Dynamics of the core, geodynamo

Abstract

“The mechanism for generating the geomagnetic field remains one of the central unsolved problems in geoscience.” So states the report on the National Geomagnetic Initiative (NGI) prepared by the U.S. Geodynamics Committee, et al [1993], with advice from the NGI Workshop held in Washington D.C. in March 1992. All analyses of the geomagnetic data point to the core as containing the source of the field and “The basic premise that virtually everyone accepts is that the Earth's magnetism is created by a self‐sustaining dynamo driven by fluid motions in Earth's core” (NGI, p.135). Dynamical questions at once arise, such as “What is the energy source driving those motions?” Jacobs [1953] proposed that the solid inner core (SIC) is the result of the freezing of the fluid outer core (FOC). Verhoogen [1961] noticed that the release of latent heat at the inner core boundary (ICB) during freezing would help drive thermal convection in the FOC, and Braginsky [1963] pointed out that the release of the light alloying elements during fractionation at the ICB would provide compositional buoyancy. These two sources suffice to supply the geodynamo with energy throughout geological time, even in the absence of dissolved radioactivity in the core [Braginsky and Roberts, 1994a; Kuang et al, 1994]. Stevenson [1991] argues that potential differences on the core‐mantle boundary (CMB) of electrochemical origin may be partially responsible for the geomagnetic field.