Quantifying the Efficacy of mCDR with C-Star

By Sherry Lippiatt, Abigale Wyatt, and Alicia Karspeck

At [C]Worthy, we are building the foundation of a scientifically credible marine carbon dioxide removal (mCDR) market that is grounded in robust monitoring, reporting, and verification (MRV). Our goal is to enable science-based quantification of how much carbon dioxide (CO₂) is removed from the atmosphere during an mCDR deployment.

To that end, we’ve developed C-Star, a software platform that runs regional ocean models: systems of equations that simulate ocean physics (like currents, temperature, salinity) and the interactions between ocean chemistry (like how carbon moves into, out of, and through the ocean) and simple marine organisms. C-Star runs these models to simulate ocean conditions both with and without an mCDR deployment. By comparing the two scenarios, we calculate the reduction in atmospheric CO₂ as a result of the deployment.

One mCDR approach we model is Ocean Alkalinity Enhancement (OAE). This involves adding alkaline materials (e.g. ground basalt rock or limestone) or removing acid from seawater, in order to increase the capacity of seawater to absorb and store atmospheric CO₂. The videos below show modeling simulations of a hypothetical OAE deployment near the tip of the Olympic Peninsula in Washington State, where alkalinity is added to the ocean over the course of ten months. For illustration purposes, the simulation adds an amount of alkalinity that is roughly 1000 times what would be added in a typical field test.

• The first panel (left) shows the spread of a plume of seawater with slightly elevated alkalinity as a result of the OAE deployment. Darker green areas indicate more of the added alkalinity, while the lighter green areas are where there is less. Even though we are simulating an addition of alkalinity that would be considered large relative to today’s pilot projects, the deployment leads to a very small change in alkalinity compared to the background ocean: a maximum of a 2% increase over average background levels. The plume of slightly elevated alkaline seawater dissipates as it is mixed with surrounding water. 
• The second panel (middle) illustrates when and where there is a “net flux” of CO₂ from the atmosphere into the ocean, meaning that the added alkalinity is either increasing the CO₂ removed from the atmosphere or decreasing the amount of CO₂ released from the ocean (we measure the exchange of CO₂ between the ocean and atmosphere in units of g/m²/day). The darker blue areas near the deployment location indicate a greater change in the net CO₂ exchange, and the white patches that extend out from the deployment are where the net change is smaller. The exchange of CO₂ between the atmosphere and ocean varies with wind speed, so at locations and times when winds are low there may be little change in CO₂ flux and a patch may momentarily disappear in the video. Key takeaways from this panel are that the additional CO₂ removal as a result of the OAE deployment occurs slowly, over a very large area of the ocean, and results in very small deviations from average background concentrations in seawater.
• The third panel (right) shows the total reduction of atmospheric CO₂ over the course of the ten month simulation. The deployment’s total net CO₂ removal is just over 200,000 tons. 

These simulations don’t just quantify CO₂ removal—the model also reveals where and how far seawater with elevated alkalinity spreads. This can be helpful for evaluating potential ecosystem impacts. For example, if a local community or regulatory agency is concerned about changes in seawater pH (which will slightly increase during the early stages of the deployment), the model can help inform a targeted monitoring plan based on when and where (how far from the point source) pH excursions due to alkalinity enhancement are possible. 

The ocean models we use in C-Star are validated by decades of peer-reviewed science. But for the carbon markets, scientific rigor isn’t enough—the modeling that underpins carbon credit transactions needs to be transparent, auditable, reproducible and accessible to folks in both industry and research. That’s why C-Star is designed to meet the highest standards of both science and accountability. We are building trust and confidence in open system MRV, accelerating innovation, and fostering sustained investment in these potential climate solutions.