7 October 1999

Surfing in the Alps? Maybe by 8999

by Kate Melville

The huge Antarctic ice sheet could be in its death throes! An immense expanse of Antarctic ice that has been receding steadily for 10,000 years may pose the most immediate threat of a large sea level rise because of its potential instability. The West Antarctic Ice Sheet - about 360,000 square miles, or roughly the size of Texas and Colorado combined - rests on the Antarctic land mass below sea level, which makes it particularly susceptible to rising sea level.

A complete collapse would raise global sea level 15 to 20 feet, enough to flood many low-lying coastal regions (and particularly low lying island nations). At least this is the theory of the research team led by Howard Conway, Associate Professor of Geophysics at the University of Washington. The study has been published in the October 8th issue of Science.

Human-caused climate change may hasten the ice sheet's demise, but there might be nothing humans can do to slow or reverse the trend. Conway is quoted as saying, "Collapse appears to be part of an ongoing natural cycle, probably caused by rising sea level initiated by the melting of the Northern Hemisphere ice sheets at the end of the last ice age. But the process could easily speed up if we continue to contribute to warming the atmosphere and oceans."

Using evidence gathered from raised beaches and radar imaging of subsurface ice structures to reconstruct historic changes, the scientists found the ice sheet has both thinned and decreased in area since the last glacial maximum 20,000 years ago.

The regions ice covering was once as much as a half-mile thick.

The timing of deglaciation was determined by carbon-dating of samples found on beaches that are now up to 90 feet above the current sea level.

Other evidence came from Roosevelt Island, an island of ice in the Ross Sea. While floating ice now surrounds the island, computer simulations suggest that ice in the area was once about 1,600 feet thicker during the last ice age.

The researchers found that the grounding line (the boundary between floating ice and grounded ice) has receded about 800 miles since the ice age and has withdrawn an average of about 400 feet per year for the last 7,600 years. The average is similar to the current rate, and there is no indication the retreat is slowing at all.

Other scientists have found evidence suggesting the West Antarctic Ice Sheet might have disintegrated in the past. Fragments of tiny algae called diatoms have been recovered from cores drilled through the ice and into the land beneath. It is believed diatoms require open water to build their colonies, which suggests the region once was free of ice, perhaps as recently as 130,000 years ago between the last two ice ages.