My research activities in physical oceanography aim at understanding better the role of the ocean in climate change. I analyze the observed variability during the last 50 yr and, using numerical simulations of varying complexity, quantify the respective contribution of each process of interannual to multi-decadal variability that influence hydrography and circulation. I also diagnose the ocean component of climate models to evaluate how realistic the simulated variability is, so as to assess the likeliness of future climate predictions. Multiple regions are in the scope of my scientific projects: the North Atlantic, the southern tip of Africa, the Southern Ocean, the Caribbean islands... Overall, I am interested in all features of the Meridional Overturning Circulation and the global circulation of heat. Finally, I contribute to the development of ocean models for regional and global configurations, paying particular attention to the sources of uncertainty in realistic ocean simulations.