This thesis is mainly focused on the variability of the vertical structure of the ocean surface and the processes of deep water formation. Results are based on many platforms measuring in-situ: ships, profiling floats, "gliders" (unmanned autonomous underwater vehicle), and surface buoy moorings. In the first part, we characterize the variability of the ocean mixed layer in the Mediterranean. We present the first Mediterranean climatology of the seasonal thermocline and the upper ocean heat storage rate based on a comprehensive collection of temperature profiles of the last 44 years (1969-2012), including more than 190,000 profiles. This climatology highlights the high temporal and spatial variability of the mixed layer and of the seasonal ...