The radiocarbon content of atmospheric CO2 (14CO2) varies due to a number of factors. After the near-doubling of the 14CO2 loading in the early 1960s (due to atmospheric nuclear weapons testing), many studies examined the fate of this 'bomb 14C' to understand exchange processes of CO2 with the surface reservoirs. Today, however, the atmosphere and surface reservoirs are close to equilibrium with respect to bomb 14C, and instead, changes in 14CO2 more strongly reflect the response to the addition of 14C-free fossil fuel CO2 to the atmosphere. We use an atmospheric transport model to simulate recent atmospheric 14CO2, and compare this to observations at several sites over the Northern Hemisphere continents. We show that, in the Northern Hemisphere, 14CO2 variability is dominated by the effect of fossil fuel CO2 emissions. The model simulates the time trends quite well, including both the overall secular trend and the seasonal cycle. A seasonal cycle in 14CO2 is observed at the high altitude sites of Niwot Ridge, Colorado, and Jungfraujoch, Switzerland, but the magnitude varies from year to year. Our modeling studies demonstrate that this inter-annual variability can be explained by differences in atmospheric transport. This is in contrast to CO2 concentration seasonal cycles, which are dominated by seasonal changes in CO2 source strengths.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 0365 Troposphere: composition and chemistry;
- 0368 Troposphere: constituent transport and chemistry;
- 0428 Carbon cycling (4806);
- 0454 Isotopic composition and chemistry (1041;