Gubbins, D, Alfè, D and Davies, CJ (2013) Compositional instability of Earth's solid inner core. Geophysical Research Letters, 40 (6). 1084 - 1088. ISSN 0094-8276
Abstract
All models that invoke convection to explain the observed seismic variations in Earth's inner core require unstable inner core stratification. Previous work has assumed that chemical effects are stabilizing and focused on thermal convection, but recent calculations indicate that the thermal conductivity at core temperatures and pressures is so large that the inner core must cool entirely by conduction. We examine partitioning of oxygen, sulfur, and silicon in binary iron alloys and show that inner core growth results in a variable light element concentration with time: oxygen concentration decreases, sulfur concentration decreases initially and increases later, and silicon produces a negligible effect to within the model errors. The result is a net destabilizing concentration gradient. Convective stability is measured by a Rayleigh number, which exceeds the critical value for reasonable estimates of the viscosity and diffusivity. Our results suggest that inner core convection models, including the recently proposed translational mode, can be viable candidates for explaining seismic results if the driving force is compositional. Key Points Partitioning of O and S between inner and outer cores is time dependent Inner core is unstable to compositional convection, contrary to previous studies Thermal effects are stabilising, making composition the only driving force.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | ©2013. American Geophysical Union. All Rights Reserved. Reproduced in accordance with the publisher's self-archiving policy. |
Keywords: | Inner core; Convection; Light elements |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst of Geophysics and Tectonics (IGT) (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 09 Nov 2015 09:37 |
Last Modified: | 23 Jun 2023 21:46 |
Published Version: | http://dx.doi.org/10.1002/grl.50186 |
Status: | Published |
Publisher: | American Geophysical Union |
Identification Number: | 10.1002/grl.50186 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:85235 |