Vast Iceberg Dislodged in Antarctic Collision
HOBART, Tasmania, Australia, February 26, 2010 (ENS) - A massive iceberg has broken away from the Mertz Glacier in the Australian Antarctic Territory after another enormous iceberg, B9B, collided with the tongue of the glacier, a joint Australian French study has discovered. The new iceberg and the one that rammed it loose could together affect world ocean circulation, scientists said today.

Satellite imagery from the European Space Agency's ENVISAT shows the iceberg separation occurred on February 12 and 13, but the discovery was just announced today by the researchers at a news conference in Hobart.

The new iceberg and the tongue of the Mertz Glacier (Photo © Australian Antarctic Division)

One of the largest icebergs ever to be monitored by scientists, the giant piece of floating ice measures 48 miles long and 22 miles wide. It has a surface area of 965 square miles and an average thickness of 1,300 feet.

In metric terms, the new iceberg is 78 kilometers long overall and 33 to 39 km wide with an average thickness of 400 meters.

The joint Australian - French study, undertaken at the Antarctic Climate and Ecosystems Cooperative Research Centre in Hobart, and in France, was initiated in 2007 during the International Polar Year to study the tongue of the Mertz Glacier and the calving of icebergs from it.

Australian scientists working on this study are: Dr. Rob Massom, Dr. Neal Young, and Dr. Barry Giles - all of the Antarctic Climate and Ecosystems Cooperative Research Centre and Australian Antarctic Division.

The French scientist working on this study is Dr. Benoit Legresy of the Laboratoire d'Etudes en Geophysique et Oceanographie Spatiales, LEGOS in Toulouse, France.

The Mertz Glacier has had a large crack in it for two decades. The scientists described the crack today, saying, "Two large rifts cutting through the southern part of the glacier tongue have been developing over many years. Rifting progressed from the eastern margin of the Mertz Glacier in the 1990s until 2002 when another rift started to develop from the western side."

"Recently the two rifts had almost joined and the western rift subsequently became very active, leaving the northern part of the glacier tongue attached like a loose tooth," they said.

This satellite image from ENVISAT shows iceberg B9B, lower right, breaking the new iceberg from the tongue of the Mertz Glacier. (Image courtesy ESA)

The scientists say satellite images show that the recently calved Mertz iceberg is moving into the Adelie Depression, a coastal basin between the Mertz Glacier and the French Antarctic station of Dumont D'Urville to the west.

This depression is one of the major sites of dense water formation which drives the world's deep ocean circulation.

The dense water is formed from ocean water that circulates onto the continental shelf and interacts with the glacier tongue, and by high rates of sea ice formation in an area of unfrozen sea water surrounded by ice near the glacier.

The future position of the two giant icebergs will likely affect local ocean circulation, sea ice production, and deep water formation, the scientists said.

The Mertz Glacier Polynya, an area of unfrozen sea water surrounded by ice that forms each winter, occupies the area immediately northwest of the Mertz Glacier Tongue and in the neighboring coastal bays.

The scientists say strong off-shore winds across this area maintain high sea ice formation rates which are crucial to the formation of very saline dense shelf water, a major ingredient of the world ocean circulation.

"These polynyas constitute places of high biodiversity and food concentration for birds and marine mammals, in particular emperor penguins, the only birds to reproduce during winter in Antarctica," they said.

The emperor colony at Pointe Geologie, next to Dumont d'Urville, is closely dependent on the ocean resources. Therefore, the scientists said, significant modifications in the marine environment may have large consequences, not only on the local biodiversity but also on this emblematic penguin colony, which was brought to world attention in the movie by Luc Jacquet, "March of the Penguins."

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