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New Study: Ice Sheet Retreat Led to Rapid Methane Hydrate Release at End of Last Ice Age
7
June, 2017
Andreassen
et al. found evidence of large craters embedded within
methane-leaking subglacial sediments in the Barents Sea, Norway. They
propose that the thinning of the ice sheet at the end of recent
glacial cycles decreased the pressure on pockets of hydrates buried
in the seafloor, resulting in explosive blow-outs. This created the
giant craters and released large quantities of methane into the water
above. — Science
******
At
the end of the last ice age, a warming world released a portion of
its carbon stores into the atmosphere. The result was, ultimately, an
increase in atmospheric CO2 by around 100 parts per million and in
increase in atmospheric methane by around 300 parts per billion.
This
increase in greenhouse gasses was a direct response to the Earth
warming by approximately 4 degrees Celsius over the course of about
10,000 years. Under a present human-forced warming that is currently
1.2 C above late 19th Century averages and that
is predicted to reach between 3.3 and 7 C warming this Century if
fossil fuel burning continues,
it is important to consider what additional carbon forcing the Earth
System will produce under such an extreme and short-term temperature
departure.
A
new study recently published in Science indicates that these massive
craters in the sea bed off Svalbard formed as methane hydrate
erupted from the sea bed when ice sheets retreated at the end of the
last ice age. Many of these craters are over a kilometer wide. Image
source: K. Andreassen/CAGE.
One
subject of concern is the behavior of methane hydrate deposits under
warming conditions. It is estimated that upward of trillions of tons
of hydrate exist in various frozen deposits around the world. And
that even a fractional release from these deposits could contribute
to the increasing greenhouse gas overburden in our atmosphere and
further exacerbate warming. A potential for such a release in the
short term would add risk of increased warming this Century on top of
planned emissions from human fossil fuel burning — adding urgency
to already necessary rapid emissions cuts (and a related swift
transition to renewable energy based economies).
Paleoclimate
Evidence of Massive Hydrate Release
This
past week, a new study entitled — Massive
blow-out craters formed by hydrate-controlled methane expulsion from
the Arctic seafloor —
lends credence to concerns regarding hydrate release as a potential
amplifier to human warming. The study found that as ice sheets
retreated and as pressure was relieved from the sea floor near
Svalbard 12,000 years ago, pockets of methane hydrate rapidly
migrated toward the surface as they turned to gas. This newly
gasified methane formed large, high-pressure, mounds on the sea
floor. Such mounds were unstable. Sensitive to changes in the local
environment, they generated explosive outbursts which released
considerable volumes of methane into the ocean and ultimately also
added heat-trapping carbon to the Earth’s atmosphere.
The
lead author of the study, Karin Andreasson, a professor at the CAGE
Centre for Arctic Gas Hydrate, Environment and Climate noted
in Phys.org last week that:
As [the] climate warmed, and the ice sheet collapsed, enormous amounts of methane were abruptly released. This created massive craters that are still actively seeping methane.
Though
the methane craters formed off Svalbard around 12,000 years ago as
the ice sheet retreated, they are linked to deeper methane pockets
and are still leaking gas into the ocean today. Image source:
Andreia Plaza Faverola/CAGE.
The
researchers characterized these blow-out mounds as similar to those
that have recently been forming in the Russian permafrost in places
like Yamal and Yakutia.
And their research indicates that a process like the one that
occurred off Svalbard at the end of the last ice age may be at play
as permafrost thins and as gas beneath this cap of frozen soil more
rapidly migrates toward the surface — creating unstable blow-out
mounds. Researchers also indicated that places presently locked in
surface ice — like Greenland and Antarctica — could generate
further methane blow out risk as ice sheets melt, withdraw and remove
pressure from the methane deposits beneath them.
Conditions
in Context
These
are important findings due to the fact that paleoclimate evidence of
past large-scale hydrate release provides a study-identified
mechanism for how permafrost hydrates and gas deposits are being
liberated due to present warming, how such warming may increase their
rate of liberation in the future, and how ice sheet withdrawal could
contribute to this hydrate liberation trend.
What remains highly
uncertain is the ultimate volume of hydrate response to a given level
of warming over a given period and how significantly such releases
would contribute to the already very considerable heat forcing
provided by human emissions. That said, the new study does add to
serious concerns regarding the potential for future warming and
greenhouse gas levels — which will tend to be higher than present
model studies indicate due to generally not accounting for these
kinds of Earth System carbon feedbacks.
Links:
Hat
tip to TodaysGuestIs
Hat
tip to Andy in San Diego
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