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Australia: The Land Where Time Began |
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Antarctica
– The Threat Beneath
The
Australian ice-breaker RSV Aurora
Australis had been attempting to batter its way through the heavy
sea ice off the coast of East Antarctica for several days and was still
trying to get through to their objective, to reach a part of Antarctica
that previous attempts had failed to reach.
The
attempt was saved when a wind change blew the ice away from the shore,
which opened up a path through the pack ice. In January 2015 the ship
eventually reached the coast of Antarctica shortly after midnight.
Rintoul’s research team were the first scientists to reach the Totten
Ice Shelf, a vast floating ice ledge that is the marine extension of the
largest glacier in East Antarctica. For more than 12 hours the research
team carried out non-stop probing of the water temperature and salinity,
the speed and direction of the ocean currents as well as the shape and
depth of the seabed. They also deployed automatic instruments that would
continue operating after the ship had departed.
The
first direct observations made by Rintoul’s team confirmed a fear they
had for a long time: that the floating glacier tongue can be melted away
from below by the warmer ocean waters surrounding it (Rintoul, S. R. et
al., 2016). They suggested this could explain the thinning of the Totten
Ice Shelf that had been occurring over the past few decades.
Some
of the scary truths about East Antarctica, that vast, flat landmass to
the east of the Transantarctic Mountains (see ‘Ice King’), are being
revealed by findings such as these . East Antarctica is of a similar
size as the entire USA, the majority of which stands on a high plateau
that is about 4,093 m above sea level, where the temperature can go as
low as -95oC. Researchers believed that the East Antarctic
Ice Sheet had been stable in the past and was not likely to change in
the future, because it was so cold and isolated, which is in stark
contrast to the West Antarctic Ice Sheet, which is much smaller, which
has raised alarms because many of its glaciers have been retreating
rapidly.
According to Tas van Ommen, a glaciologist with the Australian Antarctic
Division in Kingston, near Hobart, almost everything that had been
believed to be known about East Antarctica has proven to be wrong, as
has been shown by research over the past few years. His team found by
flying planes carrying instruments capable of probing beneath the ice
that a large part of East Antarctica is well below sea level, and as a
result is more vulnerable to the warming ocean than previously believed.
Also uncovered were clues that the massive Totten Glacier, which alone
holds about as much ice as all of West Antarctica, has shrunk and grown
repeatedly in the past (Aitken, A.R.A. et al., 2016) – which is also a
sign that it could again retreat in the future.
Though East Antarctica doesn’t appear to be losing much ice at the
present, there are indications that it is being affected by the rising
temperature of climate change and is changing in measureable ways.
According to Oiu this is disconcerting because the East Antarctic Ice
Sheet is more than 10 times the size of the West Antarctic Ice Sheet. If
just all of the ice below sea level in East Antarctica melted the oceans
would be raised by 20 m.
In
order to better predict what will happen in the future research is being
carried out to gather as much information as possible about East
Antarctica. The concern about the East Antarctic Ice Sheet is that it
might reach a tipping point over the next few centuries. According to
Rintoul once the retreat of the glaciers goes beyond a certain point
things might get worse very rapidly which would cause a rapid rise in
sea level.
East
Antarctica is a region that has been neglected by climate researchers
for a long time; Rintoul was among the first scientists who warned about
possible trouble in that region. In 2013 his team combined satellite
imagery, airborne surveys and climate models to detail the behaviour off
ice around the margin of Antarctica. Evidence was found that 6 ice
shelves in East Antarctica, including Totten, were melting from below at
much higher rates than expected, and some of them were even rivalling
fast-retreating glaciers in West Antarctica (Rignot, Jacobs, Mouginot &
Scheuchl, 2013).
When
the researchers took a closer look at some of those glaciers in East
Antarctica there were more surprises. It was shown by satellite imagery
and airborne surveys between 1996
and 2013 that the Totten Glacier surface had dropped by 12 m and it’s
grounding line, the point on the coast where the tongue of the glacier
begins to float on the ocean, had retreated inland by up to 3 km (Li et
al., 2015).
Stokes et al. analysed
satellite data that had been obtained between 1996 and 2012 covering all
of the Antarctic coastal regions. There was no net ice gain or loss in
most areas. The Wilkes Land region with an area larger than Greenland,
that includes the Totten Glacier, is the only exception (Miles, Stokes &
Jamieson, 2016). In this region ¾ of the glaciers retreated between 2000
and 2012. According to Stokes, Wilkes Land may be the weak point in in
the East Antarctica Ice Sheet.
Ommen et al. flew over
Antarctica to probe the underside of the Totten Glacier. The landscape
beneath the ice is of fundamental importance for how the glaciers flow
and the ways in which they respond to climate change. When an
international initiative, ICECAP (International Collaboration for
Exploration of the Cryosphere through Aerogeophysical Profiling) 10
years ago to survey systematically the landscape of East Antarctica
nothing was known about the landscape beneath the ice.
Every southern summer the aircraft of ICECAP have been crisscrossing the
vast continent using radar as well as gravitational and magnetic sensors
to detect the landscape beneath the ice. Appearing to be featureless,
the ice sheet is continually changing, with snow dunes sculpted by the
wind and the ice simmering in thousands of shades under the unearthly
Antarctic light; it has been compared to another planet.
The
flights have revealed an astoundingly dramatic landscape that is hidden
beneath the ice that is relatively flat. The existence of a 1,100 km
long canyon, which is the longest in the world, and almost as deep as
the Grand Canyon, has been confirmed by glaciologist Sun Bo at the Polar
Research Institute of China in Shanghai. Van Ommen et
al. discovered that 21 %m of
the catchment of the Totten Glacier is more than 1 km below sea level,
in previous flights over Wilkes Land, an area that is 100 times larger
than had previously been estimated. It wasn’t expected to be as
extensive as has been found.
Underwater troughs were also found that extended from the edge of the
Totten Ice Shelf to the grounding line that was 125 km inland, as deep
as 2.7 km below sea level (Greenbaum et al., 2015). Warming waters from
offshore could be allowed by this deeply contoured landscape to rapidly
reach and erode the ice from below.
When
RSV Aurora Australis reached
Totten in 2015 it was the first chance scientists had to study the fate
of that water. Warm water at 0.3oC was detected near the
glacier tongue by Rintoul’s team, which was much warmer than the
-2oC, which is the
freezing point of sea water (Rintoul, S. R. et al., 2016). It is the
water temperatures higher than freezing that are driving the rapid melt
rates. The automated instruments that were left in place after the
expedition moved out of the ice have shown that the elevated water
temperatures are present throughout the year. Rintoul et
al. suggest that if the
channel that has been found recently is used by the sea water to reach
the grounding line of the Totten Ice Shelf, they will be at least 3.2oC
warmer than the freezing point at that depth, which Rintoul says “would
be really bad news”
It
has been found that there are lakes beneath the Antarctic ice sheet that
periodically send flood waters towards the coast, and these are another
threat, originating in the Antarctic interior, to the ice shelves. Lake
Cook, that is located beneath the ice sheet in Wilkes Land drained
suddenly 10 years ago flushing 5.2 billion m3 of flood water,
which was the largest event of this type to have been reported in
Antarctica . According to Leigh Stearns, a glaciologist at the
University of Kansas in Lawrence, this type of flood could be another
destabilising factor, which causes the ice to flow more rapidly leading
to more calving of icebergs.
Troubled past
According to researchers these are not just hypothetical scenarios. It
has been revealed by studies over the last few years that East
Antarctica has lost a lot of ice in the past, and could possibly do so
again in the near future.
A
2010 expedition that was supported by the Integrated Ocean Drilling
Program, which retrieved seafloor sediments off the coast of East
Antarctica, found some evidence for the loss of large amounts of ice in
the past. Getting those sediments proved to be a dangerous endeavour, as
the ship had to repeatedly stop drilling to dodge massive icebergs. For
ocean drilling the waters surrounding Antarctica are some of the
challenging environments for ocean drilling.
It
was revealed by the drilling that there had been surprising changes in
the history of the East Antarctic Ice Sheet. It had long been believed
that since the East Antarctic Ice Sheet had formed about 14 million
years ago it had remained at its current size. It was believed it is a
very large stable ice mass that wasn’t responding to climate change.
It
was revealed by the seafloor sediments that at many times between 5.3 Ma
and 3.3 Ma, in the Pliocene, a time when atmospheric temperatures were
up to 2oC above those of the present, it had expanded and
contracted (Cook et al., 2013). A clear was received every time there
was a warm period, which suggests that the ice sheet was sensitive to
climate warming.
According to the researchers they have some intriguing preliminary
results from the most recent interglacial period, between 129,000 years
ago and 116,000 years ago, a time when the Earth was as warm as it is at
the present. At that time the ice sheet retreated slightly less than it
did during the Pliocene, which was much warmer, which was a big surprise
to the researchers.
Based on these results it seems a certain amount of ice can be lost
quite easily with only a small amount of warming.
Future
Researchers are becoming increasingly concerned about the future, as the
vulnerability of East Antarctica comes into focus. Computer models that
simulate the ice sheets response to a changing climate are the only way
to forecast decades or centuries into the future.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |