We’re pleased to share that the Puro.earth’s Ocean Storage of Biomass (OSB) methodology—now renamed Marine Anoxic Carbon Storage (MACS) - has been approved by the Puro.earth Advisory Board, marking a significant milestone in the development of this new approach to durable, ocean-based carbon removal. 

This approval follows months of scientific consultation, stakeholder feedback, and internal review. It reflects both the potential of the MACS approach and our shared commitment to developing a methodology that is scientifically credible, environmentally responsible, and grounded in real-world feasibility. 

As we prepare for publication of the methodology in the coming months, we want to highlight some important updates and clarify what this means for the future of MACS. 

Grounded in Science, Guided by Integrity 

The MACS methodology is designed to enable long-term carbon removal by depositing sustainably sourced, lignin-rich biomass into deep, oxygen-depleted (anoxic) marine basins. These basins slow microbial decomposition and naturally limit animal activity, creating conditions that offer strong potential for long-term, durable carbon storage. 

While the scientific rationale is strong, this is still an emerging field—and we recognize that with innovation comes both excitement and scrutiny. We welcome both. The MACS methodology has been developed to reflect the best available scientific knowledge, while maintaining the flexibility to evolve as new insights emerge. 

Durability Update: A More Conservative, Credible Claim 
 
Following expert input from our Advisory Board, including leading marine scientists like Dr. Ali Mashayek (University of Cambridge), we have revised the expected carbon storage duration from 1,000+ years to 200+ years. 

“While the geochemical conditions in anoxic basins can, in theory, preserve carbon for millennia, our current ability to monitor and verify these outcomes over such long timescales is limited. Taking a conservative approach is the right move for scientific credibility and market trust.” – Dr. Ali Mashayek 

This update reflects our commitment to scientific integrity. A 200+ year durability claim still represents a meaningful, long-term climate solution over several centuries—and one that we can stand behind with confidence. Specific storage sites may have a wide range of durability projections, and the 200+ durability claim is therefore generally a conservative estimate for suitable anoxic basins globally. 

No Credits Yet: Field Trials Are Ongoing 

To date, no MACS projects have been audited or issued credits, and all activity remains at the field trial stage. These trials are vital for generating real-world data and validating the assumptions of the methodology. However, most projects do not yet have permits that allow permanent biomass placement—meaning they are not eligible for audit or verification. Puro.earth requires every project to be fully permitted prior to the issuance of CORCs, in compliance with all applicable local, regional, national or international marine environmental protection regulations. We firmly believe that by establishing the first standard methodology for MACS even before commercial operations have begun, we are helping to advance critical R&D efforts and build the trust needed to support the development of future national and international policies. 

This reflects the reality of operating within evolving regulatory frameworks and the importance of building social license. It also demonstrates a careful, phased approach to commercialization. Puro.earth carefully follows the development of international marine policies, and we are committed to aligning with their guidance. 

Addressing Environmental and Social Concerns 

We are aware of concerns around how marine carbon storage methodologies might be misused or misunderstood. The MACS methodology is designed to prevent this. It includes: 

• Strict site selection and environmental screening criteria 
• Pre- and post-deployment monitoring requirements 
• Adaptive management protocols 
• Safeguards to prevent illegal dumping or unsanctioned activity 

We also recognize that some aspects—such as the long-term behavior of anoxic zones—require further research. These aren’t being ignored. Instead, they are being addressed through the development of an R&D roadmap, new collaborative research proposals, and ongoing dialogue with leading marine scientists around the world. 

Built to Evolve: A Living Methodology 

The MACS methodology includes a comprehensive monitoring, reporting, and verification (MRV) framework—combining lab experiments, modeling, and field sampling. Monitoring is required before, during, and for a minimum of 15 years after deployment. As scientific knowledge and monitoring technologies improve, so will the methodology. 

At a recent MACS workshop in Bucharest, researchers from 25 institutions across 14 countries came together to identify key knowledge gaps and help shape a coordinated research agenda for the field. These discussions are already translating into action — and the MACS methodology will continue to evolve as new findings emerge. The group’s core message was clear: proceed with caution, but proceed. Scaling up field trials in a measured, science-led manner is essential to deepen understanding of regional baselines, reduce uncertainty, and support robust environmental monitoring. At the same time, there was a shared sense of urgency — a recognition echoed not only across the MACS research community, but more broadly within the marine CDR space. As Ocean Visions CEO Brad Ack noted at the recent Biennial Summit, this is a critical moment to advance solutions responsibly and at pace. 

Puro.earth’s role is to ensure that all operations are grounded in scientific rigor and conducted with strong environmental and social safeguards at their core. 

What’s Next?

• Public release of the methodology is planned for June 2025. 
• No credits will be issued until projects meet all requirements, including verified long-term storage capability. 
• Continuous improvement will guide all future iterations, informed by new science, feedback from stakeholders, and the results of field trials. 

Our Commitment 

We believe in the potential of marine carbon removal to play a meaningful role in global climate solutions. But that potential must be earned—through transparency, integrity, and continuous improvement. 

The approval of the MACS methodology by our Advisory Board marks a major step forward, but it is just the beginning. We will continue to work with scientists, project developers, environmental experts, and the public to ensure MACS evolves responsibly. 

Thank you to everyone who contributed feedback during the public consultation. You may view all the public comments and our responses here.