Continuous millennial decrease of the Earth's magnetic axial dipole

Wilbor Poletti , Andrew J. Biggin , Ricardo I. F. Trindade , Gelvam A. Hartmann , Filipe Terra-Nova (1)

1 LPG - Laboratoire de Planétologie et Géodynamique [UMR 6112]

Since the establishment of direct estimations of the Earth's magnetic field intensity in the first half of the nineteenth century, a continuous decay of the axial dipole component has been observed and variously speculated to be linked to an imminent reversal of the geomagnetic field. Furthermore, indirect estimations from anthropologically made materials and volcanic derivatives suggest that this decrease began significantly earlier than direct measurements have been available. Here, we carefully reassess the available archaeointensity dataset for the last two millennia, and show a good correspondence between direct (observatory/satellite) and indirect (archaeomagnetic) estimates of the axial dipole moment creating, in effect, a proxy to expand our analysis back in time. Our results suggest a continuous linear decay as the most parsimonious long-term description of the axial dipole variation for the last millennium. We thus suggest that a break in the symmetry of axial dipole moment advective sources occurred approximately 1100 years earlier than previously described. In addition, based on the observed dipole secular variation timescale, we speculate that the weakening of the axial dipole may end soon.

Mots clés: Geomagnetism; Archaeointensity; Axial dipole; Archaeomagnetic dataset; Data selection criteria

Domaines: Planète et Univers [physics]

Wilbor Poletti, Andrew J. Biggin, Ricardo I. F. Trindade, Gelvam A. Hartmann, Filipe Terra-Nova. Continuous millennial decrease of the Earth's magnetic axial dipole. Physics of the Earth and Planetary Interiors, 2018, 274, pp.72-86. ⟨10.1016/j.pepi.2017.11.005⟩. ⟨insu-03663869⟩