The change in the global water cycle due to climate change is one of the greatest challenges facing society, as dry regions become drier and wet regions become wetter. The problem is that 85% of evaporation and 77% of precipitation occur over the oceans and the global water cycle is poorly understood due to difficult observational conditions over the oceans. The goal of the project FreshOcean is to gain a comprehensive understanding of the dynamics and changes in salinity and associated thermal fields at sea surfaces and the near-surface layer, and how they relate to evaporation processes. The focus is an expedition to the central Atlantic Ocean with its high surface salinity, i.e., evaporation rates exceed precipitation rates. During the expedition, an autonomous catamaran will be used, capable of collecting high-resolution sea surface data. Observations will be supported by measurements from buoys, ship-based measurements, and satellites. In addition, a comprehensive set of experiments will be conducted in a mesocosm facility at the University of Oldenburg, where the driving forces for evaporation can be controlled and a mechanistic understanding can be achieved.