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| Enlarge ImagePuma and Jaguar are autonomous underwater vehicles (AUVs) designed to overcome the technical challenges that now preclude under-ice operations in the Arctic Ocean. They will home in to an acoustic beacon and latch onto a wire suspended from a hole in the ice. Puma has sonars and sensors to search wide areas and detect temperature, chemical, or turbidity signals from hydrothermal vent plumes (the green lasers detect particulates in the water). Puma can track the plume back to its seafloor source, where Jaguar then will be deployed to hover with camera and lighting systems,high-resolution sonar, and a manipulator arm for close-up imaging, mapping, and sampling.
(Illustration by E. Paul Oberlander, Woods Hole Oceanographic Institution ) |
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| Enlarge ImageAn expedition in 2007 is planned to search for, map, and sample hydrothermal vents for the first time beneath the ice-covered Arctic Ocean, along the Gakkel Ridge. (Illustration by Jayne Doucette, WHOI Graphic Services) |
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Rob Reves-Sohn, Associate Scientist
Geology and Geophysics Department
Woods Hole Oceanographic Institution Imagine you have inherited a magnificent medieval castle. You wander
its corridors, climbing spiral staircases to hidden towers, delving
purposefully into subterranean caverns, and delighting in the details
of its architecture, history, and artistic treasures. Over time you
come to realize there is a great North Wing that has long been sealed
off from the rest of the castle.
You’ve found old documents in
the library describing construction of the North Wing, and it appears
as though it was built using rare materials that are not found anywhere
else in the castle. As best as you can tell the castle’s main
thermostat is inside the North Wing, which adds some urgency because
lately the castle seems to be getting inexplicably warmer. And, perhaps
most intriguing, recent evidence suggests that something—perhaps even
something unusual—might actually be living in there.
Even so,
it might be more accurate to confess that you’ve just got to gain
entrance to the North Wing—because not being able to enter rooms in
your own house is unbearable.
Finding a way in
You come to realize, however, that you’re not the first to try.
Numerous intrepid individuals have dedicated themselves to the pursuit
over the years, their stories comprising a veritable tome of
frustration and failure. And why? Because the North Wing is hidden
under a moat of water more than two miles deep, which, in turn, is
covered by a permanent layer of ice.
Moreover, it is so far
north that the compasses and gyroscopes typically used for navigation
are essentially useless. The tools required to get through ice and into
the abyss to explore the North Wing cannot be bought at any price. You
will have to make them yourself.
You have probably guessed by
now that the castle in this mental exercise is Earth, and the North
Wing is the vast, ice-covered Arctic Ocean Basin. If the old adage is
true that we know more about the surface of our neighboring planets
than we do about Earth’s ocean basins (and it is), then nowhere is it
more true than the Arctic Basin.
A blank spot on the map of Earth
Deep-sea research is hard enough as it is. But cover the ocean you’re
trying to explore with a permanent ice cap, limit your available field
season to a few months that are not too cold and dark, and factor in a
generally inaccessible location at the very top of the world, and you
can begin to appreciate why we know so little about the Arctic Basin.
In fact, were it not for a few Russian and American scientists whiling
the months away in camps on drifting ice floes, we would know almost
nothing at all about the earth’s great North Wing. (Actually, U.S. and
Soviet navies also gathered data about the Arctic during the heyday of
Cold War submarine warfare, but this information is generally
classified.)
The human spirit cannot abide a puzzle with a
missing piece. But this is especially so when the missing piece could
fill in crucial details about the origin of Earth’s oceans, the
evolution of life, and our planet’s susceptibility to climate change.
An unexplored frontier
For climatologists and physical oceanographers, it is often said that
the Arctic is a canary in the environmental coal mine. In a warming
world, the Arctic’s delicately balanced ocean circulation and sea ice
appears vulnerable to disruptions that could have dramatic impacts on
Earth’s oceans and climate. Thus, climate change drives a large
percentage of Arctic research.
But the Arctic Basin is so
unknown and unique, it probably holds more undiscovered scientific
treasures than any other ocean basin on Earth. Perhaps the hardest
challenge is deciding which fundamental scientific questions to attack
first.
For marine biologists, for example, the Arctic
represents a potential gold mine. About 65 million years ago, the
Arctic Ocean basin became enclosed, with no deepwater connections to
any other ocean basin on Earth. Species and biological communities in
the Arctic Ocean may have developed and evolved in isolation, possibly
making the Arctic a sort of marine equivalent of Australia. (See The Evolutionary Puzzle of Seafloor Life).
A 21st-century voyage of discovery
In 2001, Woods Hole Oceanographic Institution (WHOI) scientist Henry
Dick was part of a team that conducted the most detailed exploration to
date of the Gakkel Ridge, which transects the eastern Arctic Basin and
is perhaps the most enigmatic tectonic plate boundary on Earth. Like
all mid-ocean ridges, the Gakkel Ridge is an undersea volcanic mountain
chain where magma erupts to create new ocean crust that spreads out on
both sides of the ridge. It was thought to be spreading so slowly,
however, that it would have little volcanic and hydrothermal activity
on it.
But Dick and colleagues found tantalizing clues of
active volcanism and ubiquitous hydrothermal venting on the Gakkel
Ridge. What’s more, they gathered evidence that seafloor spreading on
the Gakkel Ridge occurs in a fundamentally different way compared to
other previously explored ridges. (See Earth’s Complex Complexion)
Dick and colleagues recovered rocks from the Gakkel Ridge composed of
materials that normally reside in the mantle deep within Earth’s
interior, and that are rarely found on Earth’s surface. These rocks are
perhaps the closest modern analogues to the kind of volcanic rocks that
erupted billions of years ago in the early stages of Earth’s history.
They have a distinct chemistry that affects their interaction with
seawater circulating through hydrothermal vent systems. (See The Remarkable Diversity of Seafloor Vents)
These chemical reactions release exceptionally large amounts of
chemical “food” for the kinds of evolutionarily ancient microbes that
reside at the roots of the Tree of Life. (See Is Life Thriving Deep Beneath the Seafloor?)
The hydrothermal vent fields on the Gakkel Ridge could therefore
provide a means to study hydrothermal activity on an early Earth, and
possibly even provide clues to the origin of life on this planet.
Many questions, little data
Scientists only began to get their first detailed look at the Arctic
seafloor between 1995 and 1999, when the U.S. Navy and the National
Science Foundation (NSF) teamed up to use Navy nuclear submarines for
unclassified scientific investigations.
We still have almost no
data from most of the mountain chains in the Arctic Basin, so we’re
still guessing about their composition, age, and origin. Yet, the
sparse evidence we do have suggests that the Arctic Basin did not form
the same way other ocean basins did, and that it may have the oldest
extant ocean crust in the world.
That’s why we dream about
retrieving data from beneath the Arctic ice cap, and why we have begun
to harness 21st-century technology to make those dreams come true.
Nuclear subs are far too expensive to build and operate, and besides,
they are crushed like tin cans at full Arctic seafloor depths. Instead,
in our quaint New England village of Woods Hole, we are developing
autonomous underwater vehicles (AUVs) and other advanced
deep-submergence technologies that can open up the Arctic Basin to
scientific investigation.
Overcoming the ice barrier
Though many scientists dream of getting beneath the ice to study the
Arctic Basin, the long-standing commitment to ocean technology and
instrumentation at WHOI gives scientists here the opportunity to turn
dreams into reality. We formally began a program to develop AUVs
specifically for under-ice operations in the Arctic in January 2000
when the NSF Office of Polar Programs awarded WHOI a grant to design,
fabricate, and test a prototype vehicle called APOGEE, the Autonomous
Polar Geophysical Explorer. The objective was to develop a swimming
robot that can carry a variety of scientific sensors to explore the
most inaccessible regions of the Arctic Basin, and that can be deployed
and recovered through a small hole in the ice.
Life is easier
if AUVs can simply pop up on the ocean surface for recovery, but Arctic
pack ice adds complications. APOGEE was designed with critical acoustic
navigation and control systems that allow it to navigate to a homing
beacon, latch itself to a wire suspended from a hole in the ice, and
ultimately be recovered by scientists on an icebreaker or an ice camp.
Without this essential capability, an AUV in the Arctic would almost
certainly be lost.
To the Arctic and beyond?
We conducted our last set of sea trials with APOGEE in 2003. Now, we
have begun to build the next generation of Arctic vehicles—under a
joint grant (with the University of Maryland’s Space Systems Lab) from
the Astrobiology Science and Technology for Exploring Planets program
of the National Aeronautics and Space Administration.
Our
mission will be to use AUVs to find, map, and sample hydrothermal vent
fields on the Gakkel Ridge. We will develop instrumentation that will
guide future efforts to search for life on Europa, a Galilean moon of
Jupiter, which may have two necessary ingredients for life: active
volcanism and an ocean—albeit an ice-covered one.
The mission
will also allow us to study Arctic vent fields for the first time. We
will use a small group of purpose-built AUVs, each with different
characteristics and equipped with state-of-the-art sensor systems. They
will work in concert to study Arctic vent fields. For example, a
“bloodhound” AUV (named Puma, for Plume Mapper) will be
equipped with sensors that can detect tiny telltale temperature,
chemical, or turbidity signals in the water. It will survey a wide area
to “sniff out” one of the hydrothermal vent plumes that Henry Dick got
whiffs of in 2001 and follow it back to its vent field source on the
seafloor.
Once a vent is found, “hummingbird” AUVs (named Jaguar),
will be deployed. These will be able to hover in place, and equipped
with camera and lighting systems, high-resolution sonar, and a
manipulator arm with storage canisters, they will be used for mapping,
imaging, and sampling at vent sites.
Fully autonomous
methods have never been used to find and image, not to mention obtain
samples from, vent fields in any ocean, not to mention an ice-covered
one. The technical challenges are serious and legion, but they are
worthy of a cutting-edge oceanographic institution such as WHOI. We are
of necessity drawing on the expertise, inspiration, and creativity of
dozens of experts hailing from every department within the institution.
There is no denying that we are attempting an ambitious project that
faces stiff technical challenges, but this energizes and motivates us.
Ultimately, we will succeed or fail based on the talent and dedication
of the scientists, engineers, and technicians who are conceiving,
designing, and fabricating the new instrumentation we will take to the
Arctic. Anyone who knows the people on our team would be reluctant to
bet against us.
Posted: August 23, 2004 [top] |
