The Brinicles Underwater Icicles of Death
Explained and Their Impact on Marine Life
Brinicles, sometimes called “underwater icicles of death,” are hollow ice formations that grow beneath the sea ice in polar regions when supercooled, salty brine escapes and freezes the seawater it touches. These icy tubes slowly extend downward from the ice above, resembling frozen fingers that reach toward the ocean floor. The combination of chilling cold and concentrated salt creates the right conditions for these rare and fascinating natural structures to form.
As a brinicle descends, it can trap and freeze any sea life that happens to be in its path, including small creatures such as sea stars and urchins. This dramatic effect gives brinicles their eerie nickname, as they leave behind stark reminders of their presence—patches of lifeless seafloor under the icy Antarctic waters.
What Are Brinicles?
Brinicles are rare underwater ice formations that form in cold ocean environments, particularly under sea ice. They are sometimes known by the nickname “ice stalactites” or the chilling label, “icicles of death,” due to their dramatic effect on marine life.
Definition and Characteristics
A brinicle is a tube-shaped structure made of ice that grows downward from the underside of sea ice into the ocean. It forms when supercooled brine—extremely salty and cold water—seeps out of forming sea ice and meets the less salty seawater below. This process lowers the freezing point of seawater in contact with the brine, causing ice to rapidly form around the descending plume.
Brinicles often resemble underwater icicles or ice stalactites, usually appearing clear to opaque and sometimes reaching several feet in length. Due to the unique chemical interactions, they are rarely seen except in polar regions like the Arctic and Antarctic.
These formations are transient and fragile. Their presence affects the immediate environment, particularly small marine organisms unable to escape their slow, freezing advance.
Discovery and Early Exploration
Brinicles were first noticed in scientific observations in the 1960s during research expeditions to the polar regions. Early explorers of polar seas sometimes reported odd features beneath pack ice, but it was only after underwater photography and direct scientific study improved that the brinicle phenomenon was confirmed.
Technological advances, such as underwater cameras, allowed researchers to capture real-time footage of brinicle formation. The process was observed to be rapid yet delicate, with entire brinicles forming within a few hours under the right conditions.
Although they have been known to science for decades, brinicles remain relatively rare sightings because the specific combination of temperature, salinity, and water movement is needed for their formation.
The Term ‘Icicle of Death’
The dramatic phrase “icicle of death” is used to describe brinicles due to their lethal effect on some benthic marine organisms. As the brinicle touches the ocean floor, the surrounding water quickly freezes, trapping or killing slow-moving creatures like starfish and sea urchins.
These areas beneath active brinicles may develop pockets called “black pools of death,” which are highly saline and lethal to most sea life. The nickname “icicle of death” underscores the ecological impact of these transient ice stalactites.
Researchers use this term to highlight the role of brinicles not just as geological curiosities, but as factors shaping microhabitats on the ocean floor. Their slow descent and freezing trail mark distinctive patterns in polar marine ecosystems.
How Brinicles Form
Brinicles are unusual underwater ice structures that grow beneath sea ice under very specific conditions. The process relies on interactions between freezing temperatures, saline water, and the properties of brine as seawater turns to ice.
Freezing Process in Saline Waters
When ocean water begins to freeze, the ice formation excludes most of the salt, creating nearly pure ice and pushing concentrated brine out. This super-cold brine, which has a lower freezing point than regular seawater, becomes trapped in a network of saline brine channels within the ice.
As more ice forms above, denser and colder brine accumulates, and eventually, it escapes downward through these channels. The brine’s higher density causes it to sink, creating a brine plume that starts moving toward the ocean floor.
As the brine plume comes into contact with the comparatively warmer and less saline ocean water, the temperature around the plume drops sharply, causing the surrounding seawater to freeze. This results in the formation of a hollow ice tube—the brinicle.
Role of Brine and Saltwater
The composition and movement of brine drive the development of brinicles. Brine is essentially seawater that has become significantly saltier due to the freezing process. Its salinity increases as more ice forms, and with increased salinity, the brine becomes denser and heavier than the surrounding ocean water.
Brine escaping from the ice creates a continuous flow, where the plume cools the nearby water to below its freezing point. The brine's interaction with this water triggers the immediate freezing of seawater on contact, expanding the brinicle downward.
As this process repeats, the brinicle grows as long as there is a supply of cold, dense brine. Sometimes, the accumulated brine collects into small pools known as brine pools or brine lakes on the seafloor, further affecting the surrounding marine environment.
Environments Where Brinicles Occur
Brinicles form only in specific cold-water environments where super-chilled brine and sea ice interact. Their growth is driven by water temperature, salinity, and the presence of floating sea ice over cold ocean floors.
Polar Regions and Sea Ice
Brinicles are mainly found in polar regions, such as the Arctic and Antarctic. These locations offer the combination of very low temperatures and abundant sea ice that is crucial for their formation.
Thick floating ice, like the Antarctic pack near the Ross Archipelago and around Little Razorback Island, traps seawater and causes salt to concentrate as the ice forms. This creates dense, supercooled brine that eventually seeps through channels and escapes into the ocean below.
As this brine exits from under the ice, it rapidly freezes the slightly warmer seawater it encounters. This process forms the characteristic hollow, finger-like icicles of brinicles.
Observation of brinicle formation is rare, in part due to the isolated and harsh conditions of these polar environments. Scientists rely on fieldwork under floating ice and sub-zero temperatures to document these phenomena.
Ocean Floor and Sea Bed
The seafloor beneath floating sea ice provides the stage for brinicles to develop and descend. When dense brine seeps downward, it follows the contours of the ocean bed, often creating a visible path across the sediment.
As the brinicle extends to the seabed, it may envelop small pools of seawater. These pools eventually freeze, posing a threat to slow-moving bottom-dwelling creatures in direct contact.
Porous ice on the seafloor allows the supercooled brine to continue its descent, sometimes connecting with the ocean floor for several meters. This environment, often beneath thick icepacks, is necessary for sustaining brinicle growth and ensuring the phenomenon is visible long enough to be studied.
Brinicles and Sea Creatures
Brinicles form underwater when cold, salty brine descends from sea ice, freezing surrounding seawater and creating icy tubes. These structures can impact the local habitat and present hazards to various bottom-dwelling sea creatures.
Impact on Bottom-Dwelling Sea Life
Brinicles descend from sea ice toward the ocean floor as dense, supercooled brine flows downward, freezing everything in its path. When a brinicle reaches the seabed, it can trap sea creatures in quickly expanding ice.
Starfish and sea urchins, which move slowly along the seafloor, are particularly vulnerable. Ice from the brinicle can surround and immobilize them, leading to fatal conditions. The icy layer deprives these animals of mobility and isolates them from oxygenated water, resulting in death within minutes.
Brinicles create so-called “black pools of death” — isolated areas of ultra-salty, cold brine where few organisms can survive. These localized effects can cause a rapid drop in population for exposed species directly beneath the descending brinicle.
Affected Species and Ecosystem Consequences
The main species affected include brittle stars, sea urchins, and other slow-moving bottom-dwelling invertebrates. Their limited ability to escape makes them prone to being caught in the expanding ice.
Smaller fish and mobile crustaceans can often avoid brinicles, but sessile and slow creatures are at risk.
The sudden freezing can result in mass die-offs in the immediate area.
When sea urchins and starfish are killed, the balance of the benthic ecosystem shifts. Predators may lose food sources, while surviving populations can leave behind empty patches on the seafloor. This temporary habitat loss can alter local food webs, disrupt breeding grounds, and limit biodiversity along the affected region.
Physical Structure of Brinicles
Brinicles are striking ice structures formed under polar sea ice, where the unique environment produces features rarely seen outside of frozen planets. Their development involves intricate interactions between supercooled brine, ice crystals, and salty seawater.
Ice Crystals and Icy Sheath
A brinicle begins to take shape when dense, supercooled brine flows from sea ice into the surrounding sea. The brine, being colder and saltier than the seawater, causes the nearby water to freeze rapidly.
Ice crystals form spontaneously at the boundary between the descending brine and the seawater. This process creates a hard, icy sheath that surrounds the concentrated brine stream. The sheath is solid and semi-transparent, forming a protected tube through which the brine can continue to descend toward the ocean floor.
The outer surface of the brinicle is less saline and slightly less cold than the brine inside, giving it a layered structure. It can resemble an underwater icicle, but with a hollow core, and can extend for several meters.
Component Composition Function Icy sheath Pure water ice Insulates brine flow, structure Brine interior Super saline Drives downward growth Ice crystals Rapidly formed Adds strength to the sheath
Formation of Stalactites
Brinicles are often described as underwater stalactites due to their downward growth from the ice base. As the cold, salty brine exits the sea ice and sinks, it instantly freezes the less saline seawater it encounters.
This accretion of ice forms a descending icicle, or stalactite, beneath the floating ice sheet. The tip of the brinicle remains active as long as the brine continues to flow and freeze the seawater on contact.
Unlike cave stalactites, which form from mineral deposits and grow over decades or centuries, brinicles can develop within hours or days under the right conditions. The process is only possible in the polar regions, where sea ice, extremely cold temperatures, and relatively calm waters enable the necessary conditions.
Their presence under Antarctic and Arctic ice sheets highlights the complex and fascinating ice structures that can exist in environments reminiscent of a frozen planet.
Brinicles in Popular Science and Media
Brinicles have gained public recognition through detailed visual documentation and ongoing scientific investigation. Their unique formation and deadly impact on marine life have made them noteworthy in both media and research communities.
Documentaries and Visual Recordings
Brinicles appeared prominently in the BBC One documentary series Frozen Planet. The show captured time-lapse footage, revealing how these icy structures grow along the ocean floor. The imagery provided clear views of their shape and movement, highlighting how brinicles can freeze animals that cross their path.
The documentary’s stills and videos helped make the phenomenon accessible to non-scientists. These memorable recordings led to wider public interest and prompted further exploration by other filmmakers and photographers.
Such visual documentation is rare because brinicles typically form under extreme Antarctic conditions. Efforts to capture their development required specialized equipment and careful planning.
Brinicles in Scientific Research
Brinicles have intrigued scientists due to their physical processes and environmental effects. Researchers have studied the salt rejection from freezing seawater, which drives the formation of icy tubes descending to the seafloor. Cold, dense brine flows from sea ice, creating these structures in unique thermal and chemical conditions.
Scientific articles and field studies have mapped where brinicles are most likely to appear beneath Antarctic ice. Oceanographers and polar scientists examine how brinicles impact nearby ecosystems, particularly the rapid freezing of starfish and sea urchins.
Research teams combine underwater observation, chemical sampling, and temperature monitoring to analyze brinicle formation. This ongoing work helps improve understanding of polar marine dynamics, ice chemistry, and the interactions between physical processes and living species.
