🌏 The uncertain-seas of ocean CDR

The big science and policy questions to consider before taking the plunge into ocean-based carbon dioxide removal

Us land-dwellers waste a lot of breath on atmospheric carbon capture. Putting our terrestrial bias aside, the ocean is the world’s largest carbon sink—on the order of ~50x more carbon than is currently in the atmosphere.

But it’s no small feat to wring out nature’s sequestration sponge. The field of ocean-based carbon dioxide removal (CDR) is nascent, complicated, and risky—even compared with complex terrestrial carbon removal tech. Nevertheless, we’ve created such a mess on Aisle Earth that it’s now necessary to mop vigorously with all possible carbon sponges.

Venture-backed companies like Running Tide, Ebb Carbon, and Brilliant Planet are already working on solutions that would accelerate the ocean’s absorption of CO2, but the science is far from settled. At such a large scale and open system, it’s difficult to anticipate the ripple effects caused by adjusting the chemistry or biology of marine ecosystems for accelerated carbon sequestration purposes. Just measuring the efficacy and durability of carbon removal remains a huge challenge, considering oceans cover ~70% of the planet with constantly shifting currents.

Researchers and entrepreneurs working at the frontier of ocean CDR must swim against a rip current of quandaries, from regulatory and technical obstacles to equity concerns. Realistically, these gaps in knowledge and policy must be addressed before commercial viability of many potential ocean CDR business models, and certainly before responsible scaling of these climate technologies.

In a recent report, Carbon180 spelled out some of the most pressing questions and suggestions to address ocean CDR uncertainties and issues in the US. We dipped our toes into these muddy waters in conversations with Sifang Chen, Managing Science and Innovation Advisor at Carbon180, and ocean carbon cycle expert David Ho. Consider this a landscaping primer before we fully wade into a future deep dive on ocean CDR market opportunities and technologies. Of interest to you? Reach out with your perspective on ocean CDR business models. The water is literally warm!


  • Timing tension. Proving these ocean CDR methods outside the lab in a responsible manner will require regulations in place to make sure tests aren’t harming surrounding ecosystems. But developing the guidelines needed to move the industry forward while protecting the seas will also depend on data and learnings from initial projects.
  • Permitting problems. As with many climate tech sectors, permitting for ocean CDR is a major barrier. Experts are calling for governance structures and regulatory processes better-suited to ocean-based operations, which currently need sign-off from a wide assortment of state and federal agencies.
  • Scientific uncertainty. Studying something as massive as the ocean is a difficult task. While researchers are constantly working to improve our understanding of the ocean’s carbon cycles, ecosystems, and acidification, the data collected through observation is a drop in the bucket. This leaves a lot of unanswered questions about the broader repercussions of ocean CDR at scale.
  • The MRV conundrum. Monitoring, reporting, and verification (MRV) for carbon removal, which involves determining the amount of CO2 extracted and the durability of its storage, is already a complex topic in CDR circles. Throwing the magnitude and movement of the oceans into that equation makes it seem almost impossible to measure. More money for enabling tech like sensors and agreed-upon standards for MRV could develop best practices before companies are ready to start selling ocean-based carbon credits.
  • Public perception. With so many unknowns, fragile ecosystems, and often vulnerable coastal communities, it will be important for ocean CDR companies working toward deployment to begin robust public engagement early.

Ocean CDR 101

Ocean-based CDR includes an array of different techniques and technologies, broadly bucketed into biological or chemical solutions.

Source: Carbon180

Biological approaches rely on the photosynthesis of biomass—growing something (like algae) at the surface that takes in CO2 and then sinking that biomass or feeding it to other organisms. Other methods move water from the surface into the deep ocean or vice versa. The idea is to sequester the carbon from the first few hundred feet of seawater in biomass that ends up deeper in the ocean, allowing the water toward the surface to absorb more CO2 from the atmosphere.

  • Biological pathways: ocean fertilization, macroalgae cultivation, and artificial upwelling and downwelling
  • Pros: more understood pathways, closer to deployment-ready
  • Cons: greater potential for side effects within the ecosystem
Innovators in the space: Running Tide, Algiecel, Brilliant Planet, Phykos

Chemical approaches rely on chemical reactions to remove CO2 from the ocean or convert it into a more stable form. Direct ocean removal (aka direct ocean capture) uses an electrochemical process to pull CO2 from sea water and then return that water to the ocean. With ocean alkalinity enhancement, adding crushed limestone or other alkaline minerals to sea water causes a reaction with CO2 that forms inorganic carbon (like bicarbonate or carbonates), which can be stored for long periods of time.

  • Chemical pathways: ocean alkalinity enhancement and direct ocean removal
  • Pros: more of a closed system, less impact on marine environments
  • Cons: more energy-intensive, lower tech readiness
Innovators in the space: Ebb Carbon, Equatic, Vesta, Captura, Heimdal
Source: Additional Ventures

The prep work

These methods are not yet close to scalability. And even as new technologies flood the market, there are some substantial gaps in knowledge and policy that researchers, governments, entrepreneurs, and communities will need to address.

“A lot of things have to happen in tandem, because time is short,” Sifang Chen, author of the ocean CDR whitepaper, told us. “Our window for these large-scale climate actions is shrinking very quickly. We need to do research and development on this quickly, but also do it in a way that protects the ocean ecosystem. So that we’re not adding additional harm or damage to the ocean.”

Reducing the unknowns

  • The problem: Different methods of ocean CDR exist on a spectrum of tech readiness, but there’s a significant amount of high-level uncertainty across the board. How effective are these approaches at sequestering carbon? What are their impacts on the ocean’s carbon cycle, ecosystems, and marine life?
  • Potential solutions: Answering these big questions will take a well-funded research effort. Chen recommends larger research program budgets for NOAA, NSF, NASA, ARPA-E, and DARPA within the next two years in order to fill in many of the knowledge gaps before deploying ocean CDR.
  • Key takeaway: It’s still difficult to get even accurate baseline measurements of entire marine ecosystems. Supporting more of that research as well as learning more about the impacts of both biological and chemical approaches at a larger scale will be key to understanding efficacy and avoiding potential harms.

Preventing permitting woes

  • The problem: Many different agencies have to coordinate for any kind of project in the water today: NOAA, the Environmental Protection Agency (EPA), the Bureau of Ocean Energy Management (BOEM) at the Department of the Interior, the Coast Guard, and the Army Corps of Engineers, along with state agencies like a Department of Health or Department of Land and National Resources.
  • Potential solutions: Chen proposes the US create a new lead agency to handle this coordination and permitting process and also notes the need for global agreements on CDR policy to protect the oceans.
  • Key takeaway: Permitting for ocean CDR is perhaps the most pressing challenge, as the industry will need this in place in order to deploy the field tests and demonstration projects that will provide critical learnings.

Enabling MRV

  • The problem: Because there are gigaton-sized discrepancies between measured and modeled ocean CO2 uptake, validating the volume of CO2 removal made possible by ocean CDR approaches is a major challenge today. On top of that, the additional CO2 absorption that CDR makes possible in the surface ocean (now stripped of some CO2 through growing biomass or chemical reactions) occurs over a very large area and long period of time, making it extremely difficult to monitor. Better enabling tech is needed to observe important ocean properties, including partial pressure of CO2, salinity, nutrients, pH, DIC, total alkalinity, and dissolved oxygen.
  • Potential solutions: Chen proposes leveraging and expanding existing ocean-sensing efforts, like NOAA's Ocean Acidification Program, Global Ocean Monitoring and Observation Program, and Ocean Carbon Network, to monitor the impact of ocean CDR projects on these properties. David Ho, professor at University of Hawaii at Manoa and ocean carbon cycle expert, is tackling this problem through nonprofit and focused research organization (FRO) [C]worthy, along with co-founders Matthew Long and Alicia Karspek. The team aims to develop trustworthy, open-source verification of ocean CDR and the modeling tools that will enable it. Eventually, MRV will be accomplished through tech-heavy geophysical modeling, he told us. But first, those models need to be informed by the observations from early ocean CDR testing, and the companies developing technologies that would enable better measurements need more financial support.
  • Key takeaway: Agreed-upon standards for MRV, and the sensors or other tech capable of quantifying it, should be in place before sales of carbon credits from ocean CDR begin.

Scoping societal impacts

  • The problem: The broader effects of ocean CDR remain a big unknown. What happens down the food chain if, for example, growing algae at scale removes too many nutrients from an ocean ecosystem? It’s ultimately not that many steps between phytoplankton and humans, and coastal communities will be left to handle the fallout if ocean CDR methods go awry.
  • Potential solutions: Building relationships, environmental justice frameworks, and community understanding in locations where companies plan to deploy ocean CDR is essential to avoiding public pushback and responsibly conducting these initial projects. “We shouldn't make acceptance the goal. We should make capacity-building the goal—to help communities really understand what is being asked of them,” Chen said. “And to learn from the community about what they need and what their priorities are.”
  • Key takeaway: Deeper knowledge and more public engagement and education will be essential to inform communities about the potential changes in their waters and get local support and involvement.

What comes next?

While the sector continues to explore the economic questions of costs, offtakers, and value chains, the ocean CDR ecosystem will need time to identify and evaluate side effects of different methods in order to determine how to scale in a sustainable way. But time we have not.

“We just want to make sure we don’t repeat the problems of the legacy carbon market. I think people have that in mind. But we need a lot more money in MRV,” Ho said, because it enables the activities in the rest of the sector.  

As ocean CDR grows, a consortium of companies could play a role in establishing MRV standards as well as channels for knowledge transfer and information exchange, Chen said. “When that happens, that really helps the whole field to move forward.”  

Ready to jump off the deep end? Carbon180 is hiring! Curious for more Twitter takes on open-source MRV? David has thoughts and is seeking research funding for [C]worthy.

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