Development of the ecological activity index as an integrative ecosystem assessment and monitoring asset for ocean alkalinity enhancement

The oceans are the largest carbon reservoir on Earth’s surface, and methods of increasing their uptake and storage of anthropogenic carbon (marine Carbon Dioxide Removal, mCDR) are gaining interest. Ocean alkalinity enhancement (OAE) is an mCDR approach that sequesters carbon dioxide by adding alkaline materials into the marine environment. Currently, no environmental impact assessment framework exists for OAE. Here, we describe an assessment approach using public datasets of multiple trophic levels and fishing activity. We develop the ecological activity index (EAI), a quantitative tool to identify locations and times of year that minimize impacts on critical ecosystem metrics. Fishing activity and endangered species distributions are partially decoupled from measures of ocean productivity, highlighting the importance of explicitly including higher trophic levels and ocean uses into the EAI. This framework helps to establish baseline ecological activity for risk assessments and identifies priority environmental monitoring targets for OAE and other mCDR approaches.