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.Wind can easily blow the top 400 meters of water around.