Antarctica ice melt drove sea level surge

CORVALLIS, Ore., March 28 (UPI) -- At the end of the last Ice age the world's sea levels swelled, submerging the shores of coastal regions. Now researchers have pinpointed the cause of that dramatic event -- a sudden collapse of Antarctica's ice sheets.

While scientists have known about the "big melt" for over a decade, the team of American, Canadian and British scientists is the first to pinpoint its cause.

The findings highlight the important role of the Antarctica ice sheets in influencing sea levels and climate change. When the continent's ice sheets melted 14,200 years ago, it caused a 70 feet rise in sea levels in only 500 years -- a rate 20 times faster than the current pace of change.

If the expansive East Antarctica ice sheet were to give way today, it would raise the earth's sea levels by 200 feet. But such a cataclysmic event is unlikely to occur, said lead author of the study Dr. Peter Clark, professor of geosciences at Oregon State University in Corvallis, Ore.

"The only threat or concern now is the West Antarctica ice sheet which would raise sea levels about 20 feet if it were to collapse. Greenland and East Antarctica (ice sheets) are quite stable," he said.

To determine the source of the long-ago rising waters scientists developed a method for "fingerprinting" the ice sheets that existed during this period.

The fingerprinting uses the patterns created by both the rise in the total sea level and by the gravitational pull of the huge bodies of ice. The masses of the ice sheets are so large that their individual gravitational pull slightly draws up nearby waters. When a particular ice sheet melts it not only adds water to the ocean level overall but its individual pull is also lessened. As a result the waters settled into their shorelines in predictably different ways.

The team compared their predictions with contemporary data on sea level change available from shoreline fossil deposits, zeroing-in on Antarctica as the driving force behind the ancient surge in ocean levels.

Understanding this historic meltwater event could provide clues to what will happen if Antarctica's massive ice sheets melt in the future. Increasing temperatures and rising atmospheric carbon dioxide levels seen today are similar to conditions at the time of the big melt. The changes at the end of the last Ice age, however, were caused by a variety of natural forces including shifts in the Earth's orbit around the Sun due to the influence of the other planets.

That is not the case today, said Clark. No one is sure, he said, why the temperature is rising though the upward shift in carbon dioxide levels is due to human activity he said. He noted that today's changes are too gradual to be attributed to orbital shifts.

Dr. Clark's findings challenge a prominently held theory that the rise in sea levels that occurred 14,200 years ago was caused by the melt of a massive ice sheet that once covered Canada.

"He has found that this theory is on shaky ground and has shown that some of the interpretations of the past were wrong," said Dr. Richard Alley, professor of geosciences at Pennsylvania State University in University Park. "Antarctica is a player in these very large sea changes and this study focuses our attention on the South as the cause," he said.

(By Koren Capozza in San Francisco with additional reporting by Dee Ann Divis in Washington)