Ice-core researchers hope to chill out

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Fresh freezers needed to preserve ancient gas, scientists say.

Unless stored correctly, ice cores lose their value. Credit: L. Augustin/CNRS

Researchers in the United States and Europe are seeking funding so that the ice cores used to study Earth's past climate can have the same luxuriously chilly storage facilities currently enjoyed by prize tuna.

The cylindrical cores, drilled at multi-million-dollar expense from polar and glacial ice, can be kilometres long. They contain tiny bubbles of trapped air, allowing scientists to measure the concentration of carbon dioxide in the atmosphere from hundreds of thousands of years ago. The relative ratios of oxygen and nitrogen, and their isotopes, can also reveal temperature variations and help to date the trapped gas.

But oxygen is gradually lost when ice cores are stored at −20 °C to −30 °C, the standard temperature of current cold-storage facilities in the United States and Europe (M. Bender, T. Sowers and V. Lipenkov J. Geophys. Res. 100, 18651–18660; 1995).

The oxygen diffuses slowly toward the core's surface and can be lost to the air, resulting in higher ratios of nitrogen to oxygen that can distort the conclusions scientists draw from them. In 2005, Japanese researchers showed that colder storage temperatures could mitigate this gas loss (T. Ikeda-Fukazawa et al. Earth Planet. Sci. Lett. 229, 183–192; 2005), and the ice-core storage facility at the National Institute of Polar Research, Tokyo, was subsequently upgraded with technology used to maintain cold stores for high-grade tuna at −50 °C.

US researchers are now seeking roughly $5 million to rebuild cold-storage facilities at the US Army Cold Regions Research and Engineering Laboratory in Hanover, New Hampshire, which would also have its storage capacity increased by about 25%. Ian Baker, a materials scientist at Dartmouth College, also in Hanover, is leading the application for funding from the National Science Foundation. If the team gets its funding, Dartmouth would then manage the refurbished facility, which could be completed by 2010.

European scientists face a similar challenge. "We need a European-wide facility," says Eric Wolff at the British Antarctic Survey in Cambridge, UK. But a European Commission study in 2008 estimated that a new −50 °C facility, with associated research labs and teaching facilities, would cost €25 million (US$35 million), and is unlikely to be funded, says Frank Wilhelms of the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany, which houses one of four major ice-core facilities in Europe. The International Partnerships in Ice Core Sciences (IPICS), an organization of scientists, drillers and engineers from 18 nations, has also said that urgent action is needed to prevent ice cores degrading.

In the interim, Jeffrey Severinghaus, an IPICS steering-committee member from the Scripps Institute of Oceanography in La Jolla, California, says some institutions like his are building smaller units to keep parts of cores at −50 °C. These units can be created for about $15,000, but the necessary freezer adaptations void warranties and there are concerns that keeping sections of ice cores in many different locations may hamper researchers' access.

His lab is currently studying oxygen/nitrogen ratios in ice cores drilled last year for the Western Antarctic Ice Sheet Divide Ice Core project, a collaboration of US research groups. Preliminary comparisons with the Byrd ice core, drilled in 1968 in Western Antarctica, show that oxygen has been lost in the older core during storage, he says.

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US Army Cold Regions Research and Engineering Laboratory

International Partnerships in Ice Core Sciences

West Antarctic Ice Sheet Divide Ice Core Project

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Dalton, R. Ice-core researchers hope to chill out. Nature 460, 786–787 (2009) doi:10.1038/460786a

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