So
much ice has disappeared from West
Antarctica
in recent years that Earth's gravity is now weaker there, researchers
reported in the Aug. 28 issue of the journal Geophysical Research
Letters.
Earth's
gravity
fluctuates in small ways that are caused by changes in mass. When
hefty ice sheets melt, there is less ice and thus less gravitational
force pulling in that area.
The
new results come partly from the European Space Agency's GOCE
satellites, a four-year endeavor to finely map Earth's gravity. The
GOCE gravity map was combined with gravity measurements recorded from
the GRACE satellites, an ongoing NASA-Germany mission that tracks
changes in Earth's ice sheets via gravity. Merging the information
from both satellites allowed researchers to sharply illuminate West
Antarctica's ice loss.
The
satellites measured a dip in Earth's gravity field due to extensive
ice loss in West Antarctica, the new study reports. The shrinking
glaciers and ice shelves, whittled by warm ocean currents, tugged
more gently when the satellites sped by overhead. [Watch:
Antarctic Ice Loss Causes Dip In Earth's Gravity]
Each
space mission consists of two satellites orbiting near each other.
Slight distance changes occur between the satellites as they dip or
rise over gravity highs and lows. Computers translate those shifts,
sometimes smaller than a hair's width, into an estimate of Earth's
gravity field.
The
precise measurements suggest West Antarctica shed some 209 billion
metric tons (230 billion tons) of ice each year between 2009 and
2012. This region of Antarctica
may have passed a tipping point
into unstoppable collapse, according to earlier studies published
this year.
Three
of West Antarctica's retreating glaciers account for most of the ice
loss, in agreement with past studies. Between 2009 and 2012, Pine
Island Glacier lost 67 billion metric tons (74 billion tons) of ice
per year; Thwaites Glacier lost 63 billion metric tons (69 billion
tons) of ice per year; and Getz Ice Shelf lost 55 billion metric tons
(61 billion tons) of ice per year.
The
research team, led by Johannes Bouman from the German Geodetic
Research Institute, now plans to analyze ice loss from all of
Antarctica, according
to a statement from
ESA. The GOCE satellite mission ended in 2013, when the machines ran
out of fuel (as planned) and broke up in Earth's atmosphere.
It
says this methane could be released into the atmosphere as ice
retreats, contributing to climate warming.
The
findings indicate that ancient deposits of organic matter may have
been converted to methane by microbes under the ice.
An
international team reported the results in Nature journal.
Study
leader Jemima Wadham, from Bristol University, said: "This is an
immense amount of organic carbon, more than ten times the size of
carbon stocks in northern permafrost regions.
"Our
laboratory experiments tell us that these sub-ice environments are
also biologically active, meaning that this organic carbon is
probably being metabolised to carbon dioxide and methane gas by
microbes."
They
estimate that there could be hundreds of billions of tonnes of carbon
stored in methane reservoirs under the ice sheet.
The
authors say that the predicted shallow depth of these methane
reserves means that they could be destabilised by climate change, and
might act as a positive feedback on global warming.
Co-author
Dr Sandra Arndt, also from the University of Bristol, said: "It's
not surprising that you might expect to find significant amounts of
methane hydrate trapped beneath the ice sheet.
"Just
like in sub-seafloor sediments, it is cold and pressures are high
which are important conditions for methane hydrate formation."
In
their Nature paper, the authors comment that their "findings
suggest that the Antarctic Ice Sheet may be a neglected but important
component of the global methane budget". See also -
This
seems to have been known about for some time as witnessed by this
video dating back to 2010. The video seems to have some relationship with a vegetarian group!
Antarctic
melt is speeding methane release
With
ice shelves in Western Antarctica and the Peninsula already noted to
be melting due to climate change, the additional release of methane
could, due to its potency accelerate global warming beyond what
scientists have described as an irreversible tipping point
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