It’s -30 degrees Celsius, even though the Sun hangs ceaselessly in the sky. Dressed in puffy, insulated suits and gloves thick enough to both hinder dexterity and preserve fingers, a team gamely tilts a drill barrel back to horizontal. With one smooth, firm motion, a two-meter-long cylinder of ice, bursting with history, is pushed free and slides down a temporary work bench.

Disturbed from its long slumber, this ice is destined for laboratories that will liberate whatever secrets it holds. There's only one catch: it’s critical that nothing melts until it travels most of the way around the world.

This is not a futuristic scene from Jupiter’s enigmatic moon Europa, rather it's a recent one from the closest thing you’ll find on Earth—the blank expanse of Antarctica’s interior. While this work was decidedly of this world, it would be extremely unfair to describe it as anything close to easy. Beyond allowing humans to work in the harsh Antarctic environment, how does ice buried by more than a kilometer of other ice at the South Pole end up in a lab 15,000 kilometers away in order to become scientific insight?

With a brand new Antarctic ice core drilled over the past couple of years recently making its way to the United States, we took the opportunity to visit with the ice (and some of the scientists who brought it) to find out.



Go south until you can’t

Ice cores are so magical that glaciologist Richard Alley titled his book about a Greenland core The Two-Mile Time Machine. Glaciers are piles of snow so deep they compress into ice. Because the summer snow and winter snow can differ in a number of ways, the annual cycle gets preserved—literally frozen in time. As Dartmouth College’s Erich Osterberg told Ars, “They give us this opportunity to see changes in the climate on a year-by-year basis, going back for thousands of years, and there’s really no other natural archive that’s like that. Tree rings can do that for hundreds of years, and these layers that we see in the ice are just like the tree rings.”

Changes in the different isotopes of hydrogen and oxygen in the water molecules track changes in temperature and the growth of great ice sheets elsewhere, which lower sea level. Bubbles of ancient air are preserved in the ice, like Jurassic Park dinosaur DNA trapped in amber. Want to know how much CO 2 was in the air 3,000 years ago? Count the layers back and measure it.

Over the past few decades, a number of major cores have been drilled from the great ice sheets of Greenland and Antarctica. All contain faithful records of Earth’s climate, but each has different characteristics. Some reach down into much older ice than others. Some come from areas where snow accumulates faster, offering fatter layers that preserve greater detail. Different types of chemical relics may be clearly preserved.

When they were drilled matters, too. Advances in technology and technique make new measurements possible that weren’t an option for earlier cores.

The newest specimen in the Antarctic collection is the US-National-Science-Foundation-funded South Pole ice (SPICE) core, a 1,750-meter-long stick of ice drilled just a few kilometers from the permanent Amundsen-Scott South Pole Station. Obtaining it took two two-month campaigns.

One of the most distinctive aspects of this core is that it will contain a record of extremely trace gases. University of Washington researcher TJ Fudge explained to Ars, “If we’re thinking about carbon dioxide, that’s measured in parts per million. If we’re thinking about methane, that’s measured in parts per billion. This core is going to be good for measuring COS [carbonyl sulfide]; that’s measured in parts per trillion.”

“The reason this is a good site for it is that it has a unique combination of being very cold, because it’s so far [south] at the pole, yet it has a relatively high snowfall because it gets moisture [traveling] from the West Antarctic side over to the East Antarctic side,” he continued. Higher snowfall means thicker annual layers of ice, so you can make measurements at higher resolution—even if you need a fair number of trapped bubbles of gas to make your delicate measurement. Since the South Pole is so isolated even by Antarctic standards, the ice contains little in the way of impurities that make measuring trace chemicals difficult.

From the South Pole, you’d have to go at least 1,000 kilometers (in some flavor of “north”) to reach the next site where a deep ice core has been drilled. Since Antarctica’s climate varies from place to place, geographical coverage is important—put the records together and you can start detecting nuanced patterns in the climate system.

Other ice cores trade resolution for span, reaching back further in time. The Antarctic Dome C core, for example, went back a staggering 800,000 years, encompassing the last eight glacial cycles (or “ice ages”). Researchers are currently searching for a site where million-year-old ice might be found at the bottom. For its part, SPICE captured more than 40,000 years of climate history in 1,750 meters of ice.

That’s long enough to include several useful time periods—the last glacial period (when an ice sheet covered half of North America), the current “interglacial” period, and the major transition between them. If we want to know exactly where our activities are directing the climate to go, it helps to study the paths it has taken in the past.