'Garden of Eden' lost in iceberg explosion

By SIMON COLLINS science reporter

Divers have found a "Garden of Eden" of cold-adapted sea creatures living deep beneath an iceberg in Antarctica - then watched as the iceberg exploded and destroyed the creatures' haven.

The United States-New Zealand diving expedition found a dense growth of sponges, sea cucumbers, feather duster worms and other marine life on the sea floor under the iceberg near Cape Hallett, 600km north of Scott Base.

The co-leader of the expedition, Dr Greg Stone, of Boston's New England Aquarium, said the iceberg appeared to have been wedged on the site for three to five years, sheltering the creatures from moving icebergs which scar the bottom of the ocean in most of the seas around Antarctica.

"It was a Garden of Eden in one of the most inhospitable places on Earth," he said.

But just six hours after the expedition's Tauranga-based 36-metre boat Braveheart left the spot, a lump of the iceberg about the size of six city blocks suddenly heaved upwards, crashed back down and exploded, shattering shards of ice over five square kilometres.

It was a natural event caused by the gradual spread of cracks in the ice, but Dr Stone believes the 18 people on the Braveheart who were woken by the explosion at 1am may have been the first humans ever to see an iceberg blow up at such close quarters.

The event dramatically demonstrated the insecurity of life for the creatures on the Antarctic floor.

Dr Stone, who gave a lecture about the trip in Auckland this week, said it also showed how quickly the ice could disintegrate if global warming pushed polar temperatures above a "tipping point".

"We are beginning to realise that these things can happen almost instantly," he said. "It actually can be catastrophic, and the processes behind them we are just now beginning to figure out."

Dr Stone, who has made two previous expeditions to Antarctica, chose to dive in the Ross Sea after an iceberg the size of Northland, called B-15, broke off the Ross ice shelf in March 2000.

He said the polar regions and the tropics showed the greatest effects of global warming on marine life.

In the tropics, he has explored the effects on coral reefs, where higher temperatures have killed the marine algae which are eaten by the tiny polyps that build coral structures. Without the algae, the coral bleaches and eventually dies.

"About 11 per cent of the historical extent of coral reefs has been lost through coral bleaching and a further 16 per cent is severely damaged," he said.

On the Antarctic Peninsula, south of South America, he has recorded reduced populations of microscopic krill, which provide the food for larger animals such as penguins and whales.

By the time he got to the Ross Sea in early 2001, B-15 had broken up into hundreds of smaller icebergs spread over the region "as far as the eye could see".

Although icebergs have always carved off Antarctica around the edges, he said the rate of warming in the Antarctic Peninsula - 2-4C in the past 50 years - was unprecedented.

Dr Stone and his wife, biologist Austen Yoshinaga, have visited New Zealand regularly for the past 14 years to study the Hector's dolphin, a rare species of about 7000 animals found around the South Island.

With Akaroa Conservation Department manager Alistair Hutt, he developed a "pinger" which can be attached to fishing nets and emits a sound at a frequency which keeps the dolphins away, while not scaring off other fish.

Mr Hutt said the device was adopted by the Canterbury Inshore Fishermen's Association and had successfully kept the dolphins out of fishing nets.

He said Dr Stone was "very influential" because he provided honest scientific information and did not get involved in politics.