I had no idea the Pacific and Atlantic Oceans did not mix! Because there is a huge difference in salinity between the clear water of the Pacific Ocean that comes from melting glaciers, is cool and low in salt, while the water from the Atlantic Ocean has a high salt concentration from many rivers along South America.  Therefore, the two oceans have different densities, which makes the waters almost impossible to mix. https://www.youtube.com/watch?v=uqgaqEFkuko Source: Vidya Nantha / youtube