Antarctic ice shelves 'tearing apart', says study

Matthew Knight in CNN: A new satellite study of ice shelves in West Antarctica has revealed they are steadily losing their grip with adjacent land and could intensify the acceleration of ice loss in the area. The ice shelves (floating extensions of land-based ice sheets) in the eastern Amundsen Sea Embayment are fracturing at their margins on rocky bay walls, according to glaciologists from the University of Texas at Austin's Institute for Geophysics (UTIG).

Lead author of the study Joseph MacGregor said in a statement: "Typically, the leading edge of an ice shelf moves forward steadily over time, retreating episodically when an iceberg calves off (breaks off and floats out to sea), but that is not what happened along the shear margins."

"Anyone can examine this region in Google Earth and see a snapshot of the same satellite data we used, but only through examination of the whole satellite record is it possible to distinguish long-term change from cyclical calving," MacGregor added.

The study, which examined satellite data from 1972 to the end of 2011, is the most comprehensive yet of ice shelf evolution say the scientists, and reveal substantial changes which were "especially rapid" during the past decade. The shear margins which bind the ice shelves laterally are now heavily rifted they say, resembling cracks in a mirror when observed in satellite images.

"As a glacier goes afloat, becoming an ice shelf, its flow is resisted partly by the margins, which are the bay walls or the seams where two glaciers merge," Ginny Catania, assistant professor at UTIG said in a statement. "An accelerating glacier can tear away from its margins, creating rifts that negate the margins' resistance to ice flow and causing additional acceleration," she added....

From NASA, the Pine Island Glacier in West Antarctica