How It Works

Quick Facts

Market Position

Early-stage pathway with increasing scientific and commercial interest. Multiple pilot projects underway, supported by initiatives like Ocean Visions or Carbon to Sea .

Carbon Removal Potential

Varies widely and depends on the pathway
For example, estimates for Ocean Alkalinity Enhancement range from 100 MtCO₂ per year to 10 GtCO₂ per year (Fuss et al., 2018)

Co-Benefits

Biochar delivers a range of co-benefits, particularly in agriculture and construction.

Ocean Health

Ocean alkalinity enhancement (OAE) can help counteract ocean acidification, improving conditions for marine life.

Ecosystem Productivity

Microalgae cultivation supports biodiversity by increasing primary production in nutrient-poor waters.

Infrastructure Integration

Some methods can be paired with existing wastewater or desalination systems, enabling efficient and cost-effective deployment.

The Science

Enhancing the Ocean’s Natural Carbon Cycle

The ocean is an important sink for anthropogenic CO₂ and has absorbed roughly 30% of our emissions between the beginning of the industrial revolution and the mid-1990s (Gruber et al., 2019), making it a critical component of the global carbon cycle. Marine Carbon Dioxide Removal (mCDR) builds on this natural role by accelerating or amplifying oceanic carbon uptake and storage processes.
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Several pathways are under development:

Ocean Alkalinity Enhancement (OAE)

OAE increases the ocean’s capacity to absorb CO₂ by introducing alkaline materials—such as sodium hydroxide, lime, or magnesium compounds—into seawater. These substances raise ocean alkalinity, which allows more CO₂ to be drawn from the atmosphere and converted into bicarbonate and carbonate ions. Some of these react to form solid carbonates that settle on the seafloor, creating durable carbon storage over geological timescales.
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OAE may be deployed at coastal facilities using wastewater or desalination effluent streams, or discharged into the open ocean from ships. Research is ongoing to assess dilution patterns and avoid unintended ecological effects, such as localized pH shifts.

Biomass Sinking

This method relies on biological uptake of CO₂ during plant growth. Macroalgae (seaweed) or other biomass—either ocean-grown or land-based—is cultivated to absorb atmospheric carbon. Once mature, the biomass is sunk to the deep ocean. Low oxygen levels and cold temperatures in these depths minimize decomposition, effectively locking the carbon away for centuries to millennia.
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Sustainability depends on careful biomass sourcing and a thorough understanding of deep-sea ecosystems to avoid adverse impacts.

Microalgae Cultivation & Sequestration

Phytoplankton, the microscopic plants that form the foundation of the marine food web, naturally absorb large quantities of CO₂ via photosynthesis. This approach enhances their growth in nutrient-poor waters through artificial fertilization or upwelling techniques, thereby boosting natural CO₂ drawdown. A portion of the carbon absorbed is exported to the deep ocean as organic matter, where it may remain sequestered for long durations.
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Pilot studies are exploring how to balance productivity with ecosystem stability, particularly avoiding unintended outcomes like algal blooms or oxygen depletion.

Measurement, Monitoring, and Ecosystem Considerations

Across all these approaches, reliable measurement, monitoring, reporting, and verification are complex and can only be improved through increased funding for pioneering initiatives and transparent, granular tracking of removal value chains. Carbon flows in the ocean are diffuse, and potential ecological impacts must be closely monitored.
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A growing number of research networks, including Ocean Visions and Carbon to Sea, are working to build the scientific and technical infrastructure needed to safely scale mCDR.