Ultimate Depth - a Journey to the Bottom of the SeaUltimate Depth - a Journey to the Bottom of the Sea 

Sunlight zone

Where is it? 
The sunlight, or epipelagic, zone is the first 200 metres of the ocean.

What’s it like? 
Sun shines through the water, supporting a diverse ecosystem. 

What lives there? 
With mostly warm temperatures and lots of light, it hosts various habitats, like coral reefs and kelp forests, and millions of familiar species, from fishes to turtles and stingrays.

How do we know what’s there? 
This is the ocean we know best: where we play, dive, fish and explore. Easiest to visit, it is also the most under threat from pollution and overfishing.

Why is it important? 
Seagrasses and other plants use carbon dioxide, water and energy from the sun to produce oxygen in a process called photosynthesis. They make so much that every second breath we take is thanks to the ocean. 

Twilight zone

Where is it?
The twilight, or mesopelagic, zone extends from 200 to 1,000 metres below the surface.

What’s it like? 
It is a meeting place: the space between the sunlit upper layers and the pitch-black deep sea. The largest animal migration on earth happens every day between the twilight and sunlight zones, as creatures rise to feed in shallower waters at night. 

What lives there? 
In this dimly lit region, animals start looking strange to us, as they adapt to darker and colder conditions. 

How do we know what’s there? 
Just beyond the reach of divers, remotely operated and tethered technologies help us to understand ocean chemistry and biodiversity. 

Why is it important? 
As the ocean’s biological pump, it helps to regulate Earth’s climate by carrying carbon from the surface to storage in the deep. It is seen as the next frontier for fishing and medicines from the sea.

Midnight zone

Where is it? 
The midnight, or bathypelagic, zone is 1,000 to 4,000 metres below the surface.

What’s it like? 
Dark, always dark. This is the average maximum depth of waters around Australia.

What lives there? 
In this perpetual darkness, bioluminescence (the biochemical production of light) becomes a critical adaptation for communication, hunting and defence. Colour has disappeared and many fishes become dark, translucent or silverised to hide from prey. 

How do we know what’s there? 
Deep-tow cameras and CTs (conductivity, temperature and depth) sensors are plunged to the depths to measure ocean conditions and record life.

Why is it important? 
The midnight zone is one of the largest habitats on the planet, but we know very little about it. It is the ocean’s nursery – many larvae grow up here before migrating to other zones as adults.
 

Abyssal zone

Where is it? 
The abyssal zone stretches from 4,000 to 6,000 metres. 

What’s it like? 
One of the flattest places on the planet, it holds most of the world’s seafloor and is a realm of perpetual darkness.

What lives there? 
In this vast underwater desert, we find polymetallic nodules that produce ‘dark oxygen’ and superhot hydrothermal chimneys, which shouldn’t – but do –support a diversity of life. 

How do we know what’s there? 
A suite of technologies like bottom sleds, dredges, nets, landers and corers are used to sample the deep, while sonar maps the depths. 

Why is it important? 
Most of the carbon that is transferred from the surface ends up here. The carbon stored in the abyss helps to keep our global climate stable. Long considered a barren wasteland, the abyss is under threat from deep-sea mining.

Hadal zone

Where is it? 
The hadal zone, named after Hades, the Greek god of the underworld, is the deepest part of the ocean. It extends from 6,000 metres below the surface to a maximum depth of approximately 11,000 metres in the Mariana Trench.

What’s it like? 
Long, needle-like trenches in the sea bottom are completely dark and only 4 degrees Celsius, with the crushing pressure of up to 11 kilometres of water pushing down from above.

What lives there? 
The extreme pressure and low food supply mean that there are fewer deep-sea species here. Only twenty-seven people have visited the Mariana Trench ‘in person’, travelling in three unique submersible vessels. 

Why is it important? 
We know more about our Moon and Mars than about these mysterious depths and how they affect the ocean, our climate, life on Earth and the future of humankind.

Dive to the depths of the ocean with acclaimed filmmaker, explorer, inventor, and environmental entrepreneur James Cameron.