Geomagnetic intensity and 14 C abundance in the atmosphere and ocean during the past 50 kyr

We have used a new sedimentary record of geomagnetic field intensity, combined with published volcanic data, to examine the extent to which geomagnetic changes have affected 14 C production in the past. The production record was then converted into an atmospheric Δ 14 C signal using a 4‐box model of past oceanic circulation. The results indicate that changes in geomagnetic field intensity account for at least 80% of the Δ 14 C shift documented by published U‐Th data, which are of the order of 500 per mil with respect to a constant production hypothesis. Model simulations show that changes in past oceanic circulation account for only ±100 per mil of Δ 14 C variation, which is within the uncertainty of the geomagnetic correction. In terms of dating, these results show that the radiocarbon ages have to be shifted by 2 to 3.5 kyr towards older ages during the 20–40 ka interval.