Nearly three-quarters of our “blue planet” is covered by vast expanses of oceans. Not only do these seawaters play a crucial role in regulating the climate and weather patterns on Earth, they absorb nearly 30 percent of human carbon dioxide pollution. But the increase of greenhouse gas emissions in the Anthropocene era is pushing our oceans, and the planet's carbon cycle, to the brink.

Capturing CO₂ from the oceans and storing it permanently—known as ocean-based carbon dioxide removal (CDR)—could be a game-changer for fighting climate change. To help find these solutions, the $100M XPRIZE Carbon Removal competition is encouraging innovators from around the world to find the best, most scalable CDR technology. Teams developing “Ocean” solutions are finding ways to remove CO₂ from our oceans and store it safely and durably.

IMPROVING OCEAN HEALTH AND ADDRESSING THE CARBON CRISIS

These teams have proved that there are many ways to deploy ocean-based CDR. Some teams opted for biological solutions, including revitalizing the species in our oceans already working to capture and store carbon. Many marine mammals and plants have the remarkable ability to store significant quantities of carbon, but according to the IUCN Red List, approximately 30 percent of marine mammal species are at risk of extinction. By addressing the issues of biodiversity loss and habitat degradation, ecosystem restoration offers a powerful avenue for ocean-based CDR. Similar to planting trees on land, revitalizing ecosystems like mangrove forests, tidal salt marshes, and seagrass meadows allows these natural systems to better trap and store carbon. 

Beyond revitalization, some teams are also pursuing cultivation of microalgae and macroalgae (also known as kelp and seaweed) for CDR. Algae possess the ability to absorb large quantities of carbon dioxide during photosynthesis, making them an efficient carbon sink. Brown algae, for example, are estimated to remove up to 550 million tons of carbon dioxide per year. By expanding algae cultivation, we can enhance the ocean's capacity to capture and store carbon.

Beyond these natural systems, simple minerals also offer the ability to enhance the oceans’ ability to capture carbon. With ocean alkalinity enhancement, teams add alkaline substances, such as crushed limestone or silicate minerals, to the ocean, raising its pH and making it less acidic. This not only helps protect coral and shelled animals from dissolving due to ocean acidification, but allows the ocean water to absorb more CO₂ from the air. It is crucial in this process to carefully consider and monitor the potential adverse environmental and social impacts of this approach, including the mining necessary to harvest the alkaline substances. 

We can also benefit from the incredible scale and depth of our planet’s oceans. In deep sea storage, scientists inject carbon dioxide into the very deepest layers of the ocean to sequester it. Alternatively, with artificial downwelling, manmade vertical currents transport surface water rich in CO₂ to the ocean depths. Artificial upwelling, conversely, transports nutrient-rich water from the oceans’ depths up to the surface to stimulate the growth of phytoplankton that capture CO₂. Each of these methods allows the ocean to store carbon dioxide in its depths, preventing its release into the atmosphere.

For all of these solutions, there is still a great deal of work to be done by scientists, technology developers, policy makers, and local communities to ensure that they are brought to the field responsibly, with careful and well considered tests designed to showcase the efficacy and sustainability of these solutions while moderating their risks.

OCEAN-BASED CDR IN XPRIZE CARBON REMOVAL FINALS

Out of the 1,300 teams from 88 countries that competed in the XPRIZE Carbon Removal competition, XPRIZE chose 20 finalist teams, including four Ocean track teams, to move on to the last leg of the competition. This final phase before the competition’s end included site visits to see the innovative technology in action and robust validation procedures. 

Our oceans present an opportunity to remove and store carbon dioxide at significant scale. By actively pursuing these ocean-based CDR methods, we can leverage the seas as a vital climate solution and work towards a more sustainable future for our planet. 

Learn more about these competing teams and their technology in the first episode of our recently released XPRIZE Carbon Removal docuseries, which focuses on the Ocean track. New episodes will be released weekly, covering each of the prize tracks. Stay tuned! 

THE AUTHOR