Brinicles are unique formations of ice that hang downwards from the undersides of sea ice. This phenomenon occurs in the extremely cold and salty waters of the polar regions, where temperatures can drop well below freezing. Brinicles, also known as "icicles of death," are formed when a flow of extremely cold, dense saltwater sinks to the seafloor.
To understand how brinicles form, it is essential to grasp the concept of saltwater's behavior at supercold temperatures. When saltwater freezes, it forms ice with a lower salt content, as the salt is expelled from the forming ice crystals. This causes the remaining unfrozen water to become saltier and denser. In polar regions, where the temperatures are already freezing, this supercooled and super-salty water can reach temperatures as low as -20 degrees Celsius.
The formation process starts when seawater on the surface freezes, forming sea ice. Underneath the ice, cold polar water, denser than the surrounding seawater, begins to sink towards the seafloor. As this dense water sinks, it displaces the less dense water and creates a downward flow. Along with this flow, tiny ice flowers can form on the underside of the sea ice, creating a fragile icy structure.
The next stage of brinicle formation occurs when the brine-rich, supercooled water reaches the ocean floor. As the dense water spreads across the seabed, it starts to freeze the surrounding seawater. The ice that forms is not only colder but also saltier than the surrounding seawater, due to the rejection of salt during the initial freezing process. As a result, the ice continues to extract more and more salt from the surrounding water, causing the saltwater to become even denser.
The extreme density of the sinking water causes it to flow downwards like a brinicle. This icy tube grows gradually, elongating as more and more seawater freezes on contact. The brinicle's downward growth creates a hollow tube of ice that traps the surrounding water inside. The trapped water on the seabed freezes, forming a solid icy base that supports the structure.
Over time, the brinicle can reach the seafloor and continue growing upwards, while the surrounding seawater freezes around it. This growth process can take several hours, resulting in brinicles that can reach lengths of up to several meters. The expanding formation eventually becomes too heavy to support itself, causing it to collapse and disintegrate.
In conclusion, brinicles are formed by the sinking of extremely cold, dense saltwater, which freezes the surrounding seawater upon reaching the ocean floor. This continuous freezing creates a hollow tube of ice, known as a brinicle, that can grow downwards towards the seafloor and upwards above the sea ice. The unique combination of freezing temperatures, salt content, and seawater dynamics create these captivating formations in the polar regions.