6.1A Stores and Fluxes
The biogeochemical carbon cycle consists of carbon stores of different sizes (terrestrial, oceans and atmosphere), with annual fluxes between stores of varying sizes (measured in Pg/Gt), rates and on different timescales.
Carbon is found everywhere: oceans, rocks, soils, the atmosphere and in all forms of life - without carbon, life would not exist as we know it. The well-being and functioning of the Earth depends on carbon and how it cycles through the Earth's systems.
The carbon cycle is the cycle by which carbon moves from one Earth sphere (atmosphere, hydrosphere, lithosphere and biosphere) to another. It is a closed system, but made up of interlinked subsystems which are open and have inputs and outputs.
It is made up of two main component:
- stores
- function as sources (adding carbon to the atmosphere) and sinks (removing carbon from the atmosphere)
- fluxes/flows
- movements of carbon from one store to another; provide the motion in the carbon cycle
Stores
Carbon exists in different forms, depending on the store:
These stores vary in size, capacity and locations. The biosphere contains both terrestrial and oceanic locations
- atmosphere: as carbon dioxide and carbon compounds, such as methane
- hydrosphere: dissolved carbon dioxide
- lithosphere: as carbonate in limestones, chalk and fossil fuels, as pure carbon in graphite and diamonds
- biosphere: as carbon atoms in living and dead organisms
These stores vary in size, capacity and locations. The biosphere contains both terrestrial and oceanic locations
Fluxes
Carbon fluxes between the carbon stores of the carbon cycle are measured in either petagrams or gigatonnes of carbon per year. The major fluxes are between the oceans and the atmosphere, and between the land and atmosphere via the biological processes of photosynthesis and respiration. These fluxes vary not only in terms of flow but also on different timescales.