Julia Rosen explains how to extract ancient air from ice samples in OSU’s Ice Core Laboratory (Photo: Jeff Basinger)

A shard of ice sits on the black surface of the lab desk, buoyed in a growing puddle. Three small heads hover above in a tight huddle. “It’s cold,” notes one of the kids. Somehow, this obvious observation always catches me off guard, as if I’ve forgotten the most fundamental quality of water’s solid phase. “That’s true,” I reply, “it’s also 10,000 years old.”

“Wow!” the students chorus, and their eyes widen as they look again with renewed awe at this innocuous specimen that could have come from an ice-cube tray in their freezer. Whether I am visiting loquacious third-graders or shyly curious middle-schoolers, I am always touched by the unjaded willingness of youth to imagine and attempt to grasp the unseen. It’s the reason every scientist falls in love with science.

I analyze ice cores in the Oregon State University Ice Core Laboratory and no longer think about their cool touch. I have learned that, like people, the most interesting things about them lie hidden inside. And, like people, it takes time and patience to understand them. When we succeed, these frozen time capsules from Greenland and Antarctica allow us to reconstruct climate far into the past so that by understanding its natural rhythms and quirks, we can predict what kind of future awaits these students.

But let’s start with the obvious: a clear, smooth cylinder of ice glittering with tiny bubbles like a flute of frozen champagne. Stunningly boring to behold, only an occasional band of volcanic ash or the subtle cloudy layers formed during dusty polar winters break its translucent monotony. However, this continuity is actually an ice core’s greatest strength. It provides a complete, unbroken record of past climates, one that is unavailable in almost any other natural archive.

As detectives of Earth’s history, geologists reconstruct stories from snapshots of ancient seas and whispers of long-dead creatures, piecing together a hazy story of our planet’s past. Ice cores are the long-lost diaries of climate. Every day, they recorded the temperature, sniffed the air and noted the snowfall. They sensed changes far from their polar homes — the amount of dust lofted from Asia, the gurgle of tropical volcanoes and much more. From the top to the bottom of a core lie flakes that witnessed every moment of geologic time that elapsed in between.

Thin Air

Physicists, chemists and geologists have spent 60 years learning to translate the primordial language of ice. Early pioneers of ice-core science discovered that they could estimate temperature using the chemistry of rain and snow. As the air warms, precipitation gathers more heavy molecules and fewer light molecules (known as isotopes) of water. The ratio of these isotopes thus provides a record of temperature. These scientists had the transformative idea of using old ice to reconstruct climate by exploiting this valuable relationship.

Each new analytical tool that becomes available to scientists provides another Rosetta Stone for decoding long-lost archives of the ice. Today, we can measure trace amounts of chemical impurities deposited on the ice sheets as dust and aerosols. They tell us how sea ice waxed and waned and which way the wind blew. They reveal the fingerprints of individual volcanic eruptions. While only the pristine inner core provides suitably clean ice for these highly sensitive measurements, the “snow dust” from cutting and cleaning the core does not go to waste. It can be used, for example, to reconstruct concentrations of a rare element, beryllium-10. Produced by cosmic rays high in the atmosphere, the abundance of this element reflects shifts in solar radiation.

Lit by an Arctic midnight sun, this iceberg was spawned by one of Greenland’s fastest moving glaciers near Illulissat. About 400 feet high, it covered an area larger than a city block. (Photo: Julia Rosen)

Of all the stories that ice cores tell, however, the bubbles of air embedded within them actually contain the most impressive secrets. As snow accumulated over thousands of years, slowly hardening into solid ice and forming the massive polar ice sheets, it sealed off little breaths of ancient air between the grains of snow — the very same air we would have inhaled if we had stood on top of the ice sheet 8,000 years ago, or 80,000 or 800,000. From those microscopic samples, we can retrace the evolution of our planet’s atmosphere across almost a million years of Earth history, a period that encompasses nearly all of human existence.

Revelations

In Antarctica, where extreme cold and meager snowfall limit the flow of ice, these cores stretch back across eight glacial cycles. During each, the Earth oscillated between periods of cold climate and expansive ice, including a vast glacial blanket that smothered northern North America, and a time of balmy warmth with ice sheets comparable in size to those on Earth today. Wobbles in the planet’s orbit periodically brought it closer to and farther from the sun’s furnace, setting the rhythm of the climatic metronome.

Across these dramatic changes, carbon dioxide and other greenhouse gases rose and fell with the global temperature as the Earth’s oceans and biosphere adjusted to a changing environment. These gases both responded to climate change and amplified it through their potent ability to trap the Earth’s outgoing energy. But never in the past 800,000 years did these gases reach concentrations even remotely approaching current levels, and never did they rise so quickly, or shoot up at the end of an interglacial period when the receding sun should have lulled the Earth back into an icy slumber.

At the other pole, ice cores in Greenland felt those same changes, although the records of climate before 120,000 years ago crept away through the unstoppable march of glaciers to the sea. Nonetheless, these cores tell us something else completely new. Throughout the last cold period on Earth, which our ancestors waited out in the mild climates of Africa, the Northern Hemisphere experienced a barrage of climate changes so swift and so huge that certain places on Earth warmed by 20 degrees Fahrenheit in a matter of decades. The cause of these dramatic jolts remains a mystery, but their power to radically reorganize the Earth system attests to the inherent volatility of the world in which modern civilization has only recently made a home.

We are slowly beginning to understand the anatomy of global climate and how it changes, its geographic fingerprint and its tempo. Ice cores paint a complex and sometimes surprising picture, one that generations of scientists will spend decades trying to fully understand. We now know the correct greenhouse gas concentrations to feed into our calculations as we simulate past climates in order to validate models for the future.

Ice cores have made one thing abundantly clear: Humans are in uncharted territory. In 800 millennia of records, no entries document a climate like the one we live in today. Even as you read this, we are busy writing the next page of the ice-core diaries.

Illustration by Hank Osuna

Time to Listen

These observations from opposite poles forewarn a perilous future for our planet. We know without question that we’ve entered a period in geologic history for which there is no natural analog, and we know that the Earth’s climate can respond dramatically to perhaps even the smallest nudge.

However, the most terrifying lesson I learned from ice cores did not come from drilling into the past, but from just standing on the surface. At 80 degrees North, well above the Arctic Circle in the empty white wilds of the Greenland ice sheet, I watched a supply plane on skis repeatedly try to lift off. First the crew dumped cargo and then off-loaded all their fuel except what they needed to get home. Finally, on their seventh attempt, they succeeded.

The problem? The snow had warmed to the freezing point, and microscopic drops of water on the surface made the friction between the skis and the ice too great to break. Last summer, 97 percent of the surface of Greenland experienced temperatures above freezing, more than any year in NASA’s 30 years of satellite observations.

The ice cores have told us all they know, and now it’s up to us to listen.

Editor’s note: Julia Rosen is working toward her Ph.D. in the Oregon State University Ice Core Laboratory under the guidance of Ed Brook, professor in the College of Earth, Ocean, and Atmospheric Sciences and a Fellow of the American Association for the Advancement of Science. Support for the lab has come from the National Science Foundation’s Office of Polar Programs.

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For more information:

Analysis of Greenland Ice Cores Adds to Historical Record and May Provide Glimpse into Climate’s Future (Jan. 24, 2013)

Antarctic Ice Core Contains Unrivaled Detail of Past Climate, (Feb. 5, 2013)

"We're trying to use the natural geological archive to test how the ice sheet works," says marine geologist Joseph Stoner, whose research team is collecting evidence of past geologic and climatic changes in Greenland. (Photo: Karl Maasdam)

Why should the residents of Seattle, San Francisco, New York City and Boston worry about warming in Greenland, an ice-laden island in the North Atlantic? Because if all the water locked in the massive Greenland Ice Sheet flowed into the oceans, low-lying coastal cities worldwide would be inundated.

“The Greenland Ice Sheet could contribute up to seven meters of global sea-level rise if it were to melt,” says OSU marine geologist Joseph Stoner. “We don’t know if it’s going to melt, but that’s how much water is in the ice sheet. Therefore, we need to better understand the processes at work.”

In search of that understanding, Stoner and researchers at the University of Wisconsin-Madison are studying sediments flowing seaward in streams and rivers on the island’s southern tip. Those sediments — remnants of bedrock pulverized over eons by grinding glaciers and rushing rivers — hold clues to the ice sheet’s history across geologic time, he explains. Scientists know that the 680,000-cubic-mile chunk of snow, compressed from white to crystalline blue over many millennia, is receding. Satellite images from the past several decades show significant shrinkage. What isn’t known is the speed of melting or the extent that melting might take in coming years. By studying Greenland’s past with support from the National Science Foundation through the American Recovery and Reinvestment Act, Stoner and his colleagues hope to bring its future into clearer focus.

“The key to understanding the Greenland Ice Sheet is to use the natural record of past variability as a sort of manual to what it could do in the future,” says Stoner, an associate professor in the College of Oceanic and Atmospheric Sciences. “We’re trying to use the natural geological archive to test how the ice sheet works.”

To recreate the ice sheet’s prehistoric behavior, he and his graduate students will collect sediment samples this summer, some dating back to Earth’s infancy when the atmosphere was a soup of greenhouse gases. Tracing the origins of these silts and sands should tell the researchers where the island was exposed during “interglacial” periods — warm stretches between ice ages — and where it lay buried beneath tons of frozen snow during colder periods.

The “markers” that will reveal these ancient patterns are both chemical and magnetic, Stoner says. He explains that isotopes of lead, strontium and neodymium serve as chemical hieroglyphics, telling stories about the ages and origins of the sediments that contain them. And the magnetic properties of those sediments lend additional details to the geologic record.

To read the magnetic profiles of marine and terrestrial sediments, Stoner’s lab recently acquired a new-generation instrument: a super-conducting magnetometer for measuring the magnetic properties and composition of rocks. Instead of using liquid helium as a coolant like old-style cryogenic magnetometers do, this one compresses helium gas till it reaches 3.5 degrees Kelvin, “just a little above absolute zero,” Stoner says. “It works through super-conductivity, which only happens at extremely cold temperatures.”

Stoner’s findings could cause scientists to rethink Greenland’s role in climate-change scenarios.

“When I first got into this field, people thought ice sheets behaved really slowly,” he says. “But the geologic evidence is telling us ‘no.’ We just didn’t understand the process by which ice sheets behave quickly. It’s a reminder that just because you don’t understand the process, it doesn’t mean something’s not happening.”