Paleomagnetic Biases Inferred from Numerical Dynamos and the Search for Geodynamo Evolution

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Authors

Peter Driscoll 

Abstract

The orientation and intensity of the paleomagnetic field is central to our understanding of the history of the Earth. The paleomagnetic signature of the singular most event, inner core nucleation, however, remains elusive. In this study we study numerical dynamo simulations from a paleomagnetic perspective to explore how long observations must be time-averaged to obtain stable virtual geomagnetic pole (VGP) directions and global field intensities.
We find that running averages over $20-40$ kyr are needed to obtain stable VGPs with $\alpha_{95}<10^\circ$, and over $40-120$ kyr for $\alpha_{95}<5^\circ$. We find that models with higher heat flux and more frequent polarity reversals require longer time averages, and that obtaining stable intensities requires longer time averaging than obtaining stable directions. Running averages of local field intensity and inclination produce underestimates of VDM by factors of $0.9-0.6$ and overestimates of VADM by factors of $1-1.2$ as heat flux and reversal frequency increases. We derive a scaling law connecting reversal frequency to paleointensity bias that could be applied to records where reversal frequency is known.
Applied to the PINT paleointensity record, these biases produce little change to the overall trend of a relatively flat but scattered intensity over the last 2 Ga. A more careful debiasing applied during periods when the reversal frequency is known could reveal previously obscured features in the paleointensity record.

DOI

https://doi.org/10.31223/osf.io/uqkgp

Subjects

Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics

Keywords

Paleointensity, Geodynamo, paleomagnetism, core dynamics, numerical dynamos

Dates

Published: 2018-03-19 14:00

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License

Academic Free License (AFL) 3.0

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