A2: The Carbon
Cycle
Topic 6
, 6.1 a&b: Terrestrial Stores in
the Carbon Cycle
Cycles Stores and Fluxes
Carbon Storage Store Type (anthropogenic infuences) PgC (Average)
Carbon Cycle: The biogeochemical cycle
where carbon moves between stores via Long Term Stores: Hundreds of years-Millennia
fuxes. Carbon stores functon as: Sedimentary Rocks 100,000,000
Crustal/terrestrial
- Sources (adding carbon to the geological (Slow cycling over millennia) (Fossil fuels store
atmosphere) an extra 4000)
- Sinks (removing carbon from the
Oceanic (Deep) Dissolved inorganic carbon stored at great depths 38,000
atmosphere) (Very Slowly Cycled)
Carbon is present in the stores of:
• Atmosphere: as CO2 & compounds Short Term Stores: Seconds-Decades
such as methane From plant materials (biomass); microorganisms break 1,500
Terrestrial Soil
• Hydrosphere: as dissolved CO2 most organic mater down to CO2.
• Lithosphere: as carbonates in (Days in hot climates, Decades in colder climates)
limestone and fossil fuels (coal, oil &
gas) Oceanic (Surface) Exchanges through physical processes (CO2 dissolving in 1,000
• Biosphere: in living & dead water) & biological processes (plankton)
organisms. (Rapid cycle with atmosphere. Longer in deep ocean)
• If a source equals the sinks, the carbon
Atmospheric CO2 and CH4 store carbon as greenhouse gases 560
cycle is in equilibrium, with no change (Cycle of up to 100 years)
to the size of the stores. Changes in
the system may result in Negatve & Terrestrial Ecosystems CO2 is taken from the atmosphere by photosynthesis; 560
carbon is stored organically, especially in trees
Positve Feedback: (Rapid cycle of seconds-minutes)
• Negatve Feedback: Earth’s normal
system, maintaining a stable state &
preventng the system moving
beyond thresholds.
• Positve Feedback: When a small Geological Origins The formaton of Fossil Fuels
change in 1 component causes • Most of the earth’s carbon is geological, • Dead organisms decay anaerobically at the
changes in other components. This due to the formaton of sedimentary botom of the sea and as it decays, fossil
shifs the system towards a new carbonate rocks (Limestone) in oceans. fuels are formed.
state. • In oceans, 80% of carbon-containing rocks • Coal is formed from remains of trees &
• These changes to feedback are caused is from calcifying (shell-building) plants.
by anthropogenic infuence, increasing organisms, coral & plankton. • Oil & gas are formed from the remains of
the magnitude of fuxes. • Over millions of years, heat & pressure aquatc animals & plants.
compress the mud & carbon, forming
sedimentary rock such as shale.
