Cracking the case
Crevasse-riddled ice shelf poses logistical challenge for climate-change scientists
Posted October 8, 2010
The satellite images projected onto the wall flashed through a series of photos of the Pine Island Glacier Ice Shelf, a warp speed tour through the last several years of one of the most dynamic ice regions on the planet.
The last image — taken earlier this year before the sun plunged most of Antarctica into 24-hour winter darkness — left the room quiet. Several dark stripes ran the length of the ice shelf, like skid marks on snow.
But those black bands aren’t tire tracks — they’re crevasses, large enough to be seen from space with high-resolution satellite imagery. And the scientists want to put several field camps amid those seemingly endless rows of fissures in the ice.
“You wouldn’t want your worst enemy to go there,” noted Robert Bindschadler, emeritus scientist of the Hydrospheric and Biospheric Sciences Laboratory at NASA’s Goddard Space Flight Center, as he mulled the original target sites, which sit in a field of cracks.
Bindschadler is the lead principal investigator for the two-year field project that aims to study what’s happening between the ice and ocean underneath the floating ice shelf. The team plans to drill a hole through the 500-meter-thick ice shelf and send instruments into the cavity below to measure various water properties.
Pine Island Glacier (PIG) is the fastest flowing glacier in Antarctica, moving about 4,200 meters per year toward the edge of the continent. The ice flows into a relatively small but thick ice shelf. Thinning of that ice shelf allows the glacier to flow more quickly, ultimately adding to the global equation of sea-level rise.
Bindschadler has said in the past that it is imperative that the science community understand what’s going on in this isolated region of the Amundsen Sea.
“This is where all the action is taking place. We don’t have any choice in the matter. We have to go there,” he said previously.
That’s proving to be quite a trick.
Bindschadler became the first scientist to stand on the ice shelf in 2007 when a ski-equipped plane landed on the crevasse-ridden ice. That first and last trip to the ice shelf only lasted about 20 minutes. The ice shelf surface proved to be too hard and too rough to ensure a safe series of repeated aircraft landings needed to establish a field camp.
Plan B has required several years of patience as the logistic machine of the U.S. Antarctic Program, funded and managed by the National Science Foundation, lays the machinery for reaching the ice shelf, located 2,000 kilometers from the program’s main base, McMurdo Station.
This year several tractors will haul about 15,000 gallons of fuel and 100,000 pounds of cargo to a site near the ice shelf from another field camp called Byrd Surface Camp. That will set the stage for the 2011-12 season when Bindschadler and colleagues will be flown by helicopters from the main PIG field camp base to the ice shelf for their work.
But where to deploy their instruments?
That was the question facing the team as several of the principal investigators met last month on the campus of Pennsylvania State University, gathering like field generals to plan their final assault on the ice shelf.
Its defenses turned out to be more formidable, forcing the researchers to re-think the location of two field camps on the shelf itself where they’ll deploy their instruments the first year.
“We’ve been overtaken by reality,” Bindschadler said.
The crevasse fields aren’t the only feature of the region causing a change in strategy.
This summer an international team of researchers reported in the journal Nature Geoscience that they had found a 300-meter-high ridge on the seafloor where the ice shelf was once attached. The ridge is believed to play an important role in the changes under way at the ice shelf.
“The ridge has changed the show,” said Tim Stanton, a scientist in the Oceanography Department at the Naval Postgraduate School. His lab designs, builds and deploys unique ocean profilers, a system of instruments that moves vertically up and down on a cable through the entire water column, with power and communications at the surface. Its job is to measure and monitor the complex ocean currents swirling below the ice.
The ridge is a game-changer because it means that any deployment of the ocean profiler upstream of the ridge — remember that the ice flows toward the ocean — might have hit the raised seafloor. Now any upstream deployment of the instrument package will have to account for the ridge.
The ridge was discovered in 2009 during a research cruise aboard the USAP’s Nathaniel B. Palmer, led by chief scientist Stan Jacobs, an oceanographer at Lamont-Doherty Earth Observatory at Columbia University.
A British team aboard the ship sent a robotic submarine underneath the ice shelf where it mapped various properties of the underwater cavity, discovering the ridge along the way.
“It was really a blessing to have that information. Otherwise, it was a blank slate,” Bindschadler said of the data retrieved by the yellow submarine. “The annoying thing about the ridge is that our instruments can’t touch the floor.”
The British are also collaborators on the PIG project. A British Antarctic Survey (BAS) plane will fly over the region from BAS’ base at Rothera Station off the Antarctic Peninsula this year. The plane’s radar will provide additional details about the ice shelf that will be useful for planning the 2011-12 and 2012-13 field campaigns.
“[Pine Island] has been a focus for us for quite a few years,” said David Vaughan, a scientist at BAS who attended the strategy session at Penn State. “Pine Island is the biggest red dot” for climate change in Antarctica, he added.
Two American teams will also head to the Ice this season on separate missions.
David Holland will lead a two-person team to the edges of the glacier to recover an existing automatic weather station (AWS) he installed three years ago and move it to the PIG camp being set up this season.
Director of the Center for Atmosphere Ocean Science at New York University, Holland will also attempt to install three additional AWS systems in the region.
Meanwhile, Stanton and a separate team will join New Zealand researchers at a field camp near Erebus Ice Tongue, a glacier that pokes out about 10 kilometers into McMurdo Sound from the Ross Island coastline near Cape Evans.
The U.S. scientists will conduct a second test of the ocean profiler system on the sea ice. Last year’s “dress rehearsal” of the project successfully punched through the 200-meter-thick section of ice shelf near McMurdo Station with a hotwater drill.
It was the first time scientists had deployed such a complex ocean profiler beneath an Antarctic ice shelf, even discovering a wee marine organism with a borehole camera that preceded the profiler down the fresh hole.
However, the system malfunctioned shortly after the team left. Stanton believes he has worked out the problem and wants another shot at testing the equipment before the team does it for real in about a year.
By then there will be little room for mistakes among the crevasse fields of the Pine Island Glacier Ice Shelf.
“We’re going to be eager to bang this camp in,” Stanton said.
NSF-funded research in this story: Robert Bindschadler and Alberto Behar, Goddard Space Flight Center, Award No. 0732906; Tim Stanton, Naval Postgraduate School, Award No. 0732926; David Holland, New York University, Award No. 0732869; Sridhar Anandakrishnan, Penn State University, Award No. 0732844; Miles McPhee, McPhee Research Company, Award No. 0732804; and Martin Truffer, University of Alaska, Fairbanks, Award No. 0732730.
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