Thermochemical Stratification Beneath the Core Mantle Boundary from Coupled Core and Mantle Thermal History Models.

A stably stratified region at the top of the Earth's outer core has been advocated based on seismic and geomagnetic observations. This region should be characterised by a lack of vertical motion of the liquid, confining convection to the deeper core. Its presence will therefore impact the thermal evolution of the planet and have implications for the generation of magnetic field, yet the properties of such a layer, such as size and origin, are uncertain and require alternative constraint. We construct a coupled core and mantle thermal history model that includes a stable layer at the top of the outer core. The inclusion of the thermal history of the mantle allows for realistic time dependant boundary conditions for the top of the stable layer. Stratification is generated by the time-dependent diffusion solutions for both temperature and mass within the layer, relative to the evolution of the underlying bulk of the core. A range of initial/boundary conditions are explored within the model space to find a suite of successful models matching available constraints such as; correct present inner core radius, dynamo operation prior to inner core nucleation and present day stable stratification on the order of a few 100's km thick. Predicted radial structure within the modelled stratified layers may then be used for investigating the seismic structure of the top of the core, modelling waves or provide buoyancy profiles for geodynamo models.