Figure 2.

(Left) Change in Δ¹⁴C in atmospheric CO₂ and in two homogeneous C pools with turnover times of 5, 10, 50, and 70 years. (Right) Effect of passive organic matter on Δ(Δ¹⁴C) values in bulk SOM. Failure to account for 10% of the carbon in a passive fraction that does not change in ¹⁴C content between 1959 and 1992 will result in an underestimate of the increase in fast-cycling Δ¹⁴C and therefore of turnover time in that fraction. Thus it is important to assess whether passive components such as charcoal are present in presumed fast-cycling pools (such as low-density carbon).