Reports

Carbon-14 in Methane Sources and in Atmospheric Methane: The Contribution from Fossil Carbon

Science  21 Jul 1989:
Vol. 245, Issue 4915, pp. 286-290
DOI: 10.1126/science.245.4915.286

Abstract

Measurements of carbon-14 in small samples of methane from major biogenic sources, from biomass burning, and in "clean air" samples from both the Northern and Southern hemispheres reveal that methane from ruminants contains contemporary carbon, whereas that from wetlands, pat bogs, rice fields, and tundra is somewhat, depleted in carbon-14. Atmospheric 14GH4 seems to have increased from 1986 to 1987, and levels at the end of 1987 were 123.3 ± 0.8 percent modern carbon (pMC) in the Northern Hemisphere and 120.0 ± 0.7 pMC in the Southern Hemisphere. Model calculations of source partitioning based on the carbon-14 data, CH4 concentrations, and δ13C in CH4 indicate that 21 ± 3% of atmospheric CH4 was derived from fossil carbon at the end of 1987. The data also indicate that pressurized water reactors are an increasingly important source of 14CH4.