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CALIBRATION OF THE 14C TIMESCALE AND CONSTRAINTS OF THE GLACIAL CARBON CYCLE

LEHMAN, SCOTT  INSTAAR.
Hughen , Konrad  WHOI.
Southon, John  UC-Irvine.

A new series of 14C measurements in Ocean Drilling Program cores from the tropical Cariaco Basin, which have been correlated previously to the annual-layer counted event chronology for the GISP2 ice core, provides a high resolution calibration of the radiocarbon timescale back to 50,000 years before present. Several lines of evidence, including independent radiometric dating of events correlated to GISP2, suggest that the calendar age model is accurate. Reconstructed 14C activities varied significantly during the last glacial period, including sharp peaks synchronous with cosmogenic nuclide peaks in ice cores and marine sediments, as well as the Laschamp and Mono Lake geomagnetic field intensity minima in marine sediments. Sensitivity tests performed using a geochemical box model indicate that much of the variability can be explained by geomagnetically modulated changes in 14C production rate, together with plausible changes in the global carbon cycle during glaciation.


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