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This incredible time-lapse footage was captured by a daring oceanographer for the BBC a while ago, showing for the very first time how a brinicle forms. It’s essentially a salt water icicle that gets bigger and bigger as it hits the sea floor, and when it does its icy touch puts life to a halt instantly, like the poor sea urchins and starfish.

Frozen sea water is more like a sponge than a big lump you’re used to seeing in your kitchen freezer. In the Antarctic, this is typically as low as -20 degrees Celsius so when it meets with warm water underneath it (-2 degrees Celsius tops), the extreme temperature differences expands the salt water into an icy sheath. Because this is dense and cold, the formation called a “brinicle” sinks in a descending plume. Brinicles grow  both the Arctic and the Antarctic, and this particular one was shot by  cameramen Hugh Miller and Doug Anderson for the BBC One series Frozen Planet.

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“When we were exploring around that island we came across an area where there had been three or four [brinicles] previously and there was one actually happening,” Mr Miller told BBC Nature.

“It was a bit of a race against time because no-one really knew how fast they formed,” said Mr Miller.

“The one we’d seen a week before was getting longer in front of our eyes… the whole thing only took five, six hours.”

“That particular patch was difficult to get to. It was a long way from the hole and it was quite narrow at times between the sea bed and the ice,” explained Mr Miller.

“I do remember it being a struggle… All the kit is very heavy because it has to sit on the sea bed and not move for long periods of time.”