In:
Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 105, No. D23 ( 2000-12-16), p. 29155-29164
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 O 2 and N 2 as well as the CH 4 concentration. Extensive experimental work to determine the integrity of the extraction procedure yielded blank values and external precision which are comparable with exiting extraction procedures. Overall external precision for δ O 2 /N 2 , δ 18 O of O 2 , and δ 15 of N 2 analyses is ±2.1‰, ±0.074‰, and ±0.045‰, respectively. Variable δ O 2 /N 2 results from ice which is either completely bubbly or clathrated are in good agreement with previous measurements. Variable δ O 2 /N 2 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 δ O 2 /N 2 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 CH 4 measurements are ±19 ppb and 16 ppb, respectively. CH 4 concentrations for ice between 115 and 140 meters below the surface (mbs) from the GISPII 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 CH 4 concentration of the liberated air relative to the total air trapped in ice. Our corrected CH 4 data spanning the last 25 kyr are indistinguishable from the Brook et al. (1996) CH 4 record from the same period.
Type of Medium:
Online Resource
ISSN:
0148-0227
DOI:
10.1029/2000JD900335
Language:
English
Publisher:
American Geophysical Union (AGU)
Publication Date:
2000
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