International Expedition to the Top of the World May Hold Clues To Formation of Earth’s Crust

First Cruise of New U.S. Coast Guard Icebreaker HEALY

When the new U.S. Coast Guard icebreaker HEALY
departs Tromso, Norway, July 31 for a two-month cruise across the Arctic
Ocean, scientists won’t be studying the ice cap but the seafloor far below.
Their focus will be the Gakkel Ridge, three miles beneath the ocean surface,
the slowest spreading ridge on earth. It is a window into the earth’s
interior scientists hope will help fill a gap in their knowledge of how
the earth’s crust forms.

The expedition, funded by the National Science Foundation’s
Office of Polar Programs, has been a long time coming for Senior Scientist
Henry Dick of the Woods Hole Oceanographic Institution (WHOI), who first
proposed studying the ridge some 15 years ago. Dick is a co-principal
investigator on the cruise, and will be working with Chief Scientist Peter
Michael of the University of Tulsa and fellow co-principal investigators
Charles Langmuir and Steven Goldstein of the Lamont-Doherty Earth Observatory
at Columbia University and David Graham of Oregon State University. The
U.S. team will be working jointly with an international scientific team
aboard the German icebreaker POLARSTERN.

“Mid-ocean ridges are a means to sample the earth’s
deep interior,” Dick says. “They girdle the planet, like the
seams on a baseball, and are where new crust is formed. Energy is transferred
along the ridges from the earth’s interior to the surface, helping the
planet cool itself but also resulting in volcanic activity and the formation
of hydrothermal vents with their exotic marine life. Many clues about
how the Earth is evolving and changing to links to the origins of life
on earth may be found here, yet humans have explored very little of it.”

Click to enlarge

The Gakkel Ridge is an ultra slow spreading ridge,
meaning it is spreading less than one centimeter a year, as compared to
the fastest spreading ridges in the Pacific Ocean, which spread 20 times
faster, or about as fast as your fingernails grow.

“I am expecting to find a lot of hydrothermal
vent activity in the Arctic because this is tectonically controlled, and
with so little magma coming out of the ridge it is just like a great big
crack in the earth. Scientists previously thought there was little volcanic
activity along the Gakkel Ridge, but information from a 1999 submarine
cruise indicates there may be an isolated, very large megavolcano at the
eastern end of the ridge filling up the crack,” Dick says. “The
Gakkel Ridge is spreading so slowly that ocean crust doesn’t form as it
does on other parts of the mid-ocean ridge. Instead the mantle is spreading
right onto the sea floor. If we could see it, it would look like giant
slabs of a grass green rock called peridotite, made mostly of olivine
(familiar to many as the gemstone peridotite), rising out of the sea floor
about a mile high and over a distance of about 25 miles. The Gakkel Ridge
is like no other in the world.”

The scientists will try to recover volcanic rock samples
from the sea floor along some 500 miles of the ridge by cracking through
the ice with the two ships, one making a path for the other, to lower
a cable to the sea floor to grab some rock samples. Because of the difficulties
they face in such an effort, a number of innovative sampling tools have
been designed and built at WHOI by James Broda, who will be aboard the
ship, and Institution colleagues for this first major sampling cruise
on the ridge. With unofficial names like “Bed of Nails,” the
tools were not designed for beauty but to be practical, able to get through
the ice cover into water some 4 kilometers (about two and a half miles)
deep and hard rock on the ocean floor below. Only two samples have been
collected at the ridge by German scientists, both by piston coring, so
little is known about the ridge and the processes shaping the earth’s
surface.

“The Gakkel Ridge is unique because it is virtually
unsampled,” Dick says. “It is located in a very hostile environment,
and logistics have prevented us from getting there until now. With the
new capabilities of the Coast Guard icebreaker HEALY, U.S. scientists
will be able to collect the samples needed to address major questions
about the formation of the mid-ocean ridge, the largest geological feature
on the planet.”

“About one-third of the sea floor is formed at
very slow and ultra slow spreading ridges like the Gakkel Ridge,”
Dick adds. “The thickness of the ocean crust is highly variable and
unknown, and the exchange of magma and gases from the earth’s interior
to the sea floor appears to be less than we had thought. Understanding
the role of ocean ridge formation is critical to understanding the global
geochemical cycle, even to understanding global change.”

The 420-foot HEALY will travel some 800 miles from
Norway to the edge of the ice cap in three days at 12 knots, typical speed
for a research vessel. Once in the ice, however, the speed will slow to
a few knots, or a few miles per hour, depending on the thickness of the
ice cap. The HEALY and POLARSTERN will work in tandem sampling across
the Arctic, hoping to get close to the North Pole. They plan to sample
along some 500 miles of the ridge before returning to Tromso in early
October.

“For years many people thought that most of the
earth’s crust was uniform, like a layer cake. What we have found out in
the past few decades has totally changed that view, and I expect the results
of this cruise will further change our views.” Dick says. “At
the least, it will be an incredible adventure!”

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