I cant post links of screen shots so you wil just have to go to the DawnGuard trailer timed points to see what Im talking about. Other then the Soul Cairn Dawnguard is going to take place in Solstheim and ofcourse Skyrim itself.

Reason being if you look at the trailer at :56 mark you see a Giant creature with a club. A Frost Giant. And it looks exactly like Karstaag from Bloodmoon. 3 fingered hands, 4 eyes, 2 horns, covered in white fur. Now only three frost giants are mentioned in history. All mentioned from the island of Solstheim. 1 being Karstaag ofcourse and was killed by the player. 2nd being Guolog and was killed by someone named Einarr, as mentioned in "Thirsk, A History." Thirsk being a grand mead hall that serves as the home for a most valiant clan of Nord warriors on Solstheim, fyi. And 3rd Frost Giant rumored for the unnaturally cold fog which appeared in a valley in Solstheim.

Only 3 Frost Giants in History and are only known to be on Solstheim. 2 of the 3 are known dead. 1 to be a rumor. And 1 seen in the DawnGuard Trailer. Solstheim is not far from WinterHold eather. And it has both lush green forrest and dreaded ice/snow terrain as shown in the trailer.

And at the 1:15 mark in the trailer you see DragonsReach (WhiteRun Castle) and it seems to be taking a big part in blocking out the sun.

The world must know.