Ocean Alkalinity Enhancement: A Scalable Climate Solution Finding Its Place in the VCM
Ocean Alkalinity Enhancement (OAE) represents a promising approach to carbon dioxide removal that leverages the ocean's natural carbon absorption capabilities. This article explores the science behind OAE, its benefits and risks, and how innovative companies like Limenet are developing practical implementations. We also examine how Carbonmark is creating new pathways for novel carbon removal technologies to access carbon markets, accelerating the deployment of these critical climate solutions.
The Ocean's Role in Carbon Capture
The ocean naturally absorbs about 25% of the carbon dioxide released by human activities. It does this through chemical reactions that convert CO₂ into bicarbonate and carbonate ions. However, this process makes seawater more acidic, which harms marine life and reduces the ocean’s ability to continue absorbing CO₂. This phenomenon, known as ocean acidification, is a major consequence of climate change, threatening ecosystems, fisheries, and global food security.
Ocean Alkalinity Enhancement helps address this issue by adding alkaline substances—such as crushed limestone, olivine, or magnesium-based minerals—to seawater. These materials neutralize acidity, raise the ocean’s pH, and strengthen its natural buffering capacity — that is to say, its ability to resist changes in pH by neutralizing added acids or bases, helping maintain stable marine chemistry. As a result, the ocean can absorb more CO₂ from the atmosphere and convert it into stable forms that remain stored for thousands of years. This process mimics natural rock weathering, but operates on human-relevant timescales to help combat climate change.
What is Ocean Alkalinity Enhancement?
OAE is an engineering method for carbon dioxide removal (CDR) and mitigating ocean acidification. It aims to accelerate the ocean's natural ability to absorb and store atmospheric CO₂ by increasing the alkalinity of seawater.
How Ocean Alkalinity Enhancement Happens
Several approaches are being explored to increase ocean alkalinity, including:
Enhanced Weathering: This involves grinding naturally occurring alkaline minerals such as olivine, basalt, or limestone, and spreading them over the open ocean, beaches, or coastal areas. The dissolution of these minerals releases alkaline ions into the seawater.
Electrochemical Methods: These techniques use electricity to split seawater into acidic and alkaline components. The alkaline stream is then released back into the ocean to increase alkalinity. The acidic stream can potentially be used to dissolve alkaline minerals more rapidly.
Direct Injection of Alkaline Solutions: Alkaline liquids, such as sodium hydroxide, can be directly added to surface ocean waters.
Benefits of Ocean Alkalinity Enhancement
Carbon Removal
Research indicates that each ton of alkalinity added to the ocean can potentially sequester between 0.8 and 1.5 tons of CO₂, depending on the specific method and materials used (according to studies by the National Academies of Sciences, Engineering, and Medicine).
Scalable Potential
If implemented at a global scale, OAE could remove billions of tons of CO₂ annually, making it one of the most impactful carbon removal solutions available. The National Academies estimates a potential of 1-10 gigatons of CO₂ removal per year with proper implementation (National Academies Ocean CDR Report, 2022).
Long-Term Storage
The carbon captured through this process is stored in the ocean in stable forms that can remain for thousands of years, offering a high level of permanence.
Support for Marine Ecosystems
OAE can help create healthier conditions for marine life—especially for species like corals and shellfish, which require stable pH levels to build their shells and skeletons.
Potential Risks of Ocean Alkalinity Enhancement
While OAE holds great promise as a carbon removal strategy, several challenges must be carefully considered before large-scale deployment:
Ecological Uncertainty: The long-term effects of changing ocean chemistry—especially at large scales—are not yet fully understood.
Monitoring and Verification: Measuring how much CO₂ is actually removed and stored in the ocean over time is technically complex. It requires reliable Monitoring, Reporting, and Verification (MRV) systems.
Logistical and Operational Challenges: Mining, grinding, and transporting alkaline minerals like olivine or limestone is energy- and resource-intensive.
Energy Use and Costs: Some OAE methods—particularly electrochemical approaches—require significant energy input, which must be weighed against their carbon removal benefits.
OAE is currently in the research and pilot phase. Despite its great potential, open questions and concerns remain. However, some innovative climate startups—such as Limenet—have begun to overcome these challenges. We’ll explore this further below.
Lime as a Promising Enabler of Scalable Ocean Alkalinity Enhancement
Among the various materials considered for OAE, lime—specifically hydrated lime (calcium hydroxide, Ca(OH)₂)—offers significant advantages. Derived from limestone (CaCO₃) through a process called calcination, lime is highly reactive, dissolves quickly in seawater, and efficiently increases ocean alkalinity. This rapid reactivity makes lime a more effective and controllable solution than raw limestone, which dissolves slowly—especially in surface waters already saturated with calcium carbonate.
When lime reacts with CO₂ and seawater, it forms calcium bicarbonate (Ca(HCO₃)₂), a stable compound that can store carbon in the ocean for over 10,000 years. Because calcium bicarbonate is already a natural component of ocean chemistry, this method aligns well with marine systems and poses lower ecological risks than synthetic or industrial alternatives. However, the production and use of lime require careful engineering to ensure net-negative emissions, efficient CO₂ uptake, and minimal environmental disruption.
Limenet: Introducing pH-Equilibrated Ocean Alkalinization
Limenet has developed a breakthrough method called pH-equilibrated Ocean Alkalinization, designed to accelerate and optimize the natural carbon cycle between rocks, the ocean, and the atmosphere. This process involves producing calcium bicarbonate by reacting carbon dioxide, slaked lime (calcium hydroxide), and seawater in a controlled reactor.
The resulting calcium bicarbonate solution is then released into the ocean, mimicking and enhancing the natural geological weathering of carbonate rocks. Once dissolved, the calcium bicarbonate increases ocean alkalinity, boosting its capacity to absorb and store atmospheric CO₂. In essence, Limenet has industrialized the geological carbon cycle using a combination of electrical and thermal energy.
Unlike traditional OAE, which can suffer from slow mineral dissolution and localized chemical disruptions, Limenet’s pH-equilibrated Ocean Alkalinization process delivers balanced outputs that avoid oversaturation and abrupt shifts in seawater chemistry. Their method reliably transforms short-term carbon interactions into long-term carbon sinks.
To address the carbon footprint of lime production, Limenet uses biogenic CO₂ from biomass sources—currently, from the Iren biogas plant in Reggio Emilia—and powers the calcination process with syngas combustion, thereby closing the loop and supporting a low-emission lifecycle.
From Research to Real-World Impact
Limenet was founded by Giovanni Cappello, Stefano Cappello, Enrico Noseda, and Valdis Bisters, following five years of research conducted in collaboration with Stefano Caserini, Mario Grosso, and Simona Masina—renowned experts in biogeochemistry who formed the Desarc Maresanus research group. Together, they published over ten scientific articles related to Limenet’s technology and developed the first prototypes of the pH-equilibrated Ocean Alkalinization process. These early efforts successfully demonstrated the ability to remove CO₂ through the formation of calcium bicarbonate, establishing both the academic rigor and practical feasibility of Limenet’s approach.
Transparency and Verification
Limenet has made significant progress in transparency and digital monitoring through the development of a robust digital Monitoring, Reporting, and Verification (dMRV) system. The company works closely with RINA, a globally respected verification body with deep expertise in naval and marine auditing, to validate both its methodology and Project Design Document. RINA’s involvement brings high credibility to the process, particularly in ensuring compliance with ISO 14064-2 standards.
To maximize transparency and traceability, Limenet has also pioneered a blockchain-based tracking system. By leveraging the Polygon blockchain, they’ve created a virtual mirror of their operations, enabling seamless communication between the plant’s internal systems and decentralized databases. This ensures real-time data recording, prevents double counting, and guarantees the integrity of verified emissions data—only information validated by RINA is securely stored on the blockchain.
Scaling Impact at the World’s Largest Ocean-Based Carbon Removal Facility
Since September 2023, Limenet has operated the world’s largest ocean-based CO₂ removal facility in Augusta, Sicily. The plant currently removes 100 kg of CO₂ per hour, with a near-term target of 800 metric tons per year, and a long-term goal of scaling up to 100,000 metric tons annually by 2028.
The facility is located in a place known as Quadrilatero della Morte ("Quadrilateral of Death"), a region previously devastated by petrochemical pollution. Today, it stands as a symbol of environmental restoration and climate innovation.
Limenet’s work demonstrates how the core challenges of OAE—such as mineral reactivity, ecological safety, lifecycle emissions, and verification—can be effectively addressed through scientific research, smart engineering, and digital innovation.
Ocean Alkalinity Enhancement in the Blue Carbon Framework
Engineered carbon removal methods often struggle to fit within traditional climate approaches. However, Ocean Alkalinity Enhancement can be integrated into the blue carbon framework by complementing the organic carbon removal capacity of ecosystems such as mangroves, seagrasses, and salt marshes with long-term inorganic carbon storage.
While blue carbon has traditionally focused on nature-based solutions, there is growing interest in incorporating engineered approaches that enhance the ocean’s natural ability to absorb CO₂. Given the urgency of the climate crisis—and the ocean’s immense carbon storage potential—boosting these natural processes could be critical to meeting global carbon removal targets.
The emerging concept of “enhanced blue carbon” or “marine CDR” reflects this shift, blending ecosystems restoration with targeted interventions like OAE. Although not yet fully incorporated into existing blue carbon frameworks, continued research and the development of governance structures may pave the way for broader acceptance of these innovative solutions.
Carbonmark: Enabling Market Access for Next-Generation Carbon Removal
As novel carbon removal approaches like OAE move from laboratories to pilot-scale deployments, they often find it difficult to reach the market through traditional registries. Even when new methodologies are submitted, they can face delays of up to two years before approval. Since credits can’t be issued without approved methodologies and MRV protocols, many startups face capital gaps—they incur costs for pilot projects but are unable to access carbon finance until much later. This slows down iteration and scaling, and lowers investors’ confidence.
Carbonmark addresses this challenge by providing a flexible and transparent infrastructure specifically designed for next-generation carbon removal technologies. Through Carbonmark Direct, project developers can natively issue, track, and sell blockchain-powered carbon credits in just two weeks after independent verification. Integrated with dMRV systems, this solution ensures full transparency, integrity, and traceability—from the moment CO₂ is removed to the retirement of the corresponding credit, all in real time.
By creating a digital flow of carbon credits mirroring actual carbon removal, Carbonmark enables innovative, science-backed projects to access the voluntary carbon market without waiting years for registry approval or methodology recognition.
In a rapidly evolving climate tech landscape, Carbonmark bridges the gap between scientific innovation and market infrastructure, ensuring that impactful and verifiable solutions like pH-equilibrated Ocean Alkalinization by Limenet can scale responsibly, transparently, and urgently—right when the planet needs them most.
