When we first turned our microscope on the soil sample, bits of organic matter came into view: a tiny poppy seed, the compound eye of an insect, broken willow twigs, and spores of spike moss. Dark-colored globules produced by soil fungi dominated our view.
These were unmistakably the remains of an Arctic tundra ecosystem, proving that the entire Greenland ice sheet disappeared much more recently than people realize.
These tiny hints of past life came from a most unlikely place - a handful of dirt buried under 2 miles of ice beneath the top of the Greenland Ice Sheet. Projections of future melting of the ice sheet are unambiguous: When the ice at the top is gone, at least 90% of Greenland's ice will be gone.
In 1993, summit drillers completed the Greenland Ice Sheet Project 2 ice core, or GISP2, nicknamed the two-mile time machine. The seeds, twigs and spores we found came from a few inches of soil at the bottom of that core - soil that had been tucked away, dry and untouched, in a windowless storage facility in Colorado for three decades.
Our new analysis builds on work by others over the past decade that has undermined the belief that Greenland's ice sheet has been continuous since at least 2.6 million years ago, when the Pleistocene ice ages began. In 2016, scientists measured rare isotopes in rocks from above and below the GISP2 soil sample and used models to suggest that the ice had disappeared at least once in the past 1.1 million years.
Now, by finding well-preserved tundra remains, we have confirmed that the Greenland ice sheet did indeed melt earlier, exposing the land below its summit long enough for soil to form and tundra to grow. That tells us that the ice sheet is vulnerable and could melt again.
A landscape with arctic poppies and lichens
To the naked eye, the tiny bits of former life are unremarkable-dark specks floating among shiny grains of silt and sand. But under a microscope, the story they tell is astonishing. Together, the seeds, megaspores, and insect parts paint a picture of a cold, dry, rocky environment that existed sometime in the past million years.
Above ground, Arctic poppies grew among the rocks. Atop each stem of this small but hardy herb, a single cupped flower followed the sun across the sky to make the most of each day's light.
Tiny insects buzzed above mats of tiny rock moss, which crawled across the gravel surface and carried spores in the summer.
In the rocky soil were dark bulbs called sclerotia, produced by fungi that work with the roots of plants in the soil to give both the nutrients they need. Nearby, willow shrubs adapted to life in the harsh tundra with their small size and hairy hairs covering their stems.
Each of these living creatures has left traces in that handful of soil-evidence that Greenland's ice was once replaced by a robust tundra ecosystem.
Greenland's ice is fragile
Our findings, published August 5, 2024, in the Proceedings of the National Academy of Sciences, show that Greenland's ice is vulnerable to melting at atmospheric carbon dioxide concentrations lower than today. Concerns about this vulnerability have driven scientists to study the ice sheet since the 1950s.
In the 1960s, a team of engineers retrieved the world's first deep ice core from Camp Century, a nuclear-powered military base built into the ice sheet more than 100 miles off the northwest coast of Greenland. They studied the ice, but the bits of rock and soil that came up with the bottom of the core were of little use. They were stored and then lost until 2019, when they were rediscovered in a laboratory freezer. Our team was one of the scientists called in to analyze them.
In the Camp Century soil we also found remains of plants and insects frozen under the ice. Using rare isotopes and luminescence techniques we were able to date them to a period of about 400,000 years ago, when temperatures were similar to those of today.
Another ice core, DYE-3 from southern Greenland, contained DNA showing that part of the island was covered in spruce forests at some point within the past million years.
The biological evidence provides a compelling case for the vulnerability of the Greenland ice sheet. Together, the findings from three ice cores can only mean one thing: With the exception of a few mountainous areas in the east, the entire island must have lost ice in the past million years.
The loss of the ice cap
If Greenland's ice disappears, the geography of the world will change - and that's a problem for humanity.
As the ice sheet melts, sea levels will eventually rise by more than 23 feet, flooding coastal cities. Most of Miami will be underwater, as will much of Boston, New York, Mumbai, and Jakarta.
Today, sea levels are rising more than an inch per decade, and in some places several times faster. By 2100, when today's children are grandparents, global sea levels will likely be several feet higher.
Using the past to understand the future
The rapid loss of ice is changing the Arctic. Data on past ecosystems, such as those we have collected from beneath Greenland's ice, is helping scientists understand how the Arctic ecology will change as the climate warms.
As temperatures rise, the bright white snow melts and the ice shrinks, exposing dark rocks and soil that absorb heat from the sun. The Arctic grows greener with each passing year, thawing underlying permafrost and releasing more carbon that will further warm the planet.
Human-caused climate change is on track to warm the Arctic and Greenland to temperatures they have not experienced for millions of years. To save Greenland's ice, studies show the world must stop greenhouse gas emissions from its energy systems and reduce the amount of carbon dioxide in the atmosphere.
Understanding the environmental conditions that caused the ice sheet to last disappear and how life on Greenland responded is critical to assessing future risks to the ice sheet and coastal communities around the world.
This article is republished from The Conversation, a nonprofit, independent news organization that brings you facts and reliable analysis to help you understand our complex world. It was written by: Paul Bierman, University of Vermont and Halley Mastro, University of Vermont Read more: Paul Bierman receives funding from the US National Science Foundation and the Gund Institute for Environment. Halley Mastro receives funding from the U.S. National Science Foundation and the Gund Institute for Environment.
