Abstract Ocean Alkalinity Enhancement (OAE) in coastal and open‐ocean environments has been proposed as a scalable method for atmospheric CO 2 removal. However, the effects of OAE on marine calcifiers, such as foraminifera, remain under‐constrained. Determining the response of marine calcifiers to OAE is critical because alkalinity uptake during calcification reduces the intended CO 2 removal from the atmosphere. Here we utilize X‐Ray Micro‐Computed Tomography imaging to quantify the calcification response of Globigerina bulloide s grown in culture under two OAE scenarios. These scenarios most closely simulate equilibration with atmospheric CO 2 , corresponding to modest increases in the saturation state, and using NaHCO 3 as an alkalinity source. We assess changes in calcification using two metrics: shell density as indicated by mean CT number, and calcite mass added relative to the amount of shell elongation. An alkalinity increase of 350 μmol/kg significantly increased both metrics, indicating enhanced calcification of G. bulloides as a result of alkalinity addition. We extrapolate our culture results from G. bulloides to estimate increases in CaCO 3 flux driven by planktic foraminifera in response to large‐scale OAE deployment, and discuss factors that will impact the global, multi‐species nature of the planktic foraminiferal calcification response in the open ocean. While our preliminary results from G. bulloides point to a minor mitigating impact of foraminifera calcification on OAE efficacy, we argue that pelagic calcification should be considered when estimating OAE efficacy and future potential for deployment in the open ocean as a method for atmospheric CO 2 removal.