Carbon Fluxes


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•  Estimation of carbon fluxes due to processes in the carbon cycle

Carbon fluxes describe the rate of exchange of carbon between the various carbon sinks / reservoirs

  • There are four main carbon sinks – lithosphere (earth crust), hydrosphere (oceans), atmosphere (air), biosphere (organisms)

The rate at which carbon is exchanged between these reservoirs depends on the conversion processes involved:

  • Photosynthesis – removes carbon dioxide from the atmosphere and fixes it in producers as organic compounds 
  • Respiration – releases carbon dioxide into the atmosphere when organic compounds are digested in living organisms
  • Decomposition – releases carbon products into the air or sediment when organic matter is recycled after death of an organism
  • Gaseous dissolution – the exchange of carbon gases between the ocean and atmosphere
  • Lithification – the compaction of carbon-containing sediments into fossils and rocks within the Earth’s crust (e.g. limestone)
  • Combustion – releases carbon gases when organic hydrocarbons (coal, oil and gas) are burned as a fuel source

It is not possible to directly measure the size of the carbon sinks or the fluxes between them – instead estimates are made

  • Global carbon fluxes are very large and are therefore measured in gigatonnes (1 gigatonne of carbon = 1 billion metric tonnes)
  • Because carbon fluxes are large and based on measurements from many different sources, estimates have large uncertainties 

Global Carbon Fluxes

carbon flux

Estimating carbon fluxes requires an understanding of the factors that can affect the exchange of carbon between different sinks

  • Some of the main causes for flux change include climate conditions, natural events and human activity 

Climate Conditions

  • Rates of photosynthesis will likely by higher in summer seasons, as there is more direct sunlight and longer days
  • Oceanic temperatures also determine how much carbon is stored as dissolved CO2 or as hydrogen bicarbonate ions
  • Climate events like El Nino and La Nina will change the rate of carbon flux between ocean and atmosphere
  • Melting of polar ice caps will result in the decomposition of frozen detritus

Natural Events

  • Forest fires can release high levels of carbon dioxide when plants burn (loss of trees also reduces photosynthetic carbon uptake)
  • Volcanic eruptions can release carbon compounds from the Earth’s crust into the atmosphere

Human Activity

  • Clearing of trees for agricultural purposes (deforestation) will reduce the removal of atmospheric CO2 via photosynthesis
  • Increased numbers of ruminant livestock (e.g. cows) will produce higher levels of methane
  • The burning of fossil fuels will release carbon dioxide into the atmosphere

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•  Analysis of data from air monitoring stations to explain annual fluctuations

Atmospheric CO2 concentrations have been measured at the Mauna Loa Observatory (in Hawaii) since 1958 by Charles Keeling

From these continuous and regular measurements a clear pattern of carbon flux can be seen:

  • CO2 levels fluctuate annually (lower in the summer months when long days and more light increase photosynthetic rates)
  • Global CO2 trends will conform to northern hemisphere patterns as it contains more of the planet’s land mass (i.e. more trees)
  • CO2 levels are steadily increasing year on year since the industrial revolution (due to increased burning of fossil fuels)
  • Atmospheric CO2 levels are currently at the highest levels recorded since measurements began

Changes in Carbon Dioxide Levels (Keeling Curve)

keeling curve

Data is now being regularly collected at a variety of field stations globally, using standardised measurement techniques

  • All stations show a clear upward trend in atmospheric CO2 concentrations year on year, with annual fluctuations
  • Different monitoring stations may have slightly different trends due to seasonal variations and the distribution of local vegetation

Analysing Carbon Data

Carbon data can be plotted and analysed using the online database at CDIAC (Carbon Dioxide Information Analysis Centre)

  • This website stores data on atmospheric CO2 levels, which can be imported into an Excel spreadsheet in order to graph

How to use the CDIAC database:

  • Access the CDIAC website (click on the link to redirect)
  • Click on ‘Atmospheric Trace Gases and Aerosols’ (under ‘Data' tab at top of page)
  • Select ‘Carbon dioxide’ from the list of greenhouse gases
  • Choose a monitoring station / network (e.g. Scripps Institution of Oceanography Network)
  • Download data from a particular site (e.g. South Pole, Antarctica)
  • Paste data of interest into an Excel spreadsheet to produce a graphical display (e.g. Jan 2000 – Dec 2007)

Using the conditions listed above, the following carbon data was plotted using Excel:

antarctic carbon data