1. Under the Surface
  2. In the Twilight Zone

In the Twilight Zone

The Twilight Zone is the most exciting and important place you may have never heard of. Beneath the surface of the ocean, where sunlight runs out, the Twilight Zone, a vast ecosystem teeming with life, begins.

What is the Twilight Zone?

The Twilight Zone is a layer of the ocean spanning across the whole of Earth, beginning at two hundred metres below the surface, and ending at 1km down – where the pressure would be equivalent to ten elephants standing on your head!

What lives in the Twilight Zone?

The Twilight Zone has many extraordinary creatures, adapted to life in this challenging environment. For example, they may be bioluminescent for camouflage or have huge mouths to make the most of rare encounters with prey in the dark.

There are many Twilight Zone creatures that are likely to be new and alien-looking to you, such as the Common Fangtooth. But there are others you are much more likely to have heard of, such as the Giant Squid and the Sperm Whale.

Did you know…?

Scientists think that the largest animal migration on Earth may take place in the Twilight Zone, every day!

At dusk, phenomenal numbers of creatures – fish, squid, shrimps – rise nearer to the surface to feed, using the dark of night to avoid predators. This would take the prize from birds, who see a huge annual migration of five billion.

Why is it important to protect the Twilight Zone?

Not only is the Twilight Zone full of marine life, it is also crucial to how the ocean takes up and stores carbon dioxide from the atmosphere in a process known as the biological carbon pump. Without life in the ocean providing this pump we think atmospheric carbon dioxide concentrations could be 50% higher than they are even now.

Did you know…?

The ocean contains more than 50 times more carbon than the atmosphere.

Key parts of the biological carbon pump:

  • Phytoplankton

    The surface ocean is full of tiny plants called phytoplankton and, like trees and grasses, they use carbon dioxide to grow. Phytoplankton are a vital part of the ocean food chain, creating huge amounts of new plant material each year – as much as all land plants combined, including rainforests! This material is eaten by tiny creatures such as copepods, which in turn are eaten by bigger animals and so on, reaching creatures such as the giant squid and sperm whale.

  • Marine commuters

    Many animals in the twilight zone commute up to the surface at night, and back down to the depths of the Twilight zone to respire during the day, transporting carbon dioxide away from the atmosphere and storing it deep in the ocean.

  • Marine Snow

    All the growth and feeding in the surface ocean creates a huge amount of debris from dead creatures and the waste products of living ones, known as marine snow.

    Marine snow sinks in the ocean, taking large amounts of carbon with it. The deeper it gets the longer it stays away from the atmosphere. Small creatures such as copepods actively feed on marine snow, meaning 90% is recycled within the Twilight Zone. 10% of marine snow sinks even deeper, which is important in helping maintain atmospheric carbon dioxide levels lower than they would otherwise be.

What threatens the health of the Twilight Zone?

This Twilight Zones’ role in the Earth’s climate is something we need to keep in mind when weighing up the risks of taking resources from the ocean.

There are three human activities in particular that may put the Twilight Zone under pressure:

    • Carbon dioxide removal – essentially using the ocean to remove carbon dioxide from the atmosphere with the aim of reducing future global warming.
    • Deep-sea mining – nodules found on the sea floor are rich in the metals we need for our technology. Areas such as the Clarion Clipperton Zone in the Pacific, spans over 3,000 miles with 400,000 square miles already contracted to mining companies. Waste from harvesting nodules maybe released nearer the surface in the nodule, impacting the ecosystem.
    • Fishing – the surface ocean has roughly one billion tonnes of fish, but it has recently been estimated that there are many more in the Twilight Zone, drawing attention to it as a potential source.

Twilight Zone podcast

Professor Stephanie Henson explains what’s happening in the Twilight Zone. This video is part of the ‘Into the Blue Podcast’ series.

What is the NOC doing to investigate the Twilight Zone?

The NOC is very active in leading research into the Twilight Zone, which includes leading the Joint Exploration of the Twilight Zone Ocean Network (JETZON) programme, which has been officially endorsed to focus on the Twilight Zone by the United Nations Ocean Decade.

The JETZON programme includes over 20 projects linking 30 countries. JETZON will see scientists from the NOC collaborate with global partners to study the impact of fishing, deep-sea mining and climate change on this largely unexplored ocean region. JETZON will bring together global scientists including students so that the international scientific community can obtain the greatest insight into the Twilight Zone from ongoing work and can maintain focus on this potentially threatened environment.

Learn more about the JETZON programme, and other NOC-led projects within the programme

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