  A new mechanism of double-component convection is discovered. It emerges in a
horizontal layer of Boussinesq fluid as a stable stratification due to flux
boundary conditions is added to an unstable gradient specified by fixed
boundary values. A large enough perturbation substantially decreases the stable
flux gradient but fails to mix the unstable fixed-value gradient. Steady
finite-amplitude flows reminiscent of Rayleigh--Benard convection then arise
even as the net background stratification is stable, emphasizing the importance
of the identified mechanism for double-component fluid systems.
  V2 Abstract: A new mechanism of double-component convection is discovered. It
emerges in a horizontal layer of Boussinesq fluid as a stable stratification
due to flux boundary conditions is added to an unstable gradient specified by
fixed boundary values. Driven by this mechanism, steady finite-amplitude flows
reminiscent of Rayleigh--Benard convection arise even when the background
density stratification is stable.
