Meeting Abstract
Recent studies have provided spirited debate about whether biologically generated (or biogenic) mixing can have an impact on mixing in the ocean. Estimates of biological energetic inputs to the ocean show that the biogenic contribution to mixing is of the same order as winds and tides. Biogenic ocean mixing is a complex problem that requires detailed understanding of a variety of factors that include marine organism behavior, morphology, swimming mechanics, and the physical environment. An additional constraint in understanding mixing by swimming organisms is defining a metric that allows for accurate comparison between biological and physical processes in the ocean independent of the length scale used. Here we employ a dynamical systems technique to quantify mixing efficiency, and analyze small-scale mixing induced by a rhizostome medusa Phyllorhiza punctuate. Animals were placed in a glass filming vessel, and fluid motion was quantified using high-speed Digital Particle Image Velocimetry. To evaluate how mixing induced by swimming changes with morphology, the oral arms were excised from an individual P. punctuate and flow measurements were obtained. The measured velocity fields are then used to quantify mixing efficiency. Changes in morphology (i.e., removal of oral arms) dramatically altered the measured flow fields by reducing fluid drift, thereby reducing mixing efficiency. These observations have implications for the types of organisms that have the potential for large scale mixing in the ocean.
