The carbon cycle is the biogeochemical cycle by which carbon is exchanged between the biosphere , lithosphere, hydrosphere and atmosphere of the earth. Carbon is the basic constituent of all organic compounds and is the major elements forming around 49% of the weight of the organisms . the atmosphere also consist around 0.032% carbon. carbon is fixed in the form of plants through photosynthesis. During photosynthesis carbon dioxide present in the air (atmosphere) and dissolved in the water is used . A large amount of carbon dioxide is also found dissolved in oceans Oceans comprise of 50% more carbon dioxide in comparison to atmosphere.
The major source of carbon in all living beings , dead organic matter and fossils deposits is in the form of carbon dioxide . in the environmental phase, carbon dioxide resides in the reservoir or sinks such as atmosphere or the surface water. The surface water is present in lakes rivers and oceans . The four main reservoir of carbon namely atmosphere, terrestrial biosphere (usually includes freshwater system) ‚oceans and sediments (includes fossils rules) are interconnected with each other . About 99% of the total carbon is present on the earth’s crust as deposit of coal, petroleum, peat and limestone . weathering of rocks , burning of fossils fuels , volcanic activity returns the bound carbon to the atmospheric aquatic reservoir.
The exchange of carbon between to the atmosphere aquatic reservoir occurs because of various chemical , physical ‚geological and biological processes . The oceans contains largest pool of carbon near the suface of the earth . According to estimate carbon pool involved in global carbon cycle is around 55000 gigatons. The oceans contain 38000 gigatons of active carbon pool as bicarbonate and carbonate ions.
The carbon dioxide (gaseous form of carbon) from the atmospheric reservoir is taken up by the producers and then transferred to consumer to decomposer and back to reservoir. Atmospheric carbon dioxide is absorbed by plants and other photosynthetic organism present in the terrestrial ecosystem. This way the carbon dioxide enters the organismic phase . About 4 — 9 × 10 13 kg of carbon dioxide is fixed through photosynthetic activity of plants each year . the living organisms convert carbon dioxide into organic food material which are passed to other trophic level of the food chain. Carbon dioxide enters the environmental phase via cellular energy production I.e. respiration of the organism in the grazing abd detritus food chains.
In aquatic environment dissolved carbon dioxide carbon dioxide is utilised by phytoplankton. Carbon present as bicarbonate and carbonates gets converted into carbon dioxide that is used by phytoplankton . the carbon dioxide released during respiration is also reutiliized by the phytoplankton. The carbon dioxide released during respiration is also reutilized by the phytoplankton to produce more biomass . carbon bound in the shells of snails , foraminifera as carbonates is also deposited in sediments after the death of animals . A significant fraction of carbon gets buried in the sediment and is removed from circulation.
The carbon dioxide present in atmosphere exists in dynamic equilibrium with that present in oceans . Atmospheric carbon dioxide gets easily dissolved in water or the aquatic phase through precipitation . The dissolved carbon dioxide forms carbonic acid which dissociate to form hydrogen and carbonate ions. The Rate of reaction depends upon the concentration of carbon dioxide . All these events shift the equilibrium of the carbon concentration. Some amount of bio carbonate ions are used by aquatic plants during photosynthesis. Other molecules of carbon monoxide (CO) , methane (C6H12O6) and many others as well as many ions containing carbon .
The global carbon budget is the balance of the exchange (incomes and losses ) of carbon between the reservoir or one specific loop (eg. Atmosphere biosphere) of the carbon cycle . an examination of the carbon budget of a pool or reservoir can provide information about whether the pool or reservoir is functioning as a source or sink for carbon dioxide. The difference between the carbon uptake by plants during photosynthesis and released through respiration gives the net primary productivity. the rate of primary productivity and decomposition determines the rate at which carbon cycles through the ecosystem . In warm wet ecosystem such as tropical rainforests, the production and decomposition rates are high , hence the carbon is cycled quickly . in cooler ecosystem the decomposition is slow hence the dead organic matter accumulates . The production and use of carbon dioxide varies depending upon the temperature availability.
Human Impact on Carbon cycle
Industrial revolution and increasing human activities such as large scale fossils fuel burning have increased the concentration of carbon dioxide in the environment. Before the industrial revolution a balanced amount of carbon dioxide has increased several hundred folds.
According to an estimate around 8 billion tons of carbon dioxide is added to the atmosphere each year and levels have increased by 35% in the last 130 years . The amount has increased mainly due to combustion of fossils fuels and deforestation.
As the level of carbon dioxide increases , the global temprature also increase. This is because carbon dioxide traps the heat escaping from earth. The rise in temperature alters. The rainfall pattern affecting the agricultural production.
The changes in food production can affect the survival of species present. In an area . Indirectly the rise in temperature can lead to melting of glaciers , raising the sea level by several meters and hence threatening the survival of organisms living in the coastal areas.