Equilibrium profiles as a function of depth z. Panel (a): heavy-element mass fraction X_Z. Dotted and dashed curves show the profiles expected from gravitational settling alone (X_set) and thermohaline convection alone (X_th). The solid curve is the equilibrium profile X_eq obtained when both processes operate together and the resulting total flux becomes constant (see the text). The dotted vertical line marks the critical depth z_c below which settling dominates over thermohaline mixing, and the dotted–dashed line marks the equilibrium mixed-layer depth h_eq. Panel (b): corresponding heavy-element fluxes at equilibrium, normalized to the accretion flux F_acc. Dashed and dotted curves show the thermohaline (F_th) and settling (F_set) contributions, whereas the solid curve shows the total flux.