SAN FRANCISCO – An Ohio State University study has revealed a complex picture of change that is occurring in the West Antarctic Ice Sheet (WAIS).
Scientists here are calibrating data from NASA's Ice, Cloud, and land Elevation Satellite (ICESat), and using the satellite to study the ice streams that carry ice from the interior of the WAIS out to sea.
Early results of the study clearly show that all the ice streams of the WAIS have changed substantially in the last five years, but each in its own way, explained Bea Csatho, research scientist at Ohio State's Byrd Polar Research Center (BPRC) and head of the calibration project.
Csatho presented those early results on December 10 in a poster session at the American Geophysical Union meeting in San Francisco.
According to the ICESat data, some WAIS ice streams are thickening and others are thinning; some are flowing faster than before, and others are slowing down.
Launched in January 2003, ICESat uses a radar-like system called lidar to measure whether ice sheets in the polar regions are growing or shrinking. If the ice is shrinking, then global sea levels could rise over time, and ICESat will attempt to gauge the extent of such effects.
The Ohio State scientists are calibrating the ICESat data by comparing it to a baseline data set taken by NASA's Airborne Topographic Mapper.
ICESat is designed to detect changes in ice sheet surface elevation as small as 1.5 centimeters (0.6 inches) per year over areas that measure 100 kilometers by 100 kilometers (62 miles by 62 miles). This is a real feat, Csatho said, since rough and variable landscapes are notoriously difficult to map.
"Given the terrain, we were very happy to get such a good accuracy," she said.
An aerial composite image showing the whole of the Antarctic Continent. The West Antarctic Ice Sheet appears on the left of the image. [click for larger version]
Mapping the surface of ice sheets poses a challenge to scientists because there are few, if any, landmarks such as mountains sticking out above the ice that can be used as reference points for the satellite measurements.
To verify the accuracy of ICESat, scientists mapped part of the Antarctic Dry Valleys with NASA's Airborne Topographic Mapper.
NASA sponsored a project for Ohio State to develop new software tools to process this reference data set, and the resulting digital elevation models depict the surface of the Dry Valleys with unprecedented details and accuracy.
The scientists then chose to use ICESat for their ongoing study of ice streams in the WAIS, because they had access to data previously collected by a group at the University of Texas that could be used for comparison. This work was funded by the National Science Foundation.
When the scientists made their comparison, what they found was a new, complex picture of the WAIS that raises more questions than it answers, said Kees van der Veen, visiting associate professor of geological sciences and research scientist at BPRC.
Ice streams are currents of ice flowing within a larger mass of ice. The thickness of a stream and flow rate are indications of larger changes in the ice.
NASA image showing newly named ice streams on the West Antarctic Ice Sheet. Three of the ice streams were named for Ohio State researchers. [click for larger version]
This new ICESat study comes not long after the Advisory Committee for Antarctic Names honored van der Veen and ten other glaciologists by renaming WAIS ice streams after them.
"It's an honor of course, but it's led to the interesting situation of me studying the Van der Veen Ice Stream," he said, laughing.
The new data from ICESat indicate that the WAIS is undergoing many changes.
The Whillans Ice Stream -- named after late Ohio State glaciologist Ian Whillans -- is slowing down, the Ohio State researchers reported. Upstream, parts of the ice stream are thinning, while downstream, parts are thickening.
"The flow has slowed and it's showing signs of shutting down," van der Veen said. "When that happens, the flow of ice from the interior of that region will basically stop, as happened to the neighboring Kamb Ice Stream, which came to a virtual standstill some 150 years ago."
Meanwhile, van der Veen's namesake ice stream has shown even more complex behavior. It appears to have stopped thinning and is now is gaining mass.
The Kamb Ice Stream is also expanding, and showing signs that its flow will increase.
Taken together, this activity amounts to a great deal of change for the region, all within five short years, said Csatho.
"These are really big changes," van der Veen concurred. "So the question we have to ask now is, why?"
While the ice in East Antarctica is grounded on a continental landmass, the WAIS is grounded only on a series of islands below sea level -- a fact that has caused scientists to suspect that its condition may be particularly sensitive to climate change.
Some have debated whether global climate change could cause the WAIS to collapse. The break-off from the ice sheet of huge, tabular icebergs in recent years has increased those suspicions.
If so much ice melted into the oceans at once, sea levels could rise as high as 20 feet all over the world, within a single century. The results would have serious impacts on coastal communities, and change the faces of the continents as we know them.
It's a dire prediction. But the recent increase in activity of the WAIS does not necessarily mean that the prediction will come true, van der Veen said. To the contrary, he feels that the new ICESat data shows the situation to be much more complex than that.
"The important lesson here is, you can't look at the flow of any single ice stream and say, 'there goes West Antarctica,'" he said.
Csatho agreed. "There are very complex interactions happening in the WAIS. It's actually very exciting that we have tools like ICESat, so that during our lifetime we can learn more about what's going on," she said. "Antarctica is becoming the best-mapped continent in the world."
Other Ohio State scientists on the project include Toni Schenk, professor of civil and environmental engineering and geodetic sciences; Catherine Tremper, an image processing consultant to the university; Sung Woong Shin, a postdoctoral researcher at BPRC; and Yushin Ahn, Taehun Yoon, and Kyung In Huh, all current graduate students.
They are working with Robert Thomas, a scientist with EG&G Services; William Krabill, a scientist at NASA's Laboratory for Hydrospheric Processes at Wallops Flight Facility in Virginia; Vandy Spikes, a graduate student at University of Maine's Climate Change Institute; and Impeyong Lee, formerly a postdoctoral researcher at BPRC, and now a professor of geoinformatics at the University of Seoul, Korea.
Materials provided by Ohio State University. Note: Content may be edited for style and length.
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