MercoPress. South Atlantic News Agency

Scientists monitor calving of huge Antarctic iceberg

Antarctica has a “loose tooth” and scientists are gathering data to determine when, how, and why it will fall off. The loose tooth is actually a partial rift in the Amery ice shelf which eventually will cut through the entire ice shelf, dropping an iceberg into the ocean, a process called “calving.” The last time a significant chunk of ice broke off was in 1964.

Scientists from Scripps Institution of Oceanography at the University of San Diego and Australian universities, Tasmania and Canberra, have recently been studying both the long term and the short term behavior of these loose teeth, particularly in the Amery Ice shelf, which is the largest ice shelf in East Antarctica.

The 'loose tooth' is an area of about 30 by 30 km, and currently an approximately east-to-west (transverse) fracture of this section is moving at approximately 10-14 m/day. In other words, over one year, the transverse fracture will extend further eastwards by about 4-5 km and it will widen as it breaks off from the main ice shelf. The ice shelf itself is moving forwards in a northerly direction at about 1300 m/yr.

With the help of NASA satellites and terrestrial GPS equipment, Helen Amanda Fricker of Scripps monitored the lengths of two rifts on the Amery Ice Shelf from 1996 to 2004. She found that while the rifts have widened steadily over the last five years, they widen much faster during Antarctica's summer months ? December to March.

"There's a lot we don't know about how rifts propagate on ice shelves, but our conclusions give us some hints, including the finding that iceberg calving may be temperature dependent" said Fricker.

In the second study, Jeremy Bassis used GPS measurements and seismometers to monitor movements and vibrations of the tooth. He and his team found that the iceberg separated in bursts ? sometimes as much as 600 feet over four hours ? and would then normal, slow widening would occur for a period of 10 to 24 days. Data from each study will help fill the rifts in scientists' understanding of iceberg calving.

An array of seismometers has been deployed to 'listen' to the cracking and snapping of the fracture. The GPS array consists of 6 sites positioned around the tip of the fracture (within 300 m to 2 km away), that continuously record data.

"People have understood that rift propagation is an important phenomenon and now we have new data that can really take us places," said Jean-Bernard Minster, from Scripps and a co-author on both studies.