Methane, ethane, and propane production in Greenland ice core samples and a first isotopic characterization of excess methane
Methane, ethane, and propane production in Greenland ice core samples and a first isotopic characterization of excess methane
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DOI：
10.5194/cp-19-999-2023
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发表时间：
2023-05
影响因子：
4.3
通讯作者：
Michaela Mühl;J. Schmitt;B. Seth;James E. Lee;J. Edwards;E. Brook;T. Blunier;H. Fischer
中科院分区：
文献类型：
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作者：
Michaela Mühl;J. Schmitt;B. Seth;James E. Lee;J. Edwards;E. Brook;T. Blunier;H. Fischer
抽象的。极地冰中捕获的空气提供了过去大气成分的独特记录，从甲烷（CH4）等主要温室气体到乙烷（C2H6）和丙烷（C3H8）等短命微量气体。最近，通过比较使用不同提取方法获得的 CH4 记录，发现格陵兰岛冰中末次冰期的 CH4 浓度存在差异。在离散测量的富含灰尘的冰芯部分中检测到甲烷含量升高，表明该过程对熔体提取技术敏感。为了阐明潜在机制，我们进行了有针对性的实验，并分析了 12 至 42 kyr 时间间隔内的甲烷以及短链烷烃乙烷和丙烷的样品。在这里，我们报告了烷烃浓度升高的发现，其与冰样本中矿物粉尘的量呈线性比例。烷烃的产生发生在经典湿法萃取技术的熔融萃取步骤中，并且在尘埃冰样品中达到 14 至 91 ppb 的 CH4 过量。我们首次记录了过量甲烷、乙烷和丙烷的共同生产，观测到的乙烷和丙烷浓度至少超过其过去的大气背景值的 10 倍。与生产量无关，过量烷烃以大约 14:2:1 的固定摩尔比产生，表明它们具有共同的来源。测得过量甲烷的碳同位素特征为(-47.0±2.9) ‰，其氘同位素特征为(-326±57) ‰。通过过量烷烃的联产率和过量甲烷的同位素组成，我们建立了指纹，使我们能够限制潜在的形成过程。该指纹与微生物起源不相符。此外，产热气体在输送到格陵兰岛的尘埃颗粒上的吸附-解吸过程似乎不太可能发生。相反，烷烃模式似乎表明土壤和植物叶子中发现的有机物的非生物分解。
Abstract. Air trapped in polar ice provides unique records of the past atmospheric composition ranging from key greenhouse gases such as methane (CH4) to short-lived trace gases like ethane (C2H6) and propane (C3H8). Recently, the comparison of CH4 records obtained using different extraction methods revealed disagreements in the CH4 concentration for the last glacial in Greenland ice. Elevated methane levels were detected in dust-rich ice core sections measured discretely, pointing to a process sensitive to the melt extraction technique. To shed light on the underlying mechanism, we performed targeted experiments and analyzed samples for methane and the short-chain alkanes ethane and propane covering the time interval from 12 to 42 kyr. Here, we report our findings of these elevated alkane concentrations, which scale linearly with the amount of mineral dust within the ice samples. The alkane production happens during the melt extraction step of the classic wet-extraction technique and reaches 14 to 91 ppb of CH4 excess in dusty ice samples. We document for the first time a co-production of excess methane, ethane, and propane, with the observed concentrations for ethane and propane exceeding their past atmospheric background at least by a factor of 10. Independent of the produced amounts, excess alkanes were produced in a fixed molar ratio of approximately 14:2:1, indicating a shared origin. The measured carbon isotopic signature of excess methane is (-47.0±2.9) ‰ and its deuterium isotopic signature is (-326±57) ‰. With the co-production ratios of excess alkanes and the isotopic composition of excess methane we established a fingerprint that allows us to constrain potential formation processes. This fingerprint is not in line with a microbial origin. Moreover, an adsorption–desorption process of thermogenic gas on dust particles transported to Greenland does not appear very likely. Instead, the alkane pattern appears to be indicative of abiotic decomposition of organic matter as found in soils and plant leaves.