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A brinicle (
brine Brine is a high-concentration solution of salt (NaCl) in water (H2O). In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawater, on the lower end of that of solutions used fo ...
icicle, also known as ice stalactite) is a downward-growing hollow tube of ice enclosing a plume of descending brine that is formed beneath developing
sea ice Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's ...
. As
seawater Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has app ...
freezes in the polar ocean, salt brine concentrates are expelled from the sea ice creating a downward flow of dense, extremely cold, and
saline water Saline water (more commonly known as salt water) is water that contains a high concentration of dissolved salts (mainly sodium chloride). On the United States Geological Survey (USGS) salinity scale, saline water is saltier than brackish water, ...
, with a lower freezing point than the surrounding water. When this plume comes into contact with the neighboring
ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...
water, its extremely low temperature causes ice to instantly form around the flow. This creates a hollow
stalactite A stalactite (, ; from the Greek 'stalaktos' ('dripping') via ''stalassein'' ('to drip') is a mineral formation that hangs from the ceiling of caves, hot springs, or man-made structures such as bridges and mines. Any material that is soluble an ...
, or
icicle An icicle is a spike of ice formed when water falling from an object freezes. Formation and dynamics Icicles can form during bright, sunny, but subfreezing weather, when ice or snow melted by sunlight or some other heat source (such as ...
, referred to as a brinicle.


Formation

The formation of ice from
salt water Saline water (more commonly known as salt water) is water that contains a high concentration of dissolved salts (mainly sodium chloride). On the United States Geological Survey (USGS) salinity scale, saline water is saltier than brackish water, ...
produces marked changes in the composition of the nearby unfrozen water. When water freezes, most impurities are excluded from the water crystals; even ice from seawater is relatively fresh compared to the seawater from which it is formed. As a result of forcing the impurities out (such as salt and other ions)
sea ice Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's ...
is very
porous Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...
and spongelike, quite different from the solid ice produced when
fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does includ ...
freezes. As the seawater freezes and salt is forced out of the pure ice
crystal lattice In geometry and crystallography, a Bravais lattice, named after , is an infinite array of discrete points generated by a set of discrete translation operations described in three dimensional space by : \mathbf = n_1 \mathbf_1 + n_2 \mathbf_2 + n ...
, the surrounding water becomes more saline as concentrated brine leaks out. This lowers its freezing temperature and increases its
density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematica ...
. Lowering the freezing temperature allows this surrounding, brine-rich water to remain liquid and not freeze immediately. The increase in density causes this layer to sink. 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. Water moves from high to low concentrations. Because the brine possesses a lower concentration of water, it therefore attracts the surrounding water. Due to the cold temperature of the brine, the newly attracted water freezes. 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 brine (now so salt-rich 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, dense water sinks as a plume. Its outer edges begin accumulating a layer of ice as the surrounding water, cooled by this jet to below its freezing point, ices up. A brinicle has now been formed, resembling an inverted "chimney" of ice enclosing a downward flow of this supercooled, 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. The inner wall temperature of the stalactite remains on the salinity-determined freezing curve, so as the stalactite grows and the temperature deficit of the brine goes into the growth of ice, the inner wall melts to dilute and cool the adjacent brine back to its freezing point. 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. The salinity of the liquid water within the brinicle has been confirmed to vary depending on the temperature of the air. The lower the temperature, the greater the brine concentration. A January 2014 along the coast of the
White Sea The White Sea (russian: Белое море, ''Béloye móre''; Karelian and fi, Vienanmeri, lit. Dvina Sea; yrk, Сэрако ямʼ, ''Serako yam'') is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is s ...
recorded that at an air temperature of −1 °C the brine salinity was between 30 and 35 psu while the salinity at sea was 28 psu. When the temperature was −12 °C the salinity of the brine increased to between 120 and 156 psu.


Structure

At the time of its creation, a brinicle resembles a
pipe Pipe(s), PIPE(S) or piping may refer to: Objects * Pipe (fluid conveyance), a hollow cylinder following certain dimension rules ** Piping, the use of pipes in industry * Smoking pipe ** Tobacco pipe * Half-pipe and quarter pipe, semi-circul ...
of
ice Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opa ...
reaching down from the underside of a layer of
sea ice Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's ...
. Inside the pipe is extremely cold and saline water produced by the growth of the sea ice above, accumulated through brine channels. At first, brinicles are very fragile, the walls are thin, but the constant flow of colder brine sustains the brinicle growth and hinders its melt that would be caused by the contact with the less cold surrounding water. As ice accumulates and the walls becomes thicker, brinicles becomes more stable. A brinicle can, under the proper conditions, reach down to the
seafloor The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...
. To do so, the supercold brine from the
pack ice Drift ice, also called brash ice, is sea ice that is not attached to the shoreline or any other fixed object (shoals, grounded icebergs, etc.).Leppäranta, M. 2011. The Drift of Sea Ice. Berlin: Springer-Verlag. Unlike fast ice, which is "fasten ...
overhead must continue to flow, the surrounding water must be significantly less saline than the brine, the water cannot be very deep, the overhead sea ice pack must be still, and currents in the area must be minimal or still. If the surrounding water is too saline, its
freezing point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...
will be too low to create a significant amount of ice around the brine plume. If the water is too deep, the brinicle is likely to break free under its own weight before reaching the seafloor. If the icepack is mobile or currents too strong, strain will break the brinicle. Under the right conditions, including favorable ocean floor topography, a
brine pool A brine pool, sometimes called an underwater lake, deepwater or brine lake, is a volume of brine collected in a seafloor depression. The pools are dense bodies of water that have a salinity that is three to eight times greater than the surround ...
may be created. However, unlike brine pools created by
cold seep A cold seep (sometimes called a cold vent) is an area of the ocean floor where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool. ''Cold'' does not mean that the temperature of the seep ...
s, brinicle brine pools are likely to be very transient as the brine supply will eventually cease. On reaching the seafloor, it will continue to accumulate ice as surrounding water freezes. The brine will travel along the seafloor in a down-slope direction until it reaches the lowest possible point, where it will pool. Any bottom-dwelling sea creatures, including
starfish Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfis ...
or
sea urchin Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells ( tests) ...
s, can be encased in this expanding web of ice and be trapped, ultimately freezing to death.


Research history

Brinincles have been known since the 1960s. The generally accepted model of their formation was proposed by the US
oceanographer Oceanography (), also known as oceanology and ocean science, is the scientific study of the oceans. It is an Earth science, which covers a wide range of topics, including ecosystem dynamics; ocean currents, waves, and geophysical fluid dynami ...
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''.


References

{{Reflist


External links


'Brinicle' ice finger of deathAttenborough's polar trip: The tech that made Frozen Planet possible
Sea ice