All the ancient ice extracted in cylindrical cores in different regions of the planet has accumulated in layers over millennia like a gigantic tiramisu. Whether in cores extracted from Antarctica, Greenland or Alpine glaciers, the formation process is the same: snow is deposited on the frozen ground and compacts over the centuries until it becomes the cake with different layers of ice that climatologists extract from the depths and use for their reconstructions.
Inside are written the details of the climate of tens of thousands of years ago, not only in the air bubbles of past atmospheres, but in structural changes that are not yet well known and whose the understanding of much more precise models depends.
In a small isolated room in a building in Bilbao, at 30°C below zero, Patricia Muñoz and Nicolás González are working to solve this problem by studying the microstructure of ice. Both are equipped with protective suits against the cold and examine under a microscope several samples from the interior of the northeast Greenland ice flow, a fragment of a 120 meter deep core from the EastGRIP project.
They are in the ice laboratory of the Basque Center for Climate Change (BC3), called IzotzaLab, and are examining a very thin layer of ice as if it were a secret codex. Only, instead of letters, it is its small cracks and bubbles which describe the changes in tension and temperature accumulated over the centuries.
A climate elevator
“Our task is to explain the process of transforming snow granules into ice,” explains Sérgio Henrique Faria, director of the laboratory, during elDiario.es’ visit to its facilities. “As snow settles, a series of physical and photochemical processes cause this climate record to form; If you don’t know these details, you can dive into the deep ice and draw conclusions that aren’t entirely accurate. »
Our task is to explain the process of transforming snow granules into ice
Sergio Henrique Faria
— Director of the IzotzaLab laboratory
If you take one of these cores and visually go through it from top to bottom, explains the specialist, you will see that in the upper and more recent layers, the ice is much more porous, while as the Weight accumulates and recedes over time. it becomes a stronger structure. In samples of up to 3,000 meters of ice taken from Antarctica, he says, as you go down, you see how the pores shrink until they concentrate into tiny bubbles. “The older the fragment, the tighter it is and has fewer pores,” explains Nicolás González.
“This gives information about when the snow fell, because it compacts differently depending on the temperature,” says Faria. “Temperature affects microstructure by changing crystal size: when it is higher, the crystals tend to be larger and when it is colder, they are smaller.” You can’t know how many degrees the thermometer would have read, but you can document the sequence of colder or warmer periods.
From 800 meters deep, we begin to notice gray and white layers which provide information about changes over longer periods of the more distant past; The dark areas where impurities accumulate correspond to glacial periods and the lighter ones to warmer interglacial periods, because in the former the seas recede and more sediment accumulates on the ice.
How to do an “autopsy” on ice
Another source of information lies in the small cracks observed in the structure of the ice, because they show how the crystals came together and where different stresses occurred. “This is why it is so important that there is no sudden change in temperature of the witnesses from the time they are brought in until we handle them, because their tendency is to relax and these cues would be lost”, underlines Nicolás González. Its objective is to maintain it at an average temperature of -50ºC to paralyze him and stop expanding. “It’s like doing an autopsy on ice,” he admits. “We ask: why were you stressed? This detail is particularly important in the sample brought from Greenland, which belongs to an ice river that moves at a speed of about 55 meters per year.
A layer of impurities produces weakness in the horizontal plane and causes what is above to slide more quickly.
Nicolas Gonzalez
— Researcher at the IzotzaLab laboratory
The speed at which the ice slides is conditioned, at the same time, by the presence of impurities such as ash or mineral particles, which also influence the transformation of snow into ice and overall affect the structure. In a recent study with ice collected from the Pyrenean glaciers of Mount LostFor example, González found dust particles, probably from the Sahara, deposited a few hundred years ago.
“What is interesting is that small changes on this scale can modify the speed at which the glacier moves,” underlines the researcher. “Imagine you have the ice mass, a layer with a lot of lateral continuity of impurities; it is a layer of weakness in the horizontal plane that causes what is above it to slide more quickly. “A glacier disappears because it goes downhill, and the faster it moves, the faster it disappears.”
A plop! from the distant past
The source of information that everyone thinks of when talking about ancient ice is the air from past atmospheres that contains the bubbles trapped in the ice thousands of years ago. This is not the specific object of study of this laboratory, although it analyzes its content thanks to collaboration with the analytical chemistry teams of the UPV/EHU. “If you go down, the bubbles will contain samples from older climates,” explains Patricia Muñoz. And the deeper they are, the more the air is compressed, which can cause small disturbances that ruin the material. “Sometimes there is a risk that a bubble will damage the sample we are looking at under the microscope,” he explains.
There is sometimes a risk that a bubble will damage the sample we are looking at under the microscope.
Patricia Munoz
— Researcher at the IzotzaLab laboratory
Sérgio Henrique Faria has been working with these samples for 20 years and admits to still being excited by the idea that these bubbles contain air trapped for thousands of years. It is this pressure process that differentiates naturally accumulated ice from that which humans create in a refrigerator. “Old ice is more porous and cuts more easily, the other is like a block, it cracks,” he describes. The fact that it contains compressed air explains why if you put it in water it starts to generate a sort of effervescence, when a quantity of air which was confined in a very small space is suddenly released .
“I worked with ice at 2,000 meters in Antarctica and I could hear this sound,” he recalls. “One day I was looking through the microscope and, by pure coincidence, I saw a bubble of only a few microns explode under my objective and produce a plop! This air had been locked away for 87,000 years!
A look at the last 800 years
Among the 600 kilos of ice that have arrived at IzotzaLab over the past two years from various locations around the world – divided into dozens of cores and stored in two trunks – the BC3 team is studying with particular interest those that arrived ago months from Greenland via Japan. It is a core that covers the most superficial 120 meters of ice, which reaches an age of around 800 years and is analyzed from bottom to top. Researchers believe this will help understand the transformation processes of snow and ice, in addition to bringing us closer to the moment when our activity changed the atmosphere forever, after the industrial revolution.
“At the moment we don’t see a turning point in the microstructure of the ice, but we still have a lot of work to do,” says Faria. Their efforts focus on deciphering the signs inscribed in the ice in the form of cracks, distortions and bubbles as if they were the typography of a secret language. In one of the images, the light passing through the sample allows us to appreciate the process by which the snow turns into ice again, as if we had stopped time. In another, taken in surface light and on a scale 10 times smaller, the spaces left by bubbles broken when cutting the sample look like black stones seen from above on an Arctic ice sheet.
“It would be enough for an art exhibition,” says Nicolás González in front of the screen. “We are the first to look at this and we work with artificial intelligence that allows us, just by capturing these types of images, to see all the main characteristics, bubble size, cracks, etc.,” adds -he. “Our goal is to propose a new model that is better than existing ones, a new standard that would affect all climate studies of the past, both those of the poles and of glaciers,” explains the laboratory director.
“The historical climate record is measured in points every meter or every ten meters, but in the latest research we are already moving to the scale of centimeters,” Faria summarizes. In other words, it is as if in the book on climate we have so far only been able to read the titles of the chapters, but we had to start to understand the first sentences. “We need to refine the register and improve our interpretations; There is very strong pressure from the community to create a more refined model that explains the transformation of snow into solid ice and reduces the uncertainty of the models that the IPCC will manage in the years to come,” he concludes.
