There is more than warships to be found in the murky depths

Vanishingly little sunlight manages to find its way through the twilight zone. Situated between 100m and 1,000m beneath the surface of the ocean, these gloomy depths are a mysterious place: cold and dark, unfriendly and inhospitable.

It’s not just the lack of light that means we know relatively little about what lives and dies down there. Satellites can only tell us what is happening on the surface of the seas, and instruments moored to the bottom give us information only about the ocean floor.

To find out more about what lies between therefore means going on research expeditions. I’ve just returned from one to South Georgia, where I spent months in the choppy waters of the South Atlantic.

But that’s all part of the fun. These are, quite literally, uncharted waters. The surface of the world is heavily mapped, but what lies beneath the seas is not. We know more about the surface of the Moon than we do about the bottom of the ocean.

The knowledge that every expedition I participate in will involve discovering something no one else has discovered before is absolutely thrilling. I think I know, therefore, how Paul Allen, the Microsoft billionaire, must have felt when his team discovered the wreck of the USS Lexington, an aircraft carrier sunk during the Second World War hundreds of miles off Australia’s east coast.

The drive to explore the seas is the same impulse that has propelled men and women to venture into space. Within the oceans and out in the void, there are so many mysteries still to unravel. There is a sense that we may find almost anything out there. On land, that sense has been unmatched since explorers stepped on to continents for the first time.

Robots do much of the actual diving these days. They are far more versatile than they used to be and can keep going for months if necessary. Manned deepsea exploration is extremely unusual, and dangerous, so we scientists remain on board the research ship, taking readings and analysing data. But that doesn’t lessen the sense of adventure or surprise. On my last expedition, our trawling nets brought up a truly massive jellyfish.

There can be downsides. It can be choppy out on the open seas – I usually get seasick for the first few days. You’re stuck on the same ship – a relatively small vessel – with the same 50-odd people, miles away from land, for weeks or months at a time, eating with them, sharing your living space with them, working with them. People can get irritable and arguments occasionally break out.

There can be a lot of waiting, too, when the weather gets rough and I have played more games of Scrabble than I like to contemplate. Paul Allen’s research ship probably has a few more luxurious distractions. But, basic or not, it’s still a wonderful way to work: we get to know our colleagues and collaborators very closely, develop deep friendships and share the thrill of discoveries.

My next expedition will be off the coasts of Namibia and South Africa. The scenery will be different; the twilight zone will have its own distinct character. But the adventure will still be there – and the discoveries we hope to make will be just as exciting.

Dr Stephanie Henson is a senior scientist at the National Oceanography Centre FOLLOW Stephanie Henson on Twitter @Stephahenson; READ MORE at telegraph.co.uk/opinion