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Science 9 January 2004:
Vol. 303. no. 5655, pp. 202 - 207
DOI: 10.1126/science.1090300
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Research Articles

14C Activity and Global Carbon Cycle Changes over the Past 50,000 Years

K. Hughen,1* S. Lehman,3 J. Southon,4 J. Overpeck,5,6 O. Marchal,2 C. Herring,1 J. Turnbull3

A series of 14C measurements in Ocean Drilling Program cores from the tropical Cariaco Basin, which have been correlated to the annual-layer counted chronology for the Greenland Ice Sheet Project 2 (GISP2) ice core, provides a high-resolution calibration of the radiocarbon time scale back to 50,000 years before the present. Independent radiometric dating of events correlated to GISP2 suggests that the calibration is accurate. Reconstructed 14C activities varied substantially during the last glacial period, including sharp peaks synchronous with the Laschamp and Mono Lake geomagnetic field intensity minimal and cosmogenic nuclide peaks in ice cores and marine sediments. Simulations with a geochemical box model suggest that much of the variability can be explained by geomagnetically modulated changes in 14C production rate together with plausible changes in deep-ocean ventilation and the global carbon cycle during glaciation.

1 Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution (WHOI), Woods Hole, MA 02543, USA.
2 Department of Geology and Geophysics, Woods Hole Oceanographic Institution (WHOI), Woods Hole, MA 02543, USA.
3 Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO 80309, USA.
4 Department of Earth System Science, University of California, Irvine, CA 92697, USA.
5 Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA.
6 Institute for the Study of Planet Earth, University of Arizona, Tucson, AZ 85721, USA.

* To whom correspondence should be addressed. E-mail: khughen{at}whoi.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)