All the ancient ice extracted in cylindrical cores in different areas of the planet has accumulated in layers over millennia like a gigantic tiramisu. Whether in the cores extracted from Antarctica, Greenland or the Alpine glaciers, the formation process is the same: the snow is deposited on the frozen terrain and becomes compacted as the centuries pass 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 atmospheres of the past, but in structural changes that are not yet well known and on whose understanding depends the models being much more precise.
Inside a small isolated room in a building in Bilbao, at 30ºC below zero, Patricia Muñoz and Nicolás González are working on solving this problem by studying the microstructure of ice. Both are equipped with protective suits against the cold and are looking under a microscope at several samples from the interior of the northeast Greenland ice stream, 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), baptized as IzotzaLab, and they scrutinize a very thin sheet of ice as if it were a secret codex. Only, instead of letters, it is its small cracks and bubbles that describe the changes in tension and temperature accumulated over centuries.
A climate elevator
“Our task is to explain the process of transformation of snow granules into ice,” explains Sérgio Henrique Faria, director of the laboratory, during elDiario.es’ visit to its facilities. “When the snow becomes compacted there are a series of physical and photochemical processes that cause this climate record to be formed; If you don’t know those details you can go into deep ice and reach conclusions that are not exactly correct.”
Our task is to explain the process of transformation of snow granules into ice
Sergio Henrique Faria
— Director of the IzotzaLab laboratory
If you take one of these cores and visually go over it from top to bottom, the specialist explains, you will see that in the upper and more recent layers the ice is much more porous, while as the weight accumulates and recedes in the Over time it becomes a more solid structure. In samples of up to 3,000 meters of ice taken in Antarctica, he says, as you descend you see how the pores shrink until they concentrate in tiny bubbles. “The older the fragment, the tighter it is and has fewer pores,” explains Nicolás González.
“This offers information about when the snow fell, because it compacts differently depending on the temperature,” says Faria. “Temperature affects the microstructure by causing the size of the crystals to change: when it is higher, the crystals tend to be larger and when it is colder, they are smaller.” You cannot know how many degrees the thermometer would have read, but you can document the sequence of colder or warmer periods.
From 800 meters deep, gray and white layers begin to be noticed that provide information about changes in longer periods of a more remote 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 sediments accumulate on the ice.
How to do an “autopsy” on ice
Another source of information is the small cracks observed in the structure of the ice, as they show how the crystals came together and where the different stresses occurred. “That 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 clues would be lost,” highlights Nicolás González. Its objective is to keep it at an average of -50ºC to paralyze it and stop expanding. “It’s like doing an autopsy on ice,” he admits. “We are asking: why have you been stressed?” This detail is particularly important in the sample brought from Greenland, which belongs to a river of ice that moves at a rate of about 55 meters per year.
A layer of impurities produces weakness in the horizontal plane and causes what is on top to slide faster
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 influences the transformation of snow into ice and affects the structure globally. In a recent study with ice collected from the Pyrenean glaciers of the Monte PerdidoFor example, González has found dust particles, probably from the Sahara, that were deposited a few hundred years ago.
“The interesting thing is that small changes at this scale can modify the speed at which the glacier moves,” the researcher emphasizes. “Imagine that you have the mass of ice, a layer with a lot of lateral continuity of impurities; that is a layer of weakness in the horizontal plane that makes what is above it slide faster. “A glacier disappears because it moves downward, and the faster it moves, the sooner it disappears.”
A plop! from the distant past
The source of information that everyone has in mind when we talk about ancient ice is the air from past atmospheres that contain the bubbles that were trapped in the ice thousands of years ago. It is not the specific object of study of this laboratory, although they do analyze the content thanks to the collaboration with the analytical chemistry teams of the UPV/EHU. “If you go downwards, the bubbles will have samples of older climates,” explains Patricia Muñoz. And the deeper they are, the more compressed the air is, which can cause small disturbances that ruin the material. “Sometimes there is a risk that a bubble will damage the sample we look at under the microscope,” he says.
Sometimes there is a risk that a bubble will damage the sample we look 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 that he continues to be excited by the idea that these bubbles contain air that has been trapped for thousands of years. It is this pressure process that differentiates naturally accumulated ice from the one humans create in a refrigerator. “The 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 begins to generate a kind of effervescence, when a quantity of air that was confined in a very small space is suddenly released.
“I have worked with ice from 2,000 meters in Antarctica and I have been able to hear that sound,” he recalls. “Once I was looking into the microscope and, by pure coincidence, I saw how a bubble just a few microns in size exploded under my lens and produced a plop! That air had been locked up for 87,000 years!”
A look at the last 800 years
Among the 600 kilos of ice that have arrived at the IzotzaLab in the last two years from various places in the world – distributed in dozens of cores and kept in two chests – the BC3 team studies with special interest those that arrived months ago from Greenland through Japan. It is a core that covers the most superficial 120 meters of ice, which reaches an age of around 800 years and is being analyzed from the bottom up. Researchers believe that it will help to understand the transformation processes of snow and ice, in addition to getting closer to the moment when our activity changed the atmosphere forever, after the industrial revolution.
“At the moment we do not see a turning point in the microstructure of the ice, but we have a lot of work left,” explains Faria. Their efforts focus on deciphering the signs written in the ice in the form of cracks, deformations 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 is still transforming into ice, as if we had stopped time. In another, taken with surface light and on a scale 10 times smaller, the spaces left by the broken bubbles 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 are working with artificial intelligence that allows us, just by entering this type of images, to see all the main characteristics, size of the bubbles, cracks, etc.,” he adds. “Our goal is to propose a new and better model than the existing ones, a new standard that would affect all climate studies of the past, both those of the poles and glaciers,” says the director of the laboratory.
“The historical climate record is measured in points that are every meter or every ten meters, but in the latest research we are already going to the scale of centimeters,” summarizes Faria. In other words, it is as if in the climate book we have only been able to read until now the titles of the chapters, but we needed to begin to understand the first phrases. “We have 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 coming years,” he concludes.
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