昆明大气降水稳定同位素与西南(印度)季风强度

Characteristics of Stable Isotopes in Precipitation and Southwest (Indian) Monsoon Intensity at Kunming

根据全球降水同位素观测网(GNIP)提供的昆明站大气降水氢氧稳定同位素数据及其气象资料,对昆明站1986~1992、1996~2003年共计15年的月均和年均大气降水氢氧同位素组成及其影响因素进行分析和研究。结果表明:昆明月均及年均同位素组成均落在中国和全球降水同位素的变化范围之内,并呈现明显的季节及年际变化。昆明大气降水中δD和δ18O主要受到水汽来源影响,而且在季节和年际尺度上存在较大差异。经计算得出:昆明雨季(5~10月)降水中氧同位素值81.7%受当地降水量控制,18.3%受气温影响,这说明昆明大气降水中δ18O受降水量和气温的协同影响,但以降水量对其影响为主;通过年降水量与西南季风指数对比证实,昆明年降水量与西南季风指数呈正相关性,但与δ18O呈显著的负相性,由此说明在季风影响显著的单一态地区,可以用降水δ18O值指示降水强度或季风强度,这种季风强度-大气降水量-δ18O三者之间的关系可为研究石笋中所蕴含的环境信息提供依据。另外,通过与香港降水同位素对比研究,发现二者的d值虽然均呈现旱季高于雨季的季节性变化趋势,但它们的平均d值几乎相同,由于昆明与香港所处地理位置和距离海洋远近的差异明显,说明二者的水汽来源不同,昆明降水主要受印度洋的西南季风控制,香港降水则主要来源于太平洋控制的东南季风。昆明大气降水线斜率和截距的季节及年际变化趋势可用云下二次蒸发和动力分馏效应来解释。

Using isotope and meteorology data at Kunming station from the GNIP, the average monthly and annual hydrogen and oxygen stable isotopic compositions and the main factors of 15 years (1986-1992 and 1996-2003) at Kunming station were analyzed. The average monthly and annual hydrogen and oxygen stable isotopic compositions fall within the scope of changes in China and the global isotopes of precipitation, and the seasonal and interannual variations are significant. Hydrogen and oxygen stable isotopic compositions of precipitation at Kunming are mainly influenced by vapor source. There exist obvious differences in the seasonal and interannual scales. The local precipitation amount and air temperature determine 81.7% and 18.3% oxygen isotope values in the rainy season, respectively. Even the δ18O in precipitation affected by the precipitation amount and air temperature, the precipitation amount has a stronger affect on the δ18O in precipitation than the air temperature. In addition, the relationship between annual precipitation and Indian monsoon indexes show a positive correlation, but a significant negative correlation with δ18O in precipitation, illustrating that δ18O in precipitation indicates monsoon or rainfall intensity. The relationship between monsoon intensity and precipitation amount and the δ18O in precipitation can provide a scientific support on the meaning of the isotope of the stalagmites. Comparing the isotopes of precipitation in Kunming with that from Hong Kong station, their d values have distinct seasonality with lower values in the rainy season and higher values in the dry season, but they have almost similar values. Nevertheless, geographical location and distance from sea are different, illustrating that the vapor sources are different. Precipitation in Kunming is affected mostly by southwest monsoon from Indian Ocean, but the rainfall in Hong Kong is mainly controlled by southeast monsoon from Pacific Ocean. The seasonal and interannual variation trends of slope and intercept of Kunming precipitation can be explained by below-cloud secondary evaporation and dynamic fractionation effect.