Agnès Genevey

ArcheoInt: An upgraded compilation of geomagnetic field intensity data for the past ten millennia and its application to the recovery of the past dipole moment

[1] This paper presents a compilation of intensity data covering the past 10 millennia (ArcheoInt). This compilation, which upgrades the one of Korte et al. (2005), contains 3648 data and incorporates additional intensity and directional data sets. A large majority of these data (

Secular variation study from non-welded pyroclastic deposits from Montagne Pelée volcano, Martinique (West Indies)

87%) were acquired on archeological artifacts, and the remaining

The Mayans: Climate determinism or geomagnetic determinism?

13% correspond to data obtained from volcanic products. The present compilation also includes important metadata for evaluating the intensity data quality and providing a foundation to guide improved selection criteria. We show that

Are there connections between the Earth's magnetic field and climate?

50% of the data set fulfill reasonable reliability standards which take into account the anisotropic nature of most studied objects (potsherds), the stability of the magnetization, and the data dispersion. The temporal and geographical distributions of this sub–data set are similar to those of the main data set, with

Does Earth's magnetic field secular variation control centennial climate change?

72% of the data dated from the past three millennia and

Possible impact of the Earth's magnetic field on the history of ancient civilizations

76% obtained from western Eurasia. Approximately half of the selected intensity data are associated with at least an inclination value. To constrain the axial and full dipole evolution over the past three millennia requires that we avoid any overrepresentation of the western Eurasian data. We introduce a first-order regional weighting scheme based on the definition of eight widely distributed regions of 30° width within which the selected data are numerous enough. The regional curves of virtual axial dipole moments (VADM) and of mixed VADM-virtual dipole moments (VDM) averaged over sliding windows of 200 years and 500 years testify for strong contributions from either equatorial dipole or nondipole components. The computation of global VADM and mixed VADM/VDM variation curves, assuming an equal weight for each region, yields a dipole evolution marked by a distinct minimum around 0 B.C./A.D. followed by a maximum around the third-fourth century A.D. A second minimum is present around the eighth century A.D. This variation pattern is compatible with the one deduced from earlier, more

Geomagnetic field hemispheric asymmetry and archeomagnetic jerks

Abstract We present palaeomagnetic data obtained from large clasts collected in non-welded pyroclastic deposits from Montagne Pelee volcano (Martinique Island, West Indies). These deposits, dated by the 14C method from 5000 yr BP to the present, comprise block- and ash-flows, ash- and pumice-flows and pumice fallouts. Alternating fields treatment was as a routine chosen to demagnetise large samples for which the magnetisation was measured with a specially designed inductometer. The mean directions obtained from block- and ash-flow deposits of the 1902 and 1929 eruptions are in good agreement with the expected geomagnetic directions at these times in Martinique. The so-called P1 eruption (∼1345 AD), which is characterised by a rarely observed transition from a Peleean to a Plinian eruptive style, allows a direct comparison of the palaeomagnetic directions obtained from the three types of pyroclastic deposits. All deposits provide identical mean directions, which further demonstrates the suitability of the non-welded pyroclastic deposits for geomagnetic secular variation study with a very good accuracy and precision. The possibility of using pyroclastic deposits is promising for obtaining a wider distribution of sampling sites, which may better allow us to constrain our knowledge on the geomagnetic secular variation. We find that large geomagnetic changes occurred in Martinique during the last millennium, while the variations appear more limited prior to this period.

Evidence for rapid geomagnetic field intensity variations in Western Europe over the past 800 years from new French archeointensity data

Climatic variations since the end of the last ice age have been large enough to influence the fate of ancient civilizations, and deciphering the exact role of climate in the history of old societies is an active and challenging domain of research [e.g., deMenocal, 2001]. This potential influence, which serves as the foundation of ‘climate determinism,’ can be viewed as the response of natural-resource-dependent, agriculture-based communities to climatically driven environmental changes. In some cases, these could have provoked major damage in economic and social organization of the societies, thus paving the way for political disintegration. Could this climate variability be connected with the Earths magnetic field? If so, a link might be found between the past geomagnetic field behavior and the history of humanity. This article explores that potential link, using a case study of the Classic Maya civilization.