he overall objective of the BELCANTO III project was to conduct targeted process studies and develop new proxies to construct and validate a realistic 3D ice-ocean biogeochemical model for the area south of latitude 30°S, based on improved understanding of the different factors regulating interactions between the atmosphere, ocean circulation and biogeochemical cycles and on synthesis/collection of existing/new data sets. The specific objectives were: - to improve our understanding about the iron cycling, with focus on the significance of iron-organic matter interactions for iron bioavailability and the efficiency of the biological pump (WP1) - to quantify nutrient consumption, CO2 uptake and C-export by assessing seasonality and interannuality of nutrient (Si, N) uptake; reconstruct carbon uptake and export from the surface layer via a multi-proxy approach; provide a relevant data set for 3D-NEMO-SWAMCO model validation (WP2) - to characterise the biogenic particles exported from the surface to the twilight zone and study their fate by quantifying remineralisation rates (WP3) - to model biogeochemical cycles in the modern Southern Ocean including seaice biogeochemistry (WP4) - to estimate impact of future climate change in the Southern Ocean through process-studies and modelling approaches (WP5).