The leading edge
ICECAP project to explore subglacial basins below sea level in East Antarctica
Posted January 16, 2009
If the global climate change story has a lead protagonist south of the Equator, it’s West Antarctica, a marine-based ice sheet discharging ice into the ocean about as fast as Greenland is in the Arctic.
Scientists generally consider East Antarctica, a much larger and thicker ice sheet, still a minor character in the worldwide warming scenario. But there are signs that even this behemoth may be responding to changing climate — and parts of the ice sheet may be more sensitive than first believed.
Researchers from the United States, United Kingdom and Australia have teamed up to explore one of the last relatively uncharted areas of East Antarctica, an expanse that may prove to be the soft underbelly of the ice sheet, the chink in the armor. In this region, roughly the size of Mexico, two huge subglacial basins sit well below sea level, like most of the West Antarctic Ice Sheet.
“That’s probably been the area that’s controlled the evolution of East Antarctica, the fast changes over East Antarctica, over the last 10 million years,” said Don Blankenship, a research scientist at the Jackson School’s Institute for Geophysics at the University of Texas at Austin (UTIG). Blankenship is also the principal investigator on the project, an International Polar Year initiative dubbed ICECAP, for Investigating the Cryospheric Evolution of the Central Antarctic Plate.
Beginning in January 2009, the ICECAP team will use an upgraded World War II-era DC-3 aircraft with a suite of geophysical instruments to measure the thickness of the ice sheet and the texture, composition, density and topography of the bedrock below the ice.
“The large basins of East Antarctica — Wilkes Basin, Aurora Basin, the Adventure Trench and the Astrolabe Basin — are all well below sea level and are all connected to the coastline and each other by channels that are continuously below sea level,” explained Andrew Wright, post-doctoral researcher on the ICECAP project from the University of Edinburgh in the UK.
“Some of the biggest glaciers in Antarctica … each of which is associated with one of the deep East Antarctic basins, have recently been showing signs of surface lowering similar to those observed on the big glaciers in West Antarctica,” he added. ICECAP will focus its work on the Wilkes and Aurora basins.
Why is it a problem if that ice sits below sea level? Increases in atmospheric temperatures alone can’t melt these blocks of ice. The ocean plays a key role as warm water flows up under ice shelves and melts them from below. This speeds the flow of the ice sheet, which is grounded to the bedrock, into the water.
Scientists estimate the West Antarctic Ice Sheet could raise sea levels about six meters if wholesale melting and breakup occurred. All the ice in East Antarctica could push sea levels by more than tenfold of that estimate were it all to disintegrate, though much of it is above sea level. Still, the ice in the low-lying area targeted by ICECAP is at least a couple of kilometers thick.
“It has several times as much sea level [potential] over these sub-marine basins as West Antarctica does,” Blankenship noted. “The same sorts of instabilities that apply to West Antarctica apply to East Antarctica.”
Moving west to east
Blankenship and colleagues in Texas have been winging their way above Antarctica’s frozen wastes for nearly 20 years doing aerogeophysical surveys of the ice sheets and the rock below. In collaboration with colleagues like Martin Siegert, a glaciologist and ICECAP principal investigator who heads the School of GeoSciences at the University of Edinburgh, Blankenship has mapped out the West Antarctic Ice Sheet using a suite of geophysical instruments.
But he, Siegert and others are also interested in the subglacial lakes that run below East Antarctica like a municipal waterworks. Lake Vostok is the most famous of the subglacial reservoirs, but there are dozens of these bodies of water,which don’t freeze because of the enormous pressures of the ice above them.
A recent study published online in the journal Nature Geoscience used satellite data that revealed a complex network of subglacial plumbing in which water periodically cascades from one lake to another. Water acts as a lubricant, reducing friction at the base of the ice and making the ice flow faster.
Blankenship said it is important for the science community to learn more about East Antarctica’s hydrological system and to map out the boundaries between ice and rock. That will help the researchers understand the ice sheet’s evolution and what role the lakes play in its formation and dynamics.
“The big problem is that very little was known about the boundary conditions in East Antarctica,” Blankenship said. “There are a few places that have been covered pretty well, but the majority of the place is unexplored.” Some work took place in the 1970s, but little has transpired since then.
Blankenship and Jack Holt, also with UTIG, worked with the British Antarctic Survey (BAS) in 2004-5 to explore what Blankenship called the last piece of unknown West Antarctica, the Amundsen Sea Embayment. Using airplanes with radar antennas strapped under the wings, the scientist created detailed topographic maps of the rocks and sediment that form the bed on which the ice sits.
“It’s miserable working out there,” Blankenship said. “The weather is horrible, but we got really lucky and we were able to do [the whole airborne] program.”
UTIG’s aerogeophysical work, he explained, provides a sort of roadmap that other researchers use for more detailed studies of process like the ice-ocean interaction. “That will be going on for years and years, trying to understand the Thwaites and Pine Island glaciers, in particular, in West Antarctica,” Blankenship said.
The time is right to move on to East Antarctica, he added. “We’re just the leading edge. We always go in first.”
The U.S. National Science Foundation (NSF), the U.K. Natural Environment Research Council, the Australian Antarctic Division (AAD) and the University of Texas are providing funding for ICECAP.
The Australians are offering the use of their coastal research base, Casey Station, as the hub of operations for the first season of the three-year project. That allows the researchers to fly the converted DC-3 without relying on fuel caches in the field. The British and the University of Texas covered the costs of the plane upgrades, while the NSF and AAD pay for the personnel and deployments, according to Blankenship.
“This is a real IPY project, where everybody is chipping a lot in,” he noted. ICECAP will use the U.S. Antarctic Program’s McMurdo Station for sorties in future seasons.
Added Wright, “I think the important thing is that the level of funding necessary, and the need to use the Antarctic bases [and] logistics of more than one country in order to access the regions of interest, means that projects of this scale can only be attempted as collaborations between nations.”
A flying laboratory
The ICECAP team will fly eight-hour missions out of Casey Station every good-weather day over a three-week period, according to Tas van Ommen, a glaciologist with the Australian Antarctic Division and ICECAP principal investigator. “The hope is to cover a radial pattern of flight lines covering most of the Aurora subglacial basin,” he explained.
The instruments aboard the plane include ice-penetrating radar to record echoes from the ice surface and base as well as from within the ice sheet, the University of Edinburgh’s Wright explained. Radar antennas installed beneath the wings of the aircraft transmit and receive the signals.
“Data [are] recorded in flight, but require processing to make it useful,” he said. “We will also measure and record changes in the Earth’s gravity and magnetic fields, which, when combined with the radar measurements of ice thickness, can be used to determine information about the rock types and large-scale geology beneath the ice sheet.”
The aircraft also sports a magnetometer within a tail-boom that sticks about 3 meters from the rear of the aircraft. “Accurate position information is important for this kind of survey, so GPS and aircraft altitude [and] orientation sensors are an important part of our equipment,” Wright said.
Going way back
The survey will also help pinpoint the location where scientists might expect to find ice that is more than one million years old. The Australians are particularly interested in drilling an ice core that could provide a paleoclimate record that would complement data from marine sediment cores, according to van Ommen.
Scientists can use ice cores to recreate past climate by analyzing the trapped gases and dust in the ice. The oldest ice core record, also from East Antarctica, stretches back about 800,000 years.
The million-year mark is not just a psychological barrier to break, van Ommen explained. “We see in the marine sediment record that before about 1.3 million years … ice age cycles beat with a rhythm of around 41,000 years. For the last 800,000 years, though, ice ages have waxed and waned on a 100,000-year cycle.”
Said Blankenship, “People really want to understand what throws the switch between 40,000 and 100,000 years. In other words, what does it take to change the climate like that, and it’s down there right around 1 million years.”
Theories exist, van Ommen said, “and one general line of argument implicates a background change in overall planetary [carbon dioxide]. Understanding this has clear implications for predicting where we head in a high CO2 future, and in our general understanding of mechanisms.”
NSF-funded research in this story: Don Blankenship (principal investigator), Ian Dalziel, Lawrence Lawver and Jack Holt, University of Texas at Austin, Award No. 0733025.
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