School of Earth &Environment, University of Leeds, Leeds LS2 9JT, UK.
Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093-0225, USA.
Nat Commun. 2017 May 30;8:15593. doi: 10.1038/ncomms15593.
Extreme variations of Earth's magnetic field occurred in the Levant region around 1000 BC, when the field intensity rapidly rose and fell by a factor of 2. No coherent link currently exists between this intensity spike and the global field produced by the core geodynamo. Here we show that the Levantine spike must span >60° longitude at Earth's surface if it originates from the core-mantle boundary (CMB). Several low intensity data are incompatible with this geometric bound, though age uncertainties suggest these data could have sampled the field before the spike emerged. Models that best satisfy energetic and geometric constraints produce CMB spikes 8-22° wide, peaking at O(100) mT. We suggest that the Levantine spike reflects an intense CMB flux patch that grew in place before migrating northwest, contributing to growth of the dipole field. Estimates of Ohmic heating suggest that diffusive processes likely govern the ultimate decay of geomagnetic spikes.
地球磁场的极端变化发生在公元前 1000 年左右的黎凡特地区，当时磁场强度迅速上升和下降了 2 倍。目前，这种强度峰值与地核发电机产生的全球磁场之间没有一致的联系。在这里，我们表明，如果起源于核幔边界（CMB），那么黎凡特地区的峰值必须跨越地球表面的 >60°经度。尽管年龄不确定性表明这些数据可能在峰值出现之前就已经采样了磁场，但几个低强度的数据与这种几何限制不兼容。最能满足能量和几何约束的模型产生的 CMB 峰值宽度为 8-22°，峰值为 O(100) mT。我们认为，黎凡特地区的峰值反映了一个强烈的 CMB 通量斑块，它在向西北迁移之前在原地增长，为偶极场的增长做出了贡献。对欧姆加热的估计表明，扩散过程可能控制着地磁尖峰的最终衰减。
