Abstract The abyssal ocean may provide adequate sequestration for Carbon Capture and Storage and Carbon Dioxide Removal. The transit of carbon from seafloor release to ocean surface can take millennia, as it occurs through many water pathways characterized by long‐tailed transit‐time distributions (TTDs). However, multi‐millennial simulations of TTDs are typically prohibitively expensive. Here, we introduce an idealized but computationally efficient methodological framework for computing TTDs offline from climate‐model archives. We applied this framework to one Earth System Model to estimate the deep ocean sequestration efficiency for the 2030s and 2090s ocean circulations. We found that sequestration is most efficient on abyssal plains isolated from deep branches of the conveyor belt, such as the North Pacific Basins, where less than 10% of the water reaches the surface after 1,000 years. The climate‐warming‐induced slowdown of the 2090s deep‐ocean circulation extends return times by about 30%, which exceeds internal climate variability (∼20 ${\sim} 20$%).

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