Brinicle
A brinicle (brine icicle, also known as an ice stalactite) is a downward-growing hollow tube of ice enclosing a plume of descending brine that is formed beneath developing sea ice. As seawater freezes in the polar ocean, salt brine concentrates are expelled from the sea ice, creating a downward flow of dense, extremely cold, saline water, with a lower freezing point than the surrounding water.