We aim to understand the marine elemental fluxes at the level of organisms, ecosystems and at the global scale. To this end, we build hypotheses based on oceanographic field observations, test them in controlled phytoplankton lab experiments and use the results to develop mathematical models. Using this approach, we not only gain knowledge about limitations and trade-offs in physiological key process of marine algae, but also about altered ecological processes under climate change. The close exchange between biologists and modellers strongly supports the development of our marine biogeochemical model REcoM. When embedded into a large-scale ocean circulation model, we can project the future of the oceanic carbon sink, the conditions for marine life, and put a specific focus on the polar regions. With regard to applying and developing biogeochemical proxies, we strive towards a mechanistic understanding to improve reconstructions of the oceanic carbonate system, which are central for assessing CO₂ fluctuations in geological history as climate change analogues. With this expertise and approach, our section positions itself at the crossroads of the three principal AWI divisions: Bio, Geo and Climate.