10,000-Year-Old Antarctic Ice Shelf Could Disappear Before Decade's End

_{It's the Final Act for Larsen B Ice Shelf, NASA Finds}

_NASA,

_{14 May, 2015}

_{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 is likely to disintegrate completely before the end of the decade.}

A team led by Ala Khazendar of NASA's Jet Propulsion Laboratory in Pasadena, California, 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.

"These are warning signs that the remnant is disintegrating," Khazendar said. "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 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. 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 IceBridge, 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 spaceborne synthetic aperture radars operating since 1997.

Khazendar noted his estimate of the remnant's remaining life span was based on the likely scenario that a huge, widening rift that has formed near the ice shelf's grounding line will eventually crack all the way across. The free-floating remnant will shatter into hundreds of icebergs that will drift away, and the glaciers will rev up for their unhindered move to the sea.

Located on the coast of the Antarctic Peninsula, the 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. Its three major tributary glaciers are fed by their own tributaries farther inland.

"What is really surprising about Larsen B is how quickly the changes are taking place," Khazendar said. "Change has been relentless."

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. The 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 the small glacier is 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.
The research team included scientists from JPL; the University of California, Irvine; and the University Centre in Svalbard, Norway. The paper is online at:

http://go.nasa.gov/1bbpfsC

NASA uses the vantage point of space to increase our understanding of our home planet, improve lives and safeguard our future. NASA develops new ways to observe and study Earth's interconnected natural systems with long-term data records. The agency freely shares this unique knowledge and works with institutions around the world to gain new insights into how our planet is changing.
For more information about NASA's Earth science activities, visit:

http://www.nasa.gov/earth

Vast Antarctic ice shelf a few years from disintegration, says Nasa

Remnant of Larsen B Ice Shelf, about half the size of Rhode Island, is expected to break apart completely around the year 2020, adding to sea level rises

the Guardian,

15 May, 2015

The last intact section of one of Antarctica’s mammoth ice shelves is weakening fast and will likely disintegrate completely in the next few years, contributing further to rising sea levels, according to a Nasa study released on Thursday.

The research focused on a remnant of the so-called Larsen B Ice Shelf, which has existed for at least 10,000 years but partially collapsed in 2002. What is left covers about 625 sq miles (1,600 sq km), about half the size of Rhode Island.

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 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.

“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 Eric Rignot, co-author of the study and a glaciologist at Nasa’s Jet Propulsion Laboratory in Pasadena, California.

Almost 200 countries have agreed to negotiate a United Nations (UN) pact by the end of 2015 to combat global climate change, which most scientists expect will bring about more flooding, droughts, heat waves and higher seas.

The UN Intergovernmental Panel on Climate Change has cited a probability of at least 95% that accelerated warming of the planet has been triggered by human activities, led by atmospheric emissions of greenhouse gases from the burning of fossil fuels.

The study, published online in the journal Earth and Planetary Science Letters, was based on airborne surveys and radar data.

Thinning Antarctic ice shelf could contribute to sea level rise, says study

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The study’s lead scientist, Ala Khazendar, said analysis of the data reveals that a widening rift in Larsen B will eventually break it apart completely, probably around the year 2020.

Once that happens, glaciers held in place by the ice shelf will slip into the ocean at a faster rate and contribute to rising sea levels, scientists say.

The study also found Leppard and Flask, two main tributary glaciers of the ice shelf, have thinned by between 65 and 72 feet (20 to 22 meters) in recent years, and the pace of their shrinking has accelerated since the immediate aftermath of the 2002 partial collapse of the ice shelf.

_{10,000-Year-Old Antarctic Ice Shelf Could Disappear Before Decade's End, NASA Study Finds}

Thinning Antarctic ice shelf could contribute to sea level rise, says study 

_{From Radio NZ in March}

Antarctic ice shelves melting at increasing rates


A 2014 documentary

Under the Antarctica - Full Documentary

The Antarctic ice sheet is one of the two polar ice caps of the Earth. It covers about 98% of the Antarctic continent and is the largest single mass of ice on Earth. It covers an area of almost 14 million square km and contains 26.5 million cubic km of ice.

That is, approximately 61 percent of all fresh water on the Earth is held in the Antarctic ice sheet, an amount equivalent to 70 m of water in the world's oceans. In East Antarctica, the ice sheet rests on a major land mass, but in West Antarctica the bed can extend to more than 2,500 m below sea level. The land in this area would be seabed if the ice sheet were not there.

The icing of Antarctica began with ice-rafting from middle Eocene times about 45.5 million years ago and escalated inland widely during the Eocene - Oligocene extinction event about 34 million years ago. CO2 levels were then about 760 ppm and had been decreasing from earlier levels in the thousands of ppm. Carbon dioxide decrease, with a tipping point of 600 ppm, was the primary agent forcing Antarctic glaciation.

The glaciation was favored by an interval when the Earth's orbit favored cool summers but Oxygen isotope ratio cycle marker changes were too large to be explained by Antarctic ice-sheet growth alone indicating an ice age of some size. The opening of the Drake Passage may have played a role as well though models of the changes suggest declining CO2 levels to have been more important.

Ice enters the sheet through precipitation as snow. This snow is then compacted to form glacier ice which moves under gravity towards the coast. Most of it is carried to the coast by fast moving ice streams. The ice then passes into the ocean, often forming vast floating ice shelves. These shelves then melt or calve off to give icebergs that eventually melt.

If the transfer of the ice from the land to the sea is balanced by snow falling back on the land then there will be no net contribution to global sea levels. A 2002 analysis of NASA satellite data from 1979 - 1999 showed that while overall the land ice is decreasing, areas of Antarctica where sea ice was increasing outnumbered areas of decreasing sea ice roughly 2:1.

The general trend shows that a warming climate in the southern hemisphere would transport more moisture to Antarctica, causing the interior ice sheets to grow, while calving events along the coast will increase, causing these areas to shrink. A 2006 paper derived from satellite data, measures changes in the gravity of the ice mass, suggests that the total amount of ice in Antarctica has begun decreasing in the past few years.

Another recent study compared the ice leaving the ice sheet, by measuring the ice velocity and thickness along the coast, to the amount of snow accumulation over the continent. This found that the East Antarctic Ice Sheet was in balance but the West Antarctic Ice Sheet was losing mass. This was largely due to acceleration of ice streams such as Pine Island Glacier. These results agree closely with the gravity changes.

The estimate published in November 2012 and based on the GRACE data as well as on an improved glacial isostatic adjustment model indicates that an average yearly mass loss was 69 ± 18 Gt/y from 2002 to 2010. The West Antarctic Ice Sheet was approximately in balance while the East Antarctic Ice Sheet gained mass. The mass loss was mainly concentrated along the Amundsen Sea coast