Menabreaz L., Bourles D. L., Thouveny Nicolas. (2012). Amplitude and timing of the Laschamp geomagnetic dipole low from the global atmospheric Be-10 overproduction : contribution of authigenic Be-10/Be-9 ratios in west equatorial Pacific sediments. Journal of Geophysical Research. Solid Earth, 117, p. B11101. ISSN 0148-0227.
Titre du document
Amplitude and timing of the Laschamp geomagnetic dipole low from the global atmospheric Be-10 overproduction : contribution of authigenic Be-10/Be-9 ratios in west equatorial Pacific sediments
Journal of Geophysical Research. Solid Earth, 2012,
117, p. B11101 ISSN 0148-0227
Authigenic Be-10/Be-9 ratios were measured along a sediment core collected in the west equatorial Pacific in order to reconstruct cosmogenic Be-10 production variations near the equator, where the geomagnetic modulation is maximum. From 60 to 20 ka, the single significant Be-10 production impulse recorded at 41 ka results from the geomagnetic dipole low that triggered the Laschamp excursion. No significant Be-10 overproduction signature is recorded at the age of the Mono Lake excursion (similar to 34 ka). A compilation of authigenic Be-10/Be-9 records obtained from sediments was averaged over a 1 kyr window and compared with the 1 kyr averaged Be-10 flux record of Greenland ice cores. Their remarkable similarity demonstrates that Be-10 production is globally modulated by geomagnetic dipole variations and redistributed by atmosphere dynamics. After calibration using absolute values of the virtual dipole moment drawn from paleomagnetic database, the authigenic Be-10/Be-9 stack allows reconstructing the geomagnetic dipole moment variations over the 20-50 ka time interval. Between 48 and 41 ka, the dipole moment collapsed at a rate of -1.5 x 10(22) A m(2) kyr(-1), which will be an interesting criterion for the assessment of the loss rate of the historical field and the comparison of dipole moment loss prior to excursions and reversals. After a 2 kyr duration of the minimum dipole moment (similar to 1 x 10(22) A m(2)), a slow increase started at 39 ka, progressively reaching 5 x 10(22) A m(2) at 20 ka. The absence of a significant dipole moment drop at 34 ka, the age of the Mono lake excursion, suggests that the duration and amplitude of the dipole weakening cannot be compared with that of the Laschamp. This study provides a reliable basis to model the production of radiocarbon and in situ cosmogenic nuclides and to improve the calibration of these dating methods.
