Geomagnetic spikes on the core-mantle boundary

Christopher Davies,Christopher Davies,Catherine Constable

doi:10.1038/ncomms15593

Christopher Davies, Christopher Davies + Show 1 more

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https://doi.org/10.1038/ncomms15593

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Abstract

Extreme variations of Earth’s magnetic field occurred in the Levant region around 1000 BC, when the field intensity rapidly rose and fell by a factor of 2. No coherent link currently exists between this intensity spike and the global field produced by the core geodynamo. Here we show that the Levantine spike must span >60° longitude at Earth’s surface if it originates from the core–mantle boundary (CMB). Several low intensity data are incompatible with this geometric bound, though age uncertainties suggest these data could have sampled the field before the spike emerged. Models that best satisfy energetic and geometric constraints produce CMB spikes 8–22° wide, peaking at O(100) mT. We suggest that the Levantine spike reflects an intense CMB flux patch that grew in place before migrating northwest, contributing to growth of the dipole field. Estimates of Ohmic heating suggest that diffusive processes likely govern the ultimate decay of geomagnetic spikes.

Highlights

Extreme variations of Earth’s magnetic field occurred in the Levant region around 1000 BC, when the field intensity rapidly rose and fell by a factor of 2
The intensities recorded in Jordan[10] and Israel[11] around 980 BC correspond to local virtual axial dipole moment (ADM) (VADMs) of approximately 200 ZAm2
We assigned an uncertainty to the spike age of ±100 years, which is similar to the age uncertainty on the Jordanian data and to the average age uncertainty of the paleointensity data used to construct CALS10k

Summary

Introduction

Extreme variations of Earth’s magnetic field occurred in the Levant region around 1000 BC, when the field intensity rapidly rose and fell by a factor of 2. Similar features have been reproduced in geodynamo simulations[3] and have been used as criteria for assessing whether simulations produce Earth-like behaviour[4,5,6] Whether these kinds of spatial variations can reflect long-term behaviour of the geomagnetic field requires detailed observations preceding the historical period. The highest geomagnetic field intensities on record have been recovered from archeomagnetic artefacts from the Levantine region dated at around 1000 BC At this time the global field was unusually strong, with an increasing[7,8,9] axial dipole moment (ADM) of B95–100 ZAm2. By 1500 BC a small flux patch has emerged under NE Africa/Saudi Arabia, which intensifies until 1000 BC before later moving north and west This patch may be related to the Levantine spike there is no obvious signature in the surface intensity (Fig. 4b), and the VADM

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