Pictured: The incredible secret world at the bottom of the sea

In a year-long mission, a BBC team probed a small part of the earth's amazing undersea world. They completed 1000 dives and explored seven different oceans across the globe. What they found was extraordinary...

To most of us, seas and oceans are featureless expanses. On a good day, the vast surfaces stretching endlessly towards the horizon provide a picturesque foil for a sunset.

Yet these glassy waters hide an extraordinary world.

In fact, we know more about the surface of Mars than we do about the deep ocean floors, which is why a team of experts decided to probe a small part of the planet's seas, and film it for an eight-part TV series, to be shown on BBC2 next month.

Headed by Paul Rose, ex-base commander of the British Antarctic Survey and dive trainer to the US navy, the Oceans team includes maritime archaeologist Lucy Blue, marine biologist and oceanographer Tooni Mahto, and conservationist Philippe Cousteau, grandson of the celebrated underwater pioneer Jacques.

Over a year, they set up eight expeditions to seven different seas and oceans across the globe - spending more than 700 hours underwater, and completing 1,000 dives.

Their aim was to seek out the hidden secrets of our oceans and, ultimately, to better understand how much we rely on these enigmatic and alien places.

Four-fifths of all life on Earth is found beneath the waves, and scientists estimate a million new species are out there waiting to be discovered.

Below the surface of the oceans there are mountains that would dwarf the Himalayas, waterfalls bigger than Niagara and more active volcanoes than anywhere else on the planet.

The mid-ocean ridge, a chain of mountains that runs through all the great seas, is 37,300 miles long, with an average height of 3,000 metres.

Together, the oceans make up an unimaginably vast environment wrapped around more than 70 per cent of the surface of the planet.

It is no surprise, then, that a new species was discovered by the team during almost every deepsea dive.

But there was more to find, including underwater caves that preserved the remains of lost civilisations and wrecks that spoke of ancient battles.

They saw rare and endangered creatures and dived in alien marine environments: pitch-black waters turned purple by toxic bacteria, and eerie tannin-stained waters housing bizarre creatures.

They even dived into a throng of sharks to test out a new repellent - and were relieved to find it worked.

Unfortunately, they also found found evidence of the changes wrought by mankind - warming seas destroying unique ecosystems and overfishing decimating entire species.

But there were also signs of hope: coral that harbour a special heat-resistant algae that could also protect the other reefs of the world, and marine creatures with amazing abilities to adapt to their changing world.

And, in the Arctic, they discovered a potentially new species of amphipod - a great find, as these tiny creatures provide a crucial link in the entire Arctic Ocean food chain.

There were numerous other highlights, including a rare encounter with a green-eyed six-gill shark, a dive alongside Seri Indians, and swimming in the presence of the terrifying Humboldt squid.

Here, they exclusively share with us some of the amazing sights they found under the sea.

• Extracted from Oceans: Exploring The Hidden Depths Of The Underwater World by Paul Rose and Anne Laking, BBC Books, £20. (c) Paul Rose and Anne Laking, 2008. To order a copy at £18 (p&p free), tel: 0845 155 0720. Oceans starts on BBC2 on 12 November.

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