Department of Earth System Science

Seven short-lived atmospheric trace gases were measured in 25 ice core samples from Summit, Greenland. Samples were selected from contemporaneous sections of fluid- and dry-drilled ice cores to examine what effects using n-butyl acetate as the drill fluid would have on the measurements. The gases include three light alkanes, C₂H₆, C₃H₆, and n-C₄H₁₀; two methyl halides, CH₃Cl and CH₃Br; and two sulfur compounds, OCS and CS₂, with gas ages from 125 to 325 years before present. Alkane levels are comparable to measurements in modern Arctic air, although C₂H₆ exhibits greater variability than expected compared with C₃H₆ and n-C₄H₁₀. These results are not consistent with the idea that the alkanes are primarily of anthropogenic origin, suggesting that the ice cores may not truly record a paleoatmospheric signal with respect to these gases. The CH₃Br results are consistent with previous observations of “excess” CH₃Br in Greenland firn air. In situ production processes appear to overwhelm the paleoatmospheric signal of this gas. CH₃Cl exhibits the same effect to a lesser extent. OCS levels are similar to those in Antarctic ice cores and appear to reflect paleoatmospheric levels. CS₂ results are similar to the limited database of modern atmospheric measurements. Only C₃H₈ and n-C₄H₁₀ exhibit clear evidence of contamination because of the presence of the drill fluid. The results indicate that it is possible to analyze many trace gases in fluid- and dry-drilled ice samples. However, it appears that in situ production may significantly alter the levels of some trace gases in Greenland ice cores.