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Instruments and Methods: A novel method for obtaining very large ancient air samples from ablating glacial ice for analyses of methane radiocarbon

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https://ir.library.oregonstate.edu/concern/articles/rr172000p

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  • We present techniques for obtaining large (∼100 L STP) samples of ancient air for analysis of ¹⁴C of methane (¹⁴CH₄) and other trace constituents. Paleoatmospheric ¹⁴CH₄ measurements should constrain the fossil fraction of past methane budgets, as well as provide a definitive test of methane clathrate involvement in large and rapid methane concentration ([CH₄]) increases that accompanied rapid warming events during the last deglaciation. Air dating to the Younger Dryas-Preboreal and Oldest Dryas-Bølling abrupt climatic transitions was obtained by melt extraction from old glacial ice outcropping at an ablation margin in West Greenland. The outcropping ice and occluded air were dated using a combination of δ¹⁵N of N₂, δ¹⁸O of O₂, δ¹⁸O[subscript ice] and [CH₄] measurements. The [CH₄] blank of the melt extractions was <4 ppb. Measurements of δ¹⁸O and δ¹⁵N indicated no significant gas isotopic fractionation from handling. Measured Ar/N₂, CFC-11 and CFC-12 in the samples indicated no significant contamination from ambient air. Ar/N₂, Kr/Ar and Xe/Ar ratios in the samples were used to quantify effects of gas dissolution during the melt extractions and correct the sample [CH₄]. Corrected [CH₄] is elevated over expected values by up to 132 ppb for most samples, suggesting some in situ CH₄ production in ice at this site.
  • This is the publisher’s final pdf. The published article is copyrighted by the International Glaciological Society and can be found at: http://www.igsoc.org/journal/
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  • Petrenko, V. V., Severinghaus, J. P., Brook, E. J., Muhle, J., Headly, M., Harth, C. M., ... Smith, A. M. (2008, March). Instruments and methods: A novel method for obtaining very large ancient air samples from ablating glacial ice for analyses of methane radiocarbon. Journal of Glaciology, 54(185), 233-244. doi:10.3189/002214308784886135
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  • 54
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  • 185
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  • This work was supported by US National Science Foundation grants OPP 02-21470 (to J.P.S.) and OPP 02-21410 (to E.J.B.), a Packard Fellowship (to J.P.S.) and American Chemical Society Petroleum Research Fund grant No. 42551-AC2 (to E.J.B.). We thank the Danish Polar Center and Greenland Home Rule for permission to carry out this research.
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