6. Carbon Cycle: Stores, transfers and local and global cycle

What is the difference between a carbon sink and source?

Carbon sinks absorb more carbon than they release whereas sources do the opposite.

What are the 5 stages of the slow carbon cycle?

1. CO2 absorption from the atmosphere into the hydrosphere in the oceans. Naturally acidic rainfall dissolves surface rocks and transfers soluble bicarbonate compounds via rivers to the sea

2. Marine plants (phytoplankton) absorb CO2 and marine creatures take in carbon to construct shells. Shell remains fall to the sea bed when they die

3. Carbon rich accumulations of deposits may be converted to carbon rich rocks eg: limestone by compression and heat

4. The sedimentary rock may eventually become a collision margin as they move in the direction their plate moves so they could become a mountain range and be once again exposed to weathering and erosion and return to the sea as eroded carbonate rocks

5. Or if at a subduction zone the carbon rich rocks may be ejected from volcanic eruptions in the form of gaseous compounds into the atmosphere

Give an example of carbon in the lithosphere? GLOBAL

• 99.9% of carbon can be found in sedimentary rocks eg: limestone. Millions of gigatonnes

• This is the largest store of carbon and is formed over millions of years so is a long term store of carbon.

• 0.004% of carbon is stored in fossil fuels eg: coal and oil

• SLOW cycle

Give examples of carbon in the hydrosphere? GLOBAL

• CO2 can be dissolved in rivers, lakes and oceans via diffusion. 38,000 Gt

• Oceans are the second largest store of carbon on Earth containing 0.04% of carbon on Earth

• This is in the form dissolved inorganic carbon

• Since the industrial revolution oceans now absorb more carbon from the air due to more emissions

• Carbon is constantly being used by marine organisms, lost as output to lithosphere or gains as an input from rivers and erosion

• SLOW cycle

Give an example of carbon in the biosphere? GLOBAL

• Carbon is stored in the tissues of living organisms and is transferred into the soil when they die and decay as plant/animal litter

• Vulnerable to climate change and results in carbon storage in forests declining

• Peat - the accumulation of partically decayed vegetation/organic matter which is unique to peatlands and forms in wetland conditions. The water saturation there creates anaerobic conditons slowing the rate of decomposition

• Rainforests eg: Brazil are the main locations for the carbon to be stored giving tropical rainforests a positive NPP all year round whereas deciduous forests have a negative NPP in winter.

• Fast cycling store

Give examples of carbon in the atmosphere? GLOBAL

• 0.001% of the Earth’s atmosphere contains carbon in the form CO2 and methane (CH4)

• Human activity caused C02 levels to increase by 40% since the industrial revolution

• Fast cycle

Give examples of carbon in the cryosphere? GLOBAL

• Less than 0.01% of carbon is in the cryosphere

• Most of the carbon is in the soil areas of the permafrost where decomposed plants and animals froze into the ground

• If permafrost melted a powerful positive feedback loop accelerates global warming beyond human-caused emissions.

What is the difference between slow and fast cycles of carbon?

• Fast carbon cycles are between the land and the atmosphere and only take a matter of days

• Slow carbon cycles are between surface bedrock and the atmospheric or ocean stores

Explain how photosynthesis is a carbon flux in the fast carbon cycle?

• Photosynthesis is where organisms convert: Carbon Dioxide +Water → Oxygen and Glucose using light energy

• The plants are sequestering carbon and acting as a carbon sink

• This is part of the fast carbon cycle as it takes min/hr/day

Explain how respiration is a carbon flux in the fast carbon cycle?

• Occurs when plants and animals convert: Oxygen + Glucose → Carbon Dioxide + Water

• This happens because at night photosynthesis stops due to no light

• Despite this releasing carbon, plants are a net carbon sink as they absorb more CO2 than they emit

Explain combustion as a transfer in the fast carbon cycle?

When fossil fuels or organic matter is burnt they emit the CO2 into the atmosphere which was previously locked inside them. Eg: wildfires

Explain decomposition as a transfer in the fast carbon cycle?

• When living organisms die and are broken down by decomposers (bacteria) which respire so C02 is returned to the atmosphere

• Some organic matter may be returned to the soil where it’s stored adding carbon matter to the soil

Explain diffusion as a transfer in the ocean carbon cycle?

• Oceans absorb CO2 from the atmosphere increasing their acidity through gas exchange

• This causes coral bleaching so many of the world’s coral reefs are under threat

• Carbon can also be exchanged from the ocean to atmosphere as the carbon-rich water from deep in the oceans may rise releasing CO2

Explain weathering and erosion as a transfer in the ocean carbon cycle?

• Acid rain transfers carbon into the oceans. This can be natural or anthropogenic releasing sulphur dioxide

• Carbonation weathering can cause CO2 to mix with rainwater creating carbonic acid which erodes rocks such as limestone and the water cycle can transport them to help build the shells of marine creatures

Explain sequestration as a slow carbon cycle transfer? (natural)

• Where carbon from the atmosphere is transferred into sedimentary rocks or fossil fuels

• This happens through burial and compaction when dead animal and plant material is compacted capturing the carbon → creating limestone

What are the pros of CCS (Carbon capture and storage) as a human carbon sequestration?

• Can be fitted to existing power stations

• Captures 90% of carbon produced

• There’s a demand for CO2 from big TNC’s such as Coca-Cola so transport systems via pipeline already exist

What are the cons of CCS (Carbon capture and storage) as a human carbon sequestration?

• High cost

• Increased energy demand for power stations

• May not fit in power stations

• Leakage risk which will damage ecosystems

• Uncertain in long-term liability - who will be responsible for leaks, will carbon stay down there for centuries

• Some say money should be spent on renewable energy instead

Explain the vegetation succession as the carbon cycle at a local scale?

• This is the climatic climax where there is a vegetation succession.

• In the UK this would be woodland whereas in Brazil it may be a rainforest.

• Here the ecosystem is fully developed and stable so an environmental equilibrium is achieved and will not change dramatically as the equilibrium will counteract the change

• Eg: psammoseres are a succession of sand dunes leading to a woodland

• Carbon is in soil humus and there is the highest primary productivity of carbon at the woodland as the plants compete for light

picture shows lithosere environment