Outer-core compositional stratification from observed core wave speed profiles

George Helffrich, Satoshi Kaneshima

Research output: Contribution to journalArticle

101 Citations (Scopus)

Abstract

Light elements must be present in the nearly pure iron core of the Earth to match the remotely observed properties of the outer and inner cores. Crystallization of the inner core excludes light elements from the solid, concentrating them in liquid near the inner-core boundary that potentially rises and collects at the top of the core, and this may have a seismically observable signal. Here we present array-based observations of seismic waves sensitive to this part of the core whose wave speeds require there to be radial compositional variation in the topmost 300-‰km of the outer core. The velocity profile significantly departs from that of compression of a homogeneous liquid. Total light-element enrichment is up to five weight per cent at the top of the core if modelled in the Fe-O-S system. The stratification suggests the existence of a subadiabatic temperature gradient at the top of the outer core.

Original languageEnglish
Pages (from-to)807-812
Number of pages6
JournalNature
Volume468
Issue number7325
DOIs
Publication statusPublished - Dec 9 2010

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All Science Journal Classification (ASJC) codes

  • General

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