In the early 16th century, Spanish explorer Vasco Núñez de Balboa crossed the Isthmus of Panama in 1513 and sighted the great "Southern Sea" which he named Mar del Sur (in Spanish). Afterwards, the ocean's current name was coined by Portuguese explorer Ferdinand Magellan during the Spanish circumnavigation of the world in 1521, as he encountered favorable winds on reaching the ocean. He called it Mar Pacífico, which in Spanish, Portuguese and Italian means 'peaceful sea'.
"Southern sea" sounds reasonable from the viewpoint of early Nordic seafarers. Based on a quick glance of the map, all of the Atlantic is south of Sweden.
