Block 6 (The Global Carbon Cycle) Flashcards
Define the carbon cycle
A biochemical cycle, in which carbon moves between the lithosphere, oceans, atmosphere
What type of system is the global carbon cycle?
Closed (no matter in or out, but energy can move in or out)
What components is the global carbon cycle made up of?
- Fluxes (inputs + outputs)
- Stores/reservoirs
Carbon flows through abiotic + biotic things. What sphere is the abiotic things?
Geosphere - e.g. rock
At what time scale does carbon move through the geosphere?
Long time scale (slow)
At what time scale does carbon move through the biosphere?
Biosphere (e.g. plants)
Define carbon stores/reservoirs
Places in the Earth’s system where carbon can be found
Carbon flows through abiotic + biotic things. What sphere is the biotic things?
Biosphere
What are the 5 global carbon stores?
- Lithosphere + sedimentary rock
- Oceans
- Fossil fuels
- Biosphere
- Atmosphere
What is the percentage of global carbon stored + average residence time in the lithosphere store?
- 99.9%
- 150 mill yrs
What is the percentage of global carbon stored + average residence time in the ocean store?
- 0.064%
- 25 mill -> 1250 mill
What is the percentage of global carbon stored + average residence time in the fossil fuel store?
- 0.007%
- 150 mill yrs
What is the percentage of global carbon stored + average residence time in the biosphere store?
- 0.003%
- 18 yrs
What is the percentage of global carbon stored + average residence time in the atmosphere store?
- 0.001%
- 6 yrs
Define residence time?
Time carbon is held in a store
Define mass balance
The theory that the total amount/mass of global carbon doesn’t change (it just shifts between stores)
What is the mass balance of the global carbon is fixed?
Approx 1.85 bill bill tonnes
Define fluxes/flows
Movements/transfers of carbon between stores
Define inputs
The flux movement of carbon into a store
Define outputs
The flux movement of carbon out of a store
Define processes
Physical mechanisms that drive the inputs/outputs from stores (e.g. photosynthesis)
Give 3 ways that the carbon cycle is relevant for humans?
- Carbon is ubiquitous (everywhere)
- Carbon is a building block (for humans + living beings)
- Carbon has become an important factor in anthropogenic climate change
What did The Paris Agreement + COP-26 agree on carbon emissions?
- Must be lowered
- Global temps should stay within 1.5C increase of pre-industrial levels
What type of carbon is stored in biotic things?
Organic carbon
What type of carbon is stored in abiotic things?
Inorganic carbon
What are the 3 types of carbon pathways we must know?
- Between land + atmosphere (at a local, short term scale)
- Between ocean + atmosphere
- Between land + oceans
Which of the three carbon pathways is the ‘fast’ pathway? Why?
Between land and atmosphere
Carbon has relatively short residence times in land + atmosphere stores
What are the processes involved in the land-atmosphere carbon pathway?
1) Fossil fuel combustion
2) Carbon sequestration + photosynthesis
3) Respiration
4) Decomposition
Outline the fossil fuel combustion process in the land-atmosphere carbon pathway
- Burning coal, oil, natural gas releases CO2 into atmosphere
- Land -> Atmosphere
- (Provides 85% of global energy consumption)
Outline the carbon sequestration + photosynthesis process in the land-atmosphere carbon pathway
- Sequestration = CO2 removed from atmosphere + stored as liquid or solid.
- Photosynthesis = natural sequestration done by green plants. CO2 removed from atmosphere,combined with water, leaves glucose + O2.
- Atmosphere -> Land
- Photosynthesis formula: 6C02 + 6H20 -> C6H1206 + 602
- (Opposite of respiration - happens slightly faster)
Outline the respiration process in the land-atmosphere carbon pathway
- Living organisms release CO2 when they react glucose + oxygen together to release energy
- Land -> Atmosphere
- Respiration formula: C6H12O6 + 6O2 -> 6CO2 + 6H20
- (Opposite of photosynthesis - happens slightly slower)
Outline the decomposition process in the land-atmosphere carbon pathway
- When organic matter dies it is broken down, releasing CO2
- Land -> Atmosphere
- Physical breakdown processes: wind + water
- Chemical breakdown processes: leaching + oxidation
- Biological breakdown processes: bacteria/fungi feed and digest
When is the rate of the decomposition process fastest?
In warm, oxygenated conditions
What is Net Primary Productivity (NPP)?
Rate new organic matter is produced by photosynthesis (per unit area, per unit time)
Where is NPP highest?
Warm water estuaries, marshes, rainforests
What are the processes involved in the ocean-atmosphere carbon pathway?
- Physical (inorganic) carbon cycle pump
- Biological (organic) carbon cycle pump
Outline the process of the physical (inorganic) pump in the ocean-atmosphere carbon pathway
DOWNWELLING (Atmosphere -> Ocean)
- CO2 diffuses from atmosphere to water surface
- Dissolved CO2 moves into deep water as cold water (dense) sinks
UPWELLING (Ocean -> Atmosphere)
- CO2 in deep water can move up to surface as warm water (less dense) rises
- CO2 in surface water diffuses into atmosphere
Outline the process of the biological (organic) pump in the ocean-atmosphere carbon pathway
- Atmosphere -> Ocean
- CO2 from atmosphere absorbed by phytoplankton in photosynthesis
- Phytoplankton eaten by other marine organisms, who gain carbon
- These marine organisms are eaten by others, carbon passes through marine food web
- Some carbon falls to sea floor as they die + is squashed into sediment
Which of the 3 carbon pathways is ‘slow’? Why?
Land-Ocean
Happens in a long sequence that takes a long time
What is the sequence of the land-ocean carbon pathway?
1) Weathering
2) Transport to oceans
3) Marine shells
4) Lithification
Outline the sequence of the land-ocean carbon pathway
1) Weathering
- Rocks broken down in situ
- Carbon is left in the form of soluble bicarbonates
- Most commonly this is by carbonation
2) Transport to oceans
- Dissolved bicarbonates move to oceans
- Transported by: channel flow, through flow, groundwater flow
3) Marine shells
- In oceans, dissolved bicarbonates are used by marine organisms to make shells
4) Lithification
- Marine organisms die
- Carbon-rich shells are lithified (turned into rock)
- An oceanic sediment layer/‘carbon pool’ is formed
- Eventually, some carbon is returned to atmosphere by tectonic movements (CO2 released from subducting melting rock)
What is carbonation? What is its significance in carbon pathways?
- Type of chemical weathering
- Rainwater combines with dissolved CO2 to create a weak carbonic acid that changes rock containing limes -> bicarbonates
- Most common weathering process in first stage of the land-ocean carbon pathway
