Saurer M
Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.
Isotopes Environ Health Stud. 2003 Jun;39(2):105-12. doi: 10.1080/1025601031000108633.
Natural variations in the oxygen isotope ratio 18O/16O are occurring in the hydrological cycle as a result of isotope fractionations during evaporation and condensation. These processes imprint a valuable climatic signal in the precipitation, which is stored in ice caps as well as in the cellulose of trees. Recent developments in the continuous-flow analysis of 18O/16O of organic matter now enable a systematic application of this method in tree rings. It becomes possible to build maps of the past oxygen isotope distribution in continental areas, yielding important information on regional climate changes. In this paper, the factors influencing the isotope composition of tree rings are discussed with an example from trees in northern Eurasia. Oxygen isotope values of Larix, Picea and Pinus trees were measured over a large climatic gradient extending from Norway to Siberia. The spatial isotope variations were highly correlated to the annual mean temperature (r2 = 0.84), whereby the slope of the corresponding regression line was 0.35%/degrees C. When considering the changes in 18O/16O during the 20th century, not only the temperature, but also changes in the precipitation patterns have to be considered, in particular the observed increase in the amount of winter precipitation.
由于蒸发和凝结过程中的同位素分馏作用，水文循环中氧同位素比率18O/16O存在自然变化。这些过程在降水中留下了宝贵的气候信号，降水被储存在冰盖以及树木的纤维素中。目前，有机物质18O/16O连续流分析的最新进展使得该方法能够系统地应用于树木年轮研究。绘制大陆地区过去氧同位素分布地图成为可能，从而获得有关区域气候变化的重要信息。本文以欧亚大陆北部树木为例，讨论了影响树木年轮同位素组成的因素。在从挪威到西伯利亚的大气候梯度范围内，测量了落叶松、云杉和松树的氧同位素值。空间同位素变化与年平均温度高度相关（r2 = 0.84），相应回归线的斜率为0.35%/摄氏度。在考虑20世纪18O/16O的变化时，不仅要考虑温度，还要考虑降水模式的变化，特别是观测到的冬季降水量增加。
