In the mysterious world below the ice of the Arctic and Antarctic sea, salty frozen fingers of ice slowly descend towards the ocean floor …
Brinicles are structures that resemble stalactites that reach all the way down to the seabed, extinguishing life for all creatures in it’s paths.
The waters freezing process forces out salt, creating intensely cold, salty water, called brine that does not freeze because of the high salt content. This is heavier than normal sea water and why it tends to sink. On the way down, the super-cold brine will freeze any surrounding water that it comes in contact with and As the water freezes, it forms an icy tube around the brine. When it reaches the sea floor, the cold brine extends across the seabed. This ice can grow fast enough to overtake slow moving marine life such as starfish and sea urchins, engulfing them and fatally freezing them to the spot.
Fortunately for these creatures, brinicles require relatively calm conditions at sea for them to grow, they’re not all that common.

The best description of what a brinicle is, would be to call it an underwater icicle, or ice stalactite
A complex phenomenon a brinicle is limited in size by the depth of the water, the growth of the overlying sea ice fueling its flow, and the surrounding water itself.

The concentrated brine is cold enough to freeze other seawater on contact and, as it descends, forms a tube shape with the inner wall constantly melting and the outer wall freezing, growing downwards into an icy stalactite.

When the brinicle reaches the sea floor, The entire process generally takes between four and twelve hours.