The Biogeochemical Process of the Carbon Cycle
[inlineImage|link|a96dafab10b043cdbe6e9d4a6c4b005988a39476||[inlineImage|center|e6b1363d6dc3554233784f129744e89284490ffd|Global Carbon Cycle Diagram Showing Storage and Flux|]]
This cycle is driven by three biogeochemical processes.
1. Biological Component
This is the process of photosynthesis and respiration by plants and living organisms. In photosynthesis the plants remove CO2 and H2O from the atmosphere and due to sunlight, process these into sugars and starches. The sugars give the plants energy to grow. Some CO2 is expelled back to the atmosphere and this process is known as respiration. In the carbon cycle, respiration provides the flux for the carbon. Photosynthesis provides a carbon pool in the stems and trunks of trees, as shown below:
2. Geological Component
This is powered by the movement of tectonic plates that can cause volcanic action, with clouds of dust and gases including CO2 being emitted into the atmosphere. The major tectonic plates are shown below. The second image is not a nuclear explosion; it’s a volcano erupting.
Another part of the geological component, the rock cycle interacts with the carbon cycle through the weathering of rocks. The rocks are broken down by this weathering and the resulting ions are carried to the oceans by rivers and streams. Here they are converted to minerals such as calcite (CaCO3) through chemical reactions with sea water, eventually forming limestone. The limestone can be subjected to high temperatures causing it to melt and rise to the surface as CO2.
The CO2 can also be released gradually through ocean seeps or in larger quantities, and more violently by an underwater eruption much like an underwater volcano. The flux between the oceans and the atmosphere, part of the ocean carbon cycle, is shown here.
3. Chemical Component
This is a human activity due to emissions from the combustion of fossil fuels and cement production. If we look back to the start of CO2 emissions to the atmosphere, this began during the Industrial Revolution in the 1750’s. It was in this period that Britain began to use coal to provide steam and iron foundries were springing up. These processes produced large amounts of CO2 emissions that have continued to rise to today’s estimated total of 29 GtC (gigatons, or 29 milion tons, of carbon).
A graph showing the rise in CO2 emissions commencing from the Industrial Revolution is shown here:
Power stations worldwide are responsible for the greatest amounts of CO2 emissions. The United States emits 41% of all CO2 emissions from power stations.
Coal-fired power stations are the worst culprit and although the western world is slowly beginning to mitigate these stations, the third world are building more as coal is cheaper and readily available, making it unfortunately the most predominant fossil fuel used in power stations. Coal fired power stations emit 2249 lbs of carbon for every MWh of power produced. Oil-fired power stations emit 1672 lbs/MWh while natural gas plants having the lowest emissions of all at 1135 lbs/MWh.
This is made up of the use of fossil fuels for heating and cooling the home as well as cooking. Gas and oil are the most common fuels used, taking over from the old coal fires in developed countries.
Household energy accounts for on average of 20% of overall energy use in the developed countries and substantially more than this in the developing countries.
This sector is another high producer of CO2 from the use of petroleum and diesel in our automobiles, trucks, trains, ships and airplanes. Some emission values in grams/ton/kilometer are shown below.
However with the research and development in hybrid engines, along with hydrogen powered vehicles, emissions from transport are being reduced.
Large amounts of trees are still being cut down throughout the world to make way for cultivation of crops and to supply the furniture and building industries with wood. This is particularly prevalent in the Amazon Rain Forests where large sections are disappearing daily, and along with them goes one of the world’s largest sinks of carbon. Uses from de-forestation are shown here.
The cement making procedure is one of the most energy consuming processes in industry through all stages of its production. The energy used averages 4 GJ/Ton of cement produced whilst emitting over 2 GtC to the atmosphere. Cement clinker production using chemical reactions uses 50% of the total energy. This image is of a cement manufacturing kiln.