How did the dipole axis vary during the first millennium BCE? New data from West Europe and analysis of the directional global database
Résumé
Despite progress in the knowledge of secular variation during the first millennium BCE in Europe, data coverage remains poor at the earliest periods, especially in some regions as in the Central Mediterranean area. This study presents three new directional and six new intensity data between the 13th and the 4th centuries BCE on archaeological kilns, pottery and baked clay fragments from South Italy and France. Archaeodirections were determined after thermal demagnetizations and archaeointensities using the Thellier-Thellier protocol with corrections for the anisotropy and cooling rate effects. The new data confirm the large deviation of the direction from a Geocentric Axial Dipole field, the high geomagnetic field strength and the fast secular variation observed in Europe during the earliest half of the first millennium BCE. Another characteristic of this period is a difference of ~25° between the longitudes of the virtual geomagnetic poles inferred from European and Middle East data. This unusual behaviour can be mainly related to the Levantine Iron Age anomaly (LIAA) and its expansion from the Middle East to Europe. However, the review of the global directional database shows that almost all virtual geomagnetic poles, 96% of them coming from Europe, the Middle East, East Asia, North America and Hawaii, are 10–25° away from the rotation axis towards North Russia between 1000 and 600 BCE. The calculation of a mean global VGP curve suggests that the North geomagnetic pole followed a clockwise motion during this period with a dipole tilt up to around 14°. This study shows that a dipole axis tilt may have played an important role in the rapid secular variation in western Eurasia, although part of this variation may also be related to non-dipole fields associated with the LIAA.
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