"Perhaps the most striking example of the influence of aquatic microorganisms in global cycles is their role in the oxygenation of the Earth's atmosphere and the transfer of photosynthetically fixed carbon from the ocean's surface to the deep ocean through sinking, a mechanism referred to as the Biological Carbon Pump, the process responsible for most of the oceanic uptake of anthropogenic CO2.Mainly driven by phytoplankton sinking, the Biological Carbon Pump is, at its core, a fluid dynamical problem coupling physiological processes with biogeochemical cycles. As such, it spans multiple levels of biological organization and its study requires an integrative and interdisciplinary approach.This proposal aims at critically advancing our knowledge of the biological pump and its response to global changes in the environment by breaking through the current physiological bottleneck and examining the range of scales necessary to predict what the future is likely to hold. Specifically, I will focus on understanding the organism's role in organism-environment linkages, promoting phytoplankton to an active - physiologically controlled - performer in the carbon cycle. The interplay between active physiological responses and fluid transport, in what I like to call Complex (or Intelligent) Advection, remains largely unexplored whereas its consequences for biogeochemical cycles in the ocean are of paramount significance.The role of organisms in organism-environment interactions, its study through the integration of living and physical systems analysis, and its repercussions for the time course of adaptation and acclimation are three of the ""Grand Challenges"" in organismal biology, identified by the Executive Committee of the Society for Integrative and Comparative Biology (SICB). All three challenges will be tackled within the proposed research program for the case of one of the most successful groups of eukaryotic micro-organisms in aquatic environments: the diatoms."