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Carbon is one of the most important elements and it is a major constituent of life on Earth. This element is the primary chemical constituent of most living matter and it is found in large proportions on our planet. At any given time, carbon is stored in various reservoirs on the planet. Some of the major global reservoirs that store carbon include organic compounds, atmospheric carbon dioxide, the soil, rocks, and the ocean.
Carbon does not stay in any of these reservoirs permanently and it moves between the various stores in the process referred to as the carbon cycle. Over a time scale that extends to thousands of years, the atmosphere, land, and oceans exchange huge quantities of carbon through biological, physical, and chemical means. An understanding of the carbon cycle will assist in the understanding of the Earth’s climatic history. This paper will discuss the carbon cycle, which is the continuous movement of carbon atoms through different paths, with a focus on the two major divisions of the process and the human impact on the carbon cycle.
Defining the Carbon Cycle
The carbon cycle is the process through which carbon moves between the different carbon reservoirs. These reservoirs exist in land and water-based systems. Arwyn and Broll (2012) reveal that through its many forms, carbon can move between the “atmosphere, hydrosphere, biosphere, pedosphere, and lithosphere” (p.119). The land surface, soil, the atmosphere, water bodies, and vegetation all act as carbon stores. Each of these carbon stores can be regarded as a sink and a source.
The storage pools are considered sinks since they can take the carbon from the atmosphere and hold it (Folger, 2009). The storage pools are also considered carbon sources since they release carbon into the atmosphere through various chemical processes.
Arwyn and Broll (2012) note that the carbon cycle is the natural process through which carbon atoms are recycled. For example, the same carbon atoms produced from burning wood many years ago could become a part of a plant through photosynthesis and later became a part of a human being who consumes the plant. The carbon cycle is responsible for keeping the Earth in a stable climatic state. The carbon exchange between the various sources and skins ensures that the carbon contained in the atmosphere is at a healthy level. The carbon cycle can be divided into biological and geological cycles.
The Biological Carbon Cycle
This is the circulation of carbon between land-based and water-based systems. These systems comprise “the ocean, the atmosphere, the soil, and the biosphere” (Levin, 2009, p.43). This is collectively referred to as the surface reservoirs and the rocks are not involved. This fast carbon cycle is dependent on the biologically catalyzed reduction of inorganic carbon to form organic matter. Levin (2009) reveals that most of this carbon is reconverted to inorganic carbon through respiratory metabolism. The biological carbon cycle takes a relatively short duration of time compared to the geological carbon cycle. The movement of carbon from different pathways can take place within a few days or millennia.
In the carbon exchange between the land and the atmosphere, the photosynthesis process plays a crucial role. This chemical process is responsible for absorbing carbon from the atmosphere and converting it into energy, which is used by the plant to grow. About half of the organic material produced using photosynthesis is returned to the atmosphere through respiration (Prentice, 2001). The remainder is stored in the soil through the accumulation of dead debris. The dead debris is engaged by microbes in the soil to produce carbon dioxide, which is released back into the atmosphere.
The most significant regulator of carbon in the atmosphere in the biological carbon cycle is the Ocean. While the land-based exchange has the shortest-term effect, with the effect of the carbon exchange being felt within months or decades, the ocean has the largest effects on the longer timescale of several decades to a millennium (Intergovernmental Panel on Climate Change, 2014). Carbon flows between the ocean and the atmosphere through various mechanisms.
Photosynthesis occurs when light reacts with the phytoplankton in the ocean. The ocean might release carbon into the environment when the organisms with calcium carbonate shells die and their shells dissolve and released as carbon dioxide. Carbon is absorbed faster at greater depths of the ocean since the lower temperatures and higher pressures at these depths increase the solubility of carbon dioxide.
Geological Carbon Cycle
This carbon cycle is referred to as the “Slow carbon cycle” since it operates on multi-million-year time scales. Geological forces that have existed since the formation of the Earth produced carbonic acid, which breaks down producing water and carbon dioxide and then reconstitutes itself until an equilibrium is reached (Levin, 2009). Carbon can move between the solid and the ocean and atmosphere in this process. When rocks breakdown through weathering, they take CO2 from the atmosphere as this cash reacts with the surface water and the carbonate minerals that are contained in the rocks (Prentice, 2001).
This leads to the formation of calcium, magnesium, and silica. Erosion can transport these carbonates to rivers and eventually to the ocean. Once in the ocean, the carbonates precipitate to opal in the shells of microscopic plants. When these plants die, their shells (which contain carbon) collect at the floor of the ocean, and over time, they create limestone, which accumulates in layers forming rocks. Mathez (2013) reveals that the rocks may be buried to depths of thousands of meters over millions of years.
The pressure of the deep Earth causes the carbonate to break down giving up carbon dioxide that slowly seeps out of the crust and back into the atmosphere. The rocks may also be dragged to the Earth’s mantle where the heat causes the carbonates to break down and find its way to the surface as gas from erupting volcanoes.
The rocks serve as huge carbon reservoirs and they hold significantly more carbon compared to that contained by surface reservoirs such as the atmosphere, soil, and the ocean. Mathez (2013) states that the overwhelming majority of carbon on Earth is contained in the relatively immobile pool in the form of carbonate rocks. The long-term carbon cycle is therefore responsible for maintaining the conditions on Earth’s surface conducive to the evolution and survival of life.
Human Impact on the Carbon Cycle
The carbon cycle is a natural process that has been occurring at a relatively uniform rate for thousands of years. However, human activities have had some impact on the carbon cycle. Folger (2009) revels that human industrial activities, which began in the 17th century, have added carbon to the atmosphere at a faster rate than the oceans, soil, and vegetation can remove it. At present, the available sinks can absorb the carbon dioxide emitted from human activity in an adequate manner.
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The ocean has played a significant role in taking up the carbon generated by human activities. Mathez (2013) reports that over the past 3 decades, the ocean has successfully taken about one-third of all the carbon produced by fossil-fuel burning and it is predicted that 90% of anthropogenic carbon dioxide will eventually end up in the ocean.
However, as the various sinks accumulate more carbon, their capacity to act as sinks as well as the rate of absorption will change and this will alter the balance in the carbon cycle. Scientists predict that this might have a catastrophic effect on the Earth. Mathez (2013) warns that the carbon pathway is being altered and interfered with by the emission of greenhouse gases such as carbon dioxide. While scientists have gained an understanding of how the carbon cycle operates, there are still numerous unknowns about the process. This has led to uncertainty about the impact that the growing levels of carbon emissions dumped into the atmosphere by humans each year will have on the carbon cycle.
This paper set out to discuss the carbon cycle, which is the process by which carbon moves through the Earth system. It began by affirming the importance of the carbon element in life on Earth. It then defined the carbon cycle as the process through which carbon moves between the different reservoirs in the land and water systems. The cycle can be divided into the geological and biological carbon cycle. The geological cycle can take up to millions of years to release or take in carbon while the biological cycle can take as little as months. The impact of human activities on the carbon cycle has also been discussed.
Arwyn, J., & Broll, G. (2012). Soil Atlas of the Northern Circumpolar region. Berlin: Office for Official Publications of the European Union.
Folger, P. (2009). The carbon cycle: Implications for climate change and congress. Washington, DC: Congressional Research Service.
Intergovernmental Panel on Climate Change. (2014). Climate Change 2013: The Physical Science Basis. Cambridge: Cambridge University Press.
Levin, S.A. (2009). The Princeton Guide to Ecology. New Jersey: Princeton University Press.
Mathez, E.A. (2013). Climate Change: The Science of Global Warming and Our Energy Future. NY: Columbia University Press.
Prentice, I.C. (2001). The carbon cycle and atmospheric carbon dioxide. Cambridge: Cambridge University Press.