In general, the water on the surface of the ocean is warmer than at the bottom because it is heated by the sun. In the tropical Pacific, winds generally blow in a easterly direction. These winds tend to push the surface water toward the west also. As the water moves west it heats up even more because it's exposed longer to the sun.
Meanwhile in the eastern Pacific along the coast of South America an upwelling occurs. Upwelling is the term used to decribe when deeper colder water from the bottom of the ocean moves up toward the surface away from the shore. This nutrient-rich water is responsible for supporting the large fish population commonly found in this area. Indeed, the Peruvian fishing grounds are one of the five richest in the world.