The carbon cycle is the biogeochemical cycle through which carbon is exchanged among the hydrosphere, geosphere, pedosphere, biosphere, and atmosphere of the earth. Carbon is the major component of biological compounds and also a major component of many minerals like limestone. The carbon cycle together with the water cycle and nitrogen cycle comprises a sequence of events that are fundamental in making the earth capable of sustaining life. This cycle describes the movement of carbon during recycling and reuses all through the biosphere. It also covers the long-term processes of carbon sequestration.
The global carbon cycle is divided into different major reservoirs of carbon that are interconnected by the pathways of exchange.
Carbon exchanges between reservoirs occur due to different chemical, geological, physical and biological processes. Oceans contain the largest active pool of carbon near the earth’s surface. The natural carbon flow between the atmosphere, ocean, terrestrial ecosystem and sediments is fairly balanced in order for the carbon atoms to be roughly stable without human influence.
ATMOSPHERE
The atmosphere of the earth has two main forms of carbon: carbon dioxide and methane. Both of these gases absorb and retain heat in the atmosphere and they are partially responsible for the greenhouse effect. Methane produces a greater greenhouse effect per volume compared to carbon dioxide. However, methane exists in lower concentrations and is more short-lived than carbon dioxide. Carbon dioxide is, therefore, the more important greenhouse gas of the two.
Carbon dioxide is removed from the atmosphere mainly through photosynthesis and it enters the oceanic and terrestrial biospheres. Carbon dioxide may also dissolve directly into water bodies (lakes, oceans, etc.), and in precipitation as raindrops fall through the atmosphere. Carbon dioxide forms carbonic acid when dissolved in water. This contributes to ocean acidity.
TERRESTRIAL BIOSPHERE
The terrestrial biosphere is made up of organic carbon in all the organisms that live on land. This includes those alive or dead and carbon stored in soils. Most carbon in the terrestrial biosphere is organic carbon, while about a third of soil carbon is stored in inorganic forms like calcium carbonate. Organic carbon is the main component of all organisms that live on earth. Autotrophs extract it from the air as carbon dioxide and convert it into organic carbon. Heterotrophs receive carbon by consuming other organisms.
OCEAN
The ocean can be divided into the surface layer, mixed layer, and deep layer. The surface layer is that which makes frequent contact with the atmosphere. Carbon enters the ocean mainly through the dissolution of carbon from the atmosphere. A small fraction of this carbon is converted to carbonate. Carbon also enters the ocean through rivers as dissolved organic carbon. It is converted by organisms into organic carbon by the process of photosynthesis and it can either be exchanged all through the food chain or precipitated into the deeper layers of the ocean.
SUMMARY
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