Hi Emily - just wanted to add to your statement that the cold tongue in the equatorial eastern Pacific "comes from deep ocean water that rises up near the South American coast, and is then spread westward by surface currents." Obviously that's true and major contributor to its formation and maintenance, but in addition to the coastal upwelling there's equatorial upwelling that also contributes cold water from below the thermocline that helps maintain or enhance the cold tongue to the west of the South American coast. The stronger the Trade winds the more Ekman "pumping" will occur that will bring colder water from below upward and reinforce the cold tongue along the equatorial zone. This plays an important role during La Nina episodes when the Trade winds are typically much stronger, so more equatorial upwelling will occur and the equatorial "cold tongue" will be even colder. Thanks!