Turnover of Carbon in the Biosphere

As it has been pointed out earlier, the terrestrial ecosystems are the main sink of carbon dioxide due to the photosynthesis process. The present bulk of living organisms is confined to land, and their mass (on dry basis) amounts to 1880 x lO tons. The average carbon concentration in the dry mater of terrestrial vegetation is 46% and, consequently, the carbon mass in the land vegetation is abont 865 x 10 tons (after Bolin, 1979 and Dobrovolsky, 1994). 

In accordance with Romankevich (1988), the oceanic biomass of photosynthetic organisms contains 1.7 x 10 tons of organic carbon, C . In addition, we have to include a large number of consumers. This gives 2.3 x 10 tons of C . Totally, the oceanic organic carbon is equal 4.0 x 10 tons or about 0.5% from that in land biomass. 

Moreover, a substantial amount of dead organic matter as humus, litterfall and peat is also present in the terrestrial soil cover. The mass of forest litter is close to 200 X 10 tons, mass of peat is around 500 x 10 tons and that of humus, 2400 x 10 tons. Recalculation of this value for organic carbon amounts to 1550 x 10 tons. 

However, the greatest amount of carbon in the form of hydrocarbonate, HCO3 , (38600 X 10 tons) is contained in the ocean, 10 times higher than the total carbon in living matter, atmosphere, and soils. 

in the terrestrial ecosystems the least amount of carbon is monitored in living biomass, followed by dead biomass and atmosphere. 

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Figure 4 The global disequilibrium effect. value of CO2 currently fixed into plants (associated with photosynthetic discrimination, is lower than that of older CO2 respired back to the atmospheric CO2 (no fractionation is assumed). This is due to the rapid decrease in atmospheric associated with fossil fuel emissions, on the one hand, and to the slow turnover of carbon in the biosphere, on the other hand. A similar disequilibrium occurs in the ocean where the atmospheric trend influences the values of newly formed Die, while the ocean mean DIG pool lags behind this equilibrium values due to slow mmover rates (not shown). The atmospheric trend shown is based on the best fit line to the data of Francey et al. (1999) the land organic matter trend is obtained by appl3ung global mean = 18%o, and moving it back in time by 27 yr, the first order estimate of global mean soil carbon turnover time. The resulting 0.6%o disequilibrium for the 1990s is within the range of current estimates for both land and ocean.

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