Coral Data Reveal the Impact of the Great Acceleration on the Carbon Cycle in the Western Tropical South Atlantic

The Great Acceleration is defined as a series of unprecedented, global human‐driven changes that occurred across socio‐economic and natural compartments of the Earth system after 1950. Among the observed changes, increase in fossil fuel burning has led to a significant accumulation of carbon dioxide (CO 2 ) in the atmosphere. By absorbing roughly 30% of total anthropogenic CO 2 emissions since the 1950s, the ocean is a major carbon sink, but the extent to which the natural oceanic carbon cycle was impacted by anthropogenic CO 2 is poorly known. To understand long‐term changes in the oceanic carbon cycle, coral reconstructions are important archives of past environmental variables. The stable carbon isotopic composition of corals (δ 13 C coral ) has been considered an important proxy for assessing changes in the isotopic composition of seawater dissolved inorganic carbon (δ 13 C DIC ), which ultimately reflects isotopic changes in atmospheric CO 2 (δ 13 C CO2 ). We use δ 13 C coral from the western tropical South Atlantic to assess changes in δ 13 C DIC to understand regional changes in the oceanic carbon cycle. The coral reconstruction documents significant carbon cycle changes across the pre‐to the post‐industrial transition, resulting in a δ 13 C coral decreasing trend of −0.0204‰ year −1 from 1928 to 2018, which intensified after the 1950s, during the Great Acceleration. Moreover, our δ 13 C coral reconstruction also shows decadal‐scale fluctuations not observed in atmospheric CO 2 . Our results suggest that the South Atlantic absorbed more anthropogenic CO 2 than previously thought and indicate an accelerated decline in δ 13 C DIC associated with changes in the ocean carbon cycle.