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Sowers & Jubenville 2000
Sowers, T. and Jubenville, J. (2000). A modified extraction technique for liberating occluded gases from ice cores. Journal of Geophysical Research 105: doi: 10.1029/2000JD900335. issn: 0148-0227.

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 existing extraction procedures. Overall external precision for Δ O2/N2, Δ18O of O2, and Δ15N of N2 analyses is ¿2.1%, ¿0.074%, and ¿0.045%, respectively. Variable Δ O2/N2 results from ice which is either completely bubbly or clathrated are in good agreement with previous measurements. Variable ΔO2/N2 results from Greenland Ice Sheet Project (GISP) II ice samples spanning the clathrate formation region (1000--1500 m) are markedly different 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 region combined with a 21% difference in our extraction efficiency for bubbly versus clathrated 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 uncertainties 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 Brooket al. <1996> CH4 record from the same period. ¿ 2000 American Geophysical Union

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Abstract

Keywords
Atmospheric Composition and Structure, Evolution of the atmosphere, Atmospheric Composition and Structure, Instruments and techniques, Geochemistry, Isotopic composition/chemistry, Global Change, Biogeochemical processes
Journal
Journal of Geophysical Research
http://www.agu.org/journals/jb/
Publisher
American Geophysical Union
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