Posted on : Fri, 16 Feb 2007 10:06:01 GMT | Author : Steve Walters
WASHINGTON: Scientists have confirmed the existence of extensive network of waterways beneath a fast-moving sheet of Antarctic ice, providing clues on how "leaks" in the system affect the sea level and the ice sheets.
They say these waterways, or rather lakes, some stretching across hundreds of square miles, fill and drain so quickly that the movement can be seen by a satellite observing the surface of the continent. They observed the phenomenon using data collected by NASA's satellites now in orbit.
The scientists allay fears that global warming has created these pockets of water. They say these lakes lie some 2,300 feet below compressed snow and ice, too deep for environmental temperature to reach. However, it is necessary to understand what causes the phenomenon as it can facilitate an understanding of the impact of climate change on the ice sheet in Antarctica, says Helen Fricker of the Scripps Institution of Oceanography La Jolla, California and who headed the scientists' team in the study.
The team presented the results of the study at the annual meeting of the American Association for Advancement of Science and these are being published in the journal Science.
Co-author of the study and chief scientist at the Laboratory for Hydrospheric and Biospheric Sciences at NASA's Goddard Space Flight Center Robert Bindschadler said the discovery of such large lakes exchanging water under the thick sheets of ice has radically altered scientists' view of what is happening at the base of the ice sheet and how ice moves in that environment.
The scientists explained that the surface of the ice sheet appears stable to the naked eye, but because the base of an ice stream is warmer, water melts from the basal ice to flow, filling the system's "pipes" and lubricating the movement of the overlying ice. This web of waterways acts as a vehicle for water to move and change its influence on the ice movement. Moving back and forth through the system's "pipes" from one lake to another, the water stimulates the speed of the ice stream's flow a few feet per day, contributing to conditions that cause the ice sheet to either grow or decay. Movement in this system can influence sea level and melting of ice worldwide.
Fricker said it is necessary that the phenomenon is studied and understood as sea level rises and falls in direct response to changes in the ice.
Scientists have so far discovered more than 145 subglacial lakes, a smaller number of these acting as the plumbing system in the Antarctic. The study using satellite data showed that water is discharged from these under ice lakes into the ocean in coastal areas and it has afforded a new insight into how much and how frequently these waterways leak water and how many connect to the ocean.
Fricker and her colleagues used data from NASA's ICESat, which sends laser pulses down from space to the Antarctic surface and back. The satellite detected dips in the surface that moved around as the hidden lakes drained and filled beneath the surface glaciers, which are moving rivers of ice.
Fricker said it was thought earlier that the changes took place over years and decades, but large changes are now being seen over months.
The scientists worked on the project from 2003 to 2006 and observed the Whillans and Mercer Ice Streams, two of the fast-moving glaciers that carry ice from the Antarctic interior to the floating ice sheet that covers parts of the Ross Sea.