Global Evolution and Dynamics of the Geomagnetic Field in the 15–70 kyr Period Based on Selected Paleomagnetic Sediment Records

Norbert Nowaczyk,Sanja Panovska,Monika Korte,Jiabo Liu

doi:10.1029/2021jb022681

Abstract

AbstractReconstructions of the geomagnetic field on long time scales are important to understand the geodynamo processes in the Earth's core. The geomagnetic field exhibits a range of variations that vary from normal, dipole‐dominated secular variation to geomagnetic excursions and reversals. These transitional events are associated with significant directional deviations and very low intensities. Here we present a new, global geomagnetic field model spanning the period 70–15 ka (GGFSS70) that includes three excursions: Norwegian‐Greenland Sea, Laschamps, and Mono Lake/Auckland. The model is built from nine globally distributed, high‐resolution, well‐dated, sedimentary paleomagnetic records. The GGFSS70 indicates that the axial‐dipole component changed sign for about 300 years in the middle of the Laschamps excursion (41.25–40.93 ka). The energy comparison at the Earth's surface reveals that the axial‐dipole energy is always higher than the non‐axial‐dipole except over the Laschamps. In the other two excursions, the axial‐dipole is reduced by about one order of magnitude for the Norwegian‐Greenland Sea excursion and less for the Mono Lake/Auckland. At the core‐mantle boundary, the large‐scale non‐axial‐dipole power is comparable to the axial‐dipole power, except over the excursions when the axial‐dipole decreases, though less clearly for the Mono Lake/Auckland excursion. The axial dipole moment over the 15–70 ka varies from 0 to 8 × 1022 Am2, with an average and standard deviation of 5.1 ± 1.5 × 1022Am2. The Laschamps excursion is associated with growth and poleward movement of reversed flux patches and reversed field in the tangent cylinder at the excursion midpoint, which is not the case for the other two excursions.

Highlights

There is a long-standing interest in understanding the spatial and temporal variations of the Earth's magnetic field on all time scales
As the axial dipole moment is diagnosed to be the most variable component during geomagnetic excursions, we look at maps of Zcosθ over the core-mantle boundary (CMB) (Figure 7), which represents features that contribute to the dipole moment
We have built a magnetic field model covering the period 70–15 ka based on nine paleomagnetic records, selected to have all three components, high-resolution, good age control, and best possible global distribution

Summary

Introduction

There is a long-standing interest in understanding the spatial and temporal variations of the Earth's magnetic field on all time scales. Our knowledge of long-term multi-millennial changes is constantly advancing from findings on individual records, over paleomagnetic stacks, and estimated dipole moment variations (e.g., Channell et al, 2009; Stoner et al, 2002; Ziegler et al, 2011) to global, time-dependent geomagnetic field reconstructions (e.g., Constable et al, 2016; Korte et al, 2019; Panovska, Constable, & Korte, 2018; Pavón-Carrasco et al, 2014) including the large-scale non-dipole field. This is in reasonable agreement with an independent duration estimate of ∼1,500 years based on a paleointensity stack (Laj et al, 2014)

Methods

Results

Conclusion