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By Peter Rejcek
The spectacular disintegration of a large chunk of the
Wilkins Ice Shelf off the Antarctic Peninsula last month
may be part of an accelerating pattern of climate change
in the region.
That’s the conclusion that scientists are drawing
after more than 400 square kilometers of ice sloughed
off the southwestern front of the ice shelf. A series
of satellite images processed at the National Snow and
Ice Data Center (NSIDC) in Boulder, Colo., showed the
edge of the shelf crumbling and disintegrating in a pattern
that has become characteristic of climate-caused ice shelf
retreats throughout the northern Peninsula area, according
to NSIDC scientists.
“We were all surprised — but not really surprised
— about the Wilkins collapse,” said Hugh Ducklow,
principal investigator for the Palmer Long Term Ecological
Research (PAL LTER) program, funded by the National Science
Foundation.
The shelf is located south of the U.S. Antarctic Program’s
Palmer Station, around which scientists have conducted
a long-term study of the ecosystem for more than 15 years.
They recently proposed to extend the study area farther
south, to Charcot Island, where the Wilkins Ice Shelf
is buckling.
“It is in the new, extended southern part of our
study area, and it would seem to suggest that warming
is reaching there,” said Ducklow, a marine ecologist
and co-director of The Ecosystems Center at the Marine
Biological Laboratory in Woods Hole, Mass. “We have
not seen much evidence that there have been ecological
changes in that area, at least not to the degree we have
documented around Palmer Station.”
The Antarctic Peninsula has arguably experienced the
most dramatic rise in temperature over the last 50 years.
NSIDC reported that temperatures have climbed 0.5 degrees
Celsius each decade. PAL LTER scientists have said the
overall increase is about 6.5 degrees Celsius in the winter
since the 1950s, rising more than five times faster than
the global average.
In addition, the life cycle of winter sea ice since 1979
has dropped, on average, by three months per year around
Palmer Station, meaning it forms later and melts earlier.
Summer sea ice is virtually non-existent in the area,
and perennial sea ice has also all but disappeared.
“The sea ice plays a big role, and may have been
the thing that triggered [the ice shelf collapse] this
year,” noted Walt Meier, a scientist with NSIDC.
Meier explained that the sea ice serves as a buffer between
the ice shelf and ocean waves, which can pummel an unprotected
ice shelf, causing it to flex, particularly if it has
been weakened by melt ponds, pools of open water on the
ice surface that absorb rather than reflect heat.
“[Sea ice] acts as a damper on any ocean waves,”
Meier said. “This year we almost had no sea ice for
a significant amount of time during the summer along the
Wilkins. That allows ocean waves to build up.”
The approach of winter and a thin band of ice only a
few kilometers wide likely saved the rest of the shelf
from immediately collapsing. But it’s probably only
a matter of time before Wilkins, an ice shelf roughly
the size of Connecticut, completely disintegrates. The
question is when.
“That’s going to depend a lot on what the conditions
are next summer. If we have another summer like this year
where the sea ice went out and that area is exposed, it
certainly could be next summer. We did see a lot of melt
ponding; we did see things on the verge of breaking up,”
Meier said.
“I think we can say in the coming years, we’ll
likely see that collapse,” he added.
The Wilkins disintegration won’t raise sea levels
because it already floats in the ocean, and few glaciers
flow into it. However, NSIDC scientists and others note
that the collapse appears to be part of a pattern, and
additional ice shelves in the region may be at risk. Several
have retreated in the past 30 years, with six of them
collapsing completely — Prince Gustav Channel, Larsen
Inlet, Larsen A, Larsen B, Wordie, Muller and the Jones
ice shelves.
“It’s an indication that things are continuing
to happen, and we can maybe expect it to accelerate in
future years with other ice shelves,” Meier said.
NSIDC lead scientist Ted Scambos first discovered that
the ice shelf was collapsing in March. He then alerted
colleagues around the world, initiating an international
scramble to focus attention on the break-up. The British
Antarctic Survey (BAS) responded by sending out a Twin
Otter aircraft over the ice shelf and taking video footage.
Taiwanese scientists also assisted, taking high-resolution
color satellite images of the area using their country’s
Formosat-2 satellite.
“It’s certainly something that draws scientists’
attention. It was a really nice case of collaboration,”
Meier said. “These types of things are definitely
international efforts. No one group has all the tools
and resources to do this at once.”
The PAL LTER scientists are now even more eager to head
south. “The ice shelf breakup indicates the speed
at which things are beginning to change, and the urgency
to get into the region and start making the kinds of observations
and experimental studies we have been conducting farther
north over the past 15 years,” Ducklow said.
There may even be an upside should the Wilkins disintegrate
in the near future, he noted: “One possible advantage
of the Wilkins breakup is that we might be able to get
a little closer in, a bit farther down than before.”
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