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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. When this plume comes into contact with the neighboring ocean water, its extremely low temperature causes ice to instantly form around the flow. This creates a hollow stalactite, or icicle, referred to as a brinicle.

The formation of ice from salt 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 the seawater freezes and salt is forced out of the pure ice crystal lattice, the surrounding water becomes more saline as concentrated brine leaks out. Because the brine possesses a lower concentration of water, it therefore attracts the surrounding water. 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. A brinicle has now been formed, resembling an inverted "chimney" of ice enclosing a downward flow of this supercooled, super salinated water. 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. The salinity of the liquid water within the brinicle has been confirmed to vary depending on the temperature of the air.

At the time of its creation, a brinicle resembles a pipe of ice reaching down from the underside of a layer of sea ice. 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. To do so, the supercold brine from the pack ice 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 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. However, unlike brine pools created by cold seeps, 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 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. The first numerical model for a brinicle formation was developed in 2023 by researchers at the National University of Colombia in collaboration with the Lawrence Livermore National Laboratory.

Quick Facts

• 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.
• When this plume comes into contact with the neighboring ocean water, its extremely low temperature causes ice to instantly form around the flow.
• This creates a hollow stalactite, or icicle, referred to as a brinicle.
• 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.
• 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.

Source material: Wikipedia - "Brinicle". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.