University of (Universitetet i Tromsø - UiT)
new study in Nature Communications shows that ice sheets may be
containing vast reservoirs of methane, adding a new concern regarding
rapid ice sheet retreat.
study indicates that under the frigid weight of Barents Sea Ice
sheet, which covered northern Eurasia some 22 000 years ago,
significant amounts of methane may have been stored as hydrates in
the ground. As the ice sheet retreated, the methane rich hydrates
melted, releasing the climate gas into the ocean and atmosphere for
of gas hydrates requires high pressure; water; gas - mainly methane -
and low temperatures. Nowadays we basically consider two environments
suitable for this process to occur: subseabed along the world’s
continental margins, and permafrost areas on land and off shore, “ says principal author of the study, Dr. Alexey Portnov of CAGE –
Centre for Arctic Gas Hydrate, Environment and Climate at UiT
The Arctic University of Tromsø.
sheets – a third process
this is the first comprehensive study that shows that there is a
third process that can create, contain and maintain large amounts of
gas hydrates: ice sheets.
are heavy, can exert enormous pressure on the ground below. And they
are cold, of course. With enough supply of gas and water from
below and favorable geological setting you will likely have enormous
amounts of gas hydrates contained under modern ice sheets as well".
thick methane reservoir
theory that this may be happening beneath the Antarctic ice sheet has
been published previously in Nature. CAGE-study is a more
comprehensive take on that idea, and shows same processes taking
place in the Arctic.
from CAGE have over time collected wide-ranging observational data
offshore western Svalbard in the Arctic Ocean. This made it possible
to create robust models for a scenario of subglacial evolution of gas
hydrate reservoirs during and after Last Glacial Maximum, or last ice
age in layman´s terms.
results of the study indicate that even under conservative estimates
of ice thickness a 500-meter thick gas hydrate stability zone existed
beneath the ice sheet in the study area. This zone could have served
as a methane sink-a reservoir containing immense amounts of the
natural greenhouse gas. 1 m3 of gas hydrate contains almost 170 m3 of
the greenhouse gas methane.
melt caused release of methane
the last ice age the continental margin offshore western Svalbard,
was land covered with ice, much as Greenland and Antarctica of
today. But as the climate changed, the ice melted over a period
of thousands of years, a rapid melt in geological terms.
scientists have mapped over 1900 pockmarks - gas escape features - on
what now is the seafloor in the study area. The age of these
pockmarks has been estimated in previous studies as post-glacial,
meaning that they appeared after the ice sheet had retreated.
are evidence of gas release from the ground. We infer that the gas
hydrate zone was stable as long as the climate was cold and the ice
sheet was stable. Abrupt climate warming caused sheets to melt,
decreasing the pressure on the ground and increasing the temperature.
This destabilized the hydrates. Methane was released into rising
seawater and possibly the atmosphere." says Portnov.
the ice sheet retreated, the pressure lifted, steadily widening the
corridor for major methane release.
melting of the ice sheets due to global warming, and subsequent sea
level rise has long been a concern to scientists.
being at least 20 times more potent greenhouse gas than CO2, can
accelerate the global warming. If the same process of methane storage
is occurring under the current ice sheets, there may be a new threat
to take into the account when we are discussing ice sheet retreat in
ice sheets will not need thousands of years to melt., The Greenland
ice sheet has been losing an estimated 287 billion metric tons
per year, states NASA.
The continent of Antarctica has been
losing about 134 billion metric tons of ice per year since 2002,
albeit its ice sheet tells a more complicated story.
is difficult to study this processes in modern polar environments.
The ice sheets of Greenland and Antarctica are several kilometers
thick and examining the ground beneath them is challenging and
expensive, nonetheless. But the circumstances that were present in
formation of gas hydrate zones in the past are also present today. We
need to take that into the account when we are considering the
impacts that the rapid melt of the modern ice sheets will have on our
future climate" says Portnov.