Twigs from the Greenland ice sample

Plant debris buried under a mile of ice suggest a time of higher sea levels

Elizabeth Spears

A few days before his doctoral defense, Andrew Christ had enough on his mind, when Paul Bierman, his advisor at the University of Vermont, came up to him.

Christ recalls, “He was like, ‘We need to work in the lab.’ I’m like, ‘We really need to work in the lab?’ I am a little stressed right now.’” Never a good idea to blow off an advisor before a dissertation, of course. So Christ went. Which was a good thing because their subsequent work showed that Greenland was actually green 400,000 years ago. And that has big implications for us today.

Engineers drawing up an ice core in Greenland in 1966
Engineers drawing up an ice core in Greenland in 1966. Pic in public domain, courtesy of the ERDC Cold Regions Research and Engineering Laboratory

In the lab, Bierman handed him a tube of frozen soil extracted from a mile beneath a Greenland glacier. That tube had an odd history.

“Our Danish collaborators found it when they were moving to a bigger freezer to put more ice in,” says Christ. It was collected during an American initiative called Project Iceworm. “They were, like, ‘We need to analyze this. So we should send it to the people who know best how to do different analyses.’”

One of those people would be Bierman, who probably saw Christ as another.

Researcher Andrew Christ takes pictures of one of the samples
Researcher Andrew Christ takes pictures of one of the samples. Pic courtesy Andrew Christ

“They just look like frozen half cylinders of mud,” Christ says. “You take it out of the bag – and it was weird. … It smelled like diesel. Because when they drill the ice core, you have to use something like diesel to keep the hole from freezing. So everything smelled like gas, which is, I know, probably not great to be inhaling. But whatever.”

Bierman and Christ expected they would just be gauging the age of the ice sheet that the sample came from.

“Floating black things”

They melted down this frozen hunk of soil, separating the sand into different categories of size. Then they came upon something rather odd.

“We started to notice these little floating black things in the water,” says Christ. “My advisor, who has worked on other cores from lakes, was, like, ‘Oh, you should look at that under the microscope.”

"Floating black things"
The researchers found unexpected debris in the samples – twigs and leaves. Pic courtesy Andrew Christ

Christ obliged.

“We sucked a little up in a little pipette and then put it under a microscope … and it was a twig. So it was – wow. It was plant life that had been preserved in soil underneath almost a mile of ice.”

The vegetative matter did not look very old.

“It looked like when you get twigs and stuff in your hiking boot after the end of a day of hiking and then dump it out on the ground,” Christ says. “It looked like that. So it looked really fresh. Wow. “

There were even little leaves on some little twigs.

Here was evidence that a mile-long ice sheet in Greenland, one of the most consistently frozen parts of our planet, had once melted away, and now preserved a memory of ancient plant life.

Some of the samples
Some of the sample vegetation found. Pic courtesy Andrew Christ

“It was mind-blowing,” says Christ. “Glaciers typically erode and pulverize everything, but we found these plants … The less exciting and kind of more scary realization that came after that … We had found evidence … that part of the Greenland ice sheet had melted away and that there were plants living on the landscape.”

A message in an ice sample

This is important because it was in the northwestern part of Greenland, with ice 1.5 kilometers thick on the ground.

“To have plants there, you had to melt away an ice sheet a mile thick – a kilometer-and-a-half thick,” Christ says. “All that ice would have melted and gone into the ocean. So the sea level would have been higher.”

When people consider the ice age, they think of the furry woolly mammoths, not delicate plants from warmer climes.

Christ began to realize that the sample suggested that the global climate was significantly different at the time. So Greenland’s landscape would be more similar to the Arctic Tundra than the ice-bound vastness it is today.

Meanwhile, he had also dated the sample to about 400,000 years ago. But that was when carbon dioxide in the atmosphere was never above 290 ppm (or parts per million). Today, it is 420 ppm.

The location of the ice core.
The location of the ice core. Image courtesy Andrew Christ

“It means we have pushed our climate system into unknown territory,” Christ says. “We’re going to keep the climate warm for a long time, even if we turned off the spigot of carbon emissions now. We need to understand how [we are] going to respond to that.”

The main change Christ talks about seeing is sea-level rise, with the almost guaranteed melting of the Greenland and Antarctic ice sheets. With this kind of sea-level rise, we can imagine parts of places like New Jersey, New York, Florida being underwater.

A call to action

“If I had a magic wand and could get people to agree on everything to address the climate crisis, it would really be not only stop emitting carbon, but actually figure out ways to draw carbon dioxide out of the atmosphere,” he says. “If we take sort of the moderate approach to carbon emissions in the future, not [planning for] the worst-case scenario …, it’s going to take 30,000 years for carbon dioxide to get down to 350 parts per million…. That’s still higher than it has been over the last million years. That’s enough time to melt large ice sheets. So if we don’t start drawing carbon dioxide from the atmosphere, um, we’re going to be faced with a lot of cascading problems from climate change.”

Seeing the urgency of the project, the team has spread the work around, collaborating with researchers across the U.S. and Europe, some of whom have their own samples to compare with.

“It was deeply collaborative, and really interesting,” says Christ. “That’s actually like the way that I like doing science … I don’t like working alone on my stuff … I don’t really know that much about all of these different fields. I know enough about one specific thing. So when I get to work with someone who has ideas that inform my opinions better – or my interpretation is better – it makes for better science.”

Christ cleaning and sifting through the sample.
Christ cleaning and sifting through the sample. Pic courtesy Andrew Christ

At least on the research front, Christ has good news. Because of their unexpected findings, the National Science Foundation is funding Bierman and him to study the issue further.

Refining the search

“All of that research that we did before, it was off of just like 10 centimeters of sediment from two different spots in that core,” he says. “But there’s about three and a half meters (12 feet) of sediment left … Next time, it won’t be a surprise that there’s vegetation or fossil vegetation in it. So when we actually go and take apart the core, we can do it in a way that won’t damage any of the material. Which is great because, you know, we inadvertently probably did that before … We’re going to do really cool stuff with ancient DNA. So we can sequence all the different DNA chains in the sediment that were shut off by [ice].”

Still, taking ice cores is a little more arduous than most people imagine. It digs in slowly and repeatedly, each time coming up with a sample that fits into the hollow core of the drill. Getting down to the lower levels can take years.

Christ says the team hopes to find some animal remains, too, which may help them understand what the landscape looked like at the time.

Christ categorizing the sediments based on color
Christ categorizing the sediments based on color. Pic courtesy Andrew Christ

“We are now getting access to the bottom of ice cores from Antarctica and other parts of Greenland that haven’t been examined before,” he says. “Now we know a way to look at them, um, and figure out the significance of them.”

He hopes that data from ice cores found closer to the edges of ice sheets may help policymakers to decide what degree of warming could contribute to how much of a rise in sea levels.

A nuanced approach

“I think probably the main contribution that we have [is] not solving a climate crisis, but mitigating and adapting to it,” Christ says. He does appreciate the lure of cheap fossil energy and has himself had to settle for a more affordable gas-powered car, than an electric or hybrid one he would prefer.

As far as what he thinks about doing science, he says he is “just being very observational and paying attention to little details about whatever I’m looking at. There are a lot of things in science that are not that different from cooking or baking. You’re following a procedure to get an end result.”

Christ mulls over the analogy he made with his work with ancient ice samples, and adds a caveat:

“We don’t eat the thing at the end.”

Click here for the link to the original research article.

Elizabeth Spears is a writer, teacher and therapeutic wilderness guide.

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