Dynamical similarity of geomagnetic field reversals

Abstract

No consensus has been reached so far on the properties of the geomagnetic field during reversals or on the main features that might reveal its dynamics. A main characteristic of the reversing field is a large decrease in the axial dipole and the dominant role of non-dipole components. Other features strongly depend on whether they are derived from sedimentary or volcanic records. Only thermal remanent magnetization of lava flows can capture faithful records of a rapidly varying non-dipole field, but, because of episodic volcanic activity, sequences of overlying flows yield incomplete records. Here we show that the ten most detailed volcanic records of reversals can be matched in a very satisfactory way, under the assumption of a common duration, revealing common dynamical characteristics. We infer that the reversal process has remained unchanged, with the same time constants and durations, at least since 180 million years ago. We propose that the reversing field is characterized by three successive phases: a precursory event, a 180° polarity switch and a rebound. The first and third phases reflect the emergence of the non-dipole field with large-amplitude secular variation. They are rarely both recorded at the same site owing to the rapidly changing field geometry and last for less than 2,500 years. The actual transit between the two polarities does not last longer than 1,000 years and might therefore result from mechanisms other than those governing normal secular variation. Such changes are too brief to be accurately recorded by most sediments.

Magnetic stratigraphy constraints on the Matuyama–Brunhes boundary recorded in a loess section at the southern margin of Chinese Loess Plateau

“…With a total number of 22, the entire duration was ∼31 ka (based on a mean sedimentation rate of 4.72 cm ka −1 as calculated from L15 to S5). This is much more complex than those seen in North Atlantic sediments (Channell et al 2010), and also differs from the reconstruction of the dynamics of geomagnetic field reversals recently reported by Valet et al (2012). Further, the duration lasts too long to match with other recent records for the duration of M-B transition on the southern and central CLP Zhao et al 2014;Zhou et al 2014).…”

Paleomagnetic direction and paleointensity variations during the Matuyama–Brunhes polarity transition from a marine succession in the Chiba composite section of the Boso Peninsula, central Japan

“…5). The directional transition zone can be called the "polarity switch" of the M-B boundary (Valet et al 2012). We also define the midpoint of this zone in the Yoro-River section, which appears 1.10 m above the Byk-E tephra, as the M-B boundary at this section from a magnetostratigraphic point of view.…”

Core–Mantle Interactions

“…The largest change in amplitude probably occurs during magnetic reversals. While the general structure of the field during a reversal is not well known, we do know that the axial part of the dipole field vanishes and reappears with the opposite polarity in as little as several thousand years (Clement, 2004;Valet et al, 2012). Rapid time variations in the axial dipole create largescale electric fields in the lower mantle.…”