Dan James Bower , Michael Gurnis, Jennifer M. Jackson, Wolfgang Sturhahn

Using a numerical model we explore the consequences of the intrinsic density change (Δρ/ρ ≈ 2–4%) caused by the Fe2+ spin transition in ferropericlase on the style and vigor of mantle convection. The effective Clapeyron slope of the transition from high to low spin is strongly positive in pressure‐temperature space and broadens with high temperature. This introduces a net spin‐state driving density difference for both upwellings and downwellings. In 2‐D cylindrical geometry spin‐buoyancy dominantly enhances the positive thermal buoyancy of plumes. Although the additional buoyancy does not fundamentally alter large‐scale dynamics, the Nusselt number increases by 5–10%, and vertical velocities by 10–40% in the lower mantle. Advective heat transport is more effective and temperatures in the core‐mantle boundary region are reduced by up to 12%. Our findings are relevant to the stability of lowermost mantle structures.