SYDNEY - An iceberg's crash into an Antarctic glacier last year cracked off a huge swathe of ice, bringing to light a vast span of the Southern Ocean and providing scientists with a chance to conduct experiments that may help understand climate change.

The incident, in which the iceberg clipped the Mertz Glacier in East Antarctica and broke off nearly 78 kilometer of glacier tongue, exposed a section of ocean water previously covered in hundreds of meters of ice and brought to light marine life including sea stars as big as hubcaps.

"Suddenly the geometry of Antarctica has changed," said Steve Rintoul, an oceanographer with the Antarctic Climate and Ecosystems Cooperative Research Centre at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Tasmania.

"It was a sort of natural experiment, where the calving of the glacier tongue was not caused by climate change. This is a natural event, so nature has done the experiment for us this time."

A team of 40 Australian and international scientists, including Rintoul, visited the region during the Antarctic summer to study the impact of the calving.

Among the unanticipated biological results was the release of about 10,000 square meters of ice into the ocean when it drifted off into warmer water.

Its consequent melting decreased water salinity and sparked an intense bloom of phytoplankton. The plants need light and nutrients to grow, along with small amounts of iron, which usually comes as dust falling from the sky.

"The old ice had accumulated decades of iron dust supply, and when it broke off and melted seems to have provided the phytoplankton with between 20 and 40 years' dose of iron in a single season," Rintoul said.

Another side effect, combined with clearer water, was the exposure of sea animals including giant seastars, colorful sponges and feathery sea pens, revealed after decades in dark Antarctic waters.

Overall, researchers ended up with an unprecedented chance to test theories of how the marine ecosystem might respond to such large-scale changes, a possible foretaste of what could lie ahead with climate change.

"Some of the areas we sampled have been under ice for many decades so no ship has ever reached that area," Rintoul added.

Reuters

(China Daily 04/18/2011 page10)