Changes to the Air‐Sea Flux and Distribution of Radiocarbon in the Ocean Over the 21st Century

We investigate the spatiotemporal evolution of radiocarbon (Δ 14 C) in the ocean over the 21st century under different scenarios for anthropogenic CO 2 emissions and atmospheric CO 2 and radiocarbon changes using a 3‐D ocean carbon cycle model. Strong decreases in atmospheric Δ 14 C in the high‐emission scenario result in strong outgassing of 14 C over 2050–2100, causing Δ 14 C spatial gradients in the surface ocean and vertical gradients between the surface and intermediate waters to reverse sign. Surface Δ 14 C in the subtropical gyres is lower than Δ 14 C in Pacific Deep Water and Southern Ocean surface water in 2100. In the low‐emission scenario, ocean Δ 14 C remains slightly higher than in 1950 and relatively constant over 2050–2100. Over the next 20 years we find decadal changes in Δ 14 C of −30‰ to +5‰ in the upper 2 km of the ocean, which should be detectable with continued hydrographic surveys. Our simulations can help in planning future observations, and they provide a baseline for investigating natural or anthropogenic changes in ocean circulation using ocean Δ 14 C observations and models.