Undersea Methane Seep Ecosystem
7/26/2012 - University of California, San Diego - During a
recent oceanographic expedition off San Diego, graduate student
researchers from Scripps Institution of Oceanography at UC San Diego
discovered convincing evidence of a deep-sea site where methane is
likely seeping out of the seafloor, the first such finding off San
Such "methane seeps" are fascinating environments because of their
extraordinary chemical features and often bizarre marine life.
The area of interest, roughly
20 miles west of Del Mar, is centered on a fault zone known as the
San Diego Trough Fault zone.
Faults can provide a pathway for methane to "seep" upward toward the
Methane, a clear, highly
combustible gas, exists in the earth's crust under the seafloor
along many of the world's continental margins.
The Scripps graduate students made the discovery during the recent
San Diego Coastal
Expedition, a multidisciplinary voyage conceived and executed by
Scripps graduate students.
The cruise was funded by the
University of California Ship Funds Program, which supports student
research at sea and provides seagoing leadership opportunities.
While conducting surveys in search of methane seeps aboard Scripps'
research vessel Melville, the graduate students mapped a distinct
mound on the seafloor at 1,036 meters depth (3,400 feet), spanning
the size of a city block and rising to the height of a two-story
The area had been recommended
by Jamie Conrad, Holly Ryan (U.S. Geological Survey) and Charles
Paull (Monterey Bay Aquarium Research Institute), who surveyed the
faults in 2010.
"Below the mound," described Scripps geosciences graduate student
Jillian Maloney, "we observed a disruption in subsurface sediment
layers indicative of fluid seepage."
The Scripps researchers then deployed instruments to collect
sediment cores, gathering further evidence such as seep-dwelling
animals, sulfidic-smelling black mud and carbonate nodules.
These samples are currently
being analyzed in Scripps laboratories for chemical clues and other
telling elements of the environment.
Organisms collected from the site include thread-like tubeworms
called siboglinids and several clams.
Siboglinids lack a mouth and
digestive system and gain nutrition via a symbiotic relationship
with bacteria living inside them, while many clams at seeps get some
of their food from sulfide-loving bacteria living on their gills.
While food is scarce in much of the cold, dark ocean depths, it is
abundant at seeps due to the bacteria that proliferate around the
Microbes there are eaten by
worms, snails, crabs and clams, leading to a rich and productive
community that helps sustain the surrounding deep-sea ecosystem.
"These chemosynthetic ecosystems are considered 'hot spots' of life
on the seafloor in an otherwise desert-like landscape," said San
Diego Coastal Expedition team member Alexis Pasulka, a Scripps
biological oceanography graduate student.
"New forms of life are
continuously being discovered in these environments. Therefore, it
is important to study these ecosystems not only to further
appreciate the diversity of life in our oceans, but also so that we
can better understand how these ecosystems contribute to overall
ocean productivity and the carbon cycle."
Methane is a potent greenhouse gas, and researchers don't yet fully
understand the magnitude to which seeping methane in the ocean
contributes additional carbon to the atmosphere.
Moreover, on many continental
margins, frozen methane hydrates could represent a future energy
Along the West Coast, methane seeps are known to exist off
Oregon, California (near Eureka, Monterey Bay, Point Conception and
Santa Monica), in the Gulf of California and off Costa Rica.
"This is a significant and exciting discovery in part because of the
possibilities for future research at Scripps," said biological
oceanography graduate student Benjamin Grupe, a member of the seep
contingent on the San Diego Coastal Expedition.
"The existence of a methane
seep just a few hours from San Diego should allow Scripps scientists
to visit frequently, studying how this dynamic ecosystem changes
over days, months and years. Such regular data collection is
difficult at most cold seeps, which rarely occur so close to ports
or research institutions."
Grupe will lead a follow-up cruise in December that will revisit the
newly discovered seep to collect additional samples and learn more
about this ecosystem.
The team of graduate students
hopes to raise funds to employ technologies such as video-driven
coring instruments and towed video cameras that will give them an
up-close look at the methane seep.
The search for local seeps was one focus area of the
multidisciplinary San Diego Coastal Expedition, which included teams
of students investigating the oceanography and marine ecosystems off
San Diego and led by chief scientist Christina Frieder.
In addition to Grupe, Pasulka
and Maloney, other members of the seep team included geophysics
graduate students Valerie Sahakian and Rachel Marcuson.
R/V Melville, the oldest ship in the U.S. academic fleet, is owned
by the U.S. Navy and has been operated by Scripps Oceanography for
all of its 41 years.
"The students should be congratulated on their hard work and
perseverance leading to this exciting find," said Lisa Levin, a
Scripps professor who has studied methane seep ecosystems in most of
the world's oceans.
"Other scientists have
suspected that methane seeps were present in the San Diego region,
but these new data and samples provide the first convincing
We know very little about what
lives in deep waters-the planet's largest ecosystem-so it is not
unexpected to find surprises on the deep-sea floor right in our own
Having a 'local' seep should be a great boon to deep-sea
research, education and public outreach at Scripps."
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