Ice stalactite
An ice stalactite (also brinicle – brine icicle) 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 stalactite or icicle.
Known since the 1960s, the generally accepted model of their formation was proposed by the US oceanographer Seelye Martin in 1974.[1] 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.[2]
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Structure [edit]
Formation [edit]
The formation of ice from salt water produces marked changes in the composition of the unfrozen water. When water freezes, most impurities are forced out of solution; even ice from seawater is relatively fresh compared with the seawater it is formed from. As a result of forcing the impurities out, sea ice is very porous and spongelike, quite different from the solid ice produced when fresh water freezes.
As the seawater freezes and salt is forced out of the pure ice crystal lattice, the surrounding water becomes more saline. This lowers its freezing temperature and increases its density. The lower freezing temperature means that the surrounding water does not freeze to the ice immediately, and the higher density means that it sinks. Thus tiny tunnels called brine channels are created all through the ice as this supersaline, supercooled water sinks away from the frozen pure water. The stage is now set for the creation of a brinicle.
As this supercooled saline water reaches unfrozen seawater below the ice, it will cause the creation of additional ice. If the brine channels are relatively evenly distributed, the ice pack grows downward evenly. However, if brine channels are concentrated in one small area, the downward flow of the cold water, now so saline that it cannot freeze at its normal freezing point, begins to interact with unfrozen seawater as a flow. Just as hot air from a fire rises as a plume, this cold water descends as a plume. Its outer edges begin to accumulate a layer of ice as the surrounding water, cooled by this jet to below its freezing point, ices up. This is a brinicle: a "chimney" of ice that contains a flow of this supercold, supersaline water.
When the brinicle becomes thick enough, it becomes self-sustaining. As ice accumulates around the down-flowing cold jet, it forms an insulating layer that prevents the cold, saline water from diffusing and warming. As a result, the ice jacket surrounding the jet grows downward with the flow. It is like an icicle turned inside-out; rather than cold air freezing liquid water into layers, down-rushing cold water is freezing the surrounding water, enabling it to descend even deeper. As it does, it creates more ice, and the brinicle grows longer.
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. In 2011, brinicle formation was filmed for the first time.[3]
References [edit]
- ^ Martin, Seelye (1974). "Ice stalactites: comparison of a laminar flow theory with experiment". Journal of Fluid Mechanics 63 (1): 51–79. doi:10.1017/S0022112074001017.
- ^ Jeffs, Kathryn (2011-12-28). "Anatomy of a shoot: Filming frozen planet's brinicle". BBC. Retrieved 2011-12-28.
- ^ "'Brinicle' ice finger of death filmed in Antarctic". British Broadcasting Corporation.
External links [edit]
- Video Footage – Attenborough-narrated timelapse of brinicle formation
- 'Brinicle' ice finger of death
- Attenborough's polar trip: The tech that made Frozen Planet possible
