By Ananya Chandhok
Medill News Service, March 8, 2024
It’s not often a middle school science teacher turns in her graduated cylinder for an ice pick. But when paleoceanography called Julia Marks Peterson, she answered.
Peterson’s career pivot led her to Antarctica’s frigid hills in search of the earth’s oldest ice with the Center for OLDest Ice EXploration, or COLDEX. Between field visits, the Oregon State University fourth-year Ph.D. candidate presented her team’s findings to cutting edge researchers and students at the annual Comer Climate Conference held in southwest Wisconsin this past fall.
Deep Breath in, Carbon Dioxide out: The Key to Dating Ice and Ancient Air
In her presentation Deep Breath in, Carbon Dioxide out: The Key to Dating Ice, Peterson shared some of the first data on carbon dioxide and methane concentrations coming out of COLDEX. Currently, the team has dated ice that’s 4-million-years-old, which is older than the oldest continuous ice core record scientists have. In other words, it’s the oldest ice found so far. Cylinders of ice – or ice cores – are pulled from the ice sheets and glaciers. The ice layer is dated and air bubbles from that era can be extracted and analyzed for levels of greenhouse gases such as carbon dioxide and other gases.
The COLDEX excavation also confirmed that their deepest ice core included respiration-produced, or non-atmospheric, carbon dioxide from microbes. Understanding carbon dioxide levels helped the team identify changes in glacial cycles, from ice ages to warm spells. Carbon dioxide levels drop in the ice ages and rise in warm periods. They mirror the cycles when the earth was warmer, Peterson said. These past warm periods may provide a look into what cycles will be like towards the end of the century, Peterson said.
“What it’s telling us is that there’s sheer margins, where…the ice is behaving differently,” Peterson said. “[We’re] trying to figure out how we can better interpret old ice and if there’s different behavior down the ice column.”
The majority of the atmosphere’s changes in carbon dioxide come from the ocean, according to Peterson. “That’s what I love about ice cores,” Peterson said. “You still feel very connected to the Earth system because the atmosphere is a symptom of whatever is going on with the rest of the Earth.”
COLDEX explores for the oldest ice on Earth by drilling for cylinders or ice cores that can then be dated after the field work of from one to two months at a time. Despite the team’s success, Peterson expressed a concern — finding non-atmospheric carbon dioxide higher up in the ice core. Non-atmospheric carbon dioxide came from microbes that exhaled the compound, so the team needed to account for their respiration and “correct” the samples, Peterson said.
The team also realized that because of how the ice flowed to the site in the first place, additional data analysis would be necessary in the future.
The Alan Hills, Chills and (Ice) Drills
Marking their fourth field season, COLDEX’s excavation continued in the East Antarctic Alan Hills Blue Ice Area. However, the hills are not a conventional deep ice core site. Rather than ice and snow accumulating and flowing out of the area, the ice flows to the hills and
gets lifted to the surface — like pushing sand together to form a castle.
Instead of digging up to two-miles beneath the surface, the ice flow ensures the team only drills as far as 100 meters to hit the jackpot — old ice.
“You get this bang for your buck because you don’t have to drill very far,” Peterson said. Once excavated, aging the ice can be a challenge because its layers aren’t in chronological order because of how it flowed to the Hills in the first place. Peterson and her team dug up two more cores with a wider drill to combat previous dating and chemical identification challenges, which existed when four cores were excavated by another team in 2019.
Once the ice cores are collected, they journey to the National Science Foundation Ice Core Facility in Denver, Colorado, Peterson said. The noble gas analysis to date them was led by Sarah Shackleton, researcher at the Scripps Institute of Oceanography.
“She [Shackleton] measured Argon-40, which is produced by radioactive decay,” Peterson said. Since Argon-40 constantly leaks from the earth’s crust into the atmosphere, Peterson said, understanding its concentration is like a time-machine into hundreds of thousands to millions of years ago when the atmosphere contained that much of it.
A “Friendly Race” to Find the Oldest Ice
The Europeans, Chinese and Australians are all caught up in this “friendly race” to find the oldest ice, Peterson said, but every team has slightly different goals. COLDEX’s target is to find the oldest discontinuous, or “mixed-up” ice on earth.
“We’re trying to find ice that is from a period of time when we knew the earth was warmer,” Peterson said.
“The mid-Pliocene, is considered one of the best analogs,” she said. “Better understanding this helps us better understand our climate system’s future.” The Pliocene epoch from about 5.6 million to 2.6 million years ago.”
Peterson returned from her first field trip with memories of Antarctica’s beauty and exponentially more physical strength from hauling 100-pound ice cores, Peterson said. Her fellow researcher, Austin Carter, dubbed the phenomenon “body by Antarctica.”
“Before I went out into the field, I could do half of one pull-up, and I was pretty proud of myself,” Peterson said. “I came back five weeks later, and I could do three in a row without even blinking.”
Looking forward, Peterson and the rest of the COLDEX team plans on drilling more ice cores from the Alan Hills and the Elephant Moraine — where they’ll continue the worldwide “friendly race” in search of the oldest ice and pursue bodybuilding on the side.
Photo at top: The Center for OLDest Ice EXploration, COLDEX, traveled to East Antarctica for for their field season where the team used a one-meter-long drill to excavate 4-million-year-old ice – the oldest ice found to date. eam and the Antarctic bitter cold are always there to keep Peterson company — from one to two months at a time. Photo courtesy of Julia Peterson.
