THE CARBON CYCLE AND ENERGY SECURITY
The Carbon Cycle: the exchange of carbon between the atmosphere,
biosphere, hydrosphere and lithosphere.
It is an example of a biogeochemical cycle – a cycle in which chemicals are transferred
between living systems and the environment. AKA the recycling of nutrients between
organisms and the environment
Atmosphere = air – carbon stored as CH4 and CO2
Biosphere = all living things – carbon stored within living and dead organisms
Hydrosphere = water – carbon dissolved in the water as CO2
Lithosphere = rock – carbon stored as carbonates in limestone, chalk, and fossil fuels
In this cycle, carbon stores act as both sources that add carbon to the atmosphere and sinks
that remove carbon from the atmosphere
Brief Carbon Cycle:
Some key fuxes in the carbon cycle:
RESPIRATION – releasing carbon from biosphere into atmosphere
PHOTOSYNTHESIS – transfer of carbon from atmosphere to biosphere
DIFFUSION INTO OCEAN – of CO2, transferring carbon from atmosphere to hydrosphere
DIFFUSION OUT OF OCEAN – of CO2, transferring carbon from hydrosphere to atmosphere
SEDIMENTATION AND FOSSILISATION – of carbon in aquatc animals and seashells, transferring
carbon from biosphere to lithosphere
WEATHERING AND EROSION – of carbonate rocks, transferring carbon from lithosphere to
hydrosphere
,VOLCANIC OUTGASSING – transferring carbon from lithosphere to atmosphere
VEGETATION DECOMPOSITION TO SOIL – by microbes, transferring carbon from biosphere to
lithosphere
Diagram of stores and fuxes:
The largest carbon store is the lithosphere, whilst the second is the hydrosphere and the third
is the biosphere
Generally the fuxes are balanced out by each other, e.g. fuxes into biosphere balance out
fuxes leaving the biosphere – the same can be said for the lithosphere and atmosphere. Thus,
the system is said to be at equilibrium
This diagram however doesn’t include fuxes caused by anthropogenic interventon (human
interventonn/actonn), e.g. burning fossil fuels, deforestaton, etc. These fuxes are mostly from
the lithosphere and biosphere to the atmosphere. Therefore the system is not at equilibrium
as the fuxes coming out of stores outweigh the fuxes into stores.
, GEOLOGICAL CARBON CYCLE:
- Occurs over a larger tme scale
-> the slow carbon cycle
- To do with the carbon being locked up in terrestrial stores for millions of years
Brief diagram:
CO2 in the atmosphere reacts with rain to form carbonic acid – acid rain. During rainfall, the
carbonic acid dissolves carbon-rich rocks through chemical weathering to form carbonate ions
which are transported to the ocean via rivers where they are deposited as calcium carbonate
sediments.
The carbon is used by aquatc animals as calcium carbonate to form their shells and skeletons.
When they die, their calcium carbonate shells sink and this deposition of organic mater
lithifies to form carbonate rock – sedimentary rock.
Carbonate rocks like limestone and shale are formed animals in diferent ways:
- Limestone is formed when loose sediment made up of dead aquatc animals undergo
diagenesis where the buried sediment contains grains of CaCO3 which dissolve under pressure
when they (the grainsn) come into contact with each other through pressure dissolution. This
forms hard sedimentary rock – limestone
- Shale is formed when some carbon-containing rocks become embedded in layers of mud
which heat and compress under pressure over millions of years. Thus, forming sedimentary
rock – shale.
These both act as a long-term terrestrial carbon store
Due to tectonic spreading there is subduction of the sea foor under contnental margins – this
occurs at mid-ocean ridges (Icelandn), subducton ones at plate boundaries (Mount Etnan), and
in magma hotspots (Kilauea, Hawaiin)
The rock melts under the heat and undergoes metamorphism into metamorphic rock,
releasing small pockets of CO2 gas which rise to the surface of the magma and release the
CO2.
