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Geography Edexcel A level Carbon Cycle Summary Notes (EQ1)
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The Carbon Cycle and Energy Security 1 of 7Enquiry question 1: How does the carbon cycle operate to maintain planetary health?
Key words:
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 is made up of
interlinked subsystems which are open and have inputs and outputs.
Carbon stores- function as sources (adding carbon to the atmosphere) and sinks (removing
carbon from the atmosphere).
Carbon fluxes- (also known as flows or processes) are movements of carbon from one store to
another; they provide the motion in the carbon cycle.
Chemical weathering- is the decomposition of rock minerals in their original position by agents
such as water, oxygen, carbon dioxide and organic acids.
Outgassing- is the release of gas previously dissolved, trapped, frozen or absorbed in some
material (e.g. rock).
Carbon sequestration- is the process by which carbon dioxide is removed from the atmosphere
and held in solid or liquid form. It is the process that facilitates the capture and storage of carbon.
Carbon pumps- are the processes operating in the oceans that circulate and store carbon.
Phytoplankton- consists of the microscopic plants and plant-like organisms drifting or floating in
the sea (or freshwater) along with diatoms, protozoa and small crustaceans.
Photosynthesis- is the process by which green plants and some other organisms use sunlight to
synthesise (extract) nutrients from carbon dioxide and water.
Thermohaline circulation- is the global system of surface and deep ocean currents driven by
temperature (thermo) and salinity (haline) differences between different parts of the oceans.
Greenhouse gases (GHGs)- are primarily water vapour, carbon dioxide, methane, nitrous oxide
and ozone. These gases both absorb and emit solar radiation and, in so doing, create the so
called greenhouse effect that determines global temperatures.
Net primary productivity (NPP)- is the amount of organic matter that is available for humans and
other animals to harvest or consume.
Anthropogenic- processes and action associated with human activity.
Reservoir turnover- the rate at which carbon enters and leaves a store. It is measured by the
mass of carbon in any store divided by the exchange fluxes.
Calcareous ooze- is a calcium carbonate mud formed from the hard parts of the bodies of free-
floating organisms. They are deposits of soft mud on the ocean floor.
Systems- how the carbon cycle sustains other Earth systems.
Equilibrium- how the carbon cycle is balanced, and how that balance is disturbed by human
activities.
Feedback- the impacts of change on the carbon cycle as carbon stores are released.
Greenhouse effect- the warming of the atmosphere as gases such as carbon dioxide, methane
and water vapour absorb heat energy radiated from the Earth.
Enhanced greenhouse effect- the increase in the natural greenhouse effect, said to be caused
by human activities that increase the quantity of greenhouse gases in the Earth’s atmosphere.
6.1- Most global carbon is locked in terrestrial stores as part of the long-term geological cycle
(a) The biogeochemical carbon cycle consists of carbon stores of different sizes (terrestrial,
oceans and atmosphere), with annual fluxes between stores of varying size (measured in Pg/
Gt), rates and on different timescales.
The carbon cycle is a closed system. The system has:
• Stores
- Also referred to as pools, stocks and reservoirs.
- Can be sources or sinks.
- There are terrestrial, oceanic and atmospheric stores.
• Fluxes
- Refers to the movement or transfer of carbon between
stores.
- They create cycles and feedback.
- Measure in PgC yr-1(petagrams of carbon) or GtC yr-1
, The Carbon Cycle and Energy Security 2 of 7
- E.g. photosynthesis 103 PgC yr-1, Diffusion out of ocean 90.3 PgC yr-1, Sedimentation 0.2
PgC yr-1
• The fluxes are more important than the stores
• Estimated that 180Gt of carbon has been added to the atmosphere as result of burning fossil
fuels- triggered climate change
Carbon is present in the stores of:
• The atmosphere: stored as CO2 and methane (CH4)
• The hydrosphere: stored as dissolved CO2
• The lithosphere: stored as carbonates in limestone and fossil fuels such as coal, oil and gas
• The biosphere: stored in living and dead organisms
Terrestrial carbon stores Oceanic carbon stores Atmospheric carbon stores
About - Igneous and metamorphic - CO2 is dissolved by - Volcanic activity,
rocks don’t contain much oceans from the respiration, wildfires and
carbon, sedimentary rock atmosphere, but it only outgassing emit CO2 into
does e.g. limestone. makes up a tiny the atmospheric store.
- Geological processes have proportion of the - This store is very small
carbon trapped in the form seawater mass. when compared with
of coal, oil and natural gases - Most CO2 is stored in others.
(fossil fuels). intermediate and deep - Small changes in
- Is the largest store. water, with only about concentration affect global
- Today calcareous oozes are 2.5% in surface waters. temperature and between
found under the southern 2012 and 2017 the average
Pacific, Atlantic and western CO2 concentration,
Indian oceans, ready to be increased by 3% due to
turned into limestone rocks. human emissions.
Examples - Sedimentary rock store - Intermediate and deep - Atmosphere store 589 PgC
83,000,000 PgC ocean stores 37,100 PgC
- Surface ocean stores 900
PgC
Two main components of the carbon cycle
• The geological carbon cycle
- Slow part of the carbon cycle
- Centred on the huge carbon stores in rocks and sediments with reservoir turnover rates at
least 100,000 years
- Organic matter that is buried in deep sediments takes millions of years to turn into fossil
fuels
• The biological or physical carbon cycle
- Fast component of the carbon cycle
- Large fluxes and ‘rapid’ reservoir turnovers of a few years up to a millennia
- Carbon is sequestered in and flows between, the atmosphere, oceans, ocean sediments and
on land in vegetation, soils and freshwater.
Three forms of carbon
• Inorganic- found in rocks as bicarbonates and carbonate
- Is released by chemical weathering very slowly, decades/hundreds of years
• Organic- found in plant material
- Is released much quicker, a matter of months/seasons
• Gaseous- found as CO2, CH4 and CO
Speed of fluxes
• Quickest cycle is completed in seconds as plants take carbon from the atmosphere through
photosynthesis
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