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Is Human Warming Prodding A Sleeping Methane Monster off Oregon’s Coast?
(Plume of methane bubbles rising from the sea floor off the Oregon Coast. This image shows methane bubbles originating from the sea bed about 515 meters below the surface before dissolving into the water column at about 180 meters depth. Image source: American Geophysical Union.)
16
October, 2015
We’ve
talked quite a bit about the
Arctic Methane Monster —
the potential that a rapidly warming Arctic will force the release of
disproportionately large volumes of methane from organic material
locked in permafrost and in frozen sea bed hydrates composing volumes
of this powerful greenhouse gas large enough to significantly
increase the pace of human-forced global warming. But if we consider
the globe as a whole, the Arctic isn’t the only place where large
methane stores lurk — laying in wait for the heat we’ve already
added to the world’s oceans and atmosphere to trigger their
release. And
a new study out of the University of Washington provides yet another
indication that the continental shelf off Oregon and Washington may
be one of many emerging methane release hot spots.
For
all around the world, and beneath the broad, blue expanse of the
world’s seas, rest billions and billions of tons of frozen methane
hydrate.
A
kind of methane and ice combination, frozen hydrate is one of the
world’s most effective natural methods of trapping and sequestering
carbon. Over long ages, organic material at the bottom of the oceans
decompose into hydrocarbons, often breaking down into methane gas. At
high pressure and low temperature, this methane gas can be locked
away in a frozen water-ice hydrate lattice, which is then often
buried beneath the sea bed where it can safely remain for thousands
or even millions of years.
Most
of these deposits lay well beneath the sea bed or at extreme ocean
depths of one mile or greater. And so far, human forced warming
hasn’t been great enough to risk the destabilization of most of
these deep ocean carbon stores. But some hydrate deposits rest in the
shallower waters of continental slope systems and at depths where
current warming may now be causing them to destabilize.
Scientists
Think Methane Hydrates May be Destabilizing off Oregon
Enter a
new study by University of Washington scientists which
found “an unusually high number of bubble plumes at the depth where
methane hydrate would decompose if seawater has warmed.” The
scientists concluded that these bubble plumes were likely evidence of
methane hydrate destabilization due to a human forced warming of the
water column in the range of about 500 meters of depth.
The
warm waters, ironically, come from a region off Siberia where the
deep waters have, over recent decades, been heated to unprecedented
temperatures.
These waters have, in turn, through ocean current exchange,
circulated to the off-shore region of Washington and Oregon where
they appear to have gone to work destabilizing methane hydrate in the
continental slope zone. A paper published during 2014 hypothesized
that these warm waters would have an impact on hydrates. And the
new paper is
the first potential confirmation of these earlier predictions.
In
total about 168 methane plumes are now observed to be bubbling out of
the sea bed off the Washington and Oregon coasts. Of these, 14 are
located in the 500 meter depth range where ocean warming has pushed
temperatures to levels at which hydrate could begin to destabilize.
University of Washington researchers noted that the number of plumes
at this depth range was disproportionately high, which also served as
an indirect indicator that human heating may be causing this methane
to release.
(Locations
of methane plumes in the continental slope zone off Washington and
Oregon. The location of a disproportionate number of these plumes in
a zone now featuring a warming water column is an indication that the
human-forced heating of ocean currents is starting to drive some
methane hydrate structures to destabilize. Image source: AGU.)
“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… 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. 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.””
Implications
For Ocean Health, Carbon Cycle
Most
methane released at this depth never reaches the atmosphere. Instead,
it either oxidizes to CO2 in the water column or is converted by
ocean bacteria. That said, expanding zones of methane release can rob
the surrounding ocean of vital oxygen even as it can saturate the
water column with carbon — increasing ocean acidification and
reducing the local ocean’s ability to draw carbon out of the
atmosphere. Such a response can indirectly increase the volume of
heat trapping gasses in the atmosphere by reducing the overall rate
of ocean carbon uptake. In more extreme cases, methane bubbles reach
the surface where they then vent directly into the atmosphere,
proportionately adding to the human-produced greenhouse gasses that
have already put the world into a regime of rapid warming.
It
has been hypothesized that large methane releases from ocean hydrate
stores contributed to past hothouse warming events and related mass
extinctions like the Permian and the PETM (See A
Deadly Climb From Glaciation to Hothouse).
But the more immediate consequences of smaller scale releases are
related to declining ocean health.
According
to AGU and Dr. Johnson,
the study author:
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.
Instances
of mass sea life die-off have already occurred at a very high
frequency off the Washington and Oregon Coasts. And many of these
instances have been associated with a combination of low oxygen
content in the near and off shore waters, increasing ocean
acidification, increasing dangerous algae blooms, and an overall
warming ocean system. It’s important to note that ocean
acidification, though often cited in the media, is just one of many
threats to ocean life and health. In many cases, low oxygen dead
zones and large microbial blooms can be even more deadly. And in the
most extreme low oxygen regions, the water column can start to fill
up with deadly hydrogen sulfide gas — a toxic substance that, at
high enough concentrations, kills off pretty much all oxygen-based
life (See Hydrogen
Sulfide in the World’s Warming Oceans).
During
recent years, mass sea life deaths have been linked to a ‘hot blob’
forming in nearby waters (See
Mass Whale Death in Northeast Pacific — Hot Blob’s Record Algae
Bloom to Blame?).
However, indicators of low oxygen in the waters near Washington and
Oregon have been growing in frequency since the early 2000s. Though
the paper does not state this explicitly — increasing rates of
methane release in the off-shore waters due to hydrate
destabilization may already be contributing to declining ocean health
in the region.
Slope
Collapse, Conditions in Context
A
final risk associated with methane hydrate destabilization in the
continental slope zone is an increased prevalence of potential slope
collapse. As methane hydrate releases, it can deform the sea bed
structures within slope systems. Such systems become less stable,
increasing the potential for large underwater landslides. Not only
could these large landslides displace significant volumes of water or
even set off tsunamis, slope collapse events also risk uncovering and
exposing more hydrate systems to the warming ocean in a kind of
amplifying feedback.
In
context, the total volume of methane being released into the
off-shore environment is currently estimated to be about 0.1 million
metric tons each year. That’s about the same rate of hydrocarbon
release seen from the Deepwater Horizon blowout. A locally large
release but still rather small in size compared to the whopping 10+
billion tons of carbon being dumped into the atmosphere each year
through human fossil fuel burning. However, this release is
widespread, uncontrolled, un-cappable and, if scientists are correct
in their indications of a human warming influence, likely to continue
to increase as the oceans warm further.
Links:
Hat
tip to Humortra
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