Meghan Hodges
The ocean is the world's greatest ally against climate change. It is the planet's largest carbon sink, absorbing 30% of all carbon dioxide emissions and 90% of the excess heat generated by these emissions. The ocean's ability to absorb carbon dioxide is essential for safeguarding life on the planet. Researchers, companies, and governments are now looking to leverage the ocean's natural chemical and biological processes to absorb and store more carbon from the atmosphere. This can be done through marine carbon dioxide removal mCDR methods, which may include enhancing alkalinity to increase the ocean's carbon storage capacity. The ocean's health is critical to reducing global greenhouse gas emissions and stabilizing the Earth's climate.
| Characteristics | Values |
|---|---|
| The ocean is the world's greatest carbon sink | Absorbs 30% of all carbon dioxide emissions |
| Ocean's natural chemical and biological processes | Alkalinity enhancement encourages greater absorption of CO2 from the atmosphere |
| Ocean energy systems | Use kinetic and thermal energy of seawater to produce electricity or heat |
| Ocean habitats | Seagrasses and mangroves can sequester carbon dioxide from the atmosphere at rates up to four times higher than terrestrial forests |
| Mangroves | Store 1,000 tonnes of carbon per hectare in their biomass and underlying soils |
| Coral reefs | Cover less than 0.1% of the world's ocean but support over 25% of marine biodiversity |
| Marine CDR methods | May improve local ocean conditions that support ecosystems and economies |
| Ocean-based carbon removal | Leverages the ocean's natural chemical and biological processes to absorb and store more carbon from the atmosphere |
| Ocean-based carbon removal projects | Projects within 200 miles of a country's coastline fall under that country's jurisdiction |
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What You'll Learn
Mangroves and seagrasses sequester carbon
Mangroves and seagrasses are incredibly efficient at capturing and storing large quantities of carbon, a process known as carbon sequestration. These ecosystems are known as "blue carbon" sinks, capturing and storing carbon in coastal and marine environments.
Mangroves are some of the most carbon-rich ecosystems on Earth, storing around 1,000 metric tons of carbon per hectare in their biomass and underlying soils. They can sequester carbon within their trunks, leaves, and soil, and the carbon can remain trapped for thousands of years. Mangroves also support healthy fisheries, improve water quality, and provide coastal protection against floods and storms.
Seagrasses are another vital component of marine ecosystems, contributing to their health by maintaining water quality, stabilizing sediment, and serving as critical nurseries for commercially important species. They are key food sources for herbivores, including manatees, sea turtles, and bonnethead sharks. Seagrasses can store up to twice as much carbon as terrestrial forests per hectare, with the global seagrass ecosystem organic carbon pool estimated to be as high as 19.9 billion metric tons. Like mangroves, seagrasses can trap organic material and sediment in their roots, and their meadows can store up to 83,000 metric tons of carbon per square kilometer.
Despite their importance, mangroves and seagrasses are threatened by human activities such as deforestation, coastal development, pollution, and climate change. Mangrove forests are often cleared for agriculture, aquaculture, and urban development, releasing stored carbon and preventing future carbon sequestration. Seagrass meadows face similar threats, including damage from boat propellers, which reduce their carbon storage capacity. Conservation and restoration initiatives, such as the "Mangrove for the Future" and "Posidonia Project," aim to protect and restore these ecosystems, demonstrating the potential of blue carbon ecosystems to contribute to climate change mitigation.
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Ocean acidification and CDR methods
The ocean is the world's greatest carbon sink, absorbing 30% of all carbon dioxide emissions and 90% of the excess heat generated by these emissions. However, increasing greenhouse gas emissions have warmed and acidified seawater, reducing the ocean's ability to absorb carbon dioxide.
Ocean acidification is caused by the increasing concentration of human-induced carbon dioxide in the atmosphere and the ocean's absorption of this carbon dioxide. Carbon dioxide removal (CDR) methods aim to remove carbon dioxide from the atmosphere and store it long-term in the ocean. CDR approaches aim to leverage the ocean's natural chemical and biological processes to absorb and store more carbon from the atmosphere.
The National Oceanic and Atmospheric Administration (NOAA) has developed a Carbon Dioxide Removal (CDR) Research Strategy to outline what is known about existing technologies and what needs to be learned to make informed decisions to meet climate goals. NOAA's CDR research strategy focuses on advancing understanding by partnering with various institutions and laboratories, such as the Marine Biological Laboratory (MBL) and the Pacific Marine Environmental Laboratory (PMEL).
NOAA's Ocean Acidification Program (OAP) aims to prepare society to adapt to the consequences of ocean acidification and conserve marine ecosystems. OAP employs adaptation approaches such as using models and research to understand the sensitivity of organisms and ecosystems to ocean acidification and developing tools to monitor and mitigate changing ocean chemistry.
There are several proposed marine CDR (mCDR) methods to mitigate ocean acidification. One method is alkalinity enhancement, which involves changing the chemistry of seawater to increase its carbon dioxide storage capacity. Another approach is ocean alkalinity enhancement, which involves distributing alkaline materials like ground-up rocks into the ocean to react with dissolved carbon dioxide to form carbonates and bicarbonates that trap carbon dioxide. However, this method may introduce harmful trace minerals into the ecosystem and has challenges in measuring, reporting, and verifying carbon sequestration amounts.
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Algae and plants absorb CO2
The ocean is the world's largest carbon sink, absorbing 30% of all carbon dioxide emissions and 90% of the excess heat generated by these emissions. However, the increasing greenhouse gas emissions have affected the ocean's ability to absorb carbon. To address this, researchers are exploring the potential of algae and ocean-based carbon removal projects.
Algae, including marine algae or phytoplankton, have been found to play a crucial role in the carbon sequestration process within aquatic environments. By performing photosynthesis, algae absorb significant amounts of CO2 from the water's surface. This process involves the algae soaking up carbon dioxide, water, and sunlight to produce energy for growth and multiplication. Additionally, when algae are consumed by other organisms or die, some of the carbon they contain sinks to the ocean floor, becoming sequestered in marine sediments for extended periods.
One notable example of algae's carbon-absorbing capabilities is the study of fucoidan, a compound found in algal mucus. Brown algae, commonly known as seaweed, can sequester approximately 550 million tons of carbon dioxide annually through the production of algal mucus. This amount is equivalent to Germany's entire annual greenhouse gas emissions. Furthermore, algae can be utilized in bioreactors placed near CO2-emitting facilities, allowing for the direct capture of greenhouse gases before they enter the atmosphere.
Algae-based biofuels, also known as "green crude," have gained attention as a potential carbon-neutral alternative to fossil fuels. When cultivated for biofuel production, algae absorb carbon dioxide during photosynthesis and convert it into organic matter, effectively sequestering CO2. This process has been found to be up to 400 times more efficient than trees in removing CO2 from the atmosphere.
In addition to algae, ocean-based carbon removal projects aim to leverage the ocean's natural chemical and biological processes to absorb and store more carbon. These projects explore various techniques, such as marine CDR (mCDR) methods, to enhance the ocean's CO2 storage capacity and mitigate ocean acidification.
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Carbon sinks and carbon sources
Carbon sinks are natural or artificial reservoirs that absorb more carbon from the atmosphere than they release. Forests, for instance, absorb carbon dioxide through photosynthesis, with trees storing carbon within their tissues. The world's forests absorb 2.6 billion tonnes of carbon dioxide annually. Oceans are the largest carbon sink, absorbing 30% of all carbon dioxide emissions and holding roughly 42 times more carbon than the atmosphere. Phytoplankton, microscopic marine algae, and bacteria play a significant role in the carbon cycle, absorbing as much carbon as all the plants and trees on land combined. Other natural carbon sinks include soil, fungi, and mangroves. Mangroves are some of the most carbon-rich ecosystems, storing 1,000 tonnes of carbon per hectare.
Carbon sources, on the other hand, are processes that release carbon into the atmosphere. Human activities, such as burning fossil fuels like coal, oil, and natural gas, are major carbon sources. Electricity production is the largest source of carbon emissions, followed by agriculture and land use, and the industrial/manufacturing sector. Deforestation, a human activity that reduces the number of carbon sinks, is another example of a carbon source. Other natural sources of carbon include volcanic eruptions, forest fires, decomposition, animal respiration, and digestion.
While emissions reductions are the most effective way to mitigate ocean acidification, carbon dioxide removal (CDR) methods can also help. CDR aims to remove carbon dioxide from the atmosphere and store it long-term in the ocean or other locations. Ocean-based CDR methods leverage the ocean's natural chemical and biological processes to enhance its carbon absorption and storage capacity.
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Ocean-based carbon removal projects
The ocean is the world's greatest carbon sink, absorbing 30% of all carbon dioxide emissions and 90% of the excess heat generated by these emissions. However, the increasing greenhouse gas emissions have affected the ocean's ability to absorb carbon dioxide. To address this, researchers, companies, and governments are exploring ocean-based carbon dioxide removal (CDR) projects that leverage the ocean's natural chemical and biological processes to absorb and store more carbon from the atmosphere.
One approach to ocean-based CDR is to enhance the ocean's alkalinity, which increases its capacity to absorb and store CO2 by changing the chemistry of seawater. This method is being explored by companies like Captura, Ebb Carbon, and Equatic, which use electricity to either directly strip CO2 from the water or create alkalinity that is then added to seawater to indirectly remove carbon. Another approach is macroalgae cultivation, which has been funded by the Department of Energy since 2017, although with a focus on utilization rather than removal. Ocean Visions has also developed a roadmap for macroalgae cultivation and carbon sequestration, highlighting the need for further research and testing.
Marine CDR methods may also improve local ocean conditions and support ecosystems and economies. For example, seagrasses and mangroves can sequester carbon dioxide at rates up to four times higher than terrestrial forests, while also supporting healthy fisheries, improving water quality, and providing coastal protection. Additionally, marine protected areas, which currently cover 8.34% of the ocean, offer long-term conservation benefits and help maintain the ocean's health.
While most CDR development has been focused on land-based solutions, there is growing interest and investment in ocean-based CDR. For instance, companies like Stripe and Shopify have invested in ocean carbon removal companies, and the U.S. government has also begun to support ocean CDR initiatives. However, there are still many unknowns about the scalability, effectiveness, cost, and social and ecological impacts of ocean-based CDR approaches, and more research and testing are needed to address these questions.
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Frequently asked questions
Oceans absorb carbon through biological and chemical processes. Algae and plants absorb CO2 from the surface waters and convert it into biomass, which then sinks towards the seabed. The carbon remains trapped for decades or even centuries.
Oceans absorb 30% of all carbon dioxide emissions. The ocean already holds roughly 42 times more carbon than the atmosphere.
Oceans are the world's largest carbon sink, absorbing excess heat and energy released from rising greenhouse gas emissions. They also generate 50% of the oxygen we need. Additionally, ocean habitats such as mangroves can sequester carbon dioxide from the atmosphere at rates up to four times higher than terrestrial forests.
