Persistently well-ventilated intermediate-depth ocean through the last deglaciation

During the last deglaciation (~18–11 thousand years ago), existing radiocarbon (14C) reconstructions of intermediate waters in the mid- to low-latitude oceans show widely diverging trends, with some broadly tracking the atmosphere and others suggesting extreme depletions. These discrepancies cloud our understanding of the deglacial carbon cycle because of the diversity of hypotheses needed to explain these diverging records, for example, injections of 14C-dead geological carbon, mixing of extremely isolated waters from the abyssal ocean or changes in sites of deep-water ventilation. Here we present absolutely dated deglacial deep-sea coral 14C records of intermediate waters from the Galapagos Platform—close to the largest reported deglacial 14C depletions—together with data from the low-latitude Atlantic. Our records indicate coherent, well-equilibrated intermediate-water 14C ventilation in both oceans relative to the atmosphere throughout the deglaciation. The observed overall trend towards 14C-enriched signatures in our records is largely due to enhanced air–sea carbon isotope exchange efficiency under increasing atmospheric $${p_{{\rm {CO}}_2}}$$ . These results suggest that the 14C-depleted signatures from foraminifera are likely sedimentary rather than water mass features, and provide tight 14C constraints for modelling changes in circulation and carbon cycle during the last deglaciation. Intermediate-depth waters in the Atlantic and Pacific Oceans were well equilibrated with the atmosphere through the last deglaciation, according to radiocarbon data from deep-sea corals.