Rapid intensity variations during the second half of the first millennium BCE in Central Asia and global implications.

Abstract

<p>Recent archeomagnetic studies performed in different regions of the world have revealed unusual periods of sharp changes in intensity during the first millennium. Here we focus on the study of intensity variations between 600 BCE and 600 CE in central Asia, where an important intensity decrease seems to be present during the second half of the 1<sup>st</sup> millennium BCE. For this purpose, we present a new paleosecular variation (PSV) curve obtained from 51 new archeointensities and the selected previous data located within a radius of 1000 km around Termez (Uzbekistan). The new curve shows an intensity maximum around 400 BCE followed by a rapid decrease. When the virtual axial dipole moment (VADM) values are compared with the Dipole Moment estimations derived from different global geomagnetic models key differences are observed, suggesting an important non-dipolar effect for this feature. Finally, in order to constrain the spatial behaviour of this phenomenon and its global implications, we investigate the PSV intensity and VADM trends from twelve regions distributed among Central America, Europe and Asia. A VADM maximum is observed in Western Europe (Iberia and Germany) around 450 BCE, associated to rates of change of about 9 µT/century. This feature is also observed eastwards, in the Caucasus and the Levant, but associated to lower rates of changes. In Central Asia (Uzbekistan) our new study suggests that maximum values of about 14 µT/century, between 400-300 BCE, were achieved. In other regions, as Eastern Asia and Central America, rapid variations of the intensity are not observed during the targeted period.</p><p> </p>

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

“…In our previous study (Bonilla‐Alba et al., 2021), we already suggested that the V‐shaped intensity feature may have originated from a non‐dipole contribution of the geomagnetic field. The new intensity data acquired here further corroborate this V‐shaped pattern and contribute to a refined definition of the increasing branch by revealing high intensities at the end of the second century CE.…”

“…Data are also compared with the paleosecular variation intensity curve proposed by Bonilla‐Alba et al. (2021) and the predictions of the most recent global geomagnetic field models: ArchKalMag14k.r (Schanner et al., 2022), SHAWQ‐Iron Age (Osete et al., 2020) and SHAWQ2k (Campuzano et al., 2019). All data and models are relocated to Termez (37.3°N, 67.2°E).…”

“…The data and the models' results are plotted in Figure 5. Furthermore, we included the paleosecular intensity curve published for Central Asia in our previous study (Bonilla‐Alba et al., 2021), which was established for the time frame spanning from 600 BCE to 600 CE.…”

“…To address this issue, we have developed a regional update of the SHAWQ family paleoreconstructions using the same database as the SHAWQ family but now incorporating the high‐quality data of Bonilla‐Alba et al. (2021) and the new data from this study. This update, called SHAWQ‐U (with U indicating Uzbekistan), specifically covers the time period from 400 BCE and 400 CE and was constructed following the same approach than the SHAWQ family model (for more details, see Campuzano et al., 2019; Osete et al., 2020).…”

“…Data set were downloaded from the GEOMAGIA50.v3 database (Brown et al., 2015, 2021), which was updated in 2021 and the new data from Bonilla‐Alba et al. (2021) and Troyano et al. (2021).…”