Changes in Non‐Dipolar Field Structure Over the Plio‐Pleistocene: New Paleointensity Results From Hawai'i Compared to Global Data Sets

Abstract

A foundational assumption in paleomagnetism is that the Earth's magnetic field behaves as a geocentric axial dipole (GAD) when averaged over sufficient timescales. Compilations of directional data averaged over the past 5 Ma yield a distribution largely compatible with GAD, but the distribution of paleointensity data over this timescale is incompatible. Reasons for the failure of GAD include: (a) Arbitrary “selection criteria” to eliminate “unreliable” data vary among studies, so the paleointensity database may include biased results. (b) The age distribution of existing paleointensity data varies with latitude, so different latitudinal averages represent different time periods. (c) The time‐averaged field could be truly non‐dipolar. Here, we present a consistent methodology for analyzing paleointensity results and comparing time‐averaged paleointensities from different studies. We apply it to data from Plio/Pleistocene Hawai'ian igneous rocks, sampled from fine‐grained, quickly cooled material (lava flow tops, dike margins and scoria cones) and subjected to the IZZI‐Thellier technique; the data were analyzed using the Bias Corrected Estimation of Paleointensity method of Cych et al. (2021, https://doi.org/10.1029/2021GC009755), which produces accurate paleointensity estimates without arbitrarily excluding specimens from the analysis. We constructed a paleointensity curve for Hawai'i over the Plio/Pleistocene using the method of Livermore et al. (2018, https://doi.org/10.1093/gji/ggy383), which accounts for the age distribution of data. We demonstrate that even with the large uncertainties associated with obtaining a mean field from temporally sparse data, our average paleointensities obtained from Hawai'i and Antarctica (reanalyzed from Asefaw et al., 2021, https://doi.org/10.1029/2020JB020834) are not GAD‐like from 0 to 1.5 Ma but may be prior to that.

Geomagnetic Field Intensity During the First Millennium BCE From Royal Judean Storage Jars: Constraining the Duration of the Levantine Iron Age Anomaly

“…Bayesian modeling of the Levantine archaeomagnetic intensity curve was carried out using the age hyperparameter reverse-jump Monte Carlo Markov Chain (AH-RJMCMC) method developed by Livermore et al (2018), which was also used for the previous versions of the LAC (Shaar et al, 2020(Shaar et al, , 2022 as well as for other regional curves in the Near East or elsewhere (Cych et al, 2023;Gallet et al, 2020Gallet et al, , 2021Gallet et al, , 2023Genevey et al, 2020Genevey et al, , 2021Livermore et al, 2021). The algorithm uses piece-wise linear interpolation between vertices drawn in a random-walk-like perturbation within a space allowed by the data.…”