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Can the Earth's dynamo run on heat alone?

Gubbins, D., Alfe, D., Masters, G., Price, G.D. and Gillan, M.J. (2003) Can the Earth's dynamo run on heat alone? Geophysical Journal International, 155 (2). pp. 609-622. ISSN 0956-540X

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The power required to drive the geodynamo places significant constraints on the heat passing across the core-mantle boundary and the Earth's thermal history. Calculations to date have been limited by inaccuracies in the properties of liquid iron mixtures at core pressures and temperatures. Here we re-examine the problem of core energetics in the light of new first-principles calculations for the properties of liquid iron. There is disagreement on the fate of gravitational energy released by contraction on cooling. We show that only a small fraction of this energy, that associated with heating resulting from changes in pressure, is available to drive convection and the dynamo. This leaves two very simple equations in the cooling rate and radioactive heating, one yielding the heat flux out of the core and the other the entropy gain of electrical and thermal dissipation, the two main dissipative processes. This paper is restricted to thermal convection in a pure iron core; compositional convection in a liquid iron mixture is considered in a companion paper. We show that heat sources alone are unlikely to be adequate to power the geodynamo because they require a rapid secular cooling rate, which implies a very young inner core, or a combination of cooling and substantial radioactive heating, which requires a very large heat flux across the core-mantle boundary. A simple calculation with no inner core shows even higher heat fluxes are required in the absence of latent heat before the inner core formed.

Item Type: Article
Copyright, Publisher and Additional Information: © 2003 RAS. This is an electronic version of an article published in Geophysical Journal International: complete citation information for the final version of the paper, as published in the print edition of Geophysical Journal International, is available on the Blackwell Synergy online delivery service, accessible via the journal's website at http://www.blackwellpublishing.com/journal.asp?ref=0956-540X or www.blackwell-synergy.com
Institution: The University of Leeds
Academic Units: The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds)
Depositing User: Sherpa Assistant
Date Deposited: 06 May 2005
Last Modified: 05 Jun 2014 18:46
Published Version: http://www.blackwell-synergy.com/
Status: Published
Refereed: Yes
Identification Number: 10.1046/j.1365-246X.2003.02064.x
URI: http://eprints.whiterose.ac.uk/id/eprint/436

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