Enhanced sediment scavenging due to double-diffusive convection

River water intruding into a lake or ocean typically results in a surface l aver of warm, sediment-laden water overriding relatively dense, cold fluid. Though this system is stable with respect to density, instability may aris e as a result of the different diffusivities of sediment and heat. A series of experiments were conducted which indicated that double-diffusive convec tion (DDC) was responsible for rapid sedimentation of slowly settling parti cles. A simple theory, based upon relevant physical processes, is developed that describes this behavior. It also incorporates the previously neglecte d effects of ambient stratification on the strength of the DDC. Application of the theory and our results to field data taken from oceanic river plume s demonstrates that the flux due to double-diffusive sedimentation (DDS) ca n be at least as strong as flocculation-enhanced gravitational settling.