Brine Pools Are Lakes On The Bottom Of The Ocean
Some brine pools found in the Gulf of Mexico are more than 19 km (12 mi) long. They formed as salt—left behind from a dried-up sea, and buried beneath sediment—slowly rose up from beneath the ocean floor, dissolving to make brine. The brine is much denser than the surrounding seawater, and doesn't mix with it, creating a barrier that makes it look as though there's a lake underwater. This barrier is called a halocline.
Key Facts In This Video
See the "shoreline" of an underwater brine pool: (0:56)
The brine in brine pools is around three to five times saltier than ocean water, which is why the two liquids don't mix. (1:30)
See clumps of tubeworms on the ocean floor near a brine pool: (3:23)