A modified extraction technique for liberating occluded gases from ice cores

Todd Sowers

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16 Scopus citations

Abstract

We have developed a new dry extraction technique to extract air from large pieces of glacial ice. The primary reason for developing this technique was to be able to perform a single extraction and measure a single sample of air from an ice core sample for as many atmospheric constituents as possible. The procedure is modeled after the dry extraction - "cheese grater" design of Etheridge et al. [1988]. Extracted air samples are analyzed for the elemental and isotopic composition of O2 and N2 as well as the CH4 concentration. Extensive experimental work to determine the integrity of the extraction procedure yielded blank values and external precision which are comparable with exist-ing extraction procedures. Overall external precision for δO2/N2, δ18O of O2, and δ15N of N2 analyses is ±2.l‰, ±0.074‰, and ±0.045‰, respectively. Variable δO2/N2 results from ice which is either completely bubbly or clathrated are in good agreement with pre-vious measurements. Variable ΔO2/N2 results from Greenland Ice Sheet Project (GISP) II ice samples spanning the clathrate formation region (1000-1500 m) are markedly differ-ent from previous results obtained with a "wet" extraction procedure. We attribute the differences to variable O2/N2 ratios in bubbles and clathrates in the clathrate formation re-gion combined with a 21% difference in our extraction efficiency for bubbly versus clath-rated ice. The overall uncertainty and blank value for CH4 measurements are ±19 ppb and 16 ppb, respectively. CH4 concentrations for ice between 115 and 140 meters below the surface (mbs) from the GISP II ice core appear to be 4.3% higher than the average value measured by five other laboratories. We attribute our elevated values to uncertain-ties in the actual concentration of our working standard and small differences in the CH4 concentration of the liberated air relative to the total air trapped in ice. Our corrected CH4 data spanning the last 25 kyr are indistinguishable from the Brook et al. [1996] CH4 record from the same period.

Original languageEnglish (US)
Article number2000JD900335
Pages (from-to)29155-29164
Number of pages10
JournalJournal of Geophysical Research Atmospheres
Volume105
Issue numberD23
DOIs
StatePublished - 2000

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

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