Final Report Summary - DIASIN (Integrative Eco-mechanics of Diatom Sinking: Cellular Physiology, Complex Advection and the Biological Carbon Pump.) The proposal constitutes the first applications of modern methods from experimental and theoretical fluid mechanics and biophysics to the understanding of diatom physiologically controlled buoyancy response to environmental signals. The research program was developed within a bottom-up approach investigating in great detail the described phenomena at the level of the single organism, before scaling the results back up to populations and communities. This required an approach which combines modern techniques in fluid mechanics, video-microscopy, micro-fluidics, flow cytometry, mathematical analysis and state of the art computational tools, with biochemical and cell biological techniques. On the theoretical side, the foundation of the emerging field of Complex Advection involves the use of unconventional approaches based on a conceptual blend of chaotic advection and agent-based dynamics which has not been systematically explored and which provides extremely interesting perspectives for future research. By integrating living and physical systems analysis, we have started to disentangle the different ways by which complex advection occurs in diatoms. In particular, we have addressed here for the first time the role of buoyancy control as an active component of diatom advection. Our results clearly indicate that active buoyancy control significantly enhances the probability of cells to stay suspended high in the water column with important implications for phytoplankton ecology and the size structure of the phytoplankton community.
