Eric,
I read a paper a few years back showing measurements of the the
temperature of the Norwegian current increasing 2 degrees C since the 1970s.
Oliver
On 10/15/2015 8:28 AM, Eric Durbrow wrote:
I found this recent article extremely disturbing but perhaps I am exaggerating the
impact of possible deep-ocean methane release. Can someone provide a perspective? Is
this a potential "game-over?”
Eric
Abstract: http://onlinelibrary.wiley.com/doi/10.1002/2015GC005955/abstract
Press Release:
Warming ocean temperatures a third of a mile below the surface, in a dark ocean
in areas with little marine life, might attract scant attention. But this is
precisely the depth where frozen pockets of methane 'ice' transition from a
dormant solid to a powerful greenhouse gas.
New University of Washington research suggests that subsurface warming could be
causing more methane gas to bubble up off the Washington and Oregon coast.
The study, to appear in the journal Geochemistry, Geophysics, Geosystems, shows
that of 168 bubble plumes observed within the past decade, a disproportionate
number were seen at a critical depth for the stability of methane hydrates.
"We see an unusually high number of bubble plumes at the depth where methane hydrate would
decompose if seawater has warmed," said lead author H. Paul Johnson, a UW professor of
oceanography. "So it is not likely to be just emitted from the sediments; this appears to be
coming from the decomposition of methane that has been frozen for thousands of years."
Methane has contributed to sudden swings in Earth's climate in the past. It is
unknown what role it might contribute to contemporary climate change, although
recent studies have reported warming-related methane emissions in Arctic
permafrost and off the Atlantic coast.
Of the 168 methane plumes in the new study, some 14 were located at the
transition depth -- more plumes per unit area than on surrounding parts of the
Washington and Oregon seafloor.
If methane bubbles rise all the way to the surface, they enter the atmosphere
and act as a powerful greenhouse gas. But most of the deep-sea methane seems to
get consumed during the journey up. Marine microbes convert the methane into
carbon dioxide, producing lower-oxygen, more-acidic conditions in the deeper
offshore water, which eventually wells up along the coast and surges into
coastal waterways.
"Current environmental changes in Washington and Oregon are already impacting local
biology and fisheries, and these changes would be amplified by the further release of
methane," Johnson said.
Another potential consequence, he said, is the destabilization of seafloor
slopes where frozen methane acts as the glue that holds the steep sediment
slopes in place.
Methane deposits are abundant on the continental margin of the Pacific
Northwest coast. A 2014 study from the UW documented that the ocean in the
region is warming at a depth of 500 meters (0.3 miles), by water that formed
decades ago in a global warming hotspot off Siberia and then traveled with
ocean currents east across the Pacific Ocean. That previous paper calculated
that warming at this depth would theoretically destabilize methane deposits on
the Cascadia subduction zone, which runs from northern California to Vancouver
Island.
At the cold temperatures and high pressures present on the continental margin,
methane gas in seafloor sediments forms a crystal lattice structure with water.
The resulting icelike solid, called methane hydrate, is unstable and sensitive
to changes in temperature. When the ocean warms, the hydrate crystals
dissociate and methane gas leaks into the sediment. Some of that gas escapes
from the sediment pores as a gas.
The 2014 study calculated that with present ocean warming, such hydrate
decomposition could release roughly 0.1 million metric tons of methane per year
into the sediments off the Washington coast, about the same amount of methane
from the 2010 Deepwater Horizon blowout.
The new study looks for evidence of bubble plumes off the coast, including
observations by UW research cruises, earlier scientific studies and local
fishermen's reports. The authors included bubble plumes that rose at least 150
meters (490 feet) tall that clearly originate from the seafloor. The dataset
included 45 plumes originally detected by fishing boats, whose modern sonars
can detect the bubbles while looking for schools of fish, with their
observations later confirmed during UW research cruises.
Results show that methane gas is slowly released at almost all depths along the
Washington and Oregon coastal margin. But the plumes are significantly more
common at the critical depth of 500 meters, where hydrate would decompose due
to seawater warming.
"What we're seeing is possible confirmation of what we predicted from the water temperatures:
Methane hydrate appears to be decomposing and releasing a lot of gas," Johnson said. "If
you look systematically, the location on the margin where you're getting the largest number of
methane plumes per square meter, it is right at that critical depth of 500 meters."
Still unknown, however, is whether these plumes are really from the
dissociation of frozen methane deposits.
"The results are consistent with the hypothesis that modern bottom-water warming is
causing the limit of methane hydrate stability to move downslope, but it's not proof that
the hydrate is dissociating," said co-author Evan Solomon, a UW associate professor
of oceanography.
Solomon is now analyzing the chemical composition of samples from bubble plumes
emitted by sediments along the Washington coast at about 500 meters deep.
Results will confirm whether the gas originates from methane hydrates rather
than from some other source, such as the passive migration of methane from
deeper reservoirs to the seafloor, which causes most of the other bubble plumes
on the continental margin.
--
Dr. Oliver Wingenter
Assoc. Chair and Prof. Department of Chemistry
Research Scientist Geophysical Research Center
New Mexico Tech
Socorro, NM 87801 USA
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