Inversion des pôles · Observatoire des phénomènes naturels

Pôles · inversion

Quand le nord devient sud

Il y a environ 780 000 ans, le champ magnétique terrestre s’est inversé (Matuyama–Brunhes). L’animation rejoue le modèle GGFMB tous les 50 ans de 900 000 à 700 000 ans : l’axe du dipôle bascule et le moment s’effondre pendant la transition.

Âge: —
Polarité: —
Moment dipolaire: —

Polarité normale
Polarité inverse

Dernière inversion

≈ 780 ka

transition interprétée 799–770 ka

Durée de la transition

quelques milliers d’années

selon les reconstructions publiées

Modèle

GGFMB

Mahgoub et al. (2023)

Mahgoub et al. (2023) · Published literature; cited

Dipôle reconstruit par le modèle GGFMB (g10, g11, h11) ; lignes de champ d’un dipôle pur, longueur selon le moment. Reconstruction, pas mesure directe.

08 / DEEP TIME · GGFMB

The last magnetic reversal

A separate reconstruction of the global magnetic field, 900,000–700,000 years ago. Explore the signed axial dipole as the field changed polarity.

MODEL AGE780 ka BP

POLARITY—

AXIAL DIPOLE g₁⁰—µT

DIPOLE MOMENT—× 10²² A·m²

09 / FIELD STRENGTH

Dipole moment through the reversal

The same GGFMB epochs, in 10²² A·m². A weak field accompanies the polarity transition.

The shaded 799–770 ka interval is the authors' approximate reversal window. GGFMB is a model from sediment records; during transition the field is complex, so a single north/south pole path would be misleading.

Independent evidence: beryllium-10

Marine sediment records show increased cosmogenic ¹⁰Be production around the Matuyama–Brunhes transition as the dipole weakened. Their age models and sampling differ from GGFMB, so no point-by-point correlation is implied here.

Read the sediment study ↗

10 / POLARITY TIMESCALE

Reversals over 3.6 million years

Normal (light) and reversed (dark) polarity from the GTS2012 timescale, with two dated excursions. The bracket marks the 900–700 ka GGFMB window above.

IODP, Table T11 (GTS2012 ages) ↗Ogg (2012), GTS2012 ↗Excursion ages ↗

GGFMB data ↗Scientific paper ↗

SOURCES DE CETTE PAGE

Mahgoub et al. (2023): Mahgoub, A. N., Korte, M., & Panovska, S. (2023). Characteristics of the Matuyama–Brunhes magnetic field reversal based on a global data compilation. Journal of Geophysical Research: Solid Earth, 128, e2023JB026593. · doi:10.1029/2023JB026593
Licence : Published literature; cited

Inversion des pôles Modèle GGFMB de l’inversion Matuyama–Brunhes, 900–700 ka

Quand le nord devient sud

The last magnetic reversal

Dipole moment through the reversal

Reversals over 3.6 million years