Huge Antarctic ice shelf Larsen B gone by 2020, says NASA

Larsen B, a huge Antarctic ice shelf, is weakening super-fast and will likely collapse completely and disappear by 2020, say researchers from NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. The ice shelf is about the size of the state of Rhode Island.

The ice shelf partially collapsed in 2002. The last remaining section is flowing more quickly today and is becoming increasingly fragmented and has developed massive cracks, the scientists found.

Larsen B has three tributary glaciers, two of which are flowing much more rapidly and thinning fast, they added.

The Larsen B ice shelf is about the size of the state of Rhode Island. (Image: Wikipedia)

JPL’s Radar Science Group member, Dr. Ala Khazendar, said:

“These are warning signs that the remnant is disintegrating. Although it’s fascinating scientifically to have a front-row seat to watch the ice shelf becoming unstable and breaking up, it’s bad news for our planet.”

“This ice shelf has existed for at least 10,000 years, and soon it will be gone.”

 

Ice shelves keep glaciers in check

Ice shelves stop glaciers from flowing from Antarctica into the sea, they are the glacier gatekeepers.

When an ice shelf vanishes, glacial ice flows into the ocean much more quickly, which in turn exacerbates the rising sea level problem. A separate Princeton study forecast an almost 10-foot sea-level rise by the end of this century.

The researchers, who published their study findings in the journal Earth and Planetary Science Letters, said their study was the first to comprehensively study the health of the Larsden B remnant plus the glaciers that flow into it.

They collected and examined data on bedrock depths and surface elevations from airplanes equipped with special instruments, which participated in Operation IceBridge, a NASA airborne survey campaign that provides unprecedented data on the continent’s ice shelves, ice sheets and glaciers.

Dr. Khazendar and colleagues obtained flow speed data from synthetic aperture radars (from satellites).

The researchers say their estimate for the Larsen B ice shelf remnant’s life span was based on the probable scenario of a huge, widening rift that had formed near to the ice shelf’s ground line, which would eventually create a crack right across the whole thing.

According to Dr. Khazendar, the free-floating remnant will end up as hundreds of icebergs that will drift away, allowing the glaciers to shift towards the sea unhindered and at accelerating speeds.

The fate of the Larsen B remnant and two tributaries

The Larsen B remnant is big – it covers an area of 625 square miles (1,600 sq km), and reaches a thickness of approximately 1,640 feet (500 metres).

It has three major tributary glaciers – Leppard, Starbuck and Flask – each with its own tributary further inland.

Dr. Khazendar commented:

“What is really surprising about Larsen B is how quickly the changes are taking place. Change has been relentless.”

After Larsen B’s partial collapse thirteen years ago, the thickness and flow speeds of the glaciers changed only slightly, so scientists assumed they had remained stable.

However, this latest study found that the Flask and Leppard glaciers have thinned by 65-72 feet (20-22 metres), and have accelerated considerably over the last decade.

The Flask glacier had reached a flow speed of 2,300 feet (700 metres) per year in 2012, which represented an acceleration of 36%.

Flask’s acceleration could shoot up after the Larsen B remnant collapses completely.

After Larsen B partially collapsed thirteen years ago, the glaciers behind the collapsed part of the shelf accelerated to eight times their previous speed.

The smallest of the three glaciers, Starbuck, appears to be stable. Its channel is narrow compared to those of Flask and Leppard. Starbuck is strongly anchored to the bedrock, which probably explains its relative stability.

Principal scientist for the JPL’s Radar Science and Engineering Section, co-author Professor Eric Rignot, said:

“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.”

The study also included scientists from the University of California, Irvine, US, and the University Centre in Svalbard, Norway.

Reference: Eric Rignot, Ala Khazendar, Christopher P. Borstad, Bernd Scheuchl, and Helene Seroussi. “The evolving instability of the remnant Larsen B Ice Shelf and its tributary glaciers.” Earth and Planetary Science Letters (June 2015). DOI: 10.1016/j.epsl.2015.03.014.

Video – The Final Act of the Larsen B Ice Shelf