Large geomagnetic field anomalies revealed in Bronze to Iron Age archeomagnetic data from Tel Megiddo and Tel Hazor, Israel

Tel Megiddo by Itamar Grinberg

Tel Megiddo by Itamar Grinberg (CC BY-SA 2.0)

TitleLarge geomagnetic field anomalies revealed in Bronze to Iron Age archeomagnetic data from Tel Megiddo and Tel Hazor, Israel
Publication TypeJournal Article
Year of Publication2016
AuthorsShaar R, Tauxe L, Ron H., Ebert Y., Finkelstein I., Agnon A.
JournalEarth and Planetary Science Letters
Date Published2016/03

Geomagnetic field measurements from the past few centuries show heightened secular variation activity in the southern hemisphere associated with the south Atlantic anomaly (SAA). It is uncertain whether geomagnetic anomalies at a similar scale have existed in the past owing to limited coverage and uncertainties in the paleomagnetic database. Here we provide new evidence from archaeological sources in the Levant suggesting a large positive northern hemisphere anomaly, similar in magnitude to the SAA during the 9th–8th centuries BCE, called “Levantine Iron Age anomaly”. We also report an additional geomagnetic spike in the 8th century. The new dataset comprises 73 high precision paleointensity estimates from ca. 3000 BCE to 732 BCE, and five directional measurements between the 14th and the 9th centuries BCE. Well-dated pottery and cooking ovens were collected from twenty archaeological strata in two large contemporaneous stratigraphical mounds (tells) in Israel: Tel Megiddo and Tel Hazor. The new data are combined with previously published data and interpreted automatically using the PmagPy Thellier GUI program. The Tel Megiddo and Tel Hazor data sets demonstrate excellent internal consistency and remarkable agreement with published data from Mesopotamia (Syria). The data illustrate the evolution of an extreme geomagnetic high that culminated in at least two spikes between the 11th and the 8th centuries BCE (Iron Age in the Levant). The paleomagnetic directional data of the 9th century BCE show positive inclination anomalies, and deviations of up to 22° from the averaged geocentric axial dipole (GAD) direction. From comparison of the Levantine archaeomagnetic data with IGRF model for 2015 we infer the “Levantine Iron Age anomaly” between the 10th and the 8th centuries BCE is a local positive anomaly. The eastward extent of the anomaly is currently unknown.

Short TitleEarth Planet. Sci. Lett.

The new data illustrate a steady increase in field intensity from a local minimum at ca. 1800 BCE to a period with exceptionally high field values and fast variations between the 10th and the 8th centuries BCE. This period was accompanied by at least two geomagnetic spikes: one at ca. 980 BCE (Ben-Yosef et al., 2009 and Shaar et al., 2011), and another at the beginning of the 8th century BCE (new spike reported here). A possibly third, previously published spike, at ca. 890 BCE need further research to establish its reliability.

The Levant Iron Age anomaly is characterized with maximum field values reaching about twice the ancient axial dipole field (following model of Nilsson et al., 2014) and maximal angular deviation from geocentric axial dipole (GAD) of up to 22°. Using the 2015 IGRF model, we see similar deviations from GAD (intensity and direction) only in the southern hemisphere in areas affected by the South Atlantic Anomaly (SAA). This leads us to propose that the Iron Age geomagnetic high in the Levant was a local geomagnetic anomaly similar in scale to SAA, perhaps even larger. Further data are required to establish its geographical extent.

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