Lessons > The Carbon Cycle > For Your Consideration
You should now have some understanding of how carbon moves through the system, but you may be wondering about the mechanisms behind this flow. As you read through the following explanations, refer to your Data Table for Lesson 1 Step 2.
Atmosphere: combustion of carbon-based fuel combines carbon, C, and oxygen, O2, adding CO2 to the atmosphere. CO2 is not a by-product of fossil fuel use; it's the direct product of the very reaction that releases the energy.
Biosphere (Terrestrial Plants and Soil): plants (biomass) inhale CO2 and exhale O2. When there's more CO2 available, biomass tends to breathe in more, and therefore grow more. Most scientists now believe that plants have a limited ability to increase their growth rate. (See the Unit 12 video.) However, this is not taken into account in this model.
Surface ocean: The amount of gas dissolved in any liquid is proportional to the partial pressure of that gas in the vapor phase above the liquid (Henry's Law). As a result, if we increase the partial pressure of atmospheric CO2 (i.e. increase the concentration of CO2), then we force more CO2 gas to dissolve into the liquid. (In this case, the liquid is the ocean.) In addition to the CO2 dissolving into the liquid as a gas, CO2 reacts with H2O and forms bicarbonate ions (HCO3-) and carbonate ions (CO3--). This combustion of fossil fuels results in an increase in dissolved surface ocean carbon and a decrease in pH.
Deep ocean: Ocean chemistry involving mineral precipitation, and biological activity, and ocean currents transport the carbon from the surface ocean to the deep ocean over long time-scales.