Describing and understanding factors affecting ecosystem changes in the Southern Ocean is important for fundamental and applied reasons to provide guidelines to policy-makers for implementing necessary policies to limit greenhouse gas emissions and human activities. This requires studies conducted over long time periods to decipher the effects of global changes and the responses of living organisms which often operate over several decades. The project uses seabirds and marine mammals as sentinels of global changes in the marine ecosystems of the Southern Ocean. Through a network of four study sites from the Antarctic to sub-tropical biomes, involving 32 species of marine top predators, the observatory component of the project monitors the abundance of populations, fate of marked individuals and their distribution and abundance at sea, trophic niches and contaminant burdens, since more than 60 years for some populations. Process oriented studies will be carried on to understand how the physical environment, distribution and availability of prey affect the foraging behaviour, distribution and fitness of individuals, demographic traits and population dynamics. We will also investigate how marine predators may adapt to climate change via phenotypic plasticity or micro-evolution, and explore species interactions (predator-prey relationships, multispecies demography, synchrony) to better understand community diversity, structure and dynamics of marine top predators. By combining long term information with results from the process studies, we aim at understanding the processes though which climate affects marine ecosystems, and to make projections on the effects of future changes in these ecosystems, as well as to propose conservation measures to limit the impact of global changes on populations.