The new core paradox, the stable layer, and doublediffusive convection in Earth’s core

新地核悖论、稳定层和地核双扩散对流

• 批准号: 521319293
• 负责人: Dr. Johannes Wicht
• 金额: --
• 依托单位: Max-Planck-Institut für Sonnensystemforschung (MPS)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/521319293?language=en
• 关键词: new; core; paradox; stable; layer

Both thermal and compositional convection contributed to driving the geodynamo over its evolution. However, most numerical dynamo models to date neglect the differences between both convection types, describing the evolution of density variation with only one variable. Therefore, a number of peculiar instabilities that rely of the significant differences in diffusivities in double-diffusive dynamics can never arise in these simulations. This proves particularly problematic in the buildup and the dynamics of a stable stratified layer where one component is driving why the other suppresses motions. Seismic observations indeed suggest that a stable layer with a thickness of perhaps 100 km may exist underneath Earth’s core mantle boundary. It may actually have been there since Earth’s early history. Once Earth’s inner core started to grow, the light elements released in the crystallization process significantly contributed to powering the geodynamo. Before that time, however, the exsolution of, for example, MgO may have played a similar role. A significant contribution of compositional driving could solve the New Core Paradox, which states that the large heat flux required by a purely thermally driven dynamo would yield an unrealistically hot core and lower mantle earlier in Earth’s history. We propose to explore double-diffusive dynamos in the full-sphere (without inner core) and the spherical shell (with inner core) geometry with the numerical code MagIC. In order to better understand the peculiar doubly-diffusive small-scale instabilities arising in a stable layer, we will also conduct high-resolution box simulations with the code AFiD. The results will then be parametrized for a more realistic implementation of the outer stable layer in global MagIC simulations. Understanding the role of double-diffusive dynamics in general and the stable layer in particular for the core evolution, for the dynamo process, and the impact of the lower mantle on the dynamo is a first order problem for the SPP DeepDyn.

热对流和成分对流都有助于推动地球发电机的演变。然而，迄今为止，大多数数值发电机模型忽略了这两种对流类型之间的差异，仅用一个变量来描述密度变化的演变。 因此，在这些模拟中，依赖于双扩散动力学中扩散率的显著差异的一些特有的不稳定性永远不会出现。这证明在稳定分层层的建立和动力学中特别有问题，其中一个组件驱动另一个组件抑制运动。地震观测确实表明，在地球的核幔边界之下可能存在一个厚度约为100公里的稳定层。它可能在地球早期历史上就存在了。一旦地球的内核开始生长，在结晶过程中释放的轻元素对地球发电机的动力有很大的贡献。然而，在此之前，例如MgO的出溶作用可能起到了类似的作用。成分驱动的一个重要贡献可以解决新的核心Partial，它指出，一个纯粹的热驱动发电机所需要的大热流量将产生一个不切实际的热核心和下地幔在地球历史的早期。我们建议探索双扩散发电机在全球（无内核）和球壳（内核）的几何与数字代码MagIC。为了更好地理解在稳定层中出现的特殊双扩散小尺度不稳定性，我们还将使用代码AFiD进行高分辨率箱模拟。然后将结果参数化，以便在全局MagIC模拟中更真实地实现外部稳定层。了解一般的双扩散动力学的作用，特别是稳定层的核心演变，发电机过程，以及下地幔对发电机的影响是SPP DeepDyn的一阶问题。