Enhanced sedimentation beneath particle‐laden flows in lakes and the ocean due to double‐diffusive convection

The transport rate of particles beneath sediment‐laden overflows and interflows in lakes and the ocean can be enhanced by double‐diffusive and settling‐driven convection. In previous experiments with sediment‐laden fluid overlaying a saline layer, visual measurements could only be made in the optically clear lower layer. Hence, there was difficulty distinguishing the two processes, hindering predictions of when enhanced sedimentation occurs. We used an Acoustic Doppler Velocimeter to measure velocities and turbulence above and below the initial sediment/salt interface. The velocity of the sediment fingers in the lower layer were always larger than the Stokes settling velocity of the particles, leading to an asymmetry in the flow field of the two convective layers. Sediment fingers only dominated when there were marginal density differences between the two layers. We conclude that double‐diffusive sediment fingers control sedimentation beneath interflows in most lakes, whereas settling‐driven convection is dominant in most oceanic overflows.