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首页> 外文期刊>Geochimica et Cosmochimica Acta: Journal of the Geochemical Society and the Meteoritical Society >Measurements of C-14 in ancient ice from Taylor Glacier, Antarctica constrain in situ cosmogenic (CH4)-C-14 and (CO)-C-14 production rates
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Measurements of C-14 in ancient ice from Taylor Glacier, Antarctica constrain in situ cosmogenic (CH4)-C-14 and (CO)-C-14 production rates

机译：南极泰勒冰川的古冰中C-14的测量限制了原位宇宙成因（CH4）-C-14和（CO）-C-14的生产率

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Carbon-14 (C-14) is incorporated into glacial ice by trapping of atmospheric gases as well as direct near-surface in situ cosmogenic production. C-14 of trapped methane ((CH4)-C-14) is a powerful tracer for past CH4 emissions from "old" carbon sources such as permafrost and marine CH4 clathrates. C-14 in trapped carbon dioxide ((CO2)-C-14) can be used for absolute dating of ice cores. In situ produced cosmogenic C-14 in carbon monoxide ((CO)-C-14) can potentially be used to reconstruct the past cosmic ray flux and past solar activity. Unfortunately, the trapped atmospheric and in situ cosmogenic components of C-14 in glacial ice are difficult to disentangle and a thorough understanding of the in situ cosmogenic component is needed in order to extract useful information from ice core C-14. We analyzed very large (approximate to 1000 kg) ice samples in the 2.26-19.53 m depth range from the ablation zone of Taylor Glacier, Antarctica, to study in situ cosmogenic production of (CH4)-C-14 and (CO)-C-14. All sampled ice is >50 ka in age, allowing for the assumption that most of the measured C-14 originates from recent in situ cosmogenic production as ancient ice is brought to the surface via ablation. Our results place the first constraints on cosmogenic (CH4)-C-14 production rates and improve on prior estimates of (CO)-C-14 production rates in ice. We find a constant (CH4)-C-14/(CO)-C-14 production ratio (0.0076 +/- 0.0003) for samples deeper than 3 m, which allows the use of (CO)-C-14 for correcting the (CH4)-C-14 signals for the in situ cosmogenic component. Our results also provide the first unambiguous confirmation of C-14 production by fast muons in a natural setting (ice or rock) and suggest that the C-14 production rates in ice commonly used in the literature may be too high. (C) 2016 Elsevier Ltd. All rights reserved.
机译：碳14（C-14）通过捕集大气中的气体以及直接在近地表原地进行宇宙成因生产而结合到冰川冰中。捕获的甲烷C-14（（CH4）-C-14）是强大的示踪剂，可用于记录多年冻土和海洋CH4包合物等“旧”碳源中过去的CH4排放。捕获的二氧化碳中的C-14（（CO2）-C-14）可用于冰芯的绝对年代测定。一氧化碳（（CO）-C-14）中原位产生的宇宙成因C-14可以潜在地用于重建过去的宇宙射线通量和过去的太阳活动。不幸的是，被困在冰川冰中的C-14的大气和原位宇宙成因成分难以解开，因此需要对原位宇宙成因成分有透彻的了解，以便从冰芯C-14中提取有用的信息。我们分析了南极泰勒冰川消融区2.26-19.53 m深度范围内的巨大冰样品（约1000 kg），以研究（CH4）-C-14和（CO）-C的原地成因生产。 -14。所有采样冰的年龄都大于50 ka，这是假设一个事实，即大多数的C-14都来自最近的原位宇宙成因生产，因为古老的冰通过消融被带到了地表。我们的结果将第一个约束因素限制在了成冰（CH4）-C-14生产率上，并改善了先前对冰中（CO）-C-14生产率的估计。对于大于3 m的样品，我们发现（CH4）-C-14 /（CO）-C-14的恒定生成比率（0.0076 +/- 0.0003），这允许使用（CO）-C-14校正（CH4）-C-14用于原位宇宙成因信号。我们的结果还首次明确地证实了自然环境（冰或岩石）中的快速介子对C-14的生产，并暗示文献中常用的冰中C-14的生产速度可能太高。 （C）2016 Elsevier Ltd.保留所有权利。

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