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.
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Key Facts In This Video
See the "shoreline" of an underwater brine pool: 00:56
The brine in brine pools is around three to five times saltier than ocean water, which is why the two liquids don't mix. 01:30
See clumps of tubeworms on the ocean floor near a brine pool: 03:23
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