关键词: 祁连圆柏, 树轮, 谱分析, 低频变化

Abstract:

Qilian juniper ( Sabina przewalskii Kom ) growing in the mountainous area of the easterm part of Qaidam Basin is sensitive to climate change It can reach one millennial years old and the tree ring width chronology can be used to reconstruct climate change over the past 1000 years Power spectrum analysis, Singular Spectrum Analysis (SSA) and wavelet analysis were utilized to trace the variations recorded in two standard tree ring width chronologies (WL3 and WL4) of Qilian juniper in Shalike Mountain, Qinghai, China The power spectrum of the series showed low frequency periodicity of 200 years are most statistically significant at the 95% confidence level for both chronologies Analysis of the power spectrum of both series also showed evidently that low frequency variations of century scale are present in the chronologies It was found that the most important cycle was 200 years for both chronologies by SSA, cycle of 133 years for WL3 and 100 years for WL4 are also identified by this method The reconstructed components of paired eigenvectors of SSA showed that different scale cycles had different behaviors over the past 1000 years Wavelet analysis can provide information on the amplitude of periodic signals and their variations with time The Morlet wavelet coefficient distributions indicated that the 200 years cycle was most prevailing from the 15th to the 17th century for both chronologies, the century scale cycles were pronounced since the 18th century The prominent low value of the ring width in the second half of 15th century is affected by the cycle of 200 years, the high value in the late 20th century is the contribution of century scale periodicities One possible explanation of the low frequencies in the ring width data might be related to the fluctuations of the solar activity Narrow ring width seems to occur during quiet solar periods such as the Wolf, Sprer, Maunder and Dalton solar minima, suggesting that the low variation of the climate indicated by tree ring width may be affected by the long term change in solar activity

Key words: Qilian Juniper, tree-ring, spectrum analysis, low frequency