Arctic Submarine Uncovers Evidence Of Giant, Ancient Ice Sheets

Studying the formation and demise of these ancient ice sheets may help scientists better understand Earth's climate changes and, in particular, predict whether the melting of today's polar ice could lead to catastrophic floods in the future.

Leonid Polyak, research scientist at Byrd Polar Research Center at Ohio State, and his colleagues obtained sonar images of the Arctic Ocean floor through a unique collaboration between the U.S. Navy and civilian scientists -- the Science Ice Exercises (SCICEX) program.

The results appear in the March 22 issue of the journal Nature. Polyak's collaborators, Margo Edwards of the University of Hawaii and Bernard Coakley of Tulane University, were chief scientists on the 1999 SCICEX mission, which took place aboard the nuclear submarine USS Hawkbill.

Within two separate, somewhat elevated regions of the Arctic Ocean floor -- the Lomonosov Ridge near the North Pole and the Chukchi Borderland near Alaska -- SCICEX images showed numerous features carved into the seafloor, including matching sets of parallel grooves and ridges. Sometime in the past, Polyak said, the bottom of a very massive floating ice sheet scraped across the seafloor in both areas -- almost 1 km below the water surface at the Lomonosov Ridge and more than 700 meters below the water surface at the Chukchi Borderland.

The sonar images clearly showed objects resembling rocks and other debris that may have once been dragged along the seafloor beneath the grounded ice.

"The results were just fantastic. We had hoped to find these seafloor features, but we hadn't expected to get such beautiful images," Polyak said.

"Such amazingly coherent sets of streamlined grooves and ridges could only be made by one thing - sliding ice," Polyak continued. And only a large ice sheet could carve such a broad sets of parallel features. Free-floating icebergs, he explained, carve random patterns into the seafloor.

The finding may bolster a theory held by some scientists: that one giant ice sheet covered the entire Arctic periodically during the ice ages that occurred between 10,000 and 1.5 million years ago.

But Polyak thinks that the same features might have been carved by several large ice sheets instead of one. To find out for sure, he and his colleagues must determine whether the features formed at the same time in different regions of the Arctic Ocean. That's why the researchers have applied for funding to return to the Arctic on an icebreaker to take core samples from the seafloor.

"Even if there were two or more ice sheets instead of one, they were still giant structures of several hundred kilometers in length -- comparable to vast floating ice sheets observed today around Antarctica," said Polyak.

The researchers sought evidence of the ancient floating ice sheets in part to gather clues about the future of the West Antarctic Ice Sheet.

Unlike the ice in East Antarctica, the ice in West Antarctica is considered unstable because a large portion of it is floating. For years, scientists have debated whether a warming of earth's climate would cause the ice sheet in West Antarctica to collapse, which would cause sea levels to rise fast, possibly as high as 20 feet all over the world.

Polyak, a former biologist, says these findings also hold implications for other areas of science. For instance, he wonders how prehistoric life in the Arctic Ocean could have survived if the entire area was covered with an ice cap of several hundred meters in thickness.

This question is related to a recently proposed theory called "snowball Earth," Polyak said. The theory holds that ice completely covered the Earth's oceans at some time between 550 and 750 million years ago, drastically affecting the evolution of primitive life.

"Who knows - maybe clarifying the history of floating ice sheets in the Arctic Ocean will even help us understand the evolution of ice-bound planets, such as Jupiter's moon Europa," he said.