Global Evolution and Dynamics of the Geomagnetic Field in the 15–70 kyr Period Based on Selected Paleomagnetic Sediment Records. Issue 12 (24th December 2021)

• Record Type: Journal Article
• Authors: Panovska, Sanja; Korte, Monika; Liu, Jiabo; Nowaczyk, Norbert
• Is Part Of: Journal of geophysical research. Volume 126:Issue 12(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-12-24
• Subjects: geomagnetic field -- geomagnetic excursions -- paleomagnetic secular variation -- Laschamps excursion -- paleomagnetic sediment records; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2021JB022681
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Reconstructions 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 × 10 22 Am 2, with an average and standard deviation of 5.1 ± 1.5 × 10 22 Am 2 . 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. Plain Language Summary: Earth possesses a magnetic field that is constantly changing in time and space. Its source is located in the outer core and the mechanism by which the geomagnetic field is generated is known as the geodynamo. Studying the field on long timescales contributes to a better understanding of the source processes. The geomagnetic field can be approximated as a dipole, except during reversals and excursions. The past 70, 000 years period contains three geomagnetic excursions, the Norwegian‐Greenland Sea (65, 000 years ago), Laschamps (41, 000), and Mono Lake/Auckland (34, 000). During the excursions, the intensity is globally very low and the poles may or may not change polarity. However, they always recover to the original polarity in contrast to the reversals, when the North Pole becomes South and the South becomes North. To model the long‐term field variations, we rely on geological archives, sediments and rocks, that record and preserve the geomagnetic field. We selected the best sedimentary records in terms of magnetic components and good age control. The Laschamps excursion is the most pronounced event in this period, has the lowest dipole moment, and is observed globally. The other two events occur at regional scales and have only a moderate dipole moment decrease. Key Points: A new global geomagnetic field model covering the period 15–70 kyr is presented which includes three magnetic excursions The most pronounced event in this period is the Laschamps excursion, during which the axial dipole reverses sign for about 300 years Similarities and differences at the Earth's surface and the core‐mantle boundary among three geomagnetic excursions are discussed