Carbon Pools

Carbon is stored on our planet in the following major pools:

as organic molecules in living and dead organisms found in the biosphere;
as the gas carbon dioxide in the atmosphere;
as organic matter in soils;
in the lithosphere as fossil fuels and sedimentary rock deposits such as limestone, dolomite and chalk;
in the oceans as dissolved atmospheric carbon dioxide and as calcium carbonate shells in marine organisms.

Microorganisms are strongly involved in the carbon cycle, mediating crucial biochemical reactions discussed later in this section.

Photosynthetic algae are the predominant carbon-fixing organisms in water; as they consume CO₂, the pH of the water is raised enabling precipitation of CaCO₃ and CaCO₃, MgCO₃.

Organic carbon fixed by microorganisms is transformed by biogeochemical processes to fossil petroleum, kerosene, coal, and lignite. Microorganisms degrade organic carbon from biomass, petroleum, and xenobiotic sources, ultimately returning it to the atmosphere as CO₂.