Ice-vapor equilibrium fractionation factor of hydrogen and oxygen isotopes: experimental investigations and implications for stable water isotope studies.
Ice-vapor equilibrium fractionation factor of hydrogen and oxygen isotopes: experimental investigations and implications for stable water isotope studies.
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DOI：
10.1002/rcm.6668
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发表时间：
2013-10
期刊：
影响因子：
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通讯作者：
M. D. Ellehoj;H. Steen‐Larsen;H. Steen‐Larsen;S. Johnsen;M. Madsen
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文献类型：
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作者：
M. D. Ellehoj;H. Steen‐Larsen;H. Steen‐Larsen;S. Johnsen;M. Madsen
理论基础平衡分馏因子控制着水的相变过程中同位素组成的相对变化。40多年前发表的常用结果仅限于最低温度为-33°C。这限制了在寒冷地区的可靠性。随着最近仪器的发展，现在可以测试早期结果的准确性，并扩展温度范围。方法采用Picarro腔衰荡光谱仪和TC/EA IRMS系统，在0 ~ -40°C范围内对冰-气平衡分馏因子α进行了新颖的测量。使用这两种系统可以连续监测系统的平衡状态以及测试再现性。结果实验结果表明，δ(2) H和δ(18) O值的分馏因子与温度有关，符合平衡分馏理论。得到了分馏系数随温度变化的表达式：ln(αδ2H)=0.2133-(203.10/T+(48888/T2) ln(αδ18O)=0.0831-(49.192/T)+(8312.5/T2)。与以往的实验相比，δ(2) H的α值明显增大，而δ(18) O的α值在-20℃以下较大，在-20℃以上略小。利用α的新值，瑞利蒸馏模型显示格陵兰岛每年氘过量信号的大小和形状都发生了显著变化。这强调了定义明确的α值对于准确研究水文循环过程的重要性，并强调了本工作结果与早期工作之间差异的重要性。
RATIONALE The equilibrium fractionation factors govern the relative change in the isotopic composition during phase transitions of water. The commonly used results, which were published more than 40 years ago, are limited to a minimum temperature of -33°C. This limits the reliability in cold regions. With recent instrumental developments it is now possible to test the accuracy of the earlier results as well as extend the temperature range. METHODS Novel measurements were made of the ice-vapor equilibrium fractionation factor α between 0°C and -40°C, from a unique experimental setup using both a Picarro cavity ringdown spectrometer and a TC/EA IRMS system. Using both systems allows for continuous monitoring of the equilibrium state of the system as well as testing for reproducibility. RESULTS The results of the experiments show fractionation factors for δ(2) H and δ(18) O values, with a temperature dependency in accordance with theory for equilibrium fractionation. We obtain the following expressions for the temperature dependency of the fractionation coefficients: ln(αδ2H)=0.2133-(203.10/T+(48888/T2 ln(αδ18O)=0.0831-(49.192/T)+(8312.5/T2). Compared with previous experimental work, a significantly larger α for δ(2) H is obtained while, for δ(18) O, α is larger for temperatures below -20°C and slightly lower for temperatures above this. CONCLUSIONS Using the new values for α, a Rayleigh distillation model shows significant changes in both magnitude and shape of an annual deuterium excess signal in Greenland. This emphasizes the importance of a well-defined value of α for accurate studies of the processes in the hydrological cycle and underlines the significance of the differences between the results of this work and earlier work.