As if surviving the freezing waters of the polar regions isn’t hard enough, some marine animals face a terrifying salty underwater stalactite skulking slowly towards them. Those that don’t or can’t move away in time – like slow-moving starfish and urchins – freeze to death in its clutches.
These lethal ice tubes are known as brinicles, shortened from brine icicles because they are icicles made of brine (very salty water).
They form because the air is desperately cold compared to the mildly chilly seawater.
Above the surface, temperatures can dip as low as -40°C but the ocean water hovers at around -2°C. This causes the seawater under floating sea ice to start freezing.
The formation of this ice pushes out any salt particles, which flow into the surrounding seawater to create an extra salty liquid called brine.
This additional salt makes the water denser than normal seawater, making the brine sink down through the water column. Brine needs colder temperatures to freeze. But, as it touches the seawater around it, this frigid liquid starts to freeze the water on its outer edge, creating an eerie hollow cylinder with brine flowing inside.
- What are ice worms and how do they survive freezing conditions?
- Can any animals survive freezing? How some species stay alive despite having a body temperature of zero or below
Starting at the surface, brinicles creep like a snail downwards through the water creating a frozen trail behind them. When it reaches the seafloor, it can trap the animals it encounters and freeze them to death. That’s why some call it the ‘finger of death’,
Slowly, this perilous pipe sinks further and further until it hits the seafloor. “When it does, the treachery begins,” writes the California Academy of Sciences’ Michael Bartalos in his blog The Long View. “As the extra cold brine spreads over the seabed, it forms a web of ice, trapping everything in its path.”
Scientists have been aware of these slow-mo death traps for several decades but their formation was only filmed for the first time in 2011.
The BBC Frozen Planet footage shows the ghost-like phenomenon inching its lethal fingers downwards until it reaches the seabed. “As it touches the seafloor, it kills whatever living thing it contacts by encasing it in a tomb of ice,” says David Attenborough in the show’s narration.
Sea stars scurry around the brinicle with some, horrifyingly, even unwittingly scampering towards it, only to meet their death in its icy grasp. In one haunting frame, a perished sea star reaches its arm above the frozen ice, as if in one last, desperate attempt to escape its fate.
eliDespite being a bringer-of-death for many creatures, some scientists believe these strange ‘sea stalactites’ have the right conditions for life on Earth to begin. “Like hydrothermal vents, brinicles have high concentrations of chemical compounds, electric potentials that may help jump-start life,” writes Bartalos.
