First full‐vector archeomagnetic data from Central Asia (3 BCE to 15 CE centuries): evidence for a large non‐dipole field contribution around the first century BCE

Abstract

Unraveling the short-term behavior of the Earth's past geomagnetic field at regional scales is crucial for understanding its global behavior and, thus, the dynamics of the deep Earth. In this context, obtaining accurate full-vector geomagnetic field records from regions where archeomagnetic data are absent becomes essential. Here, we present the first full-vector archeomagnetic data from Central Asia, derived from the analysis of nine archeological kilns sampled in South Uzbekistan, dating back to the period between 200 BCE and 1429 CE. To obtain these new data, we conducted thermal and alternating field demagnetization procedures, along with Thellier-Thellier paleointensity experiments, including partial thermoremanent magnetization checks, thermoremanent magnetization anisotropy and cooling rate corrections. The comparison between the new data, previous selected data from Central Asia, and available global models reveals important differences between approximately 400 BCE and 400 CE, especially concerning the geomagnetic field intensity element. In order to investigate this in detail, we have developed a regional update of the SHAWQ global models family by incorporating, for the first time, high-quality data from Central Asia. The results suggest that this deviation is linked to non-dipolar sources of the geomagnetic field in Central Asia reaching a maximum contribution around the first century BCE. According to the updated global paleoreconstruction, this non-dipole feature, manifested at the Earth's surface as low intensities, is associated with the presence of a reversed flux patch at the core-mantle boundary beneath this region. The geomagnetic field is a global feature that changes over time and space. These changes are known over the last few centuries through direct observations collected by satellites and geomagnetic observatories. However, indirect measurements, based on the paleomagnetic study of archeological and geological materials, are needed to disentangle geomagnetic field behavior over longer time scales. In this context, archeomagnetism is the discipline that studies the direction and strength of the past geomagnetic field by investigating the magnetic properties of well dated archeological baked clay material. In order to properly describe the behavior of the Earth's magnetic field it is crucial to have a good temporal and spatial coverage of archeomagnetic data. In this work, we present the first full-vector archeomagnetic data for Central Asia, a large region that remained unexplored from an archeomagnetic point of view. The new data were obtained from 9 kilns excavated in South Uzbekistan, with ages ranging from 200 BCE to 1429 CE. We then developed a regional update of the SHAWQ global models family by incorporating, for the first time, high-quality archeomagnetic data from Central Asia. The results indicate a relevant non-dipole feature presented over this region around the first century BCE.