The size of marine particles controls many oceanic processes that ultimately affect the feedbacks between the ocean carbon cycle and the Earth's system. Among these processes the most significant are perhaps particle settling, aggregation and remineralization, because they modify the efficiency of the biological pump, i.e., the transfer of organic matter from the surface to the deep ocean. Size additionally controls the optical properties of particles that allow us to monitor the ocean carbon cycle from satellite sensors. Finally, the size of living marine particles (e.g., phytoplankton) is proportional to their carbon biomass and regulates many eco-physiological processes such as photosynthesis, respiration, nutrient uptake and grazing.Despite its relevance, the size distribution of phytoplankton and marine particles is rarely measured in the open ocean, mainly due to limitations in current instrumentation. The main objective of this application is construct a break-through instrument that will exploit novel microfluidic lab-on-a-chip technologies to overcome current instrument limitations and measure the particle and phytoplankton size distributions over an unprecedented range of sizes. The new data will eventually reduce uncertainties in the ocean carbon cycle by, among others, improving estimates of phytoplankton carbon, enhancing our understanding of phytoplankton eco-physiology in-situ and improving our knowledge of sub-micron particles.Dr. Dall'Olmo's chances of reintegrating in the European Union will be significantly improved by participation to this project. This is because, he will be able to capitalize on the newly collected data for continuing publishing in peer-reviewed journals, generating new ideas and proposal applications, as well as establishing new collaborations within and outside the European Union.