Writing in the eighth-century AD, the German writer, Paulus Warnefridi, alludes to a legend which claims that the "sea navel" lies somewhere in the North. What he describes is a maelstrom: "that very deep abyss of the waters which we call the ocean's navel. It is said twice a day to suck the waves into itself and spew them out again."

The enormous differences between falling and rising tides has led to the formation of dramatic ocean currents at certain locations in the North. Most renowned is the Moskenes maelstrom. Olaus Magnus had also heard of these currents, and he plotted them on his chart. He writes:
"In this locality, during the flood tide, the sea wells up within the caves and at ebb tide it falls again, with a force as powerful as when torrents or swift rivers come rushing down. As I have said, navigation upon this sea is extremely perilous, for those who sail at the wrong time are suddenly snatched down into spiraling abysses."