Answer:
The body of water that joins the Southeastern Pacific and the Southwestern Atlantic oceans is the Beagle Channel.
Step-by-step explanation:
The Beagle Channel is a body of water located on the island of Tierra del Fuego, at the southernmost point of the South American continent. This channel, whose sovereignty is shared between Chile and Argentina, is considered a bioceanic passage between the Atlantic Ocean and the Pacific Ocean, since its two mouths are located one in each ocean. At the shore of the channel is the city of Ushuaia, Argentina, considered the southernmost city in the world.