Online technique for isotope and mixing ratios of CH 4 , N 2 O, Xe and mixing ratios of organic trace gases on a single ice core sample
Online technique for isotope and mixing ratios of CH 4 , N 2 O, Xe and mixing ratios of organic trace gases on a single ice core sample
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单一冰芯样品上CH 4 、N 2 O、Xe同位素和混合比以及有机痕量气体混合比的在线技术
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发表时间：
2014
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通讯作者：
H. Fischer
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作者：
J. Schmitt;B. Seth;M. Bock;H. Fischer
抽象的。包含微量气体物种的冷杉和极地冰芯为研究过去大气和陆地/海洋源区的变化提供了独特的档案。在这里，我们提出了一种用于冰芯和空气样本的新在线技术，用于测量单个样本上的一系列同位素比率和痕量气体种类的混合比率。同位素比是根据甲烷、一氧化二氮和氙测定的，冰芯样品的再现性为：δ13C-CH4 为 0.15 ‰，δ15N-N2O 为 0.22 ‰，δ18O-N2O 为 0.34 ‰，δ136Xe 为每质量差 0.05 ‰（对于冰川冰的典型浓度）。混合比根据甲烷、一氧化二氮、氙、乙烷、丙烷、氯甲烷和二氯二氟甲烷测定，重现性为 CH4 7 ppb、N2O 3 ppb、C2H6 70 ppt、C3H8 70 ppt、CH3Cl 20 ppt 和 CCl2F2 2 ppt。然而，考虑到南极冰样品的测量值，C2H6 和 C3H8 的空白贡献较大。该系统由真空提取装置、预浓缩装置和与同位素比质谱仪耦合的气相色谱仪组成。 CH4 在检测前会燃烧成 CO2，而我们则绕过所有其他物种的烘箱。该高度自动化的系统仅使用约 160 克冰，相当于约 16 毫升空气，这比以前的方法要少。在单个冰样本上测量这一大组参数是新的，并且是理解通常不一起测量的参数的相位关系的关键。多参数数据集也是了解冰中有机物质原位生产过程的关键，这是在许多有机痕量气体中观察到的一个关键问题。新颖的是使用双电荷 Xe 离子测定氙同位素比率。 δ136Xe 所获得的精度适合校正重力扩散效应的同位素比率和混合比率，其优点是该信息来自同一样本。最后，Xe 混合比 δXe/空气的异常可用于检测熔体层。
Abstract. Firn and polar ice cores enclosing trace gas species offer a unique archive to study changes in the past atmosphere and in terrestrial/marine source regions. Here we present a new online technique for ice core and air samples to measure a suite of isotope ratios and mixing ratios of trace gas species on a single sample. Isotope ratios are determined on methane, nitrous oxide and xenon with reproducibilities for ice core samples of 0.15‰ for δ13C–CH4, 0.22‰ for δ15N–N2O, 0.34‰ for δ18O–N2O, and 0.05‰ per mass difference for δ136Xe for typical concentrations of glacial ice. Mixing ratios are determined on methane, nitrous oxide, xenon, ethane, propane, methyl chloride and dichlorodifluoromethane with reproducibilities of 7 ppb for CH4, 3 ppb for N2O, 70 ppt for C2H6, 70 ppt for C3H8, 20 ppt for CH3Cl, and 2 ppt for CCl2F2. However, the blank contribution for C2H6 and C3H8 is large in view of the measured values for Antarctic ice samples. The system consists of a vacuum extraction device, a preconcentration unit and a gas chromatograph coupled to an isotope ratio mass spectrometer. CH4 is combusted to CO2 prior to detection while we bypass the oven for all other species. The highly automated system uses only ~ 160 g of ice, equivalent to ~ 16 mL air, which is less than previous methods. The measurement of this large suite of parameters on a single ice sample is new and key to understanding phase relationships of parameters which are usually not measured together. A multi-parameter data set is also key to understand in situ production processes of organic species in the ice, a critical issue observed in many organic trace gases. Novel is the determination of xenon isotope ratios using doubly charged Xe ions. The attained precision for δ136Xe is suitable to correct the isotopic ratios and mixing ratios for gravitational firn diffusion effects, with the benefit that this information is derived from the same sample. Lastly, anomalies in the Xe mixing ratio, δXe/air, can be used to detect melt layers.