Slide 18 of 30
Notes:
Read Horel & Geissler Chapter 6 for a full explanation of this diagram
The numbers in boxes are the content of a reservoir. The numbers by arrows are the flux between two reservoirs. The diagram illustrates the equilibrium situation believed to have held before the industrial revolution, in which the inputs and outputs of each reservoir were in balance.
The diagram also illustrates the widely different time scales on which the contents of different reservoirs are being renewed. To estimate the renewal time (otherwise known as residence time), divide the content (in Gigatons of carbon) by the sum of the fluxes into or out of a reservoir (in Gigatons of carbon per year). This gives a rough measure of how long it is likely to be before the contents have changed significantly if the input or output fluxes are altered somewhat.
Thus for sediment the renewal time is 55,000,000 / 0.2 year, which is approximately 100 million years. It would take a drastic change in circumstances indeed to change the concentration of carbon in sediments substantially within the next century! On the other hand, for living land biota the corresponding number is 610/100 ~ 6 years. Thus, in this case, changes in the factors controlling uptake (photosynthesis) or outflow (direct respiration + tissue death) would affect the amount of living matter many times over during the next century.
Note that tissue death adds carbon to the soil reservoir. Much of that is recycled to the atmosphere within few years through respiration by fungi and bacteria making compost. A small fraction lasts a lot longer. Thus the use of a single reservoir for soil is somewhat misleading.