If you're swimming in the ocean and come across the 'finger of death' — you should probably get out

Underneath the pristine beauty of snow-capped Antarctica lies a hostile habitat that makes it difficult even for some of the natives to survive. A Weddell seal, to name one, gets locked up in a sea of ice with its breathing hole at compromise threatening its chances of survival. During winter months, with surface temperatures falling to as low as -76° Fahrenheit (-60° Celsius), the deep sea transforms into a refuge for marine life as the sea maintains a constant warmer temperature of 28.4 °F (-2 °C). But does it really protect the creatures from the dangers of the surface? Not completely. The ‘finger of death” is a rare phenomenon that is as sinister as it appears killing all life that comes its way, as documented by BBC Earth (@bbcearth) on YouTube. 

The intense contrast in temperatures, about 50 degrees, between the surface and depths of the sea causes surface sea ice to crack. This results in brine leaking from the cracks and sinking into the sea due to its higher density than seawater and forming a pillar of frozen water as the icy brine interacts with warmer water. This finger-like formation is called a brinicle. “For the creatures of the seabed, it’s a stealthy finger of death,” says the narrator. The frigid surface and warmer sea have remained so for 25 million years, protecting a diversity of life underwater barely enduring the wrath of winter cold.

But some creatures, the likes of starfish and urchins, fail to escape the brinicle that traps them in ice soon after touching down on the seabed. In the documentary, the thriving seabed is visibly alarmed as the brinicle approaches the seafloor. Flocks of starfish and urchins move away from the finger-like brinicle as soon as it touches the ground and unleashes a spell of ice that “imprisons” any and everything in its path. The spread of the ice sheet is called anchor ice. According to a report by HowStuffWorks, brinicles are incredibly fragile and may shatter at the slightest touch. They also require a precise set of conditions for its formation that make them a rare observation. 

This sinister phenomenon was first observed in the early 1970s, discovered by oceanographers Paul Dayton and Seelye Martin who then synthesized artificial brinicles in their laboratory in Seattle, according to National Geographic, as reported by the aforementioned source. Additional research is still needed to fully understand brinicles and their formation. These ice pillars are typically 25 cm in diameter and grow several meters each day, The Guardian reported. Brinicles usually entrap slow-moving creatures and freeze them to death. The name comes from the fact that brinicles are essentially composed of frozen brine, which is a highly concentrated solution of salt and water, often toxic enough to kill life.

However, brine can be a rich source of chlorides and sulfates of magnesium and potassium, per Brittanica. Natural forms of brine are prevalent in salt lakes, underground, and seawater, of course. The substance has found purpose in the human world as well, used as a preservative in meat-packing and as heat-transfer media due to their substantially low freezing temperatures.

You can follow @bbcearth on YouTube for more interesting videos on marine life.