Antarctic ice: slippin' and slidin.' (ice sheet movements found irregular in 100,000-year cycle study) (Brief Article)

For those worried that global warming might send Antarctica's glaciers sliding into the ocean--raising sea levels and provoking massive coastal flooding--there may be good news and bad. A new study suggests rising temperatures may not have any immediate impact on the West Antarctic ice sheet, the area most prone to collapse. That's good. However, that same study indicates that the ice sheet behaves erratically, sometimes collapsing suddenly without regard to global temperatures.

In an attempt to predict the ice sheet's behavior, Douglas R. MacAyeal of the University of Chicago developed a computer model using data about the ice sheet's underpinnings. He ran his model for 10 consecutive 100,000-year cycles to simulate the impact of changes in surface temperatures and sea levels over 1 million years. MacAyeal was "shocked" to find that the ice sheet collapsed into the ocean at three irregular intervals -- 190,000 years ago, 330,000 years ago, and 750,000 years ago. These collapses did not necessarily correspond with periods of surface warming. "Think of how a yo-yo would behave if you had an uncoordinated person operating it," MacAyeal told SCIENCE NEWS. "You'd have a sort of jerky, erratic behavior instead of a nice smooth action. That's what I saw."

MacAyeal's model uses recently obtained data about the layer of "till" beneath the ice. Till, a muck of ground-up rock and water, acts as a lubricant for the ice sheet, influencing whether it slides into the ocean, he says. The till apparently reacts unpredictably to both surface temperature and heating from inside Earth, MacAyeal reports in the Sept. 3 NATURE.

Polar researcher Cornelis van der Veen at Ohio State University in Columbus expresses skepticism about the till's role in the ice sheet's behavior. "In [MacAyeal's] model, the velocity of the ice stream is determined by the properties of the till," he says. "Our interpretations indicate that is not the case."