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| Antarctic |
Using measurements of the elevation of the Antarctic ice sheet made
by a suite of satellites, the researchers found that the Southern
Antarctic Peninsula showed no signs of change up to 2009. Around 2009,
multiple glaciers along a vast coastal expanse, measuring some 750km in
length, suddenly started to shed ice into the ocean at a nearly constant
rate of 60 cubic km, or about 55 trillion litres of water, each year.
This makes the region the second largest contributor to sea level rise in Antarctica and the ice loss shows no sign of waning.
Dr Bert Wouters, a Marie Curie Fellow at the University of Bristol,
who lead the study said: "To date, the glaciers added roughly 300 cubic
km of water to the ocean. That's the equivalent of the volume of nearly
350,000 Empire State Buildings combined."
The changes were observed using the CryoSat-2 satellite, a mission of
the European Space Agency dedicated to remote-sensing of ice. From an
altitude of about 700km, the satellite sends a radar pulse to Earth,
which is reflected by the ice and subsequently received back at the
satellite. From the time the pulse takes to travel, the elevation of the
ice surface can retrieved with incredible accuracy. By analysing
roughly 5 years of the data, the researchers found that the ice surface
of some of the glaciers is currently going down by as much as 4m each
year.
The ice loss in the region is so large that it causes small changes
in the gravity field of the Earth, which can be detected by another
satellite mission, the Gravity Recovery and Climate Experiment (GRACE).
"The fact that so many glaciers in such a large region suddenly
started to lose ice came as a surprise to us," continued Dr Wouters. "It
shows a very fast response of the ice sheet: in just a few years the
dynamic regime completely shifted."
Data from an Antarctic climate model shows that the sudden change
cannot be explained by changes in snowfall or air temperature. Instead,
the team attributes the rapid ice loss to warming oceans.
Many of the glaciers in the region feed into ice shelves that float
on the surface of the ocean. They act as a buttress to the ice resting
on bedrock inland, slowing down the flow of the glaciers into the ocean.
The westerly winds that encircle Antarctica have become more vigorous
in recent decades, in response to climate warming and ozone depletion.
The stronger winds push warm waters from the Southern Ocean poleward,
where they eat away at the glaciers and floating ice shelves from below.
Ice shelves in the region have lost almost one-fifth of their
thickness in the last two decades, thereby reducing the resisting force
on the glaciers. A key concern is that much of the ice of the Southern
Antarctic Peninsula is grounded on bedrock below sea level, which gets
deeper inland. This means that even if the glaciers retreat, the warm
water will chase them inland and melt them even more.
Dr Wouters said: "It appears that sometime around 2009, the ice shelf
thinning and the subsurface melting of the glaciers passed a critical
threshold which triggered the sudden ice loss. However, compared to
other regions in Antarctica, the Southern Peninsula is rather
understudied, exactly because it did not show any changes in the past,
ironically.
"To pinpoint the cause of the changes, more data need to be
collected. A detailed knowledge of the geometry of the local ice
shelves, the ocean floor topography, ice sheet thickness and glacier
flow speeds are crucial to tell how much longer the thinning will
continue."
This Story is taken from Science Daily
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