Page 2/2 - Posted April 25, 2014
Study investigates source of methane during abrupt climate changes
Scientists are aware of only a few sources with enough methane locked away to explain the jump in methane concentrations that accompanied the spikes in temperature. One would be methane frozen along the seafloor in a form called methane clathrates. Wetlands are also a possible source.
In the former, where methane is trapped by cold and pressure in the ocean floor, the gas contains virtually no carbon-14, while methane from wetlands will have trace amounts of the heavier carbon isotope. That’s because carbon-14 has a relatively short half-life, and it takes hundreds of thousands of years for methane clathrates to form along the continental slopes of the seafloor. On the other hand, methane production in wetlands is measured in decades.
If methane hydrates were the culprit, the ratio of carbon-14 found in the ancient gas freed from the glacier ice would drop as methane concentrations increase. If not, the ratio of carbon-14 would remain relatively constant if the methane source was from wetlands.
Photo Credit: Peter Rejcek
Scientist Vasilii Petrenko adjusts the system used to capture gases released by melting large ice cores.
A previous study by Petrenko and colleagues using ice cores from Greenland linked the more recent spike in methane mainly to wetlands. Ice cores drilled on Taylor Valley in 2010-11 and 2011-12 eventually confirmed the result, according to Petrenko. [See previous article — On the surface: Scientists find old ice for climate studies at top of Antarctic glacier.]
The ice from Taylor Glacier also confirmed another suspicion: Some of the carbon-14 containing methane found in the Greenland ice core was produced in situ, in the ice itself, by the bombardment of cosmic rays. Scientists already knew that cosmic rays naturally produce C14 in the ice. It was a bit of a surprise that this C14 also produced some CH4 by a chemical reaction in the ice, Petrenko said.
“We came to this place to partly test this hypothesis,” he added.
Now the team has moved on to the older Bølling–Allerød event.
It’s an effort that each year requires about two months of fieldwork, feeding the melter a steady diet of 25-centimeter-diameter ice cores. The team uses a specialized drill developed and built by the Ice Drilling Design and Operations (IDDO) group at the University of Wisconsin-Madison .
Of course, what partly makes the Taylor Glacier an ideal place to collect old ice – a relentless, scouring wind that blows away any snow accumulation – can also make it a miserable place to work.
Photo Credit: Peter Rejcek
Field camp manager Chandra Llewellyn indicates wind direction as a helicopter lands on Taylor Glacier.
“We expect it to be windy; however, this season we saw probably twice as much wind as ever before, both in the number of the windy days and in their intensity,” Petrenko said later in a University of Rochester blog . Winds were routinely above 30 kilometers per hour, with storms bringing down gusts of more than 80 kilometers per hour.
And while sunny, warm days were welcome to the team of scientists and students working 12-hour shifts, the heat was an unwelcome hindrance to the drilling operation. Eventually, the team switched to a “night shift” during Antarctica’s 24-hour days, when the sun dipped low enough below the Kukri Hills to cool the weather down a few degrees.
“We like the shade. We don’t want to be drilling warm on the surface,” explained IDDO driller Mike Jayred, because otherwise the warm ice will cause the drill to stick.
“It’s a pretty warm place to drill,” he noted.
Taylor Glacier is also the ideal place to drill back in time.
“The kinds of studies we do are pretty exciting. We actually sample the ancient atmosphere,” said PhD student Thomas Bauska at Oregon State University, who previously worked on a deep ice core in West Antarctica that would require a drill capable of going down nearly 2,000 meters to grab ice of an equivalent age.
On Taylor Glacier, the scientists drilled nearly half that much ice – but never much deeper than 15 meters.
“I never thought I’d be doing this – horizontal ice-core drilling,” Bauska said.
NSF-funded research: Vasilii Petrenko, University of Rochester, Award No.1245659 ; Jeffrey Severinghaus, University of California-San Diego Scripps Institution of Oceanography, Award No. 1246148 ; and Ed Brook, Oregon State University, Award No. 1245821 .
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