Bottom control on heat transfer in thin spherical shells: Application to ice-covered ocean worlds

The dynamical regime that prevails in sub-surface oceans of icy moons is thought to control thepattern of heat transfer in the oceans and possibly the topography of the ice layer above. However, if the heat flux across the seafloor is heterogeneous, its pattern may strongly affect the dynamics and the heat transfer in the ocean. Here we use numerical simulations of rotating convection in a thin spherical shell to explore the potential impact of heterogeneous inner boundary heat flux on the fluid dynamics and heat transfer in the thin liquid layer of icy moons. We prescribed synthetic large-scale heat flux patterns on the inner boundary corresponding to either polar or equatorial heating. Our results indicate that large-scale heating heterogeneity at the bottom of the ocean can strongly control the convection and heat transfer patterns in thin spherical shells, even for mild levels of heterogeneity amplitude. In practice, this means that an inner boundary heterogeneity can force polar or equatorial cooling at the top of the ocean, regardless of the ocean dynamics with homogeneous inner boundary conditions. Consequently, observed topographies at the surfaces of icy moons might not be deterministic of the competition between rotation and inertia in the sub-surface oceans and may provide constraints on large-scale heat flux anomalies emanating from the seafloor.