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The 14 C “bomb spike” determines the age spread and age of CO 2 in Law Dome firn and ice
Author(s) -
Levchenko V. A.,
Francey R. J.,
Etheridge D. M.,
Tuniz C.,
Head J.,
Morgan V. I.,
Lawson E.,
Jacobsen G.
Publication year - 1996
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/96gl03156
Subject(s) - firn , radiocarbon dating , dome (geology) , ice core , geology , snow , atmospheric sciences , glacier , accelerator mass spectrometry , atmosphere (unit) , mineralogy , climatology , meteorology , geomorphology , physics , paleontology
We report a precise, model‐independent determination of the age and age spread of CO 2 in air trapped in ice. A large pulse of atmospheric radiocarbon, generated in the atmosphere by nuclear tests, peaked in the early‐to‐mid 1960's. We measure the profile of the radiocarbon “bomb spike” in firn air and ice bubbles from high snow‐accumulation sites drilled in 1987 and 1993 on Law Dome, East Antarctica, by employing high precision AMS (Accelerator Mass Spectrometry). Large 14 C atmospheric growth rates and a high signal‐to‐noise ratio lead to a direct and precise determination of the CO 2 age and age‐spread in the ice. A least‐squares comparison with the atmospheric history gives a mean CO 2 age of 8.9±0.5 years at the bottom of the firn (where vertical gas diffusion ceases) with an age spread in the ice (full width of a moving average smoothing window) of 12.5±1.5 years. These results confirm the possibility of examining decadal trace gas variations prior to direct instrumental measurements.