The Carbon Cycle

• carbon is found in all earth systems in organic forms (living) and inorganic (rocks , gases & fossil fuels 🪨)
• Carbon cycle : lithosphere ⛰️

  99.9%

  stored as sedimentary rocks & fossil fuels (0.004%)
• Carbon cycle: atmosphere

  0.001%

  stored as $CO_2$ and small amounts of$CH_4$
• Carbon cycle : biosphere 🌱

  0.004%

  stored in tissues of living organisms

  die = decay = C in soil
• Carbon cycle : cryosphere ❄️

  0.01%

  most in soil in permafrost where decomposing plants/animals have froze into ground
• Carbon cycle : hydrosphere 💧

  0.04%

  $CO_2$dissolved into rivers , lakes & oceans (majority in deep ocean)

  small amount found at ocean surface where its exchanged with atmosphere
• Carbon cycle :

  process by which carbon is stored and transferred
• carbon cycle is a closed system
• some carbon is sequestered away in long term stores that's released by burning fossil fuels (input)
• Carbon budget:


  differences between systems inputs & outputs

  (balance determines if its a sink or source)
• Natural processes affecting carbon cycle:

  1. Wildfires 🔥
  2. Volcanic activity 🌋
• Wildfires 🔥:


  . rapidly transfer lots of C from biomass/soil to atmosphere

  . loss of vegetation 🌳 = ⬇️ photosynthesis = less C removed from atmosphere

  . long term: fires encourage new plant growth = remove C (neutral effect)
• Volcanic activity 🌋:

  . release C stored in magma to atmosphere as $CO_2$

  . recent ones released less C than humans

  . potential large one to disrupt cycle lots = global scale
• Human activities affecting carbon cycle :

  Industrial Revolution 🏭 = increased flows from lithosphere & biosphere to atmosphere

  1. Deforestation 🪓
  2. Land use changes
  3. Hydrocarbon (FF) extraction & use
  4. Farming 🐄
• Deforestation :

  . forests cleared for development

  . reduces store size

  burned = rapid flow into atmosphere
• Land use changes :

  . natural to urban

  . veg removed = reduces bio store

  . concrete production releases $CO_2$
• Hydrocarbon (FF) extraction & use :

  . extraction & combustion releases $CO_2$

  . without human intervention it would remain sequestered
• Farming 🐄 :

  . animals release $CO_2$&$CH_4$ into atmosphere when they respire/digest

  . ploughing releases$CO_2$ stored in soil

  . rice paddies release $CH_4$
• Carbon stores :


  1. Atmosphere
  2. Soils
  3. Fossil fuels
  4. Ocean
  5. Vegetation
  6. Earths Crust
  7. Sediments
• Carbon flows :


  1. Photosynthesis
  2. Combustion
  3. Ocean Uptake & Loss
  4. Sequestration
  5. Respiration
  6. Decomposition
  7. Weathering
• Photosynthesis:

  . plants & phytoplankton convert C stored in atmosphere into biomass using light energy = enables them to grow

  . C passed through food chain and released by respiration & decomposition
• Combustion :

  . transfers C stored in living / dead / decomposed biomass (peaty soils) to atmosphere by burning

  . wildfires 🔥
• Ocean Uptake & Loss

  . uptake : $CO_2$directly dissolved from atmosphere to ocean or taken from organisms

  . loss : carbon rich water from deep sea rises to surface and releases $CO_2$ to atmosphere
• Sequestration :

  . C from atoms captured and held in sedimentary rocks / FF formed over millions of years

  . dead animal/plant material falls to floor and compacted
• Weathering :

  . chemical weathering transfers C from atmosphere to hydrosphere/biosphere

  . atmosphere C + water vapour = acid rain ☔️

  . falls on rocks = chemical reaction = dissolves rocks

  . washed into sea = react with C in eater = calcium carbonate = used to make shells 🐢
• Decomposition :

  . C transfer from dead biomass to soil & atmosphere

  . bacteria 🦠 & fungi 🍄‍🟫 break down dead organisms = release $CH_4$

  . some C into soil as humus
• photosynthesis , respiration , combustion & decomposition are fast carbon flows
• sequestration is a slow carbon flow
• flows depend on spatial scale (eg: plant main flow is photosynthesis but ecosystem is combustion)
• Carbon cycle effects on Atmosphere & Climate :

  . affects amount of greenhouse gases (trap sun energy) = temps expected to rise (Global warming)

  . intense storms
• Carbon cycle effects on Land :

  . allows plant photosynthesis = growth

  . no decomposition = nutrients not recycled

  . changes in C stored in land (permafrost) = released to atmosphere

  . wildfire frequency due to global temp
• Carbon cycle effects on Ocean :

  . used by organisms for photosynthesis & shells

  . ⬆️ atmospheric $CO_2$ = ⬆️ ocean acidity (adverse effects on marine life)

  . global warming = may kill temp sensitive organisms = phytoplankton die = less $CO_2$ removed from atmosphere by them

  . warmer water less able to absorb $CO_2$