Brine Pools: The Deep Sea’s Most Mysterious Ecosystems

Brine pools are some of the rarest and most extreme environments on Earth; underwater lakes so salty and dense they form their own surfaces, shorelines, and slow-moving waves in complete darkness. Three to eight times saltier than normal seawater, the brine becomes so dense that it sinks into seafloor depressions and remains unmixed, forming a separate, self-contained body of water within the ocean itself. Remote, isolated, and sharply defined from the world around them, these pools stand apart as some of the most unusual ecosystems scientists have ever observed. 

Only a small number of brine pools have ever been documented, and they are concentrated in just three regions of the world: the Gulf of Mexico, the Mediterranean Sea, and the Red Sea. Most recently, our researchers discovered one in the Gulf of Aqaba, at the northern end of the Red Sea, in a deep seafloor depression where none had previously been recorded. After hours of surveying what looked like endless barren seafloor, the ROV lights finally illuminated a milky, rippling boundary across the top of one of the depressions — the unmistakable surface of a brine lake.  

These environments exist because of powerful geological forces, such as dissolving salt beds, hydrothermal circulation, or remnants of ancient seas. But once formed, they create an entirely separate world hidden only a few miles beneath us. 

Discovering an Underwater Lake 6000 Feet Deep

Life at the Edge of the Impossible 

Brine pools are lethal to most life. They are completely anoxic. Their chemistry is packed with methane and toxic compounds. Animals that enter the brine suffocate almost instantly. Their bodies settle at the bottom, preserved for years because nothing can decompose in this oxygen-free environment. These lakes are true dead zones. 

And yet, right at the boundary where seawater meets brine, life gathers in surprising abundance. Microbial mats grow in distinct bands, each community adapted to its own precise chemical niche. Mussels crowd along the shoreline, relying on bacteria inside their gills to convert methane and sulfur into energy. Tube worms, amphipods, and even small sharks routinely patrol this thin border. 

The shrimp are the most astonishing of all. They hover exactly at the interface — never crossing it — waiting for something to drift too low. When a fish or crab becomes stunned by the brine, the shrimp shoot in, grab it, and retreat before the water overwhelms them. They have learned to use the brine itself as a trap, a tool for survival in an environment where almost nothing should be possible.  

Dr. Sam Purkis, lead marine-geoscientist for the expedition and professor at the University of Miami, remarked of the Aqaba brine pool discovery during our livestream: “It’s an incredibly inhospitable environment… and yet somehow, life finds a way.” 

In nearby regions of the deep sea, hagfish add another layer of fascination. These ancient animals defend themselves with protein threads that instantly expand into massive clouds of slime, a teaspoon becoming a bucketful in seconds. The slime clogs the gills and mouths of predators, but it also gives hagfish an unusual advantage near brine pools. Because the mucus coats their skin and reduces water exchange across the body, it may allow them to tolerate brief contact with high-salinity water that would kill most fish. This means hagfish can rush into the brine edge to scavenge dying animals, then retreat unharmed — a survival strategy shaped by chemistry as much as behavior.  

The fibers in hagfish slime are strong, flexible, and biodegradable, and scientists are now studying them as templates for next-generation textiles and bio-based materials. Protective, adaptable, and remarkably efficient, their defense system reflects the kind of evolutionary engineering that thrives in the deep. 

Why Brine Pools Matter: The Power of the Unknown 

Brine pools do more than challenge our assumptions about where life can exist; they reshape our understanding of Earth itself. Because the brine is so dense and oxygen-free, anything that falls into these lakes — seagrass, sediment, storm debris — is preserved with exceptional clarity. Layer by layer, these materials create a natural archive on the seafloor. By coring beneath brine pools, scientists can reconstruct centuries or millennia of climate history: storm patterns, floods, seismic events, and shifts in regional ocean conditions. 

“We have this exquisite climate record preserved in the sediments of the brine pool, going back many centuries, probably thousands of years and possibly tens of thousands of years,” remarked Dr. Sam Purkis during the livestream on the Aqaba discovery. 

But the significance extends even farther. Brine pools help illuminate how early oceans may have functioned and how life could have originated in hydrothermal, oxygen-free environments very much like these. They also act as analogs for ocean worlds such as Europa, guiding strategies for detecting life in places far beyond Earth. Studying extremophiles at brine pools — organisms that persist, adapt, and innovate — broadens our sense of what biology can be and the conditions under which life can exist and thrive. 

Exploring the Alien World of Brine Pools

Oceanographer Dr. Samantha “Mandy” Joye, of the University of Georgia, underscored what is at stake during filming with Dr. Sylvia Earle, of Mission Blue, for Blue Planet II (part of Our Blue Planet, a joint venture between OceanX Media and BBC Earth): 

“This is more than just exploration. There's a very high probability that there are payoffs above and beyond just the basic science. Biomedical cures for disease... those kinds of payoffs, you can't put a price tag on those. And the fact that we've got ecosystems that have been barely explored and are being damaged by human activity means that we're losing stuff before we even know that it's there.” 

Above all, brine pools remind us how much of the ocean remains unexplored. Each discovery expands our understanding of life’s adaptability, Earth’s climate history, and the hidden systems shaping our planet. These underwater lakes do more than test the limits of life. They invite us to explore more deeply, to question what we think we know, and to recognize that stewardship begins with knowledge.