September 6, 2012
Glacial Thinning Rapidly Increasing In South America
April Flowers for redOrbit.com - Your Universe Online
Much has been said lately about Arctic ice melting at an alarming and record-breaking rate, but other ice fields are suffering the same effects of global warming as well.
A new study, published in the September 5 issue of Geophysical Research Letters, finds that the rate of glacial thinning has increased by about half over the last dozen years in the Southern Patagonian Icefield, compared to the 30 years prior to 2000.
The Southern Patagonian Icefield is located between Argentina and Chile in the Patagonian Andes. It is the world's second largest contiguous extrapolar ice field.
“Patagonia is kind of a poster child for rapidly changing glacier systems,” said Michael Willis, lead author and a research associate at Cornell University. “We are characterizing a region that is supplying water to sea level at a big rate, compared to its size.”
The Southern and Northern Patagonian Icefields are the largest icefields in the southern hemisphere excluding Antarctica. The results of this study show that the icefields are losing ice faster since the turn of the century and contributing more to the rising sea levels than ever before.
Previous studies showed that between 1970 and 2000 both icefields together raised global sea levels by an average of 0.042 millimeters each year. Since 2000, that number increased to 0.067 millimeters on average per year — about two percent of total annual sea level rise since 1998.
Willis and his team focused on the Southern Icefield, which loses around 20 billion tons of ice every year, which is roughly 9,000 times the volume of water stored by Hoover Dam annually. Over the last 12 years, the Southern Patagonian Icefield has lost enough water to cover the entire United States with 2.7 centimeters of water. Combined the two fields lost enough to raise that level to 3.3 centimeters.
To map the changing Southern Patagonian Icefield, Willis and his colleagues from the Center for Scientific Studies (CECs) in Valdivia, Chile, collected data from two separate satellite missions; NASA's Advanced Spacebourne Thermal Emission and Reflection Radiometer (ASTER) and the Shuttle Radar Topography Mission (SRTM).
ASTER is an imaging instrument onboard Terra, the flagship satellite of NASA's Earth Observing System (EOS) which is used to create detailed maps of land surface temperature, reflectance and elevation. SRTM obtained elevation data on a near global scale to generate a high-resolution digital topographic database of Earth during an 11-day mission aboard the Space Shuttle Endeavor in February of 2000.
The team compared 156 satellite images taken over a 12-year period from ASTER to data from the SRTM to map how the Southern Patagonian Icefield changed in height and overall size between February 2000 and March 2012.
They then compared the findings to a different set of data from the twin satellites of NASA's Gravity Recovery and Climate Experiment (GRACE).
GRACE makes detailed measurements of Earth's gravity field, which will lead to discoveries about gravity and Earth's natural systems.
“Using ASTER, we think that we have a good idea of where things are changing. But with GRACE we get a good idea of when things are changing. So we have this powerful hybrid,” Willis said. From their new map, the scientists identified individual glaciers and how much each has thinned since 2000. On average, the Southern Patagonian Icefield glaciers have thinned by about 1.8 meters (5.9 feet) per year.
“We find some glaciers are stagnant and even that some have advanced slightly but on the whole, retreat and thinning is prevalent,” Willis said. “Interestingly, we see thinning occurring up to the highest elevations, where presumably it is coldest.”
Global warming contributes to the thinning at the highest and coldest regions of the ice field, and moreover, warmer temperatures mean greater chances that rain, as opposed to snow, will fall on and around the glaciers. This double threat of warming and more rain may change the amount of water beneath the glaciers. More water means less friction, so the glaciers start to move faster as they thin, moving even more ice into the oceans. Rising lakes at the front of the glaciers may also play a part as they eat away at the ice edges faster, causing the glaciers to retreat even further.
Even though scientists have yet to understand exactly how warming temperatures will continue to influence these South American icefields, this new study provides valuable information for future predictions.
“A study like this really provides a strong data set to validate and calibrate glacial models that we could then use to simulate future changes in glaciers,” he said. “Modeling is really the only tool we have to provide future predictions.”