The Carbon Cycle - A Level Geography

• Carbon Cycle diagram

  
• Global carbon cycle

  comprised of a series of stores and flows.

  The main pathways between stores followed by carbon in this cycle include photosynthesis, respiration, oxidation and weathering.
• Stores in the Carbon Cycle

  - hydrosphere

  -bisophere

  - lithosphere

  - atmosphere

  -
• Hydrosphere


  = oceans

  - CO2 is dissolved into the ocean

  - carbon locked up within organisms (fish and phytoplankton)

  - carbon is stored within the surface level, intermediate (deep water), living organic matter (fish/plankton)
• Lithosphere


  = parts of the crust and the upper mantle

  - we find carbon in its inorganic form (fossil fuels and limestone)

  - organic form (lower quantities)

  - carbon is stored in fossil fuels, soil, peat and marine sediments (sedimentary rocks)
• Biosphere


  = living (plants and animals)

  - plant litter

  - soil humus

  -peat

  -animals

  -living vegetation
• Atmosphere


  = carbon in gaseous form.

  - CO2 found in the atmosphere (0.04%) = affect on controlling the Earth's temperature.

  - human factors (greenhouse gas effect, global warming, increased concentration of atmospheric CO2)
• Carbon as an element

  - chemically versatile

  - present in all life forms

  - cycled through the earth via the carbon cycle

  - organic carbon (biomass)

  - inorganic carbon (found in fossil fuels)
• Processes in the Carbon Cycle

  - human processes (burning of fossil fuels)

  - geological component (volcanoes)

  - photosynthesis

  - respiration

  - decomposition

  - oceanic carbon pumps

  - combustion

  - volcanic activity
• Stores in the carbon cycle

  - atmosphere

  - oceans

  - carbonate rocks

  - fossil fuels

  - plants

  - soils
• Carbon sinks definition


  = store that takes in more carbon than it releases.
• Carbon store definition


  = store that releases more carbon than it takes in.
• Slow carbon cycle definition

  = carbon stored in rocks, sea-floor sediments and fossil fuels is locked away for millions of years.

  - 10-100 million tonnes of carbon = amount circulated by the slow carbon cycle
• Sea floor sediments - slow carbon cycle

  CO2 in oceans is diffused where marine organisms make their shells and skeletons by fixing dissolved carbon together with calcium to form calcium carbonate.

  Remains of organisms sink to ocean floor when dead.

  They accumulate, heat and pressure convert them to carbon-rich sedimentary rocks
• Rocks - slow carbon cycle

  150 million years = residence time for carbon in rocks.

  carbon-rich sedimentary rocks, subducted into the upper mantle at tectonic plate boundaries, are vented to the atmosphere.

  Others are exposed at/near surface by erosion and tectonic movements are attacked by chemical weathering.
• Phytoplankton - fast carbon cycle


  = key components of the fast cycle.

  - through photosynthesis, they absorb CO2 from the atmosphere and combine it with water to make carbohydrates.
• Fast carbon cycle definition


  = carbon circulates most rapidly in the atmosphere, oceans, living organisms, and soils.

  - transfers are 10-100x faster than those in the slow carbon cycles

  - include phytoplankton
• atmosphere and oceans - fast carbon cycle

  Atmospheric CO2 dissolves in ocean surface waters while oceans ventilate CO2 back into the atmosphere.

  - through this exchange individual carbon atoms are stored in the oceans (average 350 yrs)
• Processes of the carbon cycle

  - precipitation

  - photosynthesis

  - weathering

  - respiration

  - combustion

  - decomposition
• Precipitation - processes of the carbon cycle

  - Atmospheric CO2 dissolves in rainwater to form weak carbon acid.

  - Rising concentrations (CO2) > anthropogenic emission increasing the acidity of rainfall.

  - contributed to ^ acidity of ocean surface waters with potentially harmful effects on marine life.
• Photosynthesis - processes of the carbon cycle


  - green plants/phytoplankton convert light energy into chemical energy via photosynthesis
• Photosynthesis equation

  = 6CO2 (carbon dioxide) + 6H2O (water) > C6H12O6 (glucose) + 6O2 (oxygen)
• Combustion - processes of the carbon cycle


  - occurs when organic material reacts in the presence of oxygen - releases CO2.

  = natural fuel.

  - results from human activities (deliberate firing of the forest and grassland)
• Respiration - processes of the carbon cycle

  = carbohydrates fixed in photosynthesis are converted to CO2 and water.

  - plants/animals absorb oxygen which burns carbohydrates, providing energy needed for metabolism/growth.

  - absorbs oxygen, releases CO2

  - volume of carbon exchanged via respiration = 1000x greater than that moving through the slow carbon cycle.
• Respiration equation


  = CH2O + O2 = CO2 + H2O + energy
• Decomposition - processes of the carbon cycle


  - bacteria/fungi breakdown organic matter, extract energy and release CO2 to the atmosphere and mineral nutrients to the soil.

  - rates depend on climatic conditions

  - fastest rate = warm, humid conditions
• weathering - processes of the carbon cycle


  = in situ breakdown of rocks at/near the Earth's surface by chemical, physical and biological processes.

  - weathering > rainwater (contains dissolved CO2)

  - weak carbon acid (dissolves limestone and chalk = carbonation)

  - chemical weathering = 0.3 billion tonnes into the atmsphere and oceans/year.

  - Physical weathering = freeze-thaw breaks rocks into smaller particles

  - Biological weathering = chelation
• Carbonation equation

  = CaCO3 + H2CO6 > Ca (HCO3)2
• Biological (organic pump)


  - Marine organisms drive this pump

  - Phytoplankton produce organic material

  - Carbon locked in them accumulate in sediments or decomposed and released
• Physical (inorganic pump)


  - involves the mixing of surface and deep ocean waters by vertical currents

  - CO2 enters through diffusion

  - transport water where it cools, becomes more dense and sinks (downwelling)

  - upwelling
• Land use changes - farming


  - deforestation reduces carbon storage in and above/below ground biomass

  - harvesting crops also removes carbon

  - changes to carbon cycle are less apparent on pasture land/farming replaces natural grasslands.
• Land use changes - forestry


  - trees extract CO2 from the atmosphere (carbon stored in the wood)

  - only become an active carbon sink in the 1st 100 years

  - changing land increases carbon stores

  - typical UK plantation = mature forest trees contain 170-200 tonnes = 10x higher than grassland, 20x higher than heathland.
• Diurnal Changes (24hr)


  - without sunlight photosynthesis switches off

  - carbon flows vary

  - daytime = CO2 flows from atmosphere to the vegetation

  - at night this flux is reversed
• Seasonal Changes
• Characteristics of the carbon and water cycle in the TRF

  Evapotranspiration - high rates due to high temperature, abundance of moisture and dense vegetation. Strong evapotranspiration -precipitation loops to maintain intense rainfall.

  
  

  Precipitation - average 2000m of rainfall.
• Why deforestation occurs in the TRF

  Roads - increasing accessibility to the amazon and the building of the Trans Amazonian Highway.

  
  

  Cattle ranching - account for 80% of deforested areas. As meat is becoming a large export for Brazil over 60% of beef was farmed in the Amazon.

  
  

  HSP schemes - Tucurui dam (1984) created Lago Tucurui which flooded 2500km2 of forest.

  
  

  Slash and burn leaves land infertile.
• Impact of deforestation on the TRF


  - removing trees for replacement of grasslands increases run-off and around half of rain falling onto grasslands runs directly into rivers.

  - Destroys the nutrient store (trees) and nutrients are no longer taken up by roots instead they are removed from the soils by rain.

  - Predicted that their will be a 20% decline in rainfall due to drying rainforests.

  - conflicts the tree cycle/system which can cause permanent climate change.
• Managing TRF

  REDD+ scheme


  = reduce emissions from deforestation and degradation.

  Aims to incentivise developing countries to keep their forests standing to reduce carbon emissions and enhance carbon stocks whilst contributing to national sustainable development.

  Surui group were the first to join the REDD+ scheme in 2009.
• Managing TRF

  Parica project

  This project aims to develop 100km2 of commercial timber plantation on government owned deforested land. Their plan is to have 20 million fast growing tropical hardwood seedlings planted on 4000 holdings to mature over a 25 year period.
• Managing TRF

  Expansion of protected land

  Landowners in the Amazon are required to keep 80% of land forested.