Effects of depth-dependent conductivity on the geodynamo

Abstract:

Recently the foremost challenge to the theory of the geodynamo has been upward revisions to the thermal conductivity of high pressure iron-rich liquid alloys, straining the energy budget of the core and questioning its primary source of buoyancy. However, little attention has been paid to the depth-dependence of the thermal conductivity, and how it might affect convection and dynamo action. Here we develop a method to identify the convective regions of numerical rotating hydrodynamic simulations for arbitrary control parameters and boundary conditions. We test several different types of depth-dependence for the thermal conductivity: constant, linearly increasing, and quadratic peak at the center. We compare these results to predictions from a simple 1D model to investigate how turbulent convection influences the locations of the convective boundaries. We then apply these results to the thermal evolution of the core to estimate whether stratified regions could have existed and influenced Earth’s magnetic field in the past.