Historical N₂O record from the "BHD" ice core at Law Dome

D.M. Etheridge, G.I. Pearman, F. de Silva

Commonwealth Scientific and Industrial Research Organisation, Division of Atmospheric Research, Aspendale, Victoria 3195, Australia

Period of Record

1520-1966

Methods

The 473-m-long ice core designated "BHD" was thermally drilled from the summit of Law Dome, Antarctica, by the 1977 Australian National Antarctic Research Expedition. Air bubbles from various times in the past were trapped in ice below the air-occlusion zone (~70 m for the BHD core). The atmospheric composition (CH₄, CO₂, and N₂O) of the trapped air in core samples has been analyzed. Segments of the core were selected carefully to ensure that the sample composition was not altered by either microfracturing or melting after the coring process. The core segments were placed in a stainless steel vacuum apparatus and milled into small chips to release the entrapped air. Air samples were then dried, collected in a liquid helium cold finger apparatus, and analyzed for N₂O through the use of a gas chromatograph equipped with an electron-capture detector. Two chlorofluorocarbons, CCl₃F and CCl₂F₂, were also measured, in order to check the quality of the ice core and the extraction process. In addition, air samples of known composition and comparative volume were used to test the effect of the extraction and analysis procedures on the ice core gas samples.

Calibration gases were obtained from stainless steel tanks filled cryogenically with uncontaminated maritime air at the Australian Maritime Observatory at Cape Grim. Concentrations of the calibration gases were determined by comparison with N₂O standards obtained from the Oregon Graduate Center.

Further details on the methods of sampling and analysis are given in Etheridge et al. (1988).

Law Dome
Antarctic
66° 43' S, 112°50' E
1375 m above MSL

Law Dome Trends

Law Dome References

CITE AS: Etheridge, D.M., G.I. Pearman, and F. de Silva. 1994. Historical N₂O record from the "BHD" ice core at Law Dome. In T.A. Boden, D.P. Kaiser, R.J. Sepanski, and F.W. Stoss (eds.), Trends '93: A Compendium of Data on Global Change. ORNL/CDIAC-65. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A.

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Date created 12/06/96 (jaw)