Diatoms are a particular group of phytoplankton that contribute to an estimated 20% global primary production and carbon export. Lacking swimming appendages like flagella, diatoms rely on passive advection by flows and active buoyancy regulation. At LPENS, our group is particularly interested in the regulation of their buoyancy induced by shear flows. Recently, in collaboration with Idan Tuval at IMEDEA (Mallorca) we could demonstrate for the first time that the species Coscinodiscus granii actively modulates its intracellular density when sheared by external flows. For this master internship (M1 or M2) we aim at investigating the biophysicochemical mechanisms involved in such buoyancy regulation at the single cell level. We will combine biophysical approaches, video-microscopy/optics, image analysis, microfluidic techniques, microalgal culturing techniques and data analysis in order to decipher this complex process. For M2 students, the internship can be followed with a PhD (funded through a doctoral scholarship to apply to). During the PhD the student will also have the opportunity to work on large scale biogeochemical simulations in order to investigate the effect of active buoyancy regulation on primary production and carbon export (in collaboration with Laurent Bopp at the Geoscience department), and/or to work on the coupling between such active response and turbulence through dedicated simulations (in collaboration with Idan Tuval and Jorge Arrieta at IMEDEA, Spain).