Which ocean was named by Ferdinand Magellan for its apparently calm waters?

The ocean named by Ferdinand Magellan for its apparently calm waters is the Pacific Ocean.

Magellan encountered the ocean after his expedition navigated the rough waters around Cape Horn and passed through the strait now bearing his name. Once the fleet entered the vast ocean in 1520, the conditions seemed comparatively peaceful, prompting him to call it Mar Pacífico, meaning “peaceful sea” in Spanish and Portuguese.

The name captures an observation from one stage of the voyage, not the ocean’s permanent character. The Pacific is Earth’s largest ocean and contains extensive tropical, temperate, and polar waters. It is also home to typhoons, hurricanes, powerful currents, volcanic island arcs, and major earthquake zones, so its modern reputation is hardly always tranquil.

Earlier European descriptions used other names. Vasco Núñez de Balboa called it the South Sea after seeing it from the Isthmus of Panama. Magellan’s term eventually prevailed, while the ocean was also temporarily known as the Sea of Magellan. His expedition crossed the Pacific en route to the Philippines, though Magellan himself died there in 1521.