Use of 10 Be to Predict Atmospheric 14 C Variations during the Laschamp Excursion: High Sensitivity to Cosmogenic Isotope Production Calculations

• Published in: Radiocarbon
• Main Authors: Cauquoin, Alexandre, Raisbeck, Grant, Jouzel, Jean, Paillard, Didier
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 2014
• Subjects: General Earth and Planetary Sciences; Archeology; Greenland; Antarc*; Antarctica; GRIP; NGRIP
• Online Access: http://dx.doi.org/10.2458/56.16478; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033822200049122

The Laschamp excursion is a period of reduced geomagnetic field intensity occurring 40.7 ± 1.0 kyr ago. As a consequence, cosmogenic isotope production increased dramatically and its sensitivity to solar activity was enhanced during this period. The latter occurs because a larger fraction of the lower-energy interstellar galactic cosmic-ray particles, normally excluded by the geomagnetic field, is able to reach Earth's atmosphere. This produces a cosmogenic isotope production signal with a significant structure. As high-resolution 10 Be profiles from both Antarctica (EDC) and Greenland (NGRIP-GRIP) during this crucial period are now available, one can use them as input into a box carbon cycle model in order to predict atmospheric 14 C variations due to the Laschamp excursion. For this purpose, 10 Be data are converted into 14 C, using production calculations for the 10 Be- 14 C conversion, after correction for the estimated difference of sensitivity between polar and global 10 Be deposition. Several scenarios of carbon cycle state are simulated, from preindustrial to glacial conditions. Applying two recent cosmogenic isotope production calculations for the 10 Be to 14 C conversion, we found that the resulting atmospheric Δ 14 C variations are very sensitive to which of these two are employed. For example, Δ 14 C amplitude under glacial conditions varies from 260‰ (EDC) and 320‰ (Greenland) to 430‰ (EDC) and 510‰ (Greenland) depending on the formulation used for 10 Be- 14 C conversion.