Diel Vertical Migrations of Zooplankton and Turbulent Mixing: Observations and Numerical Simulation

A strong sound scattering layer undergoing diel vertical migration was observed using a bottom mounted ADCP at 244 m depth in the Straits of Florida. Data collection was a part of the Electromagnetic Observatory funded by the Office of Naval Research and analysis of biophysical interactions is ongoing under the Gulf of Mexico Research Initiative. This project aims to understand biophysical interactions associated with diel vertical migrations in a strong current. A computational fluid dynamics model was used to model the effects of diel vertical migrations on the velocity field and turbulence signature of the Gulf Stream. Zooplankton were represented through a discrete phase model. Temperature stratification was set for both summer and winter conditions to observe seasonal differences. For each season, results from the model with particles were compared to results run in the same conditions without particles to confirm the changes in profiles were due to the zooplankton. Analysis of the ADCP data indicates a distortion to the velocity field at sunrise and sunset, only during winter months, presumably associated with turbulence due to diel vertical migrations.