Gunnbjørn was blown off course while sailing from Norway to Iceland. He and his crew sighted islands (Gunnbjörn's skerries) lying close off the coast of Greenland, and reported this find. Gunnbjørn did not land.
Greenland is physically and culturally part of North America; it is separated from Ellesmere Island by only a narrow strait, so this constitutes the first definitively established European contact with North America.
The exact date of this event is not recorded in the sagas. Various sources cite dates ranging from 876 to 932, but these must remain little more than guesses; but the early 10th century is probably more likely than earlier.
The first purposeful visit to Gunnbjørn's islands was by Snæbjörn Galti around 978, followed soon after by Eric the Red who also explored the main island of Greenland, and soon established a settlement. But neither Snaebjørn nor Eric were sailing blind; they knew well of the location reported by Gunnbjørn Ulfsson.
A number of modern placenames in Greenland commemorates Gunnbjørn, most notably Gunnbjørn Fjeld (3,694 m a.s.l.).
- Encyclopaedia Britannica 10. Chicago. 1955. p. 858.