What is "brinicle"

A brinicle ( brine icicle, also known as ice stalactite) forms beneath sea ice when a flow of extremely cold, saline water is introduced to an area of ocean water, being the undersea equivalent of a hollow stalactite or icicle.

Known since the 1960s, the generally accepted model of their formation was proposed by the US oceanographer Seelye Martin in 1974. The formation of a brinicle was first filmed in 2011 by producer Kathryn Jeffs and cameramen Hugh Miller and Doug Anderson for the BBC series Frozen Planet.