The Role of Subglacial Lakes

A slab of ice larger than the continental United States smothers much of East Antarctica. A river of ice nearly 800 kilometers long, the Recovery Ice Stream, drains part of the East Antarctic Ice Sheet, sliding roughly 35 billion tons of ice into the ocean each year.

In some places, the ice stream lumbers along at 2 to 3 meters per year, but in others, it suddenly accelerates to 50 meters per year. It is as if the ice stream slips on a banana peel. Surprisingly, the acceleration doesn’t happen on a steep slope; it happens as the ice stream passes over a relatively flat area. What causes this sudden speed up?

return to: Something under the Ice is Moving

Without satellite technology, the Recovery Ice Stream’s acceleration might be a mystery without a solution, but a team of researchers from Columbia University, NASA, and the Universities of New Hampshire and Washington combined satellite-based data from several sensors to peer across and below the ice in the area: radar data of ice velocity, photo-like images of the surface, and laser data of ice elevation. They also analyzed data from ground-based radar surveys collected between 1964 and 1966 on one of the few expeditions to traverse the area.

This image combines elevation data from the ICESat satellite and digital images from the Mosaic of Antarctica to show subglacial lakes in Dronning Maud Land, Antarctica, where the Recovery Ice Stream is located. (NASA image courtesy NASA Goddard Space Flight Center Science Highlights January 2006.)

The researchers identified four large lakes below the ice; their combined area is close to that of Antarctica’s largest subglacial water body, Lake Vostok. Their location coincides closely with an area where the Recovery Ice Stream widens and accelerates, offering a neat explanation of what enables the ice to move faster there.

Beneath an ice stream’s frigid surface, its underbelly is warmed and melted by geothermal heat and friction created as it passes over the bedrock below. The researchers deduced that once the underside of the ice stream moves over a lake, the friction disappears, and the ice speeds up. Some lake water freezes onto the bottom of the ice, but this ice is warm and soft compared to the rest of the ice stream. When the ice stream reaches the downstream side of the lake, the warmer, softer ice at its base allows the ice stream to glide over land at a substantially quicker pace.

“Large subglacial lakes that clearly initiate streaming flow in a major ice stream have never been so completely documented before,” explains one of the authors, Chris Shuman of NASA Goddard Space Flight Center. The location and influence of subglacial lakes on ice streams are among the processes that scientists must understand in order to accurately model ice streams and ice sheets and to predict their contributions to sea level.

References:
• Bell, R. E., Studinger, M., Shuman, C. A., Fahnestock, M. A., and Joughin, I. (2007). Large subglacial lakes in East Antarctica at the onset of fast-flowing ice streams. Nature, 445, 904-907.
• Kohler, J. (2007). Lubricating Lakes. Nature, 445, 830-831.
• Perkins, S. (2007). Fits and starts: What regulates the flow of huge ice streams? Science News. 171(13) Available online.
• NASA: Antarctic Ice Sheet’s Hidden Lakes Speed Ice Flow Into Ocean, May Disrupt Climate. March 5, 2007.

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The Recovery Ice Stream feeds the Filchner Ice Shelf and the Weddell Sea. Satellites revealed subglacial lakes that accelerate ice stream flow. (Image courtesy National Snow and Ice Data Center, Mosaic of Antarctica.)