Melting isn’t an option because carbon dioxide easily dissolves into water. Traditionally, scientists have used mechanical extraction methods, grinding up samples of individual layers of ice to free the air. But grinding wouldn’t be effective for the Beyond EPICA ice in the university’s storage freezer, which is kept at 50 °C below zero. The oldest ice at the very bottom of the core will be so compressed, and the individual annual layers so thin, that bubbles won’t be visible—they’ll have been pressed into the lattice of ice crystals, forming a new phase called clathrate.
“At the very bottom, we expect 20,000 years of climate history compressed in only one meter of ice,” says Hubertus Fischer, head of the past climate and ice core science group at Bern. That’s a hundredth the thickness of any existing ice core record.
The new method Krauss and Fischer are developing is called deepSLice. (A pizza menu is taped to the side of the device right under the laser warning labels, a gift from a pizzeria in Australia with the same name.) DeepSLice has two parts. The Laser-Induced Sublimation Extraction Device, or LISE, fills half a room in the team’s lab space. LISE aims a near-infrared laser continuously at a 10-centimeter slice of ice core so that it turns directly from solid to gas under extremely low pressure and temperature. The sublimated gas then freezes into six metal dip tubes cooled to 15 K (-258 °C), each containing the air from one centimeter of ice core. Finally the samples are loaded into a custom-made absorption spectrometer based on quantum cascade laser technology, which shoots photons through the gas sample to measure concentrations of carbon dioxide, methane, and nitrous oxide simultaneously. Another big advantage of this system is that it takes a lot less ice (and work) than the old method of analysis, in which scientists measured methane by melting ice (it doesn’t dissolve into water) and measured carbon dioxide by grinding ice.
DeepSLice offers “a unique capability that nobody else has,” says Christo Buizert, an ice core scientist at Oregon State University and the ice analysis lead for COLDEX (the Center for Oldest Ice Exploration)—the US equivalent of Beyond EPICA, which is currently in a “friendly race” with the Europeans to drill a continuous core down to 1.5-million-year-old ice.