Puro.earth is proud to announce that the Microalgae Carbon Fixation and Sinking (MCFS) methodology has been approved by the Puro.earth Advisory Board, marking another important step in the careful development of ocean-based carbon removal.
The ocean is by far the largest reservoir of carbon in the climate system and has a vast capacity for further CO₂ removal. Developing credible, science-led methodologies to harness this potential is essential, and MCFS is now the third marine carbon dioxide removal (mCDR) methodology approved under the Puro Standard, following Marine Anoxic Carbon Storage (MACS) and Direct Air Capture and Ocean Storage (DACOS) earlier this year.
This approval follows months of scientific consultation, stakeholder feedback, and internal review. It reflects both the potential of the MCFS approach and our shared commitment to developing methodologies that are scientifically credible, environmentally responsible, and grounded in real-world feasibility.
Together, these milestones represent meaningful progress toward responsibly scaling ocean-based carbon removal.
From consultation to approval
In June 2025, Puro.earth launched a public consultation on MCFS, inviting feedback from scientists, suppliers, and stakeholders across the carbon removal ecosystem. More than 100 comments were received, leading to strengthened safeguards around environmental monitoring, deployment scale, and durability.
This transparent process ensures the methodology reflects the best available science while remaining practical for project developers to implement
What is MCFS?
MCFS enables long-term carbon removal by fostering local microalgae (phytoplankton) growth on custom- designed engineered substrates. Once colonized, and after a pre-determined amount of time that is based on the engineered substrate material, the substrate and its attached biomass sink rapidly to the deep ocean, where carbon can be stored for centuries.
This approach is different from ocean fertilization, which disperses nutrients freely into surface waters, often triggering uncontrolled algal blooms that may persist for weeks or months, thereby risking harm to ecosystems. By contrast, the MCFS approach ensures the following components that are key to avoiding environmental harm and effective carbon removal and storage at the same time:
- Nutrients remain bound in the substrate, preventing uncontrolled leaching into the water column.
- Algae grow directly on the substrate, rather than drifting in surface waters.
- Rapid, controlled sinking ensures that algae and carbon are exported below the surface within days (maximum 30 days), minimizing ecological disruption and maximizing sequestration efficiency.
These safeguards, embedded in the methodology’s rules, ensure that MCFS is designed to leverage natural processes responsibly.
Key safeguards and requirements:
- Scale limit: maximum 1 MtCO₂ per facility.
- Controlled export: substrates and microalgae must sink within 30 days, at >20m/hour.
- Environmental safety: strict threshold criteria, with extensive pre- and post-deployment monitoring.
- Site eligibility: High Nutrient, Low Chlorophyll (HNLC) regions, within EEZs, and in areas where deep water masses ensure ≥200 years of storage.
- Robust quantification: combining direct measurements and model outputs.
Built on collaboration and innovation
The MCFS methodology was first initiated by Gigablue, whose early innovation in this field provided the foundation for translating practical experience into a certifiable framework. Development was then carried forward by Puro.earth’s science team, working closely with external consultants - a common pathway for methodology creation under the Puro Standard.
Throughout the development process and public consultation, we engaged widely with experts in marine science, academic researchers, and stakeholders from across the carbon removal ecosystem. Oceanaid CCS contributed crucial expertise in oceanography, carbon chemistry, and ocean modeling - particularly in shaping the quantification terms and rules for CORCs. More than 100 comments were received and reviewed, leading to important refinements, including stricter limits on deployment, scale, and ecological monitoring.
“We’re grateful to Puro.earth for leading the way in setting high standards for carbon removal. Their rigorous certification process gives credibility to innovative approaches like ours and builds the trust that this industry needs to scale.” - Sapir Markus Alford, co-founder and chief technology officer of Gigablue
The final approval was granted by the Puro Advisory Board, in line with our governance structure, ensuring that the methodology meets the highest standards of independence, scientific credibility, and environmental responsibility.
Importantly, MCFS is now open to other suppliers.
Learn more & get involved
The approval of the MCFS methodology is the result of open consultation, careful scientific review, and collaboration across the carbon removal ecosystem. For those who would like to dive deeper, all documentation is available here:
If you are developing a project and would like to pursue certification, you can now apply to become a Puro.earth supplier under the MCFS methodology.
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