Measurements of fluid transport by controllable vertical migrations of plankton

Diel vertical migration of zooplankton has been proposed to be a significant contributor to local and possibly large-scale fluid transport in the ocean. However, studies of this problem to date have been limited to order-of-magnitude estimates based on first principles and a small number of field observations. In this work, we leverage the phototactic behavior of zooplankton to stimulate controllable vertical migrations in the laboratory and to study the associated fluid transport and mixing. Building upon a previous prototype system, a laser guidance system induces vertical swimming of brine shrimp (Artemia salina) in a 2.1 meter tall, density-stratified water tank. A schlieren imaging system and a conductivity probe are used for measurements of the water column. Fluid transport and mixing is quantified through analysis of turbulent scales and the density profile evolution. These experiments will add to our understanding of the dynamics of active particles in stratified flows and inform the ongoing debate regarding biogenic ocean mixing.