VENTING CONCERNS
Exploring and protecting deep-sea communities
BY JANET RALOFF
esearchers cruising the South Pacific between
RTonga and Fiji study huge snails that, aided by
an abundance of bacteria housed in their gills,
feed off plumes of metal-rich compounds at
active hydrothermal vents. Scientists working off
the California coast use chemical-sniffing probes, robot-
ically driven subs, and seafloor-tethered temperature
sensors to watch flows of lava pave over a once-thriving
ecosystem at hydrothermal vents several kilometers
below the ocean’s surface. An d in waters
off Papua New Guinea, a mining com-
pany analyzes metal deposits
around inactive, underwater vol-
canoes that contain, on average,
10 times as much copper as
typical ores on land do.
These studies exemplify the
breadth of research under way at
one of Earth’s last great frontiers,
the geologically active ocean bottom. Sites include hydrothermal
vents on the 65,000-km-long ridge
that meanders through all the world’s
oceans and at deeply submerged volcanoes in the tropical west Pacific. Only
35 years ago, scientists didn’t know that
geologically active sites existed underwater.
Now, they have direct evidence of some 300
such spots and suspect that another 700 or so await
discovery. The researchers are also uncovering signs of
past geological activity at many sites.
As recently as 1990, the cost and difficulty of getting to the few
then-recognized sites limited visits by scientists. Today, however,
submerged volcanoes and other deep hydrothermal vents have
become stages for intensive research activity. Every visit to a vent
site, even a repeat visit, brings new discoveries, says Cindy Van
Dover, director of Duke University’s Marine Laboratory in Beaufort, N.C.
“Some places are so popular that you get ships [above them]
stacked up on top of one another,” notes Van Dover. If researchers
aren’t careful, she says, they’ll interfere with each other’s work or
harm the vent ecosystems.
Such concerns triggered scientists to issue, earlier this year, a code
of conduct for hydrothermal-vent research. In July, underwater volcanologist Colin Devey of the University of Kiel in Germany described
the code at the Euroscience Open Forum in Munich. His university
is the current home of InterRidge, the loosely affiliated group of
hydrothermal-vent researchers that developed the code.
Explains Devey, “On a highway with only two vehicles, having rules
of the road is fairly unimportant. But every time another vehicle
comes along, it becomes increasingly important to know such things
as which side of the road to drive on and who has the right of way.”
With scientific and mining-exploration visits to vent sites increasing, he says, “we realized we needed rules to deal with that traffic.”
The new code also serves as a self-policing protocol for investigators who conduct their research largely out of sight, usually kilometers below the sea’s surface.
HOT SPOTS The geologically active sites where these
scientists work represent two extremes of the global
tectonic system. The best characterized of these
hydrothermal vents occur at various inter-
vals along a tectonic plate’s new-forming
edge, known as a spreading zone. Earth’s
mid-ocean ridge is one near-continu-ous zone of spreading seafloor.
As two plates pull apart, breaches
occasionally permit magma to break
through the ridge’s crest, where the
molten rock heats zones of rock and
water (SN: 4/1/06, p. 202). A
spreading zone can be considered
a “linear volcano” with vent holes
occurring at various points along its
meandering crest, explains Baker,
an oceanographer at the National
Oceanic and Atmospheric Adminis-
tration’s Seattle lab.
Last December, Baker and his
colleagues traveled to a previously uncharted 400-km span
of the mid-ocean ridge in the
Pacific, just north of the Galápagos Islands. Their sophisticated equipment turned up
direct evidence of three new
hydrothermal vents in that
spreading zone and indirect evidence—hydrothermal plumes—of several more.
On the opposite end of a tectonic plate from its spreading zone
may be a subduction zone, a span where two plates collide and one
plate is forced beneath the other. Weak spots emerge near the edge
of the disappearing plate, permitting magma to punch through and
form conventional, conical volcanoes that happen to be underwater. These vulnerable areas are known as back-arc basins (SN:
6/10/06, p. 365).
Both types of hydrothermal vents—at seafloor ridges and at back
arcs—spew hot water that’s oxygen-deprived and metal-rich, and
they host a wide variety of exotic marine life. Researchers marvel
C. FISHER/RIDGE 2000 PROGRAM
NIGHT LIFE — These stalked
barnacles (Vulcanolepas osheai)
thrive at a vent site in the Lau
Basin, between Fiji and Samoa,
that’s so deep that it’s always
pitch black there. The site is part
of what biologist Charles Fisher
describes as “the center of diversity for barnacles.”
