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Tuesday, November 2, 1999 Published at 16:27 GMT


Armageddon in Antarctica

Thriving Antarctic sea floor communities are utterly destroyed

By BBC News Online's Damian Carrington

Icebergs crashing against the sea floor could be the most devastating natural disaster that any living community on Earth experiences.

Professor Lloyd Peck explains how the sea creatures are annihilated
Scientists from the British Antarctic Survey have discovered that over 99.5% of all visible sea-bed dwellers are massacred when the bergs collide with the ocean bottom.

Floods, earthquakes and even meteorite impacts cannot claim such total destruction. The project leader, Professor Lloyd Peck, told BBC News Online: "In biological terms it is outrageous - it's almost a sterile environment."

Up to 20% of the world's oceans are prone to catastrophic ice berg impacts. Even ocean floor as deep as 500m is at risk.

[ image: This impact was relatively light - big ones leave nothing but fine powder]
This impact was relatively light - big ones leave nothing but fine powder
The bergs float in and gouge and trample the communities as they rock back and forth in the tide. It is their immense weight that causes the damage.

"The biggest icebergs are the size of Oxfordshire and weigh two billion tonnes. The impact force is greater than that of cruise missiles - it's immense," says Professor Peck.

His team, including colleagues from Gent University, Belgium, set up three underwater test sites near Signy Island, Antarctica. All were destroyed within 18 months.

They dived beneath the sea and used vacuum pumps to suck up the animals living on the sea bed both before and immediately after the berg impact.

[ image: Bergs float into the shallows then rock back and forth on the sea bed]
Bergs float into the shallows then rock back and forth on the sea bed
They were shocked by the totality of the death toll. In some cases, literally everything had been ground to a fine powder.

"For animals bigger than one millimetre, there were eight really common groups and six disappeared completely," explained Professor Peck. "The removal of the other two species was over 99.5%.

"Animals smaller than one millimetre, like nematodes, went down from two million per square metre to a few hundred."

Rising from the ashes

For the first time, the scientists also tracked the recovery of the obliterated sites. It had been thought this would take years.

But the first arrivals re-colonised within a few days, simply by walking back in. The smaller creatures needed the assistance of a major storm to be swept back in. This occurred within four months, with a 150 km/h gale.

And this revealed a surprise - the berg impacts actually revitalise the sea floor communities in the same way that forest fires clear "dead wood" and allow new trees to flourish.

"The icebergs actually help to maintain the population with a larger number of young animals because it's clearing areas for settlement," says Professor Peck. "So the ice bergs do have positive effects as well."

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