A period of extreme cold makes the existence in northern Greenland impossible. When it became again possible there to survive, new migrants arrived from the interior of Canada, who moved to Greenland. The Dorset Culture spread from Hudson Bay northward and to the East, to Labrador. From 600 BP to 900BP it is present on the West coast of Greenland. This culture originated in the contact area with Indians and was thus familiar with boats, “it smelled of forest”, as the Danish researcher Jorgen Meldgaard termed it. In excavations of an Iquitag cultural site in Northern Alaska was found a toy kayak. This discovery is dated at 500 BP, that is, in the time of the Dorset culture. It represents a transition stage between the open boat and the decked one-person boat, the later kayak.

actual note:
Dorset longhouse found near Etah.
During archaeological field research in the surroundings of Etah near Smith Sund relics of the largest longhouse known so far have been found by american explorers and employees of the Greenland National Museum. There is not known a lot about those houses and their functions.
The later Dorset Culture existed in Greenland from 700 until 1300 (according to the Museum: from 600 until 900 in the Northwest and from 600 until 1100 in the Northeast) north of Thule

The harpoon heads of the Dorset culture are not identical to the blades which where used for kayak hunting. They are not similar to the ones “loose in the grip”. Copy from the book:
DEN GRØNLANDSKE KAJAK OG DEN REDSKABER
Nyt Nordisk Forlag Arnold Busk 1975