Physical and biological controls on the maintenance and dissipation of a thin phytoplankton layer

During an 8.5 h overnight study in Monterey Bay in 2005, continuous, high-resolution vertical profiles of a thin layer of phytoplankton as well as physical properties of the water were measured. The thin layer was populated by strong-swimming, vertically migrating dinoflagellates. This dataset provided a unique opportunity to apply an existing mathematical model that describes how competing convergence and divergence mechanisms contribute to the formation and structure of thin plankton layers. Compared to straining by shear, cell settling velocities, and plankton motility, vertical displacements caused by the passage of internal waves had the greatest influence on changes in layer thickness. Thus, for a model to accurately describe thin-layer dynamics in an environment with internal waves, the convergent and divergent effects of the vertical oscillations caused by internal waves must be considered.