Like Flipping a Switch: Antarctic Glaciers Sudden Race to Sea
May 22, 2015
“One of the warning signs that a dangerous warming trend is under way in Antarctica will be the breakup of ice shelves on both coasts of the Antarctic Peninsula, starting with the northernmost and extending gradually southward.”
John Mercer – 1978
Very good piece in the Christian Science Monitor explaining a new study of mass loss from a southern region of the Antarctic peninsula. We’ve been hit with a volley of devastating studies showing that “stable” Antarctic ice is much more sensitive to warming than most scientists thought a few decades ago.
The losses began suddenly in 2009 and come in addition to losses from the West Antarctic Ice Sheet, which is shedding 80 billion to 110 billion tons of ice a year, according to the study. Some losses from nearby ice shelves have been underway for decades. But the seemingly abrupt onset of significant ice losses along the southern coast of the Antarctic Peninsula is an eye-opener, suggests Dr. Gardner of JPL. Recent studies have shown that Antarctica’s two continental ice sheets are more sensitive to changes in ocean and air temperatures than previously thought, he notes. But as relatively warm water from deep reaches of the Southern Ocean moved onto the continental shelf, the thinning sped up, melting the ice shelves from underneath, the researchers of the new study concluded. – “It’s like a switch was flipped for a pretty extensive region of the peninsula,” adds Jonathan Bamber, a glaciologist at the University of Bristol in Britain and a member of the team conducting the study. “That isn’t something that you would necessarily expect based on the modeling studies that people have done.”
For most of the 2000s, satellite data shows the glaciers lost about as much ice as they gained, meaning they stayed roughly stable. But around 2009 there was “a remarkable rate of acceleration” in ice loss, the study says.
The red and orange areas in the figure below show thinning of glaciers along the Bellinghausen Sea coast. You can see the melting is much more rapid between 2010 and 2014 (right-hand image) than between 2003 and 2009 (left-hand image).
Change in glacier thickness between A) 2003 and 2009 and B) 2010 and 2014 in the Southern Antarctic Peninsula. Oranges and reds show areas of greatest thinning. Source: Wouters et al. ( 2015)
Several glaciers on the southern Antarctic Peninsula suddenly began shedding ice in 2009, satellite observations now reveal. The region has dumped the equivalent of 72 cubic miles of water—enough to fill 350,000 Empire State Buildings—into the ocean since then, researchers report today in Science. “The region changed from being quiet, in balance, to massive ice loss within a couple of years,” notes lead author Bert Wouters of the University of Bristol. “This is quite surprising, a complete shift of the dynamics in the area. It shows that the ice sheet can react very rapidly to changes in its environment.
Growing evidence has demonstrated the importance of ice shelf buttressing on the inland grounded ice, especially if it is resting on bedrock below sea level. Much of the Southern Antarctic Peninsula satisfies this condition and also possesses a bed slope that deepens inland. Such ice sheet geometry is potentially unstable. We use satellite altimetry and gravity observations to show that a major portion of the region has, since 2009, destabilized. Ice mass loss of the marine-terminating glaciers has rapidly accelerated from close to balance in the 2000s to a sustained rate of –56 ± 8 gigatons per year, constituting a major fraction of Antarctica’s contribution to rising sea level. The widespread, simultaneous nature of the acceleration, in the absence of a persistent atmospheric forcing, points to an oceanic driving mechanism.