Deep beneath the waves, far down on the ocean floor, are scenes often associated with the stuff of nightmares: translucent fish with wide black eyes capable of seeing in the dark, shell fish with bioluminescent skeletons, and colossal squid so huge that no one has yet to picture them. All these creatures, though bizarre, are somehow quite expected, but it’s doubtful whether many people would imagine a lake lying down there, too.
As unlikely as it sounds, there are a handful of underwater lakes and rivers boasting their own mini ecosystems.
How do underwater lakes form?
Underwater lakes are brine pools. And believe it or not, even though people often refer to the ocean as the briny blue, while it’s constituted of salt water it is not brine… Brine refers to water with an extremely high concentration of salt, higher than that of normal sea water. It is produced through salt tectonics, or the movement of large salt deposits.
The lake featured was discovered in the Mexican Gulf. During the Jurassic period the waters here were shallow and became cut off from the ocean. The area soon dried out, leaving a thick layer of salt and other minerals up to 8km thick. When ocean water returned after the region rifted apart, the super-saline layer at the bottom of the Gulf became an underwater lake. Now brine, which is continually released from a rift in the ocean floor, feeds the lake.
“Deep-sea mussels living on the “shore” of the Brine Pool. These mussels use methane as their primary source of food, but also filter small particles from the water. The red worms in the bottom left corner are a newly described species of polychaete. The large fish in the middle of the picture is a deep-sea eel. Such fishes commonly visit the Brine Pool, where there is more abundant food than elsewhere on the deep-sea floor.” NOAA