Slide 22 of 30
Notes:
This is the diagram for the era prior to the industrial revolution, modified to allow for the effects of human activities. Not all modifications can be measured - some are inferred from conservation of carbon together with our understanding of the processes involved.
The driving modifications are (i) the transfer of 5 GtC/y from “Sediment” directly to “Atmosphere” (the burning of coal and oil), and (ii) 2 GtC/y from “Land Biota” to the “Atmosphere” (deforestation). Of those 7 units, 3 /y remain in the atmosphere, 2 /y are passed to the ocean (driven by increases atmospheric concentrations), and 2 /y returned to “Land Biota” (photosynthesis has probably been enhanced by increased atmospheric CO2). Note that there is an error of conservation in Horel and Geisler Figure 6.5. This has been corrected here in red, on the improbable assumption that the effects of deforestation are strictly to reduce the biota, and the return flux from the atmosphere is passed entirely to the soil. Some of the flux associated with deforestation comes from the soil, and how much of the return is stored in the soil as opposed to tree trunks is also not known definitively.