In 1966, U.S. Army scientists drilled through nearly a mile of ice in northwest Greenland – pulling up a dirty tube of dirt from below. Then this frozen sediment was lost in a freezer for decades. It was accidentally rediscovered in 2017.
In 2019, Andrew Christen, a scientist at the University of Vermont, looked at it through his microscope – and could not believe what he saw: twigs and leaves instead of just sand and rock. This suggests that the ice has disappeared in the recent geological past – and that a vegetated landscape, perhaps a boreal forest, stood where a mile-deep ice sheet as large as 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 sediments. from the bottom of Greenland. Their results show that most, or all of Greenland, over the past million years, perhaps even the past few hundred thousand years, must have been ice-free.
‘Ice sheets pulverize and usually destroy everything in their path,’ says Christ, ‘but what we discovered were fine plant structures – perfectly preserved. These are fossils, but they look like they died yesterday. It is a time capsule of what used to live in Greenland that we could not find anywhere else. ”
The discovery helps to confirm a new and disturbing notion that the Greenland ice sheet has completely melted during recent hot periods in Earth’s history – periods such as those we are now causing by human climate change.
Understanding Greenland ice in the past is critical to predict how it will respond to global warming in the future and how fast it will melt. As about 20 meters of sea level is bound in the ice of Greenland, every coastal city in the world is in danger. The new study provides the strongest evidence yet that Greenland is more fragile and sensitive to climate change than previously understood – and is in danger of melting irreversibly.
“This is not a twenty-generation problem,” says 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 on March 15 in the Proceedings of the National Academy of Sciences.
FIND THE ICE
The material for the new PNAS study came from Camp Century, a Cold War military base dug into the ice shelf far above the Arctic Circle in the 1960s. The real purpose of the camp was a super-secret effort, called Project Iceworm, to hide 600 nuclear missiles under the ice near the Soviet Union. As cover, the military offered the camp as a polar science station.
The military mission failed, but the science team conducted important research, including drilling a 4560-foot-deep iron core. The scientists of the Camp Century were focused on the ice itself – part of the then emerging attempt to understand the deep history of the ice age of the earth. They were apparently less interested in a little dirt collected under the ice core. 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 waned for decades – until it turned up when the cores were moved to a new freezer.
More about how the core was lost, rediscovered in some cake pots and subsequently 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 spans the past 2.6 million years – portions of the ice in Greenland continued even during warmer periods called ‘interglaciers’. But most of this general story is composed of indirect evidence in mud and rock washed up from the island and collected by foreign ocean-dwellers. The extent of Greenland’s ice sheet and the types of ecosystems that existed before the last interglacial warm period – which ended about 120,000 years ago – have been hotly debated and poorly understood.
The new study makes it clear that the deep ice in Camp Century – about 75 kilometers inland from the coast and only 800 kilometers from the North Pole – has melted completely at least once in the last million years and was covered with vegetation, including moss and maybe trees. The new research, supported by the National Science Foundation, joins data from two other ice cores from downtown Greenland, collected in the 1990s. Sediment from the bottom of these cores also indicates that the ice sheet has been missing for some time in the recent geological past. The combination of these cores from downtown Greenland with the new insight of Camp Century into the far northwest, gives researchers an unprecedented view of the shifting fate of the entire Greenland ice sheet.
The team of scientists used a series of advanced analytical techniques – none of which were available to researchers fifty years ago – to investigate the sediment, fossils and waxy coating of leaves found at the bottom of the Camp Century ice core. For example, they measured the proportions of rare forms – isotopes – of both aluminum and the element beryllium that form only in quartz when the ground is exposed to the air and can be hit by cosmic rays. These ratios showed scientists a window on how long rocks on the surface have been exposed to low ice. This analysis gives the scientists a kind of watch to measure what has happened in Greenland in the past. Another test used rare forms of oxygen, found in the ice in the sediment, to indicate that precipitation must have fallen at much lower altitudes than the height of the current ice sheet, indicating the absence of ice sheets, writes the team. By combining these techniques with studies of luminescence that exposed the amount of time since sediment to light, radiocarbon dating of pieces of wood in the ice, and the analysis of how low ice and debris were arranged, the team was able to make clear that most, if not the whole, Greenland has not melted at least once during the last million years – which has made Greenland green with moss and lichen, and perhaps with spruce and spruce.
And the new study shows that ecosystems of the past have not been forgotten by the centuries of glaciers and ice sheets dumped on top. Instead, the story of these living landscapes remains trapped under the relatively young ice that has formed on top of the ground, frozen in place, and keeps it quiet.
In a 1960s film about the Century created by the military, the narrator notes that “more than ninety percent of Greenland is permanently frozen under a frost.” This new study makes it clear that it is not as permanent as we ever thought. “Our study shows that Greenland is much more sensitive to natural climate warming than we previously thought – and we already know that humanity’s uncontrolled warming of the planet’s natural rate is much greater than that,” says Christ, a postdoctoral researcher in the College of Arts & Sciences and Gund Institute.
“Greenland may seem far-fetched,” says UVM’s Paul Bierman, “but it could melt fast and plunge into the oceans enough that New York, Miami, Dhaka – choose your city – would go underwater.”
In this video, Paul Bierman explains the urgent significance of this new study: