利用树木年轮宽度资料重建川西米亚罗地区过去200年夏季温度的变化

TREE RING-BASED SUMMER TEMPERATURE RECONSTRUCTION OVER THE PAST 200 YEARS IN MIYALUO OF WESTERN SICHUAN, CHINA

利用川西高原米亚罗地区林线位置高山柏(Sabina squamata)的年轮宽度资料,分析了树轮年表和气候要素的关系。通过相关和响应函数分析得出,树木径向生长对于夏季(6～7月)温度响应最为敏感,上年冬季到早春(12～3月)温度也对树木生长有一定的影响,而年表与降雨没有明显的关系。最终利用树轮年表重建了该地区过去200年(1810～2009年)的夏季(6～7月)平均温度的波动历史,重建方程的方差解释量为43.2%(调整自由度后为41.9%)。重建温度序列的平均值为12.49℃,标准差为0.515℃,其波动特征大致可以分为3个阶段:1850年以前的寒冷时期、1850～1950年的温暖时期以及1950年以后的温度平缓波动时期。重建序列最为寒冷的时期为1810～1830年,其中1824～1825年为最寒冷的年份;重建序列最为温暖的时期是发生在19世纪下半叶(1850～1903年)和20世纪上半叶(1911～1950年),其中1863年和1925年是最温暖的年份。重建温度序列的主要冷期和暖期与周围地区其他对于温度响应敏感的树木年轮和冰芯材料以及冰川进退记录均有较好的对应关系,这表明本研究的重建序列较为可靠,是可以指示研究地区过去温度波动历史的。

Several studies have previously been conducted in Western Siehuan and demonstrated the fidetlty ot tree-ring records to dendroclimatologieal research. However, climate variability of this region during past centuries still remains diffieuh to depict clearly, mainly due to the paucity of the high-resolution paleoelimatic evidence. Using tree-width data of Sabina squamata in Milyaluo,Western Siehuan of China,our objectives are to determine the main climate responses in diameter growth and seek to understand the regional climate variability within this ecological complex area. The study area（31.4° - 31.92°N, 102.58° -103.07°E） is situated in M iyaluo forest zone, in the watershed of Zagunao River（ one of the major tributaries of the upper Min River）. The sample site （31.63′N, 102.96°E） of S. squamata in this study is located in Jiabigou country. In total, we collected 45 cores from 45 living trees of S. squamata in a treeline site（3750m above sea level）at the southern slope side. Samples were dated and processed using basic dendrochronological techniques. A total of 38 increment cores were eventually crossdated and selected for chronology development,whereas seven poor quality cores（ not cross-datable at the 99% significant level）were excluded from further analysis. Several statistics were used to identify common patterns of interannual growth variability, and correlation and response function analyses were used to determine the basic response patterns of radial growth to climate. The result was a robust standard chronology（from 1785 to 2009 A. D. ）with strong signal strength back to 1810 A. D. ,and with variability retained at the multi-decadal scale. Correlation and response analysis revealed that tree growth at this site was mostly governed by temperature in summer （June to July） , and temperature from winter to early spring（prior December to current March）played a secondary role in explaining the climate related variance in ring records. In contrast, no consistent response pastern was found between the chronology and precipitation. The summer（June to July）temperature reconstruction, spanning 1810 - 2008 A. D., could explain 43.2% the variance （ adjusted for degrees of freedom was 41.9%） contained in the instrumental data from the calibration period 1955 - 2002 A.D. The mean and standard deviation of the reconstruction were 12.49℃ and 0. 515℃ , respectively. Three prominent stages could be identified in our reconstruction ： a comparatively cold period prior to 1850 A. D., followed by a consistent temperature increase during the period of 1850 - 1950 A. D. and a near normal temperature state during the late half of 20^th century. The extreme cold event occurred during 1810 - 1830,reaching minimum values during 1824 - 1825 ,while the most distinct warm event occurred at late half of the 19th century（ 1850 -1903 ）and first half of 20^th century （1911 - 1950） , reaching maximum values in 1863 and 1925. The reconstruction revealed similarities at inter-decadal frequencies with tree-ring reconstructed temperatures from nearby regions, as well as the δ^18O value of ice cores and recorded glacier fluctuations in the surrounding high mountains,which suggested the fidelity of the local temperature sensitivity of our tree-ring data. This reconstruction will improve coverage and length of paleoclimatie data for Western Sichuan, and contribute to the fundamental information on large-scale climate variability of this remote region with short-term instrumental data.