Discovery News had an article about the possibility of their being Native American blood in the Icelandic line from around the year 1000. Their study was genetic. At first when I read it, I thought how are they going to argue that, when it could be introduced at a much later time, but they dealt with this issue. So by the time I was done reading the article I was convinced.
However, on further reflection, I have to admit that they seem to have gone for the most romantic explanation. Yes, Greenland can sometimes be thought to be more Americas than Europe, but wouldn't a more likely explanation be that the mingling happened in Greenland and that Greenland settlers brought it back? Because the Norse were in Greenland a lot longer than they were in North America. And that colony disappeared, but we know that settlers came back from there to Iceland. Hey, even the ones who went to North America were mostly from Greenland, and some of them ended up back in Iceland.
I approve the tendency to reach for the romantic. It is what I would have done. But it seems there is a much more likely scenario than the one that they propose.