Deep Sea Brine Pools

 

The salinity of oceans varies.  Oceans collect salt and minerals from every river that flows into them.  Heavy rainfall near the equator decreases the salinity because fresh water falls and flows into the ocean.  The Red Sea has the saltiest ocean water because of the region’s low rainfall and high evaporation rate.  The Red Sea also has the highest number of deep sea brine pools. Brine pools are depressions on the seabed filled with super salty water (roughly three to ten times saltier than the surrounding ocean) . Only a few dozen have ever been discovered worldwide.  In addition to the Red Sea they are also found in the Gulf of Mexico and the Mediterranean Sea. They range in size from tiny (1m²) to 120km².

Brine pools formed in the Red Sea because, about 10 million years ago, the sea was cut off, dried out and left a deep layer of salt.  The sea has now returned and seeped into fault lines, dissolving the salt into a thick sludge that settles in  depressions and forms pools.  Brine pools can also be formed by salt tectonics where geological processes expose salt layers that dissolve and then settle, and by geothermally heated brine at plate boundaries.

In 2020 researchers from the University of Miami discovered deep-sea brine pools in the Gulf of Aqaba, off the coast of Saudi Arabia.  The pools are at a depth of about 1770m and were discovered  by a remotely operated underwater vehicle during the last five minutes of a 10 hour dive.  Uniquely the pools in the Gulf of Aqaba are only 1.25 miles from shore (others in the Gulf are 15.5 miles offshore) and, as a result, offer a glimpse into the past.  They have trapped and preserved sediments from the coast which, due to minimal biological disturbances, are revealing a 1000 year history of flash floods, earthquakes and tsunamis. This is due to the preservative effect of brine pools.  Researchers found a crab that had been dead for 8 years (how did they know?) but still had its soft tissue intact.

Brine pools completely lack oxygen, making them one of the most extreme environments on the planet.  A bizarre discovery, made by the team from the University of Miami, was that one 10 foot brine pool is a “100% kill zone” meaning it can paralyse and kill any marine animal that swims into it.  Nevertheless, they are full of microbial life. Microbes from other red Sea brine pools have provided molecules with anti-cancer and anti-bacterial properties that could potentially contribute to novel medicines.

Another future use of brine pools is to harness the salinity as a power source using the variations in buoyancy to raise and push down high salinity water.  The energy created could be harnessed to provide power via a turbine. (I tried to understand this but I’m not sure that I really do).

Lithium for use in renewable energy, eg batteries and electric cars, is traditionally extracted through evaporation from ponds on land.  The lithium in deep-sea brine pools makes then attractive targets for extraction.  I think it would be mad if the growing demand for lithium for “green” technologies becomes a potential threat to the unique and largely unknown biodiversity of these rare and strange brine pools.