Arctic drill core comes to Bern "Because the ice is so precious, we can't take any risks"

An ice core that allows us to look back at least 1.2 million years of climate history - this record has been achieved by the international Beyond EPICA project, in which Hubertus Fischer's team from the University of Bern is also involved. The professor explains their research here.

Professor Fischer, have you just returned from Antarctica?

I personally wasn't in Antarctica this year, but two of my colleagues were. There are a total of 16 people from various institutes in the field. Many are from the Alfred Wegener Institute in Bremerhaven, for example, as they are in charge of the drilling. There are researchers on site from countries such as Italy, France, Denmark and Switzerland

No one has ever drilled as deep as you?

You can't say "that deep". There are ice cores from deeper layers. But there is no ice core that continuously yields ice this old. In the past, people always tried to go to the thickest parts of the ice. Then you usually have melting underground because there is a geothermal flow that heats the ice on the rock bed from below like a hotplate. Very little, of course: only around 50 milliwatts per square meter. But if the ice is too thick, then there is so much insulation on the rock bed that the ice on the rock bed becomes so warm that it starts to melt, and then the old ice is gone.

So the location of the borehole is crucial?

That was exactly the important thing in our project: to find a point that is as thick as possible, but not too thick, so that the temperature is still below minus 2 degrees Celsius, and a drilling point with a low precipitation rate so that you have as much old ice as possible at depth. And there are very few such points in the Antarctic

Why is less precipitation better?

The less precipitation you have, the more annual layers there are in the ice core. We drill from top to bottom, and the deeper we go, the older the ice becomes. Glacier ice is a plastic material - in other words, it deforms. The layer thicknesses are thinned downwards in the vertical direction and expanded in the horizontal direction. As a result, the age increases much faster with depth and the ice flows very slowly from the point where we are drilling to the coast, where it eventually breaks off as an iceberg over hundreds of thousands to millions of years.

About the person

Bild: Uni Bern/Adrian Moser

Hubertus Fischer is Professor of Experimental Climate Physics and Head of the Department of Climate and Environmental Physics and Scientific Advisor and Group Leader at the Oeschger Center for Climate Research at the University of Bern.

How do you actually know how old the material from a certain depth is?

Our ice core is 2800 meters long. The old ice, 1.2 million years old, was found at a depth of 2485 meters. How do we know how old it is? We took the first measurements in the field to reconstruct the climatic temperature at the drilling point. They were so clear that we were able to count the ice age-warm period cycles and compare them with other climate archives - for example, marine sediments that exist over this time range. They really do look the same, right down to the speckle. In other words, we know exactly which time interval we are in.

How do the drill cores get to Europe?

The ice cores are now being transported back. They arrive in a special minus 50 degree refrigerated container. We have two of these, both of which will be transported to Italy on the Italian research vessel Laura Bassi. One is filled, the other travels empty on the ship. If one of the containers causes problems, the samples can still be moved to the other. Both refrigerated containers have a double refrigeration unit. So we have double redundancy: because the ice is so precious, we can't take any risks. After arriving in Italy, the containers are transported to Bremerhaven by truck.

Do the German colleagues get everything?

No, the European scientists meet there in June and July to cut up the ice. The individual samples are packed in different boxes and distributed to the various institutes. An important part of the ice then arrives in Bern in August and we then carry out gas measurements, for example of greenhouse gas concentrations.

How does the distribution work?

There is, of course, a scientific plan that sets out in advance what goals we are pursuing. Our institute specializes in gases, for example greenhouse gases. Others specialize in the temperature parameter. They use stable isotopes of water. Some, for example us, also investigate chemical components that are dissolved in ice, while others measure cosmogenic isotopes. Everyone has their own specialty. To cover the entire scientific plan, we also need many partners. There are so many thousands of samples that one laboratory alone cannot measure them. This means that we sit down together beforehand and discuss: Who does what? How can we get the best quality?

Is there a risk that the drill core contains ancient viruses that could plague the earth again?

There are probably things in the ice of the past that no longer exist today. But it has to be said: Antarctica is of course the cleanest place you can imagine. So if you get sick there, it's only because you bring in a virus. If you get there healthy and stay there for three months, you won't get sick. That has probably been the case for the last 1.2 million years. It really is the only clean air area on earth that we still have.

Can spores or pollen be found in ice cores?

In principle, of course, they are also present in ice cores, but the Antarctic is so far away that there is virtually no pollen to be found. You can discover something in alpine ice cores from Switzerland, for example, or in ice from Greenland, but it's not much.

What kind of climate do you expect 1.2 million years ago?

The real scientific question is about the mid-Pleistocene transition. Here in the Alps, of course, we know the normal ice age cycles: there was an ice age about every 100,000 years. 80,000 years is cold, and in between there is a warm period like we have for 10,000 to 20,000 years. It was different 1.2 million years ago. There was a warm period every 40,000 years. But the ice ages were not as pronounced. So the volume of ice was not as large as in the last 800,000 years. But they fluctuated back and forth more quickly. And we don't really know why.

How do ice ages actually occur?

In principle, ice ages are caused by changes in the Earth's orbital parameters, resulting in more or less energy coming from the sun. But this change in the Earth's orbital parameters has always been similar over the last few million years. This means that there must be internal feedbacks on the Earth itself that have led to more ice. And one of the usual suspects is, of course, the CO₂ concentration.

What effect does it have?

If, for example, the CO₂ concentrations are reduced a little geologically over time, this would mean that, in principle, the climate has become colder and this may have led to longer and more extensive ice ages. However, this can only be confirmed or falsified if the CO₂ concentration can be measured, and this can only be measured on Antarctic ice cores.

In order to be able to draw conclusions about our climate.

It is important to understand how such long-term changes came about in the past and whether, for example, climate models that we use now for future predictions are also able to explain this past. This is a kind of validation: you can test how good the models are.

Do they go back 1.2 million years or even further?

We were able to clearly assign these climate cycles up to 2485 meters. In other words, we are now certain that we definitely have 1.2 million years of unaltered climate history. We have a lot more ice underneath. This also shows variations, but the measurements we can make in the field are not yet good enough to say how old the ice is. We probably have much older ice. What we don't know is whether there are folds, for example. For that, we simply have to go to a higher resolution and take other measurements.

So it's probably more than 1.2 million years old?

Probably yes, we have at least another 100 meters or so of ice that probably contains a climate signal, but we don't know exactly how old the material is. And there's another ice underneath that may not be climatically interesting, but is extremely interesting from a glaciological point of view. We call it stagnant ice. This is ice that is obviously no longer thinning out vertically. It can be found in many places in the Antarctic and it is not yet understood why this is the case, where it comes from or how it forms.

Is there enough material to carry out more detailed investigations?

What we can still measure, for example, is the composition of the noble gas. This is a very exciting thing because by determining the content of argon, krypton, xenon and also nitrogen, which is not actually a noble gas, we can reconstruct the average temperature of the ocean. We go out onto the ice and can measure the ocean quantitatively with a physical thermometer. The only catch is that, at 900 grams, we need a relatively large amount of ice. The plan is to drill through only the deep ice at Little Dome C again next year so that we can then carry out these measurements with this extra ice.

What other gases play a role?

What we can still measure is the noble gas composition. This is a very exciting thing, because by determining the content of argon, krypton, xenon and nitrogen, which is not actually a noble gas, we can reconstruct the average temperature of the ocean. We go out on the ice and can measure the ocean quantitatively with a physical thermometer. The only catch is that, at 900 grams, we need a relatively large amount of ice. The plan is to drill another ice core next year to take these measurements.

You could create a temperature curve of the ocean over time.

Precisely, averaged over the entire ocean. This temperature is one of the most important parameters apart from CO₂, because the ocean contains almost all of the Earth's energy content, which changes between ice ages and warm periods. We are always talking about 1.5 degrees in the atmosphere. The ocean is only a fraction of that in degrees Celsius, but in terms of energy, there is much more in the ocean. More than 90 percent of the warming energy is in the ocean. That's why it's so important to know how warm the ocean was.

Do these gases also tell us something about past volcanism and tectonics?

You can't tell that from the noble gases. But there are of course other ways. We can measure the sulphate emitted by volcanoes. So we can see large eruptions directly in our ice core. And we can even measure isotopes and then know whether they came via the stratosphere or directly via the troposphere. We do this together with colleagues in the UK, for example, who specialize in these measurements.

How is this research ultimately funded?

The majority of the money - eleven million euros - Beyond EPICA receives from the EU as part of the HORIZON2020 research program, but the Swiss National Science Foundation has also contributed three million francs to the major logistical costs. Ice core research is a good example of how many scientific questions can only be solved through European collaboration.