Continuous and simultaneous measurement of triple-oxygen and hydrogen isotopes of liquid and vapor during evaporation experiments
Continuous and simultaneous measurement of triple-oxygen and hydrogen isotopes of liquid and vapor during evaporation experiments
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蒸发实验期间连续同时测量液体和蒸汽的三氧和氢同位素
DOI：
10.1002/rcm.9078
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发表时间：
2021
影响因子：
2
通讯作者：
Brady M
中科院分区：
文献类型：
--
作者：
Brady M
氧、氢同位素是研究现代和过去水文循环的重要工具。先前的蒸发实验使用液体和/或蒸气的间歇测量，或者没有测量水的所有同位素。在这里，我们描述了一种蒸发实验系统，该系统允许使用腔衰荡激光光谱（CRDS）以高精度同时和近连续地测量液体和水蒸气的所有同位素体。方法蒸发液体通过注射泵从封闭的再循环回路周期性地采样，该注射泵向蒸发器输送恒定的水供应，实现20，000 ppmV H2O（±132，1σ）。蒸汽直接从蒸发室取样。结果对于液体测量，Allan方差分析表明，氧同位素的最佳数据收集窗口为34 min，氢同位素的最佳数据收集窗口为27 min。δ 17 O、δ 18 O和δ 2 H的平均标准误差分别为±0.0081‰、±0.0081‰和±0.019‰。对于导出的参数17 O-过量和d-过量，平均值的标准误差分别为5.8/mcg和0.07‰。对于气相，所有同位素体的12.5 min数据窗口导致δ 17 O值的平均标准误差为±0.012‰，δ 18 O值的平均标准误差为±0.011‰，δ 2 H值的平均标准误差为±0.023‰。对于导出的参数，平均值的标准误差为9.2每微克（17 O-过量）和0.099‰（d-过量）。这些测量结果的斜率ln（δ 17 O + 1）与ln（δ 18 O + 1）和ln（δ 2 H + 1）与ln（δ 18 O + 1）的95%置信限始终很窄。该方法的应用将有助于验证蒸发的理论模型和进行实验，以模拟自然系统中的蒸发和同位素平衡。
RationaleOxygen and hydrogen isotopes are important tools for studying the modern and past hydrological cycle. Previous evaporation experiments used episodic measurement of liquid and/or vapor or did not measure all isotopologues of water. Here, we describe an evaporation experimental system that allows all isotopologues of liquid and water vapor to be measured simultaneously and near‐continuously at high precision using cavity ring‐down laser spectroscopy (CRDS).MethodsEvaporating liquid is periodically sampled from a closed recirculating loop by a syringe pump that delivers a constant supply of water to the vaporizer, achieving a water vapor concentration of 20,000 ppmV H2O (±132, 1σ). Vapor is sampled directly from the evaporation chamber. Isotope ratios are measured simultaneously with a Picarro L2140‐iCRDS instrument.ResultsFor liquid measurements, Allan variance analysis indicates an optimum data collection window of 34 min for oxygen isotopes and 27 min for hydrogen isotopes. During these periods, the mean standard error is ±0.0081‰ for δ17O values, ±0.0081‰ for δ18O values, and ±0.019‰ for δ2H values. For the derived parameters17O‐excess and d‐excess, the standard error of the mean is 5.8 per meg and 0.07‰, respectively. For the vapor phase a 12.5 min data window for all isotopologues results in a mean standard error of ±0.012‰ for δ17O values, ±0.011‰ for δ18O values, and ±0.023‰ for δ2H values. For the derived parameters, the standard error of the mean is 9.2 per meg for17O‐excess and 0.099‰ for d‐excess. These measurements result in consistently narrow 95% confidence limits for the slopes of ln(δ17O + 1) vs ln(δ18O + 1) and ln(δ2H + 1) vs ln(δ18O + 1).ConclusionsThe experimental method permits measurement of fractionation of triple‐oxygen and hydrogen isotopes of evaporating water under varying controlled conditions at high precision. Application of this method will be useful for testing theoretical models of evaporation and conducting experiments to simulate evaporation and isotopic equilibration in natural systems.