Scientists were amazed to discover plants beneath miles of Greenland ice

In 1966, US military scientists drilled through nearly a mile of ice in northwest Greenland – and pulled a five-meter tube of soil from the bottom. After that, this frozen sediment was lost in a freezer for decades. It was accidentally rediscovered in 2017.

In 2019, University of Vermont scientist Andrew Christ looked at it through his microscope – and couldn’t believe what he saw: twigs and leaves instead of just sand and stone. That suggested that the ice had disappeared in the recent geologic past – and that an overgrown landscape, perhaps a boreal forest, stood where a miles deep ice sheet the size of Alaska stands today.

Over the past year, Christ and an international team of scientists – led by Paul Bierman at UVM, Joerg Schaefer at Columbia University and Dorthe Dahl-Jensen at the University of Copenhagen – have studied these unique fossil plants and sediment. from the bottom of Greenland. Their results show that most of Greenland must have been ice-free for the past million years, perhaps even the last few hundred thousand years.

“Ice sheets usually pulverize and destroy everything in their path,” says Christ, “but what we discovered was delicate plant structures – perfectly preserved. They’re fossils, but they look like they died yesterday. It’s a time capsule of what used to be. living in Greenland that we couldn’t find anywhere else. “

The discovery confirms a new and disturbing understanding that Greenland ice has completely melted away during recent warm spells in Earth’s history – periods like those we are now creating with man-made climate change.

Understanding the Greenland ice sheet in the past is critical to predicting how it will respond to global warming in the future and how quickly it will melt. With some twenty feet of sea-level rise trapped in the ice of Greenland, every coastal city in the world is at risk. The new study provides the strongest evidence yet that Greenland is more vulnerable and sensitive to climate change than previously believed – and is at great risk of irreversible melting away.

“This is not a twenty-generation problem,” said Paul Bierman, a geoscientist at UVM in the College of Arts & Sciences, Rubenstein School of Environment & Natural Resources, and fellow at the Gund Institute for Environment. “This is an urgent problem for the next 50 years.”

The new research was published March 15 in the Proceedings of the National Academy of Sciences.

Under the ice

The material for the new PNAS study came from Camp Century, a Cold War military base dug into the ice sheet far above the Arctic Circle in the 1960s. The real purpose of the camp was a top-secret attempt, called Project Iceworm, to hide 600 nuclear missiles under the ice near the Soviet Union. As a cover, the military presented the camp as a polar science station.

The military mission has failed, but the science team has conducted important research, including drilling a 1,450-meter deep ice core. Camp Century scientists focused on the ice itself – part of the nascent effort at the time to understand the deep history of Earth’s ice ages. Apparently they were less interested in a little bit of dirt coming out from under the ice core. Then, in a truly cinematic series of strange plot twists, the ice core was moved from an army freezer to the University of Buffalo in the 1970s, to another freezer in Copenhagen, Denmark, in the 1990s, where it languished for decades – until the surfaced when the cores were moved to a new freezer.

More on how the core was lost, rediscovered in a number of cookie jars, and then studied by an international team gathered at the University of Vermont in 2019, can be read here: Secrets Under the Ice.

For much of the Pleistocene – the icy period that spanned the last 2.6 million years – parts of Greenland’s ice persisted even during warmer periods called “interglacials.” But most of this overall story is composed of circumstantial evidence in mud and rock washed off the island and collected from offshore ocean drilling. The extent of the Greenland ice sheet and the types of ecosystems that existed there before the last interglacial warm period – which ended about 120,000 years ago – are hotly debated and poorly understood.

The new study reveals that the deep ice at Camp Century – some 120 miles inland from the coast and only 800 miles from the North Pole – has completely melted at least once in the past million years and was covered with vegetation, including moss and maybe trees. . The new research, supported by the National Science Foundation, matches data from two other central Greenland ice cores collected in the 1990s. Sediment from the bottom of these cores also indicates that the ice sheet had disappeared for some time in the recent geologic past. The combination of these centers from central Greenland with the new understanding of Camp Century in the far northwest gives researchers an unprecedented picture of the changing fate of the entire Greenland ice sheet.

The team of scientists used a range of advanced analytical techniques – none of which were available to researchers fifty years ago – to examine the sediment, fossils and waxy layer of leaves at the bottom of the Camp Century ice core. For example, they measured ratios of rare forms – isotopes – of both aluminum and the element beryllium that are formed in quartz only when the ground is exposed to air and can be hit by cosmic rays. These ratios gave the scientists an idea of ​​how long rocks were exposed to the surface versus buried under ice sheets. This analysis gives the scientists a kind of clock to measure what happened in Greenland in the past. Another test used rare forms of oxygen found in the ice in the sediment to reveal that the precipitation must have fallen at altitudes much lower than the height of the current ice sheet, “demonstrating the absence of ice sheets,” the team writes. . By combining these techniques with luminescence studies that estimate the amount of time since sediment was exposed to light, radiocarbon dating of pieces of wood in the ice, and analysis of how ice sheets and debris were arranged, the team could be clear that most, if not all, of Greenland melted at least once in the last million years – turning Greenland green with moss and lichens, and maybe spruce and spruce.

And the new study shows that ecosystems of the past have not been forgotten by centuries of glaciers and ice sheets that have swept over the top bulldozers. Instead, the story of these living landscapes remains trapped under the relatively young ice that formed on the ground, frozen in place and holding them still.

In a 1960 film about Camp Century, made by the military, the narrator notes that “more than 90 percent of Greenland is permanently frozen under an arctic ice.” This new study makes it clear that it is not as permanent as we once thought. “Our study shows that Greenland is much more sensitive to natural global warming than we previously thought – and we already know that the uncontrolled warming of the planet by humanity is vastly outpacing the natural rate,” says Christ.

“Greenland may seem far away,” says UVM’s Paul Bierman, “but it could melt quickly and pour into the oceans enough that New York, Miami, Dhaka – choose your city – will go under water.”