### Abstract

- Top of page
- Abstract
- 1. Introduction
- 2. Numerical Models
- 3. Results
- 4. Discussion and Conclusions
- Acknowledgments
- References
- Supporting Information

[1] Using a numerical model we explore the consequences of the intrinsic density change (Δ*ρ*/*ρ* ≈ 2–4%) caused by the Fe^{2+} 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.