Methods of Inferring Turbulence Intensity and its Relation to Zooplankton Distributions using Underwater Glider Data

The influence that turbulence has on zooplankton behavior and distributions is complex. A correlation between turbulence and zooplankton aggregations has been found in diverse oceanic habitats. Traditional observations of turbulence and zooplankton in the field are often limited in quantity, time, and space. Underwater gliders present an opportunity to collect relevant data for sustained periods at unprecedented resolution. In this study, we use data from gliders equipped with turbulent microstructure, 300-kHz echosounder, and CTD instrumentation to explore: 1. the performance of turbulence parameterizations applied to more readily available glider CTD data by comparing CTD data-derived estimates of turbulence intensity to coincident estimates from microstructure data; and 2. the role of turbulence in setting acoustically-inferred zooplankton distributions over longer time scales and at higher spatiotemporal resolution than is feasible using ship-based data. In our case-study, we find that in specific conditions both the finescale parameterization and Thorpe scale method applied to glider CTD-data produce estimates of turbulence that are useful for describing both its statistical and spatiotemporal distribution. We therefore conclude these parameterizations can be useful in the study of the influence of turbulence on zooplankton distribution using data from gliders when microstructure observations are not available. We exploit this result to consider the influence of turbulence on zooplankton distributions in Roseway Basin on the Scotian Shelf, a place known as a good foraging ground with large zooplankton aggregations, and where gliders have been deployed to observe zooplankton distributions through high-frequency acoustic observation for 4 years. The use of turbulence parameterizations greatly expands the glider data available for our study, and illustrates the potential for these methods to contribute to studies on turbulence influence on zooplankton distributions.