Antarctic Glacier May Yield Clues To Global Climate Change

Hongxing Liu, a geography professor in the College of Geosciences at Texas A&M University, along with Kenneth Jezek of Ohio State University, has been awarded nearly a quarter of a million dollars from the National Science Foundation (NSF) to analyze remotely sensed data from the glacier. The two researchers will be spending the next three years trying to figure out, via computer programs, the thickness of the Lambert ice sheet and its mass balance as it edges toward the sea. Then they will look for answers as to how such glaciers might respond to world climate.

"The Lambert glacier is the largest such ice mass in the world," Liu said. "We believe that studying its movement and mass balance will yield clues that can help us understand the role of glaciers in global climate change."

Their work won't require Liu or Jezek to leave their offices, since they'll be analyzing computer data generated by sensors aboard satellites. They will use data provided by two missions of the Canadian Radarsat satellite, which provided complete coverage of the entire Antarctic continent over a 30 day period in 1997 and over three months in 2000, both at 25m resolution.

The researchers will also be dealing with optical stereo data collected by the Aster sensor onboard the recently-launched NASA Terra satellite, which yields good topographic resolution at the 15m level. Resolution refers to the area represented by each pixel on the satellite image. High-resolution satellite data, showing less area and more detail, is manipulated with sophisticated software to form maps composing a geographical information system (GIS).

"Satellites provide the comprehensive observations needed for modern scientific investigations of ice flow dynamics and mass balance in the Lambert glacier basin," Liu observed. "Optical sensors are affected by clouds and often saturated due to the high albedo of snow for visible wavelengths. This limits their use in Polar regions.

"With the ability to fly unimpeded by the harsh climate, to peer through clouds and to observe day and night, satellite-borne microwave instruments can provide large-scale coverage of the Antarctic ice sheet at very high resolution."

Mass balance measurements tell researchers just how much ice is being formed from compression of snow. Ice thickness is in turn constrained by the surface topography of an area, which, for the Lambert glacier, is still largely unmapped. Liu and Jezek will be using paired radar imaging (interferometric SAR and SAR stereo techniques) to extract a digital elevation model (DEM) and ice velocity maps for the area.

Ice flow velocity is also controlled by an area's surface topography. The researchers will be using radar interferometry data providing full coverage of the glacier on the centimeter level of motion to determine the speed and direction of the Lambert glacier's movement. Data on ice motion and land surface topography, combined with readings from radar echo soundings of the bedrock underlying the glacier, will be used to help estimate the thickness of the ice at any point on the Lambert glacier.

Finally, Liu and Jezek will integrate their research to address the role of glaciers in the dynamics of climate change.

"The theory is that the stability of glaciers is related to sea level change," Liu said. "Any significant change in a glacier's ice thickness or rate of movement could lead to changes in sea level. A catastrophic interpretation of the theory speculates that collapse of the Antarctic ice sheet could raise sea level as much as 60 meters worldwide."

Liu observed that only long-term monitoring of the glacier will help scientists judge whether it is stable or not. He noted that global warming could affect the glacier's stability.

"It is expected that any changes in regional and global climate will result in mass changes in ice streams and glaciers," Liu said. "However, this mechanism is far from being understood.

"In principle, warming leads to reduction of ice. Another possible scenario is that, in a slightly warmer climate, precipitation increases, and high precipitation of snow over Antarctica adds mass to the ice. So, until we've done more analysis, we can't predict what will most likely happen."