A bizarre underwater "icicle of death" filmed by a BBC crew.

Hugh had little room to position himself and the cameras under the ice

"With timelapse cameras, specialists recorded salt water being excluded from the sea ice and sinking. The temperature of this sinking brine, which was well below 0C, caused the water to freeze in an icy sheath around it. Where the so-called brinicle met the sea bed, a web of ice formed that froze everything it touched, including sea urchins and starfish. The unusual phenomenon was filmed for the first time by cameramen Hugh Miller and Doug Anderson for the BBC One series Frozen Planet."

Link to "Brinicle" article on BBC