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

Fig.2 Radiocarbon calibration data from various sources. 14C Activity and Global Carbon Cycle Changes
over the Past 50,000 Years

Science,
Volume 303, Number 5655, 9 January 2004.


K. Hughen1, S. Lehman3, J. Southon4, J. Overpeck5,6,
O. Marchal2, C. Herring1, J. Turnbull3

1 Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
2 Department of Geology and Geophysics, Woods Hole Oceanographic Institution, 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
5,6 Department of Geosciences and Institute for the Study of Planet Earth, University of Arizona, Tucson, AZ 85721, USA.

ABSTRACT:
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.

DATA:
Download the Cariaco Basin 14C data from the WDC Paleo Archive in Text or Microsoft Excel format.

Fig. 3. Atmospheric d14C for the past 50 cal. ka B.P.
Fig. 3.
Atmospheric d14C for the past 50 cal. ka B.P. Symbols are the same as those in Fig. 2A. Cariaco error bars represent independent uncertainty in d14C due to 1-sigma d14C age error. Light gray shading shows additional uncertainty in Cariaco d14C due to calendar-age error that is not independent from sample to sample, but rather would shift sections of the curve together within the limits of the shading. Dotted line is modern preindustrial atmospheric d14C, defined as 0 per mil. Upper and lower limits were determined by adding and subtracting 1 sigma errors to the calendar age and recalculating d14C with the use of the new calendar ages.

To read or view the full study, please visit the Science website.
It was published in Science, Volume 303, Number 5655, 9 January 2004.


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5 February 2004