The influence of below-cloud secondary effects on the stable isotope composition of hydrogen and oxygen in precipitation at Calgary, Alberta, Canada
The influence of below-cloud secondary effects on the stable isotope composition of hydrogen and oxygen in precipitation at Calgary, Alberta, Canada
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DOI：
10.1111/j.1600-0889.2007.00291.x
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发表时间：
2007-01
期刊：
影响因子：
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通讯作者：
Haidong Peng;B. Mayer;S. Harris;H. Krouse
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文献类型：
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作者：
Haidong Peng;B. Mayer;S. Harris;H. Krouse
测定了1997年1月至2001年12月在加拿大阿尔伯塔省卡尔加里采集的短期降水样品（n = 436）中氢（δ2H）和氧（δ18O）的稳定同位素组成。雪和大量降雨（≥4 mm）样品δ2H和δ18O值的线性回归分别得到δ2H = 7.72 × δ18O + 5.02和δ2H = 7.50 δ18O + 0.27的相关方程。相比之下，少量降雨样品(≤4 mm) δ2H和δ18O值之间的相关方程表明，随着降水的减少，斜率和截距值逐渐降低。同位素数据与当地温度、相对湿度和降水量等参数的相关性证明，少量雨样在从云底下降到地面的过程中经历了二次蒸发，同时伴随着质量依赖的同位素分馏。因此，卡尔加里降水的同位素组成，可能也包括北美大平原地区的其他地点，都受到云下次生效应的影响。由于5年观测期间约有1 / 3的降水事件是累积小于4 mm的降水，云下次生效应导致使用量加权月平均δ2H和δ18O值计算的局地降水线斜率和截距值（δ2H=7.43 × δ18O-2.79）比仅基于同位素资料计算的雪和大降水事件的方程略有降低。利用单个样品（非数量加权）的δ2H和δ18O值计算的相关方程（δ2H = 7.11 δ18O-11.60）得到了由于少量降雨样品的显著影响而导致的最低斜率和截距值。
Stable isotope compositions of hydrogen (δ2H) and oxygen (δ18O) for short-term precipitation samples (n = 436) collected at Calgary, Alberta, Canada, between January 1997 and December 2001 were determined. Linear regression between δ2H and δ18O values of snow and large amount rain samples (≥4 mm) yielded correlation equations δ2H = 7.72 × δ18O + 5.02 and δ2H = 7.50 δ18O + 0.27, respectively. In contrast, correlation equations between δ2H and δ18O values for small amount rain samples (≤4 mm) resulted in progressively lower slope and intercept values with decreasing precipitation. Correlations of isotope data with parameters such as local temperature, relative humidity, and precipitation amount provided evidence that small amount rain samples undergo secondary evaporation accompanied by mass dependent isotope fractionation during their descent from the cloud base to the ground. Hence, the isotope compositions of precipitation at Calgary, and likely also at other locations in the North American Great Plains region, are influenced by below-cloud secondary effects. Since about one-third of the precipitation events in the 5-yr observation period were rain samples accumulating less than 4 mm, below-cloud secondary effects resulted in a slight decrease of slope and intercept values of the local meteoricwater line (δ2H=7.43 × δ18O-2.79) calculated using amount-weighted monthly average δ2H and δ18O values compared to equations based on isotope data for snow and large amount rain events only. The correlation equation (δ2H = 7.11 δ18O-11.60) calculated using δ2H and δ18O values of individual samples (non-amount weighted) yielded the lowest slope and intercept values caused by the significant influence of small amount rain samples.