Europe’s Triumphs and Troubles Are Written in Swiss Ice
Pollen frozen in ice in the Alps traces Europe’s calamities, since the time Macbeth ruled Scotland.
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As plague swept through Europe in the mid-1300s, wiping out more than a third of the region’s population, a glacier in the Alps was recording the upheaval of medieval society.
While
tens of millions of people were dying, pollen from the plants, trees
and crops growing in Western Europe were being swept up by the winds and
carried toward the Alps.
They became trapped in snowflakes and fell onto the region’s highest mountain, the Monte Rosa massif.
Over time, the snow flattened into ever-growing layers of ice, storing a
blow-by-blow record of regional environmental change.
Centuries
later, the crop pollens trapped in the ice reveal the collapse of
agriculture associated with the pandemic, as bad weather led to poor
harvests and fields lay fallow because there was no one left to work
them.
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For
more than 50 years, scientists have drilled ice cores in the Arctic and
Antarctica to reconstruct uninterrupted records of climate change over
hundreds of thousands of years. But these glaciers can be difficult to
get to and they are far from where most people on Earth live.
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Mid-
to low-latitude glaciers, on the other hand, tend to be more accessible
and lie at the heart of thousands of years of human activity. The Colle
Gnifetti glacier, sitting near the Swiss-Italian border, and with a central location on the continent, has put it on a crash course with Europe’s dust for roughly 10,000 years.
Sandra
Brügger, a climate scientist at the Institute of Plant Sciences and the
Oeschger Centre for Climate Change Research at the University of Bern, developed a technique to study the pollen,
fungal spores, charcoal and soot locked in an ice core drilled from
this Swiss glacier. She is aiming to disentangle the ways extreme
weather, innovation, crop failures and pollution have shaped Europe since 1050, when Macbeth ruled Scotland.
Pollen
levels rise and fall during the century, but their most pronounced
peaks and valleys coincide with notable events. Europe suffered through a
spate of calamities during the 14th century. Before the Black Death,
there was the Great European Famine. Historical accounts tell of the
relentless rains that spoiled back-to-back harvests in parts of Europe
from 1315 through 1317, and may have helped bolster the plague’s grip.
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Ms. Brügger tracked
the cereal and hemp pollen over time, noting their rise and fall. In
the early 1300s, these crop pollen levels drop precipitously. “People
were starving and there wasn’t much agricultural activity anymore,” Ms.
Brügger said.
The Black Death took greater
hold of Europe from 1347 to 1351, killing 75 million people, and the
pollens vanished as agriculture came to a halt. “There’s just nothing
for five to 10 years,” she said. Then, as villages recovered, the pollen
levels rebound.
The ice core
reveals more than Europe’s 14th century agricultural crises. It
chronicles the expansion of pastureland, the increasing globalization of
the economy, the onset of industrialization and the occurrence of
extensive wildfires through the ages. The results, presented at the Polar 2018 meeting in Switzerland in June,
may be the first continuous study of pollen and fungal spores in a
European ice core to be captured at intervals of once every decade.
Few
people have conducted detailed studies of pollen in ice cores before,
said Raymond Bradley, a geoscientist at the University of Massachusetts,
Amherst, and an expert in using lake-bed sediment cores to reconstruct
past climates. “Most ice cores are polar and they are a long way from
major vegetation regimes. Those studies that were done were pretty
boring, they didn’t show much,” he said.
In
the fall of 2015, a six-person crew flew by helicopter from Zermatt,
Switzerland, to the saddle of the Colle Gnifetti glacier. They carried
with them a ton of equipment, including tents, cookstoves, food and a
solar-powered drill.
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“It’s
a bit risky,” said Margit Schwikowski, an atmospheric chemist at the
Paul Scherrer Institute and the Oeschger Centre, who is leading the
study of the ice core. “You’re at 4,500 meters and you have the risk of
high-altitude sickness. You don’t have time to acclimatize.”
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For
four days, the drill bored into the ice — and back in time — until it
hit bedrock. The team flew home with two ice cores, each spanning the
entire thickness of the glacier and covering 10,000 years. The ice is
more compressed near the bottom of the core, so the top 65 meters of the
core contain data from 1050 until 2015, with the remaining 9,000 years
crammed into 50 meters of ice.
Back
in the lab, Dr. Schwikowski and her colleagues dated the different
sections of the ice core using water, lead and carbon isotopes, and by
identifying “dating horizons” such as well-known volcanic eruptions,
Saharan dust transport and nuclear weapons tests. Once the timeline was
in place, Ms. Brügger began tracking pollen, spores and soot in the
samples using a light microscope. In all, she counted more than 40,000
pollen grains in the ice core.
More articles on the science of ice cores
History frozen in time
Grass
pollens were abundant in the segments that corresponded to the years
1100 to 1200. During the Medieval Warm Period, temperatures in Europe
and the nearby North Atlantic were as warm or warmer than they are now,
and crops and forests flourished. The spike in grass pollens
corresponded to the expansion of open landscapes, a transition from
forests to pastures. She also found the highest levels of a spore from a
fungus called Sporormiella that grows only on dung.
“It’s a sign that it’s not only an open landscape, but that we also have a lot of cattle,” she said.
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The
record becomes more complex in 1750, which marks the expansion of the
European economy and the start of the Industrial Revolution.
Historical
records tell us that Columbus introduced maize to Europe in 1493, but
maize pollen doesn’t show up in the ice core until the mid-1700s, a sign
that its large-scale regional production didn’t take off immediately.
It was also around this time that European society started to become
more industrial and urban. This is mirrored in the ice core with the
first traces of small spherical carbon particles, evidence of a
transition from wood to coal burning in Central Europe.
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Although
poets, landowners, chroniclers and others noted these historical
events, manual record-taking can be imperfect and limited in geography,
and they don’t quantify their scale over the whole region. Coupling
ice-core data with historical records can yield new insights, said
Alexander More, historian and climate scientist at Harvard University
and the Climate Change Institute at the University of Maine in Orono.
“The combination provides a level of insight that is just not matched by
either type on their own,” he said.
Many
scientists, including Dr. Schwikowski, are concerned about the fate of
these glaciers under climate change. Some glaciers are beginning to melt
as temperatures rise. Meltwater from the upper layers of the glacier
trickle through the airspaces between the snow granules, smearing the
chemical signals and making the core unusable. Colle Gnifetti has, thus
far, been spared, because of its high altitude.
“It
is becoming more and more difficult to find a glacier that is not
melting and that can still be used for research,” said Dr. Schwikowski.
“The object for our research is melting away.”
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