Arthur, King of the Arctic?

The Heroic Age points to an idea that I wasn't really familiar with before: that King Arthur was, at one point, credited with conquering the New World via Greenland.

According to Thomas Green, John Dee, when conjuring up precedent for a British Empire, relied not only on stories about Prince Madoc and St. Brendan, but also upon the idea that Arthur himself ruled the whole of the North. Now, Geoffrey credited him with conquering Scandinavia, but went no further--indeed, who knows what Geoffrey even knew of Greenland?  Scholars believed that Dee had invented this story, but Green points out that apparently it does predate Dee:

§7.  Mercator included a legend to his great wall map of 1569 that referred to Arthur in the following way:

Touching the description of the North parts, I have taken the same out of the voyage of James Cnoyen of Hartzevan Buske, which allegeth certain conquests of Arthur king of Britaine, and the most part, and chiefest things among the rest he learned of a certain priest in the king of Norway's court, in the year 1364. This priest was descended (in the fifth generation) from them which King Arthur had sent to inhabit these Islands

The article discusses whether this ultimately goes back to Geoffrey's Scandinavian conquest story, or whether it perhaps goes back to an even earlier tradition of a frozen Otherworld to the north. Of course, it's no surprise that anyone would connect a mythical conquest of the North with the Norwegian settlements of North America, and concoct a story of King Arthur doing the same, but earlier. And how irresistible the idea would be to an incipient British Empire.