carbon 6.1 - 5

• The 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 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
• Carbon source

  Any store that emits more carbon than it stores
• Stores of Carbon Cycle

  • The atmosphere as CO2 and methane
  • The hydrosphere as dissolved CO2
  • The lithosphere as carbonates in limestone and fossil fuels like coal, gas and oil
  • The biosphere in living and dead organisms
• Carbon Sequestration


  The transfer of carbon from the atmosphere to other stores, can be both natural and artificial
• 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
• The lithosphere is the main store of carbon, with global stores unevenly distributed
• Photosynthesis


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


  Plants and animals convert oxygen and glucose into energy which then produces the waste products of water and CO₂
• Plants absorb more CO₂ than they emit, so are net carbon dioxide absorbers (from the atmosphere) and net oxygen producers (to the atmosphere)
• Combustion


  Fossil fuels and organic matter such as trees are burnt, emitting CO₂ into the atmosphere
• Decomposition


  Living organisms die and are broken down by decomposers, returning CO₂ into the atmosphere
• Diffusion


  The oceans can absorb CO₂ from the atmosphere
• Sedimentation


  Shelled marine organisms die and their shell fragments fall to the ocean floor and become compacted over time to form limestone
• Weathering and Erosion

  Inorganic carbon is released slowly through weathering: rocks are eroded on land or broken down by carbonation weathering
• Metamorphosis

  Extreme heat and pressure forms metamorphic rock, during which some carbon is released and some becomes trapped
• Volcanic outgassing


  CO2 found in the Earth's crust is released during a volcanic eruption or from a fissure in the Earth's crust
• The quickest cycle in the carbon cycle is completed in seconds as plants absorb carbon for photosynthesis and then they release carbon when they respire
• Dead organic material in soil may hold carbon for hundreds of years
• Ocean sequestration


  The transfer of CO2 into the sea
• Small changes in oceanic carbon levels can have significant global impacts
• The majority of the processes which take the CO2 out of the atmosphere and into the ocean occur in the top surface layer which makes up only a small proportion of the water in the world's ocean
• The Biological Carbon Pump


  Phytoplankton take in carbon and turn it into organic matter, which is then passed through the marine food web
• The Physical Pump

  Oceanic circulation provides a constant source of new water on the surface while transferring surface water into the deep ocean, enabling the ocean to store so much carbon
• Thermohaline Circulation

  An ocean current that produces both vertical and horizontal circulation of cold and warm water around the world's oceans
• The rate of absorption of CO2 into the ocean depends on ocean temperatures. The colder the water, the more CO2 is absorbed
• Terrestrial Sequestration


  Primary producers sequester carbon through the process of photosynthesis
• 95% of a tree's biomass consists of CO2 which is sequestered and converted to cellulose
• The amount of carbon stored in trees depends on the balance of respiration and photosynthesis
• Carbon fluxes due to terrestrial organisms vary diurnally and seasonally
• Tropical areas such as Brazil and Indonesia have seen a decrease in carbon stocks of around 5 Gigatons of Carbon (GtC) in the last 25 years, but Russia, USA and China have seen an increase
• Decomposition


  • Faster in tropical climates with high rainfall, temperatures and oxygen levels
• Amount of carbon stored in trees

  Depends on the balance of respiration and photosynthesis
• Carbon fluxes due to terrestrial organisms

  1. Diurnally - positive from atmosphere to ecosystem during day, negative from atmosphere to ecosystem at night

  2. Seasonally - high atmospheric CO2 in northern hemisphere winter, low in spring as plants grow
• Forest area changes


  • Pink - forest area lost
  • Purple - forest area gained