The purpose of sea monsters in "Carta Marina".  

Image 1) "Carta Marina"

"Carta Marina"  is the oldest known map of Scandinavia. And it's drawn by Olaus Magnus (1490-1557) in 1539. That man used 12 years for that work. The thing is that the purpose of sea monsters on that map is simple. They are meant to warn people that water is a dangerous element. 

And if the ship goes too far, it faces many things like pirates. But the fact is that the purpose of those figures might also remember that blue color is water. In the year 1539 maps were not so common as they are today. 

Another thing is that the ships were more primitive in that time than they were in the time of the great sails at 18h. century. Things like giant squids also gave innovation for imaginational stories about "Krakens" and large snakes. The purpose of those stories might be also to warn about sea snakes and squids that can be dangerous.  The giant squid and colossal squids can be large, and they can also be dangerous. 

Another thing is that there is an image of the whirl in "Carta Marina", and the sea whirls can sink small ships. The thing is that the ships that Hansa used at the Baltic Sea were smaller and they had more primitive navigation tools than in ships that Columbus used in the American exploration.  So the purpose of the images of sea monsters was simply to give a warning about the sea monsters. 

The myth of "Kraken"

Image 2) The impression about "Kraken" attacking ship. The origin of that legend might be in colossal squids. And the overstating the size of that monster could be seen in that image. 

Image 3) In Jules Verne's novel "Twenty Thousand Leagues Under the Seas"  is introduced more realistic sea monster. That means the giant squid can be 9-15 meters long. Somedays those giant sea animals are found on the shores. 

By the way, Colossal squids are living on the Southern side of Earth. But there is the possibility that some unique individuals are swimming or drifting to the coast of Norway. But also giant squids are extremely large. So that sea monster might be behind the stories of "Krakens". The thing is that the "Krakens" was first mentioned in the Norwegian stories from the 12th century. 

The thing is that those sea monsters are mentioned as being half crabs and half squids. There have been introduced many theories about this sea monster. And some people believe that the "Kraken" was originally the tale of the "Hydra" the Greek sea monster. 

Then that tale turned into a story about "Kraken". There are introduced many explanations for that sea monster and the most popular is that "Kraken" was the giant squid. And some other people have introduced that this "Kraken" is a UFO or some kind of hybrid species. But that theory is only the theory. 

https://en.wikipedia.org/wiki/Carta_marina

https://en.wikipedia.org/wiki/Colossal_squid

https://en.wikipedia.org/wiki/Giant_squid

https://en.wikipedia.org/wiki/Olaus_Magnus

Images:

Image 1) https://en.wikipedia.org/wiki/Carta_marina

Image 2) https://en.wikipedia.org/wiki/Kraken

Image 3) https://en.wikipedia.org/wiki/Kraken

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