Diel Vertical Migration of Mesozooplankton: Large Mixing by Small Animals?

Diel Vertical Migrations (DVM) of mesozooplankton aggregations are hypothesized to trigger biogenic mixing. Lab studies have shown that the vertical migration of swarms of model organisms results in large-scale momentum and scalar transport via flow instabilities. However, it is unclear how to scale these results to inform the physics of the upper ocean. Here we outline a new approach for assessing DVM effects by: (1) characterizing DVM from ocean-color satellite observations; (2) developing a lab-based, continuum model parameterization of fluid transport by DVM; and (3) implementing the acquired DVM characteristics and swimmer parameterization in a global-ocean biogeochemistry model with a realistic representation of mesozooplankton physiology and behavior. Focusing on (2), we measured the flow field of individuals and aggregations of relevant copepod species using bright-field and 2-D PIV, respectively. We discuss the effects of aggregation density, migrating direction, and the energetic length scales on the induced fluid transport and mixing. Our study will provide a unique framework for incorporating vertically-migrating organism behavior and the associated physical processes into state-of-the-art ocean circulation models to quantify marine ecosystem structure accurately.