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 from Nature Communications suggests that it might be absorbing more carbon than this. 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.
When carbon dioxide dissolves in water, it changes the pH making the ocean more acidic – a phenomenon called ocean acidification. This acidity harms marine life, especially organisms with calcium carbonate shells and skeletons.
According to the United Nations, the ocean also captures up to 90 percent of the excess heat generated by global carbon emissions. This buffering effect helps moderate global temperatures and slows down the pace of warming.
While the ocean is a tremendous heat absorber, it comes at a cost. The absorbed heat contributes to rising sea temperatures, which can disrupt ocean currents and marine ecosystems.
What is a Carbon Sink?
A carbon sink is any reservoir that absorbs and stores more carbon from the atmosphere than it releases. In contrast, a carbon source can also absorb carbon from the atmosphere. However, it releases more than it takes away.
Carbon sinks play a vital role in the natural carbon cycle. In a healthy cycle, the amount of carbon released is balanced by the amount absorbed by sinks. Human activities like burning fossil fuels disrupt this balance, releasing more carbon than sinks can absorb. This excess carbon dioxide traps heat in the Earth’s atmosphere, further accelerating global warming.
Natural Carbon Sinks
The Earth depends on three types of carbon sinks. These are:
- Forests
- Soils
- Oceans
Forests
Through photosynthesis, trees absorb carbon dioxide and release oxygen. The carbon is stored in the tree’s biomass (trunks, branches, roots, and leaves). Tropical rainforests in Congo, Amazonia and Southeast Asia act as significant carbon sinks due to their size and long lifespans.
Despite emitting twice as much carbon dioxide as they emit, tropical rainforests are threatened by deforestation due to land conversion for plantations, cattle ranching and draining of peat soils. This vicious cycle weakens the crucial contribution that forests make in mitigating the impacts of climate change.
Soil
Healthy soil is a major carbon storehouse. Plants deposit organic matter (leaves, roots) into the soil, where it is broken down and stored by soil microbes. Land management practices that promote healthy soil, such as reduced tillage and cover cropping, can help to increase soil carbon storage.
An article by Yale E360 states that “more carbon resides in soil than in the atmosphere and all plant life combined; there are 2,500 billion tons of carbon in soil, compared with 800 billion tons in the atmosphere and 560 billion tons in plant and animal life.”
Oceans
Studies have shown that ocean habitats, with their unique ecosystems, can sequester carbon at rates as high as four times greater than terrestrial forests.
Phytoplankton are microscopic marine plants, similar to algae, and exist in vast numbers near the ocean’s surface. Through photosynthesis, they use sunlight and dissolved carbon dioxide to produce organic matter, just like trees do on land. This process effectively removes 40 percent of atmospheric carbon, becoming the building block for their growth.
Mangroves and seagrasses also play a significant role. Their dense root systems trap and store organic matter from both land and sea, further contributing to the ocean’s impressive carbon sequestration abilities.
Mangroves store an average of 1,000 tonnes of carbon per hectare. Moreover, they are also champions of healthy fisheries, providing food security for many. Mangroves act as natural shields to protect our coasts from storms and floods and also improve water quality – a triple threat against climate change.
Seagrasses can store up to 700 tonnes of carbon per hectare. Home to a host of diverse organisms, these underwater meadows contribute to the overall health and resilience of the marine environment. They also act as natural filters, trapping sediment and pollutants from the water column, and can reduce the impact of runoff on coastal ecosystems.
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 climate change by absorbing a staggering amount of heat from rising greenhouse gas emissions. This immense thermal burden has triggered a cascade of consequences, including:
- 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.
Interestingly, the ocean was a carbon source before the Industrial Revolution when the natural exchange of carbon between the atmosphere and the ocean was more balanced. Today the proliferation of human activities like burning fossil fuels has tipped the scales and its role has been reversed to become a carbon sink.
So, what is the future of the ocean?
The impacts of climate change pose a serious threat to life on Earth. Even if the worst-case scenario is avoided, the natural process of removing excess carbon from the atmosphere could take millions of years. This highlights the importance of acting now to mitigate the impact of climate change.
The Efficiency of New Environmental Policies
The UN Climate Change Conference (UNFCC COP27) 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 is closing rapidly.
The conference’s main objective was to build on previous successes, but there were concerns 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. 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, Earth’s largest carbon sink, has absorbed a significant portion of our greenhouse gas emissions. But, relying solely on this is not a sustainable strategy.
This isn’t just about fairness to the ocean – it’s about acknowledging the rapidly shrinking window for climate action. At COP27, world leaders have a critical opportunity to demonstrate their commitment to a healthier planet. Meeting established emission targets isn’t just a box to be ticked – it’s a critical first step.
We must prioritize aggressive emissions reduction strategies to lighten the burden on our oceans and secure a livable future for generations to come.
Investing in and implementing innovative solutions like carbon capture and storage technologies alongside protecting and restoring natural carbon sinks will be key to winning the fight against climate change.
Ocean Insights: Hear From Our Experts
By Dr. Rabiah Ryklief
Principal Scientist and Lecturer of Marine Science, with a PhD in Zoology
Healthy coral reefs, vital for tourism and fisheries, are threatened by ocean acidification. Rising sea levels could disrupt vital coastal infrastructure and displace millions. Therefore, by investing in protecting and restoring the ocean's carbon sequestration abilities, we're not just mitigating climate change, we're investing in a sustainable blue economy that can thrive for generations. A healthy ocean is not just good for the planet - it's also good for business.
FAQs
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. Today, burning fossil fuels for transportation, heat and electricity is the largest carbon source. The best way to protect the ocean is to stop burning fossil fuels and adopt environmentally sustainable power sources.
What happens when the ocean absorbs too much carbon dioxide?
Increased carbon storage leads to ocean acidification. Rising acidity levels harm creatures like coral and shellfish, disrupting the food chain. This weakens the ocean’s ability to act as both a carbon sink and a healthy marine habitat.
What are the two oceanic carbon sinks?
The ocean uses two main methods to store carbon. The Biological Pump uses phytoplankton to capture carbon dioxide near the surface, then as they’re eaten and die, this carbon sinks to the deep ocean floor for long-term storage. Ocean Circulation relies on deep ocean currents to physically transport dissolved carbon dioxide away from the surface and store it in the ocean depths.
