The Complex Quest to Store Atmospheric Carbon in the Ocean
Start-ups are testing marine carbon removal, but measuring success remains a difficult challenge.
1Ocean Carbon Removal Ambitions
Start-ups are currently testing methods to pull carbon dioxide from the atmosphere and store it within the ocean. By adding alkaline substances to seawater, these companies aim to shift dissolved carbon into stable forms. This process mimics natural mineral weathering but operates at a scale intended to impact global climate targets.
2Halifax Harbor Field Trials
Planetary Technologies conducted trials in Halifax Harbor by releasing an alkaline slurry into power plant cooling water. Researchers used rhodamine dye and sensors to track how the treated water dispersed. Measuring the exact amount of carbon captured remains difficult because the signal is small and the ocean environment is constantly moving.
3The Challenge of Measurement
Marine carbon dioxide removal relies on complex models to verify carbon credits. Because seawater currents disperse treated water, direct measurement is often impossible. Companies must reconstruct the chemical changes after the water leaves the outfall. This ambiguity creates significant hurdles for establishing the credibility of carbon removal claims in open systems.
4Chemical Mechanisms Explained
The process leverages the ocean's carbonate system by converting dissolved carbon dioxide into bicarbonate and carbonate ions. Planetary Technologies uses magnesium oxide feedstock to create an alkaline slurry. This chemical shift lowers surface carbon concentration, allowing more gas to dissolve from the air, potentially locking it away for thousands of years.
5Modeling Carbon Sequestration
Oceanographers use high-resolution computer simulations to estimate carbon removal efficiency. In one study, a model showed that treated water achieved 60 percent of its maximum potential removal within a year. These simulations track how long water remains at the surface, which is critical for calculating the total carbon exchange with the atmosphere.
6Ecological Safety Concerns
Researchers are actively monitoring for potential ecological damage caused by magnesium hydroxide exposure. Lab studies indicated that certain phytoplankton and mussel species could be harmed by high concentrations. Scientists emphasize the necessity of rigorous assessment to ensure that these carbon removal techniques do not cause lasting harm to local marine food webs.
7Public and Regulatory Resistance
Several projects have faced significant local opposition and regulatory scrutiny. Planetary Technologies abandoned a project in England after protests, while a Vesta trial in North Carolina was scaled back due to environmental concerns. International bodies have identified ocean alkalinity enhancement as a technique requiring priority scrutiny to prevent potential widespread or lasting damage.
8Lessons from Iron Fertilization
The history of ocean iron fertilization serves as a warning for the current field. Early experiments showed that while phytoplankton blooms were easy to trigger, they failed to prove durable carbon storage. The 2012 incident involving Russ George highlighted the dangers of commercial geoengineering without adequate oversight or measurable, long-term carbon removal results.
9The Failure of Running Tide
Running Tide, which raised $70 million to grow kelp on floating buoys, shut down in 2024. The company struggled with scaling offshore operations and the high costs of measurement, reporting, and verification. Founder Marty Odlin cited weak demand and the extreme expense of proving carbon removal in open-water systems as primary reasons.
10Onshore Electrolysis Alternatives
Equatic is testing an onshore approach at the Port of Los Angeles using electrolyzers to separate seawater into alkaline and acidic streams. This method allows for direct measurement of carbon removal within controlled containers. By tracking every gram of carbon, the company aims to provide the transparency and trust that open-water systems currently lack.
11Energy Demands and Scalability
Onshore carbon removal requires significant electricity, with Equatic estimating 2.5 megawatt-hours per ton of carbon. Scaling this to one billion tons annually could consume 8 percent of global electricity production. While hydrogen production might offset some costs, the high energy demand remains a major factor for the long-term viability of these technologies.
12Future of Carbon Accounting
The industry faces a divide between cheaper open-water models and more expensive, verifiable onshore methods. Buyers are already purchasing future credits, yet the lack of standardized measurement remains a critical risk. The future of marine carbon removal depends on whether companies can prove their impact through rigorous, transparent, and scientifically validated data.