Carbon Cycle

The Carbon Cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major component of many minerals such as limestone. 

Carbon Cycle Definition

The Carbon Cycle is a biogeochemical cycle where different forms of carbon compounds are cycled through the Earth’s various systems like the atmosphere, biosphere, hydrosphere, and geosphere.

Carbon Cycle Steps

The following are the steps involved in the Carbon Cycle process:

1. Entry of Carbon into the Atmosphere

The entry of carbon (in the form of carbon dioxide) into the atmosphere marks the start of the carbon cycle. Before this, carbon dioxide goes through the process of respiration (a process by which organisms release energy from their food) and combustion (a process of burning). Such processes both involve releasing carbon dioxide into the atmosphere.

2. Carbon dioxide intake by Producers

The carbon dioxide present in the atmosphere enters the terrestrial biosphere by means of green plants and algae that take up CO₂ during the process of photosynthesis. Producers are a group of living beings capable of converting the inorganic form of carbon (CO₂) into organic form (carbohydrates). Photosynthesis is an essential step of the carbon cycle, primarily responsible for the movement of carbon from the atmosphere to the biosphere. Besides, in the case of the oceanic reservoir, the atmospheric carbon dioxide dissolves into the water to be utilized by various underwater producers. In the presence of energy (solar or chemical), the inorganic carbon dioxide is converted into an energy-rich organic form.

3. Passing of the Carbon Compounds in the Food Chain

The organic form of carbon produced by producers then moves through the food chain as consumers feed on producers, resulting in the movement of carbon from one form of life to another. The organic form of carbon also undergoes changes as it moves through the consumers. These consumers utilize these compounds to produce energy and release carbon dioxide into the atmosphere by the process of respiration. Consumers convert some of the carbon into biomolecules and store them for living processes.

4. Release of carbon by decomposition

Eventually, as all the plants and consumers die, their dead bodies are feed upon by different decomposers. These decomposers convert the organic form of carbon into the inorganic form so that a cycle is formed. These decomposers include microorganisms like fungi and some bacteria that feed on the complex organic compounds and convert them into a simpler inorganic form.

Carbon Cycle Examples

There are different reservoirs in different ecosystems, all of which can absorb, the release of transport carbon from one form to another.

1. Atmosphere-: The atmosphere serves mainly as a passive reservoir for carbon. It stores carbon-containing gases that have escaped from the other two reservoirs as a result of their volatility. Carbon dioxide is the most important form of carbon in the atmosphere, which is released either via respiration or by combustion.
2. Biosphere-: The biosphere consists of living components of the Earth and the ocean carbon reservoir, resulting in a terrestrial and ocean biosphere. The terrestrial biosphere also acts as a sink for excess atmospheric CO₂ because plants are sensitive to the amount of CO₂ in the air. When plants secure adequate light and nutrients in controlled experiments, they grow faster in ambient air containing elevated concentrations of CO₂.
3. Lithosphere-: The lithosphere acts as a reservoir of inorganic carbon in the form of soil and rocks. The lithosphere contains large amounts of carbon in limestone and shale, which take part in the slow carbon cycle. Volcanic activity causes the release of carbon dioxide into the atmosphere, helping in maintaining a balance.

Carbon Cycle Diagram

Importance of Carbon Cycle

1. Carbon is an essential element for all life, so understanding how it moves helps us to understand biological processes and factors that influence them.
2. One form carbon takes is the greenhouse gas carbon dioxide, CO₂. Increased levels of carbon dioxide insulate the Earth, causing temperatures to rise. Understanding how carbon dioxide is absorbed and released helps us understand the climate and predict global warming.
3. Carbon is not in balance, so it’s important to learn where it is being stored and released. The rate at which carbon is deposited into living organisms is not the same as the rate it is returned to the Earth. There is about 100x more carbon in the living matter than in the Earth. Burning fossil fuels releases massive amounts of carbon into the atmosphere and to the Earth.
4. The carbon cycle is tied to the availability of other elements and compounds. For example, the carbon cycle is tied to the availability of oxygen in the atmosphere. During photosynthesis, plants take carbon dioxide from the air and used it to make glucose (stored carbon), while releasing oxygen.

Carbon Cycle on land

• Dominated by photosynthesis of plants absorbing CO2 from the atmosphere.
• Carbon is stored within biomass, such as tropical and temperate forests.
• Carbon is transferred to the soil via leaf litter, roots and plant debris upon decomposition.
• Bacterial action in decomposition releases CO2 back to the atmosphere.
• Carbon is cycled quite rapidly through organic (living) systems between the atmosphere, vegetation (dominant biomass) and soils and is called the Fast Carbon Cycle.
• Human impact on this sub-cycle is considerable. The clearing of natural vegetation for urbanisation and agriculture is a major change to the biomass component and affects the carbon exchange between atmosphere and soil. Clearing vegetation by burning releases much stored carbon to the atmosphere very rapidly.

Carbon Cycle in the Oceans

• This is essentially a carbon cycle but in the sea. Ecologically, oceans take in more carbon than it gives out. Hence, it is called a “carbon sink.”
• Marine animals convert carbon to calcium carbonate and this forms the raw building materials require to create hard shells, similar to the ones found in clams and oysters.
• When organisms with calcium carbonate shells die, their body decomposes, leaving behind their hard shells.
• These accumulate on the seafloor and are eventually broken down by the waves and compacted under enormous pressure, forming limestone.
• When these limestone rocks are exposed to air, they get weathered and the carbon is released back into the atmosphere as carbon dioxide.

Carbon Cycle in the Atmosphere

• Atmospheric carbon is usually in the form of carbon dioxide (CO2) or methane (CH4). Both are natural greenhouse gases, with methane being over 20 times more powerful in absorbing solar radiation, but much shorter-lived in the atmosphere, than CO2 (about 12 years as opposed to 50).
• Carbon dioxide combines with water molecules in clouds to form carbonic acid-, and naturally-acidic rain. This leads to terrestrial weathering and can contribute to ocean acidification.
• Outputs from the atmosphere include absorption by surface vegetation and by oceans in the atmosphere-ocean gas exchange.
• Human impacts on the carbon cycle are most directly implicated in increasing atmospheric CO2 through the burning of fossil fuels.

Global Carbon Cycle

It is the complex transformations and fluxes of carbon between the major components of the Earth system. Carbon is stored in four major Earth reservoirs, including the atmosphere, lithosphere, biosphere, and hydrosphere.

Frequently Asked Questions