A New Method for Analyzing ¹⁴C of Methane in Ancient Air Extracted from Glacial Ice Public Deposited

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  • A New Method for Analyzing 14C of Methane in Ancient Air Extracted from Glacial Ice
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  • We present a new method developed for measuring radiocarbon of methane (¹⁴CH₄) in ancient air samples extracted from glacial ice and dating 11,000–15,000 calendar years before present. The small size (~20 μg CH₄ carbon), low CH₄ concentrations ([CH₄], 400–800 parts per billion [ppb]), high carbon monoxide concentrations ([CO]), and low ¹⁴C activity of the samples created unusually high risks of contamination by extraneous carbon. Up to 2500 ppb CO in the air samples was quantitatively removed using the Sofnocat reagent. ¹⁴C procedural blanks were greatly reduced through the construction of a new CH₄ conversion line utilizing platinized quartz wool for CH₄ combustion and the use of an ultra-high-purity iron catalyst for graphitization. The amount and ¹⁴C activity of extraneous carbon added in the new CH₄ conversion line were determined to be 0.23 ± 0.16 μg and 23.57 ± 16.22 pMC, respectively. The amount of modern (100 pMC) carbon added during the graphitization step has been reduced to 0.03 μg. The overall procedural blank for all stages of sample handling was 0.75 ± 0.38 pMC for ~20-μg, ¹⁴C-free air samples with [CH₄] of 500 ppb. Duration of the graphitization reactions for small (<25 μg C) samples was greatly reduced and reaction yields improved through more efficient water vapor trapping and the use of a new iron catalyst with higher surface area. ¹⁴C corrections for each step of sample handling have been determined. The resulting overall ¹⁴CH₄ uncertainties for the ancient air samples are ~1.0 pMC.
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  • Petrenko, V. V., Smith, A. M., Brailsford, G., Riedel, K., Hua, Q., Lowe, D., & Brook, E. J. A new method for analyzing ¹⁴C of methane in ancient air extracted from glacial ice [Electronic version]. Radiocarbon, 50(1), 53-79.
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  • description.provenance : Submitted by Deanne Bruner (deanne.bruner@oregonstate.edu) on 2012-02-07T19:43:39Z No. of bitstreams: 1 BrookEdwardCEOASNewMethodAnalyzing.pdf: 199506 bytes, checksum: a04452432ad36161efeaecfdecb415e3 (MD5)
  • description.provenance : Made available in DSpace on 2012-02-07T19:43:39Z (GMT). No. of bitstreams: 1 BrookEdwardCEOASNewMethodAnalyzing.pdf: 199506 bytes, checksum: a04452432ad36161efeaecfdecb415e3 (MD5) Previous issue date: 2008

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