The Lagrangian nature of fingering convection

We investigate the Lagrangian properties of fingering convection in a parameter regime that is far beyond marginality, but that does not lead to staircase formation. We find that most fluid particles perform very short vertical excursions before switching direction. Only a small fraction of them travels vertically in the same direction for lengths substantially larger than the typical spatial scales associated with fingering instabilities. These long travels are associated with vertical velocities, buoyancy anomalies and advective fluxes constrained within a relatively narrow range of values. Despite their limited occurrence, they contribute the overwhelming majority of the up-gradient buoyancy flux. A description of fingering convection emerges that partitions the fluid into an incoherent background, where fluxes may be down-gradient, and a set of relatively long-lived, coherent, buoyancy-carrying structures that travel vertically, interacting with each other.