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

• Main Authors: Petrenko, Vasilii V., Severinghaus, Jeffrey P., Brook, Edward J., Muhle, Jens, Headly, Melissa, Harth, Christina M., Schaefer, Hinrich, Reeh, Niels, Weiss, Ray F., Lowe, Dave, Smith, Andrew M.
• Format: Article in Journal/Newspaper
• Language: English; unknown
• Published: International Glaciological Society
• Subjects: Greenland
• Online Access: https://ir.library.oregonstate.edu/concern/articles/rr172000p

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/