Page 2/2 - Posted September 18, 2009
Core drilling as much an art as a science
Mosley-Thompson thinks it will be possible to find glacial stage ice — ice at least 20,000 years old, dating back to when the northern and southern ice sheets reached their maximum extent before retreating and ushering in a relatively stable era of climate.
Still, even during the current Holocene, which began about 12,000 years ago, the climate made some wild swings. For example, based on a large dust event found in tropical and subtropical cores the Thompsons have recovered and analyzed, there was a severe drought about 4,000 years ago that lasted for some three centuries. Yet that event doesn’t show up in any of the continental cores drilled in Antarctica.
Might it show up in the more northerly LARISSA ice core?
“It was a very large drought. It was associated with some societal collapses in the Middle East, the beginning of the first Dark Age, and it is very well recorded in the Andes,” Mosley-Thompson said. “We’re very curious to see if this large event shows up in Antarctica.”
By studying these previous, abrupt natural events such as the drought, the paleoclimatologists hope to learn more about human influences, from increasing atmospheric carbon dioxide to clear-cutting Amazonian rainforests.
“They’re very important,” Mosley Thompson said of abrupt climate change events. “First, it is essential just to know that they happened. And then, hopefully, by piecing together multiple records from different locations we can get a better sense of what the driver or drivers might have been.”
Those answers — and undoubtedly new questions — will come later after the Thompsons and their colleagues have analyzed the core. First, of course, they have to drill into the ice and get the cores back to the United States.
The ice-coring operation is scheduled to take about 45 days with a six-person crew, living in tents and working under a geodesic dome about seven meters in diameter. The team will build a trench where the ice cores will be stored until a plane arrives each week with fresh supplies and fuel.
The cores will be packed into insulated boxes and flown back to the nearby British Antarctic Survey’s Rothera Base , where they will be stored in freezers until the RVIB Nathaniel B. Palmer makes a quick port call to retrieve them.
Generators power the elecromechanical drill, which consists of outer and inner barrels. The outer barrel has anti-torques at the top that hold it stationary in the hole, with an electrical motor at the top, all of it suspended on a cable, and lowered and raised by a winch topside.
The inner barrel does the work of cutting into the ice. After the drill has swallowed about a meters-length of ice, the scientists pull the drill to the surface, disconnect the barrel, push the ice out and process the core — making various measurements about its weight, appearance, density and other notable characteristics. The ice goes into a plastic sleeve and then into a heavy cardboard tube that is placed in the storage trench. All the equipment is cleaned and the drill is sent back down to take another bite out of the ice.
“Then it’s just repeat, repeat, repeat,” Mosley-Thompson said.
Eventually, the deeper ice that is very cold and under great stress begins to fracture as the drill bores down. When this happens, the team will switch to a thermal drill, which applies heat to an electric element that melts its way down into the ice. The amount of power provided to the heater element dictates the drilling rate. Too much power could burn up the heater element.
“There is a science to ice-core drilling, but there’s also an art to it,” Mosley-Thompson said. “Experience is the best teacher.”