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