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Going to the edge
Project combines glaciology, oceanography to answer questions about the interaction between ice sheets and the ocean
Posted November 22, 2007
Scientist Bob Bindschadler’s choice for a place to conduct research in West Antarctica shares some of the same criteria as those of his colleagues fanning out across Antarctica for the International Polar Year (IPY).
“It’s a hard place to get to. It’s a terrible place to work,” he says of the crevasse-ridden Pine Island ice shelf, adjacent to the West Antarctic Ice Sheet (WAIS), where he will work this season.
But the possible scientific payoff is also IPY worthy, considering the question he hopes to answer: “How is the ocean tickling the ice sheet and why is the ice sheet responding so dramatically?”
The objective is to study the interaction of the ocean and the fast-moving glacial ice of Pine Island Glacier. Bindschadler and his colleagues believe that, based on satellite imagery, warm, salty ocean water is a key component chipping away at the edges of the continent’s ice sheets and quickening the pace by which glaciers dump ice into the ocean.
“The signature from those [satellite] observations is pretty clear: that the changes are largest at the perimeter of the ice sheet and decrease in magnitude as you go inland,” he explained. “That says to us that the trigger, the driver of these changes, is the ocean.”
Chief scientist with the Hydrospheric and Biospheric Sciences Laboratory at NASA’s Goddard Space Flight Center, Bindschadler said that until recently the technology wasn’t available to make the sort of measurements scientists need to model ice and ocean interaction below the ice sheet.
Those models are important in predicting how WAIS will react to climate change as global warming ratchets up ambient and ocean temperatures. Conservative estimates predict the ice sheet, if it were to disintegrate completely, would raise sea level by five meters.
Reconnaissance missionBut before anything can happen, the researchers must determine if they can even go to work. The site they’ve chosen is a dynamic area home to the two, fastest-moving glaciers on the continent – Pine Island and Thwaites glaciers, both of which pour into the Amundsen Sea.
“Job one is to land and survive,” Bindschadler said. He has identified one area where he believes a Twin Otter can safely land and where he and colleague David Holland from NYU can make some basic measurements.
The site is about 35 kilometers from the calving edge of the 800-square-kilometer ice shelf. That’s close to where they expect to find the grounding line, where the warm dense ocean water hits the ice in contact with the bedrock.
“We’re pretty sure that’s where the melt rates are the highest and where these key processes are most intense,” Bindschadler said.
The idea is to pack light for this visit. The scientists will set up an automatic weather station to beam back climate data through the austral winter. Meteorologists are also interested in the information, as the area represents one of the biggest weather gaps on the planet, according to Bindschadler.
They will also set up two GPS receivers to determine ice velocity and ocean tides. The latter measurement will indicate how much flex the ice shelves are experiencing. Two British field researchers, working farther upstream on the glacier, will spend a week at the Americans’ camp and use ice-penetrating radar to measure the ice thickness and, more importantly, changes in the thickness.
A second, nearby research team will visit with seismic equipment to measure the depth of the water. “That’s something we want to know because that’s critical for setting up next year’s sub-ice instrumentation and for modeling the water circulation underneath the ice shelf,” Bindschadler said.
Looking belowIf all goes as planned, work would begin in earnest the next two field seasons to use a hot water drill to bore through the 500-meter-thick ice and lower instruments into the ocean cavity below.
A video camera is among instrument the scientists will send down the borehole. What does the ice underneath look like? Is it smooth? Is it rough? No one knows, Bindschadler said.
Graphic Credit: Bob Bindschadler
This illustration shows the dynamic between the ocean and ice sheets.
They will also deploy small, oceanographic profilers through the 13-centimeter-wide hole. The profiler will continuously run up and down a cable measuring current, temperature and salinity, transmitting the information up a cable frozen into the borehole to an Inmarsat terminal that beams the data to a satellite.
It’s an exciting study, according to Kelly Falkner, program manager of the newly created Antarctic Integrated System Sciences (AISS) department in the Office of Polar Programs at the National Science Foundation. AISS and NASA are co-funding the project.
“That will be the first direct set of observations beneath an ice shelf like this that extend throughout the year,” she said.
Eventually, the research team hopes to bore several holes over the two field seasons to characterize the horizontal currents, another important factor for modeling the interaction between ocean and ice.
This is an example of the sort of science that IPY supports: lots of unknowns with big potential for discovery. How deep will the water be? Will the profiler work? It’s been used in the Arctic, where the ice is only a few meters thick.
“There’s a lot of unknown and a bit of finesse, but these scientific questions must be answered. We have no choice but to try and get the answers,” Bindschadler said.
NSF-funded research in this story: Robert Bindschadler, NASA Goddard Space Flight Center.