Carbon dioxide biosphere-atmosphere exchange

Bonan, G. B. (1991). Atmosphere-biosphere exchange of carbon dioxide in boreal forests, /. Geophys. Res. 96, 7301-7312. 

Friedlingstein, P., Fung, I., and Field, C. (1997). Decadal variation in atmospheric-biospheric CO, exchange, in Extended Abstracts of the Fifth International Carbon Dioxide Conference, Cairns, Australia, 8-12 September 1997, p. 268. 

The carbon-14 isotopes enter the biosphere when carbon dioxide is taken up in plant photosynthesis. Plants are eaten by animals, which exhale carbon-14 in COj. Eventually, carbon-14 participates in many aspects of the carbon cycle. The continual exchange between carbon in living tissue and carbon in the atmosphere means that the ratio of carbon-14 to carbon-12 in living matter will be the same as that in the atmosphere. When an individual plant or animal dies, however, the carbon-14 isotope in its cells continues to decay, but is no longer replenished, so the ratio of " C to decreases. These same processes occur when carbon atoms are trapped in coal, petroleum, or wood preserved underground, and in Egyptian mummies. As the years pass, there are proportionately fewer nuclei in a mummy than in a living person. 

First I want to review some relevant information regarding the global carbon cycle and the processes that affect atmospheric concentrations of carbon dioxide. There are vast reservoirs of carbon in the system (see Figure 3.1) that can exchange fairly rapidly with the atmosphere, which contains about 750 gigatons (1 gigaton = 10 tons) of carbon (GtC). The terrestrial biosphere and soils contain about 2,000 GtC the mixed layer of the ocean contains about 1,000 GtC and the deep oceans, 38,000 GtC. 

Once produced the radiocarbon is quickly oxidized to " C02. This radiocarbon-labelled carbon dioxide is mixed throughout the atmosphere through the atmospheric circulation. This mixing is very rapid within each hemisphere, but not so rapid across the equator. As part of the global carbon cycle (see Fig. 1), carbon dioxide exchanges between the surface oceans and the atmosphere and is also absorbed by photosynthesis into green plants and thereby into the biosphere. 

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