Topic 6 - The Carbon Cycle & Energy Security
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, 6.1a - Stores & Fluxes
The carbon cycle moves carbon between Earth's spheres (atmosphere, hydrosphere, lithosphere,
and biosphere) in a closed system with open subsystems that have inputs and outputs.
Key Components:
1. Stores: Act as sources (adding carbon) or sinks (removing carbon).
2. Fluxes: Movements of carbon between stores, measured in petagrams (Pg) or gigatonnes
(Gt) annually.
Carbon exists in different forms, depending on the store:
• Atmosphere: CO₂ and CH₄ regulate temperature.
• Hydrosphere: Dissolved CO₂ supports marine life and ocean storage.
• Lithosphere: Carbon stored in rocks, fossil fuels, and pure forms (graphite, diamonds).
• Biosphere: Carbon in living organisms and organic material.
Fluxes: These are the flows of carbon between stores, measured in petagrams (Pg) or gigatonnes
(Gt) of carbon per year.
Major Fluxes:
• Oceans ↔ Atmosphere: Absorption and release of CO₂.
• Land ↔ Atmosphere: Photosynthesis (absorbs CO₂) and respiration (releases CO₂).
Variation: The rate and amount of carbon moving in these fluxes can vary:
• Flow: How much carbon is moving (e.g., larger fluxes in certain seasons).
• Timescale: Some fluxes happen quickly (like daily photosynthesis), while others take longer
(like carbon being stored in the ocean for hundreds of years).
6.1b - Geological Origins of Earth's Carbon
Formation of Geological Carbon
Sedimentary Carbonate Rocks:
• Formed in oceans when marine organisms (like plankton, coral, and shellfish) extract
calcium carbonate (CaCO₃) from seawater to build their shells and skeletons.
• When these organisms die, their remains accumulate on the ocean floor and over millions
of years, compression and cementation form limestone and other carbonate rocks.
Biologically Derived Carbon:
• Formed from organic material (plants, plankton, and organisms) buried & compressed
over time.
2
, • Shale: Organic-rich sediments compressed in low-oxygen environments over millions of
years.
• Coal: Ancient plant material compressed & heated in swamps, forming peat and then coal.
• Oil and Natural Gas: Plankton & microorganisms decompose on the ocean floor &
transform into hydrocarbons under heat & pressure.
6.1c - Bio-geochemical carbon cycle
4 key processes in this cycle are;
Removing CO2 from atmosphere Releasing CO2 into atmosphere
Photosynthesis: plants and Respiration: plants, animals, and microbes release CO₂
phytoplankton absorb CO₂ from the back into the atmosphere by breaking down glucose for
atmosphere and convert it into energy.
glucose and oxygen, transferring
carbon to the biosphere. Decomposition: microorganisms break down dead
organisms, releasing CO₂ (or methane in anaerobic
environments) back into the atmosphere or soil.
Combustion: burning of fossil fuels & biomass releases
CO₂ into the atmosphere.
Chemical Weathering Process
• Carbonic Acid Formation: CO₂ dissolves in rainwater, forming carbonic acid, which reacts
with silicate minerals in rocks.
• Ions Released: This weathering releases calcium (Ca²⁺) and bicarbonate (HCO₃⁻) ions into
rivers, which are transported to the oceans.
Formation of Calcium Carbonate (CaCO₃)
• Marine Organisms: Use calcium and bicarbonate ions to form calcium carbonate in shells
and skeletons.
• Sedimentation: Dead organisms accumulate and form carbonate rocks (e.g., limestone)
over time.
Carbon Return to Atmosphere
• Tectonic Processes: Subduction of carbonate rocks leads to volcanic eruptions that
release CO₂ back into the atmosphere.
• This is part of the slow carbon cycle, which takes millions of years, compared to the faster
biological processes.
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1
, 6.1a - Stores & Fluxes
The carbon cycle moves carbon between Earth's spheres (atmosphere, hydrosphere, lithosphere,
and biosphere) in a closed system with open subsystems that have inputs and outputs.
Key Components:
1. Stores: Act as sources (adding carbon) or sinks (removing carbon).
2. Fluxes: Movements of carbon between stores, measured in petagrams (Pg) or gigatonnes
(Gt) annually.
Carbon exists in different forms, depending on the store:
• Atmosphere: CO₂ and CH₄ regulate temperature.
• Hydrosphere: Dissolved CO₂ supports marine life and ocean storage.
• Lithosphere: Carbon stored in rocks, fossil fuels, and pure forms (graphite, diamonds).
• Biosphere: Carbon in living organisms and organic material.
Fluxes: These are the flows of carbon between stores, measured in petagrams (Pg) or gigatonnes
(Gt) of carbon per year.
Major Fluxes:
• Oceans ↔ Atmosphere: Absorption and release of CO₂.
• Land ↔ Atmosphere: Photosynthesis (absorbs CO₂) and respiration (releases CO₂).
Variation: The rate and amount of carbon moving in these fluxes can vary:
• Flow: How much carbon is moving (e.g., larger fluxes in certain seasons).
• Timescale: Some fluxes happen quickly (like daily photosynthesis), while others take longer
(like carbon being stored in the ocean for hundreds of years).
6.1b - Geological Origins of Earth's Carbon
Formation of Geological Carbon
Sedimentary Carbonate Rocks:
• Formed in oceans when marine organisms (like plankton, coral, and shellfish) extract
calcium carbonate (CaCO₃) from seawater to build their shells and skeletons.
• When these organisms die, their remains accumulate on the ocean floor and over millions
of years, compression and cementation form limestone and other carbonate rocks.
Biologically Derived Carbon:
• Formed from organic material (plants, plankton, and organisms) buried & compressed
over time.
2
, • Shale: Organic-rich sediments compressed in low-oxygen environments over millions of
years.
• Coal: Ancient plant material compressed & heated in swamps, forming peat and then coal.
• Oil and Natural Gas: Plankton & microorganisms decompose on the ocean floor &
transform into hydrocarbons under heat & pressure.
6.1c - Bio-geochemical carbon cycle
4 key processes in this cycle are;
Removing CO2 from atmosphere Releasing CO2 into atmosphere
Photosynthesis: plants and Respiration: plants, animals, and microbes release CO₂
phytoplankton absorb CO₂ from the back into the atmosphere by breaking down glucose for
atmosphere and convert it into energy.
glucose and oxygen, transferring
carbon to the biosphere. Decomposition: microorganisms break down dead
organisms, releasing CO₂ (or methane in anaerobic
environments) back into the atmosphere or soil.
Combustion: burning of fossil fuels & biomass releases
CO₂ into the atmosphere.
Chemical Weathering Process
• Carbonic Acid Formation: CO₂ dissolves in rainwater, forming carbonic acid, which reacts
with silicate minerals in rocks.
• Ions Released: This weathering releases calcium (Ca²⁺) and bicarbonate (HCO₃⁻) ions into
rivers, which are transported to the oceans.
Formation of Calcium Carbonate (CaCO₃)
• Marine Organisms: Use calcium and bicarbonate ions to form calcium carbonate in shells
and skeletons.
• Sedimentation: Dead organisms accumulate and form carbonate rocks (e.g., limestone)
over time.
Carbon Return to Atmosphere
• Tectonic Processes: Subduction of carbonate rocks leads to volcanic eruptions that
release CO₂ back into the atmosphere.
• This is part of the slow carbon cycle, which takes millions of years, compared to the faster
biological processes.
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