由于对流平移引起的地球内核上方熔化诱导的分层
Melting-induced stratification above the Earth's inner core due to convective translation
摘要：
除了全球南北各向异性（1），还有两个与地球内核有关的神秘的地震学观测结果：东半球和西半球之间的不对称（2-6）以及在外核底部存在一层地震速度降低的层（6-12）。这个250公里厚的层被解释为轻元素（13）中成分减少的稳定分层区域。在这里，我们表明，这层可以产生同时结晶和熔化的表面上的内核，并在内核中的热对流的平移模式可以产生足够的熔化和结晶，分别在每个半球上的致密层的发展。我们提出的动力学模型引入了一个明显的不对称之间的熔化和结晶半球，形成的基础上，也解释了东西不对称。目前的平移速度被发现是典型的1亿年的内核完全更新，这是一个到两个数量级的增长速度比内核的半径。轻元素造成的浮力通量的强烈不对称性预计将对外核的动力学和地球发电机产生影响。
英文摘要：
In addition to its global North-South anisotropy(1), there are two other enigmatic seismological observations related to the Earth's inner core: asymmetry between its eastern and western hemispheres(2-6) and the presence of a layer of reduced seismic velocity at the base of the outer core(6-12). This 250-km-thick layer has been interpreted as a stably stratified region of reduced composition in light elements(13). Here we show that this layer can be generated by simultaneous crystallization and melting at the surface of the inner core, and that a translational mode of thermal convection in the inner core can produce enough melting and crystallization on each hemisphere respectively for the dense layer to develop. The dynamical model we propose introduces a clear asymmetry between a melting and a crystallizing hemisphere which forms a basis for also explaining the East-West asymmetry. The present translation rate is found to be typically 100 million years for the inner core to be entirely renewed, which is one to two orders of magnitude faster than the growth rate of the inner core's radius. The resulting strong asymmetry of buoyancy flux caused by light elements is anticipated to have an impact on the dynamics of the outer core and on the geodynamo.
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