A Global View on Geomagnetic Excursions Through the Past 100 kyr
Abstract
Recently devised spherical harmonic paleomagnetic field models GGF100k and LSMOD.2 offer a new global view on several geomagnetic excursions throughout the past 100 kyr. Excursions are brief episodes where the magnetic field directions deviate strongly from normal dipole orientation, and are accompanied by lows in field intensity. Globally best documented is the Laschamp excursion (~41 ka BP), found in volcanic rocks and sediments from all over Earth. Other excursions, such as the Post-Blake (~95 ka), Norwegian-Greenland Sea (~60 ka), Mono Lake / Auckland (~33 ka) and Hilina Pali (~17 ka) excursions have been found only regionally or in a smaller number of records, and their ages in general appear more widely dispersed. The global field models suggest that all these excursions are caused by weakening of the axial dipole field contribution, with little change in the level of non-axial-dipole secular variation. Excursions seem to manifest globally when power in the axial dipole drops significantly below that in non-dipole terms, while regional excursions seem to correspond to less drastic decreases in the axial dipole strength. Directional excursion signatures ascribed to the Mono Lake and Hilina Pali excursions observed in different parts of the world might be series of temporally offset regional excursions during prolonged times of low axial dipole field. Consequently, care should be taken when considering geomagnetic excursions as stratigraphic markers for dating purposes. Virtual geomagnetic pole paths for all these excursions indicate some longitudinal preference, falling in particular in the Pacific region. The models can be used to explore for indications of systematic mantle control on the geodynamo. However, all interpretations have to consider certain limitations of the models due to distribution, reliability and chronologies of the available data.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMGP34A..02K
- Keywords:
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- 1513 Geomagnetic excursions;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1517 Magnetic anomalies: modeling and interpretation;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1522 Paleomagnetic secular variation;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1535 Reversals: process;
- timescale;
- magnetostratigraphy;
- GEOMAGNETISM AND PALEOMAGNETISM