The ocean absorbs 25 percent of carbon dioxide emissions and generates 50 percent of the Oxygen we need, making it the world’s most significant carbon sink and ally against climate change.

New evidence in a Nature Communications paper shows that it might be absorbing more carbon than this. The experts discovered that the very surface of the ocean is currently cooler than a few meters below, indicating an increase in the ability of the ocean to absorb greenhouse gases.

Plastics polluting the ocean
Plastics polluting the ocean

According to the United Nations, it also captured up to 90 percent of the excess heat that carbon emissions generated.

What is Carbon Sink?

A carbon sink is any reservoir that absorbs and stores more carbon from the atmosphere than it releases. A carbon source can also absorb carbon from the atmosphere. However, it releases more than it takes away.

Volcanic eruptions and burning fossil fuels are some of the best examples of carbon sources.

Burning fossil fuels
Burning fossil fuels

Types of Carbon Sinks

The Earth depends on three types of natural carbon sinks. These are:

  • Green plants
  • Soil
  • Ocean

Green Plants

Green plants use water, sunlight, and carbon dioxide to make their food through photosynthesis. This process occurs within the leaves of green plants and in the cells of microscopic organisms.

Once photosynthesis is complete, these plants or organisms release Oxygen.

They consume lots of carbon and release massive amounts of Oxygen in exchange.


Fertile agricultural soil is made up of large amounts of carbon that help it retain water. After photosynthesis, plants release excess carbon into the soil. At the same time, the soil captures carbon from the roots of rotting plants and leaves.

Green plants and the soil collectively absorb 30 percent of carbon dioxide emissions.


As we’ve seen earlier, the ocean is the world’s largest carbon sink. It is home to millions of green plants and other aquatic organisms known as phytoplankton. When other organisms feed on phytoplankton or plants, they consume the carbon and store it temporarily within their body cells. After death, they sink through the ocean, moving carbon dioxide from the surface of the ocean into the depths.

The surface water also absorbs some carbon dioxide from the atmosphere.

Moreover, studies have shown that ocean habitats can sequester carbon at rates as high as four times higher than terrestrial forests. Here is how mangroves and coral reefs benefit the environment:

  • Mangroves: Store an average of 1,000 tons of carbon per hectare. Moreover, they support healthy fisheries, protect coastal areas against storms and floods, and improve water quality.
  • Coral reefs:  Cover less than 0.1 percent of the ocean but support more than 25 percent of marine biodiversity. In addition, they are a source of tourism revenue, source of medicine, coastal protection, and more for one billion people.

Coral reefs underwater
Coral reefs underwater

The Future of the Ocean

The ocean plays a central role in reducing carbon dioxide emissions and stabilizing the Earth’s temperature and climate.

Unfortunately, the ocean has taken the brunt of increasing greenhouse gas emissions. It has absorbed almost all the heat arising from these emissions. The heat is responsible for the following:

  • Sea-level rise: Rose an average of 4.5 millimeters per year from 2013 to 2021, intensifying the occurrence of extreme events like coastal hazards, deadly storms, and tropical cyclones.
  • Marine heatwaves: They could bleach the world’s coral reefs by the end of the century if the trend continues.
  • Loss of marine biodiversity: Experts warn that over half of the world’s marine species may disappear from the face of the Earth by 2100.

Ocean acidification and ice-melting are other effects of increasing greenhouse gas emissions.

So, the ability of the ocean to act as a carbon sink has helped to reduce global warming, but this benefit comes at a high cost.

Please note that the ocean was a carbon source before the industrial era.

Nevertheless, the increasing atmospheric carbon dioxide concentrations have forced the ocean to absorb this greenhouse gas.

So, what is the future of the ocean?

Global warming and climate change might eliminate life from the face of the Earth in a few years if humans don’t take action at the right time. After that, the carbon cycle might take millions of years to move excess carbon to the most suitable reservoir.

Thus, pollution exposes life to greater danger than the ocean.

The Efficiency of New Environment Policies

The UN Climate Change Conference (UNFCC COP 27) was underway in Egypt at the time of writing this post. As expected, the organizers kept reminding the participants that the window for climate action was closing rapidly.

The conference’s main objective was to build on previous successes, but we were concerned about whether the conference would realize the goal.

When the Kyoto Protocol was adopted in 1997, many people expected that we would be able to reduce greenhouse gases to 5.2 percent below 1990 levels in less than ten years. After a series of meetings mired in disputes, the objective was aborted. The 196 participants at the COP21, held in 2015, signed the UNFCC to replace the 1997 treaty.

Like the Kyoto Protocol, this new landmark diplomatic accomplishment is facing some challenges. However, it’s better than the first since the US and other key nations play a central role.

However, other than a few countries that have shown commitment to meeting their emission targets, the majority haven’t done much.

Implementing policies geared toward reducing greenhouse gas emissions requires political goodwill and finance. So, since funding issues haven’t been conclusively addressed, more needs to be done to help the ocean and other carbon sinks.

What Next for Carbon Sinks?

The ocean is the largest carbon sink, but it would be unfair if we allowed it to continue taking the brunt of increasing greenhouse gas emissions due to the inability to take action when we still have the opportunity.

All parties attending the UNFCC COP 27 should meet their emission targets to demonstrate they understand that the window for climate action is closing fast.

At the same time, everyone needs to take personal initiative. Each of us needs to conserve water, reduce pollutants, and cut down on what we throw away. We should also choose suitable seafood, buy less plastic, bring reusable bags home, and use less energy.  

As responsible people who know the benefits of protecting the largest carbon sink, we must fish responsibly, practice safe boating, and respect habitat. What’s more, we need to volunteer for cleanups near the ocean and in our communities and speak up for everyone to understand the effects of their actions.


Why is the ocean the largest carbon reservoir?

The ocean is the largest carbon reservoir since it contains carbonates, which escalate the absorption of carbon dioxide. According to estimates, the ability of the ocean to absorb this gas is at least ten times higher than fresh water. So, if you are asking why the ocean is the largest carbon sink, it contains high quantities of this chemical substance.

Which part of the ocean is the most significant carbon sink?

The Deep Sea and its water column are part of the ocean that scientists believe is the most significant carbon sink. Research on its large-scale future is yet to be completed. However, there are indications that the Deep Sea might stop absorbing large amounts of carbon soon because of the increasing rate of ocean acidification.

What is the largest carbon source?

Before the industrial revolution, the ocean was the largest carbon source. Unfortunately, it’s the largest carbon reservoir today. On the other hand, burning fossil fuels for transportation, heat, and electricity is the largest carbon source. In other words, the best way to protect the ocean today is to stop burning fossil fuels and adopt eco-friendly power sources.

What are the major problems associated with the ocean absorbing so much carbon dioxide?

The major problem associated with the ocean absorbing so much carbon dioxide is seawater acidity. It threatens the ability of corals and shellfish to build their skeletons. Moreover, it affects the health of other marine species, leading to food scarcity and health problems worldwide. For this reason, pollution is interfering with the ability of the ocean to serve as a carbon source and habitat for different types of fish and other marine species.

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