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 ?14C decline in deep oceanic basins over the past 25 kyr. The ?14C decline mirrors the drop in reconstructed atmospheric ?14C, 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 ?14C 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 ?14C records. We find that the fit residuals can largely be explained by data uncertainties and that the surface water ?14C values producing the fit are within the bounds provided by contemporaneous values of atmospheric and deep water ?14C. On the other hand, some of the surface ?14C 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 ?14C 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.