COLDEX: The search for Earth’s oldest ice and new climate solutions

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By Christian Elliott, Dec. 9, 2021 –

Even summer days are cold in the Allan Hills Blue Ice Area, a meteorite-strewn expanse of glacier flanked by mountains at the eastern edge of the Antarctic ice sheet near the McMurdo Station research center.

Jeff Severinghaus, a paleoclimatologist at the Scripps Institute of Oceanography, and his colleagues at Princeton University discovered here in 2017 a 2.7-million-year-old chunk of glacial ice containing bubbles of trapped air from Earth’s ancient atmosphere.

That ice turned out to be contaminated by modern air, destroying its link to climate conditions millions of years ago. But the discovery reinvigorated the quest in the ice core science field to find the world’s oldest ice. Right now, the continuous record from a single ice core goes back only about 800,000 years.

Ed Brook operates a saw in Antarctica, slicing an ice core into smaller pieces. (Courtesy of Ed Brook)

In coming years, the world will be a much warmer place – average temperatures will increase by 2 to 3 degrees Celsius (3.6 to 5.4 degrees Fahrenheit), and arctic temperatures will rise by twice that rate. Over the next 10 years, paleoclimatologists hope to extend the ice core record back to 3 million years ago, when they know from climate clues in deep sea sediment cores that the Earth was last that warm. As the planet heats up today, many questions remain. How bad will hurricanes get? How frequent will forest fires become? How high will seas rise?

“The only practical way to know the answers to these questions is to get ice cores that are 3 million years old,” Severinghaus said. “It’s the only way to look into our future and see what we’re in for.”

Severinghaus has spent the last 25 years in Antarctica and in his lab in California studying the composition of gases in polar ice. Ice cores, he said, are key to understanding how Earth’s climate changes with varying levels of atmospheric carbon dioxide.

“There’s no other way to get a sample of the ancient atmosphere, other than the air bubbles in ice cores,” Severinghaus said. “From the ice cores, we learned that carbon dioxide concentrations have never been as high as they are today.”

The natural atmospheric carbon dioxide concentration over the last million or so years was 280 parts per million during warm spells and 180 parts per million during the cold snaps of ice ages. Today, CO2 levels hover at an unprecedented 420 parts per million due to human-generated fossil fuel emissions.

A new collaborative global effort is hot on the trail of the ancient ice, Severinghaus reported at the annual fall Comer Climate Conference, held virtually this year on Oct. 4-5.


Ed Brook, a paleoclimatologist at Oregon State University, received the good news in Februrary – the National Science Foundation selected his proposal for an ice-core-focused Science and Technology Center he calls COLDEX, the Center for Oldest Ice Exploration.

Over the prior two years, Brook brought together 30 of the nation’s leading paleoclimatologists representing 13 universities to jointly apply for the grant, which includes $25 million in funding over five years with a likely extension to 10 years and $50 million in total. Brook said the center represents the ice core field finally uniting a “critical mass” of researchers to justify such a massive investment in paleoclimate research.

Ed Brook presents COLDEX’s goals at the virtual Comer Conference on Oct. 4.

“It was so rewarding, because the right collaborators really stepped up and were interested in making this happen,” Brook said. “But it’s not for the faint of heart to try to organize this many people.”

As the Earth continues to warm, the race to find Antarctica’s oldest ice and understand historic climate change is accelerating – across the continent, the EU, Japan, Australia and Russia also are beginning multimillion-dollar drilling operations, and China’s effort has been underway, with slow progress, since 2012.

With its unprecedented level of funding, COLDEX’s explicit goal is to drill a single continuous deep ice core 1.5 million years old that is likely to be between 1.5 and 2 miles long and then extend the record back further to 3 million years through a composite of discontinuous “snippets” of ice from across the continent. Even though the Antarctic sheet is 2 miles thick in some places, it flows, melts and fractures over time, so researchers think 1.5 million years is the limit for a single core in one location. The oldest ice tends to exist in chunks at the windswept rocky edges of the sheet, like at the Allan Hills site.

“When you get back to 3 million years, there’s no ice that’s still intact stratigraphically – it’s all chopped up and mixed out of order, like a deck of cards that’s been shuffled,” said Severinghaus, who’s a co-principal investigator on COLDEX.

“These patches are out there,” Brook said. “But we don’t know exactly where they are or how many of them there are.”

Severinghaus compares reconstructing the ice core record to an archaeologist reassembling pieces of broken pottery to build a whole. Thanks to advances in geochemistry – paleoclimatologists can now study ancient atmospheric changes using argon, nitrogen, krypton and xenon isotopes in addition to the less accurate oxygen isotopes used in the 1970s – and the fact that atmospheric gas composition is the same throughout the world at any given point in time, COLDEX researchers can put together hundreds of puzzle pieces of ice from across Antarctica in the correct historical order.

McMurdo Station (USAP South Pole Webcam)

“We’re pretty confident we can construct a continuous composite record of the ancient atmosphere,” Severinghaus said. “It’s just going to be a bit of detective work.”

Drilling the 1.5-million-year-old deep ice core might prove just as challenging. Drilling ice cores is a slow, expensive process that requires heavy equipment. Researchers must travel inland, far from McMurdo Station, and establish a base camp where they’ll live and work for the season, which lasts the austral summer – October to February – when the sun never sets. During the winter, temperatures sink to -50 degrees Celsius (-58 degrees Fahrenheit), and the continent plunges into continuous darkness.

“It’s like being at sea,” Brook said. “There’s nothing to see except for snow. And it’s cold. The work is hard.”

Drilling rigs cut through the ice sheet a few meters at a time, and researchers hoist out heavy sections of core as the drill descends. It’s a slow, repetitive process. A 3,000-meter core (more than 1.8 miles) could take up to three seasons – three years – to complete.

The challenge, then, is to find an inland site with deep and old enough ice to justify setting up the COLDEX drilling camp. But much of the deep interior of the Antarctic ice sheet where that old ice likely is has never been mapped – scientists don’t know how deep the ice is.

“It’s just a blank spot on the map,” Severinghaus said. “So, we’re doing basic exploration at this point.”

The first five years

The COLDEX initiative kicked off in earnest in September. Brook is currently hiring researchers, coordinating with NSF logistics contractors to organize trips to Antarctica and building websites and lab spaces. Initial fieldwork – including testing a new fast thermal melt probe called Ice Diver in Greenland – is set to begin in 2022.

A staff member retrieves an ice core at the National Ice Core Lab in Denver, Colorado. (NSF NICL)

While some scientists – including Severinghaus and the Princeton team – continue searching for chunks of old ice at the ice sheet’s fringes and drill rapid 100-meter shallow cores there using Severinghaus’ Rapid Access Ice Drill, others will begin reconnaissance work to find the best site for the 1.5-million-year-old core.

“We’re going to be doing airborne radar echo sounding with new technology in a broad region from the South Pole towards Dome A,” an ice coring site, Brook said. “We’re looking to gather data that would help us put teams on the ground to do detailed radar in specific locations.”

Antarctic “domes” are the highest points on the ice sheet – locations where steady snowfall piled up over thousands of years to create particularly thick ice ideal for drilling old cores. A European team extracted the 800,000-year-old record core in 2013 at Dome C. Japan plans to drill for a 1.5-million-year-old core at Dome Fuji, Russia at Dome B, and Europe and Australia at Dome C.

Recent advances in aerial ground-penetrating radar make it possible for scientists to detect the thickness of the ice sheet as well as layers of dust impurities that indicate colder versus warmer periods – and thus the relative age of the ice. Ground teams will then follow up at two candidate sites with the Ice Diver reconnaissance drill, which can date ice quickly using a laser that detects dust variations, to narrow the choice down to one site.

“We want to know before we get into the $50 million logistics of drilling a deep ice core that the target ice is really there,” Severinghaus said.

The second five-year period will be dedicated to drilling and extracting that 1.5-million-year-old deep ice core and sharing it with the entire field for data analysis.

That core will also help scientists answer the mystery of the Mid-Pleistocene Transition. Around 1.2 million years ago, the length of the transition between cold and warm climate periods abruptly shifted from 41,000 to 100,000 years. Scientists think changes in atmospheric carbon dioxide were to blame, but an older core would provide proof.

Diversifying polar science

COLDEX has another priority as well. As of 2020, only 10% of doctoral degrees in geoscience went to people of color. Faculty of color only hold 3.8% of tenure-track geoscience department positions. It’s a continuing problem, and one that’s received repeated coverage in the journal Nature in recent years.

“Earth science has a diversity problem.” Brook said. “Some other fields have made progress, but that’s just not true in the earth sciences. And polar science is near the worst end of that spectrum, at least anecdotally. The exploration of Antarctica and Greenland has been perceived as a white male thing for quite a while.”

Ed Brook works on ice core gas extraction equipment in his lab at Oregon State University. (Courtesy of Ed Brook)

That’s where the second half of COLDEX comes in – diversifying the ice core field by establishing partnerships with a variety of minority-serving organizations to combat stereotypes and form new pipelines into the field and directly into COLDEX research work over the next 10 years.

“So, it’s only half about finding the oldest ice on the planet.” Severinghaus said. “The other half is doing public facing diversity, equity, inclusion and outreach.”

For example, in the past 40 years, only 20 Native American women earned geosciences doctorates. Sarah Aarons, a paleoclimatologist and Alaska Native at Scripps, will lead a partnership with the Alaska Native Science and Engineering Program to recruit Alaska Native students into the geosciences and, through the NSF’s Research Experiences for Undergraduates program, involve them directly in COLDEX.

“We know the climate is changing twice as fast in the Arctic, and so having Alaska Native people who are experts in climate and the environment in positions in academia or government who know what’s happening in the region they’re from is really, really important,” Aarons said.

Stereotype inoculation theory states that people tend to choose to mentor other people who come from a similar racial or ethnic background or share lived experiences. With the polar sciences dominated by white male researchers, that’s a problem for recruiting new students.

“So, we also plan to do work within our own community to try to understand what kinds of biases we may have and how to overcome those and make our community more welcoming,” Brook said.

“The exciting thing about COLDEX is it’s bringing together a group of people from a really wide variety of research backgrounds into the same room who are all committed to the same goal – finding the oldest continuous ice core record – and combining our expertise to tackle that question,” Aarons said.

In November, world leaders gathered in Glasgow for the UN’s COP26 climate change conference. They were shown a vial of air from 1765, the beginning of the industrial revolution, extracted from Antarctic ice and a section of an ice core, ancient air bubbles slowly, audibly popping as it melted away in front of them. It was a powerful and urgent illustration of both polar ice’s fragility and its ability to describe our ancient atmosphere – where we’ve been and where we’re headed. Through COLDEX, our nation’s paleoclimatologists hope to provide the clearest picture yet.

Photo at top: Jeff Severinghaus (L) and fellow COLDEX participant John Goodge hold an ice and rock core recovered during a test of rapid drilling equipment designed for ancient ice reconnaissance. (Courtesy of Jeff Severinghaus)

Christian Elliott is a science and environmental reporter at Medill. You can follow him on Twitter at @csbelliott.

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