These Marines are playing in the snow. From the video's description:
U.S. Marines M1A1 tank crews work with the Norwegian Telemark Battalion on techniques of driving tracked vehicles in winter conditions on an snow/ice track.
A Norwegian Leopard 2 Main Battle Tank leads U.S. Marine M1 Abrams, from the Combined Arms Company, to various cold-weather training sites for tracked vehicles in Rena, Norway.
Watch in full-screen mode for best results.
It may be training, and hard work, but it also looks as if they're having a lot of fun. Pushing sixty-odd tons of armor plate sideways down an ice track - deliberately? That's fun!