Carbon cycle:

• Geological Carbon Cycle


  The movement and storage of carbon between the land, ocean and the atmosphere
• Forms of carbon in the Carbon Cycle


  • Inorganic (found in rocks as bicarbonates and carbonates)
  • Organic (found in plant material and living organisms)
  • Gaseous (found as CO2 and CH4 (methane))
• There is generally a balance between production and absorption (or sources and sinks) of carbon in the natural carbon cycle
• It takes a long time for equilibrium to be reached in the natural carbon cycle e.g. after a volcanic eruption
• Stores


  Terrestrial, oceanic or atmospheric
• Fluxes


  The movement/transfer of carbon between stores
• Carbon sink


  Any store which takes in more carbon than it emits (e.g. intact tropical rainforest)
• Carbon source


  Any store that emits more carbon than it stores (e.g. damaged tropical rainforest)
• Stores of carbon


  • Atmosphere as CO2 and methane
  • Hydrosphere as dissolved CO2
  • Biosphere in living and dead organisms
  • Lithosphere as carbonates in limestone and fossil fuels like coal, gas and oil
• Carbon Sequestration


  The transfer of carbon from the atmosphere to other stores, can be both natural and artificial
• Carbon sequestration example


  • A plant sequesters carbon when it photosynthesises and stores the carbon in its mass
• Main Carbon Stores (In order of magnitude)

  • Marine Sediments and Sedimentary Rocks - Lithosphere - Long-term
  • Oceans - Hydrosphere - Dynamic
  • Fossil Fuel Deposits - Lithosphere - Long-term but currently dynamic
  • Soil Organic Matter - Lithosphere - Mid-term
  • Atmosphere - Dynamic
  • Terrestrial Plants - Biosphere - Mid-term but very dynamic
• Marine Sediments and Sedimentary Rocks


  • Easily the biggest store, 66,000 - 100,000 million billion metric tons of carbon, the rock cycle and continental drift recycle the rock over time, but this may take thousands, if not millions of years
• Oceans


  • The second biggest store contains a tiny fraction of the carbon of the largest store, 38,000 billion metric tons of carbon, the carbon is constantly being utilised by marine organisms, lost as an output to the lithosphere, or gains as an input from rivers and erosion
• Fossil Fuel Deposits


  • Used to be rarely changing over short periods of time, but humans have developed technology to exploit them rapidly, though 4000 billion metric tons of carbon remain as fossil fuels
• Soil Organic Matter


  • Can store carbon for over a hundred years, but deforestation, agriculture and land use change are affecting this store, 1500 billion metric tons of carbon stored
• Atmosphere


  • Human activity has caused CO2 levels in the atmosphere to increase by around 40% since the industrial revolution, causing unprecedented change to the global climate, 750 billion metric tons of carbon stored
• Terrestrial Plants


  • Vulnerable to climate change and deforestation and as a result carbon storage in forests is declining annually in some areas of the world, 560 billion metric tons of carbon
• The lithosphere is the main store of carbon, with global stores unevenly distributed
• The oceans are larger in the southern hemisphere, and storage in the biosphere mostly occurs on land
• Terrestrial plant storage is focussed in the tropics and the northern hemisphere
• Carbon cycle transfers


  • Act to drive and cause changes in the carbon over time
  • Have impacts of varying magnitude over different lengths of time
• Biological and chemical processes

  Determine how much carbon is stored and released
• Role of living organisms

  Very important in maintaining the system running efficiently
• Photosynthesis


  1. Living organisms convert Carbon Dioxide from the atmosphere and Water from the soil, into Oxygen and Glucose using Light Energy

  2. Removing CO2 from the atmosphere, plants are sequestering carbon and reducing the potential impacts of climate change

  3. Chlorophyll in the leaves of the plant react with CO2 to create the carbohydrate glucose

  4. Helps to maintain the balance between oxygen and CO2 in the atmosphere
• The formula for photosynthesis is Carbon Dioxide + Water + Light Energy = Oxygen + Glucose
• Respiration


  1. Plants and animals convert oxygen and glucose into energy which then produces the waste products of water and CO2

  2. Chemically the opposite of photosynthesis
• During the day, plants photosynthesise, absorbing significantly more CO2 than they emit from respiration
• During the night, plants do not photosynthesise but they do respire, releasing more CO2 than they absorb
• Overall, plants absorb more CO2 than they emit, so are net carbon dioxide absorbers (from the atmosphere) and net oxygen producers (to the atmosphere)
• Combustion


  1. Fossil fuels and organic matter such as trees are burnt

  2. They emit CO2 into the atmosphere, that was previously locked inside of them

  3. This may occur when fossil fuels are burnt to produce energy

  4. Or if wildfires occur
• Decomposition


  1. Living organisms die

  2. They are broken down by decomposers (such as bacteria and detritivores)

  3. Decomposers respire, returning CO2 into the atmosphere

  4. Some organic matter is also returned to the soil where it is stored adding carbon matter to the soil
• Diffusion


  1. The oceans can absorb CO2 from the atmosphere

  2. This has increased ocean acidity by 30% since pre-industrial times

  3. The ocean is the biggest carbon store

  4. But with carbon levels increasing seawater becomes more acidic

  5. This is harming aquatic life by causing coral bleaching

  6. Many of the world's coral reefs now under threat
• Sedimentation


  1. When shelled marine organisms die, their shell fragments fall to the ocean floor

  2. They become compacted over time to form limestone

  3. Organic matter from vegetation and decaying marine organisms is compacted over time, whether on land or in the sea, to form fossil fuel deposits
• Weathering and Erosion


  1. Inorganic carbon is released slowly through weathering

  2. Rocks are eroded on land or broken down by carbonation weathering

  3. Carbonation weathering occurs when CO2 in the air mixes with rainwater to create carbonic acid which aids erosion of rocks such as limestone

  4. The carbon is moved through the water cycle and enters the oceans

  5. Marine organisms use the carbon in the water to build their shells

  6. Increasing carbon dioxide levels in the atmosphere may increase weathering and erosion as a result, potentially affecting other parts of the carbon cycle
• Metamorphosis


  1. Extreme heat and pressure forms metamorphic rock

  2. During which some carbon is released and some becomes trapped
• Volcanic outgassing


  1. There are pockets of CO2 found in the Earth's crust

  2. During a volcanic eruption or from a fissure in the Earth's crust, this CO2 can be released
• The quickest cycle


  • Plants absorb carbon for photosynthesis and then they release carbon when they respire
  • This cycle can slow down when levels of light or CO2 drop
• Dead organic material in soil


  • May hold carbon for hundreds of years
  • Some organic materials may become buried so deeply that they don't decay, or are buried in conditions unfavourable to decayers (potent low-lying gas, too much water)
  • This material will become sedimentary rocks or hydrocarbons by geological processes
• Ocean carbon sink


  Oceans store 50 times more carbon than the atmosphere