A Synthesis of Deglacial Deep-Sea Radiocarbon Records and Their (In)Consistency With Modern Ocean Ventilation

We present a synthesis of 1,361 deep-sea radiocarbon data spanning the past 40kyr and computed (for C-14-dated records) from the same calibration to atmospheric C-14. The most notable feature in our compilation is a long-term Delta C-14 decline in deep oceanic basins over the past 25kyr. The Delta C-14 decline mirrors the drop in reconstructed atmospheric Delta C-14, suggesting that it may reflect a decrease in global C-14 inventory rather than a redistribution of C-14 among different reservoirs. Motivated by this observation, we explore the extent to which the deep water C-14 data jointly require changes in basin-scale ventilation during the last deglaciation, based on the fit of a 16-box model of modern ocean ventilation to the deep water Delta C-14 records. We find that the fit residuals can largely be explained by data uncertainties and that the surface water Delta C-14 values producing the fit are within the bounds provided by contemporaneous values of atmospheric and deep water Delta C-14. On the other hand, some of the surface Delta C-14 values in the northern North Atlantic and the Southern Ocean deviate from the values expected from atmospheric (CO2)-C-14 and CO2 concentrations during the Heinrich Stadial 1 and the BOlling-AllerOd. The possibility that deep water 16-box records reflect some combination of changes in deep circulation and surface water reservoir ages cannot be ruled out and will need to be investigated with a more complete model.