NOAA/WDS Paleoclimatology - Global Synthesis of Marine Radiocarbon Data Over the last 40,000 years

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 D14C decline in deep oceanic basins over the past 25 kyr. The D14C decline mirrors the drop in reconstructed atmospheric D14C, 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 D14C 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 D14C records. We find that the fit residuals can largely be explained by data uncertainties and that the surface water D14C values producing the fit are within the bounds provided by contemporaneous values of atmospheric and deep water D14C. On the other hand, some of the surface D14C 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 Bolling-Allerod. The possibility that deep water D14C 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.