Carbon sequestration service in the Atlantic Ocean: an assessment from coastal to ocean ecosystems

The ocean plays a central role in the global carbon cycle. It regulates atmospheric CO₂ through long-term sequestration in coastal and deep-sea systems. Blue Carbon Ecosystems (BCEs)—mangroves, salt marshes, seagrass meadows, and tidal flats—are recognized for their high carbon burial efficiency per unit area and their growing relevance in climate policy. In contrast, the open ocean, driven by the Biological Carbon Pump (BCP), dominates large-scale carbon storage but is rarely considered alongside coastal systems in carbon budget assessments. Here, we present a basin-scale assessment of carbon sequestration across the Atlantic coastal and open-ocean domains. To do so, we quantified carbon fluxes and long-term stocks by harmonizing and integrating spatial datasets, Earth System Model outputs, and a data-assimilated biogeochemical framework. Coastal ecosystems show high sequestration efficiency per unit area. The open ocean, however, accounts for most of the total carbon storage due to its depth, extent, and circulation-driven redistribution of remineralized carbon. By creating a unified framework that allows to combine coastal burial processes with pelagic carbon transfer in a consistent way, this study clarifies how different definitions of sequestration shape basin-scale estimates. The results provide a robust basis for improving representation of marine carbon processes in regional and global carbon budgets, marine conservation strategies, and climate mitigation planning.