Low Tide in Blue Carbon: Is There a Path Forward for Ocean-Based Carbon Capture?

The vast majority of companies in the energy sector have announced, to varying degrees, plans to reduce or eliminate emissions from their business. Does that mean no oil and gas products? Not quite. Even in the International Energy Agency’s net-zero scenario there remains hard-to-abate sectors that require the use of fossil fuels as a feedstock or fuel for which solutions won’t be ready for several decades. For these cases, we expect energy companies to increasingly focus on purchasing offsets based on engineering carbon-removal technologies. O&G companies will need credits for offsetting emissions if they want to meet decarbonization goals. 

Today, most credits available are related to forestation; however, these credits should be considered mostly unreliable as a forest fire could re-release that carbon. While direct air capture (DAC) has attracted the most attention among engineered solutions, another option is emerging: ocean-based CO₂ removal, or blue carbon. Oceans are large carbon sinks and naturally absorb CO₂ through biomass carriers or by chemical fixation, where CO₂ is dissolved to form bicarbonate ions and hydrogen ions; bicarbonate ions react with calcium or magnesium in the ocean to form stable carbonates, while hydrogen ions increase ocean acidity. CO₂ uptake by oceans is slow, and blue carbon technologies seek to accelerate the ocean’s rate of natural CO₂ uptake and generate carbon credits. There are four key pathways for doing this:

• Direct Ocean Capture: This approach involves electrochemical deacidification or alkalinity enhancement of seawater. Electrolysis, or an electrodialysis membrane, separates seawater or brine into acidic and alkaline streams. CO₂ can be directly captured from electrochemical processes if the acid is reintroduced to seawater or solid carbonates. The deacidified water is returned to the ocean, boosting its natural CO₂ uptake capacity.  
• Biomass Fixation: Biomass, typically algae or kelp, grows on buoys at the ocean’s surface by absorbing atmospheric CO₂. After a prescribed period of growth, the biomass sinks to depths of 1,000–1,500 m, and fresh cultivation begins.
• Enhanced Weathering: This technique uses olivine or other types of magnesium and calcium silicates in coastal regions or seabed to store CO₂ as carbonates. Olivine reacts with bicarbonates to produce calcium carbonate, mimicking the ocean’s natural CO₂ uptake pathway. 
• Offshore Sequestration: This is a form of permanent sequestration of CO₂ from industrial point-source carbon capture or DAC in offshore sinks like saline aquifers or depleted O&G fields. Deployment is currently limited to the regional availability of offshore sinks and the infrastructure to transport CO₂ from source to sink.

Offshore sequestration is the outlier among these technologies as the most mature and well understood, with large commercial operations like the Porthos Project in the North Sea. While alternatives may sound attractive with claims of lower capture costs compared to DAC, blue carbon projects aren’t quite ready to bank on for meeting emissions targets for three key reasons. First, there is little standardization, as major marketplaces like Verra or Gold Standard don’t currently list blue carbon projects on their registries. Second are the complex and undetermined impacts to ecosystems. We expect blue carbon projects to face lengthy and costly environmental reviews. Lastly, no regulatory  support or tax credits exist to provide supplemental revenue streams, making financing early projects a challenge. 

Ultimately, companies should consider pursuing blue carbon projects for discovery; they don’t belong as part of an offset strategy before 2030 due to blue carbon’s relative immaturity and aforementioned barriers. Companies with seawater flow or offshore assets should consider partnering with startups in this area, leveraging their expertise in water infrastructure and offshore environments to help startups with promising technology move from lab to pilot solutions. Navigating environmental approvals and other regulatory barriers won’t be a process many startups have expertise in, but larger organizations can help shepherd them along. The potential for low costs and synergies with offshore assets make blue carbon an intriguing technology to cautiously assess, but one should ultimately do so with awareness of the steep barriers to commercial success.