Fuck Yeah Fluid Dynamics

In the frozen reaches of our planet, the atmosphere and ocean can interact in bizarre ways.  Under calm ocean conditions when the air at sea level is much colder than the water temperature brinicles—the underwater equivalent to an icicle—can form. The cold air above rapidly freezes ocean water at the surface, concentrating water’s salt content into a very cold brine which sinks rapidly. As this brine descends, it freezes the water around it into an ice sheath. As the brinicle grows and eventually reaches the sea floor, its cold temperatures can wreak havoc on the creatures living there.  

(Source: BBC)