Our planet is at a critical juncture, facing the existential crisis of climate change and escalating carbon dioxide levels in the atmosphere. Carbon removal technologies have emerged as indispensable tools in this battle, and among them, Ocean Carbon Dioxide Removal (CDR) holds great potential. In this comprehensive guide, we’ll explore how Ocean CDR can contribute significantly to the mitigation of climate change and help us pursue a sustainable and carbon-neutral future.

The Role of Oceans in Carbon Removal — A Natural Sink for Carbon

Oceans are integral to the earth’s carbon cycle. They act as natural carbon sinks, naturally absorbing about 25% of the carbon dioxide released into the atmosphere by human activities. Phytoplankton, microscopic marine plants in the ocean, consume carbon dioxide during photosynthesis, forming the base of the ocean food web and sequestering carbon in the process. Thus, amplifying the ocean’s carbon removal capabilities can substantially impact climate change mitigation and carbon sequestration.

Understanding Ocean Carbon Dioxide Removal (CDR) — Augmenting the Ocean’s Carbon Uptake

Ocean Carbon Dioxide Removal (CDR) refers to the direct enhancement of the ocean’s ability to absorb CO2 from the atmosphere through engineered methods. As a complement to terrestrial carbon capture techniques, it helps address land availability limitations and competition with other land-use objectives. By seizing the potential of our oceans, Ocean CDR addresses one of the principal aspects of climate change mitigation and carbon removal.

Types of Ocean CDR — Harnessing Minerals and Biology

Ocean CDR methods fall into two primary categories:

1. Mineralisation or Ocean Alkalinity Enhancement (OAE)

In this technique, alkaline materials like crushed limestone or olivine are added to seawater. The increased alkalinity enables the seawater to absorb more CO2 from the atmosphere and convert it into stable and harmless compounds, mitigating ocean acidification and effectively removing carbon dioxide from the atmosphere.

2. Biological Carbon Pump Enhancement (Grow & Sink)

This method involves stimulating the ocean’s natural biological carbon pump. In this approach, biotechnologies concentrate on photosynthetic marine organisms like phytoplankton that absorb carbon dioxide during growth. Ocean currents then carry these organisms, along with the absorbed carbon, into the deep ocean, sequestering the carbon away from the atmosphere.

How Does Ocean CDR Work? — Processes & Techniques

Ocean CDR encompasses several key processes and techniques to help curb climate change:

1. Ocean Alkalinity Enhancement (OAE)

In OAE, the alkaline compounds react with seawater to form bicarbonate ions, which effectively lock away carbon dioxide and mitigate ocean acidification. This method contributes to both carbon dioxide removal and the attenuation of some negative consequences of climate change.

2. Macroalgae Open-Ocean Mariculture and Sinking (MOS)

Through MOS, macroalgae farms are cultivated. These macroalgae, or seaweeds, absorb CO2 during photosynthesis. When they die off or are harvested, they sink (or are intentionally sunk) to the ocean floor, sequestering the carbon with them. Additionally, this technique presents opportunities for bioenergy production and socio-economic benefits.

3. Ocean Fertilisation

Ocean fertilisation stimulates phytoplankton growth (which consumes CO2) by adding iron and other essential nutrients to the ocean. However, its effectiveness and potential environmental impacts are still being explored. Some concerns regarding side effects and the long-term viability of this technique warrant further research and a cautious approach.

4. Blue Carbon Ecosystems

Blue carbon ecosystems, such as mangroves, saltmarshes, and sea-grass beds, play a critical role in carbon sequestration. These ecosystems can store Substantial amounts of carbon. For instance, mangroves can store up to four times more carbon per hectare than terrestrial tropical forests. Efforts to restore, protect, and enhance these crucial ecosystems can significantly contribute to carbon removal and climate change mitigation efforts.

The Benefits of Ocean CDR — Beyond Carbon Sequestration

Ocean CDR offers an array of benefits that reach beyond carbon removal, including:

  • Providing a large-scale carbon offsetting mechanism for emission-intensive industries.
  • Mitigating ocean acidification, a consequence of rising atmospheric CO2, which has detrimental effects on marine organisms and ecosystems.
  • Generating potential bioenergy resources and valuable materials from macroalgae farming and upscaling the blue bio-economy.
  • Promoting marine biodiversity and restoration through habitat enhancement and resource replenishment.
  • Reducing the pressure on terrestrial carbon removal efforts, providing an alternative pathway for carbon sequestration.

Barriers and Challenges in Scaling Ocean CDR — From Uncertainty to Infrastructure

Despite its promise, Ocean CDR faces several challenges:

  • Scientific uncertainty exists regarding the potential negative impacts of some Ocean CDR methods, especially ocean fertilisation, on marine ecosystems and the effectiveness of these techniques in sequestering carbon.
  • Existing regulatory frameworks, such as the London Protocol and the United Nations Convention on the Law of the Sea (UNCLOS), may not adequately cover some Ocean CDR techniques and their respective challenges.
  • Public perception and acceptance of large-scale interventions in the ocean require appropriate communication efforts and responsible stakeholder engagement. Further studies on society’s perception and support for Ocean CDR will impact its future development and acceptance.
  • Infrastructure and investment are necessary to ramp up Ocean CDR technologies, especially considering the large-scale operations needed to have a significant impact.

The Global Framework for Ocean-Based Carbon Dioxide Removal

Ocean CDR techniques are garnering worldwide attention. A noteworthy proponent is Professor Tom Bell, who advocates for an international framework to manage and mitigate risks associated with Ocean CDR. Events like the UN Bonn Climate Change Conference and the Global Stocktake also contribute to shaping global policies and strategies for effectively deploying Ocean CDR.

Role of Ocean CDR in Decarbonisation — Striking the Balance

To achieve a carbon-neutral future, Ocean CDR must be implemented across near, mid, and long-term decarbonization strategies. A balance must be struck between delivering high-quality carbon removal and accelerating and scaling viable carbon removal solutions. The urgency to act is clear and cannot be overstated.


Ocean CDR represents a promising new frontier in our struggle against climate change. By harnessing the power of our oceans responsibly and judiciously, we can forge a path to carbon neutrality. The future of Ocean CDR holds considerable potential, and the time to act is now. As we ride the wave towards a more sustainable future, let us ensure that we leave no stone unturned, or in this case, no seashell unexplored.


  1. National Oceanic and Atmospheric Administration (2021). Oceans & Coasts. Retrieved from 
  2. National Aeronautics and Space Administration (2021). The Ocean: A Driving Force for Weather and Climate.
  3. Royal Society (2018). Greenhouse gas removal. Retrieved from    
  4. Global Carbon Project (2020). Carbon Brief: The nine boundaries humanity must respect to keep the planet habitable. Retrieved from 
  5. Renforth, P. & Henderson, G. (2017). Assessing ocean alkalinity for carbon sequestration. Reviews of Geophysics, 55(3), 636-674. 
  6. Ocean Visions (2020). Ocean Alkalinity Enhancement. Retrieved from 
  7. NASA Earth Observatory (2011). The Ocean’s Biological Pump. Retrieved from 
  8. National Oceanography Centre, Biological Carbon Pump. Retrieved from 
  9. Ocean Visions (2020). Macro-algae open-ocean mariculture and sinking. 
  10. Beaumont, N.J. et al. (2018). The macroeconomic impact of floating macroalgae Sargassum. Environmental Management, 62(6), 1006-1016. 
  11. National Geographic Society (2019). Ocean Fertilization. 
  12. Strong, A.L. et al. (2009). Ocean Fertilization: Time to Move on. Nature, 461(7262), 347-348. 
  13. Gattuso, J-P. et al. (2018). Ocean Solutions to address Climate Change and Its Effects on Marine Ecosystems. Frontiers in Marine Science, 5(337). 
  14. Blue Carbon Initiative (n.d.). What is Blue Carbon?. Retrieved from 
  15. Nagelkerken, I. & Connell, S.D. (2015). Global alteration of ocean ecosystem functioning due to increasing human CO2 emissions. Proceedings of the National Academy of Sciences, 112(43), 13272-13277
  16. Ainsworth, T.D., et al. (2016). Climate Change Disables Coral Bleaching Protection on the Great Barrier Reef. Science, 352(6283), 338-342. 
  17. Jones, C.N. & Deane, G. (2017). International legal and regulatory issues of marine geoengineering. Marine Policy, 81, 162-171. 
  18. Nicholson, D.P., et al. (2020). What carbon removals can—and cannot—do in addressing the climate crisis. Bulletin of the Atomic Scientists, 76(6), 333-338. 
  19. Bell, T. (2016). Ocean-Based Solutions to Manage Climate Change. In P. Tortell and M.G. Rattray (Eds.), Reframing the Oceans: Custom Books, Cop23/
  20. United Nations Framework Convention on Climate Change (2017). Bonn Climate Change Conference. 
  21. Carbon180 (2020). Ocean Carbon Dioxide Removal: A research and policy roadmap.