The Ecological Activity Index tool for mapping potential ecosystem exposure to ocean alkalinity enhancement

Abstract Ocean alkalinity enhancement is being explored to remove carbon dioxide from the atmosphere, but its interactions with marine ecosystems remain uncertain. Robust data-based baseline frameworks are needed to assess where and when ecosystems may be increasingly exposed to ocean alkalinity enhancement. Here we present the Ecological Activity Index (EAI) that integrates publicly available datasets on chlorophyll a , zooplankton, and fish larvae abundance, endangered species distributions and commercial fishing activity across the United States Northeast Shelf and Slope. This framework provides a spatially and temporally resolved measure of ecosystem activity and human use. Ecological activity varies strongly across regions and seasons, with patterns that differ between parts of the food web and fisheries. Higher EAI values indicate greater overlap between ecological activity and human use, and thus potentially higher exposure. This framework establishes a quantitative approach to inform site selection, monitoring design, and environmental assessment of ocean alkalinity enhancement.