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A Ridge Too Slow?WHOI team collaborates on Chinese discovery expedition in Indian Ocean |
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| Enlarge ImageThe Southwest Indian Ridge is a spreading center between the African tectonic plate, (top left, yellow-orange) and the Antarctic plate (bottom left, red). (Image by NOAA Geophysical Data Center) |
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| Enlarge ImageThe Chinese research vessel Dayang 1, which means "big ocean," was used in the discovery of the first hot vents on the Southwest Indian Ridge. (Photo by Mr. Huisheng Lu of R/V Dayang 1) |
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| Enlarge ImageWHOI team members (left to right) Al Duester, Andy Billings, and Christopher German recover ABE from one of its three dives in the Indian Ocean. (Photo courtesy of InterRidge program) |
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| Enlarge ImageThe Chinese research team celebrates two "firsts": making the first Chinese discovery of a hydrothermal vent site, and retrieving the first mineral-rich samples from a vent site on the Southwest Indian Ridge. (Photo courtesy of Dana Yoerger, Woods Hole Oceanographic Institution) |
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| Enlarge ImageThree members of the WHOI team: Christopher German, Jian Lin, and Dana Yoerger stand before the WHOI ABE underwater autonomous vehicle on the deck of the R/V Dayang 1. (Photo courtesy of InterRidge Program) |
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| Enlarge ImageJian Lin, leader of the WHOI team (right), and Mr. Songgang Zhen, captain of R/V Dayang 1, stand before the WHOI ABE vehicle. (Photo by R/V Dayang 1 science party) |
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Ever since scientists first discovered vents gushing hot,
mineral-rich fluids from the seafloor in the Pacific Ocean 30 years
ago, they have found them in various places along the Mid-Ocean
Ridge—the 40,000-mile-long seafloor mountain chain where Earth’s giant
tectonic plates spread apart and magma rises upward.
Most hydrothermal
vent hunts have been confined to the fast-spreading Pacific Ridge and
the slow-spreading Atlantic Ridge. But in the past decade, scientists
reaching into more remote regions in the Indian and Arctic Oceans have
discovered ultraslow-spreading ridges, leaving them to wonder: Can
these ridges—spreading apart so slowly they make the speed at which
your fingernails grow seem breakneck—produce hydrothermal activity,
too?
Now an international team of scientists has found
one of the largest known hydrothermal vent fields on the ultraslow
Southwest Indian Ridge.
“The discovery of the first active vents
ever found on an ultraslow-spreading ridge is a significant milestone
event,” said Jian Lin, leader of a team of Woods Hole Oceanographic
Institution (WHOI) scientists who participated in a 20-day expedition
aboard the Chinese research vessel Dayang 1 in February and March.
The
discovery confirmed a hypothesis that scientists such as Christopher
German, chief scientist of the WHOI-operated National Deep Submergence
Facility, have harbored for at least 10 years: that vents can form all
along the mid-ocean ridge, which zigzags through the middle of the
world’s ocean basins like a giant zipper—even in ultraslow-spreading
areas. Three years ago, German and Lin further speculated that
the slower a ridge spreads, the fewer vents it would have—but the
bigger the vent fields would be.
Fast, slow, and ultraslow
The team nailed the discovery with the aid of ABE,
WHOI’s Autonomous Benthic Explorer, which has been instrumental in
recent years in helping scientists find vents on the bottom of the
ocean much more quickly than ever before. ABE,
which celebrated its 200th dive on the cruise, acts like a robotic
bloodhound: In a sequence of dives, its sensors “sniff out” temperature
and chemical clues indicating a plume of fluids from a vent and collect
valuable data scientists use to home in on the vent. It also uses
sonar to create maps of vent fields and takes photographs about 5
meters above them.
“There’s nothing quite like having
5,000 pictures over one plot of vent real estate to prove what we’ve
been saying is true,” German said. The site is at least the size of a
football stadium (120 meters by 100 meters) and among the largest known
to date.
Peter Rona, a marine geologist at Rutgers University
who discovered the first hydrothermal vents on the slow-spreading
Mid-Atlantic Ridge in the mid-1980s, tipped his hat to the team: “This
is an important discovery that significantly extends our knowledge of
seafloor hydrothermal processes to a previously unknown region of the
global ocean ridge system,” he said.
Most studies of the
chimney-like vent structures have taken place along ridges in the
“fast-spreading” East Pacific Rise (100 to 200 millimeters per year)
and the “slow-spreading” Mid-Atlantic Ridge (20 to 40 millimeters per
year). Only in recent years have scientists explored
“ultraslow-spreading ridges” (less than 20 millimeters per year) in the
Arctic and Indian Oceans.
The Southwest Indian Ridge
vent discovery adds anticipation to an expedition this summer to search
for hydrothermal vents under the Arctic Ocean ice on the Gakkel Ridge,
the second known ultraslow-spreading ridge, which scientists visited
for the first time in 2001. (See "Earth's Complex Complexion.")
An achievement for Chinese oceanography
The
discovery was a first for China. “This discovery reflects China’s
increasing contribution to ocean science in general, and ridge science
in particular,” Lin said.
In 2005-06, as part of China’s first around-the-world oceanographic expedition, Lin had sailed as U.S. chief scientist on Dayang 1
to the Southwest Indian Ridge, where scientists found tantalizing
evidence of active hydrothermal venting. They gathered critical data
that led them back to the site this year. “People have been
looking for vents on ultraslow ridges for more than 10 years,” said
Lin, a marine geophysicist and U.S. coordinator of the recent mission.
“The
Southwest Indian Ridge was an area where international cooperation
could make a difference,” said Lin, and China had the resources to fund
a mission to such a remote location, a four-day transit from a port in
Durban, South Africa, he said.
The China Ocean Mineral Resources
R&D Association (COMRA) in Beijing, China funded last year’s
expedition and ABE’s participation in the current one. COMRA, which
represents China in the International Seabed Authority, has been
exploring the deep sea for mineral resources since the early 1990s.
China
is currently increasing investments in ocean science, Lin said. COMRA’s
primary interests lay in the large mounds of sulfide deposits created
by hydrothermal vents, which are rich in copper, zinc, gold, and other
minerals, he said.
“Our Chinese colleagues were the happiest
people I’ve ever seen at sea when they brought the first samples
aboard,” said Dana Yoerger, scientist in the WHOI Deep Submergence Lab
and co-designer of ABE who participated in the expedition. Once ABE
pinpointed the site’s exact location and gathered images of it, the
Chinese team sent down its “TV grab”—essentially a grappling device
guided by a television camera—onto the site.
“They dropped it
right on the biggest, baddest structure we had mapped and got a big
chunk of a beautiful chimney that was loaded with minerals,” Yoerger
said. The Chinese scientists will return to the site early next
year with their newly built remotely operated vehicle to see it up
close and personal, he said.
Smooth sailing in rough weather
The success of the mission belied its challenging circumstances. A tropical cyclone—the outer wisps of which dealt T. rex-sized sea swells—bee-lined its way toward the Dayang 1, forcing the team to accomplish in less than one week what they had planned to do in two.
Three ABE
dives and six days later, and the landmark discovery was in the bag.
“It was the most ruthlessly efficient science we’ve ever done,” said
German. “We had some of the roughest weather I’ve ever had to deploy
and recover ABE in, and we
had no margin for error. But we knew this was our only window” to find
the vents that they suspected were there, he said.
“We’ve learned our trade with ABE and
proved we can do this very difficult science [in remote, challenging
locales] using state-of-the-art technology,” said German. The ABE
team drew confidence from vent-hunting missions in the last few years
to the South Pacific and southern Atlantic Oceans, during which ABE set a high bar for success, German said.
“It
also bodes well for our plans to further explore the southern Atlantic
into the Antarctic because we need to do more exploring, not less,”
German said. A newer and more capable version of ABE—called the Sentry—is slated to debut in 2008.
Culinary culture clash
Yoerger said it was ABE’s
third international expedition. “In every one of our international
cruises, Phase Zero, as we like to call it [gathering maps of a
suspected vent area and plume data indicating a possible vent site],
was done by the host country. Then ABE
nails it down,” he said. The wealth of data the Chinese scientists
already collected from the 2005-06 cruise and another expedition in
January-February 2007 was critical to ABE’s
remarkable success, as was WHOI engineer Andy Billings learning enough
Chinese—“up, down, backwards, forwards, stop, go, and so on”—to ensure ABE was successfully deployed and recovered each time.
Yoerger
said he and the rest of the WHOI team enjoyed the cultural challenges
of working aboard a foreign vessel. “The Chinese team was exceptional,”
he said. “They were sensitive to the fact that we were on strange
ground (for us), and they were always trying to accommodate us.”
“It
was a burden, but also a great adventure,” he said, “as was the food,
of course. I tried not to freak out when I realized there were chicken
heads in the dinner stew one night. They’re really very tasty.”
The
Chinese science party was led by chief scientist Chunhui Tao, a
geophysicist at the Second Institute of Oceanography in Hanzhou, China.
The WHOI team included Lin, German, Yoerger, Billings, and Al Duester.
“The two international teams worked exceedingly well for this kind of
complex operation,” Lin said.
—Kristen M. Kusek
This
research was funded by China Ocean Mineral Resources R&D
Association, the Census of Marine Life’s ChEss program on Deep-Water
Chemosynthetic Ecosystems, and the Charles D. Hollister Endowed Fund
for Support of Innovative Research at WHOI.
Building International Bridges to Explore Mid-Ocean RidgesIn January, Jian Lin and Chris German became the new chair and co-chair
of an international organization called InterRidge, which will be based
at Woods Hole Oceanographic Institution for the next three years.
InterRidge leverages the resources and expertise of roughly 2,500
scientists from 25 countries currently involved in ocean ridge science.
Lin said international exploration of the Southwest Indian
Ridge is a prime example of the value and necessity of InterRidge,
which helps facilitate partnerships to accomplish what any one country
would be hard-pressed to do on its own.
“The success of the
[Indian Ocean] cruise is another strong demonstration of why
international collaboration is essential, and will definitely lead to
further collaboration on greater scales with China and other partners
as well,” Lin said.
An InterRidge-facilitated expedition 10
years ago, involving French, British, and Japanese colleagues that
German led to another part of the Indian Ridge, laid the groundwork for
the hunt for vents on ultraslow-spreading ridges. It was an InterRidge
workshop in Beijing, China, in 2003 that prompted China to establish
its mid-ocean ridge research program under the leadership of John Chen,
a professor at Peking University and the current chair of
InterRidge-China. In addition, the landmark international 2001 cruise
that explored the ultraslow Gakkel Ridge beneath the Arctic Ocean—which
involved icebreakers from the U.S. and Germany—was also spearheaded
under the auspices of InterRidge.
InterRidge’s main goals are to:
1) build and maintain an interactive international mid-ocean-ridge-research community
2)
identify, through working groups, workshops and conferences, the most
compelling questions in ridge research and develop programs to
investigate them
3) act as a representative body for international ridge scientists in policy discussions
4)
communicate the importance and excitement of ridge research to the
general public and decision-makers worldwide through education and
outreach.
Visit www.interridge.org for more information.
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Posted: April 12, 2007 [top] |
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