In pursuit of the oldest ice and the newest data

Researchers from the Alfred Wegener Institute (AWI) regularly brave temperatures down to 20 degrees below zero, embarking on journeys that take them to the distant past of the ice on Greenland and Antarctica. To unlock the secrets held there, they collect ice cores, which are subsequently prepared and carefully analysed at the AWI’s ice core laboratories. In terms of their form, size and equipment, there are only three such facilities worldwide: in Japan, the USA – and Bremerhaven.

In order to understand what will happen, we have to first understand what has already happened. Though that might sound like the dedication for a book of poetry, it aptly describes researcher’s day-to-day work at the ice core laboratories. “We investigate the ice in its original state, long before there could be any human influences,” says Frank Wilhelms, a glaciologist and head of the ice-core drilling group in Bremerhaven. Since they can’t simply turn back the clock, the scientists rely on laborious measuring methods to test the ice cores. These rods of glacier ice, which are roughly ten centimetres across and nearly three kilometres long, were retrieved by drilling deep into the ice sheets of Antarctica and Greenland.

Why are they important? Because information on the past composition of the atmosphere is stored in the ice. Over the decades, layer after layer of snow – which encapsulates and preserves air and trace elements from the atmosphere – accumulates. For the AWI researchers, the resulting ice represents a veritable treasure trove – but getting to the information they need is anything but easy.

While still at the expedition site, they cut open the core and run initial tests so as to get a first snapshot of its composition. But some of their tests require delicate equipment that they can’t simply lug with them to the most remote corners of the globe, or simply take much more time to complete. For these more involved tests, the millennia-old ice is transported to Bremerhaven.

Once there, the ice is stored and tested at what is likely one of the coldest workplaces in the world. Bundled up in thick clothing, the researchers often work for hours at 20 degrees below zero in the ice core labs, which essentially look like a typical workshop. Between white foam boxes that safely hold the one-metre-long ice core segments like huge jewels, there are long workbenches with razor-sharp saws for cutting the ice with millimetre precision.

For the scientists, the exciting phase then begins with an analysis of the segments. “When the first data comes in, it’s truly elating. After all, it’s the payoff for years of fieldwork under inhospitable conditions,” says Frank Wilhelms. The researchers then use a variety of methods to coax answers from the ice, yielding clues to the development of our climate.

One method involves scanning for chemical trace elements, which include dust or salts. By analysing an ice core’s sulphate content, the staff can determine when there were past volcanic eruptions. Another question is how the temperature developed in e.g. the Antarctic hundreds of thousands of years ago. In this regard, the water’s oxygen isotopy can help. Since the ratio of different heavy isotopes of the same atom is temperature-dependent, the ice is melted and its isotope ratio is assessed.

In addition to exploring Earth’s climate history, the ice core laboratories’ second focus is on ice dynamics. According to AWI glaciologist Ilka Weikusat, “Ice is a material that undergoes many changes. Once we’re able to predict how it will develop under constantly changing conditions, we’ll also be able to make far more accurate predictions regarding how ice sheets respond to phenomena like global warming.” This is done by examining ice crystals and e.g. analysing their microstructure.

In the context of the ice cores, this means that thin slices of ice are examined using different light sources in order to find out how the ice crystals behave e.g. under pressure. The results can be very colourful. Though this may look like abstract art to non-experts, for glaciologists these colour codes indicate the ice crystals’ alignment. “We examine the ice crystals’ appearance, size and form,” says Ilka Weikusat. And these aspects can vary considerably: ice grains can be symmetrical or asymmetrical, square or serrated, long and slender or curved.

“We then look at which direction the individual crystals in a given sample are aligned in. There are certain directions in which glacial ice crystals tend to align – and they depend on physical conditions like pressure, temperature and direction of deformation.” It’s painstaking, millimetre-precise work, but it’s also essential to understanding the long-term development of ice sheets in our climate.

The AWI is a global pioneer in ice core research. “Most labs have a single focus: either climate history or dynamics. The unique thing about the AWI is that we research both aspects,” says Ilka Weikusat. The only two comparable laboratories are in Japan and the USA. “That being said, the combination we have in Bremerhaven, which allows us to comprehensively assess the samples, is one of a kind.”

Yet operating this type of laboratory entails major challenges, since major investments are often needed to ensure that the systems function reliably in critical phases and under extreme conditions. Further, the environment isn’t just hard on the equipment – the scientists working there also have to adapt. Sharing an example of the day-to-day problems they encounter, Ilka Weikusat explains: “20 degrees or more below zero isn’t exactly in our comfort zone. On top of that, there are very down-to-earth challenges like the question of which gloves to wear. You can’t just do without them, because your fingers will freeze to the ice. But thick ski gloves don’t work either, because they eventually become too stiff.”

A power outage would be nothing short of catastrophic. Accordingly, the labs are also equipped with backup generators, ensuring the refrigeration systems keep working, even in an emergency. “Ice is a highly active material because it’s never far from the melting point. If the temperature changes, the ice changes with it – which is why it’s so important to maintain a temperature of minus 20 degrees, so as to keep the samples as close to their original state as possible,” says Frank Wilhelms. In addition, to leave the door open for better and more detailed future measuring methods as they become available, only half of each ice core is used for testing; the other half is archived.

In short, an enormous amount of time and energy is invested in unlocking the information the ice holds within. But it’s all worthwhile: the oldest ice core analysed to date is eight hundred thousand years old and offers e.g. insights into the concentrations of carbon dioxide and methane throughout that timespan – information that can’t be found in any other climate archive.

Text: Helena Kreiensiek