Brine pool

A brine pool, sometimes called an underwater lake, deepwater lake or brine lake, is a volume of brine that collects in a depression on the seafloor. The water is dense and typically three to eight times saltier than the surrounding ocean, so it stays separate from it. Brine pools are found below polar sea ice, where salty water is left behind as ice forms in a process called brine rejection, and in the deep ocean. In the deep sea the salt comes either from the dissolution of large salt deposits through salt tectonics or from hot brine issuing from tectonic spreading centres. The brine often holds hydrogen sulfide and methane, which feed chemosynthetic organisms, many of them extremophiles or symbionts, living near the pool. The pools are anoxic and toxic to most marine animals.