by Pam Frost Gorder - Ohio State University News
COLUMBUS,
Ohio - A scientific expedition on a submarine in the Arctic has
found the footprints of ancient floating ice sheets -- possibly
the largest masses of ice ever to cover the earth's oceans.
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.
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