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Deep beneath the ocean’s sunlit surface is a mysterious world where most people never go: the deep sea. Here in the intense darkness the only light comes from the bioluminescent glow of weird and wondrous deep-sea creatures. The vast, cold depths are far from empty; scientists believe as many as 10 million different species live in the deep sea – a biodiversity as rich as tropical rainforests.

The deep sea is the entire ocean below 200 meters in depth – from the “twilight zone” down to the “abyss” and the deep seabed. It makes up 95% of Earth’s living space. But only recently has technology made it possible for scientists to explore the deep ocean and begin to understand its vital importance for our planet and for our lives.

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Thus far, only a tiny fraction of the deep sea has been studied. It’s the most difficult place on Earth to access: fewer humans have explored the deepest regions of the ocean than have walked on the moon. That makes the waters, seamounts, seabed, and myriad creatures of the deep an uncharted treasure trove of discovery.

And we’re finding new things all the time – from nearly 20,000 previously unknown mountains, to an “impossible” fish living at a record-breaking depth of 8,336 meters. The deep sea is an unlimited laboratory for new discoveries.


All life on Earth, including human life, depends on the deep sea. Deep ocean currents redistribute heat around the planet, driving global weather systems. Cold, upwelling waters regenerate nutrients at the ocean’s surface and fuel vital marine food webs. What’s more, the ocean has absorbed and stored over a quarter of the carbon dioxide that we’ve emitted into the atmosphere since the Industrial Revolution – just imagine how much worse climate change would be without it!

Deep-sea coral and sponge communities are largely untapped sources of microbes and other compounds that can be used in medicines, cosmetics and other commercial products. The famous PCR test used to diagnose and control the spread of COVID-19 was developed using an enzyme isolated from a microbe found in deep-sea hydrothermal vents. The next deep-sea discoveries could unlock breakthrough cancer treatments and new antibiotics, or help us fight future pandemics.


Far below the waves there are amazing and unique habitats: the abyssal plains, hydrothermal vents and cold seeps, seamounts (underwater mountains), and even the water column itself. Each is populated by distinct types of life. You can find out more on our deep-sea life and habitats page.

Did you know that the deep sea is home to incredibly rich coral systems? Corals were once thought to only inhabit the warm, shallow waters of tropical and subtropical regions, but now we find that they’ve been thriving in dark, cold waters for millions of years. In fact, over half of all known coral species are found in the deep sea. Cold-water reefs teem with life, and provide essential sanctuaries and nursing grounds for countless species.

Most deep-sea species are slow to grow and reproduce, and highly adapted to a largely stable environment. That makes them extremely vulnerable and hard to protect against the impacts of human activity. Once damaged, deep-sea habitats can take centuries to recover, and entire deep-sea species can be lost forever before we even know they exist.


1. The air you breathe

Not only is the ocean responsible for producing half the oxygen we breathe, but the deep ocean also stores massive amounts of carbon that would otherwise be in the atmosphere and contributing to global warming.

2. Every drop you drink 

Water on Earth circulates. The deep sea drives water around the Earth in a vast current system that rises and falls, regulates temperature, and controls our climate.

3. The fish you eat

Many of the fish we eat – even those caught in shallow coastal waters – spend part of their lives in the deep sea and rely on its species and habitats for food, shelter, breeding and nursery grounds. The ocean contributes to the food security of billions, which is all the more reason to protect the deep sea and keep our fish stocks healthy and productive.