The Kara Sea was a sea on planet Earth, north of the Arctic Circle.

In the late 17th century, the Kara Sea, known then as the "Mare Tartaricum", was labeled on a map of Earth. (Star Trek: Enterprise, opening credits)

This map, known as "Harmonia macrocosmica seu atlas universalis et novus, totius universi creati cosmographiam generalem, et novam exhibens", was created by Andreas Cellarius. A scan of the original can be found here. On this map, there was an island to the west of Mare Tartaricum named Nova Zemla, now known as Novaya Zemlya. This relationship of sea to island was established as early as 1611 by the Flemish cartographer Jodocus Hondius. Through a process of elimination, the author J. Huston McCullough in his analysis of the Vinland Map, proved in 2005 that the Mare Tartaricum was a 17th century name for the Kara Sea.
This sea was labeled on a 21st century-era political map of Earth seen in the remastered "The Cage". This was a Central Intelligence Agency map published either in April 2007 or September 2008. [1] [2] The difference, which was not noticeable at the resolution of the image from the episode, was the addition of Kosovo, which gained its independence between the releases. The label "Kara Sea" was not legible to the viewer.