Understanding the saltiness – or salinity – of our world's water tells us about the life within it.
Some marine organisms live in or near very high-salinity areas on the seafloor. The super salty water in these pools is called "brine."
Let's break it down!
"Hypersaline" is based on Latin terms for "over" and "salty." Brine pools are 3-10 times more salty than the normal* seawater surrounding them.
*Normal ocean salinity levels are about 35 parts per thousand.
Hypersaline brine pools can have little to no oxygen available to host living creatures. In other words, they are "anoxic," making them uninhabitable for animals.
Most brine pools are found over a mile deep on the ocean floor. This extreme habitat can be explored by a few human-occupied submersibles but are mostly visited by Remotely Operated Vehicles (ROVs).
Here ROV Hercules explores a 25 m (82 ft) diameter brine pool at 1,280 m (4,200 ft) depth, collecting video, data and samples for scientists waiting on the surface.
Some brine lakes are encrusted with beautiful crystalized salts and mineral deposits, which form salt dams that lead to smaller pools.
Brine pools are deadly hazards for most sea creatures that swim or sink into the brine. This deep sea crab wandered too close to the edge and could not escape back to safer waters. Its body now sits there, preserved in the brine. (Salted crab, anyone?)
Even though animals can't live within the brine... some of these pools are teeming with life around the edges. Here we see thousands of mussels huddled around a brine pool.
Life in Darkness and On the Edge
Sounds scary, right? However, life around the edges of a brine pool isn't all bad. It can be good for those animals and microbes that have partnered up to form a "symbiosis."
A symbiosis means two different species have formed a relationship that is mutually beneficial.
Around some brine pools, the mussels and clams have formed a partnership with bacteria that can live off the chemicals in the brine.
No Sunlight? No Problem!
The mussels and clams around brine pools have partnered with symbiotic bacteria that can make sugars (food) from energy-rich chemicals such as methane gas (a.k.a., "natural gas") that come out of the pool. This process is called "chemosynthesis."
Location, Location, Location
Chemosynthetic mussels and clams and their neighbors (e.g., shrimp and crabs) coexist on the precarious rim of the brine pool. They make good use of the complex living matrix created by the mussels, which glue themselves to each other by anchoring their natural threads.
But all these critters must be careful: Too close to the salty edge means death. Too far from the chemicals needed to survive means death.
Tiny Bubbles
When brine pools are located over fissures on the seafloor, natural gas can seep out, turning the brine into a "cold seep" habitat.
Cold seeps are habitats where microbes – and animals that have microbial symbionts – can live on methane gas that's coming out of the seafloor.
In 1983, the first cold seep was discovered in the Gulf of Mexico at 3,200 m (over 10,498 ft). Scientists have documented many more seeps – like the one off the coast of Virginia shown at right – and continue to look for more using new technologies.
A Lake in the Ocean?
The dense salty water in brine pools doesn't mix easily with the overlying seawater. Why? Because of the big difference in their densities caused by the extra weight of dissolved salt in the brine.
The sharp boundary between the brine pool and normal seawater is called an "interface." Like a surface of a lake – which is denser than the air above it – disturbing this interface can cause waves or ripples to form.
Scientists even refer to the edge of this brine pool interface as "the beach"!
Gulf of Mexico's Brine-a-palooza!
Brine pools occur in various regions of the ocean, along with the Mediterranean and Red Seas. But let's focus on the massive number of these phenomena in the Gulf of Mexico.
This 3D perspective map shows the locations of the largest cities in North America, Central America, and the Caribbean. Blue colors represent depths in the Gulf of Mexico.
Why does the Gulf of Mexico have so many brine pools? The salty origins occurred millions of years ago when this region was a dried-up shallow sea.
Buried below the Gulf, the ancient salt deposits have lower density than the overlying layers. So they flow upward...
...forming "salt sculptures" and brine pools. This color-coded map shows one area of Gulf that is about 50 km by 50 km (31 mi by 31 mi). Can you see why scientists call these the "Mickey Mouse Salt Domes"?
If you are "on the lookout" for salt domes, you don't have to go underwater! Check out this photo taken from the International Space Station.
Like the Gulf of Mexico, pressure from overlying rock layers has caused lower-density salt to flow upwards, bending the overlying rock layers and creating a dome-like structure.
Located in the Zagros Mountains of southwestern Iran, this dome is called a Kuh-e-Namak or “mountain of salt” in the Farsi language.
Brine pools are an essential part of some of the most extreme, remote and interesting ocean habitats on Earth. They provide a home to unique organisms found in very few other places, and they are still being explored and investigated....
Salt is essential. Circulating through our bodies and our seas, it impacts the health of organisms and our planet.
NASA observes salinity from space. Monitoring sea surface salinity patterns provides important clues about changes in our environment.
A narrated world tour of salinity patterns based on data from NASA's first salinity-sensing satellite, Aquarius/SAC-D.
Links and Other Information
- Blue green underwater "salt craters" [NOAA Ocean Exploration and Research]
- What are DHABs? {Woods Hole Oceanographic Institution]
- Underwater Research Vehicles [Woods Hole Oceanographic Institution]
- ROV Hercules above Edge of Brine Pool [Nautilus Live]
- Close up of Brine Pool Rim with Crystals [Nautilus Live]
- "Dead Edge" of Brine Pool [Nautilus Live]
- Brine Pool: Hot Tube of Despair [Nautilus Live]
- Mussel Bed on the Shore of Brine Pool [Nautilus Live]
- Life in DHABs [Woods Hole Oceanographic Institution]
- Approaching the Brine Pool [Nautilus Live]
- What is Symbiosis? [NOAA Ocean Exploration and Research]
- Photosynthesis vs. Chemosynthesis [Woods Hole Oceanographic Institution]
- What is the Difference between Photosynthesis and Chemosynthesis? [NOAA Ocean Exploration and Research]
- Mussels and Large Crab [Nautilus Live]
- Mussel Close Up [Nautilus Live]
- An Update on Cold Seeps in the Northwestern Atlantic Ocean [NOAA Ocean Exploration and Research]
- Can Animals Thrive Without Oxygen? [Woods Hole Oceanographic Institution]
- Stunning Underwater Brine Lake and Deep Sea Waves [Nautilus Live]
- Making Waves in a Brine Pool [Nautilus Live]
- Gulf of Mexico in 3D perspective [Wikipedia]
- Gulf of Mexico's Louann and Campeche Salt Layers [NOAA Ocean Exploration and Research]
- Measured and Estimated Seafloor Topography [Smith and Sandwell, 1997; Scripps Institution of Oceanography]
- "Mickey Mouse" Salt Domes [Ocean Explorer: Image courtesy of Gulf of Mexico 2002; NOAA Ocean Exploration and Research]
- Salt Dome in the Zagros Mountains, Iran [NASA Earth Observatory]
- Brine Pool: Photo Mosaic [NOAA Ocean Exploration and Research]
- The Geology of DHABs [Woods Hole Oceanographic Institution]
- NASA Aquarius Sea Surface Salinity Tour [NASA Scientific Visualization Studio]
- Other images used under 123rf License Agreement [ID 111438722, 41205832]