卧龙降水稳定同位素与季风活动的关系

2003-07～2004-07在四川卧龙自然保护区对逐次降水事件进行采样,分析了降水的稳定同位素特征及其与降水量、气温和风向风速等气象参数的关系.结果表明.4～8月降水的过量氘(d-excess)值为(8.4±7.4)‰,降水由东亚季风带来的大洋水汽主导;9～10月降水的d-excess值为(-7.4±12.5)‰,降水由南亚季风带来的经过强烈分馏作用的大洋水汽主导;11月～次年3月降水的d-excess值为(12.5±12.1)‰,降水由本地蒸发水汽以及西风环流带来的内陆蒸发水汽主导.季风期降水的δD和δ18O具降水量效应(r分别为-0.389、-0.380,P＜0.05),次一级是气温影响(P≤0.10).季风期降水的δD、δ18O与南风指数呈显著负相关(r分别为-0.354、-0.390,P＜0.05),表明降水中的稳定同位素比率对水汽来源与运输过程指示性很强,特别是南亚季风的暴发带来了稳定同位素比率和d-excess值都极低的降水.

Relationships Between Stable Isotopes in Precipitation in Wolong and Monsoon Activity

Stable isotopic analyses with precipitation, air temperature, wind direction and wind speed were performed in the Wolong Nature Reserve from July, 2003 to July, 2004. Results showed that d-excess values were (8.4 +/- 7.4) per thousand, (- 7.4 +/- 12.5) per thousand and (12.5 +/- 12.1) per thousand in precipitation events from April to August, September to October and November to March, respectively. Stable isotopic characteristics and d-excess values indicated that precipitation was mainly brought by the East Asia monsoon from ocean surface moisture from April to August, by the Indian summer monsoon from ocean moisture which extremely affected by rainout (strong depletion of heavy isotope) from September to October, and by Westerly from inland evaporation and local evaporation from November to March. Significant negative correlations between isotopic values and precipitation, which was amount effect, were found from April to October (r = - 0.389 for deltaD and r = - 0.380 for delta18O, p < 0.05, respectively) . Temperature effect also might affect isotopic values in precipitation (p < or = 0.10). During the active period of the East Asia monsoon and the Indian summer monsoon, stable isotopes in precipitation events had significant negative correlations with south wind index (r = - 0.354 for deltaD and r = - 0.390 for delta18O, p < 0.05, respectively), indicating that isotopic values closely associated with the origin and transport of moisture, and especially the Indian summer monsoon could bring vapors with very low isotopic values and d-excess values.