So I never knew this before, but apparently when seawater freezes, it forces salt out, thereby making the water surrounding it more saline. That starts a chain reaction with which you may be more familiar: the saline water has a lower freezing point and higher density, so as this super cold water freezes, it starts to sink away from the surface ice, creating an ice stalactite, otherwise known as a brinicle. But as David Attenborough explains, this is just the beginning:
I love how scientists have managed to figure out exactly why this happens...