Unit 3 - Physical Systems and Sustainability (9GEO01)
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Topic 6 – Carbon Cycle + Energy Security:
6.1: Most global carbon is locked in terrestrial stores as part of the long-term geological cycle
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 depend 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.
o The amount of carbon doesn’t change on earth
o It is transferred between stores
The amount of carbon on earth is enormous. Carbon is measured in Petagrams (pg) = 1 petagram = a
billion tonnes
Stores: Function as Carbon exists in different forms, depending on the store:
sources (adding Atmosphere: as carbon dioxide and carbon compounds, such as methane
carbon to the Hydrosphere: dissolved carbon dioxide
atmosphere) and
Lithosphere: as carbonate in limestones, chalk and fossil fuels, as pure
sinks (removing
carbon in graphite and diamonds
carbon from the
Biosphere: as carbon atoms in living and dead organisms
atmosphere)
These stores vary in size, capacity and locations. The biosphere contains both
terrestrial and oceanic locations
Fluxes: Movements of Carbon fluxes between the carbon stores of the carbon cycle are measured
carbon from one in either petagrams or gigatonnes of carbon per year.
store to another; The major fluxes are between the oceans and the atmosphere, and
provide the motion in between the land and atmosphere via the biological processes of
the carbon cycle photosynthesis and respiration.
These fluxes vary not only in terms of flow but also on different timescales.
Types of carbon:
1) Inorganic
a. Found in rocks as bicarbonates + carbonates
2) Organic
a. Found in plants material
3) Gaseous
a. Found as methane and carbon monoxide
Fast part of carbon cycle: plants and photosynthesis (e.g., rainforest)
Slow part of carbon cycle: ocean floor, sediment in earth’s surface + volcanoes (e.g., taiga)
Reservoir turnover: how rapidly the carbon is removed from a particular location
,Geological carbon = created in formation of sedimentary rocks (e.g. limestone and chalk) – in oceans
Biological carbon = stored in shale, coal and other sedimentary rocks
Geological Moves carbon between the land, the
Carbon oceans and atmosphere
Cycle Natural equilibrium between production
and absorption.
1) Mechanical, chemical or biological
weathering of rocks on land in situ
2) Decomposition
3) Transportation
4) Sedimentation
5) Metamorphosis
Bio- Living organisms to maintain the running of
geochemical the cycle
Carbon They control the balance between storage,
Cycle: release, transfer and absorption
1) CO2 is exchanged between atmosphere +
oceans
2) Photosynthesis: plants remove CO2 from
the atmosphere
3) Respiration: animals consume plants +
release CO2 into the atmosphere and the
water
4) Decomposition: dead plants and animals
releases CO2 into soils ad deposits carbon
on sea floor
5) Combustion: burning fossil fuels release
CO2 into atmosphere
Volcanic Outgassing:
Pockets of CO2 exist in the earths crust
Disturbance by volcanic eruptions or earthquake activity may allow pulses or more diffuse fluxes into
the atmosphere
Outgassing occurs at:
o Active or passive volcanic zones associated with tectonic plate boundaries
o Places with no current volcanic activity
o Direct emissions from fractures in earth’s crust
1) Ocean Ridges:
a. Weathering consumes CO2 (these products carried to the ocean)
b. CO2 is slowly carried to mid-ocean ridge by flow within atmosphere
c. CO2 released at mid-ocean ridges
2) Subduction Zone:
a. Weathering consumes CO2 (these products carried to the ocean)
b. Sediment subducted
, c. Partial melting of subducted material liberates CO2
d. CO2 rising in the magma – CO2 released after lava formed
Chemical weathering:
1) Chemical weathering – carbonic acid reacts with rock and takes calcium ions to rivers
2) Rivers carry particles to ocean ad sediment falls to the bottom of the sea
3) Overtime the sediment builds up causing the creation of sedimentary ricks
a. The rock stores and may be made up of carbon
b. E.g., limestone contains CO2 in the rock
Formation of fossil fuels:
1) Decomposition / deposits of animals and plants
2) Gas and oil occur in pickets in rocks
3) Natural gas is made up of tractions of oil molecules
4) Overtime the organic material and sediments are buried
5) High pressure and temperature = creation of fossil fuels
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