Shaar Ron, Gallet Yves, Vaknin Yoav, Gonen Lilach, Martin Mario A S, Adams Matthew J, Finkelstein Israel
The Institute of Earth Sciences The Hebrew University of Jerusalem Jerusalem Israel.
Université Paris Cité Institut de Physique du Globe de Paris CNRS Paris France.
J Geophys Res Solid Earth. 2022 Dec;127(12):e2022JB024962. doi: 10.1029/2022JB024962. Epub 2022 Dec 12.
Our understanding of geomagnetic field intensity prior to the era of direct instrumental measurements relies on paleointensity analysis of rocks and archaeological materials that serve as magnetic recorders. Only in rare cases are absolute paleointensity data sets continuous over millennial timescales, in sub-centennial resolution, and directly dated using radiocarbon. As a result, fundamental properties of the geomagnetic field, such as its maximum intensity and rate of change have remained a subject of lively discussion. Here, we place firm constraints on these two quantities using Bayesian modeling of well-dated archaeomagnetic intensity data from the Levant and Upper Mesopotamia. We report new data from 23 groups of pottery collected from 18 consecutive radiocarbon-dated archaeological strata from Tel Megiddo, Israel. In the Near East, the period of 1700-550 BCE is represented by 84 groups of archaeological artifacts, 55 of which were dated using radiocarbon or a direct link to clear historically dated events, providing unprecedented sub-century resolution. Moreover, stratigraphic relationships between samples collected from multi-layered sites enable further refinement of the data ages. The Bayesian curve shows four geomagnetic spikes between 1050 and 600 BCE, with virtual axial dipole moment (VADM) reaching values of 155-162 ZAm, much higher than any prediction from geomagnetic field models. Rates of change associated with the four spikes are ∼0.35-0.55 μT/year (∼0.7-1.1 ZAm/year), at least twice the maximum rate inferred from direct observations spanning the past 180 years. The increase from 1750 to 1030 BCE (73-161 ZAm) depicts the Holocene's largest change in field intensity.
在直接仪器测量时代之前，我们对地球磁场强度的理解依赖于对作为磁记录器的岩石和考古材料的古强度分析。只有在极少数情况下，绝对古强度数据集才会在千年时间尺度上连续、具有亚世纪分辨率，并使用放射性碳直接测定年代。因此，地磁场的基本特性，如其最大强度和变化率，一直是激烈讨论的主题。在这里，我们利用来自黎凡特和上美索不达米亚地区年代测定良好的考古地磁强度数据进行贝叶斯建模，对这两个量施加了严格的限制。我们报告了从以色列米吉多遗址连续18个放射性碳测年考古地层中采集的23组陶器的新数据。在近东地区，公元前1700年至550年期间由84组考古文物代表，其中55组使用放射性碳或与明确的历史年代事件的直接联系进行了年代测定，提供了前所未有的亚世纪分辨率。此外，从多层遗址采集的样本之间的地层关系能够进一步细化数据年代。贝叶斯曲线显示，在公元前1050年至600年之间有四个地磁峰值，虚拟轴向偶极矩（VADM）达到155 - 162 ZAm的值，远高于地磁场模型的任何预测。与这四个峰值相关的变化率约为0.35 - 0.55 μT/年（约0.7 - 1.1 ZAm/年），至少是过去180年直接观测推断的最大变化率的两倍。公元前1750年至1030年（73 - 161 ZAm）的增加描绘了全新世磁场强度最大的变化。
