Ocean Alkalinity Enhancement (OAE) is a proposed method to remove carbon dioxide from the atmosphere by increasing the ocean’s capacity to store carbon. While promising, its long-term effectiveness depends on how marine ecosystems respond, especially organisms that build shells (calcifiers), which are sensitive to changes in ocean chemistry.

In this study, we test how biotic calcification affects carbon removal in realistic OAE deployment scenarios at ten global sites. These scenarios are developed with industry input and reflect real-world constraints, such as political and logistical feasibility. We use two global ocean models—MOM6-COBALT and MOM6-MARBL—to capture a range of ecosystem responses and compare against a control simulation without OAE. The models include detailed tracking of carbon and alkalinity, and we examine how much carbon is removed under each scenario.

We also test how changing assumptions in the models—such as how sensitive calcification is to ocean chemistry and how deep organic material sinks—affects carbon uptake. Results show that these ecological assumptions influence estimates of carbon removal.

This work underscores the need to account for biological feedbacks in climate modeling and offers guidance for the design and evaluation of OAE and other ocean-based carbon dioxide removal strategies.