Near Antarctica, salt water gets excluded from the ice, forming bring, which sinks quickly. This brine creates an icicle that reaches down to the ocean floor, freezing everything its path. The BBC caught the phenomenon in a time-lapse film. Watch.
The science is pretty awesome (as is much science).
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 from the bottom. The salt in this newly formed ice is concentrated and pushed into the brine channels. And because it is very cold and salty, it is denser than the water beneath.
The result is the brine sinks in a descending plume. But as this extremely cold brine leaves the sea ice, it freezes the relatively fresh seawater it comes in contact with. This forms a fragile tube of ice around the descending plume, which grows into what has been called a brinicle.
[via buzzfeed]