The Earth's core as a reservoir of water
The Earth's core as a reservoir of water
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DOI：
10.1038/s41561-020-0578-1
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发表时间：
2020-05-18
影响因子：
18.3
通讯作者：
Brodholt, John P.
中科院分区：
文献类型：
--
作者：
Li, Yunguo;Vocadlo, Lidunka;Brodholt, John P.
根据对地核形成条件下水的分配行为的计算，地核可能是地球上大部分水存量的所在地，目前对地球中水的收支和分布的估计存在很大的不确定性，其中大部分是由于缺乏关于地球深部的信息。最近的研究表明，地球可能在其演化的早期阶段从富含氢的太阳星云中获得了大量的水，并且地球中的大量水可能已经分配到核心。本文采用从头算分子动力学和热力学积分技术计算了20-135 GPa和2，800 - 5，000 K下水在铁和硅酸盐熔体之间的分配。我们的研究结果表明，在核-幔分异和核-幔边界条件下，水的亲铁性随温度的升高而减弱;然而，我们发现，在还原和氧化的情况下，在成核条件下，水总是强烈地分配到铁液体中。水的亲铁性也得到了验证，通过计算平衡的铁和硅酸盐熔体中氢的分布的化学计数法。因此，我们得出结论，地球的核心可能是一个巨大的水库，包含了地球上大部分的水。除了限制挥发性物质输送的吸积模型外，这些发现还可以部分解释测得的地震速度所暗示的地核密度低的原因。
The Earth's core may host most of the planet's water inventory, according to calculations of the partitioning behaviour of water at conditions of core formation.Current estimates of the budget and distribution of water in the Earth have large uncertainties, most of which are due to the lack of information about the deep Earth. Recent studies suggest that the Earth could have gained a considerable amount of water during the early stages of its evolution from the hydrogen-rich solar nebula, and that a large amount of the water in the Earth may have partitioned into the core. Here we calculate the partitioning of water between iron and silicate melts at 20-135 GPa and 2,800-5,000 K, using ab initio molecular dynamics and thermodynamic integration techniques. Our results indicate a siderophile nature of water at core-mantle differentiation and core-mantle boundary conditions, which weakens with increasing temperature; nevertheless, we found that water always partitions strongly into the iron liquid under core-formation conditions for both reducing and oxidizing scenarios. The siderophile nature of water was also verified by an empirical-counting method that calculates the distribution of hydrogen in an equilibrated iron and silicate melt. We therefore conclude that the Earth's core may act as a large reservoir that contains most of the Earth's water. In addition to constraining the accretion models of volatile delivery, the findings may partially account for the low density of the Earth's core implied by measured seismic velocities.