Marine carbon removal methods seek to strengthen or accelerate natural biological or chemical processes that store carbon in the ocean. Some methods extract dissolved carbon dioxide from seawater to store it on land. Others involve geoengineering the upper ocean’s chemistry with minerals that will increase atmospheric drawdown of carbon. All methods, with the exception of seaweed sinking and enhanced weathering of rocks, range from theoretical to pilot stages. 

The Case for Marine Carbon Dioxide Removal (CDR)  

• The ocean’s capacity to sequester carbon is evident as it has already absorbed around 25% of CO2 and 90% of the excess heat resulting from human activities since the Industrial Revolution, significantly reducing the effects of climate change. With responsible application and scaling, marine CDR could be more efficient, less resource intensive and therefore cheaper than competitive land-based direct air capture approaches. At its highest potential, it could scale to well beyond 10 gigatons of removal. 

• As measurement, reporting, and verification (MRV) methodologies improve, so does the potential for marine CDR to offer a higher quality offset compared to existing biotic marine and atmospheric approaches due to higher permanence. Indeed, this will be a necessary step towards a robust voluntary carbon market (see our blog on carbon offsets to dive deeper into this matter). 
   
• The current marine CDR market is valued at approximately $150M due to a number of seed investments this year. Driven by a predicted annual demand of 60 – 150MTCO2 it is projected to grow exponentially to reach $500B by 2050. Without competition from other land uses and the potential for innovators to co-locate with existing coastal infrastructure, such as desalination plants and retired oil and gas assets, marine CDR could achieve greater scale. Notable examples include Equatic’s pilot plants with desalination facilities in Los Angeles and Singapore and Captura’s recent partnership with Equinor to develop a pilot plant. 

The Case Against Marine CDR 

• Although total atmospheric carbon removal potential for marine methods is uncertain, the potential ecological impact is even more so. Government and philanthropic funding are just now being deployed for research trials which is key for de-risking the technology and protecting ocean biodiversity.  

• In October, the White House Office of Science and Technology Policy (OSTP) formed a new Fast-Track Action Committee on Marine CDR to develop a comprehensive federal research and scaled testing program for promising marine CDR technologies and to coordinate public-private research activities. That said, certain geoengineering technologies could be a non-starter if found that the risks outweigh the potential benefits.   

• Like most carbon capture technologies, marine CDR is far from the price point needed to facilitate uptake to deliver impactful results. Moving seawater is energy-intensive and the risk of corrosion and/or wave damage on offshore infrastructure is high.  

• The regulation of an ocean carbon removal project varies depending on its location. Projects stationed within a radius of 200 miles from a country’s coastline would be subject to the legal authority of that country. Regions beyond this boundary are considered the “high seas” and are governed solely by international frameworks that were established prior to the existence of marine CDR. That puts certain approaches including seaweed sinking, alkalinity enhancement, and fertilization techniques in jeopardy of reaching a certain level of deployment.  

Recent Deals in Marine CDR  

November 2023: Deep Sky, a carbon removal project developer for DAC and marine CDR, secured a $54M Series A to begin planning and construction of its first commercial facility co-led by Brightspark Capital and Whitecap Venture Partners, with major participation from Investissement Québec. 

November 2023: Captura partnered with Equinor to develop a pilot plant in Norway to remove 1,000 tons of CO2 annually. 

June 2023: Equatic secured Boeing as a major customer to purchase hydrogen that will be produced from seawater filtration for sustainable aviation fuels. 

Riding the Wave 

The marine CDR market is estimated to be 5 years behind direct air capture (DAC), so it is not too late to catch this wave and ride it in a sustainable manner. Innovators and investors are actively progressing with the development of marine CDR. This should be done in ways that eliminate or significantly reduce risks to marine ecosystems and the welfare of communities that depend on them. Therefore, it is crucial to increase investment in research and establish strong governance to ensure expansion into the blue economy is not solely influenced by efficiency or profitability.