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The world's largest ice core archive is set to receive an upgrade: its cooling system is switching from banned coolants that can damage the ozone layer to a more environmentally friendly technology.
“The ultimate Replacement of refrigerants through ozone-sparing solutions is a very important, legally driven issue,” says Tas van Ommen, a climate scientist from Hobart, Australia, who is co-chair of the International Partnerships in Ice Core Sciences.
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The U.S. National Science Foundation Ice Core Facility (NSF-ICF) in Denver, Colorado, houses approximately 25,000 meters of ice cores, all drilled with NSF funding since the facility opened in 1993. This includes the core of the Vostok station in Antarctica 1, which held the record for oldest continuous ice until the early 2000s, as well as new cores from Antarctica's Allan Hills, which contain the oldest ice ever mined and are millions of years old. “They’re a hot commodity,” says Curt LaBombard, curator of the facility.
Such cores contain trapped air, particles and chemical isotopes that provide clues to past atmospheric composition and temperatures as well as events such as volcanic eruptions. Collected cores are typically cut into sections, with some sections analyzed by researchers and others stored in an archive for later study.
The Denver Archives' 1,500 cubic meter freezer is kept at a frigid -36ºC. Like many household refrigerators and air conditioners built in the 1990s, it relies on a refrigerant called hydrochlorofluorocarbon (HCFC).
Prohibited coolants
Leaks of HCFCs from manufacturing facilities or equipment can destroy the Earth's protective ozone layer. Therefore will like their even more destructive descendants, the chlorinated hydrocarbons (CFCs), HCFCs were gradually banned. The Montreal Protocol to Save the Ozone Layer, adopted in 1987, banned new HCFC production after 2020 in wealthy countries and after 2030 in poorer countries.
That's why many newer refrigerators and air conditioners use hydrofluorocarbons instead (HFCs), which are much less problematic for the ozone layer than HCFCs but can be powerful greenhouse gases – up to 15,000 times stronger than carbon dioxide. Two other large ice core archive facilities, the Canadian Ice Core Lab at the University of Alberta in Edmonton and the European ice core repository at the Alfred Wegener Institute in Bremerhaven, Germany, use HFCs.
But HFCs are also being phased out under a 2016 change to the Montreal Protocol, leaving chemists and companies looking for "substitutes for the substitutes," says Mark McLinden, who studies refrigerants at the U.S. National Institute for Standards and Technology in Boulder, Colorado.
The dismantling rules apply to new equipment, not existing ones, but LaBombard says operators of the NSF facility felt the time had come for an upgrade. The decades-old freezer is inefficient, its software is outdated and costs for maintenance and repairs are rising, says Michael Jackson, program manager for Antarctic earth sciences at NSF, who is leading the renovation.
Future-proof refrigerant
Common options for replacement refrigerants that do not damage the ozone layer and are less potent greenhouse gases include hydrofluoroolefins, propane, ammonia, and CO2. All have their advantages and disadvantages, including that some are toxic or flammable. Another large ice core deposit, in Japan, uses ammonia. Denver Archives facility managers have embraced ‘transcritical’ CO2which can behave like a gas and a liquid at the same time - an increasingly popular option for efficient commercial refrigeration systems. Jackson says that CO2, although it is a greenhouse gas, is non-flammable and “is more efficient at low operating temperatures,” adding that “it is difficult to quantify, but CO2“seems to be the most future-proof low temperature refrigerant”.
Work on the new NSF freezer is scheduled to begin in August and be completed in the first quarter of 2026.
Various universities store their own ice cores in smaller cold storage facilities. Some are watching with interest how the renovation of the NSF-ICF is going because they too have to replace outdated refrigerants. “We’re in the same boat,” says Ellen Mosley-Thompson, a paleoclimatologist at Ohio State University in Columbus. LaBombard says the team in Denver is ready and willing to help others.“We have offered help and would like to share our experiences,” he says.