The Carbon Cycle: Closed system


  • Lithosphere: over 99.9% of the carbon on earth is stored in sedimentary rock such as limestone
    • Fossil fuels: 50 00 – 10000 pt
  • Atmosphere: CO2, CH4, enters through respiration, removed by photosynthesis
    • The atmosphere contains 0.001% of carbon
  • Hydrosphere: Carbon dioxide is dissolved in rivers and lakes and oceans
    • Oceans the second largest carbon store on earth containing 0.04% of the earths carbon.
    • Surface Ocean: 725pt
  • Biosphere: Carbon is stored in the tissues of living things, transferred to soil via decomposition
    • Contains approximately 0.004% of the earths carbon
    • Plants: 560pt
  • Cryosphere: most of the carbon in the Cryosphere is in the soil in areas of permafrost where decomposing plants and animals have frozen into the ground.
    • Contains less than 0.01% of the earths carbon



Flux: refers to the movement or transfer of carbon between stores, they create cycles and feedbacks

Biggest Fluxes per year:

  • Photosynthesis: plants and phytoplankton use energy from the sun – 120 pt
  • Plant respiration – 59 pt
  • Litter fall – 59 pt
  • Soil decomposition: bacteria and fungi break down, CO2 and methane are released- 58pt
  • Ocean uptake: carbon dissolved directly into oceans or taken up by organisms- 92 pt
  • Ocean loss: carbon rich water from the deep oceans rise to the surface and release co2- 90pt
  • Burning fossil fuel s – 7.7  (10 giggatonnes of carbon from fossil fuels annually)
  • Deforestation and land use – 1.1
  • Weathering: Transfers carbon from the atmosphere into the hydrosphere and biosphere
  • Volcanoes – 0.1


Fast and Slow Carbon Flows

  • Fast flows quickly transfer carbon between sources, it only takes minutes, hours or days
    • Photosynthesis, respiration, combustion and decomposition
  • Slow carbon flows slowly transfer carbon between sources, they can take years
    • Sequestration


Natural Processes and Changes to the Carbon Stores:

  • Wildfires: Rapidly transfer large quantities of carbon from biomass to the atmosphere
    • BUT in long term can an encourage the growth of new plants, which take in carbon = Neutral
  • Volcanic Activity: carbon stored within the Earth in magma is released during volcanic eruptions


Human Activity and Changes to the Carbon Stores:

  • Hydrocarbon extraction and use: 40% more CO2 in atmosphere since 1750 because of humans burning fossil fuels
  • Farming: animals release carbon dioxide and methane when they respire and digest food
    • Ploughing releases carbon dioxide stored in soil and rice paddies releases lots of methane


The Carbon budget: the difference between the inputs and outputs of carbon – Source or Sink?


The Effects of Carbon: Keeling curve

  • Climate: greenhouse gases trap some of the sun’s energy, keeping some of the heat in
  • IPCC predict by 2100 there will be a 4OC increase
  • Land: Effects vegetation, permafrost, wildfires
  • Oceans:
    • Acidity due to absorbing more CO2
    • Phytoplankton, may not be able to survive at higher temperatures

Warmer water is less able to absorb CO2, so as temperatures rise