Ok, these are South Korean divers, and they're about to hit a hole in the ice, this is just the preparation for that. It's some sort of contest, apparently.
It seems like many different cultures have this group of people who enjoy diving into ice-cold water in the middle of the winter. In the US the women have seemed to join in, at a ratio of 10 men for every woman; looks like the South Korean women have retained their senses so far.