Gravity Forces, Salt, and Wind. During certain seasons, gravity forces from the moon and the Earth's rotation create strong currents. The Moon pushes water away from the surface. This surface water is replaced with water that rises from deep down in the ocean. Water at the bottom of the ocean has a lot of nutrients. When these currents is rise from the ocean bottom to the surface, the process is called upwelling. The main benefit of upwelling is that fish and other marine life can easily be found on the surface. Ocean currents are also affected by the level of salt in the ocean. While sea water enters the Arctic or Antarctic, much of the fresh water on the surface evaporates, and the ocean becomes saltier. Water with a high salt content is heavier than water with less salt. Eventually, northern currents(from the Arctic) flow south and change waters that are less dense. In the tropics, atmospheric winds affect the speed of surface water. Surface water in these regions flows very fast due to the strong atmospheric winds. winds can easily blow the top 400 meters of water around.