Researchers have found more than 700 previously unknown creatures including carnivorous sponges, free-swimming worms, crustaceans and molluscs in the cold, dark water around Antarctica.
The Weddell Sea has long been thought of as a featureless abyss, devoid of life. But Angelika Brandt, of the zoological institute at the University of Hamburg, who led the expedition aboard the research vessel Polarstern, said the area could potentially be "the cradle of life of the global marine species". She said: "Our research results challenge suggestions that the deep sea diversity in the Southern Ocean is poor. We now have a better understanding in the evolution of the marine species and how they can adapt to changes in climate and environments."
Katrin Linse, of the British Antarctic Survey, who also took part in the expedition, said: "It was a big surprise to discover so many new species because many of us on that expedition had already worked for years in the Antarctic shallow waters.
"The general pattern is that life decreases if you go to the deep sea because you have less food and less light. Actually we have found the opposite pattern."
She said that the most significant result of the trawls, made between 700 metres and 6.5km below the surface, had been the discovery of hundreds of new species of isopods - crustaceans distantly related to woodlice. "We had 371 species known from the Antarctic before the expedition from the trawls taken in shallow waters. From the 50 trawls taken in the deep water, we added another 585 new species."
Other highlights of the three Polarstern expeditions, published today in Nature, included sea spiders that were the size of dinner plates and a 40cm deep-sea octopus. "When you looked at it, it looked back at you, so it was interacting. Octopuses are quite intelligent animals," said Dr Linse.
The new species are distantly related to many creatures found as far away as the tropics. A genetic analysis showed that the Antarctic species resembled the earliest members of those species more closely than relatives elsewhere in the world, meaning they had evolved differently.
Another key question for scientists is how the species around Antarctica reacted to changes in climate through ice ages. The latest findings suggest the changes in ice coverage have led to an intermingling of shallow and deep water species - some died out but others took their place.
Dr Linse said that scientists would now work on putting a timescale on the evolution and adaptation of species around Antarctica as a result of climate change.