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"We're interested in gas hydrate because we believe
these deposits have played an important role in ancient global climate
change," explains Michael Riedel of Natural Resources Canada's
Geological Survey of Canada, IODP Expedition 311's co-chief scientist.
"This expedition is the first to explore a transect of deep drilling
research sites across the Cascadia Continental Margin and will yield
new data that will help us understand the deep origin of the methane
that composes the gas hydrate, how the methane is transported into the
sediments where gas hydrate exists, and how methane is eventually
released into the ocean, and possibly, into the atmosphere where it
could impact climate."
"What we've found will fundamentally change how we
investigate the impact of gas hydrate deposits," confirms IODP
co-chief scientist Timothy S. Collett of the U.S. Geological Survey,
Denver, Colo. "Expedition 311 has shown that the occurrence of gas
hydrate is much more complex than predicted. Instead of finding gas
hydrate concentrated in one layer," he explains, "near the base of the
zone where it is stable, higher concentrations of gas hydrate were
found within coarse-grained sand layers throughout core samples from
most of the sites drilled."
Scientists and engineers aboard IODP's
U.S.-sponsored research drilling vessel, the JOIDES Resolution,
drilled hundreds of meters below the seafloor and successfully
retrieved gas hydrate in long sediment cores. More than 1,200 meters
of sediment core samples were recovered from beneath the seafloor
during this 37-day expedition. Once core samples are brought onto the
ship, marine laboratory specialists work quickly to scan them using
various sensors and computers to find the gas hydrate, which is
unstable at the surface.
Most previous research on the Cascadia Continental
Margin has focused on conducting detailed, remote sensing studies to
image gas hydrate in the oceanic sediments. In past research efforts,
gas hydrate has been recovered from the Cascadia Margin area using
shallow sediment coring systems that allowed only the upper few meters
of sediment to be sampled.
Among the discoveries of Expedition 311 was a thick
section of gas hydrate lying near the seafloor surface beneath an
active vent site, known as the 'bull's-eye vent,' where methane gas
naturally seeps from the seafloor. This vent site is one of many
similar sites observed along the Cascadia Margin and scientists are
just starting to understand their role in the overall history of the
margin. The episodic nature of the venting and the potential link to
earthquake activity, as well as the possible impact on gas release
into the ocean and atmosphere, will be researched for many years to
come, when future drill site observatories will be linked with the
NEPTUNE cable observatory system. Scientists first became interested
in gas hydrate in 1982, when it was discovered during a research leg
of the Deep Sea Drilling Project, one of two U.S.-sponsored scientific
drilling programs that predate IODP. The samples were retrieved from
the Middle American Trench region, off the Pacific coast of Guatemala.
Since then, gas hydrate has been the focus of numerous studies. |
