Before explaining what a carbon sink is, it is necessary to clarify that this compound has its own cycle: the carbon cycle.
As in primary school, the water cycle is studied and we know that it evaporates, solidifies and returns to a liquid state with rain, which is stored in lakes, seas, rivers and oceans and also underground in aquifers. It happens with carbon.
the carbon cycle
Carbon is found in the atmosphere naturally and is the main element present in living beings. Our bones, proteins, muscles, are made up of carbon, just like plants: leaves, stems, woody trunks, roots… everything. it is composed of carbon.
Sometimes this carbon can be present in the form of calcium carbonate as it is in the shell of molluscs such as bivalves (clams for example), gastropods (snails and land snails), almost everything that has a shell and bones is usually calcium carbonate.
Carbon can be present in the atmosphere in the form of carbon dioxide or methane mainly. The part that is present in the atmosphere in the form of CO2 enter the cycle through plants and bacteria that carry out photosynthesis. In a very general way and without going into all the details, this CO2 is incorporated into the structure of plants and bacteria and when it is ingested by other animals it circulates through the food chain.
When living beings die, this carbon is integrated into the soil in the case of terrestrial living beings or in the case of living beings that inhabit the sea, it falls by gravity towards the bottom of the seas and oceans, being trapped at great depths. Depending on the dynamics of marine currents and the depth, this carbon, generally in the form of calcium carbonate, can circulate again and re-enter the food chain.
All this carbon that is deposited at the bottom of the oceans and soils undergoes geological processes that, speaking on a scale of millions of years, is transformed into calcium carbonate (most of the calcium carbonate that exists on earth is of biological origin) and into other types of compounds much richer in carbon such as fuels fossils: oil, natural gas, coal… and that were formed at certain moments in the life of our planet.
A each of the stages of the carbon cycle are called “stores” since we have carbon stored in the forests, in the oceans, in the soil and in the subsoil. These stores can be “carbon sinks” and others are a source of carbon due to human action, such as the burning of fossil fuels, since carbon that was stored in the soil and whose exchange with the atmosphere cannot occur naturally. under current geological conditions it is being emitted in large quantities. The carbon cycle is out of balance for this reason.
What is a carbon sink?
Once we have understood that carbon is found in the atmosphere and enters into its cycle thanks to photosynthesis, we can arrive at the definition of a carbon sink:
And carbon sink is any natural system that absorbs and stores more carbon from the atmosphere than it emits. The largest carbon sinks on our planet are forests, soil, and the ocean. To simplify: a carbon sink is a store of carbon from the atmosphere.
For example, in a forest as a whole, plants absorb CO2 that they transform into leaves, stems, trunks… and in turn they also emit CO2, although to a much lesser extent than they absorb. This type of phenomenon is also called fix carbon. Plants can fix carbon in their woody trunks, in their roots… and that carbon will not move from there except, for example, in a fire or when the trees die due to decomposition: a part will return to the atmosphere in the form of methane and carbon dioxide, through scavengers and detritus that feed on them and another part will be integrated into the soil. The animals that inhabit the forests will feed on that carbon fixed by the plants (that is why the plants are called primary producers) and they will live emitting CO2 for their own existence. However, when the global calculation of the carbon of an ecosystem is made, the net rate is that they store carbon for what are considered carbon sinks.
Main carbon sinks
As we have been mentioning throughout the article, the main carbon sinks are the soil, forests and oceans.
forests and plants
As we mentioned before, forests are one of the main carbon sinks mainly due to their great abundance and the ability to generate very durable structures over time, such as wood. For example, at the regulatory level it is estimated that a forest can be considered as a carbon absorption project after 20 years.
The main threat of these sinks are forest fires that in a short time are capable of releasing CO2 stored for decades in the vegetation.
Soil as a carbon sink
Soils are the place where life develops on the planet and is made up of mineral particles but also decomposed plant and animal matter, air, water and also countless living organisms such as bacteria, worms, arthropods that live inside the soil. floor. All of this has a large amount of carbon coming from it, as we mentioned in the example of those primary producers that are plants. This carbon is stored in the soil instead of returning to the atmosphere.
A special case of carbon storage in the soil are peat bogs, of which an example would be the Tablas de Daimiel National Park in Ciudad Real, Spain. The largest peat bogs in the world are located in Siberia, Russia.
Worldwide, the area of near-natural peatlands (more than 3 million km2) sequesters 0.37 gigatonnes of CO2 per year. Peat soils contain more than 600 gigatonnes of carbon, which represents up to 44% of all soil carbon and exceeds the carbon stored in all other types of vegetation, including the world’s forests.
Emissions from drained peatlands are estimated at 1.9 gigatons of CO2e per year. This is equivalent to 5% of global anthropogenic greenhouse gas emissions, a disproportionate amount considering that damaged peatlands cover only 0.3% of the land mass. Fires in Indonesia’s peat swamp forests in 2015, for example, emitted almost 16 million tons of CO2 per day; which is more than the entire economy of the United States. (Source: IUCN)
The oceans: the world’s largest carbon sink
The oceans are essential to remove carbon from the atmosphere and they do so through the photosynthetic organisms that make up the phytoplankton such as diatoms, dinoflagellates and other organisms. Not only do they do it through them, but they also do it by directly absorbing CO2 from the atmosphere through equilibrium with the bicarbonate ion.
The absorption of CO2 by the ocean can be reduced by the increase in temperature for purely chemical reasons, but an excess of CO2 in the ocean can also be a serious problem since it leads to ocean acidification with direct consequences on the living things that inhabit it. Here we explain in detail the acidification of the ocean.
Why is it important to protect carbon sinks?
Los current carbon sinks are the only available and effective way to remove excess CO2 from the atmosphere. Although there are many projects underway to find solutions to excess carbon in the atmosphere, these solutions are still not as effective as the solutions provided by nature.
Frequent questions
What are carbon sinks and how do they work?
Carbon sinks are those natural systems that store more carbon than they emit. In general, its operation consists in the fact that CO2 enters the natural system through photosynthesis and is integrated into natural systems in the form of trunk, roots, leaves, stems… part of this carbon continues to circulate through the system and another part It is stored in plants and soil. In addition, it enters the ocean through photosynthesis because CO2 dissolves in seawater.
What is the importance of carbon sinks?
Its importance lies in the fact that it is the only current way of eliminating the excess CO2 from the atmosphere that is being emitted by the burning of fossil fuels.
Where are the carbon sinks located?
Carbon sinks are located all over the planet where natural systems such as oceans, forests, and soil, especially peatlands, meet.
What are the main carbon reservoirs?
Carbon pools are carbon sinks, stores where carbon accumulates. It can be said that the main carbon reservoirs are carbon sinks: forests, oceans and soils.