The spatiotemporal dynamics of vertical autocatalytic fronts traveling horizontally in thin solution layers closed to the air can be influenced by buoyancy-driven convection induced by density gradients across the front. We perform here a combined experimental and theoretical study of the competition between solutal and thermal effects on such convection. Experimentally, we focus on the antagonistic chlorite-tetrathionate reaction for which solutal and thermal contributions to the density jump across the front have opposite signs. We show that in isothermal conditions the heavier products sink below the lighter reactants, providing an asymptotic constant finger shape deformation of the front by convection. When thermal effects are present, the hotter products, on the contrary, climb above the reactants for strongly exothermic conditions. These various observations as well as the influence of the relative weight of the solutal and thermal effects and of the thickness of the solution layer on the dynamics are discussed in terms of a two-dimensional reaction-diffusion-convection model parametrized by a solutal R C and a thermal R T Rayleigh number. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3122863͔ A vertical interface separating two solutions with different densities is always unstable under gravity, as the denser fluid tends to sink under the other one by forming a gravity current. When the interface is the result of the interplay between a reaction with a positive feedback and diffusion, the constant change in density across this selforganized front has both a thermal component originating from the temperature change due to the exothermicity of the reaction and a solutal component arising from the change in the chemical composition in the course of the reaction. For an antagonistic case, the combination of these two effects associated with opposite signs is investigated in an autocatalytic reaction both experimentally and theoretically. In the absence of thermal contribution, the denser product sinks, propagates at the bottom, and a single convection roll forms. The intrusion is characterized by the mixing length that scales with the height of the solution. When the temperature rise is significant, a local decrease in density is observed. The product propagates ahead on the top and several convection rolls develop as the solution cools behind the front. No stable structure evolves, and the number of cellular deformation cells in the front is determined by the height of the fluid.