Puro.earth is a carbon removal crediting platform that certifies durable carbon removal and issues CO2 Removal Certificates (CORCs) for each net tonne of CO2 removed and stored for hundreds or thousands of years. Puro CORCs are issued and retired in the public Puro Registry, enhancing transparency in carbon markets.
We are excited to announce the public consultation for our new ocean methodology - Microalgae Carbon Fixation and Sinking (MCFS) Methodology. This innovative Marine carbon dioxide removal (mCDR) leverages the ocean’s ability to uptake more CO2 from the atmosphere by enhanced growth of microalgae, which sinks in a controlled manner locking the carbon into the deep sea on climate-relevant timescales.
Overview of the Methodology
Microalgae Carbon Fixation and Sinking (MCFS) refers to a pathway which captures and sequesters carbon through additional photosynthetic activity of local phytoplankton in the surface ocean and on designated substrates, followed by an intentional and controlled export of that carbon to the deep ocean and ocean sediment.
This methodology sets a global standardized durability for a MCFS activity in the eligible site conditions in 200 years. This is labeled as COR200+. The durability of several hundred years offers a robust and scalable solution for long-term carbon sequestration in the ocean. The durability of 200 years is very conservative for MCFS activities, and it is based on an ultra conservative assumption that all sunken carbon is subject to ocean circulation and not sedimented. The project-specific ocean conditions can lead to much longer durability up to several thousand years.
MCFS activity consist of the following general steps:
Deployment of engineered substrates in regions of the ocean which have high nutrient, low chlorophyll (HNLC) conditions
Growth of additional local microalgae (phytoplankton) on the substrate, consuming carbon-dioxide dissolved in the ocean and micronutrients that are incorporated in the substrate;
Sinking of the substrates and the attached microalgae to the deep ocean;
Storage of the carbon in the slow carbon cycle of the deep ocean.
Re-capturing consumed CO2 in surface waters: The microalgae captured (fixated) carbon was already dissolved in the surface ocean, and by removing that allows for additional carbon uptake by the ocean.
A schematic illustration of the overall process of a Microalgae Carbon Fixation and Sinking (MCFS) activity.
Environmental and Social Considerations
While the MCFS pathway offers significant potential for carbon removal, it's crucial to address and mitigate key environmental and social risks on methodology and project levels. The methodology introduces safeguards and monitoring processes for effectively managing environmental and social risks, such as:
Nutrient robbing across the water column and at regional and global scales
Changes in the carbonate system chemistry
Perturbation of oxygen budgets in the benthic environment
Harmful algal blooms and toxins production
Physical harm to larger organisms in the surface ocean and smothering of benthic organisms
To mitigate environmental and social risks, the methodology requires MCFS projects to perform thorough site-specific environmental impact assessments, including baseline ecological data, and monitor them across the different stages of the deployment.
Period of Consultation
The public consultation will be open 11 June – 2 July 2025. We welcome feedback from all stakeholders during this period. Your input is invaluable to our methodology development process, ensuring transparency and informed decision-making.
Webinar
Puro will host a webinar on Wednesday, June 18th, 2025 at 11:00 a.m. Eastern/ 3:00 p.m. UTC covering key aspects. Please register for the webinar to join and submit any questions or topics you wish us to cover.
Consultation Documents
Please download the consultation documents and submit your feedback to contact@puro.earth using the provided feedback form.
Your insights and expertise will help us refine and improve this groundbreaking methodology for durable carbon removal. We look forward to your participation in shaping the future of ocean-based carbon storage solutions.
Collaboration and Innovation
This methodology is being developed in collaboration with Gigablue, Alcove Labs, and Oceanid CCS.
At Puro.earth, we believe that innovative carbon removal solutions like MCFS are crucial in our fight against climate change. We look forward to your participation in this public consultation as we work together towards a more sustainable future.
Stay tuned for more updates on our website and social media channels. Together, we can accelerate the carbon removal industry and make a lasting impact on our planet's health.
Q&A
1. How does the carbon get captured and stored in Microalgae Carbon Fixation and Sinking (MCFS)?
The MCFS approach captures carbon that is already dissolved in the surface ocean, and by that allows for additional carbon uptake by the ocean. The MCFS activities deploy designated substrates in the surface water, and result in additional photosynthetic activity (carbon fixation) of local microalgae followed by an intentional and controlled export (sinking) of that carbon-biomass to the deep ocean and ocean sediment. To complete the sequential carbon removal activity two parallel processes happen: the CO2 consumed from the surface water is re-captured and replaced by new CO2 uptake from the atmosphere and the sunken microalgae must stay in the bottom waters and not resurface and re-emit CO2.
2. How long does the CO2 remain stored and how do you know that?
The MCFS methodology defines a CORC 200+ durability of several centuries. Durability in a specific location must be at least 200 years, but the specific site durability may reach a range of several centuries or millennia depending on depth, currents, and geochemical properties, which are analyzed by combining in-situ measurements and robust ocean models. The site selection and quantification take into account when the carbon does not get efficiently re-captured or remain stored over 200+ years: a) if the re-capture in the surface water is disturbed because of downwelling and the air-sea-gas-exchange is stopped prematurely or b) if the ocean ventilation is fast and the part of microalgae-biomass can return to surface waters in less 200 years and re-emit the CO2 to the air.
3. Where in the ocean is it possible to do MCFS activities?
The methodology defines eligible site conditions in section 3.7. The allowed locations must have high nutrition levels and at the same time low chlorophyll levels, i.e. HNLC regions. The methodology limits the MCFS activities to the HNLC regions where there is plenty of macronutrients like phosphorus, but lack of micronutrients limit the growth of microalgae. The natural (baseline) MCFS activity in these areas is minimal, and the MSCF activity impact can be measured and quantified against the baseline. The HNLC regions are not found everywhere in the ocean, but there are several known regions where these conditions are met. Additionally, the activity must take place at least 12 nm from the coast and within an Exclusive Economic Zone (EEZ) of a sovereign state and in accordance with applicable regulations.
4. What impacts can this activity have on life in the ocean?
The main environmental risks identified include nutrient robbing, dimethylsulfide production, and oxygen depletion and some other potentially negative impacts to ocean life. The MCFS methodology requires every project to design, operate and monitor under strict thresholds, complying with applicable local, regional or national legislations. Every activity will assess and monitor its environmental impacts in the near and far area of MCFS deployment area. See section 4.4 - 4.5.
5. How is MCFS different from other ocean-based methodologies?
Ocean has a lot of potential pathways to remove CO2 from the atmosphere. Microalgae Carbon Fixation and Sinking (MCFS) has parallels and differences with other marine CDR pathways like Marine Anoxic Carbon Storage (MACS) and Ocean Alkalinity Enhancement (OAE).
Carbon fixation feature is common to MCFS and with (MACS), where the photosynthesis happens on land (terrestrial). In MCFS it takes place in the water when photosynthesis produces the microalgae. The difference is that MCFS does not need anoxic basins, but the sinking biomass has to remain in the deep ocean after sinking.
Ocean alkalinity is enhanced by both OAE and MCFS, but by very different means. In MCFS the acidification is lowered by microalgae consuming the dissolved CO2 when growing, in OAE the same result is reached by adding alkaline rock particles that chemically bind the dissolved CO2 to new chemical compounds, carbonates and bicarbonates.
In both OAE and MCFS the final carbon removal happens when the ocean surface water has re-captured the same amount of CO2 from the atmosphere.
6. What is the substrate fostering microalgae growth made of?
The MSCF methodology defines the outcomes that the substrate must achieve. The substrate must not include any harmful components and must contain up to 0.5% micronutrients. The methodology requires that a) the nutrients are contained in the substrate and not dissolved or free-floating in the ocean; b) the floating time is limited to 30 days and sinking speed is at least 20 m/h and the substrate density design must enable reaching these outcomes.
7. Are there other benefits from MCFS activities than the carbon removal benefit?
MCFS carbon removal activities provide co-benefits and contribute to several UN Sustainable Development Goals in addition to the SDG 13 Climate Action:
SDG 12 (Responsible Consumption and Production) by prioritizing sustainable sourcing of raw materials including waste
SDG 14 (Life Below Water) by counteracting ocean acidification and advancing research activity on ocean ecology and benthic environments
SDG 17 (Partnerships for the Goals) by involving local and indigenous communities in the development and deployment of the solution
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