Cooking with gas
Scientists extract big ice cores from Taylor Glacier for methane measurements
Posted April 25, 2014
The term “now we’re cooking with gas” takes on a completely different meaning atop Taylor Glacier.
There’s the more literal interpretation: A metal tank filled with large-diameter ice cores is being heated with a circle of five powerful propane torches. The gases once trapped in the ancient ice are released and captured through a system of tubes and vacuums housed in a nearby tent.
After three days of feeding about 1,000 kilograms of ice into the melter, scientist Vasilii Petrenko and his team will have captured enough methane gas – about 25 micrograms – for one sample that they and their colleagues can analyze to detect the rare carbon-14 isotope.
Its absence or presence in the ancient ice will tell the researchers not only about abrupt climate changes in the past, but about how modern-day sources of methane may respond to a warming world.
“We’re trying to improve our understanding of the Earth’s climate system by looking into the past – seeing how the temperature was changing, how greenhouse gases were changing,” explained Petrenko, an assistant professor of earth and environmental sciences at the University of Rochester . He is principal investigator (PI) on a three-year field project to mine tons of ice from one of the main glaciers that slowly pushes its way into the McMurdo Dry Valleys .
Methane is a potent greenhouse gas, far more powerful even than carbon dioxide at trapping heat, but it is far more diluted in the atmosphere – measured in parts per billion versus parts per million. However, at certain times in the past, methane concentrations have jumped dramatically in step with sudden spikes in temperature.
By determining the source of those big burps of methane in the past, scientists can produce more realistic climate models of how modern-day methane sources may react as permafrost melts and ocean currents warm.
Photo Credit: Peter Rejcek
Scientist Michael Dyonisius assists IDDO driller Mike Jayred with drilling an ice core on Taylor Glacier.
That’s where carbon-14 – and all that ice – comes in.
“We can’t get enough ice for these carbon-14 measurements from a conventional ice core. There’s just not enough ice,” Petrenko explained during a visit to his field camp atop Taylor Glacier, about 15 kilometers from its terminus in Taylor Valley.
Traditional ice cores are drilled at sites where the stratigraphy – the annual layers of ice – is predictably found to go from youngest to oldest with depth. The mix-and-match stratigraphy of the so-called blue ice being mined on Taylor Glacier – thanks to its location in an ablation zone where ice sublimates away directly into vapor – finds that old ice exists in large quantities at the surface.
Previous work by Petrenko and his co-PIs on the project – Jeffrey Severinghaus at the University of California-San Diego’s Scripps Institution of Oceanography and Ed Brook at Oregon State University – have mapped the ice-age stratigraphy. It’s a bit like how geologists identify strata of rock of varying ages in a formation.
In this case, the Taylor Valley researchers are targeting two distinct time periods during the roughly 10,000-year transition between the last glacial period and modern-day Holocene.
The first event occurred about 14,700 years ago, an abrupt warming that marked the start of a period known as the Bølling–Allerød that lasted for about two millennia. The climate cooled again during a time called the Younger Dryas, named after the white flower that grows near glaciers. Then, about 11,600 years ago, another rapid warming took place just before the Perboreal period and the start of the Holocene.
“Both of those had big methane increases associated with them,” Petrenko said, though the cause of these abrupt climate changes is still being debated.
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