When layers of salt and sugar solution are separated by a “diffusive” interface, interfacial waves are spontaneously generated by the turbulent convection once the system evolves to a critical value of the density–anomaly ratioR&rgr;≡&bgr;&Dgr;S/&agr;&Dgr;T(Stamp &etal;, to appear in J. Fluid Mech). The waves modulate the interfacial fluxes by modifying the interface thickness and thereby organize the otherwise random convective motions into coherent large-scale circulations. In narrow rectangular channels a wide range of conditions give rise to a single wave which propagates back-and-forth, resulting in quasi-periodic reversals of tank-scale circulations. Here it is shown that in annular and equant rectangular cavities this same coupling phenomenon produces turbulent convection cells of a traveling-wave nature, coupled to large-amplitude solitary waves on the interface. ©1997 American Institute of Physics.