A new NASA study finds the last remaining section of Antarctica’s Larsen B Ice Shelf, which partially collapsed in 2002, is quickly weakening and likely to disintegrate completely before the end of the decade.
‘This ice shelf has existed for at least 10,000 years, and soon it will be gone’ said Ala Khazendar, NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California.
A team led by Khazendar found the remnant of the Larsen B Ice Shelf is flowing faster, becoming increasingly fragmented and developing large cracks. Two of its tributary glaciers also are flowing faster and thinning rapidly.
Without Ice Shelves…?
Ice shelves are the gatekeepers for glaciers flowing from Antarctica toward the ocean. Without them, glacial ice enters the ocean faster and accelerates the pace of global sea level rise.
Antarctica has dozens of ice shelves – massive, glacier-fed floating platforms of ice that hang over the sea at the edge of the continent’s coast line. The largest is roughly the size of France.
Larsen B remnant is about 625 square miles (1,600 square kilometers) in area and about 1,640 feet (500 meters) thick at its thickest point.
Larsen B is located in the Antarctic Peninsula, which extends toward the southern tip of South America and is one of two principal areas of the continent where scientists have documented the thinning of such ice formations.
‘What is really surprising about Larsen B is how quickly the changes are taking place’ Khazendar said.
This study, the first to look comprehensively at the health of the Larsen B remnant and the glaciers that flow into it, has been published online in the journal Earth and Planetary Science Letters.
Khazendar’s team used data on ice surface elevations and bedrock depths from instrumented aircraft participating in NASA’s Operation Ice Bridge, a multiyear airborne survey campaign that provides unprecedented documentation annually of Antarctica’s glaciers, ice shelves and ice sheets.
Data on flow speeds came from space-borne synthetic aperture radars operating since 1997.
Tributary glaciers thinned
The remnant’s main tributary glaciers are named Leppard, Flask and Starbuck — the latter two after characters in the novel Moby Dick. The glaciers’ thicknesses and flow speeds changed only slightly in the first couple of years following the 2002 collapse, leading researchers to assume they remained stable.
New study revealed, however, that Leppard and Flask glaciers have thinned by 65-72 feet (20-22 meters) and accelerated considerably in the intervening years. The fastest-moving part of Flask Glacier had accelerated 36 percent by 2012 to a flow speed of 2,300 feet (700 meters) a year — comparable to a car accelerating from 55 to 75 mph.
Flask’s acceleration, while the remnant has been weakening, may be just a preview of what will happen when the remnant breaks up completely. After the 2002 Larsen B collapse, the glaciers behind the collapsed part of the shelf accelerated as much as eightfold – comparable to a car accelerating from 55 to 440 mph.
The third and smallest glacier, Starbuck, has changed little. Starbuck’s channel is narrow compared with those of the other glaciers, and strongly anchored to the bedrock, which, according to authors of the study, explains its comparative stability.
‘This study of the Antarctic Peninsula glaciers provides insights about how ice shelves farther south, which hold much more land ice, will react to a warming climate’ said JPL glaciologist Eric Rignot, a coauthor of the paper.