Two Russian divers descended 102 meters (335 feet) during an 80-minute dive, in the White Sea, setting new record.
The biggest differences between ice diving and other dives, are the access to the surface, the thickness of the sea ice (can be several meters), and the freezing of the diving regulators, that regulate the air in an air tank.
The footage emerged on Sunday, showing the process of the dive.
Elizabeth Calvert, another experienced ice diver, explains the code to NOAA:
Line signals are our only form of communication from under the ice to the surface. One pull means “o.k.” Two pulls means “give me more slack in the line.” Three pulls means “take up slack in the line.” And a lot of pulls means “pull me out!”