Carbon cycle

• 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

  
• 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


  • 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
• 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


  Pockets of CO2 found in the Earth's crust are released during a volcanic eruption or from a fissure in the Earth's crust
• The quickest 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
• 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

  
• Biological Carbon Pump


  Phytoplankton photosynthesise and take in carbon, turning it into organic matter. When they get eaten, carbon is passed through the food chain
• 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

  
• As ocean temperatures increase, the oceans will absorb less CO2 (possibly even emitting some of its stored carbon dioxide), accelerating Climate Change and leading to further ocean warming (positive feedback mechanism)

  
• Terrestrial Sequestration


  Primary producers sequester carbon through the process of photosynthesis. All living things either release or intake carbon

  
• 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 increases of around 0.3, 2.9 and 2.3 GtC respectively

  
• Non-tropical forests have seen an increase in carbon sequestration in recent years, especially in Europe and Eastern Asia, due to conversion of agricultural land and plantations to new forests

  
• Forests in industrialised regions are expected to increase by 2050 but in the global south, forests are declining
• CO2 levels in the atmosphere begin to drop during spring when plants begin to grow
• Pink


  Forest area lost
• Purple


  Forest area gained
• The map shows how forests are declining in the tropical areas in the southern hemisphere and growing in the northern hemisphere

  
• Non-tropical forests


  • Have seen an increase in carbon sequestration in recent years, especially in Europe and Eastern Asia, due to conversion of agricultural land and plantations to new forests

  
• Forests in industrialised regions are expected to increase by 2050 but in the global south, forested areas will decrease
• Rate of forest loss has decreased from 9.5 million hectares per year in the 1990's to 5.5 million hectares per year in 2010-15