Gravimetric and magnetic anomalies produced by dissolution-crystallization at the core-mantle boundary

Abstract

Using the unique data sets provided by satellite observations, correlated temporal variations in gravity and magnetic fields over a large area extending from the Atlantic to the Indian Ocean have been recently reported. On a timescale of few years to a decade, both field variations may be linked to changes at the top of the core. Here we propose that in addition to the topography generated by the convection in the mantle, the core-mantle boundary (CMB) may be in a dynamic equilibrium state, mainly controlled by a dissolution-crystallization process of the mantle silicate rocks in the liquid alloy of the core. Due to the resulting continuous changes in CMB topography, anomalies of hundreds of nGal and tens of nT yr-2 might be produced by the corresponding mass redistribution and the secondary flow generated by the associated pressure field. Numerical modeling and both gravimetric and magnetic anomaly magnitudes suggest a rate of centimeters per year and a large range of length scales for the changes in the topography at the CMB.