Underwater Brine Pool
Another interesting clip from David Attenborough's The Blue Planet: here we see an underwater lake with its own shoreline of muscles. How can this be?
Well, it's all to do with the composition of the lake. The liquid in the lake is Brine. Brine is a solution of salt in water where the saturation level is much higher than that usually found in the sea. Because the Brine is heavier than the surrounding sea water, it sinks, and forms pools and lakes at the bottom of the ocean.
The pool in the video is in the Gulf of Mexico. This pool was formed when, during the middle Jurassic period, a part of the ocean became cut-off from the main body of water. This then evaporated, leaving behind a high concentration of salt.
When normal tectonic movements caused the area to flood, a process called salt tectonics occured, which eventuated in salt being released into the ocean water, and forming a heavy liquid layer layer on the ocean floor.
The reason for the shoreline of muscles is that Brine often contains high levels of Methane, which the muscles can process into into energy. These muscles are contain bacteria which are known as Chemoautotrophs: organisms which produce energy by Chemosynthesis.
Chemosynthesis is a process where carbon, taken usually from Carbon Dioxide or Methane, is converted into organic matter by the oxidation of inorganic compounds, usually Hydrogen Sulphide, but sometimes by Hydrogen gas. It is this process that allows tube worms to extract energy from the Hydrogen Sulphide produced by ocean floor vents.