeared two years after the volcanic eruption in 1817,with an average annual temperature of 3.5?,which was less than2.42 standard deviations.Compared with the northern mid-thigh latitude regions,it is indicated that the Qinghai-Tibet Plateau also has the imprint of large-scale volcanic eruption events driving regional climate variability.This also verified the significant impact of volcanic eruptions in tropical regions on China,the northern hemisphere,and even the global temperature.(6)Globally,the period from A.D.1800 to A.D.1850 was a common cold period.The northern hemisphere,even the globe,has shown a continuous warming trend since 1900 and then reached a peak in 1940-1950.There was a brief hiatus or decline in changing trend of temperature after 1960.The more obvious downward trend is found in the Tibet Plateau through the measured records from several meteorological stations.However,the global temperature has remained substantially increasing since 2000.Interestingly,in China,the rising trend of temperature in the Tibet Plateau is higher than that in the eastern monsoon region,which is deeply influenced by human activities.All the same,the temperature change in the southeastern Tibetan is highly similar with the northern hemisphere on multiple decadal time scales.(7)As an endemic subtropical evergreen coniferous species in the eastern and southern Tibet Plateau,the SS is characterized by longer average tree-age,clear annual ring boundary,lower rate of false rings,and more sensitive to climate signals.Therefore,it is very suitable for the establishment of long-term chronology.However,compared with common tree species such as spruce,fir and juniper,there are fewer cases of SS in dendrochronological field.The value of dendrochronology with multiple proxies of SS should be further explored and elucidated,such as ring width,stable isotope,cell structure,etc.