Grant: Research Tools and Instruments - Category 1 (<$150,000)

Our long-term research goal is to determine the role of zooplankton in generating ocean turbulence. In 1966, the famous oceanographer Walter Munk concluded, based on order of magnitude calculations, that biologically-driven mixing was negligible compared to physically-driven mixing such as that generated by currents, internal tides and convection. Surprisingly, recent discoveries published in 2006 based on field measurements suggest that swarms or schools of zooplankton may be an important source of ocean turbulence during daily vertical migration. Trying to understand how biologically-driven mixing works is complicated by the fact that zooplankton are small organisms (< 2 cm) that may disturb the flow and cause turbulence at very small scales. Therefore, to obtain quantitative information on zooplankton-turbulence interactions simultaneous observations of zooplankton and small-scale flow are required. Fortunately, instruments exist for measuring such small-scale biological (zooplankton) and physical (smallest turbulent eddies) features. Video Plankton Recorders (VPR) can sample individual zooplankton and Acoustic Doppler Velocimeters (ADV) can measure accurately the three-dimensional currents within a ~ 1 cm^3 sampling volume. Our goal is to configure these two specialized intruments in order to obtain simulataneous, fine-scale measurements of zooplankton and turbulence. We already have access to a VPR that is deployed and operational at the Bonne Bay Observatory. In this proposal we seek support from NSERC to acquire an ADV that we wish to coordinate with the VPR as an instrument package to study naturally-occuring zooplankton-driven turbulence.