The Feasibility of Thermal and Compositional Convection in Earth’s Inner Core

imam ja'far ash-shadiq;

Inner core convection, and the corresponding variations in grain size and alignment, has been proposed to explain the complex seismic structure of the inner core, including its anisotropy, lateral variations and the F-layer at the base of the outer core. We develop a parametrized convection model to investigate the possibility of convection in the inner core, focusing on the dominance of the plume mode of convection versus the translation mode. We investigate
thermal and compositional convection separately so as to study the end-members of the system. In the thermal case the dominant mode of convection is strongly dependent on the viscosity of the inner core, the magnitude of which is poorly constrained. Furthermore recent
estimates of a large core thermal conductivity result in stable thermal stratification, hindering convection. However, an unstable density stratificationmay arise due to the pressure dependant partition coefficient of certain light elements.We show that this unstable stratification leads to compositionally driven convection, and that inner core translation is likely to be the dominant convective mode due to the low compositional diffusivity. The style of convection resulting
from a combination of both thermal and compositional effects is not easy to understand. For reasonable parameter estimates, the stabilizing thermal buoyancy is greater than the destabilizing
compositional buoyancy. However we anticipate complex double diffusive processes to occur given the very different thermal and compositional diffusivities.