Historical N₂O record from ice cores at Crête, Camp Century, and Byrd Station

M.A.K. Khalil, R.A. Rasmussen

Oregon Graduate Institute of Science and Technology, Portland, Oregon 97291, U.S.A.

Period of Record

3100-150 years BP

Methods

Samples from the Crête and Camp Century (Greenland) ice cores and from the Byrd Station (Antarctica) ice core were obtained from the National Science Foundation ice core facility at the State University of New York at Buffalo. Core samples were typically about 15 cm long and were kept frozen until analysis. The samples were prepared by scraping off the outer 1–3 cm to avoid contamination and cutting the samples into two or three pieces for replication of the measurements. Each replicate was sealed in an electropolished stainless steel cylinder, which was then flushed ten times with nitrogen-free helium and pressurized to 1000 torr. Afterwards the cylinders were placed in a warm water bath to melt the ice and release the trapped air bubbles. The air in the headspace of the cylinders was then sampled, and the concentrations of N₂O, CH₄, N₂, O₂, and CFCl₃ were measured.

The gas concentrations were measured by established gas-chromatographic techniques. Determinations of N₂O were made by electron capture gas chromatography (EC-GC) using a Perkin-Elmer 3920B instrument. Measurements of N₂ and O₂ were used to calculate the dilution ratio of ice core air in the helium-filled cylinders. The presence of CFCl₃ (CFC-11), an anthropogenic fluorocarbon not present before ca. 1930, was used as an index of contamination of the ice core air. For each ice core sample, the concentration of N₂O in the extracted air was calculated from the chromatographic measurement, the dilution ratio in the cylinder, and an estimate of the equilibrium partitioning of N₂O between the air and the meltwater. For further details, see Khalil and Rasmussen (1988) and Rasmussen and Khalil (1984).

Crête                                         Byrd Station
Greenland                                     Antarctica
77°11' N, 61°09' W                            79°59' S, 120°01' W

Crête, Camp Century, and Byrd Station Trends

Crête, Camp Century, and Byrd Station References

CITE AS: Khalil, M.A.K. and R.A. Rasmussen. 1994. Historical N₂O record from ice cores at Crête, Camp Century, and Byrd Station. In Trends: 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)