Using concurrent in situ measurements of animal movement and turbulent microstructure in the pelagic ocean to quantify the role of biology in ocean mixing
Abstract
The magnitude of ocean mixing due to the movement of biological organisms is a function of animal and group size, swimming velocity, turbulence and dissipation rates, ocean stratification, and other factors. However, the temporal and spatial extent of animal-driven mixing is not well understood. Some observations have shown that moving organisms can create turbulence in their path. But there are key questions that remain unknown about the extent of these processes, the magnitude of biological-driven mixing processes, and under what conditions biological mixing is important relative to other processes in the open ocean. Our project objectives are: measure turbulence in the ocean before, during, and after animal vertical migration events; combine net, optical, acoustic, and eDNA techniques to measure in situ behavior, abundance and type of migrators; quantify characteristics (taxa, numerical abundance, size, swimming velocities) of migrating organisms; determine if eDNA can estimate organism abundance relative to traditional net and acousticmethods; evaluate if eDNA techniques can resolve transitory organisms over short temporal ranges (hours to days); compare organism-caused turbulence relative to other physical oceanographic processes; determine if our results are extendable to additional areas ofNaval interest; and develop a multi-platform sampling strategy that is applicable and transferable for investigating biological-mixing in other oceanographic contexts. To achieve these goals we will combine multiple methods (microstructure, acoustic, optic, net, and eDNA) and platforms (vessel, ocean gliders, a new autonomous vertical profiler) to measure ocean mixing before, during, and after aggregations of animals move through the ocean. The majority of these measurements will be made in situ (at depth) on undisturbed animals. These sensors will also produce information (animal type and length, swimming velocities, numerical densities) needed to accurately model animal-driven turbulence quantities. We will integrate net tow, acoustic, optical, and environmental DNA (eDNA) sampling to identify organisms and address critical research questions relating to residence time of eDNA material and the relationship between eDNA quantities and animal abundance. Identical instruments for measuring microstructure and acoustic backscatter will beon both the vertical profiler and the gliders providing the ability to compare measurements from different platforms. Our field effort plan consists of two two-week-long expeditions where the gliders will provide reconnaissance information which will be used to select regions where we know: epi- and meso-pelagic organisms are abundant and that other physical mixing processes (upwelling, downwelling, frontal zones) are low to ensure that our microstructure measurements can be attributed to biological sources. Our study location is the Gulf of Mexico because: it is a deep, open ocean habitat; the vertical migrators consist of a variety of organisms ranging from small crustaceans to larger nekton which have been studied acoustically and through eDNA. However, the approach used in this project will provide methods and techniques that can be applied to other areas of Naval operational interest, as well as a predictive modeling effort to determine what conditions are necessary (both biologically and physically) for biologically-driven mixing toimpact water column structure. Approved for Public Release
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 11, 2023
- Source ID
- N000142312703
Entities
People
- Joseph Warren
Organizations
- Office of Naval Research
- Research Foundation for the State University of New York
- United States Navy