University of Vermont scientists are stunned to discover plants beneath mile-deep Greenland ice. Long-lost ice core from 1966 provides direct evidence that a deep, giant ice sheet melted off within the last million years and is highly vulnerable to a warming climate
From: University of Vermont
March
15, 2021 -- In 1966, US Army scientists drilled down through nearly a mile of
ice in northwestern Greenland—and pulled up a fifteen-foot-long tube of dirt
from the bottom. Then 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 was seeing: twigs and leaves instead of just sand and rock. That suggested
that the ice was
gone in the recent geologic past—and that a vegetated landscape, perhaps a
boreal forest, stood where a mile-deep ice sheet as big as Alaska stands today.
Over the last 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 one-of-a-kind fossil plants and sediment from the bottom of
Greenland. Their results show that most, or all, of Greenland must have been
ice-free within the last million years, perhaps even the last few
hundred-thousand years.
“Ice sheets typically 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 live on Greenland
that we wouldn’t be able to find anywhere else.”
The discovery helps confirm a new and
troubling understanding that the Greenland ice has melted off entirely during
recent warm periods in Earth’s history—periods like the one we are now creating
with human-caused climate change.
Understanding the Greenland Ice Sheet in
the past is critical for predicting how it will respond to climate warming in
the future and how quickly it will melt. Since some twenty feet of sea-level
rise is tied up in Greenland’s ice, every coastal city in the world is at risk.
The new study provides the strongest evidence yet that Greenland is more
fragile and sensitive to climate change than previously understood—and at grave
risk of irreversibly melting off.
“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 in 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.
BENEATH THE ICE
The material for the new PNAS study came from Camp Century, a Cold War military
base dug inside the ice sheet 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 close to the Soviet Union. As cover,
the Army presented the camp as a polar science station.
The military mission failed, but the
science team did complete important research, including drilling a
4560-foot-deep ice core. The Camp Century scientists were focused on the ice itself—part
of the burgeoning effort at the time to understand the deep history of Earth’s
ice ages. They, apparently, took less interest in a bit of dirt gathered from
beneath the ice core. Then, in a truly cinematic set 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 it surfaced when the cores were being moved to a
new freezer.
More about how the core was lost,
rediscovered in some 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 covering the last 2.6 million years—portions of the ice on Greenland
persisted even during warmer spells called “interglacials.” But most of this
general story has been pieced together from indirect evidence in mud and rock
that washed off the island and was gathered by offshore ocean drilling. The
extent of Greenland’s ice sheet and what kinds of ecosystems existed there
before the last interglacial warm period—that ended about 120,000 years
ago—have been hotly debated and poorly understood.
The new study makes clear that the deep
ice at Camp Century—some 75 miles inland from the coast and only 800 miles from
the North Pole—entirely melted at least once within the last million years and
was covered with vegetation, including moss and perhaps trees. The new
research, supported by the National Science Foundation, lines up with data from
two other ice cores from the center of Greenland, collected in 1990s. Sediment
from the bottom of these cores also indicate that the ice sheet was gone for
some time in the recent geologic past. The combination of these cores from the
center of Greenland with the new insight from Camp Century in the far northwest
give 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 probe the sediment, fossils, and the waxy coating of leaves
found 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 form in quartz only when the ground is exposed to the sky and
can be hit by cosmic rays. These ratios gave the scientists a window onto how
long rocks at the surface were exposed vs. buried under layers of ice. This
analysis gives the scientists a kind of clock for measuring what was happening
on Greenland in the past. Another test used rare forms of oxygen, found in the
ice within the sediment, to reveal that precipitation must have fallen at much
lower elevations than the height of the current ice sheet, “demonstrating ice
sheet absence,” the team writes. Combining these techniques with studies of
luminescence that estimate the amount of time since sediment was exposed to
light, radiocarbon-dating of bits of wood in the ice, and analysis of how
layers of ice and debris were arranged—allowed the team to be clear that most,
if not all, of Greenland melted at least once during the past million
years—making Greenland green with moss and lichen, and perhaps with spruce and
fir trees.
And the new study shows that ecosystems
of the past were not scoured into oblivion by ages of glaciers and ice sheets
bulldozing overtop. Instead, the story of these living landscapes remains
captured under the relatively young ice that formed on top of the ground,
frozen in place, and holds them still.
In a 1960’s movie about Camp Century
created by the Army, the narrator notes that “more than ninety percent of
Greenland is permanently frozen under a polar ice cap.” This new study makes
clear that it’s not as permanent as we once thought. “Our study shows that
Greenland is much more sensitive to natural climate warming than we used to
think—and we already know that humanity’s out-of-control warming of the planet
hugely exceeds the natural rate,” says Christ, a postdoctoral researcher in the
College of Arts & Sciences and Gund Institute.
“Greenland may seem far away,” says
UVM’s Paul Bierman, “but it can quickly melt, pouring enough into the oceans
that New York, Miami, Dhaka—pick your city—will go underwater.”
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