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 40 kyr and computed (for ¹⁴C-dated records) from the same calibration to atmospheric ¹⁴C. The most notable feature in our compilation is a long-term Δ¹⁴C decline in deep oceanic basins over the past 25 kyr. The Δ¹⁴C decline mirrors the drop in reconstructed atmospheric Δ¹⁴C, suggesting that it may reflect a decrease in global ¹⁴C inventory rather than a redistribution of ¹⁴C among different reservoirs. Motivated by this observation, we explore the extent to which the deep water Δ¹⁴C 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 Δ¹⁴C records. We find that the fit residuals can largely be explained by data uncertainties and that the surface water Δ¹⁴C values producing the fit are within the bounds provided by contemporaneous values of atmospheric and deep water Δ¹⁴C. On the other hand, some of the surface Δ¹⁴C values in the northern North Atlantic and the Southern Ocean deviate from the values expected from atmospheric ¹⁴CO₂ and CO₂ concentrations during the Heinrich Stadial 1 and the Bølling-Allerød. The possibility that deep water Δ¹⁴C 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.