Glaciers preserve layers of history within their ice. They offer unique insights into Earth’s past. These insights also help interpret future environmental changes. Microscopic deposits of dust, pollen, and pollutants are trapped there.
Scientists use these to examine environmental shifts over time. DRI’s Ice Core Lab previously used this technique. They highlighted atmospheric lead pollution and economic turbulence in Ancient Rome. Now, their latest study uncovers a significant find.
EUROPE’S OLDEST GLACIER ICE UNCOVERED
A glacier in the French Alps dates back to the last Ice Age. This is the oldest known glacier ice in the region. It serves as a record spanning pivotal eras. The glacier covers the development of agriculture in Western Europe. It also extends through the advent of industrialization. This glacier holds insights into an era of rapid change.
UNVEILING 12,000 YEARS OF ATMOSPHERIC HISTORY
The new study appeared in the June issue of PNAS Nexus. It examines a 40-meter long ice core. This core came from Mont Blanc’s Dôme du Goûter. Using radiocarbon dating, researchers dated the glacier. They found it provides an intact record of aerosols and climate. This record extends back at least 12,000 years.
Aerosols are small droplets and particles in the air. They include desert dust, sea salts, and volcanic sulfur. Soot from forest fires, pollutants, and human emissions are also aerosols. Glacier ice offers the most detailed record of past atmospheric aerosols. This is Europe’s first ice core record spanning the last climatic transition. Aerosols play a crucial role in regional climate. They interact with clouds and solar radiation. Insights from this ice record can inform accurate climate modeling. This applies to both past and future climates.
AN UNPRECEDENTED WINDOW INTO EUROPEAN HISTORY
“For the first time, we have a fairly complete Alpine record,” said Joe McConnell. He is Director of DRI’s Ice Core lab and co-authored the study. This record covers atmospheric and precipitation chemistry. It goes all the way back to the Mesolithic Period.
“That’s a big deal,” McConnell explained. “You have two major climate states – glacial and interglacial.” Getting a record across this huge climate change reveals extreme natural aerosol concentrations. Furthermore, human society evolved significantly. Humans transitioned from hunter-gatherers to agricultural societies. Animal domestication, mining, and vast population increase occurred. Land clearing also took place. All these changes happened around this ice core site. It spans the full range of natural and anthropogenic change. It is located right in the center of Europe, where much of Western civilization evolved.
THE SIGNIFICANCE OF THE ALPINE LOCATION
The glacier’s location in the Alps is critically important. It provides a more intact record of Europe’s local climate. This record is superior to those found in distant Arctic ice. Many aerosols drive Earth’s climate. Scientists seek to understand past variations in sources and concentrations.
“Ice cores collected from glaciers and ice sheets provide such information,” said lead author Michel Legrand. He added that droplets and particles stay in the air for only days or a week. Therefore, records from glaciers close to sources are often most informative.
The analyzed ice core was first collected in 1999. French authors of the study gathered it. It was stored in a French freezer for over 20 years. McConnell’s team brought it to DRI’s Ice Core Lab. There, specialized equipment and continuous flow analysis were used. The ice was melted down. Its chemistry was measured, layer by icy layer.
Dating the Ice and Preserving the Record
Determining the age of each ice layer can be challenging. “Here we used a unique combination of radiometric methods,” said coauthor Werner Aeschbach. This established the ice’s chronology.
Co-author Nathan Chellman noted the glacier’s preservation. “We were relieved to find that even under the unusually warm climate of the 20th century,” he said. Cold temperatures near Mont Blanc’s peak preserved the glacier. The ice record had not been impacted by melting.
The historic age of the ice base surprised researchers. It was about 40 meters deep. Another core collected less than 100 meters away at Col du Dome was much shallower. Yet, its ice was only about a century old. Scientists attribute this difference to strong wind patterns on Mont Blanc. “It’s exciting to find the first ice core from the European Alps,” said coauthor Susanne Preunkert. It contains an intact climate record. This record extends back into the last ice age.
NEW INSIGHTS INTO EUROPE’S PAST CLIMATE
The uniquely detailed ice record revealed significant temperature differences. There was about a 3 degrees Celsius difference. This occurred between the last Ice Age and the current Holocene Epoch.
Pollen records embedded in the ice were used. Reconstructions of summer temperatures during the last Ice Age were about 2 degrees Celsius cooler. This applied throughout western Europe. They were about 3.5 degrees Celsius cooler in the Alps.
The phosphorous record also told a story. It revealed vegetation changes over 12,000 years. Phosphorous concentrations were low during the last Ice Age. They increased dramatically in the early to mid-Holocene. Then, they decreased steadily into the late Holocene. This aligns with forest spread under a warmer climate. It also reflects their decline due to modern society and land-clearing.
Records of sea salt helped examine historical wind patterns. The ice core revealed higher sea salt deposition during the last Ice Age. This may have resulted from stronger westerly winds offshore of western Europe. Sea salt aerosols scatter solar radiation. They affect climate via impacts on cloud droplet size and albedo. This makes them important drivers of regional climate.
RECONCILING DUST RECORDS
The ice record tells a more dramatic story for dust aerosols. Dust concentrations were about 8-fold higher during the last Ice Age. This contradicts prior climate models. Those models simulated only a doubling of dust. The difference may be due to increased Saharan dust plumes. These plumes deposited in Europe. The ice core record is consistent with other paleoclimate data. These suggest more arid Mediterranean conditions during colder climates.
UNCOVERING MORE STORIES ENTOMBED IN THE ICE
This study is merely the beginning of the Mont Blanc ice record’s story. Researchers plan to continue analyzing it for human history indicators. Establishing the age of each ice layer is the first step. Isotopes and radiocarbon dating are used for this. With this information, scientists can now delve deeper. They can learn about past human civilizations and their environmental impact.
“Now we can start to interpret all these other records,” McConnell said. These include records of lead and arsenic. This interpretation links to human history. The information also helps understand how aerosols impact climate. It improves modeling for current and future climatic shifts. “You need a model that captures true climate variability,” McConnell explained. “To evaluate how good the models are, you’ve got to be able to compare them to observations, right? And that’s where the ice cores come in.”
