中国西部树木年轮δ^18O的气候信号

CLIMATIC SIGNALS OF TREE-RING δ^18O OVER THE WESTERN CHINA

树轮稳定氧同位素比率（δ^18O）记录在区域气候重建方面具有一定优势.树轮δ^18O记录受树木生长趋势的影响较小,保留了丰富的低频信号,对区域气候变化有较一致的响应.通过对比我国西部1901～2004年树轮δ^18O平均值和降水δ^18O空间分布特征发现,两者空间分布存在一定的相似性.在青藏高原南部树轮δ^18O为低值,而青藏高原北部树轮δ^18O为高值.树轮δ^18O平均值随树轮样点纬度的向北偏移而增大.树轮δ^18O与相邻气象站记录响应分析表明,树轮δ^18O和生长季的温度呈显著正相关,与生长季降水和相对湿度呈现显著负相关关系.旋转经验正交函数分析和空间响应分析表明,树轮δ^18O在我国西风影响区的新疆北部主要反映与区域干湿变化相关的气候信号;树轮δ^18O在西南季风影响的藏东南区主要反映区域水文气候变化信息;然而,在季风和西风影响的交汇区域,树轮δ^18O的区域气候信号相对较弱.

Here, we have synthetized 16 tree-ring δ^18O series from western part of China; most of sampling sites are distributed on the Tibetan Plateau and the arid region of Northwest China. These sites are mainly near to the local forest upper treeline. Tree samples we selected are from the regional dominant species, including spruce, fir, larch and juniper. We firstly compared the spatial patterns of the mean values of tree-ring δ^18O during the period from 1901 to 2004 with the mean values of δ^18O in precipitation, and find that tree-ring δ^18O share the similar spatial distribution pattern with precipitation δ^18O. In addition, tree-ring δ^18O shows relative lower values in the southern Tibetan Plateau, while a higher value is revealed in the northern Tibetan Plateau. Tree-ring δ^18O values increase along with the latitude of the tree-ring δ^18O sampling site, which is similar to the ＂ latitude effect＂ of δ^18O in precipitation. The climate responses between tree-ring δ^18O and meteorological dataset from the nearest tree-ring sampling sites reveal that 8＇SO in tree rings is significantly positively correlated with the growing season temperature, and is significantly negatively correlated with the growing season precipitation and relative humidity. By rotated empirical orthogonal function analysis and spatial response analysis, we point out that in northern part of Xinjiang, where climate is mainly dominated by the westerly circulations, tree-ring δ^18O reflects mainly the regional drought （moisture） conditions; in the southeastern Tibetan Plateau, where climate is dominated by the summer monsoon, tree-ring δ^18O records the regional hydroclimate variability; while in the intersection area between monsoonal area and westerly area, tree-ring δ^18O mirrors climate signals relative weakly. Our results suggest that tree-ring δ^18O can be an excellent proxy in regional climatic reconstruction based on it＇s better ability in keeping the long-frequency climatic signals over larger region. The reinforcement of the ongoing tree-ring isotopic network over the entire China will be helpful to understanding the regional climate change which is linked by differing atmospheric circulations systems and forest dynamics under the significant climate changes in the future.