The ice keeper

DENVER — “I’m a little tired of the cold,” Geoff Hargreaves says with a sigh.

No surprise there: Hargreaves works in a deep freeze — 38 degrees Celsius below zero (−36° F). As curator of the National Ice Core Laboratory, his job is to keep ice cores from Antarctica and Greenland frozen.

These cylinders — which would stretch more than 17,000 meters if laid end-to-end — are precious. They contain records of past climate and atmospheric chemistry, trapped in tiny bubbles that formed thousands of years ago and froze in chronological layers like tree rings. Melting is the enemy, destroying the layers and releasing trapped gases.

And that’s where Hargreaves (left) comes in. Cores arrive in refrigerated trucks at his sprawling facility in Denver. He tucks the shiny, meter-long core tubes onto shelves in the lab’s deep freezer. When a scientist requests a core to study, Hargreaves’ team brings the ice into the “warm” room (a toasty −24° C). They slice off part of the core and pack it in a special box that will keep it frozen for up to three days. Then they ship it. “Of course there are FedEx horror stories,” Hargreaves says.

Nearly everything at the lab is handmade and hand-engineered. For their latest and biggest project, Hargreaves and his colleagues designed a new system to efficiently collect and transport 3,400 meters of ice cores from the West Antarctic Ice Sheet Divide drilling project. The team flew from Denver to help gather the ice and, even in Antarctica, had to work in a refrigerator to keep temperatures cold enough.

Packed in 40-foot shipping containers with redundant refrigeration units, the cores made their way to McMurdo Station and then via ship to California. The final leg involved flatbed trucks to Denver. “I’ve never lost a core,” Hargreaves says.

But with all the project’s ice now safely on the shelves, there’s not much storage room left. Hargreaves’ next job is to figure how many more cores he can squeeze into his freezer. As the only federal repository for ice drilled by National Science Foundation–funded projects, the lab is, in essence, the nation’s ice library. “If the ice melts, we’re not going to go get it again,” he says.

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Climate cores

Ice cores drilled from Earth’s poles have shown scientists how the environment has changed over nearly the last million years — crucially, how atmospheric carbon dioxide levels rise and fall in concert with past temperatures. Here’s a look at what some key ice-coring projects found:

GISP/GRIP, Greenland: From the late 1970s through the early 1990s, U.S. and European teams worked to drill down to bedrock beneath the Greenland ice sheet. Together the cores provide the longest continuous environmental record (more than 100,000 years) for the Northern Hemisphere. Chemical analyses have revealed evidence of human-caused changes to Earth’s atmosphere as well as past volcanic eruptions and rapid climate change events.

Vostok, Antarctica: Russian scientists set a world record in 1998 by drilling to 3,623 meters beneath the Antarctic ice sheet. Drilling then halted for years as the team explored how it might safely penetrate deeper into the waters of the buried Lake Vostok — which it did successfully in February 2012. Studies of the deep core provided the first detailed record of how atmospheric chemistry changed over glacial cycles.

EPICA, Dome C, Antarctica: A European team drilled this core to a depth of 3,270 meters, finishing in 2004. The feat strengthened the Vostok findings and revealed a strong link between atmospheric carbon dioxide levels and temperatures through the last eight ice age cycles, back to 800,000 years ago.