This project will investigate the impact of swimming microorganisms on mixing. As a typical phenomenon, small organisms in the ocean called copepods let themselves slowly sink while agitating the fluid around them. Copepods form massive colonies and their collective motion helps bringing up nutrients, which are crucial to the organisms' reproduction, from deeper layers of the ocean. The stirring of a fluid by such swimming creatures is called biomixing. We will investigate biomixing from a variety of directions: we will model specific microorganisms, and use novel mathematical techniques to quantify their impact on fluid mixing. We will also compare the motion of these organisms as they sink to the dynamics of sedimenting particles, to see which aspects of the accumulated knowledge on sedimenting particles carry over to microorganisms, and which new features are introduced.
It is well known that mixing is greatly enhanced by fluid motion--even the simple task of heating a house would be almost impossible without air convection. Biomixing has a wide range of possible applications, beyond immediate relevance to the fluid dynamics of microswimmers. An understanding of the impact of swimming microorganisms on mixing will help understanding phenomena such as oil breakup by bacteria, which is crucial in the aftermath of oil spills, or the life cycle of large colonies of organisms. The well-being of these colonies has a profound impact on climate change, since they absorb vast amounts of greenhouse gases. In addition, there are potential applications to microfluidics, where stirring by microorganisms can assist mixing at small scales. The inclusion of graduate students into this research, and their interdisciplinary training are an integral part of this project.