This study examines how heat and light-element composition interact to drive fluid motion in a rotating spherical shell, similar to conditions in Earth’s outer core. It focuses on how light elements released at the boundary of a solid inner core influence convection in the surrounding fluid. The analysis explores how strongly thermal and compositional effects are coupled, revealing two distinct behaviors: when the coupling is weak, heat dominates and compositional effects remain near the boundary; when the coupling is strong, light elements drive vigorous convection throughout the fluid layer. As the coupling increases, flow patterns, energy distribution, and the transport of heat and composition all shift significantly. These results improve understanding of how light-element release affects convection and magnetic field generation in planetary interiors.