In winter, Antarctica doubles in size and becomes larger than the US. Air temperatures can plummet between -10°C and -60°C.
But the ocean, which is home to sea stars, Weddell seals and whales, is a considerably warmer -2°C.
As this temperature remains relatively stable, plenty of life flourishes here. But the cold temperatures on the surface can still find a way to descend into the depths of the ocean.
A briner cold, also known as a brinicle, is made of incredibly cold and salty water (a by-product of freezing, where salt brine is expelled) that descends from the sheet ice. This concentrated brine is heavier than regular sea water so starts to sink downwards.
It freezes other seawater on contact, creating a pillar of ice. And when it reaches the sea floor, it spreads out (known as anchor ice) and can fatally freeze the creatures it encounters.
Brinicles were filmed for the first time in 2011, with the Frozen Planet filming team building a specialised timelapse kit to capture their astonishing power.
Top image: a brinicle near Ross Island, Antarctica. Credit: Getty