Geomagnetism Laboratory, Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool L69 7ZE, United Kingdom
Geomagnetism Laboratory, Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool L69 7ZE, United Kingdom.
Proc Natl Acad Sci U S A. 2020 Aug 4;117(31):18258-18263. doi: 10.1073/pnas.2001217117. Epub 2020 Jul 20.
Earth's magnetic field is presently characterized by a large and growing anomaly in the South Atlantic Ocean. The question of whether this region of Earth's surface is preferentially subject to enhanced geomagnetic variability on geological timescales has major implications for core dynamics, core-mantle interaction, and the possibility of an imminent magnetic polarity reversal. Here we present paleomagnetic data from Saint Helena, a volcanic island ideally suited for testing the hypothesis that geomagnetic field behavior is anomalous in the South Atlantic on timescales of millions of years. Our results, supported by positive baked contact and reversal tests, produce a mean direction approximating that expected from a geocentric axial dipole for the interval 8 to 11 million years ago, but with very large associated directional dispersion. These findings indicate that, on geological timescales, geomagnetic secular variation is persistently enhanced in the vicinity of Saint Helena. This, in turn, supports the South Atlantic as a locus of unusual geomagnetic behavior arising from core-mantle interaction, while also appearing to reduce the likelihood that the present-day regional anomaly is a precursor to a global polarity reversal.
地球磁场目前的特征是在南大西洋出现了一个大而不断增长的异常。这个地球表面区域是否在地质时间尺度上优先受到增强的地磁变化的影响，对于地核动力学、核幔相互作用以及即将发生的磁极反转的可能性都有重大影响。在这里，我们展示了来自圣赫勒拿岛的古地磁数据，该火山岛非常适合测试这样一种假设，即在南大西洋的数百万年时间尺度上，地磁行为是异常的。我们的结果得到了正烘烤接触和反转测试的支持，产生的平均方向近似于 800 万到 1100 万年前的地心轴向偶极子所预期的方向，但伴随有非常大的方向离散度。这些发现表明，在地壳时间尺度上，圣赫勒拿岛附近的地磁长期变化持续增强。这反过来又支持了南大西洋是核幔相互作用引起的异常地磁行为的场所，同时似乎也降低了当前区域异常是全球磁极反转前兆的可能性。
