June 14, 2013
Basal Melt Responsible For Antarctic Ice Shelf Loss
redOrbit Staff & Wire Reports - Your Universe Online
The majority of Antarctica´s ice loss is caused by warm ocean waters eating away at the undersides of ice shelves, not the sudden release and breaking away of ice masses from glaciers (a process known as calving), according to new research appearing in Friday´s edition of the journal Science.
That is a far higher rate than scientists previously believed, the researchers said. The discovery could help scientists improve projections of how Antarctica — which holds approximately three-fifths of the Earth´s freshwater in its massive ice sheet — will respond to warming ocean waters, as well as how it will contribute to sea-level rise.
“The traditional view on Antarctic mass loss is it is almost entirely controlled by iceberg calving,” explained lead author Eric Rignot, a UC Irvine professor and a researcher at NASA´s Jet Propulsion Laboratory (JPL) in Pasadena. “Our study shows melting from below by the ocean waters is larger, and this should change our perspective on the evolution of the ice sheet in a warming climate.”
In fact, Rignot said the results of his team´s research could have “profound implications for our understanding of interactions between Antarctica and climate change. It basically puts the Southern Ocean up front as the most significant control on the evolution of the polar ice sheet.”
The study authors, which also include UC Irvine´s Jeremie Mouginot and Bernd Scheuchl and Columbia´s Stanley Jacobs, combined a regional climate model of snow accumulation and a new map of Antactica´s bedrock with ice shelf thickness, elevation and velocity data captured by Operation IceBridge — an ongoing NASA aerial survey of Earth´s poles.
Their goal was to determine how much ice and snowfall entered specific ice shelves, and how much made it to an iceberg, where it could be split off. By combining the data from all of their sources, Rignot and his colleagues were able to determine if the ice shelf was losing mass due to basal melting or gaining mass as a result of the basal freezing of seawater.
“In some places, basal melt exceeds iceberg calving. In other places, the opposite is true,” JPL officials explained. “But in total, Antarctic ice shelves lost 2,921 trillion pounds (1,325 trillion kilograms) of ice per year in 2003 to 2008 through basal melt, while iceberg formation accounted for 2,400 trillion pounds (1,089 trillion kilograms) of mass loss each year.
“Basal melt can have a greater impact on ocean circulation than glacier calving. Icebergs slowly release melt water as they drift away from the continent,” they added. “But strong melting near deep grounding lines, where glaciers lose their grip on the seafloor and start floating as ice shelves, discharges large quantities of fresher, lighter water near the Antarctic coastline. This lower-density water does not mix and sink as readily as colder, saltier water, and may be changing the rate of bottom water renewal.”