GEOMAGNETIC INTENSITY AND C-14 ABUNDANCE IN THE ATMOSPHERE AND OCEAN DURING THE PAST 50KYR

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 C-14 production in the past. The pro duction record was then converted into an atmospheric Delta(14)C signa l using a 4-box model of past oceanic circulation. The results indicat e that changes in geomagnetic field intensity account for at least 80% of the Delta(14)C shift documented by published U-Th data, which are of the order of 500 per mil with respect to a constant production hypo thesis. Model simulations show that changes in past oceanic circulatio n account for only +/- 100 per mil of Delta(14)C variation, which is w ithin the uncertainty of the geomagnetic correction. In terms of datin g, 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.