The RadiCal project offers to develop Radiolarians as a novel palaeo-proxy for marine silicon cycling by Calibrating the silicon stable isotope composition (δ30Si) of these organisms to their modern environment. This objective will be achieved by applying an innovative multidisciplinary approach evaluating the influence of the modern environment and taxonomy on the variability of radiolarian silicon isotope fractionation (1) in situ, (2) under laboratory-controlled conditions, and (3) from a core-top calibration study from a variety of different oceanographic basins within the Southern Ocean.