New Archeomagnetic Directional Records From Iron Age Southern Africa (ca. 425-1550 CE) and Implications for the South Atlantic Anomaly
New Archeomagnetic Directional Records From Iron Age Southern Africa (ca. 425-1550 CE) and Implications for the South Atlantic Anomaly
复制标题
DOI：
10.1002/2017gl076007
复制
发表时间：
2018-02-16
影响因子：
5.2
通讯作者：
Cottrell, Rory D.
中科院分区：
文献类型：
--
作者：
Hare, Vincent J.;Tarduno, John A.;Cottrell, Rory D.
南半球古地磁数据的匮乏限制了古分子变化模型的分辨率。同时，现代和历史领域的重要变化，包括最近的偶极衰变，似乎都起源于该地区。本文通过对铁器时代(公元425-1550年)考古资料的分析，提出了南部非洲的一个新的定向记录，将区域长期变化曲线向前延伸到第一个千年。以前的研究已经确定了在公元1225年至公元1550年之间有一个快速的方向性变化时期。新的数据使我们能够确定公元6世纪至7世纪之间较早时期的相对快速变化。文中还讨论了核幔边界重现通量排出模型的意义。此外，我们确定了这些非洲数据中记录的变化与古地磁突变的可能关系。简而言之，地球偶极磁场目前正在经历快速衰减，最好的表现是一个不断加深的低场区域，称为南大西洋异常(SAA)。这种明显的地磁场崩溃，以及对未来磁场反转的猜测，吸引了公众的想象力。但我们对SAA的历史知之甚少，这限制了我们将当前的变化放在长期背景下的能力。在这里，我们呈现了一个来自南部非洲遗址的新的磁性记录。这一新记录支持了我们之前的推断，即SAA只是非洲地核中一种反复出现的现象的最新表现--称为通量驱逐--这种现象正在对地球磁场的表达产生深远影响。
The paucity of Southern Hemisphere archeomagnetic data limits the resolution of paleosecular variation models. At the same time, important changes in the modern and historical field, including the recent dipole decay, appear to originate in this region. Here a new directional record from southern Africa is presented from analysis of Iron Age (ca. 425-1550 CE) archeological materials, which extends the regional secular variation curve back to the first millennium. Previous studies have identified a period of rapid directional change between 1225 and similar to 1550 CE. The new data allow us to identify an earlier period of relatively rapid change between the sixth and seventh centuries CE. Implications for models of recurrent flux expulsion at the core-mantle boundary are discussed. In addition, we identify a possible relationship of changes recorded in these African data with archeomagnetic jerks.Plain Language Summary Earth's dipole magnetic field is presently undergoing a rapid decay, best expressed by a deepening area of low field called the South Atlantic Anomaly (SAA). This apparent collapse of the geomagnetic field, and speculation about a future field reversal, has captured the public imagination. But we know little about the history of the SAA, limiting our ability to place current changes within a long-term context. Here we present a new magnetic record from sites of southern Africa. The new record supports our prior inferences that the SAA is just the most recent manifestation of a recurring phenomenon in the core beneath Africa-called flux expulsion-that is having a profound impact on the expression of the geomagnetic field.