Amplitude and timing of the Laschamp geomagnetic dipole low from the global atmospheric 10 Be overproduction: Contribution of authigenic 10 Be/ 9 Be ratios in west equatorial Pacific sediments

• Published in: Journal of Geophysical Research: Solid Earth
• Main Authors: Ménabréaz, L, Bourles, Didier, Thouveny, Nicolas
• Other Authors: Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2012
• Subjects: [SDU]Sciences of the Universe [physics]; Greenland; Pacific; Greenland ice cores
• Online Access: https://hal.science/hal-01420385; https://hal.science/hal-01420385/document; https://hal.science/hal-01420385/file/MENEBREAZetal-JGR-2012-PREPRINT.pdf; https://doi.org/10.1029/2012JB009256

International audience [1] Authigenic 10 Be/ 9 Be ratios were measured along a sediment core collected in the west equatorial Pacific in order to reconstruct cosmogenic 10 Be production variations near the equator, where the geomagnetic modulation is maximum. From 60 to 20 ka, the single significant 10 Be production impulse recorded at 41 ka results from the geomagnetic dipole low that triggered the Laschamp excursion. No significant 10 Be overproduction signature is recorded at the age of the Mono Lake excursion ($34 ka). A compilation of authigenic 10 Be/ 9 Be records obtained from sediments was averaged over a 1 kyr window and compared with the 1 kyr averaged 10 Be flux record of Greenland ice cores. Their remarkable similarity demonstrates that 10 Be 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 10 Be/ 9 Be 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 À1.5 Â 10 22 A m 2 kyr À1 , 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 ($1 Â 10 22 A m 2), a slow increase started at 39 ka, progressively reaching 5 Â 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.