The icy phenomenon, also known as the “Icicle of Death”, is caused by cold sinking brine.
In winter, the air temperature above the sea ice can be below -20C, whereas the sea water is only about -1.9C. Heat flows from the warmer sea up to the very cold air, forming new ice. The salt in this newly formed ice is concentrated and pushed into brine channels. As it is very cold and salty, it is denser than the water beneath. As the cold dense brine solution comes in contact with the warmer water below the surface, a brinicle forms.
Brinicles grow fairly rapidly with some studies recording growth of 2 metres in less than 10 hours. In this photo, which was taken in Antarctica’s McMurdo Sound, the ice has reached the sea floor, forming a pillar.
Here is a cool timelapse video of the formation of a brinicle, it’s a must watch!
Photo courtesy of: Bill Curtsinger