Carbon Cycle

• Carbon atoms can be arranged in many different physical forms called allotropes.

  • carbon dioxide
  • methane
  • calcium carbonate
  • hydrocarbons
  • biomolecules
• Examples of carbon sinks:

  • atmosphere
  • soil organic matter
  • ocean
  • marine sediment
  • terrestrial plants
  • fossil fuel deposits
  • permafrost & ice
• Photosynthesis:

  • transfers carbon stores in the atmosphere to biomass
  • plants and phytoplankton use energy from the sun to change carbon dioxide and water into glucose and oxygen - enabling the plant to grow
  • carbon is passed through the food chain and released through respiration and decomposition
• Positive feedback example:

  • increased temperatures due to climate change causing melting of permafrost, release of methane and co2 causing further increase in temperature
  • global temp rise = increased oceanic temperature = dissolved co2 released from warmer oceans = more co2 in atmosphere = more to act as greenhouse gas = further temp rise
• Negative feedback example:

  • increased atmospheric carbon dioxide leads to increased temperatures, promoting plant growth, plants remove and store more co2 from the atmosphere = decreased carbon dioxide in the atmosphere
• Fluxes - measurements of the rate of flow of material between the stores
• carbon store - store that absorbs more carbon than it releases
• carbon sink - releases more carbon than it absorbs
• Photosynthesis equation:

  carbon dioxide + water = glucose + oxygen
• Respiration

  • transfers carbon from living organisms to the atmosphere
  • plants and animals break down glucose for energy, releasing methane and carbon dioxide
• Decomposition:

  • when organisms die they are consumed by decomposers (bacteria and fungi)
  • During this, carbon from their bodies is returned to the atmosphere as carbon dioxide
  • Some organic matter passes into the soil where it is stored as humus
• Combustion:

  • combustion transfers carbon stored in living, dead or decomposed matter to the atmosphere by burning in the presence of oxygen. releasing products of carbon dioxide, water and energy
• Burial & compaction:

  • organic material is buried by sediments and becomes compacted
  • over time, these organic sediment containing carbon may form hydrocarbons such as oil and coal
  • e.g corals
• Carbon sequestration - describes the capturing of carbon from the atmosphere and putting it into long term storage in plants, soil, rock formations and oceans.

  types:

  • geologic
  • terrestrial/biological
• Geological sequestration - carbon dioxide is captured as its source and then ejected in liquid form to store underground. e.g Carbon capture
• Terrestrial/biological sequestration - plants capture carbon dioxide from the atmosphere and store the carbon in the stems/roots of the plant as well as in the soil . Aim is to develop a set of land management practices.
• Weathering:

  involves the breakdown of rocks

  when carbon dioxide is absorbed by rainwater it forms an acidic carbonic acid

  though reactions, rocks will slowly dissolve with the carbon being held in the solution

  this is transported via the water cycle to the oceans and carbon can then be used to build shells of marine organisms
• Oceanic carbon pumps:

  • carbon dioxide is directly dissolved from the atmosphere into the ocean. It is also transferred to the oceans when it is taken up by organisms that live there
  • carbon is also transferred from the ocean to atmosphere when the carbon rich water from deep in the ocean rises to the surface and releases carbon dioxide
• Deforestation:

  • trees and vegetations store carbon dioxide by absorbing it from the atmosphere in order to carry out photosynthesis
  • when vegetation are cut down this means that all the carbon dioxide is released back into the atmosphere leading to a faster rate of global warming.
• sere - a community of plants at any given stage of succession.

  as habitats progress over time they go through a sequence of changes called vegetation succession
• Temperature on carbon cycle:

  cooler:

  • cold rain water can hold more CO2 - chemical weathering more active
  • forest coverage would very different - affects distribution of processes such as photosynthesis and respiration
  • decomposers less effective - carbon transfer to soils is reduced
  • more water stored as ice - less transferred to oceans
  • soil is frozen - stopped CO2 soil transfer
• Temperature on carbon cycle:

  warmer:

  • melting of permafrost - releases trapped gases - enhances greenhouse effect - positive feedback
• State some natural changes in carbon cycle:

  • wildfires
  • volcanic activity
  • eccentricity
• Natural affect to carbon cycle

  Wildfires:

  can be started naturally or by lightning strikes

  • rapidly tranfer large quantities of carbon from biomass to the atmosphere. Loss of vegetation decreases photosynthesis, so less carbon can be removed from the atmosphere
  • In the longer term, however, fires can encourage the growth of new plants which take in carbon from the atmosphere for photosynthesis.
  • 1997-8 & 2003 Indonesia had lots of wildfires that burnt out of control for months
  • turned forest into a source
• Natural affect to carbon cycle

  Volcanic activity:

  • returns carbon that has been trapped in the lithosphere for millions of years
  • During Palaeozoic era, volcanoes were much more active
  • CO2 was emitted into the atmosphere, where it remained for a long period of time
  • now, volcanoes emit 130-180 million tonnes of CO2 each year whereas human activities release 30 billion tonnes form burning fossil fuels.
• Lake Nyros - Volcanoes

  • Cameroon 1986
  • 1,700-2,000 died
  • 3,500 cattle died
  • crater lake in the north west region
  • inactive volcanoes but 80km beneath is a pool of magma
  • the gases traveled up through the earth
  • cloud released has large concentrations of CO2, which is denser than oxygen.
  • travelled down the mountain, settling into valleys where it suffocated all inhabitants
• Volcanoes release gases but do not contribute to global warming due to the sulphur dioxide creates sulphur aerosols that actually reflect the suns rays. Global cooling
• Hydrocarbons - substances that only contains carbon and hydrogen. e,g coal, oil or natural gas
• Fossil fuel formation:

  • formed from prehistoric plants and animals
  • when dead, they decompose and become buries under layers of mad, sand and rock
  • they slowly decompose into organic materials ad form fossil fuels
  • overtime, work upwards through the crust until reaching rock formations called cap-rocks that are dense and prevent them seeping to the surface
• Land use - human affect to carbon cycle

  • co2 emission that result from land use change (mainly deforestation) account for up to 30% of anthropogenic emissions
  • vegetation is removed making way for buildings
  • concrete production releases lots of carbon dioxide
• Shimplings pack farm

  • Bury St Edmunds, Suffolk
  • a large organic arable farm specialising in wheat, barley, oats and quinoa
  • farm has calculated its carbon emissions 1150 tonnes CO2, mainly from fuel for machinery also nitrous oxide emissions from crop residues and green manures.
  • flock of 250 sheep contributes 6.6% of emissions
  • 40% emissions are offset by carbon sequestration from the farm
  • significant carbon sinks
• Positives of Shimplings farm pack

  • carbon sequestration in soils
  • organic agriculture can remove air
  • to increase yield in drought years as the additional carbon stored helps it to hold more water
  • By 2030, agriculture sector could be carbon neutral
• Human impacts on carbon cycle

  Deforestation:

  • logging operations remove forests, some act illegally also build roads to access more remote forest
  • forests also cut down due to urban sprawl
  • some in unintentional
  • rainforests could vanish in 100 years
  • forests soils are moist but without any protection from tree cover will ry out
  • trees also maintain the water cycle by returning vapour back to the atmosphere through transpiration
  • without trees many former forest land can quickly turn into barren deserts
• Carbon budget

  • the difference between inputs of carbon and outputs of carbon from it
  • the balance of inputs and output determines whether it acts as a carbon source or a carbon store
• carbon storage in the lithosphere

  • over 99.9% of carbon on earth is stored in sedimentary rocks such as limestone
  • 0.004% of carbon on the earth is stored in fossil fields, such as coal and oil
• storage of carbon in the hydrosphere

  • carbon dioxide is dissolved in lakes, rivers and oceans
  • the oceans the second largest store on earth, containing 0.04% of the earths carbon. The majority of carbon here is found deep in the ocean from dead organisms forming a layer of carbon rich sediment
  • a small amount is found at the surface where it is exchanged with the atmosphere
• storage of carbon in the biosphere

  • carbon is stored in the tissues of all living organisms. It is transferred to the soil when organisms die
  • contains about 0.004% of the earths carbon
  • soil humus - thick brown substance that remains after most of the litter has decomposed
  • peat - accumulation of partly decayed vegetation, formed in wetlands where it is fully saturated so oxygen cannot enter
• storage of carbon in the atmosphere

  • carbon is stored as carbon dioxide and in smaller quantities as methane in the atmosphere
  • atmosphere contains about 0.001% of the earths carbon
  • co2 is a potent greenhouse gas and plays a vital role in regulating the earths temperature
• storage of carbon in the cryosphere

  • contains less than 0.01% of the earths carbon
  • found in the soil in areas of permafrost where decomposing plants and animals have frozen into the ground
• weathering

  • chemical weathering transfers carbon from the atmosphere to the hydrosphere and biosphere
  • atmospheric carbon reacts with water vapour to form acid rain. when this acid rain falls onto rocks, a chemical reaction occurs which dissolves the rocks. The molecules resulting from this reaction may be washed into the sea. here they react with carbon dioxide dissolved in water to form calcium carbonate, which is used by sea creatures e.g to make shells