Non-adiabaticity in mantle convection

Seismic observations indicate that Earth's lower mantle is homogeneous as revealed by smooth depth variations of the bulk sound velocity and Bullen's inhomogeneity parameter eta being close to one. Here we show with 3D spherical convection simulations that it should also be non-adiabatic because a significant proportion of mantle heat sources is internal. The computer simulations predict non-adiabaticity of 100-300 degrees for the lower mantle geotherm, with eta similar to 1.01 implying that the temperature drop across the Core Mantle Boundary exceeds 1000 degrees.