Arctic submarine uncovers evidence of giant, ancient ice sheets

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.

Contact: Leonid Polyak, (614) 292-2602; Polyak.1@osu.edu
Written by Pam Frost Gorder, (614) 292-9475;
Gorder.1@osu.edu

[Editor’s note: Polyak will be out of the office March
20-22, but will be reachable by telephone and e-mail
during that time. To reach him by telephone on those
days, please contact Pam Frost Gorder at (614)
292-9475.]