Deep beneath the ocean, hidden lakes of hypersaline brine host life without the sun.

Nature · Published 3 October 2026 Swipe more like this →

In short: Brine pools are dense, underwater lakes trapped in seafloor depressions. With salinity up to eight times that of the surrounding ocean, these toxic, anoxic basins act as time capsules, preserving fallen creatures for years. Yet, in their chemical shadows, unique ecosystems thrive on energy derived from methane and sulfur.

Brine pools form through three distinct geological processes: the freezing of sea ice, which expels salt; the dissolution of ancient salt deposits; and geothermal heating at tectonic boundaries. In the Gulf of Mexico, for instance, salt layers dating to the Middle Jurassic period were buried by sediment, only to be deformed and pushed to the seafloor later. When seawater contacts these exposed deposits, it dissolves the salt, creating dense, hypersaline water that settles into depressions. Because this brine does not mix with the overlying ocean, it quickly becomes anoxic, creating a deadly environment for most aerobic life.

Despite these harsh conditions, brine pools are not barren. They host complex microbial communities that exploit sharp chemical gradients between layers. Because these environments lack sunlight, life here relies on chemosynthesis. Bacteria process methane and hydrogen sulfide to produce energy, often living in symbiotic relationships with macrofauna like mussels and tubeworms. These organisms have evolved remarkable adaptations, such as the 'salt-in' strategy used by halophilic archaea to maintain cellular function despite extreme osmotic pressure, or the synthesis of thermoprotective molecules to prevent protein denaturation in hot, high-pressure zones.

The chemical composition of these pools varies wildly, even within the same region. In the Mediterranean, the Urania basin contains sulfuric acid concentrations thousands of times higher than normal seawater, while the Discovery basin exhibits an unusual magnesium-to-sodium ratio. Scientists use metagenomic analysis to study these microbial assemblages, as many of these organisms cannot be cultivated in a lab. Beyond their biological significance, researchers have proposed using the osmotic pressure generated by these brine pools to drive turbines, potentially turning these extreme natural phenomena into a source of renewable energy.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• Why some of the world's most extreme lakes are disappearing at alarming rates
• The deadly danger of the ocean's hypersaline brine pools
• The deadly chemistry of underwater brine pools
• Life thrives where chemistry should make survival impossible
• The deep blue mystery of underwater sinkholes and their toxic secrets
• Darwin could not explain why animal fossils seemed to appear from nowhere
• Why Brazil calls its vast maritime territory the Blue Amazon to secure national funding.
• Which is Earth's deepest canyon depends on how you measure it
• Was the Boring Billion actually the most creative period in Earth's history?
• Can we bury our way out of the climate crisis using carbon capture?
• Bogs grow so slowly that losing one can take millennia to undo
• How a diplomatic truce saved one of history's greatest space missions

More in Earth science · More in Nature · Latest · A–Z · All topics