1. Carbon cycle processes/stores Flashcards
What are the major stores of carbon?
- Lithosphere: sedimentary rock and fossil fuel deposits
- Hydrosphere: Phytoplankton at surface, ocean floor sediment, shells of marine organisms
- Biosphere: Organic matter in soils, living/dead organisms
- Atmosphere: CO2 makes up 0.004% of atmosphere
What is the major long-term store of carbon on Earth?
99% of all long-term stored carbon on earth is held in sedimentary rocks (60,000,000 Gt)
Held for 150 million years
How much carbon does the atmosphere store?
600Gt
Held for 6 years
Describe photosynthesis:
Process by which plants convert water and CO2 into starch and sugar in the presence of sunlight
Describe respiration:
Process in living organisms where the intake of oxygen oxidises organic substances to produce energy and release CO2
Describe oxidation:
A chemical process that weathers certain types of rock and involves the absorption of oxygen
Describe weathering:
The breakdown of rocks exposed at, or near, the land surface by physical, chemical, and biological processes
What are the two strands to the carbon cycle?
Slow carbon cycle and the fast carbon cycle
Where is carbon stored in the slow carbon cycle?
Rocks, sea floor sediments and fossil fuels
How much carbon is circulated by the slow carbon cycle?
100 million tonnes per year
How do sea-floor sediments accumulate?
- CO2 from the atmosphere diffuses into the oceans – marine organisms fix the carbon into shells to form calcium carbonate
- When marine animals die, shells sink to ocean floor and accumulate
- Over millions of years, due to heat and pressure, they are converted into carbon-rich rocks
How is carbon released during the slow carbon cycle?
- Carbon-rich sedimentary rocks that are subducted into the mantle at plate boundaries are released during volcanic eruptions
- Chemical weathering: carbonation = precipitation containing CO2 forms a weak acid which dissolves carbonate minerals in rocks, releasing CO2 into atmosphere and via rivers/streams
What are carbonaceous rocks?
Partly decomposed organic material on land that is buried beneath younger sediment
Eg Coal, oil, natural gas
What is the fast carbon cycle?
The uptake of CO2 from the atmosphere by plants during photosynthesis and the release of CO2 back into atmosphere via respiration/decomposition
How much quicker is the fast carbon cycle than the slow carbon cycle?
Between 10 and 1000 times quicker
What are the key components of the fast carbon cycle?
Plants and phytoplankton
What are phytoplankton?
Tiny photosynthesising marine organisms on the surface waters of the ocean
Components of the fast carbon cycle x4:
Photosynthesis by plants and phytoplankton = carbon absorbed
Respiration by plants and animals = carbon returned to atmosphere
Decomposition by microbes = carbon returned to atmosphere
Dissolvement of CO2 from atmosphere into oceans and vice versa
What are the processes of the carbon cycle x7?
- Precipitation
- Photosynthesis
- Respiration
- Decomposition
- Combustion
- Carbon sequestration in oceans and sediments
- Weathering
Describe how precipitation is a process in the carbon cycle:
Atmospheric CO2 dissolves in rainwater to form a weak carbonic acid
Acidity of rainfall has increased due to rising anthropogenic emissions of carbon
Describe how photosynthesis is a process in the carbon cycle:
Plants use energy from sunlight and combine CO2 from the atmosphere with water to form carbohydrates
Carbon can be sequestered in plants for long time periods
Describe how respiration is a process in the carbon cycle:
Plants/microscopic organisms release CO2 back into atmosphere
Describe how decomposition is a process in the carbon cycle:
Fungi and bacteria return CO2 into the atmosphere (as well as GHG)
Describe how combustion is a process in the carbon cycle:
Occurs when organic matter burns in the presence of oxygen
Two types:
1. Natural use = wildfires caused by lightning strikes are essential for the health of ecosystems eg coniferous forests of the Rocky mountains
2. Fossil fuel use = (gas, oil etc) contain carbon captured by living organisms over periods of millions of years and since the industrial revolution these have been mined and combusted to produce energy = release CO2 back into atmosphere
Describe how carbon sequestration is a process in the carbon cycle:
Sequestration = long-term storage of carbon
- Oceanic carbon pump: at low latitudes warm water absorbs CO2 by diffusion and at higher latitudes, cooler water sinks and transfers carbon to the deep ocean + when it returns to surface and warms, CO2 lost back to atmosphere eg North Atlantic
- Biological carbon pump: Phytoplankton fix carbon through their shells and pass it through food chain and used by shell-building organisms. Once these die they sink and decay releasing CO2 into deep water
Describe how weathering is a process in the carbon cycle:
Weathering is the in situ breakdown of rocks at the Earth’s surface by chemical physical and biological processes
- Chemical: carbonic acid in rainwater dissolves limestone and chalk through carbonation
Chemical processes transfer 0.3 billion tonnes of carbon to the atmosphere every year
eg Yorkshire Dales
- Physical: freeze-thaw breaks rocks into smaller particles and increases surface area for chemical weathering
- Biological: chelation - rainwater mixes with dead matter in the soil to form humid acids that attack minerals in the rock eg tropical environments
