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Front. Earth Sci. | doi: 10.3389/feart.2019.00086

Robust Characteristics of the Laschamp and Mono Lake Geomagnetic Excursions: Results from Global Field Models

  • 1German Research Centre for Geosciences, Helmholtz Centre Potsdam, Germany
  • 2Institute of Earth Sciences, School of Engineering and Natural Sciences, University of Iceland, Iceland
  • 3UMR6112 Laboratoire de Planetologie et Geodynamique (LPG), France

Data-based global palaeomagnetic field models provide a more complete view of geomagnetic
excursions than individual records. They allow the temporal and spatial field evolution
to be mapped globally, and facilitate investigation
of dipole and non-dipole field components. We have developed a suite of
spherical harmonic (SH) field models that span 50 to 30 ka and include the
Laschamp (~41 ka) and Mono Lake (~33 ka) excursions. Palaeomagnetic
field models depend heavily on the data used in their construction.
Variations in palaeomagnetic sediment records
from the same region are in some cases inconsistent. To test the influence of data selection
and reliance on age models, we have built a series of SH models based upon different data sets.
A number of excursion characteristics are robust in all models, despite some
differences in energy distribution among SH coefficients. Quantities such as field morphology
at the core-mantle boundary (CMB) or individual SH degree power variations should be interpreted with caution.
All models suggest that the excursion process during the Laschamp is mainly governed by axial dipole decay and
recovery, without a significant influence from the equatorial dipole
or non-dipole fields. The axial dipole component reduces to almost zero, but does not reverse.
This results in excursional field behaviour seen globally, but non-uniformly at Earth's surface.
The Mono Lake excursion may be a series of excursions
occurring between 36 and 30 ka rather than a single excursion.
In contrast to the Laschamp, these excursions appear driven
by smaller decreases in axial dipole field strength during a time when the axial dipole
power at the CMB is similar to the power in the non-dipole field. We suggest three phases
for the 50 to 30 ka period: (1) a broadly stable phase dominated by the axial dipole (50-43 ka);
(2) the Laschamp excursion, with the underlying excursion process lasting ~5 ka (43-38 ka)
and the surface field expression lasting ~2 ka (42-40 ka); (3) a weak phase during which axial dipole
and non-dipole power at the CMB are comparable, leading to more than one
excursion between 36 and 30 ka.

Keywords: Laschamp excursion, Mono Lake excursion, magnetic field model, palaeomagnetism, Sediment records

Received: 22 Jan 2019; Accepted: 08 Apr 2019.

Edited by:

Yohan Guyodo, UMR7590 Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), France

Reviewed by:

Leonardo Sagnotti, National Institute of Geophysics and Volcanology (INGV), Italy
Simo Spassov, Royal Meteorological Institute of Belgium, Belgium  

Copyright: © 2019 Korte, Brown, Panovska and Wardinski. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Monika Korte, German Research Centre for Geosciences, Helmholtz Centre Potsdam, Potsdam, Germany, monika@gfz-potsdam.de